An advanced ion-exchange method using resin was employed to produce a novel cathode material, Fe3+xCr3+2-xCr6+4O15 (0 ≤ x ≤ 2), where some of the Cr3+ ions at the octahedral sites of Cr2O5 were substituted with Fe3+ ions. The battery cell test and X-ray photoelectron spectroscopy analysis of Cr2O5, Cr8O21, and Fe1.5Cr4.5O15 indicate a change in the capacity from 210 to 280 and 350 mA h g-1 with a change in the Cr6+/Cr3+ atomic ratio from 2 to 3 and 8 for Cr2O5, Cr8O21, and Fe1.5Cr4.5O15, respectively. The discharge capacity of the compound with the crystallographic formula Fe3+1.5Cr3+0.5(Cr6+O4)2(Cr6+2O7) is, by far, the highest reported capacity for transition metal oxide electrodes in the voltage range of 2.0-4.5 V vs Li+/Li0.
Keywords: calcium chromates; cathode materials; ion-exchange resins; iron chromates; lithium-ion batteries.