“…Theoretically, half of the capacity (~165 mAhg −1 ) should be observed at the first charge plateau of~3.1V, corresponding to the oxidation of Fe 2+ to Fe 3+ , and another half capacity should be observed for the second charge plateau of~4.6V (Fe 3+ to Fe 4+ ) 13,47,[49][50][51][52][53] . However, the initial charge capacity at the 3.1 V plateau is less than 165 mA hg -1 (~70 mA hg −1 in this work), which has also been observed in previous work 17,18,20,21,24,27,47,50,51,[53][54][55][56][57][58][59][60][61] . This commonly observed non-ideal voltage behavior has been thoroughly investigated with theoretical calculations and experimental characterization 13,50,52,62 .…”