Capacitive Energy Storage on Fe/Li3PO4 Grain Boundaries

Energy storage was realized on the interfaces between Fe and Li3PO4 nanograins in situ fabricated by discharging commercial LiFePO4 to 0.005 V vs Li+/Li. X-ray diffraction and high-resolution transmission electron microscopy indicate that both the metallic Fe and Li3PO4 nanocrystallites are stable up to 4.2 V. The solid electrolyte interphase layer on the nanocomposite does not decompose until 1.7 V according to infrared spectroscopic analysis. The Fe/Li3PO4 nanocomposite stores up to 220 mAh g(-1) of lithium without any electrochemical reactions. This is a purely lithium storage behavior distinct from that on the electrodes of supercapacitors or traditional secondary batteries.