Preparation And Electrochemical Performance Of LiMnO₂Cathode Material Of Lithium Ion Battery

With the development of technologies,demands for portable devices aretremendously increasing. Lithium ion batteries are attractive for use in the field ofmobile power source with the favorable properties of high voltage,long cyclinglife,high energy density,non-memory effect and pollution-free.LiCoO2introduced bySony Corporate in1991was the first successfully commercial cathode material forthe lithium ion batteries.However, the relatively high cost of Co raw materials isconsidered as a big drawback of LiCoO2cathode and research on the development ofnew type cathode materials to replace LiCoO2cathode is a major trend for thedevelopment of lithium ion secondary batteries. LiMnO2is a promising cathodematerial of lithium batteries because of the abundance of raw material, cheapness,safety and high theoretic capacity(285mAh/g). The present study focuses on toprepare o-LiMnO2and explores its structure，morphology and electrochemicalproperties，and the relevance between electrochemical performance and the particlemorphology were discussed．The research procedure is as follows：In this paper, the first chapter describes the development of lithium-ion batteryand quantities of research in the cathode material of lithium-ion battery,it alsosummarizes the variety of preparation methods and research status of the cathodematerials o-LiMnO2of lithium-ion batteryThe second chapter describes the experimental raw materials, equipments andthe electrochemical analyses methods used in this thesis process were introduced indetail.The third chapter explains the research of the Hydrothermal Synthesis ofo-LiMnO2.The γ-MnOOH microrods and particles were synthesized by hydrothermalmethod using KMnO4and MnSO4．The effects of different morphology andmicrostructures of the as-prepared γ-MnOOH on the structure，morphology and theelectrochemical performance of o-LiMnO2was investigated. The experimental resultsshow that the o-LiMnO2microrods displayed a superior electrochemical performanceto that of the o-LiMnO2nanoparticles, with higher discharge capacity and better cyclability.For example, at a current density of30mA/g, the o-LiMnO2microrodsdelivers the maximum capacities of LiMnO2microrods reached220.2mAh/g andremained176.7mAh/g after50cycles. It also exhibits an excellent cycling stability athigh rate, When cycling at current density of50mA/g、75mA/g、100mA/g and150mA/g,it delivered the higher capacity retention for the o-LiMnO2about84.2%、83.4%、80.9%and81.0%after50cycles.The fourth chapter mainly reports o-LiMnO2microrods was successfullysynthesized by ion exchange. γ-MnOOH microrods were first synthesized byhydromemal methods and served as precursor. The o-LiMnO2microrods wereobtained by refluxing γ-MnOOH with an excess of LiOH in distilled water at100℃for6hours. This method reduces the cost of raw materials, but the electrochemicalperformance of the o-LiMnO2microrods is poorer by ion exchange. It delivers themaximum capacities of o-LiMnO2microrods reached165.4mAh/g and remained124.9mAh/g after50cycles at the current density of30mA/g. The research on ionexchange is not mature and still needed for further experiments.The last chapter gives all overview on the originality and the deficiency in thisthesis. Some prospects and suggestions of the possible future research directions arepointed out.