The potentials of operando SQUID magnetometry for studying charging and discharging processes in Lithium and Sodium ion battery cathodesFriday (28.09.2018) 14:45 - 15:15 S1/03 - 221 Part of:
Upon charging/discharging of common lithium or sodium ion batteries, transition metal ions of the cathode materials are oxidized/reduced which is associated with a variation of their magnetic moment. Therefore, the magnetic moment may serve as highly sensitive fingerprint of the charging state enabling magnetic in-situ monitoring of the charging processes. For this purpose, an electrochemical cell was designed which allows operando measurements of the magnetic susceptibility of battery electrodes during charging and discharging in a SQUID magnetometer.
Based on our initial operando study on LiCo-Oxide , this contribution is devoted to operando studies of more complex highly application-relevant cathode material such as LiNiCoMn-oxide (so-called NMC) with Ni:Co:Mn ratios of 1:1:1 and 3:1:1. For both compositions operando measurements reveal a kink-like variation of the magnetic susceptibility with Li content x. For NMC-1:1:1 this kink indicates a subsequent oxidation of Ni from 2+ to 3+ (1≥x≥0.66) and from 3+ to 4+ (0.66≥x≥0.33) with decreasing x . For Ni-rich cathodes (NMC-3:1:1) the situation is more complex. Upon charging a simultaneous oxidation of Ni and Co from 2+ to 3+ occurs down to a Li-content of x=0.53, followed by an exclusive further oxidation of Ni from 3+ to 4+ (0.53>x>0.21).
The operando magnetometry reveals as a highly suitable tool for post-lithium batteries as well. Initial studies on the sodium battery cathode NaV-Phoshpate will also be presented.
Financial support by the Graz inter-university cooperation on natural sciences (NAWI Graz) is appreciated.
 St. Topolevec, H. Kren, G. Klinser, St. Koller, H. Krenn, and R. Würschum: In-operando SQUID magnetometry on LixCoO2 during charging/discharging, J. Sol. State Electrochem. 20 (2016) 1491-1496. DOI: 10.1007/s10008-015-3110-6
 G. Klinser, S. Topolovec, H. Kren, S. Koller, W. Gössler, H. Krenn, and R. Würschum: Continous monitoring of the bulk oxidation states in LiNi1/3Mn1/3Co1/3O2 electrodes during charging and discharging, Appl. Phys. Lett. 109 (2016) 213901. DOI: 10.1063/1.4968547