Lithium secondary battery using potassium-β-ferrite as a new cathode active material

The possibility of K+-beta-ferrite as a cathode active material for lithium secondary battery was investigated. Discharge-charge characteristics based on the lithium insertion and extraction of K+-beta-ferrite have been studied by constructing an electrochemical cell Li/1 M LiClO4 PC/K1.33Fe11O17 (K+-beta-ferrite). The cyclic voltammograms for K+-beta-ferrite were unchanged after 10 cycles of operation. The OCV (open circuit voltage) before discharge was 3.2 V vs. Li/Li+. The discharge potential maintained 2.3 V vs. Li/Li+ up to ca. 200 mAh/g at 60 degrees C under a constant current density of 0.1 mA/cm(2). According to the chemical analysis, K+-beta-ferrite at each discharge step certainly contained lithium, in agreement with the lithium content calculated by current integration. Lithium content y in K1+xLiyFe11O17 was increased up to 11. After discharge, the spinel blocks were disordered, whereas the layer structure still remained in the XRD pattern. Lithium ions seem to mainly enter into gamma-Fe2O3 layers (spinel blocks) of K+-beta-ferrite, because alkali layers could practically contain only 1.5 alkali ions for Fe11O17. The cell voltage in charge increased up to 4.5 V vs. Li/Li+ at 25 degrees C. The potential during charge was lowered to 3.7 V by raising the temperature to 60 degrees C. The XRD pattern of the cathode material at every step of charge was similar to that at 200 mAh/g of discharge. Degradation of discharge-charge characteristics was not observed after 10 cycles of operation. (C) 1998 Elsevier Science B.V. All rights reserved.