Weakly Solvating Electrolyte: Regulating Polysulfide Intermediates for High‐Performance Lithium‐Sulfurized Polyacrylonitrile Batteries

Abstract Electrolyte engineering plays a crucial role in the design of high energy‐density lithium‐sulfurized polyacrylonitrile (Li‐SPAN) batteries, a promising energy storage technology. However, current predominant electrolyte systems face challenges of anode dendrite growth and cathode polysulfide loss, which limit the cycling stability of Li‐SPAN batteries. Here, a weakly solvating electrolyte (WSE) primarily composed of diethoxy methane (DEM) is proposed to simultaneously address challenges at both electrodes. At the anode, DEM's weakly solvating capability accelerates both Li + diffusion and desolvation, preventing out‐of‐plane Li deposition and dendrite formation caused by high concentration gradients at the anode surface. More significantly at the cathode, weakly solvated Li + exhibits stronger Lewis acidity, preferentially stabilizing S 3 2− intermediates via hard Lewis acid‐base interaction. These higher‐reduction‐state intermediates promote faster subsequent lithiation and deposition reactions, reducing polysulfide loss while improving both rate and cycling performance of the batteries. These performance enhancements and the corresponding mechanisms are supported by electrochemical and spectroscopic characterizations. With this WSE, Li‐SPAN batteries achieve exceptional cycling stability (0.087% capacity fade per cycle over 500 cycles at 1 C), and pouch cell cycle life increases from 9 to 35 cycles with 90.6% capacity retention. This strategy provides valuable insights for developing high‐performance Li‐SPAN batteries.