Synthesis Of LiNi_0.5Mn_1.5O₄ As A High-voltage Cathode Material For Lithium-ion Batteries

Lithium-ion battery is a green chemical power due to their characteristics of high operating voltage,high energy density,long cycle life and environmental friendliness.However,developing cathode materials with high energy density is one of the great problems for using lithium ion batteries in electric vehicle(EV)and hybrid electric vehicle(HEV).High-voltage LiNio.5Mnl.5O4 is a one of the promising power battery cathode materials because of its high voltage region at around 4.7 V and acceptable cycling performance.Developing a new molten salt method is designed to synthesize spinel LiNi0.5Mn1.5O4 cathode material with relatively good performance.The reaction medium NaCl without lithium compound is in-situ formed in the process of precursor preparation via room temperature solid-state reactions.The effect of different heating temperatures on structure,particle morphology and electrochemical performance of the products was investigated.The results show that increasing heating temperature promotes the growth of particles,but having no obvious effect on the morphology.The sample obtained at 1000℃ has the best electrochemical performance.Moreover,LiNi0.5Mn1.5O4 was synthesized by molten salt method using KCl as the reaction medium,showing poorer properties,and the KCl was prepared by using KOH instead of NaOH in the room temperature solid-state reactions.LiNio.5Mm.5O4 was synthesized using different annealing times and the extra lithium addition.The results indicate that the two samples obtained at annealing 40 h and adding 11%extra lithium showing superior electrochemical performance.Its can deliver a high capacity of 133.8 mAh·g-1 and 131.2 mAh·g-1,respectively.LiNi0.5Mn1.5O4 material was synthesized by molten salt method and solid state reaction.The mechanism of the precursors containing chlorides can promote the formation of octahedral crystal was studied.The chlorides are the raw materials,NH4CI or forming in-situ by adding concentrated hydrochloric acid.The results show that the decomposition product HCl vapor of chlorides can promote the formation of octahedral crystal.The using of chlorides will be replaced by bromides or fluorides.The results prove that the decomposition product HBr vapor has the similar effect and contrary to HF vapor due to lower decomposition temperature.Electrochemical test shows that LiNio.5Mru.5O4 cathode materials with octahedral crystal exhibit superior rate performance and showing a high capacity retention ratio about 90%.