Dual‐Interface Regulation of Cyclic Thioether Electrolyte Additives for Enhancing the Cycling Stability of High‐Voltage Lithium Metal Batteries

The development of high‐energy‐density lithium metal batteries (LMBs) using carbonate electrolytes is severely hindered by unstable interfacial chemistry, leading to uncontrolled lithium dendrite growth and rapid performance degradation. Given that the electrode/electrolyte interface property is highly dependent on the interface interactions, this work introduces 1,4‐dithiane (1,4‐DH), an environmentally benign cyclic thioether, as a multifunctional additive for stabilizing electrode‐electrolyte interfaces in conventional carbonate electrolytes without fluorinated solvents. The 1,4‐DH additive exhibits preferentially adsorption on both Li metal anodes and NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ) cathodes, displacing solvent molecules from electrode surfaces to suppress solvent decomposition while driving localized PF 6 − enrichment at the electrode interfaces via a robust binding interaction. The additive undergoes preferential self‐decomposition during cycling to form sulfur‐rich SEI (solid‐electrolyte‐interphase)/CEI (cathode electrolyte interphase), promoting synergistic decomposition of PF 6 − simultaneously to form inorganic‐dominated interphases (LiF, Li 2 S). As a result, the lithium iron phosphate full cell achieves 87.54% capacity retention and 99.99% average coulombic efficiency over 3000 cycles. Crucially, 1,4‐DH stabilizes NCM811 cathodes against cracking, enabling prolonged cycle stability at 4.8 V. The additive further demonstrates exceptional adaptability under extreme conditions (−10 and 60 °C) and practical pouch cell configurations. This work provides a practical strategy for durable LMBs via non‐fluorinated electrolyte engineering.