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

The P2-Na_0.7MnO_2.05 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 Na_0.7Ti_xMn_(1-x)O_2.05 materials. We investigated the effects of Ti doping on the structure, morphology, Mn³⁺ concentration, and Na⁺ diffusion coefficients of Na_0.7Ti_xMn_(1-x)O_2.05. 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 Na_0.7MnO_2.05 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%.