A High‐Performance Oxidized Graphene for Dendrite‐Free Anodes and Kinetically Enhanced Cathodes of Aqueous Zn‐Ion Batteries

Aqueous Zn‐ion batteries offer the prospect to meet future energy storage demands addressing safety and sustainability concerns. Still, their practical implementation faces several issues related to electrode performance. Although carbon nanomaterials show promise in overcoming these challenges, they must be properly tuned to fully exploit their potential. Here, oxidized graphene rich in carboxylic acid groups developed via a simple electrochemical exfoliation route is used to tackle specific challenges of aqueous Zn‐ion batteries, namely, short Zn anode cycle life and sluggish cathode reaction kinetics. Thin coatings of this graphene (~3–9 μm thick) are shown to provide efficient interfacial protection to Zn electrode, mitigating side reactions and preventing dendrite evolution. The protected electrodes exhibit much longer lifespans when tested in symmetric cells (e.g., >1200 h at a current/capacity of 5 mA cm −2 /5 mA h cm −2 ), generally outperforming those using other carbon (nano)materials in this role, including graphene oxides obtained by common preparation methods. Full cells comprising protected Zn anodes and a Prussian Blue analogue as the cathode material exhibit a substantially higher retention of capacity upon cycling than that of cells with bare Zn anodes. Regarding the improvement of cathode reaction kinetics, the use of the present oxidized graphene as a conductive substrate boosts the performance of an organic cathode based on a small quinone molecule by promoting a faster charge storage kinetics than common conductive additives. Such enhancement stems from the contribution of protons as charge carriers within the cathode, which is favored by the abundance of oxygen groups.