Gibbs Free Energy‐Driven Li– MgF ₂ Composite Anodes for Stable Solid‐State Lithium Batteries

Solid‐state lithium batteries (SSLBs) with the garnet electrolyte of Li ₇ La ₃ Zr ₂ O ₁₂ have gained significant attention in recent years owing to their high energy density and excellent safety. However, the poor interfacial compatibility between Li and garnet remains a grand challenge, resulting in high interfacial resistance and uncontrolled Li dendrite growth. Herein, we propose a Gibbs free energy‐driven Li compositing strategy by incorporating a small amount of MgF ₂ into molten Li, leading to the spontaneous formation of LiF and Li–Mg alloy phases. LiF can enhance interfacial adhesion and suppress Li dendrite growth, while the Li–Mg alloy can homogenize Li flux and facilitate uniform Li deposition. As a result, the Li–MgF ₂ composite anode achieves a low interfacial resistance of 8.2 Ω cm ² , and the Li–MgF ₂ symmetric cells with garnet accomplish ultrastable cycling for over 7000 h at 0.2 mA cm ⁻² . In addition, SSLBs with Li–MgF ₂ anode and LiFePO ₄ cathode retain a capacity of 130.3 mAh g ⁻¹ over 400 cycles with a capacity loss per cycle as low as 0.035%, representing one of the best cycling stability among garnet‐based batteries. This simple yet effective Li compositing strategy opens up a broad avenue for the development and deployment of solid‐state batteries.