Layered LixNiyMnyCo1-2yO2 Cathodes for Lithium Ion Batteries: Understanding Local Structure via Magnetic Properties

The magnetic properties of layered LiNiyMnyCo1-2yO2 (y = 0.5, 0.45, 0.4, and 1/3) compounds are studied in order to understand the transition metal ion distributions via their magnetic interactions. In LiNi0.5Mn0.5O2, an increase of magnetization is found below 100 K with ac magnetic susceptibility revealing broad peaks at 96, 40, 13, and 7 K. The low-temperature neutron diffraction and heat capacity studies do not reveal long-range magnetic ordering; the magnetic component of heat capacity shows a broad peak at 10 K. This behavior is explained by assuming a nonrandom distribution of transition metals. The 96 K transition is attributed to the ordering of clusters of Ni2+ spins in the transition metal and lithium layers, which are coupled by a 180° superexchange mechanism. The wide 40 K peak is explained by an increase of the cluster size due to intralayer Ni and Mn spin ordering, by analogy with antiferromagnetic ordering transitions in Li2MnO3 at 36.5 K and in NaNi0.5Mn0.5O2 at 55 K. The continuing incre...