Ultrafast One‐Step Synthesis of Garnet‐Type Solid Electrolytes With Modified Surface and Microstructure for Solid‐State Lithium‐Metal Batteries

Abstract Garnet‐type Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (LLZTO) solid electrolytes provide the necessary electrochemical stability and ionic conductivity for solid‐state lithium‐metal batteries (SSLMBs). However, their wider application is hindered by their high interfacial resistance with electrodes and a lengthy synthesis process. This study presents the synthesis of densified LLZTO electrolytes using unconventional Li 2 O and Li 2 ZrO 3 precursors through an ultrafast (≈60 s) Joule heat‐assisted synthesis approach in a single‐step process. The lower sintering temperature of Li 2 ZrO 3 compared to traditional ZrO 2 precursor yields LLZTO with larger grains, resulting in enhanced Li + conductivity (7.0 × 10 −4 S cm −1 at 25 °C), reduced electronic conductivity (1.7 × 10 −10 S cm −1 ), and higher density (94.2%). Applying a 52–80 nm Sn:SnF 2 coating on the LLZTO surface using a melt‐quenching approach produces a uniform interlayer that chemically converts to Li‐Sn alloy and LiF upon contact with lithium, resulting in a near‐zero interfacial resistance and a critical current density of 4.2 mA cm −2 at 25 °C. The SSLMBs, incorporating Sn:SnF 2 ‐coated LLZTO electrolyte with NMC811 cathode, demonstrate remarkable initial capacity (181.1 mAh g −1 ) and cycle performance (88.63% capacity retention at 3000th cycle). The results indicate that this approach has the potential to advance the commercial fabrication technology for high‐performance solid electrolytes for SSLMBs.