Synergistic Effects of Double Substitution in LiNi[sub 0.5−y]Fe[sub y]Mn[sub 1.5]O[sub 4] Spinel as 5 V Cathode Materials

Spinel oxides with formula are known to be interesting electrode materials for lithium-ion batteries. These materials show a significant near 5 V capacity, which results from changes in the oxidation state of the transition metal M. In this work, compounds of the series have been characterized. The charge/discharge curves of lithium test cells using these compounds as active electrode material show two plateaus. The first one, below 4.5 V, is ascribed to a pair, while the second, between 4.5 and 5.1 V, can be attributed to and pairs. High capacity and excellent capacity retention is obtained for some compositions with intermediate values. The suppression of the multiphase mechanism of insertion-deinsertion commonly found for by iron substitution is evidenced for compositions in the range. The change in mechanism is correlated with the improvement in electrochemical performance. Moreover, cation distribution, which includes the presence of iron in the tetrahedral sites of the spinel structure, stabilizes the solid upon prolonged cycling. © 2004 The Electrochemical Society. All rights reserved.