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

•Interface engineering for surface-cleaned SSE was proposed via HMP.•Li2CO3 impurity was removed and interfacial resistance was reduce to 28.15 Ω·cm2.•Symmetric cell exhibits an excellent cycling stability for 1200 h.•Superior capacity retention remains 89.5% after 500 cycles (0.2C).•The work is potentially utilized for large-scale industrial production of SSLBs. Solid-state lithium batteries (SSLBs) with garnet-type Li6.5La3Zr1.5Ta0.5O12 (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.