Ethanol-assisted hydrothermal synthesis of LiNi_0.5Mn _1.5O₄ with excellent long-term cyclability at high rate for lithium-ion batteries

High voltage spinel LiNi_0.5Mn_1.5O₄ has been synthesized by an ethanol-assisted hydrothermal method. LiNi _0.5Mn_1.5O₄ has also been synthesized by a precipitation method and hydrothermal method for comparison. The materials were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical tests. The ethanol-assisted hydrothermal process improves the dispersity and decreases the size of particles in the presence of ethanol. With small size particles, LiNi_0.5Mn_1.5O₄ has an excellent rate capability. Its discharge capacity is 81.7 mA h g^-1 at a high rate of 20 C. On the other hand, the ethanol-assisted hydrothermal process mixes the reagents homogeneously and improves the crystallinity. It leads to low impurities and low Mn³⁺ ion content, which are beneficial for electrochemical performance. The LiNi_0.5Mn_1.5O₄ exhibits remarkable long-term cyclability. After 1000 cycles at a 5 C discharge rate, its discharge capacity is 102.1 mA h g^-1 with a capacity retention ratio of 88.1%. It also has good high temperature performance with a capacity retention of 82.0% after 200 cycles at 55 °C.