Resreach On Doping And Coating Modification Of 5V Cathode Material LiNi_0.5Mn_1.5O₄ For Lithium Ion Battery

]In recent years, due to the increasing crisis of energy and environment and the rapid development of electronic information industry, more and more attentions have been paid to the lithium-ion batteries. Comparision with the anode and electrolyte, the cathode materials of lithium ion batteries have been crucial factors that restrict their development and application. 5V cathode material spinel LiNi_0.5Mn_1.5O₄ is proved to be one of the studying hotspots of lithium ion cathode materials since its stable structure and high discharge voltage. However, the disadvantage of capacity fade limits its commodification. In this paper, spinel LiNi_0.5Mn_1.5O₄ was synthesized by sol-gel method, and co-doping and surface coating modifications have been adopted to enhance the cycling performance, respectively.Firstly, the method of Cr³⁺ and F- co-doping was used to improve the cycling stability of LiNi_0.5Mn_1.5O₄ cathode material, and the effects of substitution of different transition metal elements by Cr³⁺and Cr3 + content were investigated. The studies showed that Cr³⁺ and F- co-doping did not change the structure of material, and significantly improved the cycling stability and rate capability. By the comprehensive comparison, LiNi_0.5Mn_1.4Cr_0.1O_3.95F_0.05 showed the best performance. It expressed higher capacity at 4.7 V platform, and the capacity retention was 93.8% after 100 cycles.Cation vacancy was introduced into the co-doping materials to enhance the rate capacity. The prepared LiNi0.325Mn1.5Cr0.1O3.95F0.05 showed the excellent rate capability and stable cycle performance. Its discharge capacities were 123.89 mAh·g^-1 and 104.44 mAh·g^-1 at 5C and 10C discharge rate, respectively, and the capacity retention was 97.5% after 50 cycles at 0.2C charge-discharge current. CV and EIS measurements showed that the enhancement of rate performance was due to the existence of vacancies, which reduced the resistance of lithium ion deintercalation and improved solid diffusion coefficient and the electrochemical activity.Secondly, AlF₃ and TiO₂ were coated on the surface of LiNi_0.5Mn_1.5O₄, and the influence on the cycling performance caused by the coating content of AlF₃ and TiO₂ was researched. It was found that the coating AlF₃ can effectively restrict the corrosion of the cathode materials and the dissolution of active substances, and the effect was getting more outstanding with the increase of coating amounts. The electrochemical performance of LiNi_0.5Mn_1.5O₄ with 3 mol% coating AlF₃ was the best, the capacity was 119.23 mAh·g^-1 with capacity retention of 94.5% mAh·g^-1 at room temperature after 50 cycles, while it was 116.29 mAh·g^-1 with capacity retention of 84.0% after 50 cycles at 55℃. The coating TiO₂ played a role of HF collectors. When the coating amount was 3 mol%, it showed the best cycling performance. The capacity retention was 92.5% after 100 cycles at room temperature, and 77.9% after 50 cycles at 55℃.