Spectroscopic analyses of 0.5Li[Ni0.8Co0.15Zr0.05]O2–0.5Li[Li1/3Mn2/3]O2 composite cathodes for lithium rechargeable batteries

In this work we have investigated the lithium ion intercalation behavior in wet chemical synthesized 0.5Li[Ni0.8Co0.15Zr0.05]O2–0.5Li[Li1/3Mn2/3]O2 composite cathodes. Impedance spectroscopy in conjunction with micro-Raman spectroscopy and X-ray photoelectron spectroscopy measurements are performed to understand the lithium ion intercalation behavior in these composite cathodes. The Rietveld refinement of the X-ray diffractograms of the cathode powder indicates a hexagonal layered structure and minimal transitional metal cation disorder between lithium and (transition) metal layers. Probing the localized region by micro-Raman spectroscopy, it is found that in virgin cathode, monoclinic Li[Li1/3Mn2/3]O2 forms composite with hexagonal layered Li[Ni0.8Co0.15Zr0.05]O2 component. Interestingly, these cathodes transform into a hexagonal layered structure upon charging ∼ 4.8 V. The galvanostatic charge–discharge characteristics of these composite cathode is reported in the cut-off voltage limits of 4.8–1.45 V. Detailed X-ray photoelectron spectroscopy analyses of the valence states of the constituent elements are performed in virgin, fully charged and partial discharged states of the cathodes. Through the XPS analyses, the charge and discharge capacities of these cathodes are found to be due to Ni3+/Ni4+, Co3+/Co4+ and Ni2+/Ni3+ redox couples. The capacity of these composite cathodes is deteriorated when cycled repeatedly between the voltage limits of 4.8–1.45 V. The probable reasons for such findings are discussed.