Low‐Density Fluorinated Silane Solvent Enhancing Deep Cycle Lithium–Sulfur Batteries’ Lifetime

Abstract The lithium metal anode (LMA) instability at deep cycle with high utilization is a crucial barrier for developing lithium (Li) metal batteries, resulting in excessive Li inventory and electrolyte demand. This issue becomes more severe in capacity‐type lithium–sulfur (Li–S) batteries. High‐concentration or localized high‐concentration electrolytes are noted as effective strategies to stabilize Li metal but usually lead to a high electrolyte density (>1.4 g mL⁻¹). Here we propose a bifunctional fluorinated silane‐based electrolyte with a low density of 1.0 g mL⁻¹ that not only is much lighter than conventional electrolytes (≈1.2 g mL⁻¹) but also form a robust solid electrolyte interface to minimize Li depletion. Therefore, the Li loss rate is reduced over 4.5‐fold with the proposed electrolyte relative to its conventional counterpart. When paired with onefold excess LMA at the electrolyte weight/cell capacity (E/C) ratio of 4.5 g Ah⁻¹, the Li–S pouch cell using our electrolyte can survive for 103 cycles, much longer than with the conventional electrolyte (38 cycles). This demonstrates that our electrolyte not only reduces the E/C ratio but also enhances the cyclic stability of Li–S batteries under limited Li amounts.