Synthesis of porous peanut-like LiNi0.5Mn1.5O4 cathode materials through an ethylene glycol-assisted hydrothermal method using urea as a precipitant

Abstract

The high voltage spinel LiNi_0.5Mn_1.5O₄ with a peanut-like morphology and porous structure was synthesized by an ethylene glycol-assisted hydrothermal method using urea as a precipitant followed by high-temperature calcination. For comparison, the LiNi_0.5Mn_1.5O₄ sample was also synthesized in the aqueous solution in the absence of ethylene glycol (EG). The as-prepared materials were characterized by XRD, SEM, TEM, FT-IR, CV, EIS and galvanostatic charge/discharge tests. The presence of EG in the hydrothermal process improves the dispersity and decreases the particle size of the final LiNi_0.5Mn_1.5O₄ product, thus leading to its better rate capability, whose discharge capacity at a 10C rate could reach as high as 121.4 mA h g⁻¹. On the other hand, the presence of EG in the hydrothermal process could make the reagents mix more homogeneously, thus leading to higher crystallinity, lower impurity and Mn³⁺ contents, which are advantageous to the cycling performance. Furthermore, the porous structure of the LiNi_0.5Mn_1.5O₄ material could effectively mitigate the volume change caused by the repeated Li⁺ insertion/extraction process, which is also conducive to the cycling stability. The LiNi_0.5Mn_1.5O₄ cathode material synthesized by the EG-assisted hydrothermal process shows a capacity retention rate of 96.4% after 100 cycles at a 1C rate. Additionally, a possible formation mechanism for the Ni_0.25Mn_0.75CO₃ precursor with a peanut-like morphology was also proposed.