Promoting Granular Lithium Sulfide Growth by Soft Acidic-Hard Basic Ionomer Binder for Lithium-Sulfur Batteries

Abstract

Electrode passivation limits the reversibility of lithium-sulfur (Li-S) batteries. Pivoting from the prevailing approaches that focus on electrode active materials and electrolytes, herein, we introduce a class of S electrode binders based on soft acidic-hard basic (SAHB) ionomers. The SAHB binder contains a soft cation (tetraallyl ammonium ion, TA+) paired with a hard counteranion (nitrate, NO3 -), allowing matched interactions with Li polysulfides (LiPS) via soft acid-soft base (TA+-S x 2-) and hard base-hard acid (NO3 --Li+) pairings. This intermolecular coupling retards LiPS diffusion, promoting three-dimensional granular Li sulfide (Li2S) growth, guided by a high Damkohler number (Da). Consequently, the SAHB binder enables a Li-S cell to achieve a high specific capacity of 1545 mAh gsulfur -1 (corresponding to 92.3% S utilization) and stable capacity retention (71.5% after 300 cycles at a current density of 1 C), outperforming previously reported S electrode binders.