Ultra‐Stable Interface via 3D Microchannels and Liquid Metal for Ultra‐Long Lifespan Garnet‐Based Solid‐State Batteries

Garnet‐based solid‐state lithium metal batteries (SSLMBs) are promising next‐generation batteries due to their high energy density and safety. However, poor interface contacts between garnet solid electrolyte (Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 , LLZTO) and Li metal limit further application, and the conventional interface modification strategies cannot maintain interface stability under long‐term cycle, leading to dendrite growth and interlayer mechanical degradation. Here, these challenges are solved through an innovative interfacial strategy synergizing laser‐etched 3D microchannels with liquid metal (LM) Ga interlayer. Experimental result, finite element simulation, and density functional theory (DFT) calculations demonstrate that laser‐etched 3D microchannels on LLZTO can mechanically buffer stresses from volume change, while LM interlayer electrochemically in situ forms Li‐Ga/Li 2 O interlayer that improves interface wettability, homogenizes local current density, and blocks electron leakage. Therefore, the critical current density (CCD) of Li|LM‐3D@LLZTO|Li is increased to an ultra‐high value of 6.1 mA cm −2 . Moreover, it possesses over 10 000 h of cycling stability at 0.2 mA cm −2 and over 7000 h at 0.5 mA cm −2 . Besides, the Li|LM‐3D@LLZTO|LFP (LiFePO 4 ) battery achieves a capacity retention of 86.1% after 1200 cycles at 0.5 C and 86.9% after 700 cycles at 1 C. This strategy can prevent the degradation of the interface, thereby enabling ultra‐stable garnet‐based SSLMBs.