Characterization of Li charging state of Li₁₋ₓCoO₂ battery cathodes by means of SQUID magnetometry
Gregor Klinser¹, Stefan Topolovec¹, Heinz Krenn², Harald Kren³, Stefan Koller³ and Roland Würschum¹
15:00 - 17:00 Thursday 23 October 2014 Rechbauerstrasse 12, HSII Research in the field of modern battery materials demands for characterization techniques which may yield insight in the atomistic processes of battery charging and discharging. In the present work SQUID magnetometry is used in order to study the battery cathode material Li₁₋ₓCoO₂ in dependence of the degree of charging. For this purpose, samples with various degrees of lithium concentration were prepared. The Li-content was adjusted by electrochemical charging. Sample handling and measurements were performed under protective argon atmosphere.
Paramagnetic behavior of Li₁₋ₓCoO₂ is observed which is considered to be caused by the interplay of competing magnetic interactions (Curie-Weiss-, Van Vleck- and Pauli paramagnetism). The dominant Curie-Weiss behavior shows a systematic and mostly linear increase of the localized magnetic moment with decreasing Li-content down to Li₀ˌ₆CoO₂. The observed localized magnetic moment cannot exclusively be attributed to Co⁴⁺ ions which are formed by oxidation of Co³⁺ upon Li extraction, but also exchange coupling between Co³⁺ᵟ-O²⁻ᵟ pairs is supposed to play a role. Further de-intercalation of Li (x < 0.6) results in a decrease of the magnetic moment which may be associated with structural changes. In fact, in the same concentration range, a reordering of Li-vacancies could recently be detected by means of positron annihilation spectroscopy [1].
[1] P. Parz, B. Fuchsbichler, S. Koller, B. Bitschnau, F. Mautner, W. Puff and R. Würschum, Appl. Phys. Lett. 102, 151901 (2013).
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