Improvement in the Electrochemical Performances of Spinel LiMn2O4 cathodes By MnO2 coating for Lithium Ion Battery Application

Lithium ion batteries (LIBs) are considered as attractive power sources for electric vehicles (EV) and aenergy storage systems (ESS) as well as portable electronic devices due to their high energy density and long cycle life. Importantly, EV and ESS applications require high power density and thermal stability as well as low cost. In this regard, spinel LiMn₂O₄ is a promising cathode material because of its low cost, good safety, high abundance and environmental harmlessness. However, LiMn₂O₄ generally exhibits poor capacity retention especially at elevated temperatures mostly owing to the Mn dissolution. Moreover, Jahn Teller effect also causes the structural instability, which can be seen on the surface of LiMn₂O₄ at high current application. Previous literatures verify that surface-modification by coating plays an important role in electrochemical performances of LiMn₂O₄. The surface treatment of LiMn₂O₄ is known to prohibit Mn dissolution from LiMn₂O₄ electrode. In this study, the MnO₂ were prepared on the surface of LiMn₂O₄ powders. The synthesis procedure includes mixing KMnO₄ solution with ethylene glycol through oxidation-reduction reaction under ambient conditions. Electrochemical evaluation as well as storage test at elevated temperatures reveal that the surface-modification with MnO₂ enhance the rate capability and improve the storage characteristics at 60^oC of spinel LiMn₂O₄ cathode materials. In-depth analyses such as X-ray Photoelectron Spectroscopy and Electrochemical Impedance Spectroscopy are also performed to elucidate the effect of surface-modification using  MnO₂.