Self-discharge behavior of polyacenic semiconductor and graphite negative electrodes for lithium-ion batteries

▶ We monitored open-circuit potential to examine self-discharge of lithiated carbon electrodes. ▶ This was done from viewpoints of ensuring safety and reliability of lithium-ion batteries. ▶ Clear difference was observed in the self-discharge between graphite and PAS electrodes. ▶ They were related with differences in the properties of surface layers formed at the electrodes. Variations in open-circuit potential (OCP) of artificial graphite and polyacenic semiconductor (PAS) negative electrodes have been investigated as a function of the storage time in alkylcarbonate-based electrolyte solutions after their cathodic charging (electrochemical lithiation) to discuss self-discharge phenomena of these negative electrodes for lithium ion batteries. The OCP of the graphite showed a plateau at ca. 90 mV vs. Li/Li + for a long period (>8 × 10 5 s), which suggested the retention of a stage structure of lithiated graphite during the storage. The lithiated PAS electrode gave gradual changes in OCP during the storage in the carbonate-based electrolyte solutions, suggesting continuous loss of Li species in the electrode. Variations in the interfacial resistance determined by an ac method, corresponding to the changes in the structure and properties at the electrode/electrolyte interface, also showed different features for the lithiated graphite and PAS electrodes. The mechanisms of self-discharging for these carbonaceous electrodes are discussed from the results of the influences of temperature and additives on the OCP variations.