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

Li/CFx batteries are an essential energy source for advancing smart medicine and deep-space exploration, yet increasing their energy density is crucial for large-scale applications. However, CFx 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 CFx 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, achieving a high fluorine content from full interior fluorination and an altered fluorine pattern. In addition, the low fluorination temperature enabled by HPCs helped preserve the skeleton structure and improve the conductivity, resulting in an excellent maximum energy density of 2902.45 W h kg(-1) (0.05C) and power density of 74.837 kW kg(-1) at 50C. 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 CFx cathodes for ultrahigh-energy-density Li/CFx batteries, and the results pave the way for various large-scale applications of Li/CFx batteries in the future.