A process for producing a lithium-manganese-nickel oxide spinel material includes maintaining a solution comprising a dissolved lithium compound, a dissolved manganese compound, a dissolved nickel compound, a hydroxycarboxylic acid, a polyhydroxy alcohol, and, optionally, an additional metallic compound, at an elevated temperature T1, where T1 is below the boiling point of the solution, until the solution gels. The gel is maintained at an elevated temperature until it ignites and burns to form a Li—Mn—Ni—O powder. The Li—Mn—Ni—O powder is calcined to burn off carbon and/or other impurities present in the powder. The resultant calcined powder is optionally subjected 1 to microwave treatment, to obtain a treated powder, which is annealed to crystallize the powder. The resultant annealed material is optionally subjected to microwave treatment. At least one of the microwave treatments is carried out. The lithium-manganese-nickel oxide spinel material is thereby obtained.