De-intercalation of LixCo0.8Mn0.2O2: A magnetic approach

Samples of LiCo0.8Mn0.2O2 were synthesized by a wet-chemical method using citric acid as a chelating agent, and were characterized by various physical techniques. Powders adopted the α-NaFeO2 layered structure and were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and regarding their magnetic properties. Transmission Electron Microscope (TEM) revealed particles with a mean size of 100nm. Partial chemical delithiation was carried out by using an oxidizing agent. We observe that the material has ability to free lithium ions from its structure by this chemical process, which is analogous to the first step of the charge transfer process in an electrochemical cell. The rate of delithiation is determined independently by magnetic measurements and by the Rietveld refinement of the XRD spectra. Both the concentration of Mn3+–Mn4+ pairs and that of Mn4+–Mn4+ pairs formed in the delithiation process have been determined, together with that of the Mn3+–Mn3+ pairs. It shows that magnetic measurements are able to probe the distribution of Mn3+ and Mn4+ with more details than other techniques. The results are consistent with FTIR spectra, and indicate a random distribution of the Li ions that are removed from the matrix upon delithiation, which then undergo a diffusion process. Testing the material as cathode in lithium batteries revealed about 170mAhg−1 capacity, with a lower polarization and a high columbic efficiency, emphasizing the possibility of using this material as a cathode in Li-ion batteries.