The Modification Research And Properties Of Cathode Material LiCoO₂

Currently, LiCoO2 is using as the best cathode material of lithium ion batteries in the commerce. This is due to its excellent electrochemical properties, high energy density in volume and mass and easy synthesis, but the structure is unstable. The metal ion-doped and graphene coated LiCoO2 is explored by high temperature solid state method in the paper,First,Mg-doped LiMgxCo1-xO2 (x=0,0.01,0.03,0.05) phases are synthesized by high temperature solid state method. Magnesium improves the electrical conductivity and reduces the resistance of the battery, it also improves structural stability. Although the sample synthesized by doping with 0.03 Mg2+ displayed slightly lower discharge capacity than bare LiCoO2. which could reach 128 mA·h/g at 0.2C respectively. But it has the best cycling performance in all samples.Second,Ni-doped LiMg0.03NixCo0.97-xO2 (x=0,0.01,0.03,0.05) phases are synthesized by high temperature solid state method. The sample synthesized by doping with 0.03 Ni2+ displayed the highest discharge capacity 113 mA·h/g at 3C respectively. It is preferred electrochemical performance, while having a smaller impedance and good rate capability. The material which doped by Mg and Ni could overcome the shortcomings of poor high rate ability in only Mg doped and terrible cyclic ability in only Ni doped.Finally,LiMgxNiyCo1-x-yO2/C (x=0、y=0,x=0.03、y=0,x=0、y=0.03,x=0.03、 y=0.03) phases are synthesized after graphene coating LiMgxNiyCo1-x-yO2,The sample synthesized by doping with 0.03 Ni2+ displayed the highest discharge capacity. LiNi0.03Co0.97O2/C are 138 mA·h/g and 119 mA·h/g at 0.2C and 3C respectively. Capacity is very stable after 40 cycles. While LiMg0.03Co0.97O2/C showed the worst discharge capacity, they are 127 mA·h/g and 95 mA·h/g at 0.2C and 3C respectively. Mg and the graphene coating joint action the battery to reduce much more discharge capacity. While the material which doped by Ni and graphene coating could improve defect of poor high rate ability in only graphene coating and terrible cyclic ability in only Ni doped. They can improve cell conductivity and table maintenance structure. LiNi0.03Co0.97O2/C is the best electrochemical performance in all done tests.