Marcasite-FeS2@carbon nanodots anchored on 3D cell-like graphenic matrix for high-rate and ultrastable potassium ion storage

Abstract Marcasite-FeS2 has significant potential as an anode material for potassium-ion batteries (KIBs) for its lower band gap, high theoretical capacity, low cost and environmental friendliness but suffers poor cycle stability and rate capability. Here, we design a marcasite-FeS2@carbon nanodots anchored on 3D cell-like S, N co-doped graphenic matrix (m-FeS2@C-SSNFG). The 3D graphenic matrix is constructed by graphenic cages and sustained by conductive graphitic struts that can curb the agglomeration of graphenic sheets during cycling. Remarkably, the yolk-shell m-FeS2@graphenic cage structure not only ensures uniform dispersion of m-FeS2 on the cell wall, but also offers enough void room to accommodate the volume expansion of m-FeS2. Meanwhile the graphitic carbon shell wrapped around m-FeS2 also prevents the active m-FeS2 nanodots from agglomeration and dissolving into electrolyte. It is worth underlining that the phase transition from semiconductor (m-FeS2) to conductor (KxFeS2) is firstly validated through first-principles calculations, beneficial to the electron transfer and K-ions diffusion in subsequent cycles. Besides, optimizing electrolyte and cut-off voltage can further boost its long-term cycle stability. Thus, it delivers high capacity of 419 mA h g−1 after 100 cycles at 0.05 A g−1 and ultralong cycle stability of 140 mA h g−1 at 5 A g−1 over 4000 cycles.