Effect of Mo6+ doping on the structure and electrochemical properties of spinel-type LiMn2O4 cathode materials

The Jahn-Teller effect and the dissolution of Mn are significant factors contributing to the capacity degradation of spinel LiMn₂O₄ cathode materials during charging and discharging. In this study, Mo⁶⁺-doped polycrystalline octahedral Li_1.05Mn_2-xMo_xO₄ (x = 0, 0.005, 0.01, 0.015) cathode materials were prepared by simple solid-phase sintering, and their crystal structures, microscopic morphologies, and elemental compositions were characterized and analyzed. The results showed that the doping of Mo⁶⁺ promoted the growth of (111) crystalline facets and increased the ratio of Mn³⁺/Mn⁴⁺. The electrochemical performance of the materials was also tested, revealing that the doping of Mo⁶⁺ significantly improved the initial charge/discharge specific capacity and cycling stability. The modified sample (LMO-0.01Mo) retained a reversible capacity of 114.83 mA h/g with a capacity retention of 97.29% after 300 cycles. Additionally, the doping of Mo⁶⁺ formed a thinner, smoother SEI film and effectively inhibited the dissolution of Mn. Using density-functional theory (DFT) calculations to analyze the doping mechanism, it was found that doping shortens the Mn-O bond length inside the lattice and increases the Li-O bond length. This implies that the Li⁺ diffusion channel is widened, thereby increasing the Li⁺ diffusion rate. Additionally, the modification reduces the energy band gap, resulting in higher electronic conductivity.