Expanded Nanofibrous Cellulose Electrode Binder: Declustering Lithium Polysulfides for Lean-Electrolyte Li‒S Batteries

Despite their potential as an alternative to commercial lithium (Li)‒ion batteries, Li–sulfur (Li–S) batteries face challenges related to energy density limitations caused by the considerable amount of electrolyte required. Lean electrolytes have proven effective in mitigating this issue. However, they tend to exacerbate Li polysulfides (LiPS) clustering, resulting in incomplete S utilization and sluggish conversion kinetics. Here, 2,2,6,6-tetramethylpiperidin-1-oxyl radical (TEMPO)-oxidized cellulose nanofiber (TOCN) is presented as an expanded nanofibrous electrode binder for lean-electrolyte Li‒S batteries. Owing to its 1D fibrous structure and expanded inter-glucose chain distance, the TOCN binder offers more accessible active sites for intermolecular interactions with LiPS. Consequently, LiPS cluster formation is effectively suppressed even at a low TOCN binder content of 1 wt%, while a high S loading of 72 wt% is achieved. The resulting S cathode with the TOCN binder enables Li‒S cells to exhibit a remarkable specific capacity of 1221 mAh g_sulfur⁻¹ under constrained electrolyte conditions (low electrolyte-to-sulfur ratio of 2.0 µL mg_sulfur⁻¹ and low density of 0.927 g mL⁻¹), yielding a high cell-level energy density of 503 Wh kg⁻¹ that surpasses those of previously reported S cathodes based on conventional synthetic polymer binders.