Li1.20Mn0.54Co0.13Ni0.13O2 with Different Particle Sizes as Attractive Positive Electrode Materials for Lithium-Ion Batteries: Insights into Their Structure

The effect of the synthesis temperature on the chemical composition of Li1.20Mn0.54Co0.13Ni0.13O2 was considered using thermogravimetric analyses (TGA) and in situ X-ray diffraction (XRD) during thermal treatment. A continuous and small weight loss is observed above 800 degrees C because of Li evaporation, and the lamellar phase disappears to the benefit of a spinel-type phase formed above 940 degrees C. The layered structure is recovered upon cooling under air. Li1.20Mn0.54Co0.13Ni0.13O2 materials synthesized at 800, 900, and 1000 degrees C show very similar compositions, structures, and electrochemical properties despite very different crystallization states. Their average structure is alpha-NaFeO2-type and described in the R (3) over barm space group, with less than 0.02 Ni2+ ions in the Li site. This peculiar composition Li1.20Mn0.54Co0.13Ni0.13O2, with one-third of large cations (Li+, Ni2+) and two-thirds of small cations (Mn4+, Co3+) promotes the extension of the cation ordering in the slabs as revealed by the root 3a(hex) x root 3a(hex), superstructure, but without full correlation between the ordered slabs along the c(hex) stacking axis. Neutron and electron diffraction associated with NMR and Raman spectroscopies are shown to be efficient tools to get more insights into the average and local structures of these complex layered materials.