Synthesis And Modification Of LiNi_0.5Mn_1.5O₄Cathode Material For Lithium-ion Battery

With the development of lithium-ion battery industry, it is imperative to study thebatteries with high specific energy density and power density. The spinelLiNi0.5Mn1.5O4meets the above requirements wonderfully by means of its highoperating voltage (4.7V vs. Li/Li+) and high capacity (146.7mAh·g-1). In this paper,the preperation of LiNi0.5Mn1.5O4material by paraffin-assisted combustion processhas been first studied. The surface modifaction of LiNi0.5Mn1.5O4with LiCoO2/Co3O4composite has been first put forward. The electrochemical performance ofLiNi0.5Mn1.5O4/graphite and LiNi0.5Mn1.5O4/Li4Ti5O12full cells also has beeninvestigated.The LiNi0.5Mn1.5O4cathode material was prepared by paraffin-assistedcombustion process using lithium, nickel, manganese chloride as raw materials andparaffin as combustion agent. The optimal process was presented by studing theinfluence of calcination temperature and time to the structure and performance of thematerial. The test results show that LiNi0.5Mn1.5O4calcined at750℃for6h has thebest electrochemical performance, with a discharge capacity of131.2mAh·g-1at0.2Crate. After500cycles at1C,3C,5C and10C, the discharge capacities are113.8,119.7,121.7and99.2mAh·g-1, retaining88.6%,91.7%,97.3%and89.2%of themaximal attainable discharge capacities, respectively. It can be concluded thatLiNi0.5Mn1.5O4calcined at the optimal process has good rate capability and cycleperformance.The LiNi0.5Mn1.5O4cathode material prepared by sol-gel method wassurface-modified by LiCoO2/Co3O4composite. The results show that LiCoO2/Co3O4composite has been successfully coated on the surface of LiNi0.5Mn1.5O4particles, andthe electrochemical performance is improved remarkably. The initial dischargecapacities of the modified LiNi0.5Mn1.5O4improve9.1,9.6and11.6mAh·g-1at ratesof1C,3C and5C, respectively. In addition, the modified LiNi0.5Mn1.5O4retains97.8%of the maximal attainable discharge capacity (110.1mAh·g-1) after200cyclesat the rate of5C. The improvement of the electrochemical performance can be attributed to the acceleration of the electron transfer and suppression of the sidereactions by the LiCoO2/Co3O4suface modification.The electrochemical performance of positive-limited LiNi0.5Mn1.5O4/graphite fullcell was investigated. The intial discharge capacities of the full cell at0.2C,0.5C and1C rates are83.4,74.3and66.9mAh·g-1, after100cycles at the same rates, thecapacity retention ratios are67.3%,69.9%and72.5%, respectively. Theelectrochemical performance of positive-limited and negative-limitedLiNi0.5Mn1.5O4/Li4Ti5O12full cells was also studied. The results show thatnegative-limited full cell has better electrochemical performance, retaining90.7%,79.8%and74.5%of the maximal discharge capacities after100cycles at0.5C,1Cand2C rates, respectively.