Nickel-based oxide cathode material taking out from lithium-ion cell after storage for 2 years at 45 degrees C is analyzed by electron energy-loss spectroscopy in a scanning transmission electron microscope (STEM-EELS) and the result of STEM-EELS is compared with cobalt-based oxide cathode material which is treated as same manor as nickel-based oxide cathode material. The Ni-L(2,3) energy-loss near-edge structure (ELNES) spectra of nickel-based oxide cathode material show peak positions similar to original material before storage. This result indicates that nickel-based oxide material has no significant change in the surface structure. On the other hand, a remarkable shift to low energy is observed in the Co-L(2,3) ELNES spectra of the cobalt-based oxide cathode material after storage. The cycle test at 60 degrees C under the conditions of aggressive driving cycle (US06) mode for the nickel-based oxide cathode/graphite cell is also carried out. It is clear that cycle performance of the nickel-based oxide cathode/graphite cell is dependent on the depth of discharge (DOD). (C) 2010 Elsevier B.V. All rights reserved.