Insight into electrochemical and elastic properties in AFe1-xMxSO4F (A = Li, Na; M = Co, Ni, Mg) cathode materials: A first principle study

Abstract Li- and Na-transition metal fluorosulfate materials (AFeSO 4 F, A = Li, Na) are proposed as highly promising novel cathode materials for Li- and Na-ion batteries. In this study, the electrochemical performance and elastic properties of AFe 1- x M x SO 4 F (A = Li, Na; M = Co, Ni, Mg; x  = 0, 0.5, 1) are investigated from the view of first-principles calculations. The computational results reveal that the substitutions of Fe by Ni, Co and Mg enhance the intercalation voltage of the fluorosulphate materials. The density of states analysis shows that transition metal-doping AFeSO 4 F, especially for Ni doping case, could achieve better electronic conductivity in comparison with the pure phase and Mg-doped AFeSO 4 F. Further bader charges calculations give a confirmation that the Fe and Co in AFe 0.5 Co 0.5 SO 4 F play significant role in the charge transfer during delithiated or desodiated progresses, but the relatively inert character of Ni and Mg is discovered in AFe 0.5 Ni 0.5 SO 4 F and AFe 0.5 Mg 0.5 SO 4 F. LiFeSO 4 F and NaFeSO 4 F are found to be ductile from the exploration of elastic constants, whereas their delithiated and desodiated configurations have brittle character. In addition, Young’s Modulus ( E ), and Poisson's Ratio ( ν ) for LiFeSO 4 F, NaFeSO 4 F and 50% metal-doped AFe 1- x M x SO 4 F (A = Li, Na; M = Co, Ni, Mg) are also presented to explore the hardness, bond characteristic and stability against shear.