High-performance localized high-concentration electrolytes by diluent design for long-cycling lithium metal batteries

Electrolyte design is essential for stabilizing lithium metal anodes and localized high-concentration electrolyte (LHCE) is a promising one. However, the state-of-the-art LHCE remains insufficient to ensure long-cycling lithium metal anodes. Herein, regulating the solvation structure of lithium ions in LHCE by weakening the solvating power of diluents is proposed for improving LHCE performance. A diluent, 1,1,2,2,3,3,4,4-octafluoro-5-(1,1,2,2-tetrafluoroethoxy) pentane (OFE), with weaker solvating power is introduced to increase the proportion of aggregates (an anion interacts with more than two lithium ions, AGG-n) in electrolyte compared with the commonly used 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE). The decomposition of AGG-n in OFE-based LHCE intensifies the formation of anion-derived solid electrolyte interphase and improves the uniformity of lithium deposition. Lithium metal batteries with OFE-based LHCE deliver a superior lifespan of 190 cycles compared with 90 cycles of TTE-based LHCE under demanding conditions. Furthermore, a pouch cell with OFE-based LHCE delivers a specific energy of 417 Wh/kg and undergoes 49 cycles. This work provides guidance for designing high-performance electrolytes for lithium metal batteries.