Fluorinated Carbon Nanohorns as Cathode Materials for Ultra‐High Power Li/CFx Batteries

Abstract

Fluorinated carbon (CFx) has ultrahigh theoretical energy density among cathode materials for lithium primary batteries. CFx, as an active material in the cathode, plays a decisive role in performance. However, the performance of commercialized fluorinated graphite (FG) does not meet this continuously increasing performance demand. One effective way to increase the overall performance is to manipulate carbon‐fluorine (C─F) bonds. In this study, carbon nanohorns are first used as a carbon source and are fluorinated at relatively low temperatures to obtain a new type of CFx with semi‐ionic C─F bonds. Carbon nanohorns with a high degree of fluorination achieved a specific capacity comparable to that of commercial FG. Density functional theory (DFT) calculations revealed that curvature structure regulated its C─F bond configuration, thermodynamic parameters, and ion diffusion pathway. The dominant semi‐ionic C─F bonds guarantee good conductivity, which improves rate performance. Fluorinated carbon nanohorns delivered a power density of 92.5 kW kg−1 at 50 C and an energy density of 707.6 Wh kg−1. This result demonstrates the effectiveness of tailored C─F bonds and that the carbon nanohorns shorten the Li+ diffusion path. This excellent performance indicates the importance of designing the carbon source and paves new possibilities for future research.

High Energy Density of Ball-Milled Fluorinated Carbon Nanofibers as Cathode in Primary Lithium Batteries

“…Other sub-fluorinated nanocarbons would be considered to extend the proposed concept of dual sub-fluorination, e.g., graphitized carbon blacks or nanodiscs. Although the energy and power densities do not exceed the best current performances, e.g., 92.5 kW/kg in [ 7 ], 72.9 kW/Kg in [ 10 ], and 24.364 kW/kg in [ 23 ], the comparison under strictly similar electrochemical operating conditions between the initial fluorinated material and the milled one highlights benefits. This method could be used for a variety of materials [ 8 , 15 ].…”

“…Because fluorinated carbons (CFxs) exhibit the highest theoretical energy density among current cathode materials for lithium primary batteries, extensive efforts are devoted to the enhancement of either their energy density, their power density, or both (see recent review papers [ 1 , 2 , 3 , 4 ]). The very recent strategies involve (i) considering new carbonaceous precursors for fluorination or innovative fluorination routes [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ], (ii) chemical changes in the CFx, either on the surface or in the bulk [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ], and (iii) change in the electrolyte composition [ 13 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. Ball milling, a simple process for reducing the particle size of a compound, is widely used for electrode materials [ 30 , 31 , 32 , 33 , 34 ], creating more space to accumulate the LiF(s) particles formed.…”