Magnetic measurements as a viable tool to assess the relative degrees of cation ordering and Mn3+ content in doped LiMn1.5Ni0.5O4 spinel cathodes

The magnetic properties of the doped high-voltage spinels LiMn1.5Ni0.42M0.08O4 (M = Cr, Fe, Co, Cu, Al, and Ga) as well as the Mn-rich spinels LiMn1.5+xNi0.5-xO4 (x = 0, 0.05, 0.1) synthesized by a tank-reactor coprecipitation method have been investigated. It is found that the Curie temperatures correlate well with the degree of cation ordering determined by measuring the capacity value at similar to 2.7 V, which corresponds to the insertion of additional lithium into the empty 16c octahedral sites of the spinel lattice. Additionally, it is found that the saturation magnetization near 0 K provides a reliable means of calculating the Mn3+ content in each sample based on the predicted magnetic exchange interactions of the spinel structure. The magnetic results match well with the capacity values obtained in the 4 V region of the samples when assembled as cathodes in lithium-ion cells. The Mn-rich spinels offer insight into the relationship between Mn3+ content and degree of cation ordering and how they affect the magnitude of the capacity in the similar to 2.7 V region. The effects of Mn3+ content and cation ordering were isolated by examining the relationship among lattice parameter, Mn3+ content, capacity contribution at similar to 2.7 V, and Curie temperature. Thus, it is posited that the Curie temperature is a reliable qualitative means of measuring the degree of cation order in a variety of doped or Mn-rich spinel oxides.