CrPO4-Type of Compounds As Anode Materials for Na-Ion Batteries

Abstract

To date, research on sodium-ion batteries started to gain more interest. It is mainly motivated by the large abundance of sodium and the hope to produce batteries that are cheaper compared to LIBs and less prone to resource issues and safety concerns [1-3].During the last three years, our research team has developed several electroactive materials for sodium-ion batteries. Among them, the NASICON- NaFe2-xMx(PO4)(SO4)2 (M=Fe, V, Cr and 0 ≤ x ≤ 1) and the alluaudite- Na2 M 1Fe2(PO4)3 (M=Mn, Fe, Co, Ni) type of compounds. We also discovered recently several compounds crystallizing with the α-CrPO4-type of structure. These phases are very interesting since they contain several vacancies and therefore enable the intercalation of up to three sodium atoms which leads to capacities above 160 mAh/g with very stable cycling at 1C rate. In this paper, we report on the structural and electrochemical properties of the six new M-doped-VPO4 phases (M= Mn, Fe, Co, Ni, Zn, Mg). The crystal structures were solved by the Rietveld method using powder X-ray diffraction (PXRD) data. The electrochemical performances were examined by galvanometric cycling and cyclic voltammetry. The stability of the structure during cycling was followed by ex-situ PXRD experiments.The cycling performance of the Zn-doped-VPO4 phase is given in Figure 1. Cells embedding (NaPF6:EC:PC) electrolyte and Na-metal were used. Additional details on the other five new phases will be provided during the conference.Figure 1. Electrochemical performance of the newly prepared Zinc-doped-VPO4 phase at the rate of 1C vs. Na+/Na and the general intercalation mechanism for the α-CrPO4-type of structure. Reference: [1] Makino, K.; Katayama, Y.; Miura, T.; Kishi, T., J. Power Sources 2002, 112, 85−89.[2] Gaubicher, J.; Wurm, C.; Goward, G.; Masquelier, C., Nazar, L., Chem. Mater. 2000, 12, 3240−3242.[3] Jian, Z.; Zhao, L.; Pan, H.; Hu, Y.-S.; Li, H.; Chen, W., Chen, L., Electrochem. Commun. 2012, 14, 86−89. Figure 1