Electrochemical and structural studies of LiCo1/3Mn1/3Fe1/3PO4 as a cathode material for lithium ion batteries

Abstract

A solid-state reaction to synthesize a lithium multi-transition metal phosphate LiCo1/3Mn1/3Fe1/3PO4 is used in this work, which has a high voltage of 3.72 V and capacity of 140 mAh g-1 at a 0.05 C rate. From the in-situ XRD analysis, LiCo1/3Mn1/3Fe1/3PO4 has shown a high stability during cell charge/discharge, even operating at 5 V, which is due to the stable olivine structure. Although all the transition metals Co2+, Mn2+ and Fe2+ are at the same 4c site of the LiCo1/3Mn1/3Fe1/3PO4 structure, they seem to have different chemical activities and reflect on the electrochemical performance. The capacity contributed by the Co2+/Co3+ redox couple is only 20 mAh g-1, which is less than that of the Fe2+/Fe3+ and Mn2+/Mn3+ redox couples. This is because of the fact that the diffusivity of lithium ion for the Co2+/Co3+ redox couple is 10-16 cm2 s-1 which is one order less than that of the Fe2+/Fe3+ and Mn2+/Mn3+ redox couples in LiCo1/3Mn1/3Fe1/3PO4. Crown Copyright © 2010.