A mixed metal hydroxide with brucite structure is described, which contains nickel hydroxide as its main component and at least one trivalent metal selected from the group consisting of Co, Fe, Al, Ga, In, Sc, Y and La in an amount of from about 12 to about 30 atom % relative to the sum of the metal components including Ni. The invention also relates to a rechargeable battery containing a mixed metal hydroxide according to the invention as an electrochemically active material as well as a secondary batter containing the mixed metal hydroxide. The invention also relates to a process for producing a mixed metal hydroxide having a brucite structure.