Effects of zinc and manganese ions in aqueous electrolytes on structure and electrochemical performance of Na0.44MnO2 cathode material

Abstract

The sodium manganese oxide, Na_0.44MnO₂, was synthesized by a solid-state reaction routine combined with a sol–gel process using Mn(CH₃CO₂)₂·4H₂O as the manganese source. Results show that the capacity and cycling stability of Na_0.44MnO₂ cathodes are enhanced significantly by using a hybrid aqueous electrolyte (Na₂SO₄, ZnSO₄ and MnSO₄). The energy storage mechanism of as-prepared Na_0.44MnO₂ in the hybrid aqueous electrolyte is associated with the insertion/extraction of zinc and sodium multi-ions with the help of synergistic effects between zinc and manganese ions and the quasi-reversible deposition–dissolution process of Mn²⁺ ions. The Na_0.44MnO₂ electrode displays both excellent storage properties with zinc, sodium and manganese ions (∼340 mA h g⁻¹ at 100 mA g⁻¹ after 150 cycles) and reversibility (∼100% coulombic efficiency during cycling). The excellent reversibility and good cycling properties indicate that the Na_0.44MnO₂ can be a promising material for energy storage devices by using a hybrid aqueous electrolyte.