Extended Data Fig. 2: In situ XRD pattern of the mixture of transition-metal hydroxide and lithium carbonate.

(a) In situ XRD pattern at given equilibrated temperature for calcinations of precursor for layered oxide. (b) Phase and structural evolution during the synthesis. The phase fraction of Li2CO3 might be overestimated at the certain temperature region near 250 °C because of the decrease in the overall crystallinity of mixed transition metal compounds that undergo the decomposition. Nevertheless, the phase analysis result clearly verifies the distinct synthetic mechanism with the usage of Li2CO3 by which thermal dehydration of NCM hydroxide precursor is preceded into the oxide phase, followed by synthetic reaction with Li2CO3 at a much higher temperature, resulting in slow formation of layered oxide structures.