Interface-induced fast Li⁺ transport in mixed ionic-electronic conductors

Interfacial instability between lithium metal and solid-state electrolytes limits the performance of all-solid-state lithium metal batteries (ASSLBs), leading to parasitic reactions, non-uniform Li⁺ flux, and dendrite growth. Here, we develop a composite interlayer composed of the anti-perovskite Li₂OHCl_0.75Br_0.25 (AP) and carbon nanotubes (CNTs) to enhance both interfacial stability and ionic transport. The AP-CNT interlayer exhibits enhanced Li⁺ conductivity arising from interfacial electron transfer from AP to CNTs, which generates a built-in electric field that facilitates Li⁺ migration. Lithium symmetric cells incorporating this interlayer achieve a high critical current density of 2.4 mA cm^-2 at 55 °C. This design integrates chemical robustness with coupled ion-electron transport, offering a generalizable strategy for safe, dendrite-free, and high-performance ASSLBs.