The non-stoichiometric spinel Mn-Co oxide Mn2.2Co0.27O4 presents attractive properties as a rechargeable cathode in a berate buffer electrolyte (pH 9.5). The large number of cationic vacancies combined with the high oxidation state of manganese allow a stable capacity of 115 Ah kg(-1) available near 0.1 V versus Hg/HgO reference electrode. The electrochemical performance of the cathode is presented and compared with that observed in conventional KOH medium.