Li/CF_x is one of the highest-energy-density primary batteries; however, poor rate capability hinders its practical applications in high-power devices. Here we report a preparation of fluorinated graphene (GF_x) with superior performance through a direct gas fluorination method. We find that the so-called “semi-ionic” C-F bond content in all C-F bonds presents a more critical impact on rate performance of the GF_x in comparison with sp² C content in the GF_x, morphology, structure, and specific surface area of the materials. The rate capability remains excellent before the semi-ionic C-F bond proportion in the GF_x decreases. Thus, by optimizing semi-ionic C-F content in our GF_x, we obtain the optimal x of 0.8, with which the GF_0.8 exhibits a very high energy density of 1,073 Wh kg⁻¹ and an excellent power density of 21,460 W kg⁻¹ at a high current density of 10 A g⁻¹. More importantly, our approach opens a new avenue to obtain fluorinated carbon with high energy densities without compromising high power densities.

Li/CF_x cells possess the highest energy density among all lithium primary batteries. Here, the electrochemical lithiation process is elucidated through high-resolution ¹⁹F NMR, in situ⁷Li NMR and TEM methods. Fluorinated carbon CF_L (L is around 0.06 or less) is identified for the first time to be generated in the discharge process of CF_x (x ≥ 0.5) besides LiF and carbon. Moreover, the morphological evolution of the formed LiF, which affects the impedance of the battery during discharge, is illustrated as crystal nuclei of LiF, with a size of around 10 nm, which keep forming and growing into crystal grains of LiF, with a size of around 200 nm, until the surface of the CF_x particles is saturated by LiF and then both crystal nuclei and grains enlarged promptly towards the end of lithiation. This work reveals the electrochemical reaction mechanism of CF_x and provides crucial guidance to enhance the performance of the materials.

Lithium/carbon fluoride (Li/CF_x) batteries have been widely researched due to their high theoretical specific energy. To create a high-performance electrode, the fluorinated hard carbon (FHC) is prepared by direct gas-phase fluorination. It has a high F/C ratio of 0.95 based on the gravimetric method. Selecting hard carbon (HC) with a high surface area as the carbon source allows for FHC to achieve suitable interlayer spacing and specific surface area, as well as abundant pore structures to facilitate rapid lithium ion transportation. Additionally, a composite of graphene and carbon nanotubes (CNTs) is coated on the surface of FHC, enhancing electron transport speed. The resulting FHC&C exhibits a very high energy density of 1256 Wh kg⁻¹ and an excellent power density of 72,929 W kg⁻¹ at a high rate of 40 C. Moreover, compared to commercial CF_x, FHC&C exhibits higher energy and power densities, thus presenting a promising practical application prospect.

Fluorinated carbon (CF_x) has been extensively served as promising positive electrode material for lithium primary batteries due to its high energy density. However, there are comparatively far less reports about the use of CF_x on other battery systems, let alone on the research of aqueous batteries. Herein in this study, we employed CF_x as the cathode active for aqueous zinc batteries for the first time and systematically investigated its electrochemical behavior under a series of aqueous zinc-ion electrolytes. As is discovered that the F/C ratio (the x value in CF_x) of CF_x have significant effects on the electrochemical performance of aqueous Zn/CF_x batteries. Specifically, CF_0.85 exhibits excellent electrochemical property with delivering a remarkable discharge capacity of 503 mA h g⁻¹ and energy density of 388 W h kg⁻¹ (at a current rate of 30 mA g⁻¹ under temperature of 25 °C), much better than several other CF_x electrode with F/C ratio of 0.70, 0.95, and 1.10, respectively. Besides, it also exhibits decent temperature performance with discharge capacities of 550 mA h g⁻¹ at 50 °C and 460 mA h g⁻¹ at 0 °C under current density of 30 mA g⁻¹. Furthermore, the electrochemical discharge mechanism based on conversion reaction was further uncovered by applying XPS, XRD, SEM and EDS elemental analysis characterization techniques. In conclusion, these results demonstrate the potential application value of CF_x in aqueous zinc primary batteries.