Alleviating the local charge accumulation at Li/garnet interface enabling solid-state lithium batteries

[Display omitted] •A simple pre-treatment strategy of sputtered nano-thick Ag layers modifies LLZTO solid-state electrolytes.•In situ electrochemical formation of nanoscale LiAg alloy layers at the interface.•The nanoscale LiAg alloy layer alleviates the local charge accumulation at the interface.•The CCD of Li/LLZTO@Ag-20 nm/Li can behigh up to 5.1 mA/cm2. Garnet-type electrolytes have attracted special attention due to their excellent stability to lithium metal and high ionic conductivity. However, solid–solid contact and the interaction of lithium ions with surface electrons of the electrolyte produces uncontrolled lithium dendrites, resulting in poor cycle stability and safety problems, andlimiting its future use in solid-state batteries. In this study, we reduce the interfacial impedance and interfacial charge accumulation by constructing an in situ electrochemical nanoscale Li-Ag alloying interface, which solves the Li/garnet interface compactness and lithium dendrite concerns. The in situ nanoscale Li-Ag alloy interface is formed by first magnetron sputtering a 20-nm-thick Ag layer on the solid electrolyte, and then alloyed with Li by galvanostatic electrochemical treatment, which effectively improves the interfacial compactness between lithium metal and the solid electrolyte and the uniform deposition of lithium ions, as well as significantly reducing interfacial resistance and inhibiting lithium dendrite growth. The above interfacial modification decreases Li/garnet resistance from 42614 Ω cm2 to 2 Ω cm2, and the Li/LLZTO@Ag/Li symmetric cell delivers a high critical current density of 5.1 mA cm−2. The solid-state LiFePO4 (LFP)/LLZTO@Ag-20 nm/Li battery performs a specific capacity of 150 mAh g−1 at 0.1C and a high capacity retention of 90.6 % after 300 cycles at 0.5C. The nanoscale alloy interfacial layer assists in improving comprehension of charge accumulation behavior at the Li/garnet interface and provides more inspiration for further realization of solid-state batteries with high energy and safety.