Suppressed phase separation in high-voltage LiNi_0.5Mn_1.5O₄ cathode via Co-doping

Spinel LiNi_0.5Mn_1.5O₄ (LNMO) is a promising cathode material with high operating voltage and energy density. However, the poor rate performance caused by the two-phase reaction during charging and discharging limits its large-scale application. In this work, Co³⁺ doped LNMO cathode materials are prepared by co-precipitation method, and the effect of Co³⁺ doping replacing Mn⁴⁺, as well as the amount of Co³⁺ doping (LiNi_0.5Co_xMn_1.5-xO₄) are explored. Co³⁺ doping increases the content of Mn³⁺, thus improving the electronic conductivity of LNMO. Co³⁺ doping suppresses the phase transition of LNMO during discharging, which results in a smaller volume change and improves cycling stability. The presence of a solid solution intermediate allows for more uniform changes within the particles during the discharge process, thus increasing the diffusion rate of Li⁺ ion. LiNi_0.5Co_0.05Mn_1.45O₄ exhibits the best electrochemical performance compared to other samples, with a discharge specific capacity of 111.1 mAh g⁻¹ after 500 cycles at 1 C and a capacity retention of 92.4%. At 10 C high rate, the specific discharge capacity is 106.8 mAh g⁻¹. Our research reveals that Co³⁺ doping can improve the electrochemical performance of LNMO and provide a deeper insight into Co³⁺ doping of other cathode materials.