Ultralow‐Temperature Li/CF_x Batteries Enabled by Fast‐Transport and Anion‐Pairing Liquefied Gas Electrolytes

Abstract Lithium fluorinated‐carbon (Li/CF_x) is one of the most promising chemistries for high‐energy‐density primary energy‐storage systems in applications where rechargeability is not required. Though Li/CF_x demonstrates high energy density (>2100 Wh kg⁻¹) under ambient conditions, achieving such a high energy density when exposed to subzero temperatures remains a challenge, particularly under high current density. Here, a liquefied gas electrolyte with an anion‐pair solvation structure based on dimethyl ether with a low melting point (−141 °C) and low viscosity (0.12 mPa s, 20 °C), leading to high ionic conductivity (>3.5 mS cm⁻¹) between −70 and 60 °C is reported. Besides that, through systematic X‐ray photoelectron spectroscopy integrated with transmission electron microscopy characterizations, the interface of CF_x is evaluated for low‐temperature performance. The fast transport and anion‐pairing solvation structure of the electrolyte are concluded to bring about reduced charge‐transfer resistance at low temperatures, which results in significantly enhanced performance of Li/CF_x cells (1690 Wh kg⁻¹, −60 °C based on active materials). Utilizing 50 mg cm⁻² loading electrodes, the Li/CF_x still displays 1530 Wh kg⁻¹ at −60 °C. This work provides insights into the electrolyte design that may overcome the operational limits of batteries in extreme environments.