PURPOSE: To improve battery voltage, electric discharging capacity, and electric discharging cycle lifetime by carrying out electric discharging down to 0.5-1.5V which is smaller than an electric charging completion voltage, followed by electric charging, in an electric charging/discharging cycle.

CONSTITUTION: Two or more kinds of transition metal compounds are mixed at predetermined ratios, thus synthesizing transition metal oxide before insertion of a lithium ion. Otherwise, one or two or more kinds of transition metal compounds are mixed with a lithium compound at a molar ratio of 3.1 or less, thereby synthesizing transition metal oxide. The transition metal includes at least one kind of Ti, V, Mn, Co, Ni, Fe, Cr, Nb and Mo. One kind of the above transition materials is used as a negative electrode active material, where an electric charging completion voltage is set to 3.5-4V. Electric charging is carried out after electric discharging up to 0.5-1.5V in an electric charging/discharging cycle. Such transition metal oxide that the basic structure of crystal of a precursor is changed is used, and thereafter, the basic structure is not changed. An X-ray diffraction pattern is changed by insertion of a lithium ion, and then, it cannot be changed with repeated electric charging/discharging.