A method for producing a positive electrode material adapted to the Li-ion secondary batteries is disclosed. The produced material has the following formula (I), Li1+xMn2−yMyO4   (I) wherein M is Mg, Al, Cr, Fe, Co, or Ni; 0≦x≦0.4, and 0≦y≦0.2. The method is achieved by co-precipitating a gel salts with an organic acid. First, salts of Li, Mn and M are mixed with at least a solvent to form an initial solution. The mole ratio of Li, Mn and M ions in their respective salts is (1+x):(2−y):y. Next, at least a chelate is added into the initial solution to form a suspension, which is then filtered to obtain a co-precipitate. Finally, the co-precipitate is calcined and heated to obtain the final product.