Enabling room-temperature solid-state lithium-metal batteries with fluoroethylene carbonate-modified plastic crystal interlayers

Solid-state batteries (SSBs) with Li₇La₃Zr₂O₁₂ (LLZO) ceramic oxide electrolytes are attracting significant interest because of LLZO's non-flammability, excellent ionic conductivity, electrochemical stability against Li metal anodes, and processability in air. However, the poor solid-solid contact between the electrolyte and the electrodes leads to large interfacial impedances, which are detrimental to the functioning of LLZO-based SSBs. In this work, we modified the electrode|Ta-doped-LLZO (LLZTO) interfaces by employing a plastic crystal interlayer based on succinonitrile with a fluoroethylene carbonate additive. The interlayer, which can be easily applied, drastically reduces the interfacial resistances and allows the stable operation of Li-metal based batteries. A Li|LLZTO|LiFePO₄ battery with this interlayer can stably cycle at room-temperature for 50 times at 0.1 C while still retaining a capacity of 140 mAh g^-1. The symmetric Li|LLZTO|Li cell with the interlayer can cycle at 0.2 mA cm^-2 for over 150 hours. It also has a higher critical current density for the growth of dendrites compared with an analogous cell without the interlayer. In short, this work provides a facile and efficient methodology to enhance the effective Li transportation rates at the electrode|electrolyte interfaces of SSBs and can be readily applied to other types of electrolytes beyond LLZO.