Changes in oxidation state and magnetic order of iron atoms during the electrochemical reaction of lithium with NiFe2O4

The mixed transition-metal spinel oxide NiFe2O4 is used for the first time as active electrode materials vs. lithium metal in test cells. Reversible capacities close to 900 mAh/g are found. Due to the poorly crystalline nature of the products of electrochemical reaction, diffraction procedures give little information about the iron forms in the reaction products. The use of Fe-57 Mossbauer spectroscopy allows to monitor the mechanism of the electrochemical reaction with lithium of the spinel. During the first discharge, the amorphization process is accompanied by metal reduction. The reversible redox reaction Fe-111 <----> Fe-0 accounts for the cycling capacity. However, magnetic ordering is lost during the first discharge and is not recovered in subsequent cycling or in the iron metal products. (C) 2002 Elsevier Science B.V. All rights reserved.