Three birds with one stone: A multifunctional water-soluble binder for enhanced the performance of lithium-sulfur batteries

Abstract

Though polyvinylidene fluoride (PVDF) is commonly employed as a binder for lithium-sulfur (Li-S) batteries, it still faces the challenge of serious electrode fracture caused by dramatic volume changes during cycling, and lacks extended functions such as capturing dissolved lithium polysulfides (LIPSs) and promoting Li⁺ transfer. Herein, a multifunctional water-soluble binder lithium sulfonated cellulose (Cel-SO₃Li) is designed and prepared. The Cel-SO₃Li binder can capture LIPSs due to nucleophilic substitution reaction between -SO₄Li and dissolved LIPSs. Its abundant hydroxyl groups provide excellent electrode mechanical properties, which effectively alleviate sulfur volume changes during cycling. Furthermore, the -SO₃Li groups also enhance the diffusion of Li⁺ in the electrodes. In addition, density functional theory calculations reveal that the Cel-SO₃Li exhibits strong affinity and catalytic ability for LIPSs, indicating that it can effectively suppress the shuttle effect and enhance their reaction kinetics. Therefore, the electrode using Cel-SO₃Li binder reach a high initial discharge capacity of 1165 mAh/g at 0.5 C, remain 545 mAh/g after 1000 cycles with a low capacity decay rate of 0.053 % per cycle. This study proposes the concept of a multifunctional and environmentally friendly binder with the ability of "three birds with one stone" (high adhesion, fast Li⁺ diffusion, effective capture and even catalysis for LIPSs), which will contribute to accelerating applications of Li-S batteries.