Gel Polymer Electrolyte Selection for Cathode of Solid-State Lithium–Sulfur Batteries

Compared with conventional liquid electrolytes, solid-state electrolytes in lithium-sulfur batteries can efficiently counteract shuttle effects and bolster safety. Gel polymer electrolytes (GPEs) can inherit the advantages of all-solid-state electrolytes while preserving high ionic conductivity and achieving excellent interface contact. In this study, solvent molecules within GPEs are classified as either free or bound solvents, with the quantity of free solvent molecules playing a crucial role in determining the viscosity of GPEs. An increase in the free solvent molecular viscosity significantly boosts the discharge capacity and rate performance; a lower Guttmann donor number (DN) facilitates capacity retention, and a higher dielectric constant (ε) promotes the reduction of internal polarization. The theoretical framework employed for selecting a GPE is proven to be highly effective, as evidenced by the exceptional electrochemical performance demonstrated by the chosen poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) electrolyte, providing valuable insights and encouraging further development of GPEs in lithium-sulfur batteries.