A pre-doping agent for a power storage device includes a lithium iron oxide represented by Formula (1), wherein in X-ray diffractometry, a half width of a diffraction peak at a diffraction angle (2θ) of 23.6°±0.5° is 0.06° to 0.17°, and an intensity ratio (I44.6/I23.6) of a diffraction peak intensity (I44.6) at a diffraction angle (2θ) of 44.6°±0.5° to a diffraction peak intensity (I23.6) at a diffraction angle (2θ) of 23.6°±0.5° is less than 8%. The pre-doping agent for a power storage device with a large irreversible capacity can be suitably used as a power storage device, which can suppress reduction in a volume energy density of a power storage device, can reduce a production cost, can prevent decomposition of an electrolytic solution.

LixFeOy  (1)



wherein x meets 3.5≤x≤7.0 and y meets 3.1≤y≤5.0.