Symmetric dual-interphase design enables stable lithium-metal anodes for high rate ultrahigh-nickel all-solid-state batteries.

Ultrahigh-nickel all-solid-state lithium metal batteries (ASSLMBs) are promising for high-energy storage, yet their high-rate operation is limited by unstable sulfide electrolyte/lithium metal interfaces. The large lithium flux generated by LiNi0.9Mn0.05Co0.05O2 (NCM955) cathodes aggravates interfacial side reactions, nonuniform current distribution, and dendrite-induced short circuits, making stable cycling beyond 1C difficult. Herein, an asymmetric dual-interphase design is developed to regulate the ion-transport and electron-reaction processes at the sulfide/lithium interface. A highly ion-conductive Li-Al alloy is introduced on the electrolyte side to reduce interfacial transport resistance, while an in situ evolved Ta/Li hybrid phase is constructed on the lithium metal side to enhance electronic delocalization, homogenize the current distribution, and regulate lithium deposition. This cooperative interphase design increases the critical current density to 4.8 mA cm-2 and enables stable high-rate cycling of NCM955-based ASSLMBs. The full cell delivers an initial discharge capacity of 193.2 mAh g-1 and operates for 500 cycles at 1.25C without short circuiting; even at 2.5C, it maintains stable cycling for 170 cycles with an initial capacity of 144.3 mAh g-1.