From electrochemical flash sintering (EFS) to high-frequency flash sintering (HF-FS) of ionic conductors

• High-frequency flash sintering (HF-FS) enables ultra-rapid densification of ionic conductors using blocking electrodes (Pt, Au), eliminating the need for reactive interfaces. • Single-step fabrication of multilayered ceramic devices (e.g., LVP-LATP stacks) achieved in seconds, preserving electrochemical integrity. • 92% density in LATP without electrolysis, overcoming a major limitation in conventional flash sintering of ionic conductors. • Paves the way for next-generation all-solid-state batteries (ASSBs) with tailored microstructures. The development of all-solid-state electrochemical devices, such as batteries and solid oxide cells, is constrained by conventional high-temperature sintering, which is energy-intensive and limits material compatibility. In this work, we extend and generalize the Electrochemical Flash Sintering (EFS) to enable the single-step production of multilayered materials such as Li3V2(PO4)3 (LVP)/ Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP)/ Li3V2(PO4)3 (LVP). To address the inherent limitation of Flash Sintering (FS) of purely ionic conductors (LATP), namely, the requirement for reversible electrochemical reactions at the current collector/ceramic interface, we demonstrate that high-frequency (100 kHz) power pulse can trigger the flash event while bypassing interfacial constraints, regardless of electrode type. Experimental results show high densification in less than 10 seconds for LATP using blocking electrodes (Au). By decoupling the flash event from interfacial electrochemistry, this High-Frequency Flash Sintering (HF-FS) approach expands the range of compatible materials and applications, offering a rapid and electrochemically compatible route for fabricating advanced all-solid-state devices.