Tailoring Slurries Using Cosolvents and Li Salt Targeting Practical All‐Solid‐State Batteries Employing Sulfide Solid Electrolytes

Abstract Polymeric binders that can undergo slurry fabrication and minimize the disruption of interfacial Li⁺ contact are imperative for sheet‐type electrodes and solid electrolyte films in practical all‐solid‐state Li batteries (ASLBs). Although dry polymer electrolytes (DPEs) are a plausible alternative, their use is complicated by the severe reactivity of sulfide solid electrolytes and the need to dissolve Li salts. In this study, a new scalable fabrication protocol for a Li⁺‐conductive DPE‐type binder, nitrile‐butadiene rubber (NBR)‐LiTFSI, is reported. The less‐polar dibromomethane and more‐polar hexyl butyrate in cosolvents work synergistically to dissolve NBR and LiTFSI, while preserving Li₆PS₅Cl_0.5Br_0.5. It is found that the dispersion of NBR can be controlled by the fraction of the antisolvent (hexyl butyrate), which in turn affects the corresponding performance of the ASLBs. Sheet‐type LiNi_0.70Co_0.15Mn_0.15O₂ electrodes tailored using NBR‐LiTFSI outperform those prepared using the conventional insulating binder (NBR) in terms of capacity (163 vs 147 mA h g⁻¹) and initial Coulombic efficiency (78.9 vs 70.4%), which is attributed to the facilitated interfacial Li⁺ transport, as confirmed by ⁶Li nuclear magnetic resonance and electrochemical measurements. Moreover, NBR‐LiTFSI is functional at 70 °C and in a graphite anode. Finally, the promising performance of pouch‐type LiNi_0.70Co_0.15Mn_0.15O₂/graphite ASLBs is also demonstrated.