Lewis acid fluorine-donating additive enables an excellent semi-solid-state electrolyte for ultra-stable lithium metal batteries

Solid-state lithium metal battery via in-situ polymerization is considered one of the most promising candidates for commercial applications with flexibility, favorable energy density and reliable safety. However, the undesirable side reactions and lithium dendrite growth are frequently observed due to the unstable electrode/electrolyte interface and the poor ion diffusion interfacial kinetics, giving rise to the low Coulombic efficiency and unsatisfactory lifespan of the lithium metal batteries. In this work, aluminum fluoride (AlF3) Lewis acid additive was introduced into a three-dimensional crosslinked in-situ semi-solid-state polymer electrolyte via in-situ polymerization process. The results demonstrate that AlF3 additive can not only immobilize anions to improve electrochemical properties, but also construct a robust and highly adhesive solid electrolyte interphase (SEI) layer with fast Li+ diffusion kinetics to effectively protect Li metal anode from side reactions and lithium dendrite growth, which is attributed to attractive components of enriched LiF, lithiophilic Li-Al alloy and AlF3 species. It is notable that the Li/Li symmetrical batteries deliver a stable Li stripping/plating cycling over 1700 h at 0.1 mA cm−2, and the Li/LFP batteries achieve a favorable long-term cycling with a capacity retention of 93.5% over 340 cycles at 3 C rate. This strategy provides a distinctive insight to facilitate the commercial applications of lithium metal battery utilizing in-situ polymerized solid-state electrolyte.