Dynamic cross-linking of zwitterionic polymer binder based on host–guest interactions for Li-S batteries with enhanced safety and electrochemical performance

Abstract

The commercial application of lithium–sulfur (Li–S) batteries is gravely hindered by the large volume alteration, lithium polysulfides shuttling, poor ion conduction, and safety concerns. Especially under lean electrolyte and high S-loaded operation, the dramatic volume change and slow ion transport efficiency may cause a rapid capacity fading, inferior reversible capacity, and even security hazards. Herein, a dynamic cross-linking zwitterionic supramolecular binder (β-CDp-Cg-2AD) is skillfully designed to confront these issues. The amphiphilic zwitterionic would contribute to immobilize lithium polysulfide and promoting the polysulfides redox kinetics through the strong ion–dipole interactions, along with the formation of PO4--Li+ and RNH3+-S42- pairs and electron transfer. Meanwhile, the dynamic cross-linking system based on host-guest interactions enables robust cathodes to withstand volume changes and provide a relatively low cross-linking density for Li+ transmission. Combining with a wealth of oxygen heteroatoms and like polyether chain segment, the Li+ transport efficiency is further enhanced through polymer chains thermal motion in β-CDp-Cg-2AD electrode. Benefiting from these attributes, even under 7.36 mg cm−2 S-loaded and sparing electrolyte of 7.1 µL mg−1, the β-CDp-Cg-2AD electrode can also remain a high areal specific capacity of 7.60 mAh cm−2 and 96 % capacity retention after 100 cycles. Moreover, the TG-FTIR test is performed to explore the flame-retardant mechanism of β-CDp-Cg-2AD, indicating their fire safety improvement. This work not only provides a high-performance and safety improvement binder for the practical application, but inspires the exploration of the flame-retardant mechanism of all electrode components.