Molecular Engineering of Self-Folded Lithium Salts toward High-Energy and High-Power Lithium Metal Pouch Cells

Molecular engineering of electrolytes for practical high-power and high-energy lithium metal batteries (LMBs) is a significant challenge due to the difficulty of simultaneously achieving high Li⁺ transport efficiency, minimal gas evolution, and stable cathode-electrolyte and anode-electrolyte interphases (CEI and SEI, respectively), with low charge-transfer resistance. Here, we introduce a fluorinated asymmetric lithium salt, lithium (2-(2-(2,2-difluoroethoxy)ethoxy)ethyl) ((trifluoromethyl)sulfonyl)amide (LiFOA), designed to optimize electrolyte physicochemical/electrochemical properties for stable LMB pouch cells under fast cycling conditions. LiFOA features a Li⁺-affinitive side chain, which folds up and suppresses anion migration, resulting in a significantly heightened Li⁺ transference number (t_Li⁺). Moreover, the folding enables a self-cleaning mechanism for both the SEI and CEI. Thus, robust and ultrathin CEI and SEI with low charge-transfer resistance are self-evolved simultaneously. Importantly, a semifluorinated methyl terminal of the side chain further optimizes molecular folding strength with a tuned donor number, which not only elevates the electrochemical stability of the functional salt but also significantly mitigates the gas-evolution issue of the electrolyte during harsh cycling of the battery. Through this molecular design, industrial pouch cells with LiFOA achieve an outstanding combination of practical demanding performances in terms of high energy density (523 W h kg^-1 at 0.1 C), high power density (1782 W kg^-1 at 5 C), excellent cycling stability, suppressed gas evolution, modest cell volume expansion, and a significantly lowered defect under rigorous operating conditions, highlighting LiFOA's potential for next-generation high-energy-density and high-power-density practical LMB applications.