Institute of Solid State Physics


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In-operando magnetic studies on Li-ion battery cathodes during charging/discharging
S. Topolovec
Institute of Materials Physics, Graz University of Technology
14:00 - 14:20 Monday 28 September 2015 Hörsaal I, Alte Technik

In-situ magnetic measurements during electrochemical charging, with the purpose to tune magnetic properties by electrochemical processes, have recently attracted considerable attention (i.e. [1-3]). As the magnetic properties of the technologically important Li-ion battery electrode materials are sensitive to phase composition, structural disorder, defects and the oxidation state of the transition metals ions [4], such in-situ magnetic studies could also be used to provide insights into the electronic and chemical processes during charging.
Based on our recent electrochemical in-situ experiments in a SQUID [2,3,5] we have designed an electrochemical cell allowing in-operando measurements of the magnetic susceptibility of commercially used battery electrodes during charging/discharging. This is first demonstrated by the example of LixCoO2 cathodes, which show reversible variations of the magnetic susceptibility ¦Ö of up to 167% with lithium de-/intercalation. For lithium contents 1>x¡Ý0.77 the susceptibility ¦Ö, which is mainly attributed to a Pauli-paramagnetic component, varies linearly with charging. This indicates a linear rise of D(EF) with Li extraction. For x<0.77 the variation of ¦Ö can be assigned to alterations of the Co oxidation state, revealing that in addition to Co also O undergoes partial oxidation during charging. An observed further increase of ¦Ö at the beginning of the discharging process may indicate the formation of Co2+ during reduction.
Furthermore, this novel technique was applied to LixNi0.33Mn0.33Co0.33O2 cathodes, where a continuous monitoring of the oxidation states of the various transition metal ions became feasible. With Li de-/intercalation the reversible (Ni2+¡úNi3+, Ni3+¡úNi4+) and irreversible (Co3+¡úCo4+) oxidation processes could be detected and analyzed.
[1] M. Weisheit et al., Science 315 (2009) 349.
[2] S. Topolovec et al., J. Magn. Magn. Mater. 329 (2013) 43.
[3] E.-M. Steyskal et al., Beilstein J. Nanotechnol. 4 (2013) 394.
[4] N. A. Chernova et al., J. Mater. Chem. 21 (2011) 9865.
[5] S. Topolovec et al., Rev. Sci. Instrum. 86 (2015) 063903.