The invention is directed towards an electrochemically active cathode material for a battery. The electrochemically active cathode material includes a non-stoichiometric beta-delithiated layered nickel oxide. The non-stoichiometric beta-delithiated layered nickel oxide has a chemical formula. The chemical formula is LixAyNi1+a-zMzO2•nH2O where x is from about 0.02 to about 0.20; y is from about 0.03 to about 0.20; a is from about 0.02 to about 0.2; z is from about 0 to about 0.2; and n is from about 0 to about 1. Within the chemical formula, A is an alkali metal. The alkali metal includes potassium, rubidium, cesium, and any combination thereof. Within the chemical formula, M comprises an alkaline earth metal, a transition metal, a non-transition metal, and any combination thereof.