Overcoming Obstacles in Zn-Ion Batteries Development: Application of Conductive Redox-Active Polypyrrole/Tiron Anolyte Interphase

Abstract

This study is focused on overcoming obstacles in the implementation of metallic Zn for zinc-ion batteries. The major limiting factors of Zn anodes include dendrite growth, hydrogen evolution, and by-product formation. Herein, the challenges are addressed by the application of a redox-active electrode-electrolyte interphase. Cationic polypyrrole(PPy)/anionic Tiron anolyte is formulated as the mixed conducting interphase to push the limits of zinc-based energy storage. The doping/de-doping behavior of PPy stimulates the surface adsorption/desorption of Tiron attributed to the ion-induced nucleation. Testing results show that PPy as a passivating corrosive-resistant layer improves the interfacial stability of Zn metal; while releasing the redox-active anolyte boosts the charge transfer of cells by the phenol-quinone transformations. The Zn//Zn cells demonstrate an improved life from 50 to 2500 cycles with a reduced overpotential at 2 mA cm−2 and 1 mAh cm−2. In situ UV–vis spectroscopic measurements, combined with density functional theory calculations, address the redox mechanisms of PPy/Tiron anolyte. The testing of α-MnO2//Zn cells shows that the PPy/Tiron anolyte exhibits enhanced capacity and rate performance due to the pseudocapacitive effects. This study unveils a conceptually new approach based on the modification of conducting polymer with redox-active dopants toward the fabrication of high-performance Zn-anolyte batteries.