Reimagining interface processing in solid-state batteries via electrochemical flash sintering

Abstract

Electrochemical flash sintering (EFS) is a newly developed, solvent-free technique for ultrafast (∼2 s) densification of lithium-containing solid-state battery materials. Unlike conventional flash sintering—which relies on uncontrolled thermal runaway and requires high electronic conductivity—EFS couples electronic conduction in mixed conductors with Li⁺ transport across interfaces with pure ionic conductors in composite or multilayer architectures. Using spatially resolved synchrotron total scattering and pair distribution function analysis, we elucidate the mechanisms of EFS, contrasting them with conventional flash sintering of single-phase materials. Under conventional conditions, Li₃V₂(PO₄)₃ (LVP) undergoes localized decomposition and cracking at low frequencies and high currents, while Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) requires high frequencies to overcome blocking behavior—resulting in electrode melting, infiltration, and vitreous extrusion at the pellet perimeter. In contrast, EFS enables densification of LVP–LATP composites at lower frequencies that fail for either phase alone, with reactions confined to localized hotspots. In an LVP–LATP|LATP|LVP–LATP multilayer, decomposition products are more broadly distributed, including vanadium migration into the electrolyte; nonetheless, no preferential cracking or new phases were observed at electrode–electrolyte interfaces. These findings establish EFS as a viable one-step processing strategy for integrating (electro)chemically distinct phases and lay the groundwork for its broader adoption in the dry fabrication of solid-state electrochemical energy storage systems.