Aqueous\nQuaternary Polymer Binder Enabling Long-Life\nLithium–Sulfur Batteries by Multifunctional Physicochemical\nProperties

Abstract

Lithium–sulfur\nbatteries (LSBs) have been considered promising\ncandidates for application in high-density energy storage systems\nowing to their high gravimetric and volumetric energy densities. However,\nLSB technology faces many barriers from the intrinsic properties of\nactive materials that need to be solved to realize high-performance\nLSBs. Herein, an aqueous binder, that is, PPCP, based on polyethyleneimine\n(PEI), polyvinylpyrrolidone (PVP), citric acid (CA), and polyethylene\noxide (PEO), was developed. The synthesized PPCP binder has incredible\nmechanical properties, suitable viscosity, and essential functional\ngroups for developing an effective and reliable LSB system. This study\ndemonstrates that CA is crucial in cross-linking PEI–PVP polymer\nmolecules, and PEO segments significantly enhance the flexibility\nof the PPCP binder; thus, the binder can mechanically stabilize the\ncathode structure over many operating cycles. The redistribution of\nactive materials during the charge–discharge processes and\nreduction of the shuttle effect originate from the excellent chemical\ninteractions of PPCP with lithium polysulfides, which is confirmed\nby the density functional theory calculation, enabling an ultra-long\nelectrochemical cycle life of 1800 cycles with a low decay rate of\n0.0278% cycle^–1.