Ji Weijie,Luo Bi,Wang Qi,Yu Guihui,Zhang Zixun,Tian Yi,Zhao Zaowen,Zhao Ruirui,Wang Shubin,Wang Xiaowei,Zhang Bao,Zhang Jiafeng,Sang Zhiyuan,Liang Ji
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 Li 7 La 3 Zr 2 O 12 (LLZTO) with trifluoromethanesulfonic acid, its surface Li 2 CO 3 species is converted into a lithiophilic layer with LiCF 3 SO 3 and LiF components. It enables the thickness control of Li metal negative electrodes, ranging from 0.78 μm to 30 μm. Quasi-solid-state lithium-metal battery with an optimized 7.54 μm-thick lithium metal negative electrode, a commercial LiNi 0.83 Co 0.11 Mn 0.06 O 2 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 °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 μm and 7.54 μm), on its surface, inside it, or at the Li/LLZTO interface.
Inert atmosphere is normally necessary for fabrication of solid composite electrolytes (SCEs) as a crucial part of solid-state Li-metal batteries in order to avoid undesirable reactions induced by ambient moisture. Herein, we developed an air-processable technique to fabricate SCEs by employing LiCF3SO3 (LiOTf) as the Li salt, which was combined with Li6.4La3Zr1.4Ta0.6O12 (LLZTO) as the fast Li-conductor and polyvinylidene difluoroethylene/polyvinyl acetate (PVDF/PVAC) as the polymer matrix. With the assistance of trace H2O dissolved in electrolyte solution, the room-temperature Li+ conductivity of the obtained aSCE reached as high as 5.09 × 10–4 S cm–1, which was over 3 orders of magnitude higher than that of the one (iSCE, 1.93 × 10–7 S cm–1) cast by the electrolyte solution prepared in an inert atmosphere. The theoretical calculation results reveal that the oxygen atom of H2O exhibits a high propensity to interact with the Li atom in LiOTf (Li···O), thereby establishing a hydrogen bond with the oxygen atom (H···O) in N,N-dimethylformamide (solvent). Such interactions promoted the dissociation of LiOTf and led to the formation of uniform Li+ transportation channels. Simultaneously, the composition distribution was also altered, resulting in a smoother surface of aSCE and lowered crystallinity of PVDF. On this basis, the LiOTf/LLZTO/PVDF/PVAC solution at 60 °C was directly coated onto the surface of the LiFePO4 (LFP) cathode to fabricate the LFP-aSCE film after drying in an oven. The assembled LFP-aSCE/Li battery wetted by trace sulfolane exhibited an initial Coulombic efficiency of 94.7% and a capacity retention rate of up to 96% at 0.2 C (137 mAh g–1) after 180 cycles and a high capacity of 143.7 mAh g–1 at 0.5 C (150 cycles). Overall, this work could pave the way for the facile fabrication of solid electrolytes.
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