Enhancing the backbone regularity of sulfurized polyacrylonitrile for long-life Li-SPAN batteries

Abstract

The intrinsic solid–solid reactions of sulfurized polyacrylonitrile (SPAN) cathode materials present a compelling solution to tackle the serious issue of “shuttle effect” in lithium–sulfur batteries. However, the intrinsic sluggish kinetics of the SPAN cathode poses challenges to the practical application of Li-SPAN batteries, particularly under high current density. Herein, an innovative SPAN cathode material was designed to overcome the inherent kinetic limitations via a two-step strategy, including controllable pre-cyclization and stabilized vulcanization. The cyclization degree of PAN is ingeniously controlled at relatively low temperatures through oxygen-mediated pre-cyclization, which is characterized by low activation energy, slow reaction rate and limited reaction extent. The vulcanization of the as-prepared PAN leads to enhanced stability and reduced production of defective structures while sufficiently preserving the C–H bonds as the active sites for vulcanization, resulting in an air200-SPAN material with decreased defects and a highly regular backbone structure, which exhibits improved electronic conductivity and ionic diffusion. As a result, the Li-SPAN battery with the air200-SPAN cathode material exhibited superior cycling stability at a challenging 3C (1C = 600 mA h g⁻¹) current density over 1400 cycles, with a retained capacity of 427 mA h g⁻¹ (based on the composite) and an ultra-low capacity fading rate of 0.01% per cycle, demonstrating superior cycling stability. This work has illustrated its potential to address the critical challenges while offering valuable insights toward the realization of high-performance lithium–sulfur batteries.