High Voltage and Highly Reversible Redox Chemistry of In Situ Cross-linked Polydiphenylamine as an Aqueous Zinc Battery Cathode

Abstract

Organic redox-active materials are promising electrode candidates for the next generation of rechargeable batteries owing to their versatile redox chemistry, sustainability, and potential low cost. Here, we present polydiphenylamine as a moderately high voltage (1.25 V vs. Zn) and highly reversible organic cathode for aqueous zinc batteries. As revealed by cyclic voltammetry and spectroscopic analysis, the chemical oxidation-derived diphenylamine dimer electrochemically transforms into a cross-linked polymeric material during the first electrochemical oxidation (charge), which then operates by p-doping/de-doping redox of the amine center and a pseudocapacitor like solid-state charge storage mechanism during the subsequent discharge-charge cycles. With an 80 weight% active loading, the polymer cathode delivers a specific capacity of 138 mAh g-1 at 100 mA g-1 with 73% retention over 1000 cycles at 99.8% Coulombic efficiency. Excellent rate capability is evidenced by 87 mAh g-1 capacity at 400 mA g-1 and highly stable cycling of over 1200 cycles under variable current rates. Facile one-step synthesis, fast charge storage kinetics, and attractive electrochemical performance establish polydiphenylamine as a notable organic cathode candidate for aqueous zinc batteries.