Investigation on the Voltage Hysteresis of MnO for Lithium-Ion Battery Applications.

In lithium-ion batteries (LIBs), conversion-based electrodes such as transition-metal oxides and sulfides exhibit promising characteristics including high capacity and long cycle life. However, the main challenge for conversion electrodes to be industrialized remains on voltage hysteresis. In this study, MnO powder was used as an anode material for LIBs to investigate the root cause of the hysteresis. First, the electrochemical reaction paths were found to be dominated by Mn/Mn redox couple after the first lithiation from galvanostatic charging/discharging (GCD) and cyclic voltammetry (CV) measurements. Then, the voltage hysteresis was proposed to be composed of reaction overpotential (∼0.373 V) and intrinsic overpotential (∼0.377 V), which were related to the diffusion behaviors according to CV, galvanostatic intermittent titration technique (GITT), and electrochemical impedance spectroscopy (EIS) analyses. Furthermore, results revealed that the formation of disparate phase distribution during lithiation and delithiation could be the root cause of the intrinsic overpotential of MnO. These results were based on ultrahigh-resolution transmission electron microscopy (UHRTEM) and molecular dynamics (MD) simulation. It was expected that improving the diffusion behaviors of the systems could eliminate the voltage hysteresis of MnO. In summary, this paper provides an explicit insight into the hysteresis for conversion-based MnO that could also be applied to other oxide systems and very crucial to reduce energy loss for commercializing oxides as anode materials in LIBs.