Study On Hydrothermal Systhesis And Electrochemical Performance Of Lini_0.5mn_1.5o₄ Cathode Material

Spinel LiNi_0.5Mn_1.5O₄ cathode material has been considered as one of the most promising cathode materials for high energy density lithium-ion batteries due to its high operating voltage and high energy density.Based on the problem of simultaneous achievement of rate performance and cycle performance,a secondary micron-sized porous structured LiNi_0.5Mn_1.5O₄ material composed of sub-micron primary particles has been synthesized through a combination of hydrothermal route and high-temperature lithiation method.The effects of calcination temperature,hydrothermal time and molar ratio of urea to transition metal?U/TM?on the structure,morphology and electrochemical performance of the carbonate precursor and LiNi_0.5Mn_1.5O₄ material were systematically investigated.The effects of calcination temperature on the structure,morphology and electrochemical performance of LiNi_0.5Mn_1.5O₄ material were studied.The results show that with the increase of calcination temperature,the disordering degree of LiNi_0.5Mn_1.5O₄material gradually increases.In addition,the calcination temperature has a great influence on the particle morphology.The LiNi_0.5Mn_1.5O₄ material prepared at calcination temperature of 750°C exhibits a secondary micron-sized porous structure composed of sub-micron primary particles,which can improve the cyclic performance without affecting the rate performance,thus leading to better electrochemical performance.The influence of hydrothermal time on the structure,morphology and electrochemical performance of LiNi_0.5Mn_1.5O₄ was studied.XRD results show that the disordering degree of the material first decreases and then increases with the extension of hydrothermal time.SEM results show that the samples obtained at different hydrothermal times show capsule-like morphology,whose particle size first decreases and then slightly increases with the hydrothermal time.The LiNi_0.5Mn_1.5O₄ material prepared at hydrothermal time of 10 h exhibits the smallest particle size with the most uniform distribution,thus leading to its optimal electrochemical performance,in spite of its lowest disordering degree.The specific discharge capacity at 10C rate can reach 122.1 mAh·g^-11 and the capacity retention rate after 100 cycles at 1C rate is 96.1%.The effects of molar ratio of urea to transition metal?U/TM?on the structure,morphology and electrochemical performance of carbonate precursor and LiNi_0.5Mn_1.5O₄material were studied.SEM results show that U/TM ratio exerts effects on both morphology and particle size of the material.With the increase of U/TM ratio,the particle morphology changes from peanut to capsule,and the particle size first decreases and then increases.The LiNi_0.5Mn_1.5O₄ material synthesized at U/TM ratio of 2.0:1 has the smallest particle size and more uniform distribution,thus leading to its best electrochemical performance.