Synthesis And Modification Of Li-Ni-Co-Mn-O As A Cathode Material For Lithium-ion Batteries

Cathode materials are key components in lithium ion batteries. Cathode material with high nickel content inlithium ion battery has gained attention from researchers owing to its advantages in high capacity and low cost. However, the first irreversible capacity loss of material, together with the drawbacks including poor cycling performance and rate capability under high charge cut-off voltage, makes the extensive application of cathode materials in lithium ion batteries being restricted. Herein, current research focus is placed on the improvement in electrochemical performance of cathode materials. The research contents and results of the present paper are as follows:1. The homogeneous co-precipitation method was adopted to coat the surface of LiNi0.8Co0.1Mn0.1O2 with a Al2O3 coating layer by using carbamide as precipitator. The crystal structure, microstructure and electrochemical performance of the sample were characterized and measured by XRD, SEM, TEM and charge-discharge measurements. The results indicated that Al2O3 coating effectively prevented the LiNi0.5Co0.1Mn0.1O2 particles from being effectively contacted with electrolyte and suppressed the appearance of side reaction between material and electrolyte, the cycling performance and rate capability were thus improved. The 1% Al2O3 coated LiNi0.8Co0.1Mn.1O2 exhibited relatively high first discharge capacity of 189.56mAh·g-1, the first coulombic efficiency reached 87.95%, preferable cycling performance and rate capability were also obtained.2. The solid state method was employed to coat the reduced graphene oxide on the surface of LiNi0.8Co0.1Mn.1O2. The results demonstrated that the microstructure and crystal structure exhibited no obvious variation before and after coating the reduced graphene oxide. The first discharge specific capacity of LiNi0.8Co0.1Mn.1O2 under low discharge rate decreased after graphene coating. Nevertheless, the discharge capacity was higher at high discharge rate and the cycling performance of the material was also greatly improved. The sample coated with 3%graphene reserved a capacity of 94.71%after being discharged at 0.5C and cycled for 100 times. The coating effect was apparent.3. The effect of different sintering atmospheres on the electrochemical performance of LiNi0.8Co0.1Mn.1O2 material was investigated. The results showed that the samples exhibited favorable hexagonal a-NaFeO2 stratified structure after being treated in air and oxygen atmospheres. The electrochemical performance measurements of samples sintered at different atmospheres indicated that the discharge specific capacity was higher for the material sintered in oxygen atmosphere, however, the capacity retention ratio of cycling performance was lower than that of the sample sintered in air, so was the capacity retention ration when discharge was conducted from high to low rate. It can be found that different sintering atmospheres exerted great influence on the electrochemical performance of materials.