Surface modification by fluorinating agents effectively improves electrochemical characteristics of carbon anodes for lithium ion batteries. The effect of surface fluorination is different depending on surface structures of carbon materials. Fluorination of natural graphite samples with small surface areas by F2 gas and plasma treatment increases the mesopores with diameters of 2-3 nm, which leads to increase in their capacities. In the case of surface fluorination of other natural graphite samples with large surface areas by F2 and plasma treatment, surface structure change is small and main effect is surface passivation of natural graphite surface by the formation of covalent C-F bonds, which brings about increase in first coulombic efficiencies, i.e., decrease in irreversible capacities in propylene carbonate (PC)-containing solvents. High temperature treatment of petroleum coke causes the closure of edge planes by carbon-carbon bond formation with elimination of surface oxygen. This structure change brings about decrease in first coulombic efficiencies, i.e., increase in irreversible capacities of graphitized petroleum cokes. Surface fluorination of graphitized petroleum cokes by F2 and plasma treatment open the closed edges and increase the surface disorder, which provide increase in first coulombic efficiencies. On the other hand, surface fluorination by ClF3 and NF3 causes surface etching without increase in the surface disorder of petroleum cokes. The main effect of surface fluorination by ClF3 and NF3 is increase of capacities.

Surface modification of carbon anodes for lithium ion batteries by fluorine

248th National Meeting (2014)

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