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 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 3.04.5 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.