Low-Density Fluorinated Silane Solvent Enhancing Deep Cycle Lithium-Sulfur Batteries' Lifetime

Adv Mater. 2021 Sep;33(38):e2102034. doi: 10.1002/adma.202102034. Epub 2021 Aug 2.

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.

Keywords: bifunctional solvents; lithium-sulfur batteries; long-term cycling; low-density electrolytes; ultrathin lithium.