The spatial and electronic effects of polypyrrole between MnO2 layers enhance the diffusion ability of Zn2+ ions†

Abstract

New electrochemical energy storage systems have stringent requirements for energy storage materials, and traditional MnO₂ cannot comply with the requirements because of the problems of electrical conductivity and phase transition. In this work, a novel polypyrrole (PPy) intercalation MnO₂ (MnO₂/PPy-x) material was prepared and proved to be suitable for use in a high performance cathode of aqueous zinc ion batteries (AZIBs). The material characterization results proved that PPy played a key role between MnO₂ layers, and the reduction of Mn and extension of Mn–O bonds inhibited the distortion reaction of MnO₂, resulting in enhanced structural stability and excellent cycle life. In addition, electrochemical analysis revealed the H⁺/Zn²⁺ co-intercalation mechanism, and MnO₂/PPy-1 had high electrical conductivity, and fast reaction kinetics. Density functional theory (DFT) calculation proved the change of electron distribution between the MnO₂ layers. The PPy endowed MnO₂ with excellent electrical conductivity. Moreover, as an interlayer spacer, it hindered charge transfer and decreased the binding ability of Zn²⁺ and MnO₂. As a result, the electrochemical performance of MnO₂/PPy-1 was greatly enhanced. The final results demonstrated that MnO₂/PPy-1, which has a high conductivity and wide layer spacing, offered a superior capacity of 234 mA h g⁻¹ and a long cycle life of 2000 cycles at a current density of 1 A g⁻¹. In addition, according to the test results of pouch batteries, MnO₂/PPy-1 shows great potential for the flexible device market because of its superior flexibility and safety. This work provides a new method and approach for the modification of MnO₂-based materials.