New Insights into the All-Dry Synthesis of NMC622 Cathodes Using a Single-Phase Rock Salt Oxide Precursor

In this study, new insights into the all-dry synthesis of the LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622) cathode using a single-phase rock-salt (RS) oxide precursor are provided. It was found that use of a larger amount of excess Li content not only can enhance the electrochemical performance of NMC made from the RS-precursor but also increase the degree of homogeneity of the NMC cathode material. In situ XRD analysis showed that lithiation of the RS-precursor (i.e., formation of the O3-phase) starts at a higher synthesis temperature (∼450 °C) than that is required when using a hydroxide precursor (HP) and lithium carbonate (∼350 °C). Consequently, Li₂CO₃ was consumed by the reaction with the HP at low temperatures before the temperature reached the Li₂CO₃ melting point. In contrast, the reduced lithiation kinetics of the RS-precursor results in the presence of liquid Li₂CO₃ during the synthesis, which rapidly increases the rates of precursor lithiation and increases the NMC primary particle size.