A High-Performance Phenazine-Based Cathode for Aqueous Organic Zinc-Ion Battery

Abstract

Aqueous Zinc-ion batteries are very appealing for massive energy storage applications due to their inherent safety, low cost, and longevity. Nevertheless, the lack of positive electrode material (cathode) caused by the slow diffusion of Zn2+ inside solid inorganic frameworks is impeding their advancement. Organic electrode materials have recently been endorsed as a less-toxic and environment-benign substitute for traditional inorganic electrode materials. Even though, its performance is hampered by the poor rate capability and limited cycle life caused by cathode material deterioration during Zn2+ insertion/de-insertion. An efficient charge-discharge in aqueous zinc ion batteries, even at high current densities with good capacity retention, is made possible by the stability of aromatic organic heterocyclic cathode materials with the necessary intermolecular spacing. Herein, we describe a strategy to utilize a commercially available redox-active organic molecule (ROM), Phenazine (PNZ) derivative, which can offer efficient and reversible Zn2+ storage due to its high molecular symmetry with low molecular weight. The use of a cation exchange membrane and optimization of volume of the electrolyte and conductive carbon enabled the PNZ electrode to provide a better specific capacity value of 247 mAh g-1 (90% of the theoretical capacity of PNZ) at 1 A g-1 with a good capacity retention of 75 % over 300 cycles. These results indicated that exceptional water insolubility in small organic molecules like PNZ would make them a desirable electrode material for AZIBs. In contrast to conventional design ideas for organic electrode materials such as having a larger molecular weight or adding certain polar functional groups to the organic molecular bulk, our research offered fresh and insightful recommendations for the creation of simpler organic electrodes. Fig. 1. Cyclic performance with charge-discharge plots of PNZ/Katjen black carbon Zinc coin cells with Nafion 212 membrane a) capacity vs. voltage plot b) cycle number vs. capacity plot. Figure 1