Preparation And Modification Of LiNi₀.5Mn₁.5O₄as Cathode Material For Lithium Ion Batteries

With the development of electric vehicles, hybrid electric vehicles and large capacity storage battery, the requirements for lithium ion batteries’energy density and power density are put forward. The cathode material is one of the key materials for lithium ion batteries. It is the main way to improve the lithium ion batteries’energy density by researching and developing the high potential cathode material. Spinel LiNi0.5Mn1.5O4cathode material has some merits, for example discharge voltage platform at4.7V, structure stability, excellent cycle performance and low production cost. At present, LiNi0.5Mn1.5O4is the focus of the lithium ion battery cathode material.In the work, LiNi0.5Mn1.5O4material was prepared though solid-state reaction using the Ni(CH3COO)2-4H2O、Mn(CH3COO)2·4H2O and Li2CO3as raw materials. The microstructure and morphology of the samples were characterized by TG-DSC, XRD and SEM. The electrochemical performance was evaluated by galvanostatic charge/discharge cycling, CV and EIS. The system of precursor preparation conditions, sintering temperature, sintering time and annealing time are optimized by orthogonal experiment. The experimental results showed that the pure spinel LiNi0.5Mn1.5O4prepared from precursor preparation of nickel manganese compound oxide under400℃for5h, and then with the Li2CO3sintering at850℃for12h, last at650℃annealing for12h which had the best performance. At the discharge rate of0.1C and1C at room temperature, their first discharge capacities were141.59mAh/g and114.77mAh/g. After30cycles at0.1C, its capacity retention were98.59%.In order to improve the electrochemical properties, F" and Cr3+doping alone in LiNi0.5Mn1.5O4were prepared by solid state method. The effect of doping with different content on the mirostructure and electrochemical properties of the LiNi0.5Mn1.5O4were investigated. The experimental results show that When F" doped (x=0.05) LiNi0.5Mn1.5O3.95F0.05had the best electrochemical performance. The ratio of material and cycle performance of reversibility were improved, and charge transfer impedance was reduced. At the discharge rate of0.1C,0.5C,1C,2Cand5C at room temperature, their first discharge capacities were123.03mAh/g,110.4mAh/g,102.34mAh/g,88.32mAh/g and82.82mAh/g. After50cycles at0.1C and1C, their discharge capacities were121.57mAh/g and99.92mAh/g, their capacity retention were98.81%and97.3%. When Cr3+doped (x=0.1) LiCr0.1Ni0.45Mn1.45O4had the best electrochemical performance. At the discharge rate of 0.1C,0.5C,1C,2Cand5C at room temperature, their first discharge capacities were131.23mAh/g,125.66mAh/g,119.12mAh/g,104.74mAh/g and78.89mAh/g. After50cycles at0.1C and1C, their discharge capacities were125.28mAh/g and108.6mAh/g, respectively.95.43%and91.17%of the initial discharge specific capacity. The capacity was improved at large rate of discharge.Through solid state method, LiCrxNi0.5-0.5xMn1.5-0.5xO395F0.05(x=0.05,0.1,0.2) were prepared by F-and Cr3+doping together. XRD showed that all samples have high phase purity, without any impurity peak, they still kept the original spinel structure. SEM showed that all samples have obviously octahedral shape. LiCrxNi0.5-0.5xMn1.5-0.5xO3.95F0.05could ensure capacity at large rate of discharge and defend voltage platform to decline, at the same time they had good cycle performance. LiCr0.05Ni0.475Mn1.475O3.95F0.05had the best electrochemical performance. At the discharge rate of0.1C,0.5C,1C,2Cand5C at room temperature, their first discharge capacities were134.18mAh/g,128.70mAh/g,123.60mAh/g,119.60mAh/g and97.68mAh/g. After50cycles at0.1C and1C, their discharge capacities were131.47mAh/g and116.8mAh/g, respectively, their capacity retention were97.98%and94.51%.