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

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.