The impact of upper cut-off voltages on the electrochemical behaviors of composite electrode 0.3Li2MnO3·0.7LiMn1/3Ni1/3Co1/3O2

Abstract

This work has initiated an investigation on the electrochemical behaviors and the structure changes of the composite electrode 0.3Li₂MnO₃·0.7LiMn_1/3Ni_1/3Co_1/3O₂ when charged with different cut-off voltages. It is found that the charge cut-off voltages could not only affect the capacity property and coulombic efficiency, but also alter the electrode kinetics of the composite. As a consequence, the electrochemical activation of the composite electrode is highly dependent on the charge cut-off voltages: when the charge cut-off voltage is higher than 4.5 V, the inert component Li₂MnO₃ in the composite electrode is completely activated. At the meanwhile, there occurred an irreversible oxygen loss during the initial charge process, which yielded a hollow sphere in the electrode. Regardless of charge voltages, Mn ions in the composite electrode were presented in an oxidation state of +4, while Co²⁺ ions were detected at the surface of the electrode when cycled at low voltages. Ni ions in the composite could react with organic or inorganic species and then cover the surface of the cycled electrode.