Extended Data Fig. 4: EELS line scan results of nanopore in transition-metal hydroxide heated at 500 °C.

(a) STEM image of nanopore within primary particle, (b) EELS Mn L-edge, Co L-edge, and Ni L-edge in corresponding area. The oxidation state of the transition metal in the nanopore was slightly more reduced, corresponding to the typical transition-metal states in the rock-salt phase.