LixNi0.25Mn0.75Oy (0.5 ≤ x ≤ 2, 2 ≤ y ≤ 2.75) compounds for high-energy lithium-ion batteries

Abstract

Manganese-rich and cobalt-free compounds of Li_xNi_0.25Mn_0.75O_y (0.5 ≤ x ≤ 2, 2 ≤ y ≤ 2.75) were investigated as the positive electrode materials for high energy lithium-ion batteries. Compounds with x = 0.5, 1, 1.25, 1.5, and 2 were prepared by a solid-state reaction from the same carbonate precursor, Ni_0.25Mn_0.75CO₃, with an appropriate amount of Li₂CO₃. The structural and physical characteristics of these phases were determined by X-ray diffraction and scanning electron microscopy. With an increase of the lithium content, the Li_xNi_0.25Mn_0.75O_y evolved from a spinel (Fdm) structure (x = 0.5) to a mixed spinel-layered (Fdm and C2/c) structure (x = 1 and 1.25), to a more layered (Rm and C2/c) structure (x = 1.5 and 2). A similar structural trend was found for samples prepared from NiMn₂O₄–Mn₂O₃ mixed oxide, itself prepared by thermal decomposition of Ni_0.25Mn_0.75CO₃carbonate precursor, to which appropriate amounts of Li₂CO₃ were added. An increase of the lithium content also affected the size of the primary particles and the roughness of the secondary particles, without any substantial change of their spherical morphology and packing densities. Further results showed that the electrochemical performance and safety characteristics of the Li_xNi_0.25Mn_0.75O_y materials were primarily governed by their structures.