Preparation And Properties Of High Voltage Lithium Ion Battery Material LiNi X Mn 2-x O 4

In order to meet the requirements of new energy vehicles and hybrid electrical vehicles for energy storage and power lithium-ion batteries（LIBs） in contemporary society, research and development of new cathode material is top priority. Spinel LiNi_0.5Mn_1.5O₄ commonly considered as superior cathode material for LIBs, has been won extensive attention owing to its high theoretical capacity（¹47mAh/g）, high energy density, high discharge platform at around 4.7V and low cost. However rapid capacity fading of LiNi_0.5Mn_1.5O₄ also exisit due to electrolyte decomposition and poor rate capability under high temperature. In this paper, in order to address these issues, LiNi_0.5Co_4xMn_1.5-3xO₄ and concentration gradient cathode materials have been synthesized via co-precipitation method, and focuses on annealing technology, Co-doped and concentration gradient have effects on the structure, morphology and electrochemical performances of the materials.Under condition of M2+-NH3·H2O-NaOH reaction system, well dispersion, high density LiNi_0.5Mn_1.5O₄ spherical cathode material has been successfully synthesized via co-precipitation method with the help of sodium hydroxide as precipitant and ammonia as complexing agent. However, in general, carbonate and oxalate are used as precipitants for preparing LiNi_0.5Mn_1.5O₄ cathode material by co-precipitation method. During calcination process, the carbonate and oxalate precursors decomposition and the gases（CO2） releasing from precursors results in loose structure and poor compactness of final material. The impurity phase LixNi1-xO can be further reduced by post-annealing process and completely eliminated at 600℃ after annealing 20 h. Preparing LiNi_0.5Mn_1.5O₄ belongs to Fd3 m space group, micro-sized spherical particles with a diameter of around 6μm, and show excellent electrochemical performances. The initial discharge capacities of prepared cathode materials can reach 130.2mAh/g、126.8mAh/g and 113.5mAh/g at 0.1C, 0.5C and 1C rate in the range of 3.5V⁴.95 V, and it retained 92.9%（0.1C）, 89.2%（0.5C） and 80.0%（1C） of the initial capacities after 100 cycles, respectively.In order to further improve the cycling performance of LiNi_0.5Mn_1.5O₄ cathode material, well-crystallized, octahedral Co-doped LiNi_0.5Mn_1.5O₄ spherical aggregates are successfully prepared by hydroxide co-precipitation with a combinational post-annealing method. The Co-doped material is compared to pure LiNi_0.5Mn_1.5O₄, doping material has higher crystallinity and better cycling perpformance. The results show the special octahedral structure of primary particles of Co-doped LiNi_0.5Mn_1.5O₄ has clear boundary and better crystallization when x=0.02. LiNi0.5Co0.08Mn1.44O4 cathode material can reach 92.1% of the initial discharge capacity（115.5mAh/g） after 100 cycles at 1C.In order to reduce the content of Ni on the surface of LiNi_0.5Mn_1.5O₄ cathode material, to prevent adverse reactions with electrolyte and cation mixing of Li and Ni, the rod aggregations formed spheroidal concentration gradient material by hydroxide co-precipitation with a combinational post-annealing method. At 1C rate, the initial discharge capacity is near to 135.7mAh/g of concentration gradient material, and the specific diacharge capacity can reach 126.3mAh/g after 100 cycles. With the current density increasing to 2C rate, the concentration gradient material discharge capacity is near to 125.5mAh/g, showing excellent high-rate discharge performance.