Intrinsic dual active sites synchronously regulate the solvation structure and interface to boost a highly stable Zn anode

Abstract

Aqueous zinc ion capacitors (AZICs) are important candidates for next-generation high-efficiency energy storage systems due to their intrinsic safety, cost-effectiveness, and environmental friendliness. However, the cycle life and coulombic efficiency (CE) of AZICs are limited by the intrinsic interfacial kinetic instability of the Zn anode. Based on the concept of green chemistry, this study innovatively introduces a green and renewable dual-active site molecule, caprolactam (CPL), as an electrolyte cosolvent to synchronously regulate the solvation sheath structure and the electrode/electrolyte interface microenvironment to promote the stability of the Zn anode. Experiments and molecular dynamics simulations show that CPL can anchor water (H₂O) molecules in the electrolyte through its intrinsic hydrogen bond donor (–NH–) and acceptor (CO) dual active sites to replace H₂O in the Zn²⁺ solvation structure, destroy the original hydrogen bond network, and form a dynamic electrostatic protection layer at the Zn anode interface. As a result, the cycle life of Zn/Zn batteries using the ZnSO₄ + CPL electrolyte is close to 2000 h. Furthermore, the Zn//AC AZIC with the ZnSO₄ + CPL electrolyte delivers excellent capacity (70 mAh g⁻¹) and stable CE (≈100%) even after more than 30 000 ultra-long cycles at a current density of 4 A g⁻¹.