An aqueous rechargeable Zn//Co3O4 battery is demonstrated with Zn@carbon fibers and Co3O4@Ni foam as the negative and positive electrodes, respectively, using an electrolyte of 1 M KOH and 10 x 10(-3) M Zn(Ac)(2). It can operate at a cell voltage as high as 1.78 V with an energy density of 241 W h kg(-1) and presents excellent cycling. The battery is also assembled into a flexible shape, which can be applied in flexible or wearable devices requiring high energy.