An interweaving 3D ion-conductive network binder for high-loading and lean-electrolyte lithium-sulfur batteries

The binder plays a crucial role in maintaining the integrity and enhancing the conductivity of the electrode, although it accounts for a small weight fraction in the entire electrode. However, the conventional binder used in lithium-sulfur (Li-S) batteries fails to effectively tackle the challenges posed by the shuttle effect of lithium polysulfides, as well as the issues of poor conductivity and volume expansion of sulfur. These limitations greatly hinder the performance and overall efficiency of Li-S batteries. In this study, a waterborne polyurethane binder with lithium-ion (Li-ion) conductivity and an elastic 3D network structure is synthesized, integrating a diverse range of functional groups. The polyethylene glycol in the polyurethane binder significantly enhances the Li-ion conductivity due to its abundant electronegative oxygen atoms, consequently reducing the need for electrolyte. The presence of multi-functional polar groups endows the polymer binder with notable adsorption capability, effectively mitigating the undesirable shuttle effect. The 3D network formed by the crosslinking reaction between polyurethane and the aziridine crosslinker enables the accommodation of volume expansion during cycling. Benefitting from these characteristics, the designed waterborne binder endows the Li-S batteries with improved long-cycle stability and rate capability compared to polyethylene oxide and polyvinylidene fluoride binders under lean electrolyte conditions. A waterborne multifunctional 3D network binder is elaborately developed for lithium-sulfur batteries to accommodate the volume expansion, adsorb lithium polysulfides, and provide satisfactory Li-ion conductivity under lean electrolyte conditions.