Less is More: 1.0 wt%BiBr3 Enabled a Superlithiophlic Interface on Garnet for Solid‐state Batteries

Garnet‐type Li6.4La3Zr1.4Ta0.6O12 (LLZT) 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, the introduction of only 1.0 wt% BiBr3 into molten lithium at 280 °C in situ forms a mixed ion‐electronic conductor (MIEC) comprising Li3Bi and LiBr, which significantly enhances the wettability of LLZT. Thanks to its uniqueness, the BiBr3‐modified symmetric cell achieves a remarkably low interfacial resistance (15.7 Ω cm2) compared to pristine lithium (1280 Ω cm2). Furthermore, Li3Bi and LiBr provide excellent ionic conductivity and serve as superior lithium nucleation sites, guiding uniform lithium deposition on its surface and thereby suppressing dendrite formation. Therefore, it achieves a high critical current density (1.4 mA cm‐2) and stable cycling over 1100 hours at 0.1 mA cm‐2 at room temperature. When paired with a LiFePO4 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% BiBr3 effectively constructs a superlithiophilic interface on garnet electrolyte, offering a simple and effective strategy for high‐performance SSLMBs.