Preparation And Properties Of Lithium Manganese-based Cathode Materials Coated With Li₂MO₃?M=Zr?Si?

Currently,lithium-ion batteries are widely used and need to be continuously researched to meet the growing demand for new applications.The layered lithium-rich manganese-based cathode material xLi₂MnO₃·?1-x?LiMO₂?0<x<1,M=Mn,Co,Ni?does not contain cobalt or nickel,and it is cost-effective.Compared with the traditional cathode material?LiCoO₂,LiFePO₄,etc.?,it has a higher specific capacity(greater than 200 mAh·g^-1),but it still exists some problems,such as the first irreversible capacity loss and low coulombic efficiency,rate performance and poor cycle performance,etc.In this work,the lithium-rich lithium material Li[Li_0.2Ni_0.2Mn_0.6]O₂ is studied.The optimized Li[Li_0.2Ni_0.2Mn_0.6]O₂ was coated with lithium ion conductor Li₂MO₃?M=Zr,Si?to improve the first coulombic efficiency,cycle performance and rate performance of the material,conducted the following study:?1?Prepared Li[Li_0.2Ni_0.2Mn_0.6]O₂ by sol-gel method.The effects of lithium content,sintering temperature,complexing agent ratio and holding time on the morphology and electrochemical properties of the materials were investigated by means of XRD,SEM and electrochemical performance tests.The conclusions were as follows:during the preparation of samples by sol-gel method,the amount of lithium,sintering temperature,complexing agent ratio and holding time will affect the morphology and electrochemical properties of the materials.When the amount of lithium was 5wt.%and the complexing agent ratio was 1:1,the Li[Li_0.2Ni_0.2Mn_0.6]O₂synthesized at 900?for 10 h had the most complete crystal form and the best electrochemical performance.The first discharge specific capacity of 0.1C was 256.7mAh·g^-1and the coulombic efficiency was 71%.After 30 cycles of cycling at 0.5C,the specific discharge capacity was 180 mAh·g^-1and the capacity retention rate was89.1%.?2?Different proportions?0wt.%,1wt.%,3wt.%,5wt.%?of Li₂ZrO₃ layers were successfully coated on the surface of the above-mentioned optimized lithium-rich material Li[Li_0.2Ni_0.2Mn_0.6]O₂ by sol-gel method.The Li₂ZrO₃ coating layer did not change the morphology and crystal structure of the sample.The presence of the coating layer can be clearly seen under TEM.When the coating layer was 1wt.%,the first discharge specific capacity of 0.1C was 271.5 mAh·g^-11 and the Coulombic efficiency was 72.4%and reduce the first capacity loss at the same time.After 100cycles of 0.5C cycle,the specific discharge capacity was 191.5 mAh·g^-1,and the capacity retention rate was 89.5%,which was much higher than 63.7%of the uncoated sample.The discharge specific capacity was 75 mAh·g^-1 at 5C rate,and the rate performance was improved obviously.However,when the amount of coating was large,the material properties were affected,and the optimum coating ratio was1wt.%.?3?Different proportions?0wt.%1wt.%,2wt.%,3wt.%?of Li₂SiO₃ layer were successfully coated on the surface of Li[Li_0.2Ni_0.2Mn_0.6]O₂ by synchronous lithium enrichment.The Li2ZrO3 coating did not change the morphology of the sample,which caused the?003?peak in the XRD pattern to shift to the left,indicating that a small amount of Si⁴⁺was doped into the sample.The presence of the coating layer can be clearly seen under TEM.When the coating amount was 2wt.%,the first discharge specific capacity of 0.1C was 241.5 mAh·g^-1and the coulombic efficiency was 73.1%.After a 100-cycle of 0.5 C rate,the specific discharge capacity was 126.3mAh·g^-1and the capacity retention rate was 86.5%,which was much higher than62.5%of the uncoated sample.The rate performance improvement was obvious.