Confined Biomimetic Catalysts Boost LiNO3-Free Lithium-Sulfur Batteries via Enhanced LiTFSI Decomposition

Abstract

Lithium-sulfur batteries face a critical challenge

LiNO₃ limits the electrochemical stability window of electrolyte and poses safety risks. This study presents FePC@NH₂-MIL-68, a biomimetic enzyme catalyst stable in ether-based electrolytes, to address these issues, which can replace LiNO₃ and facilitate Li-anion decomposition. Theoretical and spectroscopic investigations show it promotes LiTFSI decomposition, forms robust CEI and SEI interfaces, and enhances sulfur conversions. Consequently, the FePC@NH₂-MIL-68 cell, without LiNO₃ additive, delivers a high discharge capacity of 1549 mAh g⁻¹ at 0.2 C and a low capacity decay rate of 0.067% over 1000 cycles at 1.5 C. Even under high sulfur loading of 7.9 mg cm⁻² and low electrolyte-to-sulfur ratio of 5.5 μL mg⁻¹, the cells maintain 720 mAh g⁻¹. This work emphasizes that in developing sulfur conversion catalysts, special attention must be paid to their effects on other lithium salt components, which provides a guidance for new catalysts design for metal-sulfur batteries.