Crystal orientation enabling rapid Zn2+ migration for advanced zinc-ion hybrid capacitors

Abstract

Aqueous zinc-ion hybrid capacitors (AZIHCs) are promising for large-scale energy storage given their superiority in cost and safety, whereas dendrite growth on zinc anodes limits their viability. Metal-organic frameworks (MOFs) exhibit the potential to inhibit dendrite growth due to their unique structure, but the suppression mechanism on different crystalline planes has always been overlooked. Herein, inspired by theoretical simulations, (110) crystal surfaces exhibit unique Z-type channels in ZIF-8, which significantly reduces the migration energy barrier of Zn2+ from 1.2 eV to 0.2 eV compared to the (100) crystalline surface, enabling homogeneous zinc ion deposition. Conversely, (100) surfaces hindered zinc ion transport due to their smaller pore diameter. As predicted, the lifetime of symmetric cells with as-prepared ZIF-8–110@Zn was about 18 times than that of ZIF-8–100@Zn cells at 1 mA cm-2. In-situ optical microscopy also revealed uniform zinc ion deposition with ZIF-8–110@Zn, whereas dendrite growth occurred in bare zinc and ZIF-8–100@Zn anode. Assembling it with activated carbon (AC) cathode for AZIHCs deliver a long cycle life of 3500. This pioneering study not only provides a strategy for further enhancing electrochemical performance by tuning the dominant facets of MOFs, but also provides novel insights into the mechanism of zinc anode protection.