Contribution of titanium substitution on improving the electrochemical properties of P2-Na0.67Ni0.33Mn0.67O2 cathode material for sodium-ion storage

P2-type Na0.67Ni0.33Mn0.67-xTixO2(0 <= x <= 0.4) have been synthesized as cathode materials for sodium-ion batteries, and the effect of Ti substitution on the structural evolution and electrochemical properties of Na0.67Ni0.33Mn0.67O2 are investigated in detail. Analysis results indicate that an appropriate substituted amount of Mn with Ti in the MO2 layers effectively stabilize the crystal lattice of these layered electrodes during the Na+ insertion/extraction process, which significantly improves their electrochemical performances between 2.5 and 4.4V. The discharge/charge patterns and in situ X-ray diffraction measurements expound the successful suppression of Na+/vacancy ordering and multiphase transition during the de-sodiation/sodiation process to resist the structure-induced degradation, which provide possible guidelines for exploring high performances sodium-ion batteries.