Binder Phase Engineering via Lithium Additives for Advanced Sulfur Cathodes in Lean Lithium–Sulfur Batteries

Abstract

Realizing high energy density lithium-sulfur (Li-S) batteries requires overcoming challenges associated with thick electrodes, such as poor electrolyte penetration and inefficient ion and electron transport. To address these issues, we present an innovative approach involving the modification of polyvinylidene difluoride (PVDF) binders using lithium-based additives (LiF, LiOH, LiNO 3 , LiTFSI). These lithium salts incorporated into PVDF significantly improve electrolyte wettability and reduce electrode pathway complexity, enhancing performance in thick sulfur cathodes. Enhanced sulfur utilization under limited electrolyte conditions stems primarily from the induced α-phase transformation of PVDF and improved ionic conductivity. Notably, LiF-enhanced cathodes exhibited superior performance, achieving 56.4% sulfur utilization and a high specific capacity of 945 mAh g⁻¹ with an electrolyte-to-sulfur ratio of just 8 µL mg⁻¹, representing a substantial improvement over traditional electrodes. Additionally, Li-S cells employing LiF-modified cathodes (200 µm thick, 4.0 mg cm⁻² sulfur loading) demonstrated a specific capacity of 833 mAh g⁻¹ under the same lean electrolyte conditions. This strategy of employing lithium salt additives presents significant potential for the advancement of thick electrode designs capable of effective operation at reduced electrolyte volumes.