Design\nand Reaction Mechanism of Rechargeable Lithium–Carbon\nFluoride Battery

Recharging\nprimary batteries is of great importance for increasing\nthe energy density of energy storage systems to power electric aircraft\nand beyond. Carbon fluoride (CF<i><sub>x</sub></i>) cathodes\nare characterized by high specific capacity and energy density (865\nmAh g<sup>–1</sup> and 2180 Wh kg<sup>–1</sup>, respectively).\nPreventing the crystallization of LiF with an intermediate and lowering\nthe energy barrier from LiF to CF<i><sub>x</sub></i> is\nexpected to render the Li/CF<i><sub>x</sub></i> battery\nreversible. In this study, taking the advantage of a high-voltage-stable\nall-fluorinated electrolyte containing the boron-based anion receptor\ntris(trimethylsilyl)borate (TMSB), a rechargeable Li/CF<i><sub>x</sub></i> battery was realized with a reversible capacity\nof 465.9 mAh g<sup>–1</sup> and an energy density of 1183.9\nWh kg<sup>–1</sup>, approximately 53% of that in the first\ndischarge. After the first discharge, the charge–discharge\nprofile featured rechargeable characteristics. <i>In situ</i> X-ray diffraction, <i>ex situ</i> soft X-ray absorption\nspectroscopy, pair distribution function analysis, and other measurements\nconfirmed the generation and decomposition of Li–F and C–F\nbonds during cycling. Density functional theory calculations and nuclear\nmagnetic resonance spectroscopy confirmed that TMSB serves as an anion\ncarrier through the generation of a [TMSB–F]<sup>−</sup> complex, facilitating the conversion reactions during cycling. This\nstudy demonstrated a facile and low-cost approach for realizing high-energy-density,\nreversible Li/CF<i><sub>x</sub></i> batteries.