Aqueous Quaternary Polymer Binder Enabling Long-Life Lithium–Sulfur Batteries by Multifunctional Physicochemical Properties

Lithium–sulfur batteries (LSBs) have been considered promising candidates for application in high-density energy storage systems owing to their high gravimetric and volumetric energy densities. However, LSB technology faces many barriers from the intrinsic properties of active materials that need to be solved to realize high-performance LSBs. Herein, an aqueous binder, that is, PPCP, based on polyethyleneimine (PEI), polyvinylpyrrolidone (PVP), citric acid (CA), and polyethylene oxide (PEO), was developed. The synthesized PPCP binder has incredible mechanical properties, suitable viscosity, and essential functional groups for developing an effective and reliable LSB system. This study demonstrates that CA is crucial in cross-linking PEI–PVP polymer molecules, and PEO segments significantly enhance the flexibility of the PPCP binder; thus, the binder can mechanically stabilize the cathode structure over many operating cycles. The redistribution of active materials during the charge–discharge processes and reduction of the shuttle effect originate from the excellent chemical interactions of PPCP with lithium polysulfides, which is confirmed by the density functional theory calculation, enabling an ultra-long electrochemical cycle life of 1800 cycles with a low decay rate of 0.0278% cycle–1.