In situ X-ray absorption and diffraction studies of carbon coated LiFe1/4Mn1/4Co1/4Ni1/4PO4 cathode during first charge

Synchrotron based in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) techniques are used to study electronic and crystal structure changes of the carbon coated LiFe1/4Mn1/4Co1/4Ni1/4PO4 (LiFe1/4Mn1/4Co1/4Ni1/4PO4/C) cathode material for Li-ion batteries during the first charge. In situ Fe, Mn, Co and Ni K-edge XAS results revealed that the three voltage plateaus at ∼3.6, 4.2 and 4.7 V vs. Li/Li+ are attributed to the redox reactions of Fe2+/Fe3+, Mn2+/Mn3+ and Co2+/Co3+, respectively, while the apparent capacities above 4.9 V is not originated from the Ni2+/Ni3+ redox, but very likely from the electrolyte decomposition. Interesting phase transition behaviors of LiFe1/4Mn1/4Co1/4Ni1/4PO4/C were observed with the formation of an intermediate phase and the solid solution regions. Combined in situ XAS and XRD techniques indicate fast electronic structural changes and slow bulk crystal structural changes.