Electrochemical Properties of Iron Oxides as High-Capacity Negative Electrodes for Lithium Secondary Batteries

Abstract

α-Fe2O3 fine powder that the particle size is ca. 0.3 µm were estimated as negative electrode materials for lithium cells using lithium-ion conductive organic electrolytes. The sheet-type electrodes were fabricated by using the two differential binder solutions of conventional polyvinylidene fluoride (PVDF) and polyamic acid solutions dissolved in N-methyl pyrrolidinone (NMP). The electrodes exhibited high capacities of over 1000 mAh g−1 corresponding to 6 Li per Fe2O3 at potentials ranging from the open circuit potential to 0.005 V (vs. Li/Li+) in the first charging (lithium insertion) process. First discharge capacities during lithium extraction process exhibited high capacities of over 700 mAh g−1. However, cycle life of α-Fe2O3 electrodes made using the conventional binder (PVDF) solution was poor. On the other hand, Fe2O3 electrodes made using polyamic acid solution showed better cycling performance than electrodes made from the PVDF binder solution during charge-discharge cycles and high charge-discharge efficiencies (coulombic efficiencies) over 85%. We suggest that new binders will be needed to improve cycle performance and first charge-discharge efficiencies of high-capacity iron oxide negative electrodes.