Less is More: 1.0 wt% BiBr ₃ Enabled a Superlithiophlic Interface on Garnet for Solid‐State Batteries

Garnet‐type Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 solid‐state electrolytes (SSEs) have attracted considerable attention for solid‐state lithium metal batteries (SSLMBs) due to their high ionic conductivity, wide electrochemical window, and excellent stability towards lithium. However, poor interfacial contact hinders charge transport and increases impedance. Herein, introducing only 1.0 wt% BiBr 3 into molten lithium at 280 °C in situ forms a mixed ion–electronic conductor (MIEC) of Li 3 Bi and LiBr, significantly enhancing wettability. Thanks to its uniqueness, the modified symmetric cell achieves a remarkably low interfacial resistance (15.7 Ω cm 2 ) compared to pristine lithium (1280.3 Ω cm 2 ). Furthermore, lithiophilic Li 3 Bi with high ionic conductivity improves the interfacial adhesion and regulates the Li nucleation. Meanwhile, the lithiophobic LiBr, with high interfacial energy against Li, enables effective suppression of the growth of Li dendrites by promoting the lateral growth of deposited Li metal. Therefore, it achieves a high critical current density (1.4 mA cm −2 ) and stable cycling over 1100 h, at 0.1 mA cm −2 at room temperature. When paired with a LiFePO 4 cathode, the cell retains 91.6% of its initial capacity after 300 cycles at 0.5 C, demonstrating excellent cycling stability. These findings suggest that the incorporation of 1.0 wt% BiBr 3 effectively constructs a superlithiophilic interface on garnet electrolyte, offering a simple and effective strategy for high‐performance SSLMBs.