Research And Development Of5V LiNi_0.5Mn_1.5O₄Cathode Material For Lithium-ion Batteries

LiNi_0.5Mn_1.5O₄is of great interest as a high-voltage cathode material forlithium ion battery, and has been extensively investigated in the past decades. By far,it was reported that the structure and electrochemical properties of the LiNi_0.5Mn_1.5O₄are sensitive to the preparation conditions. Moreover, the LiNi_0.5Mn_1.5O₄prepared at ahigh annealing temperature （≥850oC） adopts a cubic spinal structure with a high-symmetry （space group Fd3m）, whereas it adopts a primitive simple cubic structurewith a low symmetry （space group P4₃32） if it was annealed at a low temperature（≤700oC）. Furthermore, LiNi_0.5Mn_1.5O₄with different space group has differentelectrochemical behavior. In general, LiNi_0.5Mn_1.5O₄prepared at a high temperaturehas a relative low discharge capacity, while if it was prepared at a low temperature; itwill exhibit a high discharge capacity. However, LiNi_0.5Mn_1.5O₄prepared at a lowtemperature usually has a poor cyclic performance when it was operated at hightemperature at a high rate. Based on the problem, this work employs severalapproaches such as re-treated in N₂, Al-substituted for Ni and Mn, Ti-substituted forMn. All of which significantly improve electrochemical properties. The conclusionshave been summarized as following:1. LiNi_0.5Mn_1.5O₄prepared by a spray drying method was re-treated in N₂at500,600, and700C, respectively. Comparative studies were carried out between them.-The space group of the LiNi_0.5Mn_1.5O₄transforms from P4₃32to Fd3m when theannealing temperature is above700C. The electrochemical characteristics of thetreated samples are closely related to the annealing temperature. The sample treated inN₂at500C shows both an improved rate capability and cyclic performance at a hightemperature compared with the as-prepared sample, while the sample treated in N₂at700C dramatically shows decrease in its reversible capacity.2. LiNi_0.5-xAl_2xMn_1.5-xO₄（0≤2x≤0.15） was prepared by a spray drying method. The substitution of Al for Ni and Mn in the LiNi_0.5Mn_1.5O₄results in the structural-transformation from P4₃32to Fd3m in terms of the space group, which is believed torelate to the increase of the lithium diffusion coefficient, and consequently upgradethe rate capability. Moreover, Al substitution for Ni and Mn can effectively suppressthe dissolution of manganese into the electrolyte solution when electrode wasoperated at50oC, which is significantly improve the cyclic performances at a highrate at50oC.3. LiNi_0.5Mn_1.5O₄（0≤x≤0.2） was prepared by a spray drying method and theirstructural and electrochemical properties were studied roughly. The substitution of Tifor Mn does not change the space group. All of them remain a space group of P4₃32.The substitution of Ti for Mn decreases the charge transfer resistance, whichsignificantly improves the rate capabilities and the cyclic performances at a high rateat room temperature. Unfortunately, the substitution of Ti for Mn can not improve thecyclic performance at a high temperature. More work is necessary to study onLiNi_0.5Mn_1.5O₄（0≤x≤0.2）.