Graphene Quantum Dot Surface Coating for Improving the Electrochemical Performance of Li-Rich Li1.2Mn0.54Ni0.13Co0.13O2

Lithium-rich Li-ion battery cathode materials possess the virtues of high specific capacities and high working potential, but the severe decay of discharge potential and capacity during repeated cycling hinders the practical applications. Herein, a Li-rich Li1.2Mn0.54Ni0.13Co0.13O2 (LMNCO) material is synthesized by a carbonate co-precipitation method, and then three graphene quantum dots (GQDs)-coated LMNCO materials with different contents of GQDs are fabricated by a solvent evaporation method, in which the GQDs are prepared by a solvothermal method. The GQDs-coated LMNCO material with 3 wt % GQDs demonstrates the best electrochemical performance. For instance, the discharge specific capacity at 0.2C rate is 270.3 mAh g–1. When the charge/discharge current rate increases from 0.2C to 5C, the capacity retention is 47.1%. After 150 cycles at 1C rate, the discharge capacity decreases from 184.2 to 159.4 mAh g–1, with the capacity retained at 86.5%. Surface coating with an appropriate amount of highly conductive GQDs can effectively enhance the electrical conductivity of the LMNCO material and promote the electron transport and charge transfer process and thereby improve the specific capacity and rate performance. Moreover, the GQDs coating layer can impede the side reactions of the active material surface with the electrolyte as well as the surface structure phase transition and therefore boost the cycle stability.