Inner-stress-dissipative, rapid self-healing core-shell sulfide quantum dots for remarkable potassium-ion storage

Metal chalcogenides are considered as one of the most attractive anode materials for potassium ion batteries (PIBs), owing to their abundant resource, low cost and high energy density. Nevertheless, the issues of poor structure stability and capacity degradation caused by the intrinsic inner stress during (de)potassiation processes, have impeded the practical applicability. Herein, an effective inner-stress-dissipative strategy of constructing a core-shell architecture is designed for PIBs. Specifically, binary metal sulfide CoFeS2 quantum dots are intimately wrapped by in-situ formed carbon layer, which are also homogeneously distributed into the graphene matrix, establishing a robust core-shell structure. This rational constructed CoFeS2/C can effectively relieve the inner mechanical stress, restraining the continuous pulverization of active material. Furthermore, the covalent interaction formed between internal quantum dots and external carbon shell can strengthen the electrode integrity, achieving the effect of self-healing during the long-term potassiation processes. Additionally, the reaction kinetics can also be vastly improved with this unique nanostructure. Consequently, the CFS/C electrode operates an excellent nanostructure stability with enhanced cycling lifespan (1200 cycles at 2 A g−1 with a capacity of 205 mAh g−1) and a desirable rate capability (172.4 mAh g−1 at 10 A g−1) for PIBs. More importantly, combined with multiple in-situ/ex-situ characterizations and COMSOL simulations, the mechanism of effective inner-stress-dissipative are comprehensively revealed, providing an instructive guidance for designing other anode materials of advanced energy storage devices.