Elucidating the effects of carbon source on fluorination kinetics and the CFx structure to tailor the energy density of Li/CFx

Abstract

Li/CF_x batteries are an essential energy source for advancing smart medicine and deep-space exploration, and increasing their energy density is crucial for large-scale applications. However, CF_x cathode development is hindered due to the voltage–capacity trade-off when the actual synthesis is considered. To solve this problem, the mechanism of fluorination and key factors that affect the fluorine pattern must be determined. In this study, we propose a diffusion-controlled fluorination mechanism, and the critical role of the carbon source structure in the fluorination kinetics and fluorine pattern of the formed CF_x is revealed. As a proof-of-concept, we prepared a series of hierarchical porous carbons (HPCs) and promoted fluorination kinetics with their well-developed hierarchical pore structure, resulting in a high fluorine content from full interior fluorination and an altered fluorine pattern. In addition, a HPCs enabled low fluorination temperature helped to maintain the skeleton structure and improve the conductivity, resulting in an excellent maximum energy density of 2902.45 Wh kg^-1 (0.05 C). Orthogonal experiments, which facilitated the tailoring of battery performance, demonstrated the synergistic effect of the carbon source and fluorination temperature for the first time. This study provides theoretical and practical guidance for designing and implementing CF_x cathodes for ultrahigh-energy-density Li/CF_x batteries, and the results pave the way for various large-scale applications of Li/CF_x batteries in the future.