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

ABSTRACT 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 Li 3 N. 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 0.8 Co 0.1 Mn 0.1 O 2 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.