Flexible Quasi-Solid-State Sodium-Ion Capacitors Developed Using 2D Metal–Organic-Framework Array as Reactor

Abstract

Achieving high-performance Na-ion capacitors (NICs) has the particular challenge of matching both capacity and kinetics between the anode and cathode. Here a high-power NIC full device constructed from 2D metal–organic framework (MOFs) array is reported as the reactive template. The MOF array is converted to N-doped mesoporous carbon nanosheets (mp-CNSs), which are then uniformly encapsulated with VO2 and Na3V2(PO4)3 (NVP) nanoparticles as the electroactive materials. By this method, the high-power performance of the battery materials is enabled to be enhanced significantly. It is discovered that such hybrid NVP@mp-CNSs array can render ultrahigh rate capability (up to 200 C, equivalent to discharge within 18 s) and superior cycle performance, which outperforms all NVP-based Na-ion battery cathodes reported so far. A quasi-solid-state flexible NIC based on the NVP@mp-CNSs cathode and the VO2@mp-CNSs anode is further assembled. This hybrid NIC device delivers both high energy density and power density as well as a good cycle stability (78% retention after 2000 cycles at 1 A g−1). The results demonstrate the powerfulness of MOF arrays as the reactor for fabricating electrode materials.