A Bipolar Solvent Molecule Design for Wide-Temperature High-Voltage Lithium Metal Batteries

Abstract

Integrating Li metal anode (LMA) with a high-voltage NCM811 cathode is considered a pragmatic path in the pursuit of high-energy-density electrochemical energy storage systems. Yet, their practical application is still plagued by suboptimal cycling behavior. Numerous reports have already upgraded the cycle life of Li metal batteries (LMB) through anion-derived electrode-electrolyte interphase (EEI), but the adverse consequence brought by the inevitable decomposition of organic solvents is often underestimated. Here, a bipolar solvent molecule (1-Butanesulfonyl fluoride, BSF), is engineered by fusing an F-SO₂ polar head for dissociating Li salts and contributing to the construction of EEI, along with a (CH₂)₄ nonpolar tail to lower molecular polarity and enhance wettability. Within the BSF-based electrolyte, FSI⁻ anions and BSF coexist in the Li⁺ solvation shell, jointly contributing to the development of inorganic-rich EEI. Supported by robust interphases and expedited interfacial kinetics, the Li||NCM811 full cells (N/P = 1.05–1.8) exhibit favorable electrochemical performance over a wide temperature range from −40 to +55 °C. Furthermore, a 5.2 Ah Li metal pouch cell with a high cathode loading of 30 mg cm⁻² and lean electrolyte (1.9 g Ah⁻¹) delivers an energy density of 470 Wh kg⁻¹ and achieves 100 stable cycles.