Pillar effect induced by ultrahigh phosphorous/nitrogen doping enables graphene/MXene film with excellent cycling stability for alkali metal ion storage

Graphene’s large theoretical surface area and high conductivity make it an attractive anode material for potassium-ion batteries (PIBs). However, its practical application is hindered by small interlayer distance and long ion transfer distance. Herein, this paper aims to address the issue by introducing MXene through a simple and scalable method for assembling graphene and realizing ultrahigh P doping content. The findings reveal that MXene and P−C bonds have a “pillar effect” on the structure of graphene, and the P−C bond plays a primary role. In addition, N/P co-doping introduces abundant defects, providing more active sites for K+ storage and facilitating K+ adsorption. As expected, the developed ultrahigh phosphorous/nitrogen co-doped flexible reduced graphene oxide/MXene (NPrGM) electrode exhibits remarkable reversible discharge capacity (554 mA h g−1 at 0.05 A g−1), impressive rate capability (178 mA h g−1 at 2 A g−1), and robust cyclic stability (0.0005% decay per cycle after 10,000 cycles at 2 A g−1). Furthermore, the assembled activated carbon||NPrGM potassium-ion hybrid capacitors (PIHCs) can deliver an impressive energy density of 131 W h kg−1 and stable cycling performance with 98.1% capacitance retention after 5000 cycles at 1 A g−1. Such a new strategy will effectively promote the practical application of graphene materials in PIBs/PIHCs and open new avenues for the scalable development of flexible films based on two-dimensional materials for potential applications in energy storage, thermal interface, and electromagnetic shielding.