Surface Engineering Research For High Voltage Lithium Cobalt Oxide Batteries

Nowadays,with the continuous development of electric vehicles and consumer electronics,the requirement for the energy density of lithium-ion batteries becomes higher.Rechargeable lithium cobalt oxide(LCO)battery is a kind of battery commercialized by Sony Company in 1991.By increasing its charging voltage,its capacity density and energy density can be improved.However,there are various problems for LCO cycled at high voltage,such as the instability of cathode materials,the dissolution of active materials and the accumulation of inert materials on the surface of cathodes,which make it difficult for LCO to show ideal performance.Therefore,to solve the problems above,we have adopted some relatively simple methods to modify the materials.First,we used hydrothermal method to deposit a layer of Li-Al-PO4 composite on the surface of LCO.This surface modification can effectively protect the cathode materials and prevent its excessive reaction-with electrolyte under high voltage,thus reducing the loss of active materials and the formation of inert materials on the surface.At the same time,Al and P elements from the composite will migrate into LCO after calcination at high temperature,forming the so-called doping layer between the coating layer and bulk of LCO.The presence of Al element can stabilize the structure of the doping layer,while the presence of P element can improve the ability of lithium ion migration on the surface and stabilize the lattice oxygen at high voltage.Furthermore,the capacity of the modified material is 180.4 mAh g-1 after 200 cycles at 4.6 V,and the equivalent capacity retention is 88.6%.In addition,in the full battery system,the modified material can still deliver a capacity of 168.8 mAh g-1 after 100 cycles.In addition,the effect of Mg in the coatings was also investigated.Through coating LMF material on LCO,the cyclic stability of LCO can be effectively improved,but the capacity is not satisfactory.By mixing it with Li-Al-PO4 composite,the multi-element composite can effectively stabilize cycling at 4.6 V and even 4.7 V.Moreover,the polarization is small during the charge discharge process,which has a good effect on maintaining the stability of the material structures.