A Covalent Heterostructure of Metal Phosphide Quantum Dots Anchored in N, P Co-doped Carbon Nanocapsules for Fast and Durable Lithium Storage.

Transition-metal phosphides (TMPs) anodes for lithium ion batteries (LIBs) usually show poor rate capability and rapid capacity degradation owing to their low electronic conductivities, huge volumetric changes, as well as inferior reversibility of the discharge product Li3P. Herein, a covalent heterostructure with TMPs quantum dots anchored in N, P co-doped carbon nanocapsules (NPC) has been prepared in which the P element in TMPs is simultaneously doped into the carbon matrix. As a proof of concept, Co2P quantum dots covalently anchored in NPC (Co2P QDs/NPC) is prepared and evaluated as an anode for LIBs. The Co2P QDs/NPC electrode not only demonstrates a high capacity and an extraordinary rate performance but also delivers an impressive cyclability with a high capacity retention of 102.5% after 1600 cycles, one of the best reported values for TMPs-based electrode materials for LIBs. The covalent heterostructure can facilitate the electron/ion transfer and maintain the structural stability during the intensive cycles. Moreover, density functional theory calculations demonstrate that the interfacial covalent coupling can enhance the electrochemical reversibility of the discharge product Li3P in the charge processes via lowering the conversion reaction energies. This work presents an effective interfacial engineering strategy for developing high-performance TMPs anodes for advanced LIBs.