Preparation And Modification Of LiNi_0.5Mn_1.5O₄ As Cathode Material For Lithium Ion Batteries

Lithium ion batteries（LIBs）have been the most efficient energy storage devices since their commercialization,with the characteristics of high open-circuit voltage,large discharge capacity,long cycle life and environmental friendliness.LIBs have been widely applied to portable electronic devices and will have more extensive application prospects in hybrid electrical vehicles（HEVs）,electric vehicles（EVs）and plug-in hybrid electric vehicles（PHEVs）.At present,it is of great importance to explore high potential cathode materials with higher energy density and longer cycle life.LiNi_0.5Mn_1.5O₄ cathode material has received considerable attention because of its good cyclic properties,low production cost and relatively high capacity,with a plateau at around 4.7 V.In the work,LiNi_0.5Mn_1.5O₄ materials were prepared by a sol-gel method using the Ni（CH3COO）2·4H2O、Mn（CH3COO）2·4H2O and CH3COOLi·2H2O as raw materials,and citric acid as the chelating agent.The microstructure and morphology of the samples were characterized by TG-DSC,XRD and SEM.The electrochemical performance of materials were evaluated by galvanostatic charge/discharge text,CV and EIS.The system of calcining temperature,calcining time,sintering temperature,and sintering time are optimized by orthogonal experiment.The experimental results showed that the pure spinel LiNi_0.5Mn_1.5O₄ prepared from precursor under 450 ℃ for 5 h,and then sintering at 850 ℃ for 16 h had the best performance.At the discharge rate of 0.1 C at room temperature,the first discharge capacity was 141.93 mAh/g.After 30 cycles,it’s capacity retention were 90.42%.In order to improve the electrochemical properties of LiNi_0.5Mn_1.5O₄,LiGaxNi_0.5-0.5xMn_1.5-0.5xO₄（x=0.05,0.1,0.2）cathode materials were prepared by a sol-gel method.The effect of Ga3+ doping with different content on the physical and electrochemical properties of the Li Ni_0.5Mn_1.5O₄ were investigated.The experimental results show that When Ga3+ doped amount was 0.1,LiGa0.1Ni0.45Mn1.45O₄ had the best electrochemical performance.After 50 cycles at 0.1 C and 1 C,discharge capacities of LiGa0.1Ni0.45Mn1.45O₄ were 125.84 mAh/g and 109.45 mAh/g,respectively.Their capacity retention were 98.81% and 97.3%,respectively.At the discharge rate of 0.1 C,_0.5 C,1 C,2 Cand 5 C after 10 cycles,their first discharge capacities were 126.72 mAh/g,121.62 mAh/g,105.25 mAh/g and 85.68 mAh/g,respectively.LiGa0.1Ni0.45Mn1.45O₄ had the best electrochemical performance.It’s charge transfer resistance is 40.2 Ω,it is obviously smaller than the charge transfer resistance of LiNi_0.5Mn_1.5O₄.The ratio of material and cycle performance of reversibility were improved with appropriate content of Ga3+,the reversibility of lithium ion intercalation was enhanced and charge transfer impedance was reduced.The electrochemical performance of LiNi_0.5CeyMn_1.5-0.5yO₄（y=0.005,0.025,0.05）that were prepared by micro-rear earth metal Ce3+ doping were studied.XRD showed that all samples had high phase purity,without any impurity peak,they still keep the original spinel structure.The effect of Ce3+ doping on the morphology and particle size of the LiNi_0.5Mn_1.5O₄ was not significant.After 50 cycles at 0.1 C and 1 C,the discharge capacities of LiNi_0.5Ce0.025Mn1.4875O₄ were 124.77 mAh/g and 109.98 mAh/g,respectively.Their capacity retention were 95.65% and 91.09%,respectively.At 2 C and 5 C,the specific discharge capacity of Ce3+ doped（y=0.05）was a little higher than that y=0.005,but it is lower than that of y=0.025,which means that excessive doping does not have much effect on high rate.Appropriate amount Ce3+ doping can effectively improve the rate performance of the materials.