Microstructure of Li_1+xMn_2-xO₄ Cathode Materials Monitored by EPR of Mn⁴⁺

Abstract

Lithium-ion batteries based on lithium manganese spinel electrodes, Li_1+xMn_2-xO₄, are the state-of-the-art power sources because they appear to be safer, are cheaper to manufacture and less toxic and polluting [1,2]. Extensive research has been devoted to the synthesis, the composition and the electrochemical properties of Li_1+xMn_2-xO₄ spinels, but little work has been done on their microstructure. The stoichiometric LiMnO₄ is a normal spinel where Li and Mn occupy tetrahedral and octahedral spinel sites, respectively. The valence distribution corresponds to Li[Mn³⁺Mn⁴⁺]O₄. With an increase of Li/Mn ratio, the tetrahedral sites remain unchanged, while the excess of lithium and the manganese reside in octahedral sites. The compensation of the lithium charge is achieved by appearance of Mn⁴⁺.