Improved electrochemical performances of LiNi0.5Co0.2Mn0.3O2 modified by Graphene/V2O5 co-coating

In order to reduce the capacity degradation and improve the rate performance of LiNi0.5Co0.2Mn0.3O2 (NCM523), some decisive factors including structural stability, electronic conductivity and lithium ion diffusion coefficient are envisaged to be increased. For this purpose, surface coating with high electronic or ion conductive materials is generally conducted. Previous studies have proved that V2O5 possesses superior Li+ intercalation/deintercalation ability and low Li+ diffusion barrier, and graphene has high electronic conductivity and great HF resistance. Thus, the graphene/V2O5 co-coating is designed to improve the electrochemical performances of NCM523 in this study. The modified material retains a stable structure with low polarization and impedance. Besides, the discharge capacity is 207.7 mAh/g with 14.4 mAh/g improvement and the capacity retention is 93.1% with 7.6% enhancement at 0.1 C (1 C = 180 mAh/g) between 3 and 4.5 V after 100 cycles, and the rate performance approaches to 108.5 mAh/g at 10 C with the increasement of 54.3%. The improved performances are attributed to the following reasons: the co-coating effectively resists HF attacks on NCM523; lithium ion diffusion coefficient, storage capacity and electronic conductivity of the cathode material are simultaneously improved.