Study On Preparation And Properties Of High-Performance Cathode Materials For Lithium-Ion Battery

Lithium ion batteries have been widely used to power portable electronic devices such ascell phones and laptop computers due to their high energy density. However, the currentlyused layered LiCoO₂cathode material could deliver only50%of its theoretical capacity inpractical lithium ion batteries （140mAh/g） due to the chemical and structural instabilities atdeep charge with （1-x）<0.5in Li1-xCoO₂. Also, cobalt is relatively expensive and toxic. Thesedifficulties have generated enormous interest in alternative cathode materials. Solid solutionsbetween layered Li[Li_1/3Mn_2/3]O₂（commonly designated as Li₂MnO₃） and LiMO₂（M=Mn,Ni, Co）) have become appealing as some of them exhibit much higher capacity （²50mAh/gon charging to4.8V） with lower cost and better safety compared to LiCoO₂. In this paper, thelayered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂cathode material for rechargeable lithium-ion batterieswas successfully prepared by sol-gel method. We investigated the preparation processparameters, structure, and electrochemical performances of Li[Li0.2Mn0.54Ni0.13Co0.13]O2. Theeffects of prepared conditions on structure and electrochemical performances have beeninvestigated and the optimum synthetic conditions were obtained. The layered cathodematerials of Li[Li_0.2Mn_0.54Ni_0.13Co_0.13-xAl_x]O₂（x=0.03,0.05,0.08,0.13） andLi[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂-xFx（x=0.03,0.05,0.08） were investigated by XRD, SEM,constant-current charge and discharge tests, cyclic voltammetry, et al.The layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂material by Al³⁺and Cr³⁺doping wasinvestigated. The layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13-xAl_x]O₂（x=0.03,0.05,0.08,0.13）materialswere prepared by sol-gel method. The sintering time was12h, the preparation temperatureswere800℃,850℃and900℃respectively. The prepared materials were characterized withXRD and SEM. The electrochemical performances of the materials were tested byconstant-current charge-discharge tests at room temperature （25℃） and at high temperature（55℃）. The results showed that the prepared samples possessed well-layered structure,uniform distribution of grain size and good morphology. TheLi[Li_0.2Mn_0.54Ni_0.13Co_0.08Al_0.05]O₂sample with best performance can be obtained at sinteringtemperature of900℃,which initial specific discharge capacity was272mAh/g at roomtemperature and283.7mAh/g at high temperature，and after60cycles the specific dischargecapacity was still238.9mAh/g at room temperature. It was evident that doping of Al3+canimprove the initial discharge capacity and the stability of structure.The cathode materials of Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O_2-xF_x（x=0.03,0.05,0.08） wereprepared by sol-gel method. The sintering time was12h, the preparation temperatures were800℃,850℃and900℃respectively. The results indicated that the obtained materialspossessed layered structure. The Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O_1.95F_0.05sample exhibited the bestelectrochemical performance can be obtained at sintering temperature of800℃, which initialspecific discharge capacity was268.1mAh/g at room temperature and281.8mAh/g at hightemperature, and after60cycles the specific discharge capacity was still242.6mAh/g at roomtemperature.Therefore，the conclusion could be drawn that F-substitution elevated thecapacity and improved the cyclability of the layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂material.