Regeneration of Fully-discharged Graphite-Fluoride Lithium Primary Battery as Electrochemical Capacitor

This paper reports that the fully-discharged graphite-fluoride Li primary battery (GF/Li battery) can be regenerated as a hybrid capacitor with a higher energy density than the electric double layer capacitor (EDLC) using an activated carbon electrode. The graphite-fluoride (GF) positive electrode of the GF/Li battery is electrochemically defluorinated during the fully-discharged process to be converted to a nanocomposite consisting of carbon and LiF particles. The nanocomposite as the discharge product behaves as a capacitor-like electrode, so the fully-discharged GF/Li battery can be stably charged/discharged as a hybrid capacitor with the capacitor-type electrode (defluorinated GF electrode) and the battery-type negative electrode (Li metal). This hybrid capacitor, i.e., “graphite-fluoride Li capacitor (GF/Li capacitor)”, exhibited the maximum volumetric energy density of 52 Wh L−1 (at the power density of 71 W L−1), which is higher than that of the EDLC and comparable to that of the Li-ion capacitor. In this paper, the improvement of the cyclability by using the graphite/Li bilayer negative electrode and the charge-discharge mechanism are also discussed for the GF/Li capacitor.