Silver nanoparticle−decorated MnO2 for promoted Mn4+/Mn2+ redox reaction in aqueous Zn−MnO2 batteries

Abstract

Rechargeable aqueous Zn−MnO2 batteries have garnered increasing attention recently due to intrinsic safety, high theoretical capacity, appealing output voltage, and low material cost. However, challenges still exist in exploring for high−performance manganese oxides capable of delivering comparable capacity to the Zn anode. Herein, a composite material made of layered MnO2 decorated with Ag nanoparticles (Ag NPs) can be prepared by a one−step hydrothermal reaction. The silver decoration strategy can provide facile electron transport of the composite cathode and induce structural vacancies via forming Ag−O−Mn bond. These features enable the AgMO cathode to exhibit smaller charge−transfer resistance (23.0 vs 41.3 Ω) and accelerated ion transport kinetics (1.25×10−10 vs 3.90×10−11 cm2 s−1). More importantly, the presence of Ag NPs is found to promote the reaction kinetics of Mn4+/Mn2+ redox. By taking these advantages, the AgMO sample exhibits a higher attainable capacity of 333 mAh g–1 at 0.3 A g–1 compared with the Ag−free counterpart (MO, 268 mAh g–1). Moreover, AgMO demonstrates better rate performance with the discharge capacity of 109 mAh g–1 at 8 A g–1 (90 mAh g–1 for MO), and a specific capacity of 93 mAh g–1 can still be achieved for AgMO after 2000 cycles at 4 A g–1 (55 mAh g–1 for MO). This work presents a holistic approach to enhance the energy storage capability of MnO2 cathode in rechargeable aqueous Zn−ion batteries.