Synthesis And Electrochemical Performance Of High-voltage Spinel Lini_0.5Mn_1.5O₄

LiNi0.5Mn1.5O4can meet the demands of electrochemical performances for large power equipments as a result of its high discharge voltage, power density and lower cost. But, some disadvantages impose restriction on its commercialization, such as discharge capacity reducting quickly at high rate and cycling performance deteriorating at high temperature. To research and improve rate capability and cycling performance of LiNi0.5Mn1.5O4, the material is synthesized by hydrothermal method and solid-state method and modified by MnO2nanosheet.In order to improve rate capability and cycling performance of LiNi0.5Mn1.5O4, we have tried to produce LiNi0.5Mn1.5O4cathode with core-shell structure through a simple hydrothermal mode. During the process of hydrothermal reaction, we can effectively control the speed of the precipitation for transition metal to obtain the carbonate precursor with a certain degree of concentration gradient. After sintering with lithium salt, the obtained LiNi0.5Mn1.5O4not only has concentration gradient in some extent but also possesses a core-shell structure. LiNi0.5Mn1.5O4synthesized through this process route has made greater progress with respect to the rate capability and cycling performance, for example, the discharge capacity can reach to118.6mAh/g at the rate of10C, the capacity retention ratio is close to95%after30cycles at55℃.Spherical LiNi0.5Mn1.5O4particles are prepared by the route of solid-state ball mill and spray drying. They are expected to increase the battery capacity due to a higher tap density and have a more stable structure. LiNi0.5Mn1.5O4sintered at three different temperature all show excellent cycling performance, but the oxygen deficiency rises with the increase of temperature, so the calcination temperature is set at900℃. After annealing treatment, the LiNi0.5Mn1.5O4show extremely excellent cycling performance and rate capability, for example, capacity fading is only4mAh/g when the discharge rate increased from0.5C to2C, they deliver a discharge capacity of108mAh/g at7C, and there is barely capacity fading at1C after50cycles.MnO2nanosheet with two-dimention layer structure has been chosen to modify the surface of LiNi0.5Mn1.5O4. MnO2nanosheet could improve rate capability and initial coulombic efficiency of LiNi0.5Mn1.5O4because of its good electrical conductivity, on the other hand, it can automatically deposit to the surface of LiNi0.5Mn1.5O4forming a core-shell structure to better cycling performance. After coated by MnO2nanosheet, the structure and morphology of the original material do not change. At0.5C, the capacity retentions are all close to100%for different content of MnO2nanosheet modified LiNi0.5Mn1.5O4after50cycles. The sample of the1%MnO2nanosheet coated presents scarcely capacity decrease when current density increases from0.5C to2C, near to130mAh/g, and it delivers a capacity of121mAh/g at5C, expressing superior rate capability.