Graphene quantum dots coated LiCoO2 for improved cycling stability and thermal safety at high voltage

Abstract Surface coating is an efficient strategy to enhance the interfacial stability of the electrode. Graphene quantum dots (GQDs) have advantages of excellent dispersion in water, outstanding electron and ion conductivities and high specific surface area. In this work, GQDs were coated directly on the surface of LiCoO2 particles (GQDs-LiCoO2) through liquid phase method. Compared to bare LiCoO2, the cycling performance, rate capacity and thermo-stability of the GQDs-LiCoO2 have been significantly improved in the voltage range of 3.0–4.5 V. GQDs-LiCoO2 showed a much higher capacity retention than that of bare LiCoO2 (82.8 % vs 46.1 %) after 100 cycles at 0.5 C. The excellent improvement of the GQDs-LiCoO2 was mainly attributed to the formation of a uniform, stable, dense and well-conductive protective layer on the surface of LiCoO2 particles by the surface coating of GQDs. The detailed analysis of the cycled electrodes reveals that the GQDs coating stabilizes the crystal structure of LiCoO2 and suppresses undesirable interfacial side reactions between the cathode and electrolyte, leading to the improvement of battery performance.