Electrolyte with single salt and single solvent enables FeS2-based lithium metal batteries with all-climate high performance

FeS₂ is a next-generation cathode for lithium metal batteries (LMBs) due to its low cost and ultra-high energy density. However, FeS₂-based LMBs suffer from poor cycling stability. Herein, we propose a rationally designed electrolyte, using trimethoxy (3, 3, 3-trifluoropropyl) silane (TSi) as a single solvent and lithium bis-(fluorosulfonyl) imide (LiFSI) as a single salt to improve the performance of FeS₂-based LMBs in all climates (-20 °C to +60 °C). Without introducing costly diluents and high concentrations lithium salts, TSi's weakly solvating ability helps maintain the solvation structures with rich anions, effectively suppressing lithium polysulfides (LiPSs) dissolution. The electrolyte, consisting of 2.5 M LiFSI dissolved in TSi (2.5 M LiFSI-TSi), exhibits a high Li⁺ transference number and low desolvation energy, leading to uniform lithium deposition/stripping on the anode and the formation of a stable cathode-electrolyte interphase (CEI). Consequently, the Li/FeS₂ cell is endowed with a long lifespan (over 4000 h) and a high capacity retention (90.4%). Moreover, the cell also demonstrates an outstanding ability to fast charge (2–10C) and withstand wide temperature ranges. This research confirms that the electrolytes based on siloxane solvents are advanced in all-climate high-energy-density LMBs.