Solid-State Lithium Cells Based on Fluorinated Fullerene Cathodes.

The electrochemical characteristics of fullerenes and fluorinated fullerenes have been investigated by cyclic voltammetry and galvanostatic discharge using solid‐state lithium cells , and , MEP‐7 = a polyphosphazene derivative). In the cyclic voltammograms of and , the first half‐wave potential of is found to be 0.2 V more positive than that of , suggesting that the electron affinity of is slightly larger than that of . For the fluorinated fullerenes, cyclic voltammetry gives one irreversible reduction peak at a high potential, which has been verified to be due to the reduction of the C‒F bonds by x‐ray photoelectron spectroscopy. From the discharge curves of , and , a high utility of 90% is obtained. Changes in electronic structure of the cathode materials upon discharge are examined by x‐ray photoelectron spectroscopy and open‐circuit voltage dependence on cathode utilities, and the discharge reaction mechanism is deduced. The open‐circuit voltage dependence reveals that the electronic structure of fluorinated fullerenes changes continuously as a homogeneous electrochemical reduction proceeds.