Synthesis And Electrochemical Properties Of LiNi_0.5Mn_0.5O₂Cathode Material For Lithium-ion Battery

As a cathode material of lithium-ion secondary batteries, LiNi_0.5Mn_0.5O₂has theadvantages of high working voltages, high specific discharge capacity, stable plateau,and so on, which attracts people’s extensively attention. In this paper, layeredLiNi_0.5Mn_0.5O₂material was synthesized by high temperature solid reaction statemethod and co-precipitation method. Meanwhile, the influence factors in the processof synthesis were optimized, and we used the Al₂O₃as a coating material to improve itsperformance. TG/DTA, XRD, SEM, galvanostatic charge/discharge methods, cyclicvoltammograms, and AC impedance spectroscopy were used in studying materials ofdifferent synthetic methods.High temperature solid state reaction method is extremely simple, so it suit tolarge scale production. In the preparation process of the high temperature solid statereaction method, the initial doped lithium quantity, different sintering temperature andtime were selected as the influence factor of LiNi_0.5Mn_0.5O₂material’s structure,morphology and properties. The experimental results show that the material blendinglithium content over5%was sintered in the air for12h at the temperature of900℃exhibits the best structure, morphology and properties. At the current of0.1C（27.6mAh/g）, the discharge capacity reached to129.77mAh/g at the first time, andthe value was100.85mAh/g after30cycles between the voltage of2.8V⁴.6V.In order to improve the performance of the material, we took the relative complexco-precipitation method to preparation LiNi_0.5Mn_0.5O₂material, and the influence ofpH value to the property was also discussed. The result shows that the LiNi_0.5Mn_0.5O₂sample obtained at the pH of11has the best performance. Compared with the hightemperature solid state reaction method, the discharge capacity reached to208.04mAh/g at the first cycle, and the capacity retain155.38mAh/g after30cycles at thecurrent of0.1C in the same sintering schedule.Finally, the best material prepared from co-precipitation coated by Al₂O₃wasdiscussed, and the research result shows that discharge capacity and the cycleperformance get significant improvement. When the coating quantity is1.5%wt, theLiNi_0.5Mn_0.5O₂material has the optimal performance. At that time, the discharge capacity was197.25mAh/g at the first cycle, and the value was169.96mAh/g after30cycles.