A functionalized separator enables dendrite‐free Zn anode via metal‐polydopamine coordination chemistry

Abstract

Designing a multifunctional separator with abundant ion migration paths is crucial for tuning the ion transport in rocking‐chair‐type batteries. Herein, a polydopamine‐functionalized PVDF (PVDF@PDA) nanofibrous membrane is designed to serve as a separator for aqueous zinc‐ion batteries (AZIBs). The functional groups (OH and NH) in PDA facilitate the formation of ZnO and ZnN coordination bonds with Zn ions, homogenizing the Zn‐ion flux and thus enabling dendrite‐free Zn deposition. Moreover, the PVDF@PDA separator effectively inhibits the shuttling of V‐species through the formation of VO coordination bonds. As a result, the Zn/NH4V4O10 battery with the PVDF@PDA separator exhibits enhanced cycling stability (92.3% after 1000 cycles at 5 A g−1) and rate capability compared to that using a glass fiber separator. This work provides a new avenue to design functionalized separators for high‐performance AZIBs.

Dendrite‐Free Engineering toward Efficient Zinc Storage: Recent Progress and Future Perspectives

“…These Zn protrusions then expedite the inhomogeneous distribution of Zn 2+ diffusion and electric field around them. With the cycle number increasing, Zn dendrite growth enhances the surface roughness, and consequently continuous growth of harsh needle‐shaped Zn dendrites gives rise to capacity fading of Zn‐ion batteries [9c,11b] . Upon repeated battery cycles, Zn dendrites could fall off from the anode surface to become “dead Zn”, or even pierce the separators to trigger the battery short circuit due to Zn's high Young's modulus of 108 GPa, thereby resulting in irreversible device failure particularly at large current densities [6b,c,13] .…”

“…Apart from hydrogel polymer electrolytes, battery separators as the key assembly component can also prevent physical contact between the two electrodes to avoid short circuits and regulate the Zn 2+ flux [2a,9c,50] . The commonly used glass fiber separator in current Zn‐ion batteries owns remarkable hydrophilicity and electronic insulation to tolerance the harmful Zn dendrite growth [4b,6b] .…”

“…Thus, rational design of advanced separator material with tailored ion‐transfer highways and high mechanical strength is critical to regulate the Zn 2+ flux for dendrite‐free and uniform Zn deposition. Recently reported strategies includes both the optimization of existing separator membranes and the innovative exploitation of novel multifunctional separators [2a,6b,9c,50–51] . As an example, the glass fiber membranes were modified with the introduction of 2D C 3 N 4 nanosheets, which functioned as a Zn 2+ ‐ion distributor to physically promote the Zn 2+ penetration via pore tunnels in the separator network and further guide the Zn 2+ flux through the chemical coordination effect with C 3 N 4 [6b] .…”

“…Besides, novel multifunctional separators like cellulose/Nafion‐based membranes have also contributed to the homogeneous Zn 2+ distribution and the termination of dendrite growth and other side reactions. Zhou's group proposed the preparation of a polydopamine‐functionalized nanofibrous membrane as the separator for high‐performance Zn‐based batteries, in which −OH and −NH‐ functional groups in polydopamine promoted the Zn 2+ coordination with the Zn−O and Zn−N bonds, thus unchoking the Zn 2+ flux for dendrite‐free zinc deposition [9c] . At 2/5 mA cm −2 , serious protrusion agglomeration occurred on the substrate surface with the conventional glass fiber, while the substrate surface with the as‐obtained nanofibrous membrane separator was homogenous with no cracks/pores (Figure 8).…”

Supramolecule-Based Excluded-Volume Electrolytes and Conjugated Sulfonamide Cathodes for High-Voltage and Long-Cycling Aqueous Zinc-Ion Batteries

“…By optimizing electrolyte compositions, adjusting zinc anode interfaces, and other strategies, the long-term cycling performance of zinc anodes can be obviously improved. − The top-view and side-view morphologies of Zn anodes after 500 cycles in different electrolytes at 5.0 C are shown in the scanning electron microscopy (SEM) images (Figure S23). After adding HBCD into the electrolyte, a smooth Zn anode surface without obvious zinc dendrite growth was observed (Figure S23a,c,e).…”