Solvent–Binder Engineering for a Practically Viable Solution Process for Fabricating Sulfide-Based All-Solid-State Batteries

Abstract

The commercial viability of sulfide all-solid-state batteries (ASSBs) has been hindered by limited solvent compatibility in solution processing as sulfide solid electrolytes (SEs) degrade in polar solvents. This constraint significantly restricts binder selection, which is critical for both performance─particularly at low pressures─and processability. This study addresses this critical issue by investigating thermoplastic polyurethane (TPU) as a binder dissolved in 1,6-dichlorohexane (DCH), a solvent specifically tailored for sulfide ASSBs. TPU demonstrates outstanding adhesion properties in composite anode, cathode, and SE layers, which not only enhance the long-term cycling performance but also enable double-cast solution processing with minimal binder content for electrode-SE layer manufacturing. A silicon-graphite (Si-Gr)-based pouch-cell fabricated through this solution process maintained 80% capacity retention over 100 cycles under practical conditions (40 μm SE layer, 25 °C, and 2 MPa), validating its practical feasibility. The successful implementation of this optimized solvent–binding system for solution processing represents a significant advancement toward practical ASSB technologies.