Enhanced Rate Capability and Cycle Performance of Titanium-Substituted P2-Type Na_0.67Fe_0.5Mn_0.5O₂ as a Cathode for Sodium-Ion Batteries

In this study, we developed a doping technology capable of improving the electrochemical performance, including the rate capability and cycling stability, of P2-type Na_0.67Fe_0.5Mn_0.5O₂ as a cathode material for sodium-ion batteries. Our approach involved using titanium as a doping element to partly substitute either Fe or Mn in Na_0.67Fe_0.5Mn_0.5O₂. The Ti-substituted Na_0.67Fe_0.5Mn_0.5O₂ shows superior electrochemical properties compared to the pristine sample. We investigated the changes in the crystal structure, surface chemistry, and particle morphology caused by Ti doping and correlated these changes to the improved performance. The enhanced rate capability and cycling stability were attributed to the enlargement of the NaO₂ slab in the crystal structure because of Ti doping. This promoted Na-ion diffusion and prevented the phase transition from the P2 to the OP4/″Z″ structure