Lithium Iron Orthosilicate Cathode - American Chemical Society

Lithium Iron Orthosilicate Cathode: Progress and Perspectives Jiangfeng Ni,*,† Yu Jiang,† Xuanxuan Bi,‡ Liang Li,*,† and Jun Lu*,‡ †

College of Physics, Optoelectronics and Energy, Center for Energy Conversion Materials & Physics (CECMP), Soochow University, Suzhou 215006, PR China ‡ Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, United States ABSTRACT: The pursuit of cathodes with a high capacity is remarkably driven by the ever increasing demand of high-energy lithium ion batteries in electronics and transportation. In this regard, polyanionic lithium iron orthosilicate (Li2FeSiO4) offers a promising opportunity because it affords a high theoretical capacity of 331 mAh g−1. However, such a high theoretical capacity of Li2FeSiO4 has frequently been compromised in practice because of the extremely low electronic and ionic conductivity. To address this issue, material engineering strategies to boost the Li storage kinetics in Li2FeSiO4 have proven indispensable. In this Perspective, we will briefly present the structural characteristics, intrinsic physicochemical properties, and electrochemical behavior of Li2FeSiO4. We particularly focus on recent materials engineering of silicates, which is implemented mainly through advanced synthetic techniques and elaborate controls. This Perspective highlights the importance of integrating theoretical analysis into experimental implementation to further advance the Li2FeSiO4 materials.

R

Table 1. Electrochemical Characteristics of Some Cathodes for Lithium Ion Batteries

echargeable ion batteries are crucial energy storage devices that can power portable electronics and automobiles.1,2 Among various batteries currently available,3−6 lithium ion batteries (LIBs) definitely play the most important role in our daily life, owing to their high energy density, power output, and long cycling life. Because conventional cathodes such as LiCoO 2 , LiMn 2 O 4 , Li[Ni1/3Co1/3Mn1/3]O2, and LiFePO4 afford only a limited capacity in the range of 120−165 mAh g−1, it is urgent and imperative to exploit high-energy cathode materials.7,8 Thus, the search for and development of high-capacity cathode materials have become an essential task for battery material researchers. Material innovation is a prominent route toward sustainable capacity and high energy density.9 Since its discovery in 2005, polyanionic lithium iron orthosilicate (Li2FeSiO4) has drawn considerable attention because of its high theoretical capacity of 331 mAh g−1, low cost, and resource abundance.10 Li2FeSiO4 is expected to exhibit two redox peaks, one at 2.8 V (Fe2+/Fe3+) and the other at 4.0−4.8 V (Fe3+/Fe4+, vs Li+/Li unless otherwise designated), with a specific energy beyond 1100 Wh kg−1, which is markedly greater than those of conventional cathodes (Table 1). Although the other silicates potentially have the same capability for two-electron capacity,11 they suffer from poor structural integrity (Li2MnSiO4)12 or inefficient electrode/electrolyte interphase at high operation voltage (Li2CoSiO4 and Li2NiSiO4).13 They are less appealing for © XXXX American Chemical Society

a

cathode

reversible capacity (mAh g−1)

average potential (vs Li+/Li)

energy density (Wh kg−1)

LiCoO2 LiMn2O4 Li[Ni1/3Mn1/3Co1/3]O2 xLi2MnO3·(1−x)LiMO2 LiFePO4 LiMnPO4 LiCoPO4 Li2FeSiO4a

150 120 165 250 165 145 130 331

3.9 4.1 3.7 3.5 3.4 4.0 4.8 3.4

580 490 610 875 560 580 620 1120

Theoretical values are adopted for Li2FeSiO4.

practical utilization, although future progress might occur with new high-potential electrolytes. This Perspective provides a short summary on the past decade of state-of-the-art developments of Li2FeSiO4 cathode material for LIBs. We will briefly summarize the achievements in the material design through engineering techniques and the major challenges that are still present in the research on highperformance Li2FeSiO4 cathode materials. It is worth noting that there are already excellent reviews of the polyanionic and Received: May 27, 2017 Accepted: July 7, 2017

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DOI: 10.1021/acsenergylett.7b00452 ACS Energy Lett. 2017, 2, 1771−1781

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silicate cathodes.14−17 However, in this Perspective, we place special emphasis on the underlying correlation between the structural characteristics, such as crystalline shape, pore construction, and facet tuning, and the electrochemical behaviors. By summarizing these material synthesis, structure, modification, and performance relationships, we hope this Perspective not only offers a timely summary of the recent progress of Li2FeSiO4 cathode material but also sheds light on the development of more advanced cathode materials with high energy density.

Li2FeSiO4 offers a promising opportunity for next-generation batteries because it affords a high theoretical capacity of 331 mAh g−1. Information on crystalline structure is essential to understanding the Li+ ion transport mechanism and designing the electrode structure to achieve full utilization of the high theoretical capacity of Li2FeSiO4. Li2FeSiO4 exhibits intriguing structural characters and rich polymorphs, strongly dependent on the synthetic approach and temperature.18 The structure of Li2FeSiO4 is built of infinite corrugated layers of [SiFeO4] lying on the ac-plane and linked by LiO4 tetrahedra along the b-axis. The structure is highly sensitive to crystalline disorder and defects, the amount of which is dependent on the synthesis conditions.19 Previously, the structure of Li2FeSiO4 was assigned to be isostructural with Li3PO4, in which all the tetrahedrally coordinated Li, Fe and Si trigonal pyramids are identical in the orientations.20 This model was later challenged by Nishimura et al., who suggested that FeO4/SiO4 trigonal pyramids periodically take opposite orientations in Li2FeSiO4.21 Generally, three common polymorphs have been confirmed for Li2FeSiO4: monoclinic P21/n, orthorhombic Pmn21, and orthorhombic Pmnb. They are different in the linking manner of the LiO4, FeO4, and SiO4 tetrahedra, as shown in Figure 1. The Li site in Pmn21 and Pmnb is surrounded by four and three Fe2+ ions, respectively, whereas in the P21/n polymorph both Li sites are present.22 Local environments of FeO4 in the three polymorphs are also different. A FeO4 tetrahedron shares two edges with LiO4 tetrahedra in the Pmnb phase, while it shares one or no edges with LiO4 tetrahedra for the P21/n and Pmn21 lattices, respectively.23 These structures can be prepared by varying heat treatment temperatures. With increasing temperature, the average Fe−O distance gets shorter, and the structure evolves. The orthorhombic Li2FeSiO4 (Pmn21) can be obtained at a lower temperature treatment, such as 200 °C. This structure consists of infinite corrugated layers of composition [SiFeO4]x lying on the ac-plane and linked along the b-axis by LiO4 tetrahedra. Within the layers, each SiO4 tetrahedron shares its corners with neighboring FeO4 tetrahedra, and vice versa. The Li2FeSiO4 evolves to be monoclinic phase (P21/n) by thermal annealing at higher temperatures (∼700 °C) as ordering of tetrahedra is a thermodynamically driven process. At higher thermal temperatures (∼900 °C), another orthorhombic Pmnb phase of Li2FeSiO4 can be obtained. This new orthorhombic structure is isostructural with Li2CoSiO4, having lattice parameters of a = 0.6285 nm, b = 1.0659 nm, and c = 0.5073 nm.24 This variation in the structure and the bond length has a direct reflection in the redox potential, as the short interatomic distances imply a stronger Fe−O bond and a higher Fe−O distortion.25 It is speculated that more crystalline

Figure 1. Structures of Li2FeSiO4 polymorphs: (a) space group P21/n, (b) space group Pmnb, (c) space group Pmn21. LiO4 tetrahedra, pink and brown; FeO 4 tetrahedra, green; SiO 4 tetrahedra, blue. Insets show the linkage manner of LiO4 with the surrounding FeO4. Reprinted from ref 22. Copyright 2013 American Chemical Society.

polymorphs may be discovered, depending on the amount of defects and the degree of Li/Fe disordering. The rich polymorphs endow the Li2FeSiO4 material with unique potentiality for battery application and deserve continuous exploration efforts. The transport of electrons and ions plays the key role in the cathode materials. In the Li2FeSiO4 lattice, the FeO4 tetrahedra are well-separated by LiO4 and SiO4 tetrahedra. The distance between adjacent Fe ions in Li2FeSiO4 (0.434 nm) is much larger than that in the LiFePO4 (0.387 nm).26 Therefore, it is unlikely that the direct hopping of electrons among Fe ions would occur. This leads to a large band gap of 2−3.3 eV and an extremely low electronic conductivity of 6 × 10−14 S cm−1 at room temperature.27 The Li extraction potential for the Fe2+/ Fe3+ redox in Li2FeSiO4 is 3.1 V, which is substantially higher than that of LiFeO2 because of the inductive effect of the SiO4 group, as observed in phosphate materials.28 Further oxidation of Fe3+ to Fe4+ is possible but needs a much higher potential, disregarding the Li2FeSiO4 polymorphs. This huge increase in the potential is a consequence of the high stability of the d5 configuration of Fe3+, which can be tuned by N and F substitution, as predicted by first-principles calculations (Figure 2a,b).29 The high voltage and the large band gap indicate that the Fe3+/Fe4+ redox reaction concomitant with the extraction of the second Li+ ion in Li2FeSiO4 is rather difficult in practice. The band gap of Li2FeSiO4 can be narrowed by orbital hybridization between transition metal and O through cation substitution, as recently projected by density functional theory (DFT) calculation.30 The calculation reveals a shift of the Fermi level toward and crossing the conduction band with Fe substituted by Ti, indicating an n-type doping effect due to introduction of extra electrons in the conduction band. With 1772


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Figure 2. (a, b) Formation energy and average voltage of Li2FeSiO4 by N and F substitution. (a) Calculated formation energies of the Li2−xFeSiO3.5F0.5 ordered structures as a function of the lithium content. (b) Calculated voltage−Li composition profiles for Li2FeSiO4 (green), Li2FeSiO3.5N0.5 (blue), and Li1.5FeSiO3.5F0.5 (red). Asterisks correspond to Fe ions coordinated to the N or F substituents. Reprinted with permission from ref 29. Copyright 2011 Elsevier. (c, d) Pathways for lithium ion migration between corner-sharing Li(1) and Li(2) sites in the cycled structure of Li2FeSiO4. (c) The first path involves hops A and B in the c direction. (d) The second path involves hops C and D in the b direction (SiO4 tetrahedra, yellow; Li(1)O4 tetrahedra, dark blue; Li(2)O4 tetrahedra, light blue; FeO4 tetrahedra, brown). Reprinted from 32. Copyright 2011 American Chemical Society.

transport within the lattice. This, however, remains a significant challenge, and related experimental evidence is required. Although the total understanding of the carrier transport mechanism is still lacking, significant progress has been made in the synthesis of this promising cathode material. Li2FeSiO4 material is expected to show sluggish Li reaction kinetics owing to the slow migration of the charge carriers. Therefore, electrochemical activity of Li2FeSiO4 material is strongly correlated to the size, shape, texture, facet, and defect, which might be precisely tailored by varying the synthetic approach and conditions. During the past years, a myriad of synthesis routes have been developed to optimize electrochemical activity of Li2FeSiO4 powders. These synthesis routes can be roughly divided into two main parts: solid-state synthesis and soft chemistry synthesis. Solid-state synthesis is the most robust and conventional method to fabricate powder materials for lithium ion batteries.15,34 This approach is simple and ideal for continuous scalable production and has been industrially used in the synthesis of battery materials. In solid-state synthesis of Li2FeSiO4, Li, Fe, and Si precursors are ground and milled, followed by annealing treatment at temperatures higher than 600 °C. Naturally, thermal treatment needs to be performed under Ar/H2 atmosphere to ensure the Fe2+ in the final product.35 Conventional solid-state reactions generally produce micrometer-sized Li2FeSiO4 particles, which feature a high crystallinity but poor activity. To tackle this issue, Li2FeSiO4/C

5% Ti doping, the band gap of Li2FeSiO4 is narrowed from 2.13 to 1.46 eV, and the electron concentration and electrical conductance are drastically enhanced. Lithium diffusion paths in Li2FeSiO4 have not been clearly established previously because of difficulty in experimental probing. Most works adopt DFT calculation to simulate the ion migration paths and mechanisms.28,31 Armstrong and coworkers have identified two feasible Li migration paths in electrochemically cycled Li2FeSiO4.32 The first path involves corner-sharing Li1 and Li2 sites with an overall trajectory along the c-axis direction, while the second path involves longer Li hops between Li1 and Li2 sites in the b direction. Atomic simulation reveals that Li hop in the c direction (hops A and B in Figure 2c and d) has the lower migration energy of 0.9 eV compared with the hops along the b-axis. This result suggests zigzag paths for Li transport along a corner-sharing network of Li sites. As Li migration energy is greater than the 0.6 eV reported for LiFePO4, slower Li diffusion and lower rate capability for Li2FeSiO4 are rationalized. Suitable metal element doping or substitution in Li2FeSiO4 is capable of tuning the size of Li migration path and the activation barrier, leading to modified Li diffusivity.30 It is reasonably believed that the transport of charge carriers (electron and ion) in Li2FeSiO4 is strongly coupled.33 Thus, a key issue in the research of Li2FeSiO4 is to establish an accurate transport model and uncover the factors governing their 1773


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based on an ascorbic-acid assistant hydrothermal reaction.44,45 With microwave assistance, the hydrothermal (or solvothermal) synthesis may be more rapid and energy-effective, because microwave heating arises from the direct absorption of microwave energy into the materials.46 Supercritical fluid reactions represent a powerful synthetic approach because the fluid exhibits unique properties such as gaslike diffusivity and low viscosity.47 Rangappa et al. performed the supercritical fluid synthesis of Li2FeSiO4 in mixed solvent of aqueous ethanol and obtained ultrathin Li2FeSiO4 nanosheets at 400 °C in only 10 min (Figure 3).48 Through this approach, Li2MnSiO4 and other nanosheets could also be fabricated, indicating its general potential in the electrode material synthesis. Li2FeSiO4 ↔ LiFeSiO4. The redox mechanism involved in Li2FeSiO4 has captured much attention as Li2FeSiO4 exhibits rich polymorphism and undergoes complex phase transformation and structural evolution. Most research on the electrochemical redox mechanism focuses on the extraction− insertion of one Li+ from Li2FeSiO4, because extracting reversibly two Li+ ions is challenging.49−51 This reaction (Li2FeSiO4 ↔ LiFeSiO4) leads to a specific capacity of 165 mAh g−1. On the basis of X-ray diffraction analysis, Mössbauer spectroscopy, and electrochemical analysis, Nytén et al. proposed that electrochemical extraction of one Li+ in Li2FeSiO4 was a typical two-phase reaction, which was accompanied by the concomitant oxidation of Fe2+ to Fe3+.49 The Pmn21 phase of Li2FeSiO4 is structurally reversible, although a significant rearrangement of Li+ ions (in the 4b sites) and Fe2+ ions (in the 2a sites) occurs. As the Li/Fe antisite mixing decreases the energy required for electrochemical Li reaction, the charge potential shifts from 3.1 to 2.8 V after the initial cycle. However, the discrepancy between the proposed model and structural data has generated immense debate.22,32,37,52 Chen et al.22 and Armstrong et al.32 proposed that the Li2FeSiO4 changed from the initial monoclinic (P21) phase to a stable orthorhombic (Pmn21) phase upon the first cycling. As a result, Li+ transport paths and corresponding Li−Li separations in the cycled structure are quite different from the original material. In

composites are generally introduced. A thin carbon coating can be obtained either from in situ decomposition of carbon precursor or added during the mixture of raw materials. The carbon modification not only increases the electronic conductivity but also serves as admixture to prevent the particles from undesirable growth. Recently, a molten flux route that baths raw materials in molten alkaline salts has been developed for the synthesis of Li2FeSiO4. By this route, Kojima et al. could prepare 1 kg of phase-pure Li2FeSiO4 powder in (Li0.435Na0.315K0.25)2CO3 flux under a CO2−H2 atmosphere at a low temperature of 500 °C.36,37 Overall, solid-state synthesis still suffers from inhomogeneous growth of particles and impurities and poor quality control and reproducibility.

Li-storage kinetics in Li2FeSiO4 can be tailored through advanced synthetic techniques and elaborate controls. These issues arising in the solid-state synthesis may be wellmitigated by soft-chemistry approaches such as sol−gel, hydrothermal (or solvothermal), and supercritical fluid reaction.38 Sol−gel synthesis is one of the most popular softchemistry approaches used for the synthesis of Li2FeSiO4. In such a process, most raw materials are dissolved in solvents like water and ethanol and homogeneously mixed at the molecule level. Thus, reaction temperature can be lowered and shortened reaction time is usually required, at the same time, the resultant products exhibit a high degree of purity.27 Naturally, chelation agents play a vital role in the formation of sol and gel, and the final product. Chelation agent can be selected from organic acids39 and polymers.40 Hydrothermal (or solvothermal) reaction is another popular soft-chemistry approach frequently applied in the synthesis of Li2FeSiO4. This synthesis promises crystalline materials with great versatility.41,42 Hydrothermal synthesis is capable of fabricating Li2FeSiO4 nanostructures with well-defined shape and finely tuned size. Yi et al. obtained about 30 nm Li2FeSiO4 nanoparticles in ethylene glycol solvent.43 Very recently, Ni et al. reported three-dimensional (3D) porous Li2FeSiO4 nanocrystals with a mean size of 60 nm

Figure 3. TEM images of the as-prepared samples: (a, b) Li2FeSiO4 and (d, e) Li2MnSiO4 nanosheets. (c, f) HRTEM images of Li2FeSiO4 and Li2MnSiO4 nanosheets with SAED patterns in the inset. Reprinted from ref 48. Copyright 2012 American Chemical Society. 1774


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Figure 4. Schematic summary of the phase transition behavior exhibited in the Li2FeSiO4−LiFeSiO4 system upon cycling at C/10 and C/50 rate. Bold and broken arrows indicate the charge and discharge processes, respectively. Reprinted from ref 53. Copyright 2014 American Chemical Society.

electrode materials.67 It helps to establish a conductive network for electron transport, thereby leading to a high capacity delivery and rate capability of Li2FeSiO4.17 A popular way toward this target is constructing an in situ coating layer of carbon, which can be derived from versatile organic precursors.68−70 In addition, the formation of a carbon layer provides a reductive environment, which suppresses the possible oxidation of Fe2+ species. Carbon modification in Li2FeSiO4 can also be realized by nanocarbons such as graphene57,71 and carbon nanotubes (CNTs),72 owing to their better conductivity over amorphous carbon. Both graphene and CNTs feature superb conductivity, large surface, and structural flexibility, which are recognized as essential components of highly active electrodes.73,74 In these composites, the nanocarbons serve as a conducting and flexible support, providing a fast path for electron movement. Meanwhile, the Li2FeSiO4 particles act as spacers to avoid the agglomeration of nanocarbon fractures.74,75 The synergy makes their integration particularly effective. An overview about this integration is depicted in ref 17, in which two typical configurations, the random and the ordered assembly, are compared. In light of the uniform integration of nanocarbon and Li2FeSiO4, Figure 5 shows the fabrication of the coaxial structure of CNT and Li2FeSiO4. The CNT@Li2FeSiO4 coaxial core−shell structure can be fabricated via either CNT@SiO2 or CNT@Fe2O3 route. Zhao and co-workers demonstrated the in situ generation of Li2FeSiO4 coating on CNT through a CNT@SiO2 intermediate.72 The coaxial composite discharged

contrast, Kojima et al. suggested that the monoclinic (P21) phase of Li2FeSiO4 could be well-preserved upon cycling and the structural difference was only associated with cation disordering of Li+, Fe2+, and Fe3+.37 To solve this dispute, Masese et al. designed an elaborate experiment to track the structural evolution of Li2FeSiO4 upon Li extraction.53 Figure 4 indicates the structural change of Li2FeSiO4 is dependent on the relaxation time upon charge and discharge. At a low rate such as C/50, Li/Fe antisite mixing can be fully relaxed and a thermodynamically stable orthorhombic LiFeSiO4 can be reached upon Li extraction. At a higher current rate, significant Li/Fe antisite mixing cannot occur because of limited time, thereby retaining the metastable monoclinic LiFeSiO4 phase. This rate-dependent phase transition has been recently confirmed by Lu and co-workers.38 In all the mechanisms discussed, it is explicit that the cation mixing in electrochemically cycled Li2FeSiO4 material is severe and might be the driving force for the phase evolution. LiFeSiO4 ↔ FeSiO4. In recent years, the extraction of the second Li+ ion from LiFeSiO4 has been closely investigated. Li+ ion extraction from LiFeSiO4 features another two-phase transformation.54 This electrochemical process is possibly accompanied by the redox reaction of O2− rather than Fe3+, because the potential from Fe3+ to Fe4+ is so high that the charge transfer may also occur in oxygen. This finding is experimentally confirmed by X-ray absorption measurements.55 No significant Fe K-edge edge shift is visible between LiFeSiO4 and FeSiO4 phases, while O K-edge measurements reveal significant contribution of the O 2p band. Similar phenomena have previously been confirmed for high-voltage cathodes such as LiCoPO4 and LiNi0.5Mn1.5O4.56 However, whether the transformation between LiFeSiO4 and FeSiO4 is a two-phase process is still controversial.55 Therefore, in-depth understanding of the redox behavior and phase evolution of the Li2FeSiO4 is still urgently needed.28 Approaching the high capacity of Li2FeSiO4 requires the efficient material design to address the issue of low mobility of charge carriers.27 To this end, numerous material engineering strategies have been developed. Most of the strategies leverage the knowledge developed recently for polyanionic phosphates, which can be roughly classified as carbon modification,57,58 ion doping,59,60 size reduction,61,62 porosity construction,63,64 and phase hybridization.65,66 Carbon Modif ication. Carbon modification is simple but extremely effective in enhancing the electrochemical activity of

Figure 5. Schematic illustration of the fabrication process of CNT@ Li2FeSiO4 coaxial structure via (a) CNT@SiO2 and (b) CNT@ Fe2O3 routes. 1775


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Figure 6. First-principles calculated structure properties and electrochemical performance for the cycled Li2FeSiO4 (L2FS, inversed Pmn21) with and without Ti doping. (a) Full relaxed configuration for the cycled Li2FS, half- (LiFeSiO4 (LFS)) and fully- (FeSiO4 (FS)) delithiated structures, the dominant Li-ion diffusion path in the cycled Li2FS and a heavy distortion lead to the structure phase change or even structure fracture in the fully delithiated structures. (b) The structural representation of the fully delithiated structures by Ti atoms with d-orbit substituted at Fe sites; the four “pink cycles” mean strong coupling effect among the TiO4, FeO4, and SiO4 tetrahedra. (c) Calculated formation enthalpy of Ti- and Sn-doped Li2FeSiO4. TiFe, TiSi, and SnFe mean Ti doping at Fe sites, Si sites, and Sn doping at Fe sites, respectively. Except for the red data (P21/n), all the left data are for doped inversed Pmn21 Li2FeSiO4. (d) Typical galvanostatic charge− discharge curves at 0.2C (1 C = 166 mA g−1), (e) rate capability from 0.2C to 10C for 5% Ti- or Sn-doped and pristine Li2FeSiO4 samples. Reprinted with permission from ref 30. Copyright 2016 Elsevier.

a stable capacity of 240 mAh g−1, corresponding to 1.44 Li+ ions per formula unit. In another case, Zhu and co-workers reported a 3D graphene-based Li2FeSiO4 composite fabricated through a template method.71 The 3D-G/Li2FeSiO4/C composite exhibited a high capacity of 313 mAh g−1 (93% of the theoretical value) and excellent rate capability, discharging 313, 255, 215, 180, 150, and 108 mAh g−1 at rates of 0.1, 1, 2, 5, 10, and 20C, respectively, The superior capabilities are believed to be cooperative results of nanostructured Li2FeSiO4 and 3D porous graphene. Further research demonstrated that graphene modification could increase the apparent Li diffusion coefficient of Li2FeSiO4, because the ion diffusion process is tightly coupled with electron movement.57 Ion Doping. Ion doping has been explored to introduce lattice defects and additional electron bands, thereby modulating the electronic structure and mobility of charge carriers.76 In the case of Li2FeSiO4, ion doping in either Fe or Si sites is possible, depending on the dopant and its chemical state.77,78 When a Fe2+ is substituted by an electrochemically active divalent ion such as Mn and Ni, both elements contribute to the redox reaction and the capacity. For instance, Mn-doped Li2FeSiO4 materials exhibit additional redox plateau of Mn2+/Mn3+ with a higher capacity compared to the undoped materials.78 If this dopant is an inactive species such as Mg and Zn, it would not contribute to the capacity but act as pillars to stabilize the lattice structure, thereby enabling higher charge and discharge stability.60 Moreover, Zn doping would enhance the Li diffusivity of Li2FeSiO4 owing to the expanded diffusion channel due to the larger size of Zn2+.78 If an aliovalent cation could be incorporated into the Li2FeSiO4 materials, vacancies at Li sites may be generated because of the need for charge balance. Li vacancies may contribute to intrinsic ionic conductivity, thereby leading to improved electrochemical performance.60 Figure 6 shows the structural properties and electrochemical performance for the

Li2FeSiO4/C with and without Ti doping by first-principles calculations.30 The results proved that optimized Ti substitution could remarkably enhance the structural stability and electrochemical activity of Li2FeSiO4, as a result of the strong orbital hybridization between Ti (3d and 4s orbitals) and O (2p orbital). As shown in Figure 6d, the Ti-doped Li2FeSiO4 exhibits a higher discharge potential at 2.75 V compared to the undoped Li2FeSiO4, indicative of improved kinetics by Ti doping. Note that this discharge potential is much lower than the predicted value of 3.1 V, which might be due to Li/Fe antisite displacement. More importantly, an extremely high capacity of 317 mAh g−1 with amazing capacity retention of 75% for 2000 cycles is achieved via this Ti-doping strategy. Alternatively, Li-deficient (Li vacancy doped) Li2FeSiO4 exhibits much better battery performance in terms of the discharge capacity, cycling stability, and rate capability in comparison with the Li2FeSiO4/C composite.77 Besides cation and vacancy doping, anion doping is also a promising route toward high-performance Li2FeSiO4 materials. Armand and coworkers suggested that the N-doped Li2FeSiO4 could approach the theoretical capacity, because the N3− anions are also active toward Li.29 Size Reduction. Downsizing the Li2FeSiO4 particle to nanoscale can shorten the diffusion distance for charge carriers while simultaneously increasing the surface area accessible to Li+ ions.79 Both advantages are beneficial to mitigate the slow kinetics issue of Li2FeSiO4. Reducing the Li2FeSiO4 size is a straightforward strategy but requires specific treatment because of severe grain growth upon crystallization. Preparation of nanoscale Li2FeSiO4 materials can be realized by nanosized raw materials,39 but it is more efficient to control the synthetic approaches and procedures.43,62,70,80 Xia’s group prepared Li2FeSiO4/C nanocomposites via a mild solvothermal method followed by vapor deposition of carbon.43 The Li2FeSiO4/C nanocomposite was composed of Li2FeSiO4 nanocrystals and 1776


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the transport of electrons on the surface, while ion doping speeds the electron transport in bulk and sometimes the ion transport as well if proper ions are selected. Both size reduction and porosity constructions can enlarge the accessible area and decrease the length of the ion diffusion, which is equal to speeding the movement of the electron and ion. From the viewpoint of energy, the latter would be more effective because it does not significantly reduce the packing density. Phase hybridization has a similar effect on carbon modification, but it also acts on ion transport in some cases. Table 2 summarizes

was connected by the mutual cross-linked carbon conductive matrix. The composite delivered a discharge capacity of 154 mAh g−1 at 1C. Mu’s group demonstrated that 3D frameworks of Li2FeSiO4 nanocrystal achieved a capacity of 211 mAh g−1 at 0.1C.61 Porosity Construction. A porous structure is attractive from the viewpoint of electrochemistry, because the pores allow efficient penetration, transport, and storage of the electrolyte within the electrode for fast mass transport.81 Zheng et al. synthesized a porous Li2FeSiO4/C nanocomposite with the average size of 30 nm by a tartaric acid assisted sol−gel method. This material afforded a reversible capacity of 132 mAh g−1 at 1C.80 Yang’s group fabricated a porous Li2FeSiO4/C nanocomposite with a hierarchical porous structure using an in situ template.64 The macropores provided electrolyte channels for fast ionic transport, while the micropores offer large, accessible electrochemically active areas for the Li insertion reaction. Consequently, the Li2FeSiO4/C composite demonstrated a very high capacity of 254 mAh g−1 at room temperature with excellent cycling stability and rate capability. Recently, Ni et al. designed 3D porous hierarchical Li2FeSiO4/C and Li2FeSiO4/ CNT nanocomposites, where Li2FeSiO4 nanocrystals were dispersed into porous carbon or CNT matrix.44,45 Both composites exhibited high activity toward Li cycling, outperforming the counterpart without carbon painting and other Li2FeSiO4 materials. The authors attributed the high activity to the 3D porous structure and carbon nanopainting, which endowed the material with efficient electrolyte penetration and rapid electron transport. Moreover, if an ordered porous structure can be engineered, Li storage performance of Li2FeSiO4 will be largely boosted. This is because the ordered pores enable full exposure of active materials to the electrolyte but also markedly facilitate the kinetics of ion diffusion and electron transport.82−85 Phase Hybridization. Some researchers engineered Li2FeSiO4 hybrids by incorporating a second phase to tailor the electrochemical activity. The second phase could be a good electron conductor65 or ion conductor,66 thereby mitigating the transport issue in Li2FeSiO4. Bai et al. developed a hybrid material of 0.8 Li2FeSiO4/0.4Li2SiO3/C with the incorporation of Li2SiO3 as a lithium ionic conductive matrix.66 The hybrid material showed a capacity of 240 mAh g−1 at a rate of 10 mA g−1 with good cyclic stability. The presence of amorphous Li2SiO3 was the key to this high activity; it separated the Li2FeSiO4 particles into small nanodomains and provided a fast Li+ diffusion channel. Chen’s group demonstrated that a hybrid of intergrown Li2FeSiO4 and LiFePO4 delivered a capacity of 284.7 mAh g−1 at 0.5C, which was much higher than that of the Li2FeSiO4/C counterpart.86 This improved electrochemical performance originated from reduced electrochemical polarization as a result of enhanced conductivity and diffusivity through phase hybridization.

Table 2. Electrochemical Performance of Some Engineered Li2FeSiO4 Materials at Room Temperature material Li2FeSiO4/rGO/C Li2FeSiO4/CNT Li2Fe0.95Ti0.05SiO4/C Li2FeV0.1Si0.9O4/C LiFePO4/C LiFePO4/C Li2FeSiO4/C Li2FeSiO4/CNT/C Li2FeSiO4/Li2SiO3/C

materials engineering strategy carbon modification carbon modification ion doping ion doping size reduction size reduction porosity construction porosity construction phase hybridization

electrochemical performance 178 mAh g−1 mAh g−1 at 180 mAh g−1 cycles 317 mAh g−1 mAh g−1 at cycles 159 mAh g−1 154 mAh g−1 211 mAh g−1 254 mAh g−1 mAh g−1 at 214 mAh g−1

ref

at 0.1C 119 2C at 1C for 120

57

at 0.2C, 90 10C for 2000

30

at 0.06C at 1C at 1C at 0.06C, 178 1C at 0.1C

59 43 61 64

240 mAh g−1 at 0.06C

72

45 66

the electrochemical performance of some engineered Li2FeSiO4 materials. In most case, the high capacity and rate performance could not be achieved by a single material engineering method; which method or method combination contributes most to the performance improvement is worth further investigation.87,88 On the other hand, development of a synthesis method which generates high-quality materials and also can be scalable to manufacturing level requires not only clear understanding of the carrier transportation mechanism but also further innovative material engineering method development. In summary, Li2FeSiO4 is promising for next-generation LIBs because of its large capacity and energy density. At present, realizing the high capacity of Li2FeSiO4 reversibly and sustainably in reality represents a main challenge because of sluggish reaction kinetics caused by extremely slow mobility of charge carriers. During the past decade, significant material progress has been achieved, largely relying on innovations in advanced synthetic techniques and sophisticated strategies to control the intrinsic material properties. Li2FeSiO4 materials composed of uniform nanoparticles with high phase purity can be readily fabricated via a wide array of synthetic routes. When further modified with doping or substitution, carbon nanopainting, and hybridization, these Li2FeSiO4 nanomaterials exhibit a high capacity delivery and good rate capability, because the transport of electrons and ions in these materials has been greatly boosted. Currently, a reversible capacity of 300 mAh g−1 and a practical energy density of 750 mWh g−1 are accessible in the case of Li2FeSiO4 nanosheets at 45 °C48 and Ti-doped Li2FeSiO4 nanoparticles at room temperature.30 The latter is particularly exciting because its synthesis via solid-state process is intrinsically scalable, affordable, and reproducible.

This Perspective highlights the importance of integrating theoretical analysis into experimental implementation in further advancing Li2FeSiO4 materials. Although material engineering methods of Li2FeSiO4 synthesis are divided into several sections for clarity of discussion, these materials strategies play a different role in addressing the kinetic issue. In most case, carbon modification greatly boosts 1777


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Li2FeSiO4 is still faced with great performance challenges in practice unless it can afford an energy beyond Li-rich oxide cathodes.89−91 The future exploration of Li2FeSiO4 is to fully approach its two-electron reaction capacity at ambient temperature and normal cycling conditions. This is quite ambitious, and significant gaps in our knowledge still remain. Toward this goal, we propose some considerations with regard to future directions. First, most Li2FeSiO4 materials reported do not show favorable electrochemical performance at ambient temperatures, although the dimensions of some samples approach atomic thickness. Thus, improvement of kinetics related to intrinsic electron and ion mobility continues to be one of the core challenges. Future work may focus on the utilization and optimization of the materials engineering strategies, in which ion doping is the one method that can address the coupled electron and ion transport of Li2FeSiO4 simultaneously. Meanwhile, the combination of various engineering approaches represents a promising direction. Materials engineered by several approaches have more chances to overcome the transport issues of electrons and ions to a great extent. Second, Li2FeSiO4 crystallizes in several polymorphs that exhibit different ordering of Li+, Fe2+, and Si4+. This disordering continuously evolves upon Li cycling of Li2FeSiO4. What is the driving force triggering this structural disordering and evolution remains a myth. Moreover, we should consider how to synthesize the highly disordered Li2FeSiO4 structure directly, which can essentially avoid the structural evolution on cycling and retain good phase integrity. Third, deep understanding of the phase transition upon Li+ ion extraction− insertion is crucial to the future development of Li2FeSiO4 materials. However, knowledge in this field is still superficial; thus, advanced characterization techniques such as in situ or operando tools, which can provide a more comprehensive image of the real-time evolution of electrode materials, are required. With information obtained by the in situ techniques, it would possible to reveal the process of structural disordering, phase transition, and transport limitation of Li2FeSiO4 materials in the cell. On the other hand, first-principles computation using DFT has been widely used in materials science. The computation plays an increasingly important role in the design and optimization of electrode materials and Li2FeSiO4 material in particular. Recent success of computation in the development of electrode materials encourages researchers to explore its potentiality. Thus, future works that integrate theoretical calculation into in situ experiments are desired to provide new insight into the electrochemical processes in Li2 FeSiO4 materials.92,93

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professor of Physics and leads a team working on various types of energy storage systems. Yu Jiang received his B.S. degree from Soochow University in 2016. He is currently working toward the Master degree at Soochow University. His research interest focuses on electrochemical materials for battery applications. Xuanxuan Bi received her M.S. in Chemistry from The Ohio State University in 2015. Now she is a Ph.D. candidate at The Ohio State University and also a guest graduate appointee at Argonne National Laboratory. Her research focuses on the development of electrode materials for battery technologies. Liang Li received his Ph.D. degree from Institute of Solid State Physics, Chinese Academy of Sciences in 2006. Since August 2012, he has been a full professor iat Soochow University in China. His research group focuses mainly on controlled synthesis, novel physical properties, and nanoscale devices for energy-related applications. His group’s website is http://ecs.suda.edu.cn. Jun Lu is a chemist at Argonne National Laboratory. His research interests focus on the electrochemical energy storage and conversion technology, with main focus on beyond Li-ion battery technology. Dr. Lu earned his bachelor degree in Chemistry Physics from University of Science and Technology of China (USTC) in 2000. He completed his Ph.D. at the University of Utah in 2009.

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ACKNOWLEDGMENTS We are grateful for the financial support of the National Natural Science Foundation of China (51672182, 51422206, 51302181, 51372159), 333 High-Level Talents Project in Jiangsu Province, the Thousand Young Talents Plan, the Jiangsu Natural Science Foundation (BK20151219, BK20140009), Six Talent Peaks Project in Jiangsu Province, and of the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD). J.L. gratefully acknowledges support from the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office. Argonne National Laboratory is operated for DOE Office of Science by UChicago Argonne, LLC, under Contract Number DE-AC02-06CH11357.

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REFERENCES

(1) Chu, S.; Cui, Y.; Liu, N. The path towards sustainable energy. Nat. Mater. 2017, 16, 16−22. (2) Dunn, B.; Kamath, H.; Tarascon, J. M. Electrical energy storage for the grid: a battery of choices. Science 2011, 334, 928−35. (3) Guo, Z.; Wang, Y.; Song, Y.; Li, C.; Su, X.; Wang, Y.; Cai, W.-b.; Xia, Y. A multifunction lithium−carbon battery system using a dual electrolyte. ACS Energy Lett. 2017, 2, 36−44. (4) Yu, B.-C.; Park, K.; Jang, J.-H.; Goodenough, J. B. Cellulose-based porous membrane for suppressing li dendrite formation in lithium− sulfur battery. ACS Energy Lett. 2016, 1, 633−637. (5) Myung, S.-T.; Maglia, F.; Park, K.-J.; Yoon, C. S.; Lamp, P.; Kim, S.-J.; Sun, Y.-K. Nickel-rich layered cathode materials for automotive lithium-ion batteries: Achievements and perspectives. ACS Energy Lett. 2017, 2, 196−223. (6) 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, B.; Salehi-Khojin, A.; Sun, Y. K.; Curtiss, L. A.; Amine, K. A lithium-oxygen battery based on lithium superoxide. Nature 2016, 529, 377−82. (7) Whittingham, M. S. Ultimate limits to intercalation reactions for lithium batteries. Chem. Rev. 2014, 114, 11414−43.

AUTHOR INFORMATION

Corresponding Authors

*E-mail: jeff[email protected]. *E-mail: [email protected]. *E-mail: [email protected]. ORCID

Jiangfeng Ni: 0000-0002-1649-4282 Jun Lu: 0000-0003-0858-8577 Notes

The authors declare no competing financial interest. Biographies Jiangfeng Ni received his Ph.D. degree in Chemistry from Peking University in 2008. After a three-year postdoctoral study, he moved to Soochow University, China in 2011. At present Dr. Ni is a full 1778


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(8) Gong, Z.; Yang, Y. Recent advances in the research of polyaniontype cathode materials for Li-ion batteries. Energy Environ. Sci. 2011, 4, 3223−3242. (9) Wang, J.; Sun, X. Olivine LiFePO4: the remaining challenges for future energy storage. Energy Environ. Sci. 2015, 8, 1110−1138. (10) Nyten, A.; Abouimrane, A.; Armand, M.; Gustafsson, T.; Thomas, J. O. Electrochemical performance of Li2FeSiO4 as a new Libattery cathode material. Electrochem. Commun. 2005, 7, 156−160. (11) Arroyo-de Dompablo, M. E.; Armand, M.; Tarascon, J. M.; Amador, U. On-demand design of polyoxianionic cathode materials based on electronegativity correlations: An exploration of the Li2MSiO4 system. Electrochem. Commun. 2006, 8, 1292−1298. (12) He, G.; Manthiram, A. Nanostructured Li2MnSiO4/C cathodes with hierarchical macro-/mesoporosity for lithium-ion batteries. Adv. Funct. Mater. 2014, 24, 5277. (13) Longo, R. C.; Kc, S.; Cho, K. Ionic and electronic mobility in multicomponent olivine silicate cathode materials for Li-ion batteries. J. Electrochem. Soc. 2014, 161, A1461−A1467. (14) Islam, M. S.; Dominko, R.; Masquelier, C.; Sirisopanaporn, C.; Armstrong, A. R.; Bruce, P. G. Silicate cathodes for lithium batteries: alternatives to phosphates? J. Mater. Chem. 2011, 21, 9811. (15) Masquelier, C.; Croguennec, L. Polyanionic (phosphates, silicates, sulfates) frameworks as electrode materials for rechargeable Li (or Na) batteries. Chem. Rev. 2013, 113, 6552−6591. (16) Gummow, R. J.; He, Y. Recent progress in the development of Li2MnSiO4 cathode materials. J. Power Sources 2014, 253, 315−331. (17) Ni, J.; Zhang, L.; Fu, S.; Savilov, S.; Aldoshin, S.; Lu, L. A review on integrating nano-carbons into polyanion phosphates and silicates for rechargeable lithium batteries. Carbon 2015, 92, 15−25. (18) Sirisopanaporn, C.; Masquelier, C.; Bruce, P. G.; Armstrong, A. R.; Dominko, R. Dependence of Li2FeSiO4 Electrochemistry on Structure. J. Am. Chem. Soc. 2011, 133, 1263−1265. (19) Boulineau, A.; Sirisopanaporn, C.; Dominko, R.; Armstrong, A. R.; Bruce, P. G.; Masquelier, C. Polymorphism and structural defects in Li2FeSiO4. Dalton Trans. 2010, 39, 6310−6316. (20) Dominko, R.; Bele, M.; Gaberšcě k, M.; Meden, A.; Remškar, M.; Jamnik, J. Structure and electrochemical performance of Li2MnSiO4 and Li2FeSiO4 as potential Li-battery cathode materials. Electrochem. Commun. 2006, 8, 217−222. (21) Nishimura, S.-i.; Hayase, S.; Kanno, R.; Yashima, M.; Nakayama, N.; Yamada, A. Structure of Li2FeSiO4. J. Am. Chem. Soc. 2008, 130, 13212−13213. (22) Chen, R.; Heinzmann, R.; Mangold, S.; Chakravadhanula, V. S. K.; Hahn, H.; Indris, S. Structural evolution of Li2Fe1‑yMnySiO4 (y = 0, 0.2, 0.5, 1) cathode materials for Li-ion batteries upon electrochemical cycling. J. Phys. Chem. C 2013, 117, 884−893. (23) Zhang, P.; Hu, C. H.; Wu, S. Q.; Zhu, Z. Z.; Yang, Y. Structural properties and energetics of Li2FeSiO4 polymorphs and their delithiated products from first-principles. Phys. Chem. Chem. Phys. 2012, 14, 7346−7351. (24) Sirisopanaporn, C.; Boulineau, A.; Hanzel, D.; Dominko, R.; Budic, B.; Armstrong, A. R.; Bruce, P. G.; Masquelier, C. Crystal structure of a new polymorph of Li2FeSiO4. Inorg. Chem. 2010, 49, 7446−7451. (25) Sirisopanaporn, C.; Dominko, R.; Masquelier, C.; Armstrong, A. R.; Mali, G.; Bruce, P. G. Polymorphism in Li2(Fe,Mn)SiO4: A combined diffraction and NMR study. J. Mater. Chem. 2011, 21, 17823−17831. (26) Wu, S. Q.; Zhu, Z. Z.; Yang, Y.; Hou, Z. F. Structural stabilities, electronic structures and lithium deintercalation in LixMSiO4 (M = Mn, Fe, Co, Ni): A GGA and GGA + U study. Comput. Mater. Sci. 2009, 44, 1243−1251. (27) Dominko, R. Li2MSiO4 (M = Fe and/or Mn) cathode materials. J. Power Sources 2008, 184, 462−468. (28) Eames, C.; Armstrong, A. R.; Bruce, P. G.; Islam, M. S. Insights into changes in voltage and structure of Li2FeSiO4 polymorphs for lithium-ion batteries. Chem. Mater. 2012, 24, 2155−2161. (29) Armand, M.; Tarascon, J. M.; Arroyo-de Dompablo, M. E. Comparative computational investigation of N and F substituted

polyoxoanionic compounds: The case of Li2FeSiO4 electrode material. Electrochem. Commun. 2011, 13, 1047−1050. (30) Yang, J.; Zheng, J.; Kang, X.; Teng, G.; Hu, L.; Tan, R.; Wang, K.; Song, X.; Xu, M.; Mu, S.; Pan, F. Tuning structural stability and lithium-storage properties by d-orbital hybridization substitution in full tetrahedron Li2FeSiO4 nanocrystal. Nano Energy 2016, 20, 117−125. (31) Liivat, A.; Thomas, J. O. Li-ion migration in Li2FeSiO4-related cathode materials: A DFT study. Solid State Ionics 2011, 192, 58−64. (32) Armstrong, A. R.; Kuganathan, N.; Islam, M. S.; Bruce, P. G. Structure and lithium transport pathways in Li2FeSiO4 cathodes for lithium batteries. J. Am. Chem. Soc. 2011, 133, 13031−13035. (33) Ellis, B.; Perry, L. K.; Ryan, D. H.; Nazar, L. F. Small polaron hopping in Li(x)FePO4 solid solutions: coupled lithium-ion and electron mobility. J. Am. Chem. Soc. 2006, 128, 11416−11422. (34) Ni, J.; Kawabe, Y.; Morishita, M.; Watada, M.; Takeichi, N.; Sakai, T. Pyroxene LiVS2O6 as an electrode material for Li-ion batteries. J. Power Sources 2010, 195, 8322−8326. (35) Li, L.-M.; Guo, H.-J.; Li, X.-H.; Wang, Z.-X.; Peng, W.-I.; Xiang, K.-X.; Cao, X. Effects of roasting temperature and modification on properties of Li2FeSiO4/C cathode. J. Power Sources 2009, 189, 45−50. (36) Kojima, T.; Kojima, A.; Miyuki, T.; Okuyama, Y.; Sakai, T. Synthesis method of the Li-ion battery cathode material Li2FeSiO4 using a molten carbonate flux. J. Electrochem. Soc. 2011, 158, A1340− A1346. (37) Kojima, A.; Kojima, T.; Sakai, T. Structural analysis during charge-discharge process of Li2FeSiO4 synthesized by molten carbonate flux method. J. Electrochem. Soc. 2012, 159, A525. (38) Lu, X.; Wei, H.; Chiu, H.-C.; Gauvin, R.; Hovington, P.; Guerfi, A.; Zaghib, K.; Demopoulos, G. P. Rate-dependent phase transitions in Li2FeSiO4 cathode nanocrystals. Sci. Rep. 2015, 5, 8599. (39) Qu, L.; Fang, S.; Yang, L.; Hirano, S.-i. Li2FeSiO4/C cathode material synthesized by template-assisted sol-gel process with Fe2O3 microsphere. J. Power Sources 2012, 217, 243−247. (40) Zhou, H.; Einarsrud, M. A.; Vullum-Bruer, F. High capacity nanostructured Li2FeSiO4/C with Fe hyperstoichiometry for Li-ion batteries. J. Power Sources 2013, 235, 234−242. (41) Ni, J.; Gao, L. Effect of copper doping on LiMnPO4 prepared via hydrothermal route. J. Power Sources 2011, 196, 6498−6501. (42) Ni, J.; Han, Y.; Gao, L.; Lu, L. One-pot synthesis of CNT-wired LiCo0.5Mn0.5PO4 nanocomposites. Electrochem. Commun. 2013, 31, 84−87. (43) Yi, J.; Hou, M.-y.; Bao, H.-l.; Wang, C.-x.; Wang, J.-q.; Xia, Y.-y. In-situ generation of Li2FeSiO4/C nanocomposite as cathode material for lithium ion battery. Electrochim. Acta 2014, 133, 564−569. (44) Zhang, L.; Ni, J.; Wang, W.; Guo, J.; Li, L. 3D porous hierarchical Li2FeSiO4/C for rechargeable lithium batteries. J. Mater. Chem. A 2015, 3, 11782−11786. (45) Wang, W.; Liang, H.; Zhang, L.; Savilov, S. V.; Ni, J.; Li, L. Carbon nanotube directed three-dimensional porous Li2FeSiO4 composite for lithium batteries. Nano Res. 2017, 10, 229−237. (46) Muraliganth, T.; Stroukoff, K. R.; Manthiram, A. Microwavesolvothermal synthesis of nanostructured Li2MSiO4/C (M = Mn and Fe) cathodes for lithium-ion batteries. Chem. Mater. 2010, 22, 5754− 5761. (47) Devaraju, M. K.; Tomai, T.; Honma, I. Supercritical hydrothermal synthesis of rod like Li2FeSiO4 particles for cathode application in lithium ion batteries. Electrochim. Acta 2013, 109, 75− 81. (48) Rangappa, D.; Murukanahally, K. D.; Tomai, T.; Unemoto, A.; Honma, I. Ultrathin nanosheets of Li2MSiO4 (M = Fe, Mn) as highcapacity Li-ion battery electrode. Nano Lett. 2012, 12, 1146−51. (49) Nytén, A.; Kamali, S.; Haggstrom, L.; Gustafsson, T.; Thomas, J. O. The lithium extraction/insertion mechanism in Li2FeSiO4. J. Mater. Chem. 2006, 16, 2266−2272. (50) Zhang, P.; Zheng, Y.; Yu, S.; Wu, S. Q.; Wen, Y. H.; Zhu, Z. Z.; Yang, Y. Insights into electrochemical performance of Li2FeSiO4 from first-principles calculations. Electrochim. Acta 2013, 111, 172−178. (51) Nytén, A.; Stjerndahl, M.; Rensmo, H.; Siegbahn, H.; Armand, M.; Gustafsson, T.; Edström, K.; Thomas, J. O. Surface character1779


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Perspective

ization and stability phenomena in Li2FeSiO4 studied by PES/XPS. J. Mater. Chem. 2006, 16, 3483−3488. (52) Dominko, R.; Arčon, I.; Kodre, A.; Hanžel, D.; Gaberšcě k, M. In-situ XAS study on Li2MnSiO4 and Li2FeSiO4 cathode materials. J. Power Sources 2009, 189, 51−58. (53) Masese, T.; Orikasa, Y.; Tassel, C.; Kim, J.; Minato, T.; Arai, H.; Mori, T.; Yamamoto, K.; Kobayashi, Y.; Kageyama, H.; Ogumi, Z.; Uchimoto, Y. Relationship between phase transition involving cationic exchange and charge-discharge rate in Li2FeSiO4. Chem. Mater. 2014, 26, 1380−1384. (54) Lv, D.; Bai, J.; Zhang, P.; Wu, S.; Li, Y.; Wen, W.; Jiang, Z.; Mi, J.; Zhu, Z.; Yang, Y. Understanding the high capacity of Li2FeSiO4: In Situ XRD/XANES study combined with first-principles calculations. Chem. Mater. 2013, 25, 2014−2020. (55) Masese, T. N.; Tassel, C.; Orikasa, Y.; Koyama, Y.; Arai, H.; Hayashi, N.; Kim, J.; Mori, T.; Yamamoto, K.; Kobayashi, Y.; et al. Crystal structural changes and charge compensation mechanism during two lithium extraction/insertion between Li2FeSiO4 and FeSiO4. J. Phys. Chem. C 2015, 119, 10206−10211. (56) Hu, M.; Pang, X.; Zhou, Z. Recent progress in high-voltage lithium ion batteries. J. Power Sources 2013, 237, 229−242. (57) Zhang, L.-L.; Duan, S.; Yang, X.-L.; Peng, G.; Liang, G.; Huang, Y.-H.; Jiang, Y.; Ni, S.-B.; Li, M. Reduced graphene oxide modified Li2FeSiO4/C composite with enhanced electrochemical performance as cathode material for lithium ion batteries. ACS Appl. Mater. Interfaces 2013, 5, 12304−12309. (58) Zhu, H.; Wu, X.; Zan, L.; Zhang, Y. Superior electrochemical capability of Li2FeSiO4/C/G composite as cathode material for Li-ion batteries. Electrochim. Acta 2014, 117, 34−40. (59) Hao, H.; Wang, J.; Liu, J.; Huang, T.; Yu, A. Synthesis, characterization and electrochemical performance of Li2FeSiO4/C cathode materials doped by vanadium at Fe/Si sites for lithium ion batteries. J. Power Sources 2012, 210, 397−401. (60) Zhang, S.; Deng, C.; Fu, B.; Yang, S.; Ma, L. Doping effects of magnesium on the electrochemical performance of Li2FeSiO4 for lithium ion batteries. J. Electroanal. Chem. 2010, 644, 150−154. (61) Yang, J.; Kang, X.; Hu, L.; Gong, X.; Mu, S. NanocrystallineLi2FeSiO4 synthesized by carbon frameworks as an advanced cathode material for Li-ion batteries. J. Mater. Chem. A 2014, 2, 6870−6878. (62) Hasegawa, G.; Sannohe, M.; Ishihara, Y.; Kanamori, K.; Nakanishi, K.; Abe, T. New Li2FeSiO4−carbon monoliths with controlled macropores: effects of pore properties on electrode performance. Phys. Chem. Chem. Phys. 2013, 15, 8736−8743. (63) Fu, R.; Li, Y.; Yang, H.; Zhang, Y.; Cheng, X. Improved performance of Li2FeSiO4/C composite with highly rough mesoporous morphology. J. Electrochem. Soc. 2013, 160, A3048−A3053. (64) Chen, Z.; Qiu, S.; Cao, Y.; Qian, J.; Ai, X.; Xie, K.; Hong, X.; Yang, H. Hierarchical porous Li2FeSiO4/C composite with 2 Li storage capacity and long cycle stability for advanced Li-ion batteries. J. Mater. Chem. A 2013, 1, 4988−4992. (65) Li, D.; Xie, R.; Tian, M.; Ma, S.; Gou, L.; Fan, X.; Shi, Y.; Yong, H.-T.-H.; Hao, L. Improving high-rate performance of mesoporous Li2FeSiO4/Fe7SiO10/C nanocomposite cathode with a mixed valence Fe7SiO10 nanocrystal. J. Mater. Chem. A 2014, 2, 4375−4383. (66) Bai, J.; Gong, Z.; Lv, D.; Li, Y.; Zou, H.; Yang, Y. Nanostructured 0.8Li2FeSiO4 /0.4Li2SiO3/C composite cathode material with enhanced electrochemical performance for lithium-ion batteries. J. Mater. Chem. 2012, 22, 12128−12132. (67) Ni, J.; Li, Y. Carbon nanomaterials in different dimensions for electrochemical energy storage. Adv. Energy Mater. 2016, 6, 1600278. (68) Lv, D.; Wen, W.; Huang, X.; Bai, J.; Mi, J.; Wu, S.; Yang, Y. A novel Li2FeSiO4/C composite: Synthesis, characterization and high storage capacity. J. Mater. Chem. 2011, 21, 9506. (69) Yan, Z.; Cai, S.; Zhou, X.; Zhao, Y.; Miao, L. Sol-gel synthesis of nanostructured Li2FeSiO4/c as cathode material for lithium ion battery. J. Electrochem. Soc. 2012, 159, A894−A898. (70) Xu, Y.; Li, Y.; Liu, S.; Li, H.; Liu, Y. Nanoparticle Li2FeSiO4 as anode material for lithium-ion batteries. J. Power Sources 2012, 220, 103−107.

(71) Zhu, H.; Wu, X.; Zan, L.; Zhang, Y. Three-dimensional macroporous graphene-Li2FeSiO4 composite as cathode material for lithium-ion batteries with superior electrochemical performances. ACS Appl. Mater. Interfaces 2014, 6, 11724−33. (72) Zhao, Y.; Li, J.; Wang, N.; Wu, C.; Ding, Y.; Guan, L. In situ generation of Li2FeSiO4 coating on MWNT as a high rate cathode material for lithium ion batteries. J. Mater. Chem. 2012, 22, 18797− 18800. (73) Ni, J.; Zhao, Y.; Liu, T.; Zheng, H.; Gao, L.; Yan, C.; Li, L. Strongly coupled Bi2S3@CNT hybrids for robust lithium storage. Adv. Energy Mater. 2014, 4, 1400798. (74) Zhao, Y.; Liu, T.; Xia, H.; Zhang, L.; Jiang, J.; Shen, M.; Ni, J.; Gao, L. Branch-structured Bi2S3−CNT hybrids with improved lithium storage capability. J. Mater. Chem. A 2014, 2, 13854−13858. (75) Zhao, Y.; Gao, D.; Ni, J.; Gao, L.; Yang, J.; Li, Y. One-pot facile fabrication of carbon-coated Bi2S3 nanomeshes with efficient Listorage capability. Nano Res. 2014, 7, 765−773. (76) Ni, J.; Zhao, Y.; Chen, J.; Gao, L.; Lu, L. Site-dependent electrochemical performance of Mg doped LiFePO4. Electrochem. Commun. 2014, 44, 4−7. (77) Huang, X.; Chen, H.; Zhou, S.; Chen, Y.; Yang, J.; Ren, Y.; Wang, H.; Qu, M.; Pan, Z.; Yu, Z. Synthesis and characterization of nano-Li1.95FeSiO4/C composite as cathode material for lithium-ion batteries. Electrochim. Acta 2012, 60, 239−243. (78) Deng, C.; Zhang, S.; Yang, S.; Fu, B.; Ma, L. Synthesis and characterization of Li2Fe0.97M0.03SiO4 (M= Zn2+, Cu2+, Ni2+) cathode materials for lithium ion batteries. J. Power Sources 2011, 196, 386− 392. (79) Zaghib, K.; Guerfi, A.; Hovington, P.; Vijh, A.; Trudeau, M.; Mauger, A.; Goodenough, J. B.; Julien, C. M. Review and analysis of nanostructured olivine-based lithium recheargeable batteries: Status and trends. J. Power Sources 2013, 232, 357−369. (80) Zheng, Z.; Wang, Y.; Zhang, A.; Zhang, T.; Cheng, F.; Tao, Z.; Chen, J. Porous Li2FeSiO4/C nanocomposite as the cathode material of lithium-ion batteries. J. Power Sources 2012, 198, 229−235. (81) Wang, B.; Al Abdulla, W.; Wang, D.; Zhao, X. A threedimensional porous LiFePO4 cathode material modified with a nitrogen-doped graphene aerogel for high-power lithium ion batteries. Energy Environ. Sci. 2015, 8, 869−875. (82) Fu, S.; Ni, J.; Xu, Y.; Zhang, Q.; Li, L. Hydrogenation driven conductive Na2Ti3O7 nanoarrays as robust binder-free anodes for sodium-ion batteries. Nano Lett. 2016, 16, 4544−4551. (83) Ni, J.; Wang, W.; Wu, C.; Liang, H.; Maier, J.; Yu, Y.; Li, L. Highly reversible and durable Na storage in niobium pentoxide through optimizing structure, composition, and nanoarchitecture. Adv. Mater. 2017, 29, 1605607. (84) Ni, J.; Fu, S.; Wu, C.; Zhao, Y.; Maier, J.; Yu, Y.; Li, L. Superior sodium storage in Na2Ti3O7 nanotube arrays through surface engineering. Adv. Energy Mater. 2016, 6, 1502568. (85) Ni, J.; Fu, S.; Wu, C.; Maier, J.; Yu, Y.; Li, L. Self-supported nanotube arrays of sulfur-doped TiO2 enabling ultrastable and robust sodium storage. Adv. Mater. 2016, 28, 2259−2265. (86) Gao, H.; Hu, Z.; Zhang, K.; Cheng, F.; Chen, J. Intergrown Li2FeSiO4.LiFePO4-C nanocomposites as high-capacity cathode materials for lithium-ion batteries. Chem. Commun. 2013, 49, 3040−2. (87) Liu, J.; Fan, X.; Liu, X.; Song, Z.; Deng, Y.; Han, X.; Hu, W.; Zhong, C. Synthesis of cubic-shaped Pt particles with (100) preferential orientation by a quick, one-step and clean electrochemical method. ACS Appl. Mater. Interfaces 2017, 9, 18856−18864. (88) Liu, J.; Chen, B.; Kou, Y.; Liu, Z.; Chen, X.; Li, Y.; Deng, Y.; Han, X.; Hu, W.; Zhong, C. Pt-Decorated highly porous flower-like Ni particles with high mass activity for ammonia electro-oxidation. J. Mater. Chem. A 2016, 4, 11060. (89) Li, Y.; Wu, C.; Bai, Y.; Liu, L.; Wang, H.; Wu, F.; Zhang, N.; Zou, Y. ACS Appl. Mater. Interfaces 2016, 8, 18832. (90) Li, Y.; Bai, Y.; Bi, X.; Qian, J.; Ma, L.; Tian, J.; Wu, C.; Wu, F.; Lu, J.; Amine, K. ChemSusChem 2016, 9, 728. (91) Li, Y.; Bai, Y.; Wu, C.; Qian, J.; Chen, G.; Liu, L.; Wang, H.; Zhou, X.; Wu, F. J. Mater. Chem. A 2016, 4, 5942. 1780


ACS Energy Letters

Perspective

(92) Meng, Y. S.; Arroyo-de Dompablo, M. E. Recent advances in first principles computational research of cathode materials for lithiumion batteries. Acc. Chem. Res. 2013, 46, 1171−1180. (93) Lu, J.; Wu, T.; Amine, K. State-of-the-art characterization techniques for advanced lithium-ion batteries. Nat. Energy 2017, 2, 17011.

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