Cr3+ Redox Couple in Polyanion Compounds

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Cite This: ACS Appl. Energy Mater. 2018, 1, 928−931

High-Voltage Cr4+/Cr3+ Redox Couple in Polyanion Compounds Kosuke Kawai,† Wenwen Zhao,† Shin-ichi Nishimura,†,‡ and Atsuo Yamada*,†,‡ †

Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan ‡ Elemental Strategy Initiative for Catalysts & Batteries (ESICB), Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan S Supporting Information *

ABSTRACT: Higher-voltage operation is crucial to increase the energy density of rechargeable batteries. Here we explored the Cr4+/Cr3+ redox couple in a polyanion framework for a high-voltage sodium battery cathode. An archetypal NASICON-phase Na3Cr2(PO4)3 exhibited a reversible redox activity at ca. 4.5 V versus Na/Na+, offering further scope for searching new high-voltage materials based on Cr4+/Cr3+ redox couple.

KEYWORDS: Na-ion batteries, high-voltage, cathode, chromium, phosphate, NASICON

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Na7V3(P2O7)4, and Na2+2xFe2−x(SO4)3, have been identified while their average operating potentials lie around 4.0 V versus Na/Na+.15−17 On the further development of high-voltage class cathode materials, utilizing other transition metals is a significant challenge. Theoretical calculation by Hautier et al. predicted that redox potential of a Cr4+/Cr3+ couple in a phosphate framework would be at ca. 4.9 V versus Li/Li+,18 while the experimental verification has been very limited to date. The only example was reported by Herklotz et al., demonstrating electrochemical oxidation of monoclinic Li3Cr2(PO4)3, but with small reversible capacity of 32 mAh g−1, which, however, turns out to occur only at the surface of particles.19 Therefore, demonstrating an active Cr4+/Cr3+ redox reaction in phosphate matrix is an urgent task before further exploration. Herein, we investigated the electrochemical properties of NASICON-type compound Na3Cr2(PO4)3 to demonstrate the Cr4+/Cr3+ redox couple operating around 4.5 V versus Na/Na+ in a sodium cell. Na3Cr2(PO4)3/acetylene black (AB) composite powder was synthesized by the solid-state method. First, Cr2O3 (first grade, Wako) and NaH 2 (PO 4 ) 3 (Wako, min 99.0%) in the stoichiometric ratio were ball-milled with 5 wt % excess of AB (Li-400, DENKA) on the basis of the product weight. Then, the pelletized mixture was heated in a tubular furnace under Ar flow for 22 h at 1123 K and 12 h at 1173 K with intermediate grinding. The obtained powder was observed by

or the past three decades, lithium-ion batteries (LIBs) have dominated the portable electronics market, and nowadays, its application is extending to larger-scale energy storage systems for electric vehicles and stationary use for leveling renewable energy. As the market expands, sodium-ion batteries (SIBs) can be a possible alternative due to the abundance of sodium in the earth’s crust and the sea.1,2 However, inherently higher redox potential of Na/Na+ than Li/Li+ by ca. 0.35 V brings about lower operating voltages of a cell. To overcome this disadvantage, high-potential cathode materials for SIBs are required. Use of the inductive effect in polyanionic frameworks is a major strategy to increase the redox potential of a transition metal while increasing structural integrity and safety.3,4 Sulfate ion (SO4)2− demonstrates the highest electronegativity and hence the strongest inductive effect among all polyanions, while compounds containing (SO4)2− are apt to decompose above ∼400 °C (generating SO2 gas) and are highly hygroscopic. Phosphate compounds, being chemically much more stable but less electronegative, form practical candidates. Among them, NASICON-type compounds AxM2(PO4)3 (A = Li, Na; M = transition metal) have been widely studied because of their high sodium-ion conductivity and robust structures, incorporating various transition metals (M = Ti, V, Mn, Fe, Co, Ni) as redox centers.5−11 In addition to the selection of anionic species, the transition metal has a critical influence on operating potential. So far, some cobalt- and nickel-based materials are known as 4 V class cathodes, for example, Na2−2xCo1+xP2O7 (∼4.0 V vs Na/Na+) and Na4M3(PO4)2P2O7 (∼4.4 V and ∼4.8 V vs Na/Na+ for M = Co and Ni, respectively).12−14 More abundant options containing vanadium or iron, such as Na3V2(PO4)2F3−xOx, © 2018 American Chemical Society

Received: November 4, 2017 Accepted: February 22, 2018 Published: February 22, 2018 928

DOI: 10.1021/acsaem.7b00105 ACS Appl. Energy Mater. 2018, 1, 928−931

Letter

ACS Applied Energy Materials field-emission scanning electron microscopy (FE-SEM) (S4800, HITACHI) with an acceleration voltage of 1 kV. Synchrotron X-ray powder diffraction patterns were obtained at the beamline 8B of Photon Factory (PF), High Energy Accelerator Research Organization (KEK) Tsukuba, Japan. The wavelength was calibrated to be 1.10901 Å using a diffraction pattern of standard reference material, (SRM640d, NIST). For all XRD measurements, borosilicate glass capillaries (Hilgenberg GmbH or Müller GmbH) were adopted as sample holders. The collected data was analyzed by Rietveld refinement program, TOPAS-Academic Ver. 6. The working electrode was fabricated by a wet slurry process: mixing 80 wt % Na3Cr2(PO4)3/AB, 10 wt % AB, and poly(vinylidene difluoride) (KUREHA) in N-methyl pyrrolidone (Kanto Chemical Co., Inc., min. 99.0%) to form a homogeneous slurry, spreading the slurry on an aluminum current collector and then drying the sheet at 338 K in a vacuum condition overnight. The counter electrode was Na metal (Wako). The separator was a glass filter (GB-100R, Advantec). The electrolyte was 1 M NaPF6 ethylene carbonate/ diethyl carbonate (1:1 vol) (battery grade, Kishida Chemical). Electrochemical tests were conducted by using 2032-type coin cells assembled in an Ar-filled groove box. Cyclic voltammetry was measured at a constant rate of 1.0 mV s−1 in a potential region between the rest potential and 5.2 V versus Na/Na+. For all galvanostatic charge/discharge measurement, the C-rates were calculated by defining 1 C as the current density of 117 mA g−1, and the potential region was between 2.5 and 4.7 V versus Na/Na+. Ex situ synchrotron XRD patterns were collected at the beamline described above. Coin cells at the various charging and discharging states were disassembled in a groove box filled with Ar, and then the working electrodes were washed with dimethyl ether and dried at 353 K under a vacuum condition. Powder peeled from the working electrodes was enclosed in the same glass capillaries mentioned above. The oxidation state of chromium during the charging and discharging process was measured by X-ray absorption near edge structure (XANES) spectroscopy at room temperature in a transmission mode at the BL-9A of PF, KEK, Japan. Data analyses were performed with Athena software.20 The synchrotron XRD pattern and its Rietveld refinement for as-prepared Na3Cr2(PO4)3/acetylene black (AB) powder are shown in Figure 1. Most of the reflections could be indexed to a rhombohedral lattice with a space group R3̅c, which

accords to a typical high-temperature form of NASICON structure.21−23 Lattice constants were a = b = 8.661(3) Å and c = 21.736(7) Å. Small additional diffraction peaks were observed in a low 2θ region below 20°, which reflects the superstructure formed by Na+ ordering. A similar observation was also reported in Na3M2(PO4)3 (M = Ti, V, Fe).24,25 The detailed crystallographic data are listed in Tables S1 and S2. An SEM image in the inset of Figure 1 shows a wide range of particle diameters from 2 to 10 μm embedded in nanometer particles of AB. A cyclic voltammogram of the Na3Cr2(PO4)3/AB electrode is shown in Figure 2a. Only one redox couple at ca. 4.5 V versus Na/Na+ was identified, which is competitive with Co3+/Co2+ and Ni3+/Ni2+ in a polyanion matrix.12−14 Galvanostatic charge/discharge curves in Figure 2b indicated that an initial

Figure 2. Electrochemical properties of Na3Cr2(PO4)3/AB electrode in Na half-cell: (a) a cyclic voltammogram of the first cycle at a scan rate of 1.0 mV s−1; (b) 1st, 2nd, 3rd, and 20th galvanostatic charge/ discharge curves between 2.5 and 4.7 V (vs Na/Na+) at the rate of 0.5 C for charging and 1 C for discharging; (c) first galvanostatic discharge curves after maintaining the cell at 4.70 V (vs Na/Na+) for the various time durations. C-rates were 0.5 C for charging and 1 C for discharging.

Figure 1. Rietveld refinement of the as-prepared Na3Cr2(PO4)3/AB electrode. Black arrows indicate peaks ascribed to superstructure. An SEM image of synthesized Na3Cr2(PO4)3/AB particles is shown in the inset. 929

DOI: 10.1021/acsaem.7b00105 ACS Appl. Energy Mater. 2018, 1, 928−931

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ACS Applied Energy Materials charge capacity at a current rate of 0.5 C was ∼98 mAh g−1, which is equal to 84% of the theoretical capacity (117 mAh g−1 for 2 Na per formula unit) with a single voltage plateau, and the reversible discharge capacity was ∼79 mAh g−1 exhibiting a small potential difference of ca. 0.2 V between charging and discharging curves. Figure 2c shows galvanostatic discharge curves after maintaining the cell at 4.7 V (vs Na/Na+) for the various time durations. A continuous increase in overvoltage with evident initial voltage bumps indicates the time-dependent degradation in this system could be initiated at the partial surface prohibiting the smooth nucleation of the discharged phase. Structural evolution during the charge/discharge process was investigated using ex situ synchrotron XRD measurement. The depths of charge or discharge at which the XRD patterns were collected are marked as A−E in Figure 3a. XRD patterns are

Figure 4. Cr K-edge XANES spectra of Na3Cr2(PO4)3/AB electrode in (a) first charging process and (b) first discharging process. The spectrum of Cr2O3 is a reference as a compound containing Cr(III).

4p dipole transition. Their contributions become evident at high valence states due to the missing 3d electron and the local structural change around Cr. The reversible shift of the main edge also indicates the redox activity of the Cr4+/Cr3+ couple. The Cr4+/Cr3+ redox couple in the polyanion framework was demonstrated to generate an extremely high potential in the sodium cell. As an initiating example, NASICON-type Na3Cr2(PO4)3 showed reversible electrochemical activity at ca. 4.5 V versus Na/Na+ with an initial charging capacity of 98 mAh g−1 comparable to 84% of the theoretical capacity (117 mAh g−1) for 2 Na per formula unit. In addition to the wellknown high potential with Ni3+/Ni2+ and Co3+/Co2+ redox couples shown in Figure 5, the Cr4+/Cr3+ redox couple in several polyanion framework systems now warrants exploration of new high-voltage cathode materials. However, excessive oxidation or spontaneous disproportionation could produce highly toxic Cr6+, which should be recognized as a possible important risk.

Figure 3. (a) First charge/discharge curve at which each XRD pattern was collected; 0.5 C for charging and 1 C for discharging. (b) Ex situ XRD patterns at various charge/discharge states during the first cycle. Enlarged views in angular region [17.0−18.0°] are shown on the right. Each letter of the alphabet from A to E corresponds to the state at which the XRD pattern was collected as indicated in part a.

shown in Figure 3b. Upon charging, new peaks grew at the expense of the peak intensity for the original phase. All of the original peaks recovered in a reversible manner upon discharging. These typical features for a “nucleation-growthtype” mechanism are consistent with the flat charge/discharge profile at the specific generating voltage of 4.5 V versus Na/ Na+. Cr K-edge XANES spectra were measured to check the valence state of chromium in Na3−xCr2(PO4)3. A series of spectra obtained at various states of charge or discharge is shown in Figure 4. Upon charging, intensity for the pre-edge peak (5988−5994 eV) increased, while the main edge shifted to higher energy by ca. 1 eV. The pre-edge peak is composed of the 1s−3d quadrupole transition and the oxygen-mediated 1s−

Figure 5. Positions of the M(n+1)+/Mn+ redox couples with various polyanions (M = transition metal). 930

DOI: 10.1021/acsaem.7b00105 ACS Appl. Energy Mater. 2018, 1, 928−931

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Structure and Properties for Sodium Extraction. Nano Lett. 2016, 16, 7836−7841. (11) Wang, H.; Chen, C.; Qian, C.; Liang, C.; Lin, Z. Symmetric Sodium-Ion Batteries Based on the Phosphate Material of NASICONStructured Na3Co0.5Mn0.5Ti(PO4)3. RSC Adv. 2017, 7, 33273−33277. (12) Kim, H.; Park, C. S.; Choi, J. W.; Jung, Y. Defect-Controlled Formation of Triclinic Na2CoP2O7 for 4 V Sodium-Ion Batteries. Angew. Chem., Int. Ed. 2016, 55, 6662−6666. (13) Nose, M.; Nakayama, H.; Nobuhara, K.; Yamaguchi, H.; Nakanishi, S.; Iba, H. Na4Co3(PO4)2P2O7: A Novel Storage Material for Sodium-Ion Batteries. J. Power Sources 2013, 234, 175−179. (14) Zhang, H.; Hasa, I.; Buchholz, D.; Qin, B.; Geiger, D.; Jeong, S.; Kaiser, U.; Passerini, S. Exploring the Ni Redox Activity in Polyanionic Compounds as Conceivable High Potential Cathodes for Na Rechargeable Batteries. NPG Asia Mater. 2017, 9, e370. (15) Park, Y. U.; Seo, D. H.; Kwon, H. S.; Kim, B.; Kim, J.; Kim, H.; Kim, I.; Yoo, H. I.; Kang, K. A New High-Energy Cathode for a NaIon Battery with Ultrahigh Stability. J. Am. Chem. Soc. 2013, 135, 13870−13878. (16) Kim, J.; Park, I.; Kim, H.; Park, K. Y.; Park, Y. U.; Kang, K. Tailoring a New 4V-Class Cathode Material for Na-Ion Batteries. Adv. Energy Mater. 2016, 6, 1502147. (17) Barpanda, P.; Oyama, G.; Nishimura, S.; Chung, S.-C.; Yamada, A. A 3.8-V Earth-Abundant Sodium Battery Electrode. Nat. Commun. 2014, 5, 4358. (18) Hautier, G.; Jain, A.; Ong, S. P.; Kang, B.; Moore, C.; Doe, R.; Ceder, G. Phosphates as Lithium-Ion Battery Cathodes: An Evaluation Based on High-Throughput Ab Initio Calculations. Chem. Mater. 2011, 23, 3495−3508. (19) Herklotz, M.; Scheiba, F.; Glaum, R.; Mosymow, E.; Oswald, S.; Eckert, J.; Ehrenberg, H. Electrochemical Oxidation of Trivalent Chromium in a Phosphate Matrix: Li3Cr2(PO4)3 as Cathode Material for Lithium Ion Batteries. Electrochim. Acta 2014, 139, 356−364. (20) Ravel, B.; Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: Data Analysis for X-Ray Absorption Spectroscopy Using IFEFFIT. J. Synchrotron Radiat. 2005, 12, 537−541. (21) D’Yvoire, F.; Pintard-Scrépel, M.; Bretey, E.; de la Rochère, M. Phase Transitions and Ionic Conduction in 3D Skeleton Phosphates A3M2(PO4)3: A = Li, Na, Ag, K; M = Cr, Fe. Solid State Ionics 1983, 9−10, 851−857. (22) de la Rochère, M.; d’Yvoire, F.; Collin, G.; Comès, R.; Boilot, J. P. NASICON Type Materials - Na3M2(PO4)3 (M = Sc, Cr, Fe): Na+Na+ Correlations and Phase Transitions. Solid State Ionics 1983, 9−10, 825−828. (23) Lucazeau, G.; Barj, M.; Soubeyroux, J. L.; Dianoux, A. J.; Delmas, C. Neutron Scattering and Diffractuion Study of Na3Cr2(PO4)3, NaZr2(PO4)3 and Na3ZrMg(PO4)3. Solid State Ionics 1986, 18−19, 959−963. (24) Kabbour, H.; Coillot, D.; Colmont, M.; Masquelier, C.; Mentre, O. α-Na3M2(PO4)3 (M = Ti, Fe): Absolute Cationic Ordering in NASICON-Type Phases. J. Am. Chem. Soc. 2011, 133, 11900−11903. (25) Chotard, J.-N.; Rousse, G.; David, R.; Mentré, O.; Courty, M.; Masquelier, C. Discovery of a Sodium-Ordered Form of Na3V2(PO4)3 below Ambient Temperature. Chem. Mater. 2015, 27, 5982−5987.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsaem.7b00105. Details of the Rietveld refinement results of synchrotron X-ray powder diffraction, and electrochemical performance and synchrotron X-ray powder diffraction pattern of full charged phase with Miller indices and lattice constants (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Kosuke Kawai: 0000-0003-3840-2198 Shin-ichi Nishimura: 0000-0001-7464-8692 Atsuo Yamada: 0000-0002-7880-5701 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The present work was financially supported from the Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT), under the “Element Strategy Initiative for Catalysts & Batteries” (ESICB) project. The synchrotron XRD experiments were performed under KEK-PF User Program (No. 2015G684). K.K. acknowledges financial support from “Materials Education Program for the Future Leaders in Research, Industry, and Technology” (MERIT) project.

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REFERENCES

(1) Kubota, K.; Komaba, S. Review - Practical Issues and Future Perspective for Na-Ion Batteries. J. Electrochem. Soc. 2015, 162, A2538−A2550. (2) Kim, H.; Kim, H.; Ding, Z.; Lee, M. H.; Lim, K.; Yoon, G.; Kang, K. Recent Progress in Electrode Materials for Sodium-Ion Batteries. Adv. Energy Mater. 2016, 6, 1600943. (3) Padhi, A. K.; Nanjundaswamy, K. S.; Masquelier, C.; Goodenough, J. B. Mapping of Transition Metal Redox Energies in Phosphates with NASICON Structure by Lithium Intercalation. J. Electrochem. Soc. 1997, 144, 2581−2586. (4) Masquelier, C.; Croguennec, L. Polyanionic (Phosphates, Silicates, Sulfates) Frameworks as Electrode Materials for Rechargeable Li (or Na) Batteries. Chem. Rev. 2013, 113, 6552−6591. (5) Jian, Z.; Hu, Y.-S.; Ji, X.; Chen, W. NASICON-Structured Materials for Energy Storage. Adv. Mater. 2017, 29, 1601925. (6) Delmas, C.; Cherkaoui, F.; Nadiri, A.; Hagenmuller, P. A Nasicon-Type Phase as Intercalation Electrode: NaTi2(PO4)3. Mater. Res. Bull. 1987, 22, 631−639. (7) Senguttuvan, P.; Rousse, G.; Arroyo Y De Dompablo, M. E.; Vezin, H.; Tarascon, J. M.; Palacín, M. R. Low-Potential Sodium Insertion in a Nasicon-Type Structure through the Ti(III)/Ti(II) Redox Couple. J. Am. Chem. Soc. 2013, 135, 3897−3903. (8) Saravanan, K.; Mason, C. W.; Rudola, A.; Wong, K. H.; Balaya, P. The First Report on Excellent Cycling Stability and Superior Rate Capability of Na3V2(PO4)3 for Sodium Ion Batteries. Adv. Energy Mater. 2013, 3, 444−450. (9) Gao, H.; Li, Y.; Park, K.; Goodenough, J. B. Sodium Extraction from NASICON-Structured Na3MnTi(PO4)3 through Mn(III)/Mn(II) and Mn(IV)/Mn(III) Redox Couples. Chem. Mater. 2016, 28, 6553−6559. (10) Zhou, W.; Xue, L.; Lü, X.; Gao, H.; Li, Y.; Xin, S.; Fu, G.; Cui, Z.; Zhu, Y.; Goodenough, J. B. NaxMV(PO4)3 (M = Mn, Fe, Ni)

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NOTE ADDED AFTER ASAP PUBLICATION This article was published ASAP on February 26, 2018, with some incorrect changes made to the text. The corrected version was reposted on February 26, 2018.

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DOI: 10.1021/acsaem.7b00105 ACS Appl. Energy Mater. 2018, 1, 928−931