Ultra-Low 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 system 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, we report 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. Besides that, through systematic X-ray photoelectron spectroscopy integrated with transmission electron microscopy characterizations, we evaluate the interface of CF x for low-temperature performance. We conclude that the fast transport and anion-pairing solvation structure of the electrolyte brings about reduced charge transfer resistance at low temperatures, which resulted in significantly enhanced performance of Li/CF x cells (1690 Wh kg -1 , -60 °C;1172 Wh kg -1 , -70 °C based on active materials). Utilizing 50 mg cm -2 loading electrodes, the Li/CF x still displayed 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. This article is protected by copyright. All rights reserved.