Enhancing 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 notorious issues of "shuttle effect" in lithium-sulfur batteries. However, the intrinsic sluggish kinetics of the SPAN cathode posts challenges to the practical application of Li-SPAN batteries, particularly under high current density. Herein, an innovative SPAN cathode material was designed to deal with 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 the oxygen-mediated pre-cyclization, which is characterized with low activation energy, slow reaction rate and limited reaction extent. The vulcanization of as-prepared PAN displays enhanced stability and reduced production of defective structure, while sufficiently preserving the C-H bonds as the active sites for vulcanization, resulting in 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 applied with air200-SPAN cathode material exhibited a superior cycling stability at a challenging 3 C (1 C=600 mA h g-1) current density over 1400 cycles, with a retained capacity of 427 mA h g-1 (based on 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 these critical challenges while offering valuable insights toward the realization of high-performance lithium-sulfur batteries.