Charging of lithium cobalt oxide battery cathodes studied by means of magnetometry

摘要

The variation of the structural and electronic properties of LixCoO(2) upon electrochemical Li-extraction was studied over wide range concentration of 1 >= x >= 0.20 by means of SQUID magnetometry. The ex-situ measurements performed for 13 different compositions were supplemented by operando measurements of the magnetic moment during repetitive electrochemical in-situ cycling of the Li-concentration. From the temperature-dependent measurements an effective magnetic susceptibility with Curie Weiss behavior and an additional temperature-independent part due to Pauli and Van Vleck magnetism is derived. The increase of the temperature-independent susceptibility with Li-extraction reflects a concomitant increase of the electronic density of states and, in addition, indicates an Anderson-type of the occurring nonmetal metal transition. The effective magnetic moment reveals that only a fraction of 30% of the charge is transferred to Co upon Li-extraction indicating a complex oxidation behavior involving oxygen. Exposure to ambient atmosphere gives rise to a complete oxidation of Co. The results on the structural variation with Li-concentration are compared with accompanying measurements by X-ray diffraction and by our recent defect studies by positron annihilation. (C) 2016 Elsevier B.V. All rights reserved.