Janus Separator with a Graphene Mesosponge Empowers High-Rate Zn-Ion Hybrid Capacitors

High Resolution Image Download MS PowerPoint Slide Aqueous Zn-based energy storage systems are attractive for safe and low-cost energy storage, but their practical application is limited by Zn dendrite growth, hydrogen evolution, and corrosion at the Zn anode. Herein, we report a Janus separator prepared by functionally modifying a cellulose nanofiber (CNF) membrane with a conductive graphene mesosponge (GMS) layer, solving the dendrite growth and parasitic reaction issues to realize stable Zn anodes. Benefiting from the high electrical conductivity, large surface area, and mesoporous structure of the GMS, the GMS-CNF separator homogenizes the electric field, lowers the local current density, and facilitates rapid Zn 2+ desolvation. As a result, the GMS-CNF separator enables uniform Zn deposition, delivering stable Zn plating/stripping in symmetric Zn//Zn cells for over 1200 h at 1 mA cm − 2 and 0.5 mAh cm −2 with a low overpotential of ∼22 mV and over 350 h at 5 mA cm −2 and 2.5 mAh cm −2 . Remarkably, it maintains stable charge−discharge even at an extremely high current density of 40 mA cm −2 . In Zn//AC hybrid capacitors, the Janus separator lowers charge-transfer resistance, improves capacitive response, maintains stable operation up to 12,000 cycles at 10 mA cm −2, and enables stable rate performance up to 100 mA cm −2 . These findings demonstrate that separator modification with porous carbon is a powerful strategy for advancing high-rate and long-life aqueous Zn-based energy storage devices.