Operando Monitoring of Charging Processes in Battery Cathodes by Magnetometry and Positron Annihilation

Abstract

Research in the field of modern battery materials demands characterization techniques which allow an inspection of atomistic processes during battery charging and discharging. Two powerful tools for this purpose are magnetometry and positron-electron annihilation. The magnetic moment serves as highly sensitive fingerprint for the oxidation state of the transition metal ions, thus enabling to identify the electrochemical ”active” ions. The positron lifetime on the other hand, is sensitive to open volume defects of the size of a few missing atoms down to single vacancies providing an unique insight into lattice defects induced by charging and discharging. An overview will be given on operando magnetometry studies of the important class of LiNiCoMn-oxide cathode materials (so-called NMC with Ni:Co:Mn ratios of 1:1:1 and 3:1:1) as well as of sodium vanadium phosphate cathodes. First operando positron annihilation studies on a battery cathode material (NMC 1:1:1) demonstrate the capability of this technique for battery research.