Lewis Acid Fluorine-Donating Additive Enables an Excellent Semi-Solid-State Electrolyte for Ultra-Robust Lithium Metal Batteries

Abstract

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, due to the inherent high reactivity of the Li metal anode, the undesirable side reactions and are frequently observed at the lithium metal anode interface, giving rise to the low Coulombic efficiency and unsatisfactory lifespan of the lithium metal batteries. Hence, it is necessary to adopt the strategy of interface engineering for lithium metal anode with solid-state electrolyte via in-situ polymerization to construct a robust and effective solid electrolyte interphase (SEI). 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 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. 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 345 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.

Keywords: Keywords: Semi-solid-state polymer electrolyte, In-situ polymerization, Lithium metal anode, AlF3 additive, Solid electrolyte interphase