Molecular level distribution of black phosphorus quantum dots on nitrogen-doped graphene nanosheets for superior lithium storage

Highlights: • A facile strategy is developed for molecular level distribution of BP QDs on N-graphene. • The small size of BP QDs ensures abundant active sites and short diffusion pathways. • The molecular level distribution of BP QDs on N-graphene prevents their aggregation. • N-graphene buffers the mechanical stress and constitutes a conductive network. • The van der Waals heterostructures exhibit superior electrochemical performances. Black phosphorus (BP) is a rising star shining in the field of electrochemical energy storage because of its ability to react with up to three lithium to form a Li₃P compound, giving a theoretical capacity as high as 2596 mA h g⁻¹. However, inherent embarrassments such as low electronic conductivity and huge volume expansion drastically deteriorate its ultimate electrochemical performances. Although hybridizing BP with a conductive matrix (e.g., graphene) is a fascinating concept, its extremely high chemical inertness sets obstacles for constructing reliable interfacial interactions with graphene. Herein we report, for the first time, a facile strategy for the molecular level distribution of BP quantum dots (QDs) on nitrogen-doped graphene (N-graphene) nanosheets. The small size of the BP QDs translates into abundant active sites, short lithium diffusion pathways and little mechanical fracture, which mean excellent electrochemical kinetics. The molecular level distribution of these QDs on the N-graphene nanosheets effectively prevents their aggregation upon cycling, thereby preserving the whole structure and maintaining good stability. Besides, the N-graphene nanosheets not only buffer the mechanical stress associated with cycling, but also constitute a conductive network to ensure reversible electron transport. The synergistic superiority of the resulting van der Waals heterostructures is well demonstrated by their superior electrochemical performances, delivering a startlingly high reversible capacity of 1271 mA h g⁻¹ at 500 mA g⁻¹. We believe this strategy may provide a new route to addressing the capacity deficiency which limits the progress of LIBs towards large-size power tools.