During calcination, mass loss concludes before 725 °C. Again, this is in notable contrast to much of the literature, in which rapid mass loss and lithiation are observed near this temperature. We revisit this discrepancy and establish the origin of the rapid mass loss in the next section. The total mass loss observed in TGA is in good agreement with mass loss predicted from the overall reaction incorporating the measured oxidation of the TM precursor at the start of calcination (Figure , theoretical mass loss = 25.7%, observed mass loss = 25.6%). This supports the accuracy of our characterization of the TM (oxy)hydroxide and indicates the reaction goes to completion. This complete lithiation reaction reflects the ease of lithiation of materials with stable TM oxidation states, namely Ni 2+ and Mn 4+ , in comparison to the frequently sub-stoichiometric Ni-rich materials. The TGA curve also shows that the rate of the lithiation reaction is not constant. Specifically two lithiation regimes are observed in Figure : a more rapid lithiation from approximately 330 °C to 530 °C, followed by a slower, steady-state lithiation from approximately 530 °C to 720 °C. The mass loss at the boundary between these regimes is 21.5%, which corresponds to a Li:TM ratio of approximately 1:1. This change in lithiation rate may be a result of poor Li kinetics in the layered oxide at high Li contents, either bulk diffusion or slow reaction kinetics at the surface. It may also result simply from imperfect mixing between the TM precursor and Li source, discussed in greater detail below. The emergence of superstructure reflections only during the second lithiation regime (see SI Figure ) alternatively suggests that overlithiation past Li:TM = 1:1 may have different, slower kinetics than lithiation up to Li:TM = 1:1. Conversely, similar lithiation rate regimes (fast lithiation, followed by slower steady-state lithiation) in stoichiometric materials suggests that mechanisms general to both stoichiometric and Li-rich materials such as imperfect precursor mixing are the likely explanation.