Internal interface engineering of yolk-shell structure toward fast and robust potassium storage

Advanced anode materials with stable and fast K-ion storage behavior are of great significance for potassium-ion batteries (PIBs) toward large-scale applications, while it still remains a big challenging due to their intrinsic poor conductivity and large volume variation during cycles. Herein, we develop an internal interfacial engineering by encapsulating core-shell NiS₂@C nanoparticles within MOF-derived hollow carbon shell for superior PIB anodes. As-prepared yolk-shell NiS₂@C@C composite integrates the structure superiority of abundant interior void space, outer protective carbon shell and internal conductive carbon layer. Comprehensive experimental and theoretical methods illuminate that internal NiS₂/C interface is conductive to boost charge transport kinetics, enhance pseudocapacitive behavior, and mitigate mechanical stress in outer carbon shell. As a result, it manifests an ultrahigh capacity of 481 mA h g⁻¹ at 0.2 A g⁻¹, and guarantees the rate capability of 306 mA h g⁻¹ at 20 A g⁻¹. Moreover, it presents excellent cycle stability (358 mA h g⁻¹ after 1600 cycles at 1 A g⁻¹), which is extremely competitive among the best reported conversion anodes for PIBs.