Electrochemical and magnetic studies of Cr 3+- or Co 3+-substituted Li–Mn–Ni spinel oxides

Abstract

LiMn 1.5− x M 2 x Ni 0.5− x O 4 (M = Co or Cr, 0.0 ≤ x ≤ 0.2) compounds were synthesized by the sol–gel method. It is found from X-ray diffraction analysis that single spinel phases are obtained for both Cr 3+- and Co 3+-substitution, but a small cation mixing between the 8a and 16d sites is found only in the Co 3+-substitution case. All of the compounds exhibit M– T curves characteristic of ferromagnetic materials. As the substitution degree is raised, the saturation magnetization at 4.2 K decreases and the Curie temperature shifts lower, irrespective of the kind of the substituent. That is, the cation substitution yields a reduction of the ferromagnetism. Additionally, both Cr 3+- and Co 3+-substitution have a large influence on the electrochemical properties. The Cr 3+-substitution induces a rise in the average operating potential without a loss of redox capacity, while both the average operating potential and the redox capacity decrease with an increase in the Co 3+-substitution degree.