Lithiated and protonated spinel cobalt oxide, exhibiting high electrical conductivity thanks to the presence of structural defects, could be envisioned for asymmetric supercapacitor applications. Charge storage mechanism was investigated and it is shown that only a thin layer at the material surface was involved (less than 1 nm) during the process, so that only 20% of the total theoretical capacity was achieved. A very good electrochemical stability is found, with less than 30% of the initial capacity (similar to 70 mA . h . g(-1)) lost after 3500 cycles. (C) 2016 The Electrochemical Society. All rights reserved.