Potassium Secondary Batteries - ACS Applied Materials & Interfaces

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Review

Potassium Secondary Batteries Ali Eftekhari, Zelang Jian, and Xiulei Ji ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b07989 • Publication Date (Web): 07 Oct 2016 Downloaded from http://pubs.acs.org on October 10, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Potassium Secondary Batteries Ali Eftekhari,a,b,* Zelang Jian,c and Xiulei Ji c,*

a The Engineering Research Institute, Ulster University, Newtownabbey BT37 OQB, United Kingdom b School of Chemistry and Chemical Engineering, Queen's University Belfast, Stranmillis Road, Belfast BT9 5AG, United Kingdom c Department of Chemistry, Oregon State University, Corvallis, Oregon, 97331-4003, United States E-mail: [email protected], [email protected]

Abstract Potassium may exhibit advantages over lithium or sodium as a charge carrier in rechargeable batteries. Analogues of Prussian blue can provide millions of cyclic voltammetric cycles in aqueous electrolyte. Potassium intercalation chemistry has recently been demonstrated compatible with both graphite and non-graphitic carbons. In addition to potassium-ion batteries, potassium-O2 (or -air) and potassium-sulfur batteries are also emerging. Additionally, aqueous potassium-ion batteries also exhibit high reversibility and long cycling life. Due to potentially low cost, availability of basic materials, and intriguing electrochemical behaviors, this new class of secondary batteries is attracting much attention. This mini-review summarizes the current status, opportunities and future challenges of potassium secondary batteries.

Keywords: potassium-ion battery, potassium-air battery, potassium-sulfur battery, graphite intercalation compound, Prussian blue

Page 1 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 41

Introduction

Lithium-ion batteries (LIBs), as a ubiquitous power source, have achieved tremendous successes in portable electronics and electric vehicles. Usage of LIBs is ever increasing; however, economies of scale do not apply to LIBs, where larger production of LIBs may not reduce the price. LIBs may suffer from the technological unsustainability due to rarity and uneven distribution of lithium resources, which limits their applications, especially in the large-scale batteries for stationary storage. In pursuit of alternatives to LIBs, two nearest neighbor elements (Na and Mg) have been the focus of attention during the past two decades. Although it seems that the closest neighboring elements are the best choices for the replacement because of their property similarity, K is indeed a competitive option, where in selections of anodes and cathodes, there exist highly promising materials for K-ion intercalation. The first prototype of potassium battery was introduced in 2004 by Eftekhari,1 utilizing a Prussian blue (PB) cathode. Since then, PB and its analogues have been widely employed as low-cost cathode materials in lithium,2-16 sodium,4,17-30 calcium,31-32 and aluminum ion batteries33,34.

Electrochemistry of transition metal hexacyanoferrates has been extensively studied since the 1970s as conventional electroactive materials of chemically modified electrodes (CMEs),35,36 which were used in various electrochemical systems, including secondary batteries.37-44 The fascinating capability of PB as a cathode is its excellent cyclability for K-ion insertion/extraction over millions of reversible cycles.45-47

In almost any aspect, potassium batteries can compete with their emerging rivals, sodium (ion) batteries. Even in comparison with the well-established lithium batteries, potassium batteries have some unique advantages.

Cell Voltage A key benefit of potassium batteries is the exceptionally negative potential of the K+/K redox couple. The well-known standard potentials for Li+/Li, Na+/Na, K+/K, Rb+/Rb, and Cs+/Cs are – 3.040, –2.714, –2.936, –2.943, –3.027 vs. Saturated Hydrogen Electrode (SHE), respectively.48 In fact, Li is somehow an exception as the redox potential generally shifts toward more negative potentials by increasing the atomic number in the alkali metal group, which is due to Li-ion’s very high desolvation energy in aqueous electrolyte. This exceptional behavior of Li is not strong enough in non-aqueous electrolytes (i.e., the common environment of lithium-ion batteries) where, Page 2 of 41 ACS Paragon Plus Environment

Page 3 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


in fact, the standard potential of K+/K is even more negative than that of Li+/Li. The standard potentials in a well-known battery solvent, propylene carbonate (PC), have been theoretically calculated to be –2.79, –2.56, –2.88, –2.95, and –3.10 for Li+/Li, Na+/Na, K+/K, Rb+/Rb, and Cs+/Cs, respectively.48 However, experimental measurements showed that the standard potential of K+/K in PC is the most negative one among all alkali metal redox couples.49 Indeed, the standard potential of K+/K has an advantage over Li+/Li in non-aqueous medium.

In ethylene carbonate/diethyl carbonate (EC/DEC) electrolyte, i.e., a common electrolyte solvent combination for LIBs, it was determined that K+/K is –0.15 V vs. the Li+/Li reference.50 This is somehow symbolically interesting, as it is quite uncommon to deal with negative potentials when using a Li+/Li reference electrode. This low potential means that in the conventional cell design like Li batteries, K-based batteries may deliver a higher cell voltage by about 0.15 V, when assuming that the cathodes in potassium batteries exhibit the same operating potentials as their analogues in LIBs. This provides a uniquely superior position for K-based batteries among possible alternatives in replacement of Li-based batteries. For other alkali metals, the standard potential of Na+/Na is significantly more positive than Li and K, while heavier alkali metals than K are not suitable for battery systems due to their high cost and low specific capacity. Furthermore, electrochemical behavior at negative potentials in K-based electrolytes is somewhat more straightforward in comparison to that in Li-based and Na-based electrolyte, undergoing less complicated interfacial reactions.51

Abundance and Low Cost Both sodium and potassium are abundant elements with comparable low cost, but lithium is much more expensive due to its rarity as well as uneven distribution in the Earth’s crust, i.e., lithium is about three orders of magnitude less abundant than sodium or potassium.52 Lithium is unevenly distributed geographically, where the “lithium triangle” in South America holds ~70% of the world’s total lithium reserve. This would mean that for most countries lithium would have to be imported, potentially creating a “lithium crisis” due to the lithium commodity price volatility. This causes a concern of sustainability to meet the rapidly growing demands for LIBs. In addition to the challenged future supply of lithium to power millions of electric vehicles, recycling lithium from LIBs cheaply remains an unsolved challenge. It would be impossible to meet the needs for massive stationary energy storage by LIBs as it would starve the supplies of lithium rapidly, causing unaffordable prices. However, there has been a huge demand for stationary batteries, where the energy density or specific energy is not the priority. The two most critical metrics are the cost and Page 3 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 41

cycling stability, which requires sustainable affordability and minimal maintenance. Suitable technologies will facilitate wider installation of solar or wind energy for load leveling, smart grids, and microgrids. For strategic reasons, it is vital to develop battery technologies that are sustainable and based on cheaper and more abundant materials.

Electrochemical Behavior with Respect to PB Electrodes Among alkali metal elements, potassium salts are commonly used as both supporting electrolytes and electroactive species; this is due to their high conductivity, low cost, abundance, and straightforward electrochemical behavior.53-56 Sodium salts are comparable, but the application of lithium salts in aqueous electrochemical systems (except for Lithium Batteries) is negligible. In aqueous electrolytes, large hydrated Li-ions are usually considered unfavorable for solid-state insertion/extraction in PB type electrodes.57-59 In addition to the structural destruction of PB by Liion insertion/extraction, which is accompanied by poor cyclability; the electrochemical behavior of PB in Li supporting electrolyte is not as well defined as that in K supporting electrolyte.60-61 While redox peaks in K supporting electrolyte are sharp, indicating that the redox system occurs at a narrow range of potentials, resulting in a flat plateau in battery performance, they are quite broad in Li supporting electrolyte.

Although the rate-determining factor in this class of batteries is solid-state diffusion within the electrode materials, diffusion of the charge carrier within the electrolyte solution is of particular importance. Contrary to common sense, solvated potassium cation is smaller than those of Li-ion and Na-ion in solution. This results in a faster diffusion and higher ionic conductivity, accompanied by a greater transference number.

Classification of Potassium Secondary Batteries

Depending on the choice of electrolyte, there are non-aqueous and aqueous potassium secondary batteries. For the former, we will cover (i) potassium-ion batteries (KIBs) that employ the rockingchair operation principle as LIBs do, in which both the cathode and anode materials employ topotactic intercalation chemistry for charge storage, and (ii) potassium metal batteries, including K-O2 (or K-air) and K-Sulfur batteries. Furthermore, we will highlight the recent progress on aqueous K-ion based chemistry.


Page 5 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Nonaqueous Potassium-Ion Batteries (KIBs)

KIB Cathodes

Iron Hexacyanoferrate

Figure 1. The lattice structure (a) Prussian blue, KFeIIIFeII(CN)6 and (b) layered LiCoO2 and hypothetically layered KCoO2, where in (b) the counter ions are shown in purple, oxygen red, and alkali metal blue. The viewing direction for LiCoO2 and KCoO2 is from the cross section of the layered structure, which is evident in the case of LiCoO2 but almost indistinguishable in the case of KCoO2.

In non-aqueous potassium-ion batteries, one main issue is the cathode material, in which K-ions can be reversibly intercalated/de-intercalated. Following the first prototype of potassium-ion battery,1 still the top choice is metal hexacyanoferrates as Cui et al. and Padigi et al. recently demonstrated,62-63 which have excellent cyclability for K-ion insertion/extraction. PB, KFeIIIFeII(CN)6, and its analogues are well-known electroactive materials because of their excellent electrochemical behaviors. PB exhibits a rigid structure, where (C≡N)- groups bond with both Fe(II) and Fe(III) forming a cubic framework of iron (II) hexacyanide, or known as iron hexacyanoferrate (II), and iron (III) hexaisocyanide (Figure 1a). The “holes” in this framework are large enough to host large alkali ions, such as K-ions, 1.52 Å in radius, and water molecules. Note that the oxidation state of Fe-ions in the framework determines whether counter ions are allowed in the holes of the framework. When both irons coordinated in hexacyanide and hexaisocyanide are Page 5 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 41

Fe(III), no counter ions are allowed in the structure.

Comparing the lattice structures of PB analogues to those of common cathodes of LIBs simply reveals why the electrochemical behavior of PB is accompanied by exceptional cyclability. Alkali metals are, indeed, the pillars in the architecture of layered metal oxides, e.g., LiCoO2 and KCoO2 (Figure 1b); upon full extraction, the lattice undergoes severe structural changes. This is the reason that only half of the specific capacity of LiCoO2, which remains as a common cathode material of LIBs, can be achieved in practice; because extracting further Li-ions will result in lattice breakdown.64-65 However, the rigid cubic structure of PB is independent of the existence of counter ions, which are accommodated within the cube. This allows fast and reversible K-ion insertion/extraction.

Like any other intercalation materials, the reversibility of the redox systems depends on the size of the counter ion, which should match well with the diffusion channels. In the case of the PB family, the lattice structure perfectly matches with K+. While PB can be successfully cycled for K+ insertion/extraction, the lattice structure is destroyed after hundreds of cycles in Li electrolyte. This makes this class of electroactive materials promising candidates particularly for KIBs from the cyclability standpoint. In addition to being an alternative to LIBs, the prototypes of KIBs exhibited the potential for fabricating ever-lasting batteries, since millions of cycles were realized in cyclic voltammetry tests in aqueous conditions.45-47

Recent computational studies by Ling et al. showed how the cation size can affect the lattice energies during the intercalation process.66 While the preferred site for the intercalation of Li+ and Na+ is the face-centered 24d sites, the preferable interstitial site for larger K+, Rb+, and Cs+ intercalation is the body-centered 8c sites. They also reported a remarkable correlation between the insertion voltage in iron hexacyanoferrate (FeHCF) and the ionic radii of different alkali metals, where intercalation of larger ions leads to a higher voltage. It is 3.08 V, 3.23 V and 3.70 V for Li+, Na+, and K+, respectively, where the much higher potential provides an edge for KIBs regarding energy density over sodium-ion batteries (NIBs) if PB is used for both devices. Experimental investigation of the battery performance of PB-based Na- and K-ion batteries also revealed that Kion battery delivers a higher cell voltage, and the capacity retention is significantly better.67

The rigid structure of PB is quite stable during cycling, and the corresponding battery does not suffer from the common capacity fading as a result of structural changes or distortions. On the other Page 6 of 41 ACS Paragon Plus Environment

Page 7 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


hand, the conductivity is higher, and diffusion is much faster in comparison with conventional cathode materials of lithium-ion batteries. The open framework structure of the lattice allows fast solid-state diffusion, which is a critical parameter in rate capability of batteries. For the case of Liion intercalation, thin film PB cathode with a thickness of 120 nm has been successfully charged/discharged with an extremely high rate of 3,000 C delivering a considerable specific capacity of 85 mAh/g.13

Electrochemical behavior of iron hexacyanoferrate is based on the following two sequential redox reactions transforming Berlin green (BG, aka Prussian green) to Prussian blue (PB) and subsequently Prussian white (PW).46 FeIIIFeIII(CN)6 (BG) + K+ + e- KFeIIIFeII(CN)6 (PB)

(1)

KFeIIIFeII(CN)6 (PB) + K+ + e- K2FeIIFeII(CN)6 (PW)

(2)

PB can be oxidized to BG (1) or reduced to PW (2), which is, indeed, a general mechanism for the insertion of all monovalent cations into PB and its analogues. Padigi et al. prepared BG particles sized 50-75 nm and PB sized 2-10 µm, delivering the specific capacities of 121.4 mAh/g and 53.8 mAh/g, respectively, in an aqueous electrolyte of KNO3.63 Although the PB lattice is spacious enough for the diffusion of counter ions, solid-state diffusion is still the rate-determining step like all cathode materials of LIBs. In general, the chemical synthesis controls the lattice structure and morphology of the electroactive material, and the electrochemical behavior is heavily influenced by the initial structure of the electrodes.

The largest advantage of FeHCF as a KIB cathode is its unique crystal structure, which may be translated to long cycling life—key for stationary energy storage. Figure 1 displays that PB lattice is literally an MOF (metal organic framework) structure with a robust skeleton independent of the presence of the counter ions. However, the lattice of a simple layered metal oxide is highly dependent on the presence of the counter ions (LiCoO2 and KCoO2 in Figure 1). Thus, it is quite difficult to reversibly extract K+ from KCoO2 and intercalate it again without any structural change. Even in the case of LiCoO2, only half of the theoretical capacity is achievable, as the lattice undergoes several structural changes depending on the Li+ concentration.64 There is a hypothetical layered structure for KCoO2 by exchanging Li+ with K+, but in practice, the lattice structure is substantially changed to P4/nmm symmetry.68 Similar behavior is observed when replacing Li+ with Na+ in a layered structure, and not only the lattice structure is altered but also the morphology Page 7 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 41

undergoes a large change.69

The FeHCF lattice is not as compact as metal oxides as LIB cathodes, such as LiCoO2, where PB exhibits a density of ca. 1.8 g/cc. Thus, its volumetric capacity would be lower, which may limit the applications of FeHCF-cathode-based KIBs in portable electronics or electric vehicles. Despite excellent cyclability of PB and its analogues in KIBs, KIBs may need new types of cathode materials to satisfy all practical requirements.

Other Cathodes Recham et al. investigated potassium-based cathode materials in LIBs,70 where K-ions are substituted by Li-ions during the first cycle. This indicates that K-ion de-intercalation from most of common LIB cathode materials is feasible, but the question is whether it is possible to reversibly reintercalate K-ions into these cathode materials. Mathew et al. was able to reversibly intercalate/deintercalate K-ions into/from a nanoporous amorphous FePO4 prepared by a classical sol-gel method. The FePO4 electrode delivered an initial discharge capacity of 156 mAh/g within the range of 3.5-1.5 V vs. K+/K in an electrolyte of 1 M KPF6 in EC/DEC, and retained 70% of its theoretical capacity during 50 cycles.71

Most recently, Vaalma et al. reported a layered birnessite of K0.3MnO2 as a cathode, which exhibits a high capacity of 136 mAh/g with an average potential of 2.8 V in a voltage window from 1.5 to 4.0 V vs. K+/K.72 However, at this high cutoff potential, the reversibility of K0.3MnO2 cathode is poor, probably due to irreversible phase transition at high voltages. In the voltage window of 1.5 to 3.5 V, this compound exhibits good cycling performance, retaining 68% of its 10th cycle’s capacity after 675 cycles. Because the cathode may not contain removable K-ions, the authors assembled full cells with a pre-potassiated carbon anode of hard carbon/carbon black composite. Such a full cell exhibits an initial capacity of 80 mAh/g (based on cathode) at a current rate of 32 mA/g with an average operating potential of ~2.0 V in an electrolyte of 1.5 M potassium bis(fluorosulfonyl)imide (KFSI) solvated in 1:1 EC/DMC (ethyl carbonate/dimethyl carbonate).72 The cell capacity fades to about 50 mAh/g after 100 cycles. Potassium titanium phosphate has also been employed as a cathode material of KIBs.73 Similar to Page 8 of 41 ACS Paragon Plus Environment

Page 9 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the performance of this class of materials in LIBs, the battery performance is originally poor due to low electrical conductivity and addition of conductive agents, such as carbon black, is mandatory. As a matter of fact, most of the available cathode materials of LIBs with spacious and preferably cubic channels for diffusion might also be employed in KIBs.

Organic molecular solids can be promising for accommodating large ions due to their better structural flexibility with strains. Perylene tetracarboxylic dianhydride (PTCDA) has been recently introduced as a cathode material for potassium-ion battery with a specific capacity of about 130 mAh/g by Chen et al. and Xing et al.74-75 The performance is comparable when Na-ions are stored in this molecular solid.76 Following successful applications of Poly(anthraquinonyl sulfide) (PAQS) as a cathode material in LIBs, NIBs, and Mg-ion batteries (MIBs), Jian et al. employed PAQS as a promising cathode material in KIBs.77 Although the cell voltage is not as high as available LIBs, the battery performance is comparable. Since there is a wider range of organic materials, this is just the beginning in the quest for organic cathode materials.

Quest for Ideal Cathodes

The cathode materials tested so far are promising but still far from being ideal candidates for the practical development of KIBs. The cyclability of PB and its analogues is a noticeable advantage, but the volumetric capacity is much lower than those of LIBs due to the low density of hexacyanoferrates. Another issue is the intrinsic role of water molecules within the hexacyanoferrate lattice, where there might be of safety risk. In general, a rigid but smaller lattice is required to accommodate a considerable amount of K-ions. The key point is that Li-ion is fairly small and a simple metal oxide (e.g., LiCoO2) lattice can retain its original architecture with no structural change upon extraction of at least a large portion of Li-ions. This is not the case of Kbased materials due to the large size of K-ions, which are critical in the spatial architecture of the lattice. According to the available reports,1,72,86 the capacity of Prussian blue cathode can reach 80 mAh/g, and its average operating redox potential is 3.8 V vs. K+/K. Considering the carbon anode capacity of 262 mAh/g at C/10 and its average depotassiation potential of 0.3 V vs. K+/K, a hypothetical full cell would be able to deliver an energy density of 201 Wh/kg based on the mass of the both electrodes. Based on the state-of-the-art battery manufacturing technology, the real battery may deliver an energy density of ~110 Wh/kg in pouch cells. Although this is lower than that of LIBs or Page 9 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 41

even NIBs, if extremely long cycling life of KIBs can be demonstrated in non-aqueous electrolyte, KIBs may become a serious competitor in the market.

KIB Anodes

Carbon Anodes

Another critical component of alkali metal ion batteries is the anode material. It is generally believed that metallic anodes may not be practical because of dendrite-formation related safety issues. However, potassium is very soft as the low potassium melting point of 64 °C compared to 98 °C and 179 °C of Na and Li, respectively, renders potassium dendrites mechanically much weaker, which might avoid a dendrite-caused thermal runaway. Nevertheless, to be on the safer side, it is desirable that the anode is an intercalating material, and consequently, its operating potential and cyclability directly affect the battery performance. For LIBs, carbon-based anodes have been the most common ones not only in research but also in commercial products.

In the case of NIBs, as there is yet a mass-scale commercialization, where one of its biggest challenges is the anode. Although there are hundreds of species that can be successfully intercalated into graphite, intercalation of desolvated sodium into the gallery of graphite is thermodynamically unfavorable.78-79 One promising approach is to expand the graphite layers by simultaneous intercalation of solvent molecules,78 which is, of course, accompanied by volume expansion. For NIBs, non-graphitic carbon, including hard carbon and soft carbon are promising candidates.80-81

Interestingly, the most stable form of alkali metal graphite intercalation compound (GIC) is that of potassium. This stability is so much dominant that K-intercalated graphite is even employed as an anode material of LIBs.82 Potassium-GIC is of a stage-one structure, where one layer of potassium atoms are inserted between every graphene layer (Figure 2). Obviously, the expansion of graphite interlayers as a result of the interaction of potassium is inevitable. The energies of intercalation of alkali metals into graphite have been calculated using van der Waals density functionals and density functional theory (DFT) calculations.78,83 Figure 2 graphically summarizes the thermodynamics of possible GICs accommodating Li, Na, and K. NaCX is unstable, and its formation is thermodynamically unfavorable, whereas, the formation enthalpies of LiCX and KCX are sufficiently negative to form stable GICs, but KCX is even more favorable thermodynamically. Page 10 of 41 ACS Paragon Plus Environment

Page 11 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. Enthalpies of the formation of various alkali metal intercalated graphite compounds. (a) Li, (b) K, and (c) Na. Reprinted with permission from Ref. [78]. Copyright 2014, Royal Society of Chemistry.

Figure 3 shows computational investigations of different stages of potassium intercalation in Page 11 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 41

graphite, which is in agreement with the experimental results reported in the literature.84-85 K-GICs have been well known since 1932,8,86-87 where, in most prior art, K-GICs were prepared by thermally annealing the mixture of potassium metal and graphite under vacuum or an inert atmosphere.88-90 However, electrochemical intercalation of potassium into graphite had not been attempted until very recently.

Tossici et al. investigated KC8 as a pre-reduced anode for LIBs, in which K-ions are extracted during the first full-cell discharge, and during charge, incoming Li-ions are inserted to form a LiGIC.91-92 KC8 anode that can be formed more easily than LiC6 by thermal treatment may allow usage of a Li-free cathode in LIBs. From the perspective of using graphite containers, e.g., crucibles, for electrolysis of molten salts, Liu et al. investigated the electrochemical intercalation of potassium into graphite in molten KF, but the GIC formed is quite unstable, where exfoliated graphene layers are formed.93 Liu and Wang et al. studied hollow non-graphitic carbon nanofibers as the anode for KIBs, which showed a high initial depotassiation capacity of about 300 mAh/g. However, the cell showed relatively poor cycling performance as the specific capacity fades to 200 mA/g on the second cycle and about 80 mA/g after 20 cycles.94

Figure 3. DFT calculations for different theories based on various pathways of K intercalation into graphite. (a) Calculated potential profile for K-ions intercalation into graphite for different staging scenarios. Blue line corresponds to an intercalation staging: KC24 (Stage III) → KC16 (Stage II) → KC8 (Stage I). The green dotted line corresponds to calculated values for the previously reported staging: KC24 (Stage II) → KC8 (Stage I). The red dotted line corresponds to the averaged experimental data shifted by 26 mAh/g to correct the capacity contribution from SEI formation. (b) Scheme of the different stages of K-intercalated graphite, K is shown in blue and C in yellow. Reprinted with permission from Ref. [96]. Copyright 2015, American Chemical Society.


Page 13 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Jian et al., for the first time, reported room-temperature electrochemical potassium insertion/extraction in graphite in a non-aqueous electrolyte of 0.8 M KPF6 solvated in EC/DEC. The Graphite/K half-cell exhibited a high reversible depotassiation capacity of 273 mAh/g at C/40 (1C = 279 mA/g in forming KC8), close to its theoretical capacity of 279 mAh/g, making it a promising anode material for KIBs. Ex-situ XRD studies confirm that stage-III KC36, stage-II KC24 and stage-I KC8 form sequentially upon potassiation while depotassiation recovers graphite through phase transformations in an opposite sequence (Figure 4). Moderate rate capability and cycling performance were observed, where at C/2 in 50 cycles, the capacity retention is 50%.82

Figure 4. (A) First-cycle galvanostatic potassiation/depotassiation potential profiles at C/10. (B) XRD patterns of electrodes corresponding to marked SOCs in (A). (C) Structure diagrams of different K-GICs, side view (up) and top view (down) Reprinted with permission from Ref. [82]. Copyright 2015, American Chemical Society.

The theoretical volume expansion for graphite is 61% upon full potassiation, which causes a detrimental impact on cycling stability. The cycling performance of graphitic materials for potassiation/depotassiation can be improved by introducing enclosed nanoporosity. Xing et al. reported the synthesis of a low-density (0.92 g/cm3) polynanocrystalline graphite by infiltrating a Page 13 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 41

nanoporous graphene with chemical vapor deposition of an ethanol precursor.95 Note that the density of bulk graphite is around 2.2 g/cm3. The hollowness of this polynanocrystalline graphite is most likely enclosed without allowing the imbibing of the electrolyte as its N2 Brunauer-EmmettTeller (BET) surface area is only 91 m2/g. This new carbon material exhibit much better cycling stability as it better accommodates the volumetric expansion. Right after Jian et al.’s report on graphite KIB anode, Komaba et al. and Luo et al. also reported highly reversible electrochemical intercalation of potassium into graphite.50,96 The former group reported a capacity of 244 mAh/g for their Graphite/K half-cells, where they also investigated different binders, including polyvinylidene fluoride (PVdF), sodium carboxymethylcellulose (CMC-Na), and sodium polyacrylate (PANa). It was shown that the latter two binders help increase the first-cycle coulombic efficiency although the reversible capacity is slightly compromised. In the study by Luo et al., a reversible capacity of 208 mAh/g was reported for the graphite anode. They also investigated the K-ion storage properties of reduced graphene oxide (RGO), where a reversible capacity of 222 mAh/g was observed.96 Remarkably, K-ion intercalation into RGO significantly increases the optical transparency of RGO from 29.0% to 84.3%. Not only this indicates the uniform stacking of graphene layers but also provides an opportunity for potentially utilizing this electroactive material in photoelectrochemical cells.

To address the volumetric change of the graphite electrode during (de)potassiation and improve its cycling stability, Jian et al. synthesized bulk-sized non-graphitic carbons that have somewhat low density, i.e., ca. 1.6 g/cm3 vs. ca. 2.2 g/cm3 for graphite.82,97 These are very typical non-graphitic carbons (often called amorphous carbons): graphitizable soft carbon by pyrolysis of PTCDA and non-graphitizable hard carbon spheres (HCS) by hydrothermal carbonization of sucrose. Soft carbon displayed a high specific capacity of 270 mAh/g, comparable with that of graphite, where a pure sloping behavior is observed in its potential profiles, similar to its performance as an anode for Na-ion batteries.81 The cyclability of Soft Carbon/K half-cells is more stable than that of Graphite/K cells with capacity retention of 81.4% after 50 cycles at 2C. Soft carbon exhibits good rate capability as well, where the specific capacities of 210, 185, and 140 mAh/g were obtained at discharge rates of 1C, 2C, and 5C, respectively. The rate performance of HCS was comparable to soft carbon with specific capacities of 190 and 136 mAh/g achieved at rates of 2C and 5C, respectively. HCS exhibited, to date, the best cycling stability among graphite, soft carbon, and hard carbon, where the electrode retained 83% of its initial capacity after 100 cycles at C/10. All the above results were obtained by using PVdF as the binder for the carbon electrodes. Ongoing research from the Ji group reveals even better cycling stability when NaCMC is employed as the Page 14 of 41 ACS Paragon Plus Environment

Page 15 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


binder for these non-graphitic carbon anodes. It is very likely that PVdF reacts more with potassium or even sodium but less with lithium in the electrolyte/electrode interface, where, indeed, similar issues have been observed for NIBs as well.

Electrochemical studies of Na and K intercalation in HCS showed different rate behaviors (Figure 5).97 While the specific capacity is larger for HCS/Na at low current rates, surprisingly, compared to HCS/Na cells, HCS/K half-cells exhibit a much better rate performance. The authors measured the diffusivity values of HCS/K half-cells and HCS/Na half-cells as a function of the state of charge by galvanostatic intermittent titration technique (GITT) measurements, where the diffusivity of the former is slightly higher. The interesting comparative kinetic performance between HCS/K and HCS/Na calls for further studies, particularly by calculation/simulation. Another large factor contributing to the better rate behavior of HCS/K than HCS/Na is the higher operating potential of the former relative to its metal reference/counter electrode. On average, potassiation occurs at above 0.2 V vs. K+/K for the lower-potential quasi-plateau, whereas sodiation plateau takes place around 0.05 V vs. Na+/Na. Note that the low-potential plateau of lithiation into graphite could occur around 0.1 vs. Li+/Li. This is why upon high sodiation current rates, even a low extent of overpotential could shift the HCS/Na cells to the lower cutoff potential. This higher relative operating potential of carbon with respect to K+/K not only gives an edge for carbon anodes in KIBs in high-rate performance but also mitigates the possibility of metal plating for KIBs in full-cell practical applications.

Figure 5. Typical discharge/charge potential profiles of HCS/Na cells and HCS/K cells. Reprinted with permission from Ref. [97]. Copyright 2016, Wiley. Page 15 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 41

It should be emphasized that there remain knowledge gaps in terms of K-ion storage in carbonbased materials toward a practically acceptable battery performance. Intercalation of desolvated Na-ions in graphite is thermodynamically unfavorable; however, recent studies on co-intercalation with suitable electrolyte solvents provide a new opportunity for design of graphite anodes for NIBs.98-100 It would be interesting to learn about co-insertion of K-ions with solvent molecules in carbon materials.

Other Anodes

At the infancy of the field of KIBs, computational studies may play a large role in predicting potential electrodes. Er et al. showed that Ti3C2 MXene is a potential electrode material for KIBs with a theoretical capacity of 192 mAh/g.101 Quite recently, Sn-C has also been investigated as a potential anode material for KIBs, displaying a reversible charge/discharge performance.102 Similar to the case of sodium,80,103 insertion of potassium into Sn-C is not straightforward and is accompanied by some slow reactions, resulting in the formation of a composite rather than a crystalline structure.102

Aqueous Potassium-Ion Batteries

Among various applications of PB in electrochemical systems, PB analogues were also investigated as electrode materials for aqueous batteries. The focus has been symmetrical PB batteries where PB analogues serve as both anode and cathode. In this cell design, two redox couples of PB provide the required anodic and cathodic processes, resulting in a cell voltage of 0.68 V.104 The principle is via “disproportionation” redox reactions, as shown in the equations (1) and (2), corresponding to 0.82 and 0.18 V vs. SHE, respectively. During the charging process, the PB cathode is oxidized to BG, and the PB anode is reduced to PW. To increase the operational potential, asymmetrical hexacyanometallate cells were developed, in which a more negative anode and a more positive cathode were selected from a wide range of transition metal hexacyanometallates.37,44 An example is an aqueous KIB based on a KCrIIICrII(CN)

6

anode and a KCrIIIFeII(CN)

6

cathode (at a fully

discharged state), which delivers a cell voltage of about 1.5 V.37

Wessells and Cui et al. systematically studied the analogues of the PB family, such as


Page 17 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


KCuIIFeIII(CN)6, KNiIIFeIII(CN)6 and structures with Ni and Cu co-replacement of Fe in the hexaisocyanide sites.62,105-109 The operation voltage can be adjusted by the ratio of Cu and Ni, from 0.7 to 0.95 V vs. Ag/AgCl. For the KCuIIFeIII(CN)6 electrode, the operation reaction is: KCuIIFeIII(CN)6 + K+ + e- K2CuIIFeII(CN)6

(3)

which provides a theoretical capacity of 85 mAh/g. The electrode material was prepared by a precipitation method from an aqueous solution, where obtained material is hydrated as K0.71Cu[Fe(CN)6]0.72·3.7 H2O, and the theoretical capacity of this formula is 62 mAh/g.107 These electrodes show extremely high rate performance and excellent cycling performance. For example, KCuFe(CN)6 exhibits a capacity of 40 mAh/g at 83C, which is about 2/3 of the capacity at 0.83C, and the capacity retention is above 80% after 40,000 cycles at 8.3C (Figure 6). At 0.83C or even 8.3C, the polarization is extremely small, thus demonstrating a high round-trip efficiency, which is critical for the applications of stationary energy storage. The same group also demonstrated that PB analogues exhibit high-rate and long-cycling performance when alkaline earth metal ions, i.e., Mg2+, Ca2+, Sr2+, and Ba2+, are the counter ions.106 The large interstitial sites as well as the interaction between (C≡N)- and divalent ions being weaker compared to the case with O2- in metal oxides may facilitate the great performance, where the activation energy for the transfer of these ions may be low.

Figure 6. (a) Galvanostatic cycling of KCuFe(CN)6 at various current densities between 0.6 and 1.4 V vs. SHE. (b) Long-term cycling of CuHCF at a rate of 17 C between 0.8 and 1.2 V vs. SHE shows 83% capacity retention after 40,000 cycles (right). Reprinted with permission from Ref. [107]. Copyright 2011, Nature Publishing Group. Potassium titanium oxide has been utilized as a potential anode material.110 The capacity fading of this material is severe during the initial cycles. This is due to the fact that K-ions are too large for Page 17 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 41

insertion/extraction into metal oxides, and the lattice structure will be subjected to severe changes during initial cycling. This limits the application of available metal oxides, which have been successfully employed as anode or cathode in LIBs and NIBs. Suitable lattice structures with good diffusion channels for K-ions have yet to be found.

KIB Electrolytes

Unfortunately, no systematic research has been conducted to study the electrolyte and its role on the performance of KIBs yet. In all works devoted to KIBs, electrolytes have been typically chosen based on conventional electrolytes of LIBs. The most common electrolyte is a mixture of alkyl carbonates1 and potassium salts, such as KBF4,1 KPF6,67,74,82,96-97,102 and KFSI (potassium bis(fluorosulfonyl)imide).72 Since PB and its analogues are still the dominant cathodes of KIBs, and their preliminary studies have been conducted in aqueous media, aqueous electrolytes of common potassium salts, such as KNO3, are also employed for the studies of KIBs.62-63,107,109 This is accompanied by rapidly growing interest in aqueous LIBs. Despite being limited by a low cell voltage, aqueous KIBs with low cost, simplicity in design, and good safety are promising candidates for large-scale energy storage.

Potassium Metal Batteries

Potassium-Oxygen Battery The concept of metal-air batteries has been well known, e.g., the primary zinc-air battery,111-115 but a secondary alkali metal battery utilizing a non-aqueous electrolyte is a relatively new idea.116-121 Abraham and Jiang proposed the possibility of replacing intercalation cathode materials with a reactive cathode, in which O2 (from air) is reduced and reacts with Li-ions to form Li2O2.122 Since then, considerable attention has been paid to Li-O2 batteries.117,123-127 In a sense, the cathode of Li-O2 batteries is similar to fuel cells, as a part of the reactive species comes from outside the cell. In theory a Li-O2 battery can exhibit an energy density higher than any other known battery systems. The low atomic weight of lithium guarantees the highest possible specific capacity of a battery. However, its theoretical capacity is not practically achievable due to Page 18 of 41 ACS Paragon Plus Environment

Page 19 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


severe limitations. However, achieving a fraction would make Li-O2 batteries impressive. It should be emphasized the terminology of this topic is somewhat misleading, as the term Li-air and Li-O2 are used interchangeably. The target battery is obviously Li-air because it should work by consuming O2 from the ambient air rather than the constant supply of pure O2. However, most research works are conducted under pure saturated O2. Inappropriate comparison of different cases without considering the O2 concentration has caused some concerns. Owing to the challenges of Li-O2 batteries, Na-O2 batteries have recently become possible candidates, despite sacrificing some specific capacity. While Na-O2 batteries have some advantages over Li-O2, K-O2 batteries can be even more advantageous. For Li-O2 batteries, a critical issue is the electrochemical pathway for the formation of lithium peroxide (Li2O2), the final discharge product, where the process involves the thermodynamically unstable intermediate of lithium superoxide (LiO2).128-130 The unstable nature of LiO2 and its reactions with organic electrolyte directly contributes to the irreversible cell processes, e.g., drying up the cells. In contrast, as reported by Hartmann et al., the final discharge product of the Na-O2 batteries is crystalline sodium superoxide (NaO2), which is at least kinetically stable and is also formed with a similar mechanism.131 In this family of alkali metal superoxides, KO2 as the final discharge product of K-O2 batteries, first reported by Ren and Wu,132 is exceptionally stable both kinetically and thermodynamically, as it is even available as a chemical in the market.

For Li-O2 systems, some primary interest is to stabilize LiO2 and to increase reaction reversibility and efficiency associated to O2-. Beside catalysts, one approach is to employ ionic liquids as an electrolyte due to their wide stable electrochemical window, where 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI) is, indeed, a common ionic liquid in electrochemical experiments. The impact of cations in the ionic liquid electrolyte is evident by simply comparing the CV curves of MO2/M redox systems in an electrolyte of EMI-TFSI (Figure 7). It was shown that large (soft) cations greatly enhance the electrochemical behavior of O2/O2– redox reactions. For detailed information about Li-O2 batteries, readers may read the recent review articles.133-135



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 41

Figure 7. Cyclic voltammogram of O2/O2– in neat EMITFSI along with various salts at 0.025 M concentration on a glassy carbon (GC) electrode at 100 mV/s, showing OER overpotentials of cation-O2– as a function of cation hardness Reprinted with permission from from Ref. [129]. Copyright 2012, American Chemical Society.

Another interesting feature of a K-O2 battery is the reversibility of O2/KO2 in comparison with O2/NaO2, as shown by the cyclic voltammetry (CV) results in Figure 8 (compare the left and right columns side by side). While the KO2 peak is slightly weakened after 20 cycles, NaO2 peak is almost disappeared. This is due to the mechanism of the KO2 formation, which is through one straightforward process (as judged by the well-defined voltammetric peak). Moreover, the stability of KO2 guarantees the system reversibility for the reverse reaction. Changing the potential window in the cathodic region only affects the peak intensity with a little influence on the peak shape. This means that the progress of the cathode process does not change the reaction pathway.


Page 21 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8. Cyclic voltammetry studies of 0.025 M (left column) NaPF6, and (right column) 0.025 M KPF6 in EMITFSI. (a) Selected cycles: 1st (black), 2nd (blue), and 20th (red) scan. (b) Scans extending to various cathodic limits as listed in the inset. (c) Cyclic voltammograms of O2-saturated 0.025 M KPF6 in EMITFSI at 100 mV/s on a GC electrode: 1st cycle (black) and 20th cycle (red). (d) Incremental cathodic limits ranging from 2.38 to 1.19 V. (e) Various scan rates (10−300 mV/s). Inset shows expansion on anodic peaks. Reprinted with permission from Ref. [129]. Copyright 2012, American Chemical Society.

It should be pointed out that the redox system of KO2 is composed of two peaks, but they are hardly separable. Scan rate dependency of these peaks reveals that the second reaction is the ratedetermining step. First, a sharper CV peak indicates a flat plateau in charge/discharge profiles, where the battery can deliver a constant potential during its performance. Second, a high peak-topeak separation in CV means that there is a gap between the anode and cathode processes, i.e., cell polarization due to overpotentials (Figure 9). In other words, a higher cell voltage is needed to Page 21 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 41

charge the battery than that provided during the discharge. In any battery systems, it is vital to reduce this irreversible energy consumption to maximize the round-trip efficiency.

A key problem of Li-O2 batteries is a huge potential difference between charge and discharge potential profiles owing to high overpotentials of the reactions involved. There are two overpotentials in the superoxide reaction for (i) oxygen adsorption, and (ii) LiO2 formation. The former can be reduced by employing catalysts to dissociate O2 to form O adatoms. However, it is difficult to reduce the latter overpotential, because it is thermodynamically related to LiO2. This overpotential is much less in Na-O2 batteries in the range of ~200 mV.131,136-138 According to the electrochemical behavior described above, the overpotentials are trivial for a K-O2 battery (Figure 9). Ren and Wu have shown that the potential difference between charge and discharge of a Kbattery is as low as 50 mV without the use of catalysts.132 High polarization causes low energy (round-trip) efficiency—the ratio between energy output and energy input, where conventional powers, i.e., internal combustion engine, are criticized for, as it is only around 20%.


Page 23 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 9. Charge/discharge potential profiles for (a) K−O2 battery (0.5 M KPF6 in DME) and (b) Li−O2 battery (1 M LiCF3SO3 in tetraglyme). Both at a current density of 0.16 mA/cm2. Electrode geometric area is 0.64 cm2 . The dash lines indicate the calculated thermodynamic potentials for the batteries. Reprinted with permission from Ref. [132]. Copyright 2013, American Chemical Society.

A key challenge for developing alkali metal-oxygen batteries is to find appropriate anode materials, as it may not be practical to directly use alkali metal anodes due to safety risks, where Li is perhaps Page 23 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 41

an exception due to its relatively high melting temperature, 180 °C, if solid-state electrolytes are employed. Formation of an insoluble surface layer on metallic anodes may hinder the parasitic reactions on surface.139 Furthermore, the excellent performance of carbon anodes for K-ion intercalation might satisfy the need of an anode for a K-ion-O2 battery. In other words, not much effort is required to find a practical anode for K-O2 batteries, as they are already identified.96 In contrast, the anode issue makes Na-O2 battery less practical, because almost all studies have been conducted using Na metal anode.

Of course, the specific capacity of graphite anode is much below the theoretical expectation of alkali metal air batteries, and the quest for finding conversion anodes with high specific capacity is an active area of research for all alkali metal-air batteries. By learning from profound experience on anode materials of LIBs, it is also possible to examine new candidates for potassium anodes too. K3Sb alloy showed a high capacity of 650 mAh/g in a K-O2 battery.140

Potassium-Sulfur Battery

The mechanism of Li-S battery is somehow between LIBs and Li-O2 battery. Unlike LIBs in which the cathode operates on a topotactic solid-state intercalation reaction, Li-S cathode is based on a conversion or integration reaction of S8 and Li+ at the cathode interface. This is similar to Li-O2 batteries, in which the cathode is involved in a catalytic reaction of oxygen combining with Li-ions. However, contrary to the Li-O2 batteries, Li-S batteries have a closed system similar to LIBs. This matters when calculating the specific capacity and energy density, as the reactive species are already sealed within the cell. This also dictates the cathodic reaction pathway. While in a Li-O2 battery, the ratio of oxygen in the resulting cathodic material, LixOy decreaces, the discharge pathway of an S-cathode is from S8 to Li2S4, Li2S2, and finally Li2S. Li-S batteries face challenges associated with the cathode product intermediates of lithium polysulfides, which are soluble in the electrolyte solution. Thus, not only the cathode has a mass loss, but also the dissolved polysulfides interfere with the anode process too. The most common approach is to trap sulfur within a shell of carbon or polymers to avoid direct interaction with the electrolyte.141-150 Beyond Li-S systems, the first immediate alternative analogue is Na-S battery. Similar to the cases described above, potassium has the advantages of sodium over lithium, plus more. Hence, there are emerging interests in K-S batteries.151-152 Page 24 of 41 ACS Paragon Plus Environment

Page 25 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Similar to Na-ion, K-ion is too big (soft) to complete the reaction to reach K2S, and the final product has been reported to be K3S2.152 Further effort is needed to capture the full capacity of an S-cathode in potassium-sulfur battery because there is no thermodynamical limit for the formation of K2S in the cathode; Li2S and K2S are similar. Since it is very difficult to overcome solubility of alkali metal polysulfides in a liquid electrolyte, high-temperature alkali metal-sulfur battery was introduced utilizing a molten metal anode and a solid electrolyte.153-154 The solid electrolyte prevents the liquid metal anode from contacting with the sulfur cathode. This design is not suitable for Li-S battery due to high melting point of lithium (180 °C) but utilized for Na-S [153]. Although Na is melted at 98 °C, a temperature of ca. 350 °C is needed to reach an acceptable wettability of the solid electrolyte in contact with the molten anode. However, this type of alkali metal-sulfur battery exhibited a good cyclability.153

Another approach is to make an alloy of Na with K or Cs, which can be a liquid at room temperature.155 However, there exists another problem associated with destructive ion exchange of Na and K in the solid electrolyte.155-156 As depicted in Figure 10 (a), Al2O3 layer is cracked in contact with melted sodium, but no destructive effect for the case of potassium. Owing to its low melting point (63 °C) and excellent wettability performance, molten K anode can have an acceptable performance at a temperature below 240 °C, as can be witnessed in Figure 10 (b).

Figure 10. (a) Interaction of Na, Na-K alloys, and K with Na-Al2O3 or K-Al2O3 solid electrolytes at 150 °C. (b) Wetting behavior of liquid K on the K-Al2O3 solid electrolyte surface at various temperatures. Reprinted with permission from Ref. [151]. Copyright 2015, Wiley.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 41

A high-temperature K-S battery at operating temperature of 150 °C can deliver a specific capacity of ca. 300 mAh/g and retain it over 1,000 cycles.151

Summary and Perspective: Opportunities and Challenges

The current status of LIBs, as the most common energy storage systems of portable devices and electric vehicles, is the result of extensive research conducted during the past four decades. In any case, the need for large energy storage systems of the future cannot be satisfied by LIBs due to the limited availability of natural resources of lithium and expensive cost. Thus, there is no other choice but to find potential alternatives. Without any exaggeration, potassium batteries have certainly invaluable advantages over their sodium (and even lithium) counterparts. Among alkali and alkaline earth metals, potassium represents a unique and long-ignored opportunity for energy storage. Na and Mg batteries have been extensively studied over the past two decades, but still, the performance is not satisfactory enough for practical applications.

Potassium batteries are just at the infancy stage, and practical ideas and solutions will evolve in time. In this direction, comprehensive knowledge of LIBs can be the guiding star, but the intrinsic differences of lithium and potassium systems should be carefully taken into account.

Another important perspective is that KIBs are not necessarily a replacement to current LIBs for power devices, as can be electrochemical energy sources with their own applicability. If considering the prototype of KIBs with a PB cathode, a conventional electrolyte, and a carbon anode; the resulting battery can be inexpensive and may exhibit a good long-term performance. The only issue is the lower energy density in comparison with available LIBs. The critical requirement for maximizing the energy density is for portable devices and electric vehicles, where the battery should be in its minimum size and weight. If the goal is to build large batteries for household energy storage or load-leveling, the price is much more important than the weight.

Alkali metal oxygen and sulfur batteries are, indeed, new types, at least for practical applications. Although the primary focus has been on lithium-based batteries because of resemblance of LIBs, their commercialization may take time. Owing to the fact that the development of Li-O2 and Li-S batteries will be limited by the scarcity of natural resources sooner or later, it may be necessary to Page 26 of 41 ACS Paragon Plus Environment

Page 27 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


shift this focus towards K-O2 and K-S batteries at this preliminary stage. Indeed, potassium (39.10) is much heavier than lithium (6.94) and sodium (22.99). However, from a full-cell point of view, in the K-ion systems, the more mass from potassium ions does not occupy a large percentage of the total mass of both electrodes and the whole battery with inert mass of electrolyte, current collectors and packaging materials. For example, the K2Fe2(CN)6/C8 system (442.10) represents only 7.85% heavier than the competitive NIB system of Na2Fe2(CN)6/hard carbon (C8 with a capacity of 279 mAh/g), 409.88. Additionally, the K-ion systems may have a wider voltage window than NIB systems due to the low operating potential of potassium metal, KGICs or K-Carbon as an anode. Indeed, the argument about the NIBs’ intrinsic advantage over KIBs may not hold true. Furthermore, similar to NIBs, potassium does not form alloys with aluminum; thus, for both NIBs and KIBs, aluminum foil can be used as a current collector, which will further lower than cost.

It is safe to say that neither NIBs nor KIBs would be able to compete against LIBs regarding energy density, where in portable electronics and electric vehicles it is the most important metric unless lithium price turns completely unaffordable. The advantage of NIBs and KIBs is still the low cost and their long-term technological sustainability. Thus, the competition will be most likely between NIBs and KIBs for the market of stationary energy storage. This is not saying that NIBs and KIBs have no future in electric vehicles; there are great potentials for both to improve. Note when LIBs was first commercialized, the energy density of those LIBs was only around 100 Wh/kg, where such values have already been surpassed by some current prototypes of NIBs.

When looking back the history of research and development of LIBs, which was relatively rapid due to the tremendous existing demand for portable electronics in the 1990s, considerable attention from both academia and industry paid to LIBs paved the path for establishing an extensive knowledge pool about various features and components of LIBs. Although potassium batteries have attracted much attention during the past few years, our knowledge is still very limited, particularly about the mechanisms at an atomic scale as well as along interfaces, i.e., solid electrolyte interphase (SEI). For SEI of KIBs, it is not surprising that little has been done because even for NIBs, not much is known about the SEI on the hard carbon anode as well as various cathodes. Hence, it is vital to profoundly understand the different basic facets of potassium systems before any practical batteries can be realized. It is our opinion that the following issues are worthwhile being properly investigated/addressed to make potassium batteries practically comparable with their rivals. Page 27 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 41

(i) Identify Suitable Cathode Materials and Reveal Their K-Ion Storage Mechanisms: The size and charge density of K-ions in an electrolyte and solid materials are significantly different from those of Li and Na counterparts. Thus, conventional materials of LIBs and even newer cathode materials for NIBs cannot be simply employed in KIBs. This is the main reason that the PB family is still the most popular cathode material of KIBs, as there is comprehensive knowledge about K-ion insertion/extraction into/from PB structures. Therefore, intercalation of K-ions into possible metal oxides (which may have high specific capacity values) should be computationally and experimentally studied to fundamentally understand possible opportunities and drawbacks. For designing new cathode materials, the largest challenge is to accommodate the large strain caused by accommodation of large K-ions. To this end, conventional crystalline inorganic materials may be limited due to their rigid structures, whereas amorphous or short-range ordered materials may find much better performance. Among these materials, organic solids assembled by van der Waals force with or without crystalline structures can be promising. Of course, polymeric materials can be uniquely advantageous as well due to their structure flexibility and tunability of properties, such as conductivity and redox functionalities. As a unique advantage, KIBs may be more amenable to charge-carrier-free cathode because K-GICs and K-Carbon anode can be easily prepared by various methods, such as annealing or solution intercalation. Indeed, many impractical cathode materials explored in the last twenty years of LIB research may find their more suitable applications in KIBs.

(ii) Explore Carbonaceous Anodes: Compared to LIBs and NIBs, K-C type anodes can be more advantageous due to the higher operation potentials relative to the metal reference electrode, where the metal dendrite concern is less than Li-C and Na-C counterparts. Of course, it is common sense that potassium metal is extremely reactive and can be very dangerous, compared to Li and Na metals. One should not confuse about K-ion batteries with such an issue of the potassium metal. Electrodes containing K-ions can be safe in sealed batteries as long as dendrites and plating of potassium metal do not occur on the anode side. Please note that as most fundamental research is typically conducted with half-cells containing metallic potassium as the counter/reference electrode first, we strongly encourage researchers in the KIB field to take extra caution in handling potassium metal and tested K-containing half-cells. For K-ion full-cell batteries, metallic potassium does not have to be employed; therefore, the safety of K-ion batteries may not necessarily be more concerned about than its Li-ion or Na-ion counterparts. As graphite may work well for KIBs, the existing infrastructure of LIBs will most likely serve the futuristic KIB industry, which presents a large advantage over NIBs. However, the volume expansion of graphite anode Page 28 of 41 ACS Paragon Plus Environment

Page 29 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


upon potassiation is of a large scale, ca. 61%, which may be a stopper of the graphite anode in practical KIBs. Along this line, non-graphitic anodes with less density values, including hard carbon and soft carbon, may still put this technology back on the track of eventual commercialization. The more space in these non-graphitic carbons will be able to accommodate the “lodging” of large K-ions more easily. Thus, on the anode side, to understand the correlation between the local structures of non-graphitic carbons and the electrochemical performance of K-ion storage can be a fruitful pathway forward. We expect that capacity values higher than 279 mAh/g corresponding to C8 can be realized if the structures of non-graphitic carbons are well designed. (iii) Investigate SEI: It has taken quite a long time to understand the SEI in LIBs. At the current stage with strong interests on high-voltage cathodes and solid-state electrolytes, there remain knowledge gaps regarding fundamentals of SEI of LIBs, particularly on the cathode side and Li metal anode. For NIBs, understanding of SEI is very much limited. For KIBs, the SEI chemistry may be very much different from that of LIBs as K is a very soft cation and it prefers to precipitate with large anions. For SEI on the surface of carbon anodes in LIBs, LiF and Li2CO3 of strong ionic bonding are among the primary components. As for KIBs, SEI can be designed by purposely using large and soft anions. By comparing to the Li and K cases, Na-SEI might be challenging, as Na-ions are neither “hard” nor “soft.”. Like other batteries, SEI formation is a key step in long-term cycling performance of KIBs, as a protective SEI can avoid side reactions of the electrode surface in direct contact with the electrolyte, but a thick SEI can block further diffusion of electroactive species. It has been reported that potassium may be capable of forming a more stable SEI in comparison with Li and Na [51], but profound studies are needed to fully understand the nature and permeability of K to practically plan the optimum cell architecture.

(iv) Understand Electrode Performance in Full Cells: In lithium batteries, Li anode, which serves as the reference electrode too, is commonly used to eliminate the influence of the other half-cell while studying the anode or cathode half-cell. In half-cells, the same cell setup has been used for sodium batteries and potassium batteries as for LIBs. However, Na metal and K metal may not be as good reference electrodes as Li metal because they can be more reactive with an organic electrolyte, resulting in large Ohmic resistance and fast electrolyte degradation. In particular, potassium cannot be used at elevated temperatures due to its low melting point. This may cause an inconsistency in the fundamental studies of K cells, which should be carefully taken into account. On the other hand, chemical reactivity of potassium is generally a serious safety issue in designing K batteries. Page 29 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 41

Acknowledgements: X.J. is thankful for the financial support from the National Science Foundation of the United States, Award No. 1551693.


Page 31 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


References (1) Eftekhari, A. Potassium Secondary Cell Based on Prussian Blue Cathode, J. Power Sources, 2004, 126, 221–228. (2) Omarova, M.; Koishybay, A.; Yesibolati, N.; Mentbayeva, A.; Umirov, N.; Ismailov, K.; Adair, D.; Babaa, M.-R.; Kurmanbayeva, I.; Bakenov, Z. Nickel Hexacyanoferrate Nanoparticles As a Low Cost Cathode Material for Lithium-Ion Batteries, Electrochim. Acta, 2015, 184, 58–63. (3) Wong, M. H.; Zhang, Z.; Yang, X.; Chen, X.; Ying, J. Y. One-pot in Situ Redox Synthesis of Hexacyanoferrate/conductive Polymer Hybrids As Lithium-ion Battery Cathodes, Chem. Commun., 2015, 51, 13674–13677. (4) Sun, X.; Ji, X.-Y.; Zhou, Y.-T.; Shao, Y.; Zang, Y.; Wen, Z.-Y.; Chen, C.-H. A New Gridding Cyanoferrate Anode Material for Lithium and Sodium Ion Batteries: Ti0.75Fe0.25[Fe(CN)6]0.96·1.9H2O with Excellent Electrochemical Properties, J. Power Sources, 2016, 314, 35–38. (5) Xie, C. C.; Yang, D. H.; Zhong, M.; Zhang, Y. H. Improving the Performance of a Ternary Prussian Blue Analogue As Cathode of Lithium Battery Via Annealing Treatment, Z. anorg. allg. Chem., 2016, 642, 289–293. (6) Li, C. H.; Peprah, M. K.; Asakura, D.; Meisel, M. W.; Okubo, M.; Talham, D. R. Stepwise Reduction of Electrochemically Lithiated Core–Shell Heterostructures Based on the Prussian Blue Analogue Coordination Polymers K0.1Cu[Fe(CN)6]·3.5H, Chem. Mater., 2015, 27, 1524–1530. (7) Nie, P.; Shen, L.; Luo, H.; Ding, B.; Xu, G.; Wang, J.; Zhang, X. Prussian Blue Analogues: a New Class of Anode Materials for Lithium Ion Batteries, J. Mater. Chem. A, 2014, 2, 5852–5857. (8) Okubo, M.; Honma, I. Ternary Metal Prussian Blue Analogue Nanoparticles As Cathode Materials for Li-ion Batteries, Dalton Trans., 2013, 42, 15881–15884. (9) Moritomo, Y.; Takachi, M.; Kurihara, Y.; Matsuda, T. Synchrotron-Radiation X-Ray Investigation of Li+/Na+ Intercalation into Prussian Blue Analogues, Adv. Mater. Sci. Eng., 2013, 2013, 1–17. (10) Moritomo, Y.; Wakaume, K.; Takachi, M.; Zhu, X.; Kamioka, H. Li Intercalation of Manganese Ferrocyanide As Investigated by in Situ Valence-Differential Absorption Spectroscopy, J. Phys. Soc. Jpn., 2013, 82, 094710-094715. (11) Matsuda, T.; Kurihara, Y.; Moritomo, Y. Lithium Intercalation Properties in Manganese-iron Prussian Blue Analogues, J. Phys.: Conf. Ser., 2013, 428, 012019-012024. (12) Takachi, M.; Matsuda, T.; Moritomo, Y. Structural, Electronic, and Electrochemical Properties of LixCo(Fe(CN)6)0.9O2.9H2O, Jpn. J. Appl. Phys., 2013, 52, 044301-044307. (13) Moritomo, Y.; Zhu, X.; Takachi, M.; Matsuda, T. Fast Discharge Process of Thin Film Electrode of Prussian Blue Analogue, Jpn. J. Appl. Phys., 2012, 51, 107301-107304. (14) Moritomo, Y.; Takachi, M.; Kurihara, Y.; Matsuda, T. Thin Film Electrodes of Prussian Blue Analogues with Rapid Li+ Intercalation, Appl. Phys. Express, 2012, 5, 041801-041803. (15) Matsuda, T.; Moritomo, Y. Thin Film Electrode of Prussian Blue Analogue for Li-ion Battery, Appl. Phys. Express, 2011, 4, 047101-047103. Page 31 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 41

(16) Cheng, K.-C.; Kai, J.-J.; Chen, F.-R. Improving the Durability of Prussian Blue Based on Nano-composite Thin Film in Li+ Based Liquid Electrolyte, Electrochim. Acta, 2007, 52, 6554–6560. (17) Xie, M.; Huang, Y.; Xu, M.; Chen, R.; Zhang, X.; Li, L.; Wu, F. Sodium Titanium Hexacyanoferrate As an Environmentally Friendly and Low-cost Cathode Material for Sodium-ion Batteries, J. Power Sources, 2016, 302, 7–12. (18) Lee, H.; Kim, Y.-I.; Park, J.-K.; Choi, J. W. Sodium Zinc Hexacyanoferrate with a Well-defined Open Framework As a Positive Electrode for Sodium Ion Batteries, Chem. Commun., 2012, 48, 8416–8418. (19) Yu, S.; Li, Y.; Lu, Y.; Xu, B.; Wang, Q.; Yan, M.; Jiang, Y. A Promising Cathode Material of Sodium Iron–nickel Hexacyanoferrate for Sodium Ion Batteries, J. Power Sources, 2015, 275, 45–49. (20) Jia, Z.; Wang, J.; Wang, Y. Electrochemical Sodium Storage of Copper Hexacyanoferrate with a Well-defined Open Framework for Sodium Ion Batteries, RSC Adv., 2014, 4, 22768–22774. (21) Pasta, M.; Wang, R. Y.; Ruffo, R.; Qiao, R.; Lee, H.-W.; Shyam, B.; Guo, M.; Wang, Y.; Wray, L. A.; Yang, W.; Toney, M.-F.; Cui, Y. Manganese–cobalt Hexacyanoferrate Cathodes for Sodium-ion Batteries, J. Mater. Chem. A, 2016, 4, 4211–4223. (22) Moritomo, Y.; Goto, K.; Shibata, T. Glucose-Treated Manganese Hexacyanoferrate for Sodium-Ion Secondary Battery, J. Appl. Phys., 2015, 8, 9486–9494. (23) Takachi, M.; Matsuda, T.; Moritomo, Y. Cobalt Hexacyanoferrate As Cathode Material for Na+ Secondary Battery, Appl. Phys. Express, 2013, 6, 025802-025804. (24) Yu, S.-H.; Shokouhimehr, M.; Hyeon, T.; Sung, Y.-E. Iron Hexacyanoferrate Nanoparticles As Cathode Materials for Lithium and Sodium Rechargeable Batteries, ECS Electrochem. Lett., 2013, 2, A39-A41. (25) You, Y.; Yu, X.; Yin, Y.; Nam, K.-W.; Guo, Y.-G. Sodium Iron Hexacyanoferrate with High Na Content As a Na-rich Cathode Material for Na-ion Batteries, Nano Res., 2014, 8, 117–128. (26) Lu, Y.; Wang, L.; Cheng, J.; Goodenough, J. B. Prussian Blue: a New Framework of Electrode Materials for Sodium Batteries, Chem. Commun., 2012, 48, 6544–6546. (27) Xie, M.; Xu, M.; Huang, Y.; Chen, R.; Zhang, X.; Li, L.; Wu, F. Na2NixCo1−xFe(CN)6: a Class of Prussian Blue Analogs with Transition Metal Elements As Cathode Materials for Sodium Ion Batteries, Electrochem. Commun., 2015, 59, 91–94. (28) Wang, L.; Song, J.; Qiao, R.; Wray, L. A.; Hossain, M. A.; Chuang, Y.-D.; Yang, W.; Lu, Y.; Evans, D.; Lee, J.-J.; Vail, S.; Zhao, X.; Nishijima, M.; Kakimoto, S.; Goodenough, J. B. Rhombohedral Prussian White As Cathode for Rechargeable Sodium-Ion Batteries, J. Am. Chem. Soc., 2015, 137, 2548–2554. (29) Piernas-Muñoz, M. J.; Castillo-Martínez, E.; Gómez-Cámer, J.; Rojo, T. Optimizing the Electrolyte and Binder Composition for Sodium Prussian Blue, Na1-xFex+(1/3)(CN)6·yH2O, As Cathode in Sodium Ion Batteries, Electrochim. Acta, 2016, 200, 123–130. (30) Fernández-Ropero, A.; Piernas-Muñoz, M.; Castillo-Martínez, E.; Rojo, T. Electrochemical Characterization of NaFe2(CN)6 Prussian Blue As Positive Electrode for Page 32 of 41 ACS Paragon Plus Environment

Page 33 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Aqueous Sodium-ion Batteries, Electrochim. Acta, 2016, 210, 352–357. (31) Padigi, P.; Goncher, G.; Evans, D.; Solanki, R. Potassium Barium Hexacyanoferrate – a Potential Cathode Material for Rechargeable Calcium Ion Batteries, J. Power Sources, 2015, 273, 460–464. (32) Lipson, A. L.; Pan, B.; Lapidus, S. H.; Liao, C.; Vaughey, J. T.; Ingram, B. J. Rechargeable Ca-Ion Batteries: a New Energy Storage System, Chem. Mater., 2015, 27, 8442–8447. (33) Reed, L.; Ortiz, S.; Xiong, M.; Menke, E. A Rechargeable Aluminum-ion Battery Utilizing a Copper Hexacyanoferrate Cathode in an Organic Electrolyte, Chem. Commun., 2015, 51, 14397–14400. (34) Liu, S.; Pan, G.; Li, G.; Gao, X. Copper Hexacyanoferrate Nanoparticles As Cathode Material for Aqueous Al-ion Batteries, J. Mater. Chem. A, 2015, 3, 959–962. (35) Karyakin, A. A. Prussian Blue and Its Analogues: Electrochemistry and Analytical Applications, Electroanal., 2001, 13, 813–819. (36) Itaya, K.; Uchida, I.; Neff, V. D. Electrochemistry of Polynuclear Transition Metal Cyanides: Prussian Blue and Its Analogues, Acc. Chem. Res., 1986, 19, 162–168. (37) Eftekhari, A. A High-voltage Solid-state Secondary Cell Based on Chromium Hexacyanometallates, J. Power Sources, 2003, 117, 249–254. (38) Jayalakshmi, M.; Scholz, F. Performance Characteristics of Zinc Hexacyanoferrate/Prussian Blue and Copper Hexacyanoferrate/Prussian Blue Solid State Secondary Cells, J. Power Sources, 2000, 91, 217–223. (39) Jayalakshmi, M.; Scholz, F. Charge–discharge Characteristics of a Solid-state Prussian Blue Secondary Cell, J. Power Sources, 2000, 87, 212–217. (40) Grabner, E.; Kalwellis-Mohn, S. Hexacyanoferrate Layers As Electrodes for Secondary Cells, J. Appl. Electrochem., 1987, 17, 653–656. (41) Kuwabara, K.; Nunome, J.; Sugiyama, K. Rechargeability of Solid-state Copper Cells Utilizing Cathodes of Prussian Blue and Berlin Green, Solid State Ionics, 1991, 48, 303–308. (42) Imanishi, N.; Morikawa, T.; Kondo, J.; Takeda, Y.; Yamamoto, O.; Kinugasa, N.; Yamagishi, T. Lithium Intercalation Behavior into Iron Cyanide Complex As Positive Electrode of Lithium Secondary Battery, J. Power Sources, 1999, 79, 215–219. (43) Kaneko, M.; Okada, T. A Secondary Battery Composed of Multilayer Prussian Blue and Its Reaction Characteristics, J. Electroanal. Chem. Interf. Electrochem., 1988, 255, 45–52. (44) Eftekhari, A. A New Anode Material for Inorganic-based Rechargeable Batteries, J. Mater. Sci. Lett., 2003, 22, 1251–1253. (45) Itaya, K.; Shibayama, K.; Akahoshi, H.; Toshima, S. Prussian-blue-modified Electrodes: an Application for a Stable Electrochromic Display Device, J. Appl. Phys., 1982, 53, 804-805. (46) Itaya, K.; Ataka, T.; Toshima, S. Spectroelectrochemistry and Electrochemical Preparation Method of Prussian Blue Modified Electrodes, J. Am. Chem. Soc., 1982, 104, 4767–4772. (47) Stilwell, D.; Park, K.; Miles, M. Electrochemical Studies of the Factors Influencing the Cycle Stability of Prussian Blue Films, J. Appl. Electrochem., 1992, 22, 325–331. Page 33 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 41

(48) Marcus, Y. Thermodynamic Functions of Transfer of Single Ions from Water to Nonaqueous and Mixed Solvents: Part 3 - Standard Potentials of Selected Electrodes, Pure Appl. Chem., 1985, 57, 1129–1132. (49) Matsuura, N.; Umemoto, K.; Takeuchi, Z. Standard Potentials of Alkali Metals, Silver, and Thallium Metal/Ion Couples in N,N′-Dimethylformamide, Dimethyl Sulfoxide, and Propylene Carbonate, Bull. Chem. Soc. Jpn., 1974, 47, 813–817. (50) Komaba, S.; Hasegawa, T.; Dahbi, M.; Kubota, K. Potassium Intercalation into Graphite to Realize High-voltage/high-power Potassium-ion Batteries and Potassium-ion Capacitors, Electrochem. Commun., 2015, 60, 172–175. (51) Moshkovich, M.; Gofer, Y.; Aurbach, D. Investigation of the Electrochemical Windows of Aprotic Alkali Metal (Li, Na, K) Salt Solutions, J. Electrochem. Soc., 2001, 148, E155E167. (52) Taylor, S. Abundance of Chemical Elements in the Continental Crust: a New Table, Geochimica et Cosmochimica Acta, 1964, 28, 1273–1285. (53) Gilliam, R.; Graydon, J.; Kirk, D.; Thorpe, S. A Review of Specific Conductivities of Potassium Hydroxide Solutions for Various Concentrations and Temperatures, Int J. Hydrogen Energy, 2007, 32, 359–364. (54) Kůta, J.; Yeager, E. The Influence of Cations on the Electrode Kinetics of Ferricyanideferrocyanide System on the Rotating Gold Electrode, J. Electroanal. Chem. Interf. Electrochem., 1975, 59, 110–112. (55) Chen, S.-M.; Peng, K.-T.; Lin, K.-C. Preparation of Thallium Hexacyanoferrate Film and Mixed-Film Modified Electrodes with Cobalt(II) Hexacyanoferrate, Electroanal., 2005, 17, 319–326. (56) Eftekhari, A. Electrochemical Behavior and Electrocatalytic Activity of a Zinc Hexacyanoferrate Film Directly Modified Electrode, J. Electroanal. Chem., 2002, 537, 59– 66. (57) Jin, W.; Toutianoush, A.; Pyrasch, M.; Schnepf, J.; Gottschalk, H.; Rammensee, W.; Tieke, B. Self-Assembled Films of Prussian Blue and Analogues: Structure and Morphology, Elemental Composition, Film Growth, and Nanosieving of Ions, J. Phys. Chem. B, 2003, 107, 12062–12070. (58) Pyrasch, M.; Toutianoush, A.; Jin, W.; Schnepf, J.; Tieke, B. Self-assembled Films of Prussian Blue and Analogues: Optical and Electrochemical Properties and Application As Ion-Sieving Membranes, Chem. Mater., 2003, 15, 245–254. (59) Jin, Z.; Dong, S. Spectroelectrochemical Studies of Indium Hexacyanoferrate Film Modified Electrodes, Electrochim. Acta, 1990, 35, 1057–1060. (60) Ho, K. C.; Chen, J. C. Spectroelectrochemical Studies of Indium Hexacyanoferrate Electrodes Prepared by the Sacrificial Anode Method, J. Electrochem. Soc., 1998, 145, 2334– 2340. (61) Devadas, B.; Cheemalapati, S.; Chen, S.-M.; Rajkumar, M. Investigation of Morphologies and Characterization of Rare Earth Metal Samarium Hexacyanoferrate and Its Composite with Surfactant Intercalated Graphene Oxide for Sensor Applications, RSC Adv., 2014, 4, 45895–45902. Page 34 of 41 ACS Paragon Plus Environment

Page 35 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(62) Wessells, C. D.; Peddada, S. V.; Huggins, R. A.; Cui, Y. Nickel Hexacyanoferrate Nanoparticle Electrodes for Aqueous Sodium and Potassium Ion Batteries, Nano Lett., 2011, 11, 5421–5425. (63) Padigi, P.; Thiebes, J.; Swan, M.; Goncher, G.; Evans, D.; Solanki, R. Prussian Green: a High Rate Capacity Cathode for Potassium Ion Batteries, Electrochim. Acta, 2015, 166, 32– 39. (64) Ohzuku, T.; Ueda, A. Solid-State Redox Reactions of LiCoO2 (R3m) for 4 Volt Secondary Lithium Cells, J. Electrochem. Soc., 1994, 141, 2972–2977. (65) Ozawa, K. Lithium-ion Rechargeable Batteries with LiCoO2 and Carbon Electrodes: the LiCoO2/C System, Solid State Ionics, 1994, 69, 212–221. (66) Ling, C.; Chen, J.; Mizuno, F. First-Principles Study of Alkali and Alkaline Earth Ion Intercalation in Iron Hexacyanoferrate: the Important Role of Ionic Radius, J. Phys. Chem. C., 2013, 117, 21158–21165. (67) Piernas-Muñoz, M. J.; Castillo-Martínez, E.; Bondarchuk, O.; Armand, M.; Rojo, T. Higher Voltage Plateau Cubic Prussian White for Na-ion Batteries, J. Power Sources, 2016, 324, 766–773. (68) Jansen, M.; Hoppe, R. Zur Kenntnis Von KCoO2 Und RbCoO2[1], Z. anorg. allg. Chem., 1975, 417, 31–34. (69) Eftekhari, A.; Kazemzad, M.; Moztarzadeh, F. Effect of Na Diffusion on the Formation of Fibrous Microcrystals of Manganese Oxide, Mater. Res. Bull., 2005, 40, 2205–2211. (70) Recham, N.; Rousse, G. l.; Sougrati, M. T.; Chotard, J.-N. l.; Frayret, C.; Mariyappan, S.; Melot, B. C.; Jumas, J.-C.; Tarascon, J.-M. Preparation and Characterization of a Stable FeSO4F-Based Framework for Alkali Ion Insertion Electrodes, Chem. Mater., 2012, 24, 4363–4370. (71) Mathew, V.; Kim, S.; Kang, J.; Gim, J.; Song, J.; Baboo, J. P.; Park, W.; Ahn, D.; Han, J.; Gu, L.; Wang, Y.; Hu, Y.-S; Sun, Y.; Kim, J. Amorphous Iron Phosphate: Potential Host for Various Charge Carrier Ions, NPG Asia Mater., 2014, 6, e138-e147. (72) Vaalma, C.; Giffin, G. A.; Buchholz, D.; Passerini, S. Non-Aqueous K-Ion Battery Based on Layered K MnO and Hard Carbon/Carbon Black, J. Electrochem. Soc., 2016, 163, A1295-A1299. (73) Han, J.; Niu, Y.; Bao, S.-j.; Yu, Y.-N.; Lu, S.-Y.; Xu, M. Nanocubic KTi2(PO4)3 Electrodes for Potassium-Ion Batteries, Chem. Commun., 2016, 52, 11661-11664. (74) Chen, Y.; Luo, W.; Carter, M.; Zhou, L.; Dai, J.; Fu, K.; Lacey, S.; Li, T.; Wan, J.; Han, X.; Bao, Y.; Hu, L. Organic Electrode for Non-aqueous Potassium-ion Batteries, Nano Energy, 2015, 18, 205–211. (75) Xing, Z.; Jian, Z.; Luo, W.; Qi, Y.; Bommier, C.; Chong, E. S.; Li, Z.; Hu, L.; Ji, X. A Perylene Anhydride Crystal As a Reversible Electrode for K-ion Batteries, Energy Storage Mater., 2016, 2, 63–68. (76) Luo, W.; Allen, M.; Raju, V.; Ji, X. An Organic Pigment As a High-Performance Cathode for Sodium-Ion Batteries, Adv. Energy Mater., 2014, 4, 1400554-1400558. (77) Jian, Z.; Liang, Y.; Pérez, I. A. R.; Yao, Y.; Ji, X. Poly(anthraquinonyl Sulfide) Cathode for Potassium-ion Batteries, Electrochem. Commun., 2016, 71, 5–8. Page 35 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(78) Wang, Z.; Selbach, S. M.; Grande, T. Van Der Waals Density Functional Study of the Energetics of Alkali Metal Intercalation in Graphite, RSC Adv., 2014, 4, 3973–3983. (79) Kim, H.; Hong, J.; Yoon, G.; Kim, H.; Park, K.-Y.; Park, M.-S.; Yoon, W.-S.; Kang, K. Sodium Intercalation Chemistry in Graphite, Energy Environ. Sci., 2015, 8, 2963–2969. (80) Bommier, C.; Ji, J. Recent Development on Anodes for Na-Ion Batteries, Isr. J. Chem., 2015, 55, 486–507. (81) Luo, W.; Jian, Z.; Xing, Z.; Wang, W.; Bommier, C.; Lerner, M. M.; Ji, X. Electrochemically Expandable Soft Carbon As Anodes for Na-Ion Batteries, ACS Cent. Sci., 2015, 1, 516–522. (82) Jian, Z.; Luo, W.; Ji, X. Carbon Electrodes for K-Ion Batteries, J. Am. Chem. Soc., 2015, 137, 11566–11569. (83) Ziambaras, E.; Kleis, J.; Schröder, E.; Hyldgaard, P. Potassium Intercalation in Graphite: a Van Der Waals Density-functional Study, Phys. Rev. B, 2007, 76, 155425155424. (84) Matuyama, E. Successive Stages of a Graphite–Potassium Compound and Its Thermal Expansion, Nature, 1962, 193, 61–61. (85) Mizutani, Y.; Abe, T.; Inaba, M.; Ogumi, Z. Creation of Nanospaces by Intercalation of Alkali Metals into Graphite in Organic Solutions, Synth. Met., 2001, 125, 153–159. (86) Lerf, A. Storylines in Intercalation Chemistry, Dalton Trans., 2014, 43, 10276–10291. (87) Dresselhaus, M. S.; Dresselhaus, G. Intercalation Compounds of Graphite, Adv. Phys., 2002, 51, 1–186. (88) Hwang, D.; Utlaut, M.; Isaacson, M.; Solin, S. Electron-Energy-Loss Study of Stage-1 Potassium-Intercalated Graphite, Phys. Rev. Lett., 1979, 43, 882–886. (89) Viculis, L. M.; Mack, J. J.; Mayer, O. M.; Hahn, H. T.; Kaner, R. B. Intercalation and Exfoliation Routes to Graphite Nanoplatelets, J. Mater. Chem., 2005, 15, 974–978. (90) Kim, H.; Hahn, H. T.; Viculis, L. M.; Gilje, S.; Kaner, R. B. Electrical Conductivity of Graphite/polystyrene Composites Made from Potassium Intercalated Graphite, Carbon, 2007, 45, 1578–1582. (91) Tossici, R.; Berrettoni, M.; Rosolen, M.; Marassi, R.; Scrosati, B. Electrochemistry of KC8 in Lithium-Containing Electrolytes and Its Use in Lithium-Ion Cells, J. Electrochem. Soc., 1997, 144, 186–192. (92) Sconocchia, S.; Tossici, R.; Marassi, R.; Croce, F.; Scrosati, B. A Plastic KC8/LiMn2O4 Lithium-Ion Battery, Electrochem. Solid-State Lett., 1998, 1, 159–161. (93) Liu, D.; Yang, Z.; Li, W.; Qiu, S.; Luo, Y. Electrochemical Intercalation of Potassium into Graphite in KF Melt, Electrochim. Acta, 2010, 55, 1013–1018. (94) Liu, Y.; Fan, F.; Wang, J.; Liu, Y.; Chen, H.; Jungjohann, K. L.; Xu, Y.; Zhu, Y.; Bigio, D.; Zhu, T. In Situ Transmission Electron Microscopy Study of Electrochemical Sodiation and Potassiation of Carbon Nanofibers, Nano Lett., 2014, 14, 3445–3452. (95) Xing, Z.; Qi, Y.; Jian, Z.; Ji, X. Polynanocrystalline Graphite: a New Carbon Anode with Superior Cycling Performance for K-Ion Batteries, ACS Appl. Mater. Interf., 2016, DOI: 10.1021/acsami.6b06767. Page 36 of 41 ACS Paragon Plus Environment

Page 36 of 41

Page 37 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(96) Luo, W.; Wan, J.; Ozdemir, B.; Bao, W.; Chen, Y.; Dai, J.; Lin, H.; Xu, Y.; Gu, F.; Barone, V.; Hu, L. Potassium Ion Batteries with Graphitic Materials, Nano Lett., 2015, 15, 7671–7677. (97) Jian, Z.; Xing, Z.; Bommier, C.; Li, Z.; Ji, X. Hard Carbon Microspheres: Potassium-Ion Anode Versus Sodium-Ion Anode, Adv. Energy Mater., 2016, 6, 1501874-1501878. (98) Kim, H.; Hong, J.; Park, Y. U.; Kim, J.; Hwang, I.; Kang, K. Sodium Storage Behavior in Natural Graphite Using Ether-based Electrolyte Systems, Adv. Func. Mater., 2015, 25, 534–541. (99) Jache, B.; Adelhelm, P. Use of Graphite As a Highly Reversible Electrode with Superior Cycle Life for Sodium-Ion Batteries by Making Use of Co-Intercalation Phenomena, Angew. Chem., 2014, 53, 10169–10173. (100) David, L.; Singh, G. Reduced Graphene Oxide Paper Electrode: Opposing Effect of Thermal Annealing on Li and Na Cyclability, J. Phys. Chem. C., 2014, 118, 28401–28408. (101) Er, D.; Li, J.; Naguib, M.; Gogotsi, Y.; Shenoy, V. B. Ti3C2 MXene As a High Capacity Electrode Material for Metal (Li, Na, K, Ca) Ion Batteries, ACS Appl. Mater. Interf., 2014, 6, 11173–11179. (102) Sultana, I.; Ramireddy, T.; Rahman, M. M.; Chen, Y.; Glushenkov, A. M. Tin-based Composite Anodes for Potassium-ion Batteries, Chem. Commun., 2016, 52, 9279-9282 (103) Ge, P.; Fouletier, M. Electrochemical Intercalation of Sodium in Graphite, Solid State Ionics, 1988, 28-30, 1172–1175. (104) Honda, K.; Hayashi, H. Prussian Blue Containing Nafion Composite Film As Rechargeable Battery, J. Electrochem. Soc., 1987, 134, 1330–1334. (105) Pasta, M.; Wessells, C. D.; Huggins, R. A.; Cui, Y. A High-rate and Long Cycle Life Aqueous Electrolyte Battery for Grid-scale Energy Storage, Nat. Comms., 2012, 3, 11491155. (106) Wang, R. Y.; Wessells, C. D.; Huggins, R. A.; Cui, Y. Highly Reversible Open Framework Nanoscale Electrodes for Divalent Ion Batteries, Nano Lett., 2013, 13, 5748– 5752. (107) Wessells, C. D.; Huggins, R. A.; Cui, Y. Copper Hexacyanoferrate Battery Electrodes with Long Cycle Life and High Power, Nat. Comms., 2011, 2, 550-554. (108) Wessells, C. D.; McDowell, M. T.; Peddada, S. V.; Pasta, M.; Huggins, R. A.; Cui, Y. Tunable Reaction Potentials in Open Framework Nanoparticle Battery Electrodes for GridScale Energy Storage, ACS Nano, 2012, 6, 1688–1694. (109) Wessells, C. D.; Peddada, S. V.; McDowell, M. T.; Huggins, R. A.; Cui, Y. The Effect of Insertion Species on Nanostructured Open Framework Hexacyanoferrate Battery Electrodes, J. Electrochem. Soc., 2012, 159, A98-A103. (110) Han, J.; Xu, M.; Niu, Y.; Li, G.; Wang, M.; Zhang, Y.; Jia, M.; Li, C. Exploration of K2Ti8O17 As the Anode Materials for Potassium-ion Batteries, Chem. Commun., 2016, 52, 11274-11276. (111) Beck, F.; Rüetschi, P. Rechargeable Batteries with Aqueous Electrolytes, Electrochim. Acta, 2000, 45, 2467–2482. Page 37 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(112) Li, Y.; Dai, H. Recent Advances in Zinc–air Batteries, Chem. Soc. Rev., 2014, 43, 5257–5275. (113) Blurton, K. F.; Sammells, A. F. Metal/air Batteries: Their Status and Potential — a Review, J. Power Sources, 1979, 4, 263–279. (114) Chakkaravarthy, C.; Waheed, A. A.; Udupa, H. Zinc—air Alkaline Batteries — a Review, J. Power Sources, 1981, 6, 203–228. (115) Neburchilov, V.; Wang, H.; Martin, J. J.; Qu, W. A Review on Air Cathodes for Zinc– air Fuel Cells, J. Power Sources, 2010, 195, 1271–1291. (116) Ogasawara, T.; Débart, A.; Holzapfel, M.; Novák, P.; Bruce, P. G. Rechargeable Li2O2 Electrode for Lithium Batteries, J. Am. Chem. Soc., 2006, 128, 1390–1393. (117) Girishkumar, G.; McCloskey, B.; Luntz, A.; Swanson, S.; Wilcke, W. Lithium−Air Battery: Promise and Challenges, J. Phys. Chem. Lett., 2010, 1, 2193–2203. (118) Armand, M.; Tarascon, J.-M. Building Better Batteries, Nature, 2008, 451, 652–657. (119) Peng, Z.; Freunberger, S. A.; Chen, Y.; Bruce, P. G. A Reversible and Higher-Rate LiO2 Battery, Science, 2012, 337, 563–566. (120) Christensen, J.; Albertus, P.; Sanchez-Carrera, R. S.; Lohmann, T.; Kozinsky, B.; Liedtke, R.; Ahmed, J.; Kojic, A. A Critical Review of Li/Air Batteries, J. Electrochem. Soc., 2012, 159, R1-R30. (121) Oh, S. H.; Black, R.; Pomerantseva, E.; Lee, J.-H.; Nazar, L. F. Synthesis of a Metallic Mesoporous Pyrochlore As a Catalyst for Lithium–O2 Batteries, Nat. Chem., 2012, 4, 1004– 1010. (122) Abraham, K. M. Jiang, Z. A Polymer Electrolyte-Based Rechargeable Lithium/Oxygen Battery, J. Electrochem. Soc., 1996, 143, 1–5. (123) Scrosati, B.; Garche, J. Lithium Batteries: Status, Prospects and Future, J. Power Sources, 2010, 195, 2419–2430. (124) Lee, J. S.; Tai Kim, S.; Cao, R.; Choi, N. S.; Liu, M.; Lee, K. T.; Cho, J. Metal-Air Batteries with High Energy Density: Li-Air Versus Zn-Air, Adv. Energy Mater., 2011, 1, 34– 50. (125) Cheng, F.; Chen, J. Metal–air Batteries: from Oxygen Reduction Electrochemistry to Cathode Catalysts, Chem. Soc. Rev., 2012, 41, 2172–2192. (126) Kraytsberg, A.; Ein-Eli, Y. Review on Li–air Batteries—Opportunities, Limitations and Perspective, J. Power Sources, 2011, 196, 886–893. (127) Shao, Y.; Ding, F.; Xiao, J.; Zhang, J.; Xu, W.; Park, S.; Zhang, J. G.; Wang, Y.; Liu, J. Making Li-Air Batteries Rechargeable: Material Challenges, Adv. Func. Mater., 2013, 23, 987–1004. (128) Hummelshøj, J. S.; Blomqvist, J.; Datta, S.; Vegge, T.; Rossmeisl, J.; Thygesen, K. S.; Luntz, A.; Jacobsen, K. W.; Nørskov, J. K. Communications: Elementary Oxygen Electrode Reactions in the Aprotic Li-air Battery, J. Chem. Phys., 2010, 132, 071101-071104. (129) Allen, C. J.; Hwang, J.; Kautz, R.; Mukerjee, S.; Plichta, E. J.; Hendrickson, M. A.; Abraham, K. Oxygen Reduction Reactions in Ionic Liquids and the Formulation of a General ORR Mechanism for Li–Air Batteries, J. Phys. Chem. C., 2012, 116, 20755–20764. Page 38 of 41 ACS Paragon Plus Environment

Page 38 of 41

Page 39 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(130) Lu, J.; Lee, Y. J.; Luo, X.; Lau, K. C.; Asadi, M.; Wang, H.-H.; Brombosz, S.; Wen, J.; Zhai, D.; Chen, Z.; Miller, D. J.; Jeong, Y. S.; Park, J.-B.; Fang, Z. Z.; Kumar, K.; SalehiKhojin, A.; Sun, Y.-K.; Curtiss, L. A.; Amine, K. A Lithium–oxygen Battery Based on Lithium Superoxide, Nature, 2016, 529, 377–382. (131) Hartmann, P.; Bender, C. L.; Vračar, M.; Dürr, A. K.; Garsuch, A.; Janek, J.; Adelhelm, P. A Rechargeable Room-temperature Sodium Superoxide (NaO2) Battery, Nat. Mater., 2012, 12, 228–232. (132) Ren, X.; Wu, Y. A Low-Overpotential Potassium–Oxygen Battery Based on Potassium Superoxide, J. Am. Chem. Soc., 2013, 135, 2923–2926. (133) Feng, N.; He, P.; Zhou, H. Critical Challenges in Rechargeable Aprotic Li-O2 Batteries, Adv. Energy Mater., 2016, 6, 1502303-152326. (134) Chang, Z.; Xu, J.; Liu, Q.; Li, L. Zhang, X. Recent Progress on Stability Enhancement for Cathode in Rechargeable Non-Aqueous Lithium-Oxygen Battery, Adv. Energy Mater., 2015, 5, 1500633-1500645. (135) Lu, J.; Li, L.; Park, J.-B.; Sun, Y.-K.; Wu, F.; Amine, K. Aprotic and Aqueous Li–O2 Batteries, Chem. Rev., 2014, 114, 5611–5640. (136) McCloskey, B. D.; Garcia, J. M.; Luntz, A. C. Chemical and Electrochemical Differences in Nonaqueous Li–O2 and Na–O2 Batteries, J. Phys. Chem. Lett., 2014, 5, 1230– 1235. (137) Zhao, N.; Li, C.; Guo, X. Long-life Na–O2 Batteries with High Energy Efficiency Enabled by Electrochemically Splitting NaO2 at a Low Overpotential, Phys. Chem. Chem. Phys., 2014, 16, 15646–15652. (138) Xia, C.; Black, R.; Fernandes, R.; Adams, B.; Nazar, L. F. The Critical Role of Phasetransfer Catalysis in Aprotic Sodium Oxygen Batteries, Nat. Chem., 2015, 7, 496–501. (139) Ren, X.; Lau, K. C.; Yu, M.; Bi, X.; Kreidler, E.; Curtiss, L. A.; Wu, Y. Understanding Side Reactions in K–O2 Batteries for Improved Cycle Life, ACS Appl. Mater. Interf., 2014, 6, 19299–19307. (140) McCulloch, W. D.; Ren, X.; Yu, M.; Huang, Z.; Wu, Y. Potassium-Ion Oxygen Battery Based on a High Capacity Antimony Anode, ACS Appl. Mater. Interf., 2015, 7, 26158–26166. (141) Manthiram, A.; Fu, Y.; Chung, S.-H.; Zu, C.; Su, Y.-S. Rechargeable Lithium–Sulfur Batteries, Chem. Rev., 2014, 114, 11751–11787. (142) Xu, G.; Ding, B.; Pan, J.; Nie, P.; Shen, L.; Zhang, X. High Performance Lithium– sulfur Batteries: Advances and Challenges, J. Mater. Chem. A, 2014, 2, 12662–12676. (143) Zhang, S.; Ueno, K.; Dokko, K.; Watanabe, M. Recent Advances in Electrolytes for Lithium-Sulfur Batteries, Adv. Energy Mater., 2015, 5, 1500117-1500144. (144) Son, K.; Lee, J.; Son, Y.; Jang, J.; Cho, J. Recent Advances in Lithium Sulfide Cathode Materials and Their Use in Lithium Sulfur Batteries, Adv. Energy Mater., 2015, 5, 1500110-1500123. (145) Cao, R.; Xu, W.; Li, D.; Xiao, J.; Zhang, J. Anodes for Rechargeable Lithium-Sulfur Batteries, Adv. Energy Mater., 2015, 5, 1402273-1402295. Page 39 of 41 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 41

(146) Lin, Z.; Liang, C. Lithium–sulfur Batteries: from Liquid to Solid Cells, J. Mater. Chem. A, 2015, 3, 936–958. (147) Manthiram, A.; Fu, Y.; Su, Y.-S. Challenges and Prospects of Lithium–Sulfur Batteries, Acc. Chem. Res., 2013, 46, 1125–1134. (148) Wild, M.; O'Neill, L.; Zhang, T.; Purkayastha, R.; Minton, G.; Marinescu, M.; Offer, G. Lithium Sulfur Batteries, a Mechanistic Review, Energy Environ. Sci., 2015, 8, 3477– 3494. (149) Pang, Q.; Liang, X.; Kwok, C.; Nazar, L. F. Review—The Importance of Chemical Interactions Between Sulfur Host Materials and Lithium Polysulfides for Advanced LithiumSulfur Batteries, J. Electrochem. Soc., 2015, 162, A2567. (150) Xu, R.; Lu, J.; Amine, K. Progress in Mechanistic Understanding and Characterization Techniques of Li-S Batteries, Adv. Energy Mater., 2015, 5, 1500408-1500428. (151) Lu, X.; Bowden, M. E.; Sprenkle, V. L.; Liu, J. A Low Cost, High Energy Density, and Long Cycle Life Potassium-Sulfur Battery for Grid-Scale Energy Storage, Adv. Mater., 2015, 27, 5915–5922. (152) Zhao, Q.; Hu, Y.; Zhang, K.; Chen, J. Potassium–Sulfur Batteries: a New Member of Room-Temperature Rechargeable Metal–Sulfur Batteries, Inorg. Chem., 2014, 53, 9000– 9005. (153) Lu, X.; Xia, G.; Lemmon, J. P.; Yang, Z. Advanced Materials for Sodium-beta Alumina Batteries: Status, Challenges and Perspectives, J. Power Sources, 2010, 195, 2431– 2442. (154) Hueso, K. B.; Armand, M.; Rojo, T. High Temperature Sodium Batteries: Status, Challenges and Future Trends, Energy Environ. Sci., 2013, 6, 734–749. (155) Lu, X.; Li, G.; Kim, J. Y.; Mei, D.; Lemmon, J. P.; Sprenkle, V. L.; Liu, J. Liquidmetal Electrode to Enable Ultra-low Temperature Sodium–beta Alumina Batteries for Renewable Energy Storage, Nat. Comms., 2014, 5, 4578. (156) Koh, J.-H.; Weber, N.; Virkar, A. V. Synthesis of Lithium-beta-alumina by Various Ionexchange and Conversion Processes, Solid State Ionics, 2012, 220, 32–38.


Page 41 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table of Contents Graphic


Potassium Secondary Batteries - ACS Applied Materials & Interfaces

Recommend Documents