Design and Reaction Mechanism of Rechargeable Lithium-Carbon Fluoride Battery.

Recharging primary batteries is of great importance for increasing the energy density of energy storage systems to power electric aircraft and beyond. Carbon fluoride (CF_x) cathodes are characterized by high specific capacity and energy density (865 mAh g^-1 and 2180 Wh kg^-1, respectively). Preventing the crystallization of LiF with an intermediate and lowering the energy barrier from LiF to CF_x is expected to render the Li/CF_x battery reversible. In this study, taking the advantage of a high-voltage-stable all-fluorinated electrolyte containing the boron-based anion receptor tris(trimethylsilyl)borate (TMSB), a rechargeable Li/CF_x battery was realized with a reversible capacity of 465.9 mAh g^-1 and an energy density of 1183.9 Wh kg^-1, approximately 53% of that in the first discharge. After the first discharge, the charge-discharge profile featured rechargeable characteristics. In situ X-ray diffraction, ex situ soft X-ray absorption spectroscopy, pair distribution function analysis, and other measurements confirmed the generation and decomposition of Li-F and C-F bonds during cycling. Density functional theory calculations and nuclear magnetic resonance spectroscopy confirmed that TMSB serves as an anion carrier through the generation of a [TMSB-F]^- complex, facilitating the conversion reactions during cycling. This study demonstrated a facile and low-cost approach for realizing high-energy-density, reversible Li/CF_x batteries.