# Ultra‐Thin Hybrid Ion Exchange Interlayer for High Performance Aqueous Zn Metal Batteries

## TL;DR

A new ultra-thin hybrid layer improves the performance and lifespan of aqueous zinc metal batteries by stabilizing the zinc anode and preventing dendrite formation.

## Contribution

The development of a SPEEK/FCD hybrid interlayer that enhances Zn anode stability through ion exchange and SEI formation.

## Key findings

- Zn||Zn symmetric cells with the SPEEK/FCD interlayer show over 5500 h of stable cycling at 1 mA cm−2.
- The Zn||V2O5 full cell retains 89.8% of its initial capacity after 1000 cycles with the optimized electrode.
- The interlayer forms a ZnF2-rich SEI that suppresses parasitic reactions and stabilizes the interface.

## Abstract

The application of aqueous zinc metal batteries (AZMBs) is limited by the poor cycling stability and undesired dendritic growth of Zn anodes. Herein, a Zn anode with an ultra‐thin sulfonated poly(ether ether ketone) (SPEEK) and fluorinated carbon dots (FCDs) hybrid interlayer is developed to enhance AZMBs performance. The SPEEK/FCD interlayer possesses excellent stability and is found to play multiple functions, including effectively regulating electrolyte solvation structure by ion‐exchange groups, promoting ion transport through the ion‐exchange channels of the hybrid SPEEK/FCD interlayer, inducing the in situ formation of a stable ZnF2‐rich solid electrolyte interphase (SEI), and accommodating volume fluctuations during Zn plating/stripping cycles. As a result, at 1 mA cm−2 and 1 mAh cm−2, Zn||Zn symmetric cells with the optimized SPEEK/FCD Zn electrode exhibit an ultralong lifespan of over 5500 h, much better than that of the bare Zn electrode (119 h). In addition, at 1 A g−1 after 1000 cycles, the Zn||V2O5 full cell with the optimized electrode retains 89.8% of its initial capacity, compared to 40.3% for the bare Zn electrode. These superior performances indicate the optimized Zn electrode is promising for next‐generation AZMBs. Also, the simple and scalable method offers a valuable reference for improving the performance of other aqueous batteries and beyond.

An ultra‐thin SPEEK/FCD ion‐exchange interlayer modulates the Zn2+ solvation environment (–SO3
−), provides ion‐exchange pathways that homoginized the Zn2+ flux, and via F‐rich chemistry forms in situ ZnF2 that suppresses parasitics and stabilizes the interface; its integrity relieves interfacial stress. The interlayer delivers compact Zn, long‐life symmetric and Zn||Cu cycling, and 89.8% capacity retention over 1000 full‐cell cycles.