Effects of Ti4+ Doping on the Structural Stability and Electrochemical Performance of Layered P2-Na0.7MnO2.05 Cathodes for Sodium-Ion Batteries

The P2-Na0.7MnO2.05 cathode material has long been constrained by phase transitions induced by the Jahn–Teller (J–T) effect during charge–discharge cycles, leading to suboptimal electrochemical performance. In this study, we employed a liquid phase co-precipitation method to incorporate Ti during the precursor Mn3O4 synthesis, followed by calcination to obtain Na0.7TixMn(1−x)O2.05 materials. We investigated the effects of Ti doping on the structure, morphology, Mn3+ concentration, and Na+ diffusion coefficients of Na0.7TixMn(1−x)O2.05. Our findings revealed that the 7% Ti-doped NTMO-007 sample exhibited reduced grain agglomeration and smaller particle sizes compared to the undoped sample, thereby enhancing the electrode–electrolyte contact area and electrochemical activity. Additionally, Ti doping increased the crystal cell volume of Na0.7MnO2.05 and broadened the Na+ transport channels, significantly enhancing the Na+ diffusion coefficient. At a 0.5 C rate, the NTMO-007 sample demonstrated a specific capacity of 143.3 mAh g−1 with an 81.8% capacity retention after 100 cycles, markedly outperforming the undoped NMO sample, which had a capacity retention of only 61.5%.