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

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 LiCoO 2 particles (GQDs-LiCoO 2 ) through liquid phase method. Compared to bare LiCoO 2 , the cycling performance, rate capacity and thermo-stability of the GQDs-LiCoO 2 have been significantly improved in the voltage range of 3.04.5 V. GQDs-LiCoO 2 showed a much higher capacity retention than that of bare LiCoO 2 (82.8 % vs 46.1 %) after 100 cycles at 0.5 C. The excellent improvement of the GQDs-LiCoO 2 was mainly attributed to the formation of a uniform, stable, dense and well-conductive protective layer on the surface of LiCoO 2 particles by the surface coating of GQDs. The detailed analysis of the cycled electrodes reveals that the GQDs coating stabilizes the crystal structure of LiCoO 2 and suppresses undesirable interfacial side reactions between the cathode and electrolyte, leading to the improvement of battery performance.