A lithium-ion secondary battery comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte solution present between these two electrodes; and charging and discharging are mediated by lithium ions in the electrolyte moving back and forth between the two electrodes. As the active substance that reversely stores and releases lithium ions at the positive electrode, a lithium-containing transition metal oxide is primarily used. Technical literatures relating to positive electrode materials include Patent Documents 1 and 2.