New Insight of Ethylenediaminetetraacetic Acid Tetra Sodium Salt as

Subscriber access provided by EKU Libraries

Energy, Environmental, and Catalysis Applications

New Insight of Ethylenediaminetetraacetic Acid Tetra Sodium Salt as Sacrificing Sodium Ion Source for Sodium-Deficient Cathode Materials for Full Cells Jae Hyeon Jo, Jiung Choi, Yun Ji Park, Jiefang Zhu, Hitoshi Yashiro, and Seung-Taek Myung ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b18488 • Publication Date (Web): 17 Jan 2019 Downloaded from http://pubs.acs.org on January 17, 2019

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 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 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.

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 48 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

New Insight of Ethylenediaminetetraacetic Acid Tetra Sodium Salt as Sacrificing Sodium Ion Source for Sodium-Deficient Cathode Materials for Full Cells Jae Hyeon Jo†,z, Ji Ung Choi†,z, Yun Ji Park†, Jiefang Zhu‡, Hitoshi Yashiro§ and SeungTaek Myung*,†

†Department

of Nano Technology and Advanced Materials Engineering & Sejong

Battery Institute, Sejong University, Seoul 05006, South Korea ‡Department

of Chemistry-Ångström Laboratory, Uppsala University, Uppsala SE-

75121, Sweden §Department

of Chemistry and Biological Sciences, Iwate University, Morioka, Iwate

*Corresponding

author

Tel: 82 2 3408 3454, fax 82 2 3408 4342, e-mail: [email protected] (S. Myung)

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 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 48

020-8551, Japan ZThese

authors contributed equally to this work.

KEYWORDS: EDTA-4Na; Additive; Cathode; Sodium; Battery.

ABSTRACT: Sacrificing sodium supply sources are needed for sodium-deficient cathode materials to achieve commercialization of sodium-ion full cells using sodium-ion intercalation anode materials. Herein, the potential of ethylenediaminetetraacetic acid tetra-sodium salt (EDTA-4Na) as a sacrificing sodium supply source was investigated by intimately blending it with the sodium-deficient P2-type Na0.67[Al0.05Mn0.95]O2. The EDTA4Na/Na0.67[Al0.05Mn0.95]O2 composite electrode unexpectedly exhibited an improved charge capacity of 177 mAh (g-oxide)−1, compared with the low charge capacity of 83 mAh (g-oxide)−1 for

bare

Na0.67[Al0.05Mn0.95]O2.

The

reversible

capacity

of

an

EDTA-

4Na/Na0.67[Al0.05Mn0.95]O2//hard carbon full cell system increased to 152 mAh (g-oxide)−1 at the first discharge with a Coulombic efficiency of 89 %, whereas that Na0.67[Al0.05Mn0.95]O2 without EDTA-4Na delivered a discharge capacity 51 mAh g−1


2

Page 3 of 48 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


because of the small charge capacity. The EDTA-4Na sacrificed itself to generate Na+ ions via oxidative decomposition by releasing four sodium ions and producing C3N as a decomposition resultant on charge. It is thought that the slight increase in discharge capacity is associated with the electro-conducting nature of the C3N deposits formed on the surface of Na0.67[Al0.05Mn0.95]O2 electrode. We elucidated the reaction mechanism and sacrificial activity of EDTA-4Na, and our findings suggest that the addition of EDTA-4Na is beneficial as an additional source of Na+ ions that contribute to the charge capacity.

Introduction Recent increasing demands for lithium-ion batteries (LIBs) have led to an escalation in the price of lithium.1-3 The limited reserves and uneven distribution of lithium resources must thus be considered in any further development of LIBs. For these reasons, research directions have recently been diverted toward the exploration of post-LIBs. In particular, sodium-ion batteries (SIBs) have received attention as promising candidates to replace LIBs because of their cost-effectiveness, the natural abundance of sodium resources,


3


Page 4 of 48

and, most importantly, their similar reaction chemistry to LIBs. Despite these advantages, the large Na+ ion (1.02Å)4 relative to Li+ (0.76Å)4 can derive different physical and electrochemical

properties

during

the

electrochemical

reaction.5-8

Therefore,

intercalation-based cathode materials, which can compete with the conventional electrodes used in LIBs, have been investigated; namely, these materials typically have intercalation channels in the forms of layers,9-12 tunnels,13,14 or Na superionic conductor (NASICON)-based structures.15,16 Some layered structures such as P2-, P3-, O3-, and P’2-NaxMO2 (M = one or several transition metals) have received particular attention because of their high capacities and reasonable operation voltage in Na cells. Except the O3 structure, the P2, P3, and P’2 structures are stable when the resulting sodium content is lower than x ≤ 0.7 in NaxMeO2 (Me: metals).17-20 For a full-cell configuration that employs Na-free anode materials such as hard carbon, this sodium deficiency results in serious capacity loss because the available amount of Na+ ions as charge carriers in the compound is limited to 0.7 mol Na+ per formula unit. The effectiveness of Na-containing additives in resolving this structural imperfection has been previously demonstrated, as they underwent oxidative decomposition at high potential.21-24 Representative examples


4

Page 5 of 48 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


of these additives, called sacrificing agents, include NaN3,21,22 Na3P,23 and Na2CO3 24. The additives are added to the electrolyte and participate in the electrochemical oxidation, yielding additional charge capacity by leaving Na+ ions in the electrolyte. This process evidently contributes to reducing the first imbalance between the charge and discharge capacities. However, the concomitant release of N2 gas after the oxidative decomposition of NaN3 on charge may lead to an increase in the pressure, causing swelling of the cells.21,22 In addition, Na3P is unstable and cannot be handled in air; hence, a moisturecontrolled environment is required to treat this additive.23 Moreover, it remains unknown how the leftover phosphor behaves in the cells after the decomposition. Tarascon group demonstrated the potential of Na2CO3 as a sacrificial sodium salt; however, gas products are released by the decomposition of Na2CO3 and must be removed during cycling.24 Thus, it remains challenging to identify appropriate sacrificing additives that do not have detrimental effects on the active materials or cell performance. In addition, gas generation should be minimal, and any byproducts formed by the oxidative decomposition must be inert during the electrochemical reaction. We herein propose the use of a chelating agent, ethylenediaminetetraacetic acid tetra-sodium salt (EDTA-4Na), as the sacrificing additive.


5


Page 6 of 48

As shown in Figure 1a, although there are four moles of sodium per formula unit (EDTA-4Na), the portion of sodium (20%) is lower than that for NaN3 (35%), Na3P (69%), and Na2CO3 (21%) in molar weight (Table 1). Furthermore, the compound is composed of C–N–O chains; thus, it was assumed that oxidative decomposition may lead to the formation of electroconducting C–N compounds25 on the surface of the active materials. Moreover, EDTA4Na without any π-delocalized groups has been reported to exhibit excellent electron transport property in organic solar cells and act as a strong oxidizing agent.26-28 In this study, we report on the addition of EDTA-4Na as a sacrificial salt to compensate for the sodium deficiency in cathode materials and elucidate the role of this additive before and after oxidative decomposition. EDTA-4Na is selected as an additive because it has one Na+ ion on each carboxyl group and is known to be a strong oxidizing medium,29 which inspired us to apply it in a Na-deficient cathode to compensate for the insufficient first charge capacity. To fully utilize the sacrificing role of the additive, we intimately blend the EDTA-4Na with the active material, P2-type Na0.67[Al0.05Mn0.95]O2, instead of adding it to the electrolyte. As a result, oxidative decomposition of the EDTA-4Na, which provides additional Na+ ions, assists additional capacity to increase the first charge capacity, so


6

Page 7 of 48 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


that the first Coulombic efficiency ([discharge capacity] / [charge capacity] × 100 (%) ) improves from 200 % to 99 %. The slight increase in the discharge capacity for the EDTA4Na/Na0.67[Al0.05Mn0.95]O2 electrode is explained by the presence of the electroconducting C–N deposits on the surface of the active materials. It is challenging to test the Na-deficient P2 cathode with hard carbon anode. Unexpectedly, the EDTA4Na/Na0.67[Al0.05Mn0.95]O2 // hard carbon full-cell system delivers a first discharge capacity of 152 mAh (g-oxide)−1 with a Coulombic efficiency of 89 %, whereas that of the system using Na0.67[Al0.05Mn0.95]O2 is limited to 51 mAh g−1 because of the small charge capacity resulting from the sodium deficiency in the compound. The presence of the EDTA-4Na sacrificing agent contributes to this successful operation of the full cell. The introduction of EDTA-4Na as a sacrificing agent enables the use of several high-capacity P2- and P’2type layered cathode materials in SIBs without the need for further pre-sodiation of the cathodes or anodes.

EXPERIMENTAL Preparation of materials


7


Page 8 of 48

P2-Na0.67[Al0.05Mn0.95]O2 powders were synthesized via spray pyrolysis. Manganese (Mn(NO3)2·4H2O, ≥ 97.0 %,

Sigma Aldrich) and aluminum nitrate hydrates

(Al(NO3)3·9H2O, ≥ 98.0 %, Sigma Aldrich), and sodium nitrate (NaNO3, 99 %, Samchun) were used as the starting materials for the precursor preparation. Stoichiometric amounts of both metal nitrate hydrates and sodium nitrate were dissolved in distilled water. Citric acid (≥ 99.5 %, Junsei) as a chelating agent and sucrose (≥ 99.5 %, Samchun) as a particle growth inhibitor were added to the prepared aqueous solution with a ratio of starting materials:citric acid:sucrose to be 1:0.2:0.05. The aerosol stream was sprayed into a vertical quartz reactor with 400 °C. The as-received precursor powders were pelletized and calcined at 900 °C for 10 h in a dry air atmosphere with a flow rate of 300 ml min−1 and slowly cooled down to room temperature. The obtained precursor and final products were stored in an Ar-filled glove box to prevent contamination by moisture. To synthesize the composite with EDTA-4Na, commercial EDTA-4Na powder was first ball-milled for 2 days to reduce the particle size from 50 to 3 μm, and the ball-milled EDTA


8

Page 9 of 48 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


4Na powder was then intimately blended with the as-received P2-Na0.67[Al0.05Mn0.95]O2 powder at a ratio of 1:9 in a dry room.

Characterization High-power X-ray diffraction (XRD; 6 kW, X’Pert, PANalytical) using Cu Kα radiation was employed to analyze the crystal structure of the Na0.67[Al0.05Mn0.95]O2 and EDTA4Na/Na0.67[Al0.05Mn0.95]O2 composite. The measurements were conducted in the 2θ range of 10° ≤ 2θ ≤ 80° (0.03° step size). The FULLPROF program was used to analyze the obtained

XRD

patterns

of

the

samples.

The

particle

morphologies

of

the

Na0.67[Al0.05Mn0.95]O2 and Na0.67[Al0.05Mn0.95]O2/EDTA-4Na composite were observed using scanning electron microscope (FE-SEM; JXA-8100, JEOL) and high-resolution transmission electron microscope (HR-TEM, JEM-3010, JEOL). The chemical compositions of the products were identified using inductively coupled plasma atomic emission spectroscopy (ICP-AES, OPTIMA 4300DV, Perkin-Elmer).

Electrochemical tests


9


For

electrochemical

characterization,

the

prepared

Page 10 of 48

Na0.67[Al0.05Mn0.95]O2

and

Na0.67[Al0.05Mn0.95]O2/EDTA-4Na composite and EDTA-4Na were mixed with conducting materials (Super-P:Denka black) and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1 in N-methyl-2-pyrrolidone (NMP). The obtained slurry was applied onto Al foil and dried at 80 °C overnight under vacuum. The weight of the electrode was ~3.5 mg cm−2. Electrochemical cell tests were performed after assembling R2032 coin-type cells using Na metal as the negative electrode. The electrolyte solution was 0.5 mol dm−3 NaPF6 in propylene carbonate (PC) and fluoroethylene carbonate (FEC) by volume ratio of 98:2; the FEC in the PC solution maintains the passivation of the electrodes.2 For the full cells, commercial hard carbon (Kureha) was also used as the anode. The full cells were assembled in R2032 coin-type cells to evaluate the sacrificial effect of EDTA-4Na. Before fabricating the hard carbon anode, pre-treatment of the hard carbon was first performed at 700 °C for 2 h in an Ar atmosphere to eliminate adhered water and impurities. All the cells were fabricated into an Ar-filled glove box. The electrochemical performances of EDTA-4Na, P2-Na0.67[Al0.05Mn0.95]O2, and P2-Na0.67[Al0.05Mn0.95]O2/EDTA-4Na were firstly analyzed using cyclic voltammetry (CV) in the voltage range of 2.0–4.5 V versus


10

Page 11 of 48 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


Na+/Na with a sweep rate of 0.1 mV s−1. To determine the capacity retention, half-cells were charged and discharged in the range of 2.0–4.5 V versus Na+/Na at a current density of 15 mA g−1 (25 °C). The full cells were tested in the voltage range of 1.9–4.4 V at a rate of 30 mA g−1 at 25 °C.

Post-cycled electrode For Fourier-transform infrared (FT-IR) spectroscopy analysis, the electrode was fabricated using EDTA-4Na, conducting material (Denka black), and PVDF in a weight ratio of 8:1:1 in NMP. To identify the electrochemical response of the EDTA-4Na, the fabricated EDTA-4Na electrode was countered with a Na metal anode in a R2032 cointype cell. After charging (oxidizing) to 4.5 V versus Na+/Na, the electrode was recovered from the coin cell and rinsed in salt-free dimethyl carbonate (DMC) solution to remove residual NaPF6 salt. FT-IR spectra were recorded in attenuated total reflection mode (ATR) in the range of 4000–500 cm−1 (Perkin-Elmer, Spectrum One). To investigate the structural evolution during charging and discharging, the electrodes were examined using

ex situ XRD and X-ray photoelectron spectroscopy (XPS). The cells were first deliberately


11


Page 12 of 48

disassembled, and the electrodes were rinsed in salt-free DMC for 1 day in an Ar-filled glove box. Then, the electrodes were dried at 80 °C under vacuum for 1 day. Ex situ XRD data were obtained for the washed electrodes in the range of 10° ≤ 2θ ≤ 80° (0.03°). The resulting lattice parameter was calculated using a least-squares method. The XPS measurements (PHI 5600, Perkin-Elmer) were performed on the surfaces of the bare and Na0.67[Al0.05Mn0.95]O2/EDTA-4Na composite electrodes in macro-mode (3 × 3 mm2) using a Mg X-ray source to avoid the Auger lines produced when using an Al X-ray source. The samples were first transferred to a hermitically sealed transfer chamber (ULVAC) in a glove box and then transferred to the vacuum chamber of the XPS machine to prevent exposure to air or water molecules during the XPS measurements.

Results and discussion As shown in Figure 1a, EDTA-4Na consists of two N atoms, which bond with four carboxyl groups having four Na+ ions at the H+ site of EDTA. The SEM image in Figure 1b shows that the particle size ranged from 30 to 50 μm. To increase the reactivity of the EDTA-4Na particles in the Na electrolyte, they were ball-milled to decrease the particle


12

Page 13 of 48 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


size to 3 μm (Figure 1c). Elemental mapping revealed the presence of Na, O, and N elements in the ball-milled products (Figure 1d). Figure 2a presents a polarization curve of the EDTA-4Na electrode measured in a dynamic mode. The increase of the anodic current from 3.79 V versus Na+/Na indicates initiation of oxidative decomposition. The reaction aggressively developed from 4.2 V, and the resulting anodic current reached approximately 3 mA cm−2, which is related to the dissociation of EDTA-4Na into Na+ and EDTA− ions. This result indicates that a certain amount of Na+ ions was produced from the decomposition of EDTA-4Na salt. Note that the reaction is irreversible with no traceable variation in the current during cathodic sweep to 1.5 V. The EDTA-4Na electrode exhibited a high charge capacity of approximately 420 mAh g−1 (Figure 2b); however, the resulting discharge capacity was negligible, which is consistent with the polarization results (Figure 2a). For Na3P and NaN3, the Na3P electrode blended with conducting additive and binder presented over 600 mAh g-1, it means that the capacity per Na in Na3P delivered 200 mAh g-1. Meanwhile, NaN3 cell shown the over 300 mAh g-1, indicating that the capacity per Na in NaN3 is 300 mAh g-1. For the present EDTA-4Na, it delivered 420 mAh g-1, showing that the capacity per Na in EDTA-4Na is 105 mAh g-1. Although the portion of sodium for the EDTA-4Na is smaller than the compared compounds, the present EDTA-4Na


13


Page 14 of 48

shows higher oxidation capacity than that of NaN3. That is, the portion of Na in those compounds are not proportional to the capacity as shown in Table 1. From the XRD pattern, the electrode charged to 4.5 V formation of C3N (JCPDS card, 17-0108) in Figure 2c. Furthermore, we performed ex-situ FT-IR measurement using EDTA-4Na electrode fabricated with 3wt. % of PVDF to identify the decomposition of EDTA-Na on electrochemical oxidation to 4.5 V (Figure 2d). As a result, it presented that the relative intensities of FT-IR spectra became lower from Step 2 (3.85 V), and there were no spectra at Step 4 (4.5V); specifically, there was no appearance of O-H vibration at 3000 – 3500 cm-1 (Figure 2d, e-1, and e-2). This means that the remained water molecules were oxidatively decomposed at high voltage. Note that the EDTA-4Na (10 wt. %)/Na0.67[Al0.05Mn0.95]O2 cathode did not affect swelling of the cell composed of (Figure 2f). This finding suggests that the EDTA-4Na releases Na+ ions while simultaneously undergoing decomposition, with carbonization upon oxidation (Figures 2d and e). Similar results were reported by Shi et al.30 ToF-SIMS was employed to understand the formations of compounds associated with a C-N bond after the electrochemical oxidation at 4.5 V (Figure 3). The chemical formula of EDTA-4Na is C10H12N2O8Na∙4H2O, so that ToF-SIMS result shows the C-N bond as a C3N+ fragment (m = 50.00) for the fresh EDTA-4Na. It is evident that the oxidative decomposition of the EDTA-4Na resulted in formation of a C-N (C3N) compound. The solid product (C3N) deposited on the surface


14

Page 15 of 48 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


of electrode, so that the corresponding fragment developed with high intensity, compared to that of the fresh EDTA-4Na electrode. The contained water molecules were subject to oxidative decomposition at high voltage above 4 V versus Na+/Na, which was evidenced from the FT-IR spectrum after the polarization at 4.5 V (Figure 2d). Hence, the solid product (C3N) deposits on the surface of electrode, and the corresponding fragment developed with high intensity that agrees with the XRD pattern (Figure 2c). We examined the fresh and charged EDTA-4Na/Na0.67[Al0.05Mn0.95]O2 electrodes using XPS (Figure 4). The electrochemical oxidation resulted in a slight variation in the binding energy associated with the C–O binding, 286–287 eV (Figures 4a and b). Compared with the fresh EDTA-4Na (C10H12N2O8Na4·4H2O) (Figure 4a), the broadening of C–O binding (285.8–277.2 eV), which was observed together with C–N binding (285.8–288. 5 eV), is due to the formation of a byproduct after the electrochemical oxidation to 4.5 V. Such a change on the surface was also observed in the binding related to oxygen. The N–O binding observed in the fresh state, as shown in Figure 4c, was significantly reduced after charge to 4.5 V (Figure 4d) and discharge to 2 V (Figure 4e), indicating the disappearance of the N–O bond after the electrochemical oxidation. The C3–N binding energy (399-403 eV) was observed for all cases (Figures 4f–h); however, the C–N–C binding energy observed in the fresh state was negligible for the charged (Figure 4g), while the increase


15


Page 16 of 48

in intensity ratio of the (C)3–N binding energy at 400.4 eV versus the C–N–C binding energy at 398.5 eV highlighted the formation of cyanoethynyl, C3N, for the charged (Figure 4g) and discharged (Figure 4h) electrodes resulted from Na+ release during the oxidative decomposition to 4.5 V. From this concern, it is thought that all the sodium was extracted from EDTA-4Na, and the decomposition left electro-conducting C3N solid on the surface of electrode. Based on the XRD, FT-IR, ToF-SIMS, and XPS results, the EDTA-4Na salt undergoes anodic decomposition accompanied by releasing Na+ ions to 4 V vs. Na+/Na, as follows; C10H12N2O8Na4·4H2O  2C3N + 4CO + 8H2O + 2H2 + 4Na+ + 4e- (1). During the electrochemical reaction, the EDTA-4Na (C10H12N2O8Na4·4H2O) is decomposed to 4Na+, N–CH2–CH2–N–2[CH2-COO-], N–CH2–CH2–N–CH2–COO-, and CH2–COO- groups by breaking Na-O bond (COO-Na groups) and C-N bond (CH2-N-COO- groups) at the voltage plateau region (3.7 – 4 V in Figure 2b). At the same time, the decomposed N–CH2–CH2–N–2[CH2-COO-], N–CH2–CH2–N–CH2–COO-, and CH2–COO- groups are bonded with N atoms to generate CO and H2O. As a result, new bonds are generated between C and N as a C3N observed in the XRD pattern and ToF-SIMS as a C3N+ (m = 50.00). The subsequent oxidative decomposition of water molecules appeared in the reaction (1) results in the follow reaction above 4 V vs. Na+/Na: 8H2O  8H2 + 4O2 + 16e- (2), of which the total reaction in the whole range can be expressed as, C10H12N2O8Na4·4H2O  2C3N + 4CO + 10H2 + 4O2 + 4Na+ + 20e- (3).


16

Page 17 of 48 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 the reaction (1), the theoretical oxidation capacity for EDTA-4Na without consideration of H2O in the formula is approximately 282 mAh (g-EDTA)-1, which agrees with the capacity obtained below 4 V in Figure 2b. Hence, the long voltage plateau at 3.7 – 4 V is associated with the Na+ release activated by the oxidative decomposition of the EDTA-4Na salt. The additional capacity (138 mAh g-1) is due to the oxidative decomposition of water molecules contained EDTA-4Na (4H2O) above ~4V versus Na+/Na (corresponding to 1.23V versus standard hydrogen electrode), as evidenced from the charge curve (Figure 2b). Figure 5 presents an XRD pattern and SEM–EDX images for the EDTA4Na/Na0.67[Al0.05Mn0.95]O2 composite. Rietveld refinement was performed assuming the

P63/mmc space group, and all the diffraction peaks of the Na0.67[Al0.05Mn0.95]O2 and EDTA-4Na/Na0.67[Al0.05Mn0.95]O2 composite were confirmed as a single phase. Although the active material was mixed with EDTA-4Na (10 wt. %), it was difficult to find differences in the structural parameters in Table S1. This finding suggests that the EDTA-4Na was ambient such that the crystal structure of Na0.67[Al0.05Mn0.95]O2 was not affected by the addition of the additive. The SEM image shows that the estimated particle size of Na0.67[Al0.05Mn0.95]O2 was approximately 4 μm in diameter (Figure 5c). Blending with EDTA-4Na did not affect the particle size of Na0.67[Al0.05Mn0.95]O2 (Figure 5d). Notably,


17


Page 18 of 48

the large EDTA-4Na particles in Figure 1c were no longer visible after the blending process (Figure 5d); however, the homogeneous distribution of N observed in the EDX mapping supports the attachment of the EDTA-4Na particles on the particles (Figure 5e). The TEM image in Figure 5f further confirms that the blending process did not affect the particle morphology but led to a decrease in the EDTA-4Na particles size. Therefore, it is thought that the blending process aided by mechanical milling of EDTA-4Na with Na0.67[Al0.05Mn0.95]O2 results in selective particle size reduction of EDTA-4Na and the formation

of

a

homogeneous

distribution

of

nanosized

EDTA-4Na

onto

Na0.67[Al0.05Mn0.95]O2, with negligible damage to the crystal structure or morphology of the active materials. Our preliminary galvanostatic tests showed electrochemical oxidation of the EDTA-4Na salt from the EDTA-4Na/Na0.67[Al0.05Mn0.95]O2 composite electrode (Figure 6a), which agrees with the polarization results presented in Figure 2a. Half-cell tests were performed for the Na0.67[Al0.05Mn0.95]O2 and EDTA-4Na/Na0.67[Al0.05Mn0.95]O2 composite electrodes in Na cells. Compared with the Na0.67[Al0.05Mn0.95]O2 electrode that showed the first Coulombic efficiency approximately 200 %, the EDTA-4Na/Na0.67[Al0.05Mn0.95]O2


18

Page 19 of 48 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


composite electrode delivered a higher charge capacity, with a first Coulombic efficiency of approximately 99 %. Notably, the voltage drop in Figure 2b also appeared for the EDTA-4Na/Na0.67[Al0.05Mn0.95]O2 composite electrode (Figure 6a), which proves that the added EDTA-4Na sacrifices itself to generate Na+ ions through oxidative decomposition on charge (oxidation), which provides additional sodium ions to compensate for the sodium deficiency in Na0.67[Al0.05Mn0.95]O2. Volumetric capacity, which was converted using the tap densities for the Na0.67[Al0.05Mn0.95]O2 and EDTA-4Na/Na0.67[Al0.05Mn0.95]O2 composite that were measured to be 1.81 g cc-1 and 1.62 g cc-1, respectively, were compared in Figure S2. Although addition of the ball-milled EDTA-4Na lowered the resulting tap density of EDTA4Na/Na0.67[Al0.05Mn0.95]O2

composite,

the

calculated

volumetric

capacity

of

EDTA-

4Na/Na0.67[Al0.05Mn0.95]O2 composite (282 mAh cc-1) was comparable to that of the Na0.67[Al0.05Mn0.95]O2 (293 mAh cc-1). In addition, the first discharge capacity increased to approximately 19 mAh g−1 with the addition of the EDTA salt to the Na0.67[Al0.05Mn0.95]O2, and over 92% of this discharge capacity was retained during cycles (Figure 6b). Meanwhile, the retention was inferior (~74%) for the additive-free electrode. In practical point of view, Na3P, which is unstable and cannot be handled in air, a moisture-controlled environment is required to use this additive. In case of NaN3 and Na2CO3, the release of N2 or CO2 gases after the oxidative decomposition of NaN3 and Na2CO3 on charge may lead to an increase


19


Page 20 of 48

in the pressure, causing swelling of the cells, which must be removed after the first charge. By contrast, the half-cell for the EDTA-4Na (10 wt. %) / Na0.67[Al0.05Mn0.95]O2 // Na metal did not show such gas generation after charging to 4.5 V (Figure 2f). Above all, the first Coulombic efficiency of the half cell for the EDTA-4Na (10 wt. %) / Na0.67[Al0.05Mn0.95]O2 // Na metal was approximately 99%. It is worth mentioning of the significant improvement on the first Coulombic efficiency, compared to the NaN3 additive that exhibits the first Coulombic efficiency of ~ 150% by 20 wt. % of NaN3 addition21 or 116% by 5wt.% of NaN3 addition22. From the above point of view, a large capacity (releasing Na+ ions) accompanied by the oxidative decomposition of EDTA4Na and minimum gas generation are key issues to compensate for the insufficient charge capacity for sodium deficient P2 type cathode materials. For the EDTA-4Na electrode, delivery of the capacity of 420 mAh g-1 for the electrochemical process is sufficient because the first Coulombic efficiency between charge and discharge capacities reached ~99%. Characterization of full cells using hard carbon as the anode was performed to emphasize the effectiveness of the EDTA-4Na salt in improving the first abnormal capacity. Indeed, hard carbon electrodes are known to exhibit a large irreversible capacity32, such that a large charge capacity of the cathode is a prerequisite to negate the first irreversible sodiation capacity of hard carbon in full cells. This issue is the main obstacle to the use of P2 cathode materials in full cells. Otherwise, pre-sodiation of the cathode

and/or

anode

is

required.

Hence,

full

cells

adopting

the

EDTA-

4Na/Na0.67[Al0.05Mn0.95]O2 cathode and a hard carbon anode were balanced using a


20

Page 21 of 48 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


capacity ratio of the cathode and anode of 1.2 (Figures 7a and b). The fabricated full cell was tested in in the range of 1.9–4.4 V by applying a current density of 30 mA g−1 (0.2C) at 25 °C. For facile Na+ migration, a solid-electrolyte interphase layer must be formed for the hard anode in the first sodiation state. This is reflected in the full-cell curves below 2.7 V, and the typical feature of the voltage drop for EDTA was also observed above 3.6 V, after which the main decomposition reaction of EDTA-4Na was initiated to produce Na+ ions that compensate for the charge capacity. XRD data for the charged hard carbon reveals that Na+ ions were intercalated into the hard carbon, as confirmed by the formation of Na2C2 (23.4° (2)) and Na9.28C60 (20.2° (2)) (Figure 7c). However, these compounds were evidently less developed for the hard carbon electrode recovered from the additive-free full cell. As a result, the first charge capacity was approximately 175 mAh g−1. Compared with the Na0.67[Al0.05Mn0.95]O2 // hard carbon full cell that delivered a charge capacity of 68 mAh g−1 (Figure S3), this high capacity for the EDTA4NA/Na0.67[Al0.05Mn0.95]O2 // hard carbon full cell was due to the oxidative decomposition of the added EDTA-4Na salt as a Na+ source to increase the discharge capacity to 152 mAh (g-oxide)−1 with a first Coulombic efficiency of approximately 89 %. In contrast, the


21


Page 22 of 48

additive-free cell exhibited a small capacity (~51 mAh g−1) because of the insufficient amount of deintercalated Na+ ions from the cathode. As observed in Figure 7d, the EDTA4Na/Na0.67[Al0.05Mn0.95]O2 // hard carbon full cell exhibited acceptable capacity retention (~77%) during prolonged cycles, even though the cell performance was not fully optimized. The capacity retention can be improved by selecting appropriate cathode materials. Such a great enhancement was observed with the addition of EDTA-4Na, which provides extra Na+ ions to the hard carbon anode. The EDTA-4Na/Na0.67[Al0.05Mn0.95]O2 delivered a higher discharge capacity than the bare Na0.67[Al0.05Mn0.95]O2 (Figures 6b and 7d). One possible reason for this improvement is the improved electron transfer by the decomposed products such as C3N, which is known to have a semiconducting character with tunable narrow band gap.25 Similarly, EDTA-4Na salt has been shown to exhibit excellent electron transport property in organic solar cells by forming N-doped carbon dots via polymerization and carbonization after oxidation.33-36 In our experiment, the EDTA-4Na salt was polymerized to C3N and stick over the active particles during the oxidative decomposition, thereby creating additional conduction paths for electrons.


22

Page 23 of 48 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 related functionality of EDTA-4Na is schematically illustrated in Figure 8. The better capacity delivery observed for the EDTA-4Na/Na0.67[Al0.05Mn0.95]O2 composite electrode can thus understood. It is concluded that the EDTA-4Na additive not only had a positive effect by overcoming the small charge capacity of sodium-deficient cathode materials via the sacrificial effect but also provides additional electro-conducting paths to increase the capacity. Appropriate selection of stable parent materials is expected to have better capacity and retention for long term. The addition of the sacrificing EDTA-4Na salt enables the use of sodium-deficient P2-type cathode materials without additional pre-sodiation; therefore, this discovery will allow the fabrication of many types of full cells using different types of sodium-deficient cathode materials.

Conclusions For the first time, we investigated the role of organic EDTA-4Na as a sacrificial salt in a sodium-deficient P2-Na0.67[Al0.05Mn0.95]O2 cathode, which suffers from a small charge capacity because of the insufficient amount of sodium in the structure. The cost-effective EDTA-4Na significantly compensated for the small charge capacity via an


23


Page 24 of 48

electrochemical sacrificing process, which resulted in a sufficient amount of sodium ions and led to the construction of an electro-conducting C3N polymeric network. As a result, the formation process of EDTA-4Na/Na0.67[Al0.05Mn0.95]O2 // hard carbon full cells was simplified without requiring additional treatment such as pre-sodiation. In addition, the full cells delivered a high discharge capacity of approximately 152 mAh (g-oxide)−1 with a Coulombic efficiency of 89 % for the first cycle (formation state), retaining ~77% of the capacity after 200 cycles. The discovery of EDTA-4Na salt as a sacrificing sodium ion source indicates the substantial possibility of the commercial use of high-capacity sodiumdeficient cathode materials for the development of high-energy-density SIBs in the near future.

Associated content Supporting Information. Experimental details, additional information and figures. This material is available free of charge via the Internet at http://pubs.acs.org.

Author information


24

Page 25 of 48 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


Corresponding Author *E-mail: [email protected]

ORCID

Seung-Taek Myung: 0000-0001-6888-5376

Author Contributions zThese

authors contributed equally to this work

Notes

The authors declare no competing financial interest.

Acknowledgements The authors would like to thank Miwa Watanabe, Iwate University, for her assistance in the experimental work. The authors thank S.-J. Song of the National Center for Interuniversity Research Facilities for assistance with the TEM experiments. This research was supported by the basic Science Research Program through the National Research


25


Page 26 of 48

Foundation of Korea (NRF), funded by the Ministry of Education, Science and Technology of Korea (NRF-2017R1A05069634), and by the National Research Foundation of Korea funded by the Korean government (MEST) (NRF-2015M3D1A1069713), and by the National Research Foundation of funded by the Ministry of Science and ICT of Korea (NRF-2018K2A9A2A12000230).

References (1)

Scrosati, B.; Garche, J. Lithium Batteries: Status, Prospects and Future, J. Power

Source., 2010, 195, 2419-2430.

(2)

Sun, Y.-K.; Myung, S.-T.; Park, B.-C.; Prakash, J.; Belharouak, I.; Amine, K. High-

Energy Cathode Material for Long-Life and Safe Lithium Batteries, Nat. Mater., 2009, 8, 320-324.

(3)

Kunduraci, M.; Al-Sharab, J. F.; Amatucci, G. G. High-Power Nanostructured

LiMn2-xNixO4 High-Voltage Lithium-Ion Battery Electrode Materials: Electrochemical Impact of Electronic Conductivity and Morphology, Chem. Mater., 2006, 18, 3585-3592.


26

Page 27 of 48 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


(4)

Mahadi, N. B.; Park, J.-S.; Park, J.-H.; Chung, K. Y. S.; Yi, Y.; Sun, Y.-K.; Myung,

S.-T. Vanadium Dioxide - Reduced Graphene Oxide Composite as Cathode Materials for Rechargeable Li and Na Batteries, J. Power Source, 2016, 326, 522-532.

(5)

Slater, M. D.; Kim, D.; Lee, E.; Johnson, C. S. Sodium‐Ion Batteries, Adv. Funct.

Mater., 2013, 23, 947.

(6)

Cho, M. K.; Jo, J. H.; Choi, J. U.; Kim, J. S.; Yashiro, H.; Yuan, S.; Shi, L.; Sun, Y.

K.; Myung, S. T. Tunnel-type β-FeOOH Cathode Material for High Rate Sodium Storage via a New Conversion Reaction, Nano Energy, 2017, 41, 687-696.

(7)

Kim, S. W.; Seo, D. H.; Ma, X.; Ceder, G.; Kang, K. S. Electrode Materials for

Rechargeable Sodium-Ion Batteries: Potential Alternatives to Current Lithium-Ion Batteries, Adv. Energy Mater., 2012, 2, 710-721.

(8)

Belharouak, I.; Sun, Y.-K.; Liu, J.; Amine, K. Li(Ni1/3Co1/3Mn1/3)O2 as a Suitable

Cathode for High Power Applications, J. Power Sources, 2003, 132, 247-252.


27


(9)

Page 28 of 48

Yabuuchi, N.; Yoshida, H.; Komaba, S. Crystal Structures and Electrode

Performance of Alpha-NaFeO2 for Rechargeable Sodium Batteries, Electrochemistry, 2012, 80, 716-719.

(10)

Komaba, S.; Yabuuchi, N.; Nakayama, T.; Ogata, A.; Ishikawa, T.; Nakai, I. Study

on the Reversible Electrode Reaction of Na(1-x)Ni(0.5)Mn(0.5)O2 for a Rechargeable SodiumIon Battery, Inorg. Chem., 2012, 51, 6211-6220.

(11)

Yabuuchi, N.; Yano, M.; Yoshida, H.; Kuze, S.; Komaba, S. Synthesis and

Electrode Performance of O3-Type NaFeO2-NaNi1/2Mn1/2O2 Solid Solution for Rechargeable Sodium Batteries, J. Electrochem. Soc., 2013, 160, A3131-A3137.

(12)

Mortemard de Boisse, B.; Carlier, D.; Guignard, M.; Delmas, C. Structural and

Electrochemical Characterizations of P2 and New O3-NaxMn1-yFeyO2 Phases Prepared by Auto-Combustion Synthesis for Na-Ion Batteries, J. Electrochem. Soc., 2013, 160, A569-A574.


28

Page 29 of 48 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


(13)

Su, D.; Ahn, H. J.; Wang, G. Hydrothermal Synthesis of α-MnO2 and β-MnO2

Nanorods as High Capacity Cathode Materials for Sodium Ion Batteries, J. Mater. Chem.

A., 2013, 1, 4845-4850.

(14)

Perez-Flores, J. C.; Baehtz, C.; Kuhn, A.; Garcia-Alvarado, F. Hollandite-type

TiO2: a New Negative Electrode Material for Sodium-Ion Batteries, J. Mater. Chem. A., 2014, 1, 1825-1833.

(15)

Chen, S.; Wu, C.; Shen, L.; Zhu, C.; Huang, Y.; Xi, K.; Maier, J.; Yu, Y. Challenges

and Perspectives for NASICON‐Type Electrode Materials for Advanced Sodium‐Ion Batteries, Adv. Mater., 2017, 29, 1700431.

(16)

Park, J. S.; Kim, J. S.; Jo, J. H.; Myung, S. T. Role of the Mn Substituent in

Na3V2(PO4)3 for High-Rate Sodium Storage, J. Mater. Chem. A., 2018, 6, 16627-16637.

(17)

Konarov, A.; Choi, J. U.; Bakenov, Z.; Myung, S. T. Revisit of Layered Sodium

Manganese Oxides: Achievement of High Energy by Ni Incorporation, J. Mater. Chem.

A., 2018, 6, 8558-8567.


29


(18)

Page 30 of 48

Yabuuchi, N.; Kajiyama, M.; Iwatate, J.; Nishikawa, H.; Hitomi, S.; Okuyama, R.;

Usui, R.; Yamada, Y.; Komaba, S. P2-type Na(x)[Fe(1/2)Mn(1/2)]O2 Made from EarthAbundant Elements for Rechargeable Na Batteries, Nat. Mater., 2012, 11, 512-517.

(19)

Chen, X.; Zhou, X.; Hu, M.; Liang, J.; Wu, D.; Wei, J.; Zhou, Z. Stable Layered

P3/P2 Na0.66Co0.5Mn0.5O2 Cathode Materials for Sodium-Ion Batteries, J. Mater. Chem.

A., 2015, 3, 20708-20714.

(20)

Kumakura, S.; Tahara, Y.; Sato, S.; Kubota, K.; Komaba, S. P′2-Na2/3Mn0.9Me0.1O2

(Me = Mg, Ti, Co, Ni, Cu, and Zn): Correlation between Orthorhombic Distortion and Electrochemical Property, Chem. Mater., 2017, 29, 8958-8962.

(21)

Martinez De Ilarduya, J.; Otaegui, L.; Lopez del Amo, J. M.; Armand, M.; Singh, G.

NaN3 Addition, a Strategy to Overcome the Problem of Sodium Deficiency in P2Na0.67[Fe0.5Mn0.5]O2 Cathode for Sodium-Ion Battery, J. Power Sources., 2017, 337, 197203.


30

Page 31 of 48 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


(22)

Singh, G.; Acebedo, B.; Cabanas, M.C.; Shanmukaraj, D.; Armand, M.; Rojo, T.

An Approach to Overcome First Cycle Irreversible Capacity in P2-Na2/3[Fe1/2Mn1/2]O2,

Electrochem. Commun., 2013, 37, 61-63.

(23)

Zhang, B.; Dugas, R.; Rousse, G.; Rozier, P.; Abakumov, A.M.; Tarascon, J.M.

Insertion Compounds and Composites Made by Ball Milling for Advanced Sodium-Ion Batteries, Nat. Commun., 2016, 7, 10308.

(24)

Sathiya, M.; Thomas, J.; Batuk, D.; Pimenta, V.; Gopalan, R.; Tarascon, J.M. Dual

Stabilization and Sacrificial Effect of Na2CO3 for Increasing Capacities of Na-Ion Cells Based on P2-NaxMO2 Electrodes, Chem. Mater., 2017, 29, 5948-5956.

(25)

Yang, S.; Li, W.; Ye, C.; Wang, G.; Tian, H.; Zhu, C.; He, P.; Ding, G.; Xie, X.; Liu,

Y.; Lifshitz, Y.; Lee, S. T.; Kang, Z.; Jiang, M. C3N - A 2D Crystalline, Hole-Free, TunableNarrow-Bandgap Semiconductor with Ferromagnetic Properties, Adv. Mater., 2017, 29, 1605625.


31


(26)

Page 32 of 48

Li, Y.; Liu, X.; Li, X.; Zhang, W.; Xing, F.; Fang, J. Electrolytes as Cathode

Interlayers in Inverted Organic Solar Cells: Influence of the Cations on Bias-Dependent Performance, ACS Appl. Mater. Interfaces., 2017, 9, 8426-8431.

(27)

Li, Y.; Li, X.; Liu, X.; Zhu, L.; Zhang, W.; Fang, J. Realizing High Performance

Inverted Organic Solar Cells via a Nonconjugated Electrolyte Cathode Interlayer, J. Phys.

Chem. C., 2016, 120, 26244-26248.

(28)

Li, X.; Zhang, W.; Wang, X.; Gao, F.; Fang, J. Disodium Edetate As a Promising

Interfacial Material for Inverted Organic Solar Cells and the Device Performance Optimization, ACS Appl. Mater. Interfaces., 2014, 6, 20569-20573.

(29)

Mavalangi, S. K.; Kembhavi, M. R.; Nandibewoor, S. T. Oxidation of

Ethylenediaminetetraacetic Acid by N-bromosuccinimide in Aqueous Alkaline Medium A Kinetic Study, Turk J. Chem., 2001, 25, 355-363.


32

Page 33 of 48 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


(30)

Shi, Q.-Q.; Li, Y.-H.; Wu, Y.; Wang, Y.; Yin, X.-B.; He, X.-W.; Zhang, Y.-K. High-

Yield and High-Solubility Nitrogen-Doped Carbon Dots: Formation, Fluorescence mechanism and Imaging Application, RSC Adv., 2014, 4, 1563-1566.

(31)

Wagner, C.D.; Riggs, W.M.; Davis, L.E.; Moulder, J.F. Handbook of X-Ray Photoelectron

Spectroscopy, PerkinElmer Corp., Physics and Electronics Division, Eden Prairie, MN, 1979. (32)

Buiel, E.; Dahn, J. R. Reduction of the Irreversible Capacily in Hard-Carbon

Anode Materials Prepared from Sucrose for Li-Ion Batteries, J. Electrochem. Soc., 1998, 6, 1977-1981.

(33)

Wang, H.; Sun, P.; Cong, S.; Wu, J.; Gao, L.; Wang, Y.; Dai, W.; Yi, Q.; Zou, G.

Nitrogen-Doped Carbon Dots for “green” Quantum Dot Solar Cells, Nanoscale Res. Let., 2016, 11, 27.

(34)

Zhang, Y.-Q.; Ma, D.-K.; Zhang, Y.-G.; Chen, W.; Hunag, S.-M. N-Doped Carbon

Quantum Dots for TiO2-Based Photocatalysts and Dye-Sensitized Solar Cells, Nano

Energy, 2013, 2, 545-552.


33


(35)

Page 34 of 48

Zhao, Y.; Duan, J.; He, B.; Jiao, Z.; Tang, Q. Improved Charge Extraction with N-

Doped Carbon Quantum Dots in Dye-Sensitized Solar Cells, Electrochimica Acta, 2018,

282, 255-262.

(36)

Wang, Y.; Zhang, J.; Chen, S.; Zhang, H.; Li, L.; Fu, Z. Surface Passivation with

Nitrogen-Doped Carbon Dots for Improved Perovskite Solar Cell Performance, J. Mater.

Sci., 2018, 53, 9180-9190.


34

Page 35 of 48 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 1. Comparison of physical and electrochemical properties of several sacrificing agents.

Molecular weight / g mol-1

Oxidation capacity of additives / mAh g-1 [Capacity per Na : mAh

g-1]

Theoretical capacity of additives/ mAh g-1

Na portion in Additive content in molar weight / electrode / wt. % %

> 600 mAh g-1 Na3P 23

99.94

[ 200 mAh g-1] 804 mAh g-1

69%

Unknown

35%

70 %

21%

Unknown

20%

87 %

> 300 mAh g-1 NaN3 21,22

64.98

[ 300 mAh g-1] 412 mAh g-1 Unknown

Na2CO3 24

105.96

[Unknown] 505 mAh g-1

EDTA-4Na [our work]

420 mAh g-1 452

[ 105 mAh g-1] 237 mAh g-1


35


Page 36 of 48

Figure 1. (a) Chemical structural formula of EDTA-4Na; SEM image of (b) pristine EDTA4Na, (c) ball-milled EDTA-4Na for 2 day; (d) EDX result of (c) for Na, O and N element.


36

Page 37 of 48 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



37


Page 38 of 48

1 2

3

4

5

6

7

8

9

10

11

12

13


38

Page 39 of 48 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


1 2 3 4 5 6 7 8

Figure 2. (a) Cyclic voltammetry (CV) in the potential range 2.0 – 4.5V vs Na/Na+ with a

9

scan rate of 0.5 mV s-1 of EDTA-4Na electrode; (inset: magnification of cyclic voltammetry

10

in voltage range from 3.6 to 4.5 V), (b) First charge and discharge curves of only EDTA-

11

4Na in the voltage range 2.0 – 4.5 V vs Na/Na+ with a current density of 15 mA g-1 during

12

1st cycle; (inset: magnification of first charge curve), (c) ex-situ XRD pattern for pristine

13

and full charged electrode of EDTA-4Na; (d) FT-IR result for fresh and charged electrode

14

of EDTA-4Na (inset: the image for separator of full charged EDTA-4Na electrode), (e) FT-

15 16

IR result for PVDF and EDTA-4Na powders, and (f) (top) side view of swelling using coin cells of which the cell cover has a hole tightly covered with imide film for EDTA-4Na 0%

17 18

Na0.67[Al0.05Mn0.95]O2 (left), EDTA-4Na 10% Na0.67[Al0.05Mn0.95]O2 (middle), and EDTA-4Na 100% (right) electrodes charged to 4.5 V, and (bottom) top view for EDTA-4Na 0%

19 20

Na0.67[Al0.05Mn0.95]O2 (left), EDTA-4Na 10% Na0.67[Al0.05Mn0.95]O2 (middle), and EDTA-4Na 100% (right) electrodes charged to 4.5 V.

21


39


Page 40 of 48

1 2

3 4

5

6 7

Figure 3. ToF-SIMS data for EDTA-4Na for C3N+ (m = 50.00) spectrum for (top) the fresh state and (bottom) charged to 4.5 V in a Na cell.

8


40

Page 41 of 48 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


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Figure 4. The XPS spectra of C 1s, O 1s, N 1s (a, c, f) fresh, (b, d, g) after charged and

20

(e, h) after discharged P2-Na0.67[Al0.05Mn0.95]O2 / EDTA-4Na electrode. All binding

21

energies were referred from “Handbook of X-Ray Photoelectron Spectroscopy” 31.


41


Page 42 of 48

1 2 3 4


42

Page 43 of 48 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 5. Rietveld refinement results of (a) P2-Na0.67[Al0.05Mn0.95]O2 and (b) P2Na0.67[Al0.05Mn0.95]O2 / EDTA-4Na; The SEM images of (c) particle of P2Na0.67[Al0.05Mn0.95]O2 and (d) particle of P2-Na0.67[Al0.05Mn0.95]O2 / EDTA-4Na; (e) EDX result of (d) for Na, Al, Mn and N element. (f) TEM image of particle surface of P2Na0.67[Al0.05Mn0.95]O2 / EDTA-4Na.


43


Page 44 of 48

Figure 6. (a) First charge and discharge curves Na0.67[Al0.05Mn0.95]O2 and EDTA-4Na (10 wt. %) / Na0.67[Al0.05Mn0.95]O2, (b) the resulting cyclability of Na-half cells during 20 cycles.


44

Page 45 of 48 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 7. (a) Schematic illustration of coin-type full cell adopting P2-Na0.67[Al0.05Mn0.95]O2 / EDTA-4Na cathode and hard carbon anode, (b) first charge and discharge curves of P2Na0.67[Al0.05Mn0.95]O2 / EDTA-4Na half cell (black), hard carbon half cell (blue), and P2Na0.67[Al0.05Mn0.95]O2 / EDTA-4Na // hard carbon full cell (red), (c) the resulting cyclability of full cells for 200 cycles, (d) comparison of ex-situ XRD patterns of fresh hard carbon electrode and fully sodiated hard carbon electrode after the first charge from the P2Na0.67[Al0.05Mn0.95]O2 / EDTA-4Na // hard carbon full cell.


45


Page 46 of 48

Figure 8. Schematic illustration for reaction mechanism of EDTA-4Na during 1st cycle.


46

Page 47 of 48 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



47


Page 48 of 48

Graphical Abstract


48

New Insight of Ethylenediaminetetraacetic Acid Tetra Sodium Salt as

Recommend Documents