Synthesis and Evaluation of NaMPO4 (M=Fe, Mn, Co) Framework Polyanion Cathodes for Sodium-Ion Batteries (SIB)

Polyanion compounds are attractive for use as cathode materials because they generally have higher potentials for a given M n+/(n+1)+ redox couple in comparison to the oxide analogue. 1 In addition, the strong bonding within the polyanion group provides similar safety characteristics to oxides even though they exhibit higher working potentials. 2 The phospho-olivine LiFePO 4 has been thoroughly investigated as a cathode material for use in lithium-ion batteries since its introduction in 1997. 3 It has been determined that NaMPO 4 (M = Fe and Mn) compounds prefer the electrochemically inactive maricite structure and not the olivine structure when using conventional synthesis methods, 4 which has left the research community seeking unorthodox methods to access the olivine phase. 5 , 6 Herein we report on a NaCoPO 4 (NCP) polymorph ( Red- phase) that has previously only been observed as an impurity while attempting to synthesize other polymorphs. 7 The Red- phase was synthesized by a microwave-assisted solvothermal process using tetraethylene glycol as the solvent. Ex-situ XRD and XANES measurements indicate that during cycling the structure undergoes reversible changes and the Co 2+/3+ redox couple is partially active near 4.4 V vs. Na. The silicate family of cathode materials is rich in polymorphism 8 and has also been thoroughly investigated for use in lithium-ion batteries. Among the polymorphs investigated is Pn­ -Li 2 MnSiO 4 9 that was accessed by ion-exchange of the parent Pn­ -Na 2 MnSiO 4 compound. Yet, minimal work has been reported on the sodium analogue. 9 , 10 Considering the air sensitivity reported of the lithium version, 11 herein we report preliminary results on the effect of air exposure on the electrochemistry of Pn­ -Na 2 MnSiO 4 . § cjohnson@anl.gov Acknowledgements Work supported by U. S. DOE, Office of Science under Contract No. DE-AC02-06CH11357. We also thank the Argonne LDRD program office for additional support. References: (1) Gutierrez, A.; Benedek, N. A.; Manthiram, A. Chemistry of Materials 2013 , 25 , 4010. (2) Hautier, G.; Jain, A.; Ong, S. P.; Kang, B.; Moore, C.; Doe, R.; Ceder, G. Chemistry of Materials 2011 , 23 , 3495. (3) Padhi, A. K.; Nanjundaswamy, K. S.; Goodenough, J. B. Journal of the Electrochemical Society 1997 , 144 , 1188. (4) Bridson, J. N.; Quinlan, S. E.; Tremaine, P. R. Chemistry of Materials 1998 , 10 , 763. (5) Lee, K. T.; Ramesh, T. N.; Nan, F.; Botton, G.; Nazar, L. F. Chemistry of Materials 2011 , 23 , 3593. (6) Fang, Y.; Liu, Q.; Xiao, L.; Ai, X.; Yang, H.; Cao, Y. ACS Applied Materials & Interfaces 2015 , 7 , 17977. (7) Feng, P.; Bu, X.; Stucky, G. D. Journal of Solid State Chemistry 1997 , 131 , 160. (8) Armstrong, A. R.; Sirisopanaporn, C.; Adamson, P.; Billaud, J.; Dominko, R.; Masquelier, C.; Bruce, P. G. Z Anorg Allg Chem 2014 , 640 , 1043. (9) Duncan, H.; Kondamreddy, A.; Mercier, P. H. J.; Le Page, Y.; Abu-Lebdeh, Y.; Couillard, M.; Whitfield, P. S.; Davidson, I. J. Chemistry of Materials 2011 , 23 , 5446. (10) Murphy, D. T.; Schmid, S. In The 17th International Meeting on Lithium Batteries 2014. (11) Muraliganth, T.; Stroukoff, K. R.; Manthiram, A. Chemistry of Materials 2010 , 22 , 5754.