In-Situ Heating X-Ray Diffraction of LiNiMnCoO and LiNiMnO Made Using the All-Dry Synthesis Process.

In-situ synthesis X-ray diffraction is conducted at the Canadian Light Source to probe phase changes during the all-dry synthesis of LiNiMnCoO (NMC631) and LiNiMnO (NM73) made using either LiOH·HO or LiCO. All materials are heated up to 950 °C and held for one hour at 950 °C under flowing oxygen. The pathway to a layered phase is similar for all samples. First, a lithiated manganese oxide phase is formed at low temperature, then cations are incorporated into a rock salt phase from ≈420 °C. A spinel intermediary phase is formed before cation ordering occurs between Li and transition metal ions above 800 °C, giving rise to the intended layered hexagonal structure. Amongst the three materials tested, the layered phase of NMC631 (made using LiOH·HO) evolves at the lowest temperature of ≈820 °C and refines rapidly during the high temperature hold. The melting of LiOH coincides nicely with the oxidation of Ni, which forms the basis for the rock salt structure. It is postulated that the molten LiOH facilitates cation diffusion into the rock salt phase, allowing for an earlier formation of the layered phase in comparison to using LiCO, which has a higher decomposition temperature.