Interface engineering for garnet-type electrolyte enables low interfacial resistance in solid-state lithium batteries

Solid-state lithium batteries (SSLBs) with garnet-type Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) are one of the most promising candidates for next-generation energy storage system due to their high safety and high stability against Li metal. However, the poor interfacial contact of Li/LLZTO interface induced by Li₂CO₃ surface impurity hinders its practical application. Herein, interface engineering enabled by high-speed mechanical polishing (HMP) method is proposed to remove impurities on porous LLZTO surface and retrieve its lithiophilicity. The strong centrifugal force provided by the high rotation speed promotes the complete removal of Li₂CO₃ impurity and accelerates the Li-ion transport at Li/LLZTO interface, reducing the interfacial resistance to 28.15 Ω·cm² under ultraclean interface, which is comparable to the state-of-the-art surface treatments. Symmetric Li cells assembled with high-speed (5000 rpm) polished LLZTO exhibit a critical current density of 1.91 mA·cm⁻² and excellent cycling stability for 1200 h at 0.1 mA·cm⁻². SSLBs with LiFePO₄ cathode achieve a superior stable cycling performance with a high discharge capacity of 138.6 mA·h·g⁻¹ and a capacity retention of 89.5% after 500 cycles (0.2C). This work guides a new understanding for obtaining lithiophilic Li/LLZTO interface through a simple, low-cost, and high-efficient polishing strategy, which is potentially utilized for large-scale industrial production of SSLBs.