Li–CFx battery using a specific fluorinated nanocarbon as cathode material exhibits a capacity exceeding the expected theoretical value when used as an electrode material in primary lithium battery. Carbon nanodiscs were partially fluorinated by atomic fluorine released by thermal decomposition of TbF4, and the capacity of this material was up to 1180 mAh g−1, whereas a theoretical value of 847 mAh g−1 for the CF0.95 sample was calculated. The obtained value is also higher than the maximum one of 865 mAh g−1 expected for CF1 carbon fluorides. The discharge mechanism was investigated using mainly SEM and solid state NMR in order to understand this “extra-capacity”. Both the un-fluorinated carbon and the LiF covering, which is formed outside the carbon lattice during the discharge mechanism, play a key role for the achievement of the extra-capacity by the consumption of Li+ to form Li2F+ species stabilized by the carbon host structure formed after the electrochemical de-fluorination.