The LiyNi0.2Mn0.2Co0.6O2 electrode materials: A structural and magnetic study

Graphical abstract: EPR signal of the Li0.6Co0.6Ni0.2Mn0.2O2 composition showing that Mn4+ ions are the solely paramagnetic ions in the structure. Highlights: ► LiCo0.6Ni0.2Mn0.2O2 was prepared by the combustion method with sucrose as a fuel. ► Chemical delithiaition was performed by using NO2BF4 oxidizing agent. ► The rhombohedral symmetry was preserved upon lithium removal. ► Lithium extraction leads to Ni2+ oxidation to Ni4+ followed by Co3+ oxidation. ► The EPR narrow signal of Li0.6Co0.6Ni0.2Mn0.2O2 is due to the only active Mn4+ ions. -- Abstract: Layered LiNi0.2Mn0.2Co0.6O2 phase, belonging to a solid solution between LiNi1/2Mn1/2O2 and LiCoO2 most commercialized cathodes, was prepared via the combustion method at 900 °C for a short time (1 h). Structural and magnetic properties of this material during chemical extraction were investigated. The powders adopted the α-NaFeO2 structure with almost none of the well-known Li/Ni cation disorder. The analysis of the magnetic properties in the paramagnetic domain agrees with the combination of Ni2+ (S = 1), Co3+ (S = 0) and Mn4+ (S = 3/2) spin-only values. X-ray analysis of the chemically delithiated LiyNi0.2Mn0.2Co0.6O2 reveals no structural transition. The process of lithium extraction from and insertion into LiNi0.2Mn0.2Co0.6O2 was discussed on the basis of ex situ EPR experiments and magnetic susceptibility. Oxidation of Ni2+ (S = 1) to Ni3+ (S = 1/2) and to Ni4+ (S = 0) was observed upon lithium removal.