Biphasic Electrolyte Inhibiting the Shuttle Effect of Redox Molecules in Lithium-Metal Batteries

Redox molecules (RMs) as electron carriers have been widely used in electrochemical energy-storage devices (ESDs), such as lithium redox flow batteries and lithium-O₂ batteries. Unfortunately, migration of RMs to the lithium (Li) anode leads to side reactions, resulting in reduced coulombic efficiency and early cell death. Our proof-of-concept study utilizes a biphasic organic electrolyte to resolve this issue, in which nonafluoro-1,1,2,2-tetrahydrohexyl-trimethoxysilane (NFTOS) and ether (or sulfone) with lithium bis(trifluoromethane)sulfonimide (LiTFSI) can be separated to form the immiscible anolyte and catholyte. RMs are extracted to the catholyte due to the enormous solubility coefficients in the biphasic electrolytes with high and low polarity, resulting in inhibition of the shuttle effect. When coupled with a lithium anode, the Li-Li symmetric, Li redox flow and Li-O₂ batteries can achieve considerably prolonged cycle life with biphasic electrolytes. This concept provides a promising strategy to suppress the shuttle effect of RMs in ESDs.