INTERCALATION MECHANISM IN LITHIUM IRON-PHTHALOCYANINE CELLS

The cathode reaction mechanism in a lithium//1M LiClO4/propylene carbonate (PC)//iron-phthalocyanine (FePc) cell was investigated by X-ray diffraction and atomic absorption spectroscopy. For about 12 e-FePc depth of discharge, the FePc interlayer distance expanded by about 4.3%. About 9 Li/FePc were found in the cathode pellet by chemical analysis. After recharge, the interlayer distance returned to its initial state and the Li content decreased to 1.4 Li/FePc. These results show that Li+ intercalates to at least a 9 Li/FePc ratio and most of the discharge capacity is reversible on the first cycle. The discrepancy between the electrical charge ( 12 e-/FePc) and the actual Li content in the cathode pellet ( 9 Li/FePc) is caused by side reactions like PC decomposition and FePc anion distribution during discharge. A different capacity degradation mechanism, ClO4- intercalation during charging, may also occur.