Interface engineering enabling thin lithium metal electrodes down to 0.78 μm for garnet-type solid-state batteries

Controllable engineering of thin lithium (Li) metal is essential for increasing the energy density of solid-state batteries and clarifying the interfacial evolution mechanisms of a lithium metal negative electrode. However, fabricating a thin lithium electrode faces significant challenges due to the fragility and high viscosity of Li metal. Herein, through facile treatment of Ta-doped Li7La3Zr2O12 (LLZTO) with trifluoromethanesulfonic acid, its surface Li2CO3 species is converted into a lithiophilic layer with LiCF3SO3 and LiF components. It enables the thickness control of Li metal negative electrodes, ranging from 0.78 mu m to 30 mu m. Quasi-solid-state lithium-metal battery with an optimized 7.54 mu m-thick lithium metal negative electrode, a commercial LiNi0.83Co0.11Mn0.06O2 positive electrode, and a negative/positive electrode capacity ratio of 1.1 shows a 500 cycles lifespan with a final discharge specific capacity of 99 mAh g-1 at 2.35 mA cm-2 and 25 degrees C. Through multi-scale characterizations of the thin lithium negative electrode, we clarify the multi-dimensional compositional evolution and failure mechanisms of lithium-deficient and -rich regions (0.78 mu m and 7.54 mu m), on its surface, inside it, or at the Li/LLZTO interface. Fabricating thin lithium electrodes is challenging due to lithium's fragility and viscosity. Here, authors convert surface Li2CO3 on Ta-doped Li7La3Zr2O12 to a lithiophilic layer via trifluoromethanesulfonic acid treatment, enabling precise control over lithium metal negative electrode thickness.