Synthesis And Electrochemical Performance Of Cathode Materials Coated With Co-Al Mixed Metal Oxide For Lithium Ion Battery

Lithium ion battery is the primary choice of the green battery in the 21th century due to its advantages such as high operating voltage, brilliant cycle stability, high theoretical capacity and environmental friendly. Spinel lithium manganese oxide (LiMn2O4) with the merits of abundant manganese resources, low cost, low toxicity and ease of preparation, is a most promising candidate material for lithium ion battery. However, its cyclic stability is poor in nonaqueous electrolytes, especially at a higher temperature above 55℃. The capacity fading is mainly due to dissolution of Mn2+, Jahn-Teller effect and corrosion of HF. At present, layered LiCoO2 is the major cathode material of commercial lithium ion battery. However, the main problems of LiCoO2 cathode material are its expensive cost, low practical capacity, poor overcharge tolerance. The main reason is that the crystal structure of LiCoO2 materials undergoes irreversible phase transformation as the lithium ions deintercalate during the charging process. In order to improve cycling property of LiMn2O4 at high temperature and overcharge tolerance of LiCoO2, this paper mainly involves two aspects with surface treatment:(1) LiMn2O4 coated with Co-Al layered double hydroxide (CoAl-LDH) precursor is calcined to obtain Co-Al mixed metal oxide (CoAl-MMO) coated LiMn2O4. The CoAl-LDH coated LiMn2O4 precursor is prepared by constant value of pH titrate method, the separate nucleation and aging steps (SNAS) method and the complex coprecipitation method(constant value of pH titrate method and the SNAS method). The effects of different mehods of preparation of CoAl-LDH coated LiMn2O4 precursor on the structure, morphology and electrochemical performance of CoAl-MMO coated LiMn2O4 have been studied, the complex coprecipitation method is best. Then we study the effect of coating amounts on the structure, morphology and electrochemical cycling performance of CoAl-MMO coated LiMn2O4 prepared by the complex coprecipitation method.(2) LiCoO2 coated with CoAl-LDH precursor prepared by coprecipitation method is calcined to obtain CoAl-MMO coated LiCo02. The CoAl-MMO coating stabilizes the crystal structure, and improves the overcharge tolerance and cycling performance of LiCoO2. When the voltage range is 2.75-4.2 V and 2.75-4.4 V, and the discharge rate is 1C, the initial discharge capacity of CoAl-MMO (1.0wt.%Co,0.17wt.%Al) coated LiCoO2 is 141 mAh-g-1 and 160 mAh·g-1, and the 400th capacity retention is 93.8%and 91.3%, which is better than 87.5% and 69.2% of pristine LiCoO2 respectively.