Revealing interfacial parasitic reactions of nitrile rubber binders in all-solid-state lithium batteries

Developing all solid-state batteries (ASSBs) employing inorganic solid electrolytes is currently attracting much attention due to their possibility of improved safety in a wide operating temperature range and increased energy density compared to those from traditional lithium ion batteries. Among various kinds of solid electrolytes (SEs), sulfide SEs are widely recognized as one of the most promising candidates as they exhibit high lithium ion conductivity comparable to that of liquid electrolytes. However, it is well realized that sulfide SEs have a limited electrochemical potential window, which is closely linked to unfavorable side reactions with other components (e.g., active materials, conductive carbon, and binders) during battery operation. Herein, for the first time, we reveal a parasitic reaction of nitrile butadiene rubber (NBR), mainly used in the fabrication of wet-process electrodes for ASSBs, and also systematically investigate the chemical decomposition of nitrile substitutions in NBR, resulting in a huge interfacial resistance in the sulfide-composite electrode. To address this challenge, we propose modifying the chemical stability of nitrile groups by introducing Li ions. This modification helps suppress side reactions during the initial charge-discharge process and ultimately enhances battery performance. The nitrile components in NBR lead to an irreversible side reaction during the initial charging process. However, the problematic chemical stability of NBR has been improved through coordination chemistry, resulting in enhanced battery performance.