Dual strategies of interface engineering and core–shell structure improve potassium storage performance

Potassium-ion batteries hold practical potential for large-scale energy storage owing to their appealing cell voltage and cost-effective properties. The development of anode materials with high rate capability and satisfactory cycle lifespan, however, is one of the key factors for exploiting this electrochemical energy storage system at practical applications. Here, a bidirectional strategy is reported to obtain a double transition metal selenide CoSe2/ZnSe/C@GO core–shell heterostructure which not only promotes the diffusion of potassium ions for rapid charge transfer, but also relieves the volume expansion in long cycles to ensure the stability of the heterostructure. The results show that the presence of the heterostructure facilitates interfacial electron transport and triggers a variety of electrochemical reactions during potassiation/depotassiation, and that the core–shell structure afforded by graphene oxide stabilizes the internal heterostructure after multiple cycles. Furthermore, a K-ion capacitor is rationally constructed via core–shell heterostructure CoSe2/ZnSe/C@GO anode and commercial activated carbon cathode, the hybrid full device provides an incredibly high energy density (163.08 Wh kg−1) and high power-density (10000 W kg−1), as well as excellent cycling stability (95.6 % capacitance retention after 5200 cycles).