Robust, High-Contrast, Recyclable Zinc-Based Dynamic Windows via Synergistic Electrolyte and Interfacial Engineering

Zinc-based electrochromic devices offer a sustainable route for dynamic optical management but are plagued by poor cycling stability due to irreversible zinc plating/stripping and side reactions. Herein, we report a robust, high-contrast, and recyclable zinc-based dynamic window enabled by a synergistic electrolyte and interfacial engineering strategy. Molecular dynamics simulations and electrochemical analyses reveal a dual-ion cooperative mechanism that governs the reversibility: anions with the strongest binding affinity guide uniform Zn deposition by stabilizing the inner solvation shell, while formate anions co-enriched at the interface facilitate smooth stripping via protonation during the oxidation process. This orchestrated interplay effectively eliminates “dead Zn” accumulation and dendrite growth. Consequently, the device demonstrates a record-high lifespan of 15,000 cycles with negligible degradation and maintains a large optical modulation of >50%, along with multiple optical states (transparent, gray, black, and mirror). Furthermore, it achieves a large reflectance modulation (>50%) stable for over 2,000 cycles. This work establishes the recyclable zinc-based dynamic window as a scalable, high-performance alternative to conventional electrochromic systems, advancing the feasibility of solution-processed energy-saving windows in sustainable buildings.

💡 Research Summary

The paper presents a comprehensive strategy to overcome the long‑standing durability and performance limitations of zinc‑based reversible metal electrodeposition (RME) electrochromic windows. By simultaneously engineering the electrolyte composition and the counter‑electrode interface, the authors achieve a record‑breaking cycling life of over 15 000 transmittance‑modulation cycles and more than 2 000 reflectance‑modulation cycles while maintaining an optical contrast greater than 50 %. The electrolyte is a multi‑component, gelled system based on anhydrous dimethyl sulfoxide (DMSO) containing ZnBr₂ as the Zn²⁺ source, LiF, Li formate (LiCOOH), and poly(vinyl acetate) (PV A). Molecular dynamics simulations reveal a dual‑ion cooperative mechanism: fluoride anions (F⁻) exhibit the strongest binding affinity to Zn²⁺ (≈ –200 kJ mol⁻¹) and replace DMSO in the primary solvation shell at the electrode surface, promoting uniform nucleation and the in‑situ formation of a ZnF₂‑rich solid electrolyte interphase (SEI). This SEI suppresses side reactions, dendrite growth, and hydrogen evolution. Formate anions (HCOO⁻) bind with slightly lower affinity (≈ –170 kJ mol⁻¹) and become enriched at the interface. During the oxidation (stripping) step, the weakly acidic environment created by formate provides protons that assist the dissolution of the deposited Zn film, preventing the accumulation of “dead Zn”. PV A, despite its modest interaction energy, acts as a rheological modifier, increasing viscosity, homogenizing ion flux, and physically blocking dendritic protrusions. Experimental validation by scanning electron microscopy shows that the optimized electrolyte yields smooth, compact, dendrite‑free Zn deposits, whereas electrolytes lacking either LiF or LiCOOH produce coarse, poorly stripping films. Electrochemical impedance spectroscopy confirms low interfacial resistance (≈ 0.8 Ω·cm²) and high ionic conductivity (≈ 5 mS cm⁻¹), enabling rapid switching: deposition at –0.7 V completes in 5.5 s and stripping at +0.8 V in 7.1 s. The device operates in three distinct optical states—transparent (maximal solar transmission for heating), gray (balanced light transmission for privacy), and mirror/black (strong NIR and visible blocking for cooling). Optical measurements demonstrate ΔT > 50 % and ΔR > 50 % over the reported cycle numbers, with negligible degradation. The system also retains performance at 80 °C for more than 3 000 cycles, indicating robust thermal stability. By integrating a gel electrolyte, the authors eliminate leakage concerns and simplify solution‑processed fabrication, supporting scalability. Overall, the work establishes that a synergistic electrolyte design—leveraging strong fluoride anchoring for deposition and formate‑mediated proton‑assisted stripping—combined with polymer‑induced steric regulation, can deliver high‑contrast, multi‑state, recyclable zinc‑based dynamic windows suitable for energy‑saving applications in sustainable buildings.