Construction Of High-performance Zinc Ion Hybrid Capacitor Based On Porous Carbon Materials

Aqueous zinc ion hybrid capacitors（ZHCs）show the advantages of high safety,great cycling life and high power density,being widely considered to be a promising electrochemical energy storage device.Porous carbon is the most commonly capacitive material in ZHCs,with high specific surface area,rich raw materials and advanced pore structure.Nevertheless,the corresponding zinc ion hybrid capacitors exhibit low energy density,which restricts the further development.It is still a challenging problem to design porous carbon materials with high power density and high energy density for zinc ion hybrid capacitors.Our work focuses on synthesis and design of high-performance porous carbon materials for zinc ion hybrid capacitors.The main results of our work are as follows:（1）Hierarchical porous carbon spheres with rich nitrogen content were synthesized by polymerization-activation strategy.Hierarchical porous carbon spheres（PCS-5）exhibiting the most capacitive storage properties have been synthesized by adjusting the proportion of activator and activation temperature.The porous carbon spheres obtained by using the amino functional groups on 2,6-diaminopyridine have a high nitrogen content（8.73%）.Nitrogen-rich porous carbon spheres can provide additional pseudocapacitance that improves storage performance.With PCS-5 as the cathode material,metal Zn as the anode and 2 M Zn SO₄ as electrolyte,the aqueous ZHCs exhibit good electrochemical performance.At a current density of 0.1 A g^-1,the initial specific capacity of Zn//PCS-5ZHCs is 126.4 m Ah g^-1.Moreover,the capacity retention is 76.68%for Zn//PCS-5 ZHCs at 1 A g^-1 after 5000 cycles.At the same time,the energy storage device also provides the maximum energy density of 93.3 Wh kg^-1and power density of 7155.0 W kg^-1.（2）Honeycomb-like porous carbon（PPC）has been synthesized by a pre-oxidation and chemical activation method with polyacrylonitrile as the nitrogen and carbon source.With a specific surface area as high as 2926.4m² g^-1 as well as a pore volume of 1.41 cm³ g^-1,the material achieves rapid diffusion of electrolyte ions inside the PPC and good electrolyte ion adsorption performance.Therefore,the initial specific capacity exceeds200 m Ah g^-1(at 0.1 A g^-1)when assembled into ZHCs,and its capacity retention reaches 83.1%at 2 A g^-1after 20000 cycles.Moreover,Zn//PPC ZHCs can achieve the energy density of 102 Wh kg^-1even at a power density of 3672 W kg^-1.Besides,Zn@CC//PVA-Zn SO₄//PPC@CC ZHCs displays the specific capacity of 140.3 m Ah g^-1 at a current density of 0.1A g^-1.（3）Porous carbon fibers（CF）were synthesized by using polyacrylonitrile as raw material through the template method.Most of the pore size distribution of the porous carbon fibers is at 0.62 nm,which is beneficial to the adsorption of electrolyte ions（Sulfate ion diameter:0.58nm）.Hence,Zn//CF ZHCs exhibit very excellent electrochemical performance when CF is used as a capacitive cathode.At a current density of 2 A g^-1,the Zn//CF ZHCs exhibit very excellent cycling stability with the capacity retention of 98.3%after 20000 cycles.In addition,the Zn//CF ZHCs also exhibit the energy density of 136.2 Wh kg^-1 and the initial specific capacity of 181.7 m Ah g^-1.Besides,porous carbon fibers can not only provide short electric/ion transfer paths,but also offer rich active sites and improve ion adsorption capacity to achieve high energy storage.