Structure and electrochemical properties of MgAl co-doped spinel LiMn2O4 cathode material

MgAl co-doping and single-crystal truncated octahedral morphology strategy was employed to suppress and mitigate the Jahn-Teller distortion and Mn dissolution in spinel-type LiMn₂O₄ materials. LiMg_0.10Al_yMn_1.90-yO₄ (y = 0.03, 0.05, 0.08, 0.10, and 0.12) cathode materials were synthesized via solid-phase combustion method and the effects of varying Al contents on the crystal structures, single-crystal truncated octahedral morphology, valence states of doped elements, rate and long-cycle electrochemical performance, and Li⁺ ion migration kinetics of spinel-type LiMn₂O₄ materials were investigated. The results indicate that MgAl co-doping promotes the crystalline development of spinel-type LiMn₂O₄ material and the preferential growth of {111}, {100}, and {110} crystal planes, forming complete single-crystal truncated octahedral morphology. Among samples with different Mg and Al doping levels, the MgAl co-doped sample LiMg_0.10Al_0.05Mn_1.85O₄ exhibits superior capacity and cycle stability. At a low rate of 1C, the initial discharge specific capacity is 114.7 mAh·g⁻¹, with an 93.6 % capacity retention after 200 cycles; at high rates of 10, 15, and 20C, the initial discharge specific capacities are 94.4, 92.4, and 84.5 mAh·g⁻¹ respectively, with capacity retention rates of 84.1 %, 76.9.2 %, and 81.7 % after 1000 cycles; at high temperatures of 55 °C and rates of 1C, 5C and 10C, the initial discharge specific capacities are 113.7, 111.1 and 100.5 mAh·g⁻¹ respectively, with retention rates of 68.6 %, 46.1 % and 37.8 % after 200, and 500 cycles. The LiMg_0.10Al_0.05Mn₁₈₅O₄ sample has the lowest charge transfer resistance (168.6 Ω) and apparent activation energy (32.39 kJ·mol⁻¹), and the highest Li⁺ diffusion coefficient (1.20 × 10⁻¹¹ cm²·s⁻¹). This indicates that during charging and discharging, Li⁺ ions in this sample encounter lower resistance and energy barriers, resulting in faster migration rates, which can enhance the material's rate capacity and cycling stability.