Electrochemically prepared ultrathin two-dimensional graphitic nanosheets as cathodes for advanced Zn-based energy storage devices

Zinc-ion supercapacitors (ZISCs) exhibit great potential to store energy owing to the benefits of high power density and environmentally friendly features. However, solving the drawbacks of low specific energy and poor cyclic performance at high current rates is necessary. Thus, developing better cathode materials is a practical and efficient way to overcome these limitations. This work presents an encouraging design of two-dimensional (2D) graphite ultrathin nanosheets (GUNSs) as a cathode material for ZISCs. The experimental results show that the GUNSs-based cathode material exhibits a wide surface area and rapid charge transformation features. The 2D GUNS as a cathode was tested in three-electrode systems, and it provided an exceptionally high capacitance of 641 F/g at 1 A/g in an aqueous ZnSO electrolyte, better than GUNS-N (462 F/g at 1 A/g) and pristine graphite (225.8 F/g at 1 A/g). The 2D GUNS has a rate performance of 43.8% at a current density of 20 A/g, better than GUNS-N (35.6%) and pristine graphite (8.4%) at the same conditions. Furthermore, a ZISC device was fabricated using GUNSs as cathode and Zn-foil as anode with 1 M ZnSO electrolyte (denoted as GUNSs//Zn). The as-fabricated GUNSs//Zn device exhibits an excellent capacitance of 182.5 F/g at 1 A/g with good capacitance retention of 97.2%, which is better than pristine graphite (94.6%), and nitrogen-doped GUNS (GUNS-N ) cathode (95.7%). In addition, the GUNSs//Zn device demonstrated an ultrahigh cyclic life of 10,000 cycles, and 96.76% of capacitance was maintained. Furthermore, the GUNSs//Zn device delivers a specific energy of 64.88 W h/kg at an ultrahigh specific power of 802.67 W/kg and can run a light-emitting diode for practical applications.