A High‐Performance Garnet‐Based All‐Solid‐State Battery Fabricated Through Room‐Temperature Ultrasonic Welding

Garnet-type Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZO) has emerged as a highly promising solid electrolyte for next-generation Li metal batteries due to its high Li⁺ conductivity and stability against metallic lithium. However, its practical application is hindered by poor interfacial contact between Li and LLZO, as well as the persistent issue of lithium dendrite formation during cycling. In this study, a novel and efficient strategy is proposed to address these challenges by employing a room-temperature ultrasonic treatment combined with a LiMg alloy anode. The fabricated symmetrical UW-LiMg/LLZO/UW-LiMg cell exhibits a low interfacial resistance and achieves an unprecedented critical current density of 4.45 mA cm^-2. Furthermore, these cells demonstrate excellent cycling stability, maintaining stable lithium plating/stripping for over 1000 h at a high current density of 1 mA cm^- ² with a low overpotential of ≈30 mV. The superior performance is attributed to the enhanced anode ductility achieved through Mg alloying and the formation of an ultra-stable interface layer. The all-solid-state UW-LiMg/LLZO/LiFePO₄ battery, incorporating an ultrasonically treated alloy anode and a fluorinated cathode interface, delivers a specific capacity of 153 mAh g^-1 at 0.5 C and retains an impressive capacity retention of 90% after 200 cycles at room temperature.