Surface-fluorinated graphite anode materials for Li-ion batteries

Surface modification of graphite powder has been performed by chemical fluorination using elemental fluorine at 200 °C and 300 °C. This process leads to an increase of the BET surface area due to partial CC bond breaking. Surface analyses performed by secondary ions mass spectrometry have shown that the H + O content at the surface of graphite is significantly decreased by this fluorination treatment. Fluorinated graphite powders have been tested as negative electrodes in Li-ion battery, chronopotentiometry measurements have shown that the fluorinated graphite exhibits better electrochemical performances than raw graphite powder notably due to an increase of the surface area which allows the storage of a higher amount of lithium into the host lattice. In addition, impedance measurements performed in a delithiated state have shown a significant decrease of the total cell resistance, i.e. a decrease of both the charge transfer resistance and the resistance related to the solid electrolyte interface (SEI) layer.