Flexible composite fiber paper as robust and stable lithium-sulfur battery cathode

The lithium-sulfur battery (LSB) is a highly promising energy storage system with merits of exceptional theoretical specific capacity and energy density. However, challenges including insufficient sulfur conductivity, volume expansion, and the polysulfide shuttle effect result in rapid capacity decay and limited cycle life of the LSB, which significantly hinders its development. Inspired by the structure and forming process of paper, a fiber double network skeleton was constructed using flexible pulp fiber (PF) and highly conductive carbon fiber (CF). Following the principles of wet end chemistry in papermaking, MXene nanosheets with high adsorption and catalytic capacity for polysulfides were self-assembled on the surfaces of PF and CF to fabricate composite paper-based materials. The interwoven mesh of PF exhibited strong binding force and stable structure, providing support and protection for the CF interwoven mesh, resulting in a composite material with abundant porosity and excellent structural stability. Moreover, the CF interweaving network combined with an overlaid MXene interweaving network established an effective three-dimensional conductive pathway. When utilized as a self-supporting cathode in LSB, this composite paper-based material demonstrated outstanding cyclic stability. Under conditions of sulfur load at 2.3 mg·cm⁻² and discharge at 0.2 C, the specific discharge capacity remained at 952 mAh·g⁻¹ after 200 cycles with a capacity retention rate reaching 95.4%. The CF/PF@Mxene (CPCMX) also exhibited excellent tensile strength measured at 7.19 MPa while maintaining exceptional flexibility and electrolyte wettability. This research presents a highly promising solution for advancing the development of LSB with superior cycle stability.