Complementary Anion‐Cation Modulated Electrolyte with Balanced Conductivities for High‐Performance All‐Solid‐State Lithium‐Metal Batteries

Solid-state electrolytes with superionic conductivity and high compatibility with lithium-metal anode are essential for high specific energy all-solid-state batteries. Here, we develop an argyrodite-type solid-state electrolyte that enables fast Li⁺ transport and excellent interfacial compatibility with Li metal through a cooperative anion-cation modulation strategy. A robust anodic interface is spontaneously formed via the in situ reaction between Li metal and the tailored electrolyte. The cation Mo introduced into the electrolyte can be reduced to form a lithiophilic Li-Mo alloy, while the anion N is capable of forming highly Li-compatible Li₃N. These interfacial products promote uniform Li stripping/plating and suppress parasitic reactions at the anodic interface. Meanwhile, Mo incorporation weakens the strong N─Li electrostatic interaction, ensuring rapid Li⁺ migration within the electrolyte. The modulated electrolyte exhibits high dynamic stability and Li reversibility at the anodic side, enabling Li//Li symmetric cells to cycle stably for over 3100 h at 0.5 mA cm^-2. The Li//LiNi_0.8Co_0.1Mn_0.1O₂ batteries demonstrate an ultra-stable long cycle life with 75% capacity retention over 1500 cycles at 4C (3.0 mA cm^-2), accompanied by an outstanding average coulombic efficiency of 99.99%. This work highlights an anion-cation cooperative modulation strategy for designing electrolytes that enable high-performance all-solid-state lithium-metal batteries.