Effect of Vanadium Substitution on the Ni-Site in P2-Type Na0.67Ni0.33Mn0.67O2 in Optimized Carbonate Ester Electrolytes as Cathode for Sodium-Ion Batteries

Solid-state synthesis of novel electrode materials of P2-type layered oxides Na0.67Ni0.33-xVxMn0.67O2 (where, x = 0, 0.05, and 0.11) for the application as cathode materials in rechargeable non-aqueous sodium-ion batteries is reported. Na0.67Ni0.22V0.11Mn0.67O2 electrode delivers significantly improved capacity retention than the pristine P2-Na0.67Ni0.33Mn0.67O2 when cycled between 1.5 and 4.3 V. The effect of organic ester electrolytes with 1.0 M NaClO4 shows diverse effects in the cathode material. The best capacity retention for V-substituted electrodes is observed in Ethylene carbonate (EC): Propylene carbonate (PC): Dimethyl carbonate (DMC) (0.45: 0.45: 0.1) with 1.0 M NaClO4 salt at a C-rate of 0.2C among four different ester electrolytes investigated [PC, EC: PC (1: 1), EC: DEC (1: 1) and EC: PC: DMC (0.45: 0.45: 0.1)].