Operando magnetic susceptibility measurements on the cathode material during repetitive electrochemical cycling were performed, enabling a continuous and bulk sensitive monitoring of the charge compensation process. Upon charging and Li extraction down to the Li contents of x = 1/3, exclusively Ni undergoes oxidation in two consecutive steps, namely, for x > 2/3 and for 2/3 > x > 1/3 with a continuous transition in between. In the regime of low Li concentrations x < 1∕3, both Co- and O-ions contribute to the charge compensation. While the oxidation of Ni and O during charging is reversible, the Co oxidation is found to be irreversible.
© 2016 Author(s).
2016
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