LiFSA-KFSA binary molten salt enables durable lithium-antimony batteries at 80-100 °C

The transition to decarbonized energy systems necessitates large-scale, cost-effective grid storage solutions. While lithium-antimony (Li‖Sb) molten-salt batteries offer high power density and long cycle life, their traditional operation above 400 °C presents major engineering and cost hurdles. Here, we report a transformative Li‖Sb molten-salt battery that operates at 80-100 °C using a lithium bis(fluorosulfonyl)imide and potassium bis(fluorosulfonyl)imide (LiFSA-KFSA) binary molten salt electrolyte. This system achieves high energy density and high-power density (∼308.78 Wh kg^-1, ∼8958.12 W kg^-1) and remarkable long-term cyclability, retaining 48.68% capacity over 2000 cycles. In situ synchrotron X-ray characterization elucidates a highly reversible phase evolution in micron-sized Sb during (de)lithiation, facilitated by a stabilizing anion-derived inorganic solid-electrolyte interphase. This work redefines Li‖Sb batteries as a practical mid-temperature technology, offering a durable and potentially low-cost candidate for grid-scale energy storage.