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<i>_x</i>) 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<i>_x</i> is expected to render the Li/CF<i>_x</i> 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<i>_x</i> 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. <i>In situ</i> X-ray diffraction, <i>ex situ</i> 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<i>_x</i> batteries.