A zwitterionic polyethyleneimine binder in lithium-sulfur batteries: synergistic effects of polysulfide anchoring and Li+ transport promotion

Abstract

Lithium-sulfur (Li–S) batteries are regarded as a promising candidate for next-generation energy storage technologies due to their high theoretical capacity and energy density. However, their practical application remains constrained by critical issues such as the polysulfide shuttle effect and cathode volume expansion. To address this, a multi-functional zwitterionic polyethyleneimine-based binder (PEI-LiCF) was synthesized via nucleophilic substitution between branched polyethyleneimine (PEI) and the highly polar lithium 3-chloropropyltrifluoromethylsulfonyl imide (LiCPSI). Structural analysis confirmed the successful incorporation of oppositely charged groups—quaternary ammonium (positive) and sulfonyl imide (negative)—which form a zwitterionic network. The electrostatic interactions within this network enhance Li⁺ migration and improve its diffusion kinetics. Furthermore, the abundant polar groups in the network exhibit strong polysulfide-anchoring capabilities. With an optimized PEI:LiCPSI mass ratio of 2 : 1 (denoted PEI-LiCF₂), Li–S batteries employing this binder exhibit excellent electrochemical performance, even under a high current density of 1 C. They achieved an initial discharge capacity of 815.7 mAh g⁻¹, maintaining a reversible capacity of 511.9 mAh g⁻¹ after 500 cycles, which corresponds to an ultralow decay rate of merely 0.074% per cycle. This multifunctional water-soluble binder therefore represents a promising candidate material for high-performance Li–S batteries.