Charge storage mechanism of MnO2 cathodes in Zn/MnO2 batteries using ionic liquid-based gel polymer electrolytes

Cathode reactions in Zn/MnO2 batteries using aqueous electrolytes have been usually interpreted by the reduction of Mn4+ to Mn3+ while protons and/or cations penetrate inside the cathode. However, until now, the MnO2 storage charge mechanism using a non-aqueous gel polymer electrolyte (GPE) has not been investigated. In this work, ionic liquid-based GPEs including BMIM Tf and ZnTf2 have been employed in Zn/MnO2 batteries. Different states of charge of MnO2 cathodes used in Zn/IL-GPE/MnO2 batteries have been analyzed by XPS and EDX techniques. XPS analysis showed that Mn4+ is reduced during the discharge process at the same time as Zn2+ cations are incorporated into the cathode. Besides, Zn2+ cations insertion is accompanied by triflate anions. (C) 2015 Elsevier B.V. All rights reserved.