Reinforced Li/Garnet Interface by Ceramic Metallization‐Assisted Room‐Temperature Ultrasound Welding

ABSTRACT Solid‐state lithium metal batteries (SSLMBs), heralded as a promising next‐generation energy storage technology, have garnered considerable attention owing to inherent high safety and potential for achieving high energy density. However, their practical deployment is hindered by the formidable interfacial challenges, primarily stemming from the poor wettability, (electro) chemical instability, and discontinuous charge/mass transport between solid‐state electrolytes and Li metal. To overcome these obstacles, taking garnet‐based electrolyte (Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 , LLZTO) as a pathfinder, the ceramic metallization‐assisted room‐temperature ultrasound werlding (UW) has been developed to reinforce the Li/LLZTO interface. This ultrasound welding approach constructs a compact interface that facilitates rapid Li + /e − transport, while the formation of Li−M (M = Au, Ag, and Sn) alloy homogenizes the distribution of Li + /e − at the interface. By optimization, the atomic‐level contact achieved by ultrasound welding, coupled with a nanosized Au modification layer, significantly reduces the Li/LLZTO interfacial resistance to 5.4 Ω cm 2 , a marked decrease compared to the resistance achieved by static pressing methods (1727 Ω cm 2 ). The symmetric cell exhibits a high critical current density of 1 mA cm −2 and sustains long‐term stability for over 1600 h at 0.3 mA cm −2 , with a Li plating/stripping overpotential of < 45 mV. By incorporating a robust anode‐side interface into solid‐state lithium metal batteries, the LiFePO 4 ‐based full battery contributes 118.4 mAh g⁻ 1 after 600 cycles at 1 C (capacity: ∼100%). This study offers a facile and effective approach to bolster the interfacial stability between Li and solid‐state electrolytes, paving the way for the development of high‐performance solid‐state lithium metal batteries.