Study On The Surface Coating Technology By Solid State Reaction At Room Temperature Of LiMn₂O₄ Cathode Materials For Lithium-ion Batteries

Spinel LiMn₂O₄ is one of the most promising cathode materials of 21^st century because of high working voltage,excellent security,low manufacture cost,and environment friendly.But large-scale application is restricted own to poor electrochemical cycleability and evident capacity fading specially at elevated temperature.In order to restrain capacity fading,the research work was focused on surface modification for LiMn₂O₄ cathode by solid state reaction at room temperature for the first time.Firstly,the LiMn₂O₄ cathode was coated with Al₂O₃ by solid state reaction at room temperature.And the effects of synthesis conditions, such as coating quantity of Al₂O₃,milling pattern and by-products,on surface morphology,crystal structure and electrochemical performance of LiMn204 were investigated.On this basis,the technology was optimized as below:the coating quantity of Al₂O₃ was 1.0wt%,after planetary milling(milling speed was 180rpm),Al₂O₃-coated LiMn₂O₄ material together with by-products was calcinated at 700℃for 3h.The results showed that the structure of Al₂O₃-coated LiMn₂O₄ was spinel and that the size of particles were uniform with the average diameter of 1.0～2.0μm.The optimized Al₂O₃-coated LiMn₂O₄ had an initial capacity of 127.8mAh/g at 0.5C(74mA/g) with a voltage window of 3.2～4.35V. The capacity retentions were about 97.9%during the first 50 cycles at 0.5C and about 99.6%during the second 50 cycles at 1C separately.And at 2C the initial capacity was 120mAh/g,which showed a good cycleability and ratio performance.Its capacity retained 97.1%after cycling 50 times at 55℃,which showed good performance at elevated temperature.Besides that,the MgO coating experiment by solid state reaction at room temperature was studied.MgO-coated LiMn₂O₄ cathode material exhibited an excellent cycleability,specially at elevated temperature, which initial capacity was 124.1mAh/g and capacity retained 98.8%after cycling 50 times at room temperature,and which initial capacity was 123.2mAh/g and capacity retained 97.4%after cycling 50 times at 55℃.Finally,the surface coating mechanism for LiMn₂O₄ cathode material of solid state reaction at room temperature was also studied. Kinetic factors of solid state reaction at room temperature were investigated.On the condition of fulfiling the law of thermodynamic (â–³_rG_m＜0),water of crystallization,milling and fine reactant particles were beneficial to increase the reaction ratio.