Free-standing, flexible and stable potassium–sulfur battery enabled by controllable porous carbon cloth

Abstract

Potassium-sulfur (K–S) battery benefits from high specific capacities and natural abundance, which is deemed to be a rational choice to realize large-scale energy-storing applications. Here, a free-standing activated carbon fiber (ACF)@sulfur composite cathode (ACF@S) is designed for K–S batteries through a simple impregnation of melted sulfur into hierarchically porous ACF cloth. Taking advantages of the microstructural diversity manifested as various specific surface area, pore size and morphology, the ACF@S yields remarkable energy-storing capability due to effective dispersion, adsorption and physicochemical anchoring of soluble polysulfides. More importantly, their fiber geometries endow them with continuous channels which facilitate fast reaction kinetics. The relationships between specific surface area of ACF and electrochemical performance are also probed. Compared with ACF-1000@S (1000 is denoted as SSA = 1000 m2 g−1 and so on) and ACF-1200@S, the ACF-1500@S electrode with high content of mesopores delivers high reversible capacity of 310 mA h g−1, indicating great promise for shuttle suppression. Besides, quantitative investigations prove that surface capacitive-controlled processes play crucial role and K2Sn (n = 1,2,3) is verified as the final discharging products through multiple characterizations, including ex situ XPS and HRTEM. Our findings aim to provide essential designs and electrochemistry interpretations of structurally-controlled ACF-based composite cathode for high-performance K–S batteries.