There is demand for a power storage device composition that: compared to past lithium compounds, can suppress development of conductivity caused by blue discoloration (reduction), even when used in a reducing atmosphere; and can inhibit the generation of gases, such as carbon dioxide gas, hydrogen gas, and fluoride gas, that has been a problem in past power storage devices during use and with aging. This power storage device composition is characterized by including, as a principal component, Li2TiO3 that has an x-ray diffraction pattern for which the intensity ratio (A/B) of the peak intensity (A) at a diffraction angle of 2θ=18.4±0.1° and the peak intensity (B) at a diffraction angle of 2θ=43.7±0.1° is at least 1.10.