Yolk-Shelled Limn₂O₄Nano-materials Prepared By Ultrasonic Spray Pyrolysis And Its Electrochemical Properties

Lithium-ion batteries have been widely used in mobile phones, digital cameras and other portable electronic products for its advantages of high energy, high power, high cycle life, environment-friendly nature, and is gradually applied to electric cars and other large equipment. The energy density of lithium-ion battery mainly depends on cathode material. In recent years, LiMn2O4with spinel structure has caught much attention because of its rich resources and advantages of high voltage platform, and is considered as one of the most promising commercial lithium-ion battery cathode material.Yolk-Shell structured material can buffer the volume change during lithium deintercalation process arising from the peculiar structure characteristics, and exhibits advantages in lithium-ion battery as electrode materials. In this paper, yolk-shelled LiMn2O4cathode materials were designed and prepared using sucrose, polyethylene glycol as additives by ultrasonic spray pyrolysis, and we investigated the effect of additives types, pyrolysis temperature, calcination temperature on yolk-shell structure, proposing high-temperature gas-phase fast chemical reaction process for yolk-shell structure growth mechanism. The electrochemical properties of yolk-shelled LiMn2O4as lithium ion battery cathode materials were characterized, establishing structure-property relationship between material microstructure and electrochemical properties, main work and results are as follows:Yolk-shelled LiMn2O4cathode material was designed and prepared by ultrasonic spray pyrolysis using sucrose as additive, and the influence of concentration of sucrose, pyrolysis temperature and calcination temperature on yolk-shell structure was also explored with formation mechanism proposed during high temperature gas-phase rapid chemical reaction process. High sucrose concentration and pyrolysis temperature is the key factor to the formation of yolk-shell structure. Lithium-ion battery was built using yolk-shelled LiMn2O4as cathode materials and characterized. The initial discharge capacity is94.2mAh/g while residual capacity is58.8mAh/g after500cycles at1C rate for the yolk-shelled LiMn2O4calcined for3h at700℃.Yolk-shelled LiMn2O4cathode material was designed and prepared by ultrasonic spray pyrolysis using polyethylene glycol as additive with the effect of the polyethylene glycol molecular weight, concentration and calcination temperature on the yolk-shell structure investigated. The result showed that LiMn2O4with optimum yolk-shell structure can be prepared when polyethylene glycol having a molecular weight of1,000with concentration of0.12g/mL. Lithium-ion battery was built using this yolk-shelled LiMn2O4as a cathode materials and characterized. The initial discharge capacity was87.9mAh/g at1C rate, and the initial discharge capacity was80mAh/g at2C rate, with residual capacity of62.3mAh/g after1600cycles.Yolk-double shelled LiMn2O4nano materials was prepared under argon atmosphere by adjusting the calcination temperature and heating rate during calcination process. The formation mechanism of yolk-double shelled LiMn2O4results from twice separation between outer LiMn2O4shell and inner carbonaceous LiMn2O4spherical particles by slow combustion of carbon during the calcination process of carbonaceous LiMn2O4spherical particles. Its electrochemical properties as cathode material for lithium-ion batteries demonstrated that the initial capacity was75.5mAh/g, and residual capacity was56.3mAh/g after100cycles atl C rate.