A Facile Approach to Boost the Specific Capacity of Fluorinated Carbon Cathode for Rechargeable Na/CF_x Battery

Similar to the lithium/fluorocarbon (Li/CF_x) battery, the sodium/fluorocarbon (Na/CF_x) battery has a low price and high energy density, which presents promising application potential in the future. However, its non-ideal performance, such as low cycling life caused by large polarization, have restricted the practical use of the Na/CF_x battery. To address these challenges, the addition of a conductive agent to the CF_x cathode proves to be an effective method for enhancing the performance of the Na/CF_x battery. In this work, we introduce a facile strategy to boost the specific capacity of the CF_x cathode by incorporating a certain amount of carbon coating. As a result, the CF_x-0.10 cathode sample (coating 10 wt.% carbon) delivers superior electrochemical properties. The discharge capacities of the CF_x-0.10 battery for the initial and second cycles are 873.2 mAh g⁻¹ and 201.3 mAh g⁻¹, respectively, representing increases of over 18% and 47% compared to the pure CF_x battery. Compared to the pure CF_x battery, CF_x@C batteries exhibit a higher Coulombic efficiency, which is attributed to the catalytic effect of carbon coating for the decomposion of NaF. Additionally, electrochemical impedance spectroscopy (EIS) testing reveals that coating a specific amount of carbon dramatically reduces both the charge transfer resistance (R_ct) and interface resistance (R_sei) of the Na/CF_x battery. Based on DFT computation, a carbon coating on the CF_x cathode changes the local electric field around the CF_x particles and effectively facilitates the insertion/extraction processes of Na⁺ ions. This work provides a novel approach to enhance the electrochemical performance of rechargeable Na/CF_x batteries.