Gradient Composite Anode Enabling Stable Interfaces in Garnet‐Based Solid‐State Lithium‐Metal Batteries

ABSTRACT Solid‐state batteries (SSBs) deliver enhanced safety and high energy density using Li‐anode and high‐voltage cathodes. Garnet‐type Li 7‐ x La 3 Zr 2‐ x Ta x O 12 (LLZTO) is attractive owing to its high ionic conductivity and wide electrochemical window. However, the practical application of LLZTO‐based SSBs is hindered by poor interfacial contact with the Li‐anode due to local defects and voids, which disrupt the homogeneity of current distribution and promote Li dendrites. Herein, we have developed a gradient composite anode, LiF‐Li 9 Al 4 /Li x Ag (LAA), via a one‐step molten reaction. In this architecture, LiF preferentially resides at the LLZTO side to ensure intimate contact with LLZTO and prevent electronic leakage. The Li 9 Al 4 phase enhances interfacial wettability and reduces interfacial resistance between LiF and the metallic matrix, and the Li x Ag alloy enhances Li‐transport within the anode while promoting uniform Li deposition. Consequently, the LAA achieves an ultralow interfacial resistance of 0.6 Ω cm −2 and sustains stable lithium plating/stripping at 0.5 mA cm −2 for over 2000 h. In the LFP|LLZTO|LAA cell, the LAA exhibits excellent durability, retaining 95% of its capacity after 1200 cycles at 1C, while in NCM811|LLZTO|LAA it retains 89% over 500 cycles at 3C. Our results demonstrate the effectiveness gradient composite anode strategy for the practical development of garnet‐based SSBs.