The structural changes of T-Nb 2O 5 and V 2O 5 cathodes with discharge and recharge were investigated by X-ray photoelectron spectroscopy (ESCA) and X-ray diffractometory etc. ESCA spectra of the discharge products shows that M 5+ is reduced to a lower valence state such as M 4+ on the discharge, and the chemical bond between Li + inserted into the oxide and O 2− of the oxide exhibits a higher ionic character than that of Li 2O. X-ray diffraction measurement shows that T-Nb 2O 5 gives the reversible structural change accompanying the disorder and order of the atomic arrangement on the charge-discharge cycling. On the other hand, V 2O 5 takes two discharge steps, within the 1st step of which it gives the reversible lattice change along b-axis caused by the intercalation of Li + into the oxide layer, whereas within the 2nd step it is considered that the reaction in the charge-discharge takes place in the vicinity of the surface of the oxide particle. In both oxides, ternary phases such as Li x M 2O 5 are produced as discharge products, where x is at least 2 for Nb 2O 5 and x is at least 3 for V 2O 5.