Tactical hybrids of Li+-conductive dry polymer electrolytes with sulfide solid electrolytes: Toward practical all-solid-state batteries with wider temperature operability

The chemical vulnerability of sulfide solid electrolyte (SE) materials to organic polar solvents complicates the wet-slurry fabrication of sheet-type electrodes and SE films for practical all-solid-state Li batteries (ASLBs). Moreover, the disruption of interfacial Li+ conduction by binders is problematic. This could be relieved by blending with liquid electrolytes but at the expense of the ASLBs' thermal stability. In this study, a new tactical approach to hybridize sulfide SEs with thermally stable and slurry-fabricable dry polymer electrolyte (DPE)-type binders is reported. Along with their practicability, ester solvents bearing bulky hydrocarbons, such as benzyl acetate, dissolve both polymers and Li salts (e.g., LiTFSI) while undamaging sulfide SEs. The use of the DPE-type binder, NA-LiTFSI (NA: nitrile butadiene rubber-poly(1,4-butylene adipate)), for LiNi0.70Co0.15Mn0.15O2 (NCM) electrodes significantly improves their electrochemical performance at 30 °C. Moreover, NA-LiTFSI is highly functional at 70 °C (from 180 to 200 mA h g−1 and from 84.2 to 91.8% for initial Coulombic efficiency) and applicable for other electrodes, such as graphite (from 265 to 330 mA h g−1) and Li4Ti5O12, which is in stark contrast to the solvate ionic liquid-type binder Li(G3)TFSI. Finally, pouch-type NCM/graphite ASLBs employing electrodes made of NA-LiTFSI binders were also fabricated.