Lithium–manganese–nickel-oxide electrodes with integrated layered–spinel structures for lithium batteries

Abstract

A series of lithium–manganese–nickel-oxide compositions that can be represented in three-component notation, xLi[Mn 1.5Ni 0.5]O 4 · (1 − x){Li 2MnO 3 · Li(Mn 0.5Ni 0.5)O 2}, in which a spinel component, Li[Mn 1.5Ni 0.5]O 4, and two layered components, Li 2MnO 3 and Li(Mn 0.5Ni 0.5)O 2, are structurally integrated in a highly complex manner, have been evaluated as electrodes in lithium cells for x = 1, 0.75, 0.50, 0.25 and 0. In this series of compounds, which is defined by the Li[Mn 1.5Ni 0.5]O 4–{Li 2MnO 3 · Li(Mn 0.5Ni 0.5)O 2} tie-line in the Li[Mn 1.5Ni 0.5]O 4–Li 2MnO 3–Li(Mn 0.5Ni 0.5)O 2 phase diagram, the Mn:Ni ratio in the spinel and the combined layered Li 2MnO 3 · Li(Mn 0.5Ni 0.5)O 2 components is always 3:1. Powder X-ray diffraction patterns of the end members and the electrochemical profiles of cells with these electrodes are consistent with those expected for the spinel Li[Mn 1.5Ni 0.5]O 4 ( x = 1) and for ‘composite’ Li 2MnO 3 · Li(Mn 0.5Ni 0.5)O 2 layered electrode structures ( x = 0). Electrodes with intermediate values of x exhibit both spinel and layered character and yield extremely high capacities, reaching more than 250 mA h/g with good cycling stability between 2.0 V and 4.95 V vs. Li° at a current rate of 0.1 mA/cm 2.