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

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+–Sx2–) 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 Damköhler 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.