Electron-beam sintering achieves dual-phase transparent solid-state electrolytes for batteries

Amorphous–crystalline dual-phase grain structure often enables materials with unique performance. This is especially the case for the garnet-type solid-state electrolyte Li ₇ La ₃ Zr ₂ O ₁₂ (LLZO), which is a promising candidate for hybrid and all-solid-state lithium batteries. A major synthesis challenge, however, is that amorphous LLZO is difficult to retain via conventional sintering and even Flash Joule heating. Using electron beam focused to sub-millimeter scale with point-by-point scanning, we achieved highly localized heating to very high temperature followed by ultrafast quenching, enabling the direct fabrication of uniformly fine-grained amorphous–crystalline dual-phase LLZO. Fast ion transport offered by the crystalline grains, together with the amorphous shell that promotes a more homogeneous space-charge distribution at grain boundaries, markedly enhance the critical current density, cycling stability, and optical transparency. Our scalable fabrication route offers unparalleled tunability in electrochemical performance, and also has broad applicability for other functional ceramic systems requiring optimized electrical and optical properties.