Graphene/Ta₂O₅ co-coating to improve the electrochemical performance of cathode material LiNi_0.5Co_0.2Mn_0.3O₂ for lithium-ion batteries

The cycling and rate capabilities of LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode material under high cut-off voltage (>= 4.5 V) and high current density have attracted much attention. However, the material's insufficient intrinsic electronic/ion conductivity and interface instability are still key issues restricting its electrochemical performance.In this paper, a graphene/Ta2O5 co-coating layer is successfully fabricated on the surface of NCM523 to form a cathode material of GTa-NCM523 to enhance both the electron and lithium-ion transport during cathode operation. The GTa-NCM523 cathode material achieves a discharge specific capacity of 147.4 mAh g(-1) after 600 cycles at a voltage of 3.0-4.5 V and a rate of 1 C (180 mA g(-1)) with a capacity retention rate of 81.4 %. In contrast, the uncoated NCM523 only retains 63.2 % of its capability. At an elevated rate of 10 C (1800 mA g(-1)), the GTa-NCM523 can achieve a discharge-specific capacity of up to 113.5 mAh g(-1), which is 43.7 % higher than the uncoated NCM523. The co-coating layer can inhibit HF erosion and accelerate the movement of lithium-ions and electrons, which account for the superior electrochemical characteristics of the co-coating layer comprised of graphene and Ta2O5.