Study on the liquid-phase oxidation preparation of nickel-manganese composite oxides and their performance in high-voltage LiNi0.5Mn1.5O4 synthesis

Due to its high operating voltage, high safety, and low cost, spinel-type lithium nickel manganese oxide(LiNi_0.5Mn_1.5O₄) has become a research hotspot in the field of lithium-ion battery cathode materials in recent years. In this study, a new lithium nickel manganese oxide precursor, a nickel‑manganese composite oxide, was prepared using a liquid-phase oxidation method, and the cathode material was synthesized through high-temperature calcination. The effects of different raw material ratios on the preparation of LiNi_0.5Mn_1.5O₄ and their mechanisms were investigated. Considering that acetylene black tends to undergo thermal decomposition and electrochemical reactions in high voltage systems, leading to degradation and performance decline, Super C65 was used as a conductive agent instead of acetylene black to achieve better electrochemical performance. The experimental results indicate that when the Ni/Mn molar ratio is 1:2.5, the resulting nickel‑manganese composite oxide exhibits good crystallinity and a Fd-3 m space group structure with uniform particle dispersion and weak agglomeration. When mixed with LiOH and subjected to high-temperature calcination, with a Li/M molar ratio (M = Mn + Ni) of 0.51, the formation of the Li_xNi_1-xO impurity phase and the polarization of the material were significantly improved. The prepared LiNi_0.5Mn_1.5O₄ has uniform particle size, well-defined octahedral morphology, and pure phase characteristics. At a current density of 0.2C, the initial discharge specific capacity reaches 135 mAh/g and remains at 118 mAh/g after 200 cycles. After replacing acetylene black with Super C65, the initial discharge specific capacity of LiNi_0.5Mn_1.5O₄ at 0.2C increased to 140 mAh/g, with a discharge specific capacity of 122 mAh/g after 200 cycles, and the electrochemical impedance decreased from 304 Ω to 266 Ω. This improvement is attributed to the smaller particle size of Super C65, which can embed between the spinel material particles to form a good conductive network, increase the lattice parameters of the disordered space cluster structure, provide more diffusion paths for ions, facilitate the rapid change of element valence states, and thereby demonstrate higher electronic conductivity. Although the cycling retention slightly decreased, the overall electrochemical performance was enhanced.