Capacitive Energy Storage on Fe/Li₃PO₄ Grain Boundaries

Energy storage was realized on the interfaces between Fe and Li 3 PO 4 nanograins in situ fabricated by discharging commercial LiFePO 4 to 0.005 V vs Li + /Li. X-ray diffraction and high-resolution transmission electron microscopy indicate that both the metallic Fe and Li 3 PO 4 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/Li 3 PO 4 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.