Research On The Preparation And Electro-Chemical Properties Of The Cathode Materials For Sodium-ion Capacitors

In recent years, Na-ion capacitor（NIC） have received a great attention and gradually become a new hot spot in the field of electrochemical energy storage and conversion. NICs are also hybrid electrochemical capacitors. Compared with the electric double layer capacitor（EDLC） and sodium-ion battery（NIB）, Na-ion capacitor have taken advantages of the electrochemical performance of EDLC and NIB, due to their ability of delivering high levels of high energy, high density and long cycle-life. Compared with organic electrolytes, aqueous electrolytes are safer, more environment-friendly, lower production cost, double higher ionic conductivity. There is no need for aqueous electrolytes to add more safety devices and external protection circuitry to prevent overcharging. These advantages were explained why the NIC with aqueous electrolytes have attracted many eyes in the energy research.In this paper, preparations and electrochemical properties of Na₃V₂（PO₄）₃、NaCo₂O₄ and Na₀.44MnO₂ materials were applied to the cathode of sodium-ion capacitor. The structure and morphology of materials were characterized by XRD, TEM, SEM. NIC was assembled using Na₃V₂（PO₄）₃、NaCo₂O₄ and Na₀.44MnO₂ as cathode electrode materials and activated carbon（AC） as anode electrode material, and were tested by cyclic voltammetry, chronopotentiometry cycling and electrochemical impedance methods.Na₃V₂（PO₄）₃（NVP） and Na₃V₂（PO₄）₃/C（NVP-C） composite materials were synthesized by sol-gel method. The two samples were characterized on the structure and morphology, and electrochemical properties of Na₃V₂（PO₄）₃/AC, Na₃V₂（PO₄）₃-C/AC were researched. In optimal potential range（0-1.5V）, NVP-C/AC displayed the specific capacitance and energy density as high as 51.0 F/g and 15.9 Wh/kg at the current density of 0.65A/g. NVP-C/AC demonstrated that it retained up to 80% of the initial capacitance after 100 cycles.NaCo₂O₄ materials were synthesized by high temperature solid-state and sol-gel method. The samples were characterized on the structure and morphology, and electrochemical properties of NaCo₂O₄ were researched. In optimal potential range（0-1.5V）, the optimal sample（NaCo₂O₄/AC） calcined at 790℃ displayed energy density and power density as high as 9.4 W h/kg and 208.6 W/kg at the current density of 1A/g. NaCo₂O₄/AC demonstrated that it retained up to 80% of the initial capacitance after 200 cycles.Na₀.44MnO₂ materials were synthesized by solid-state and sol-gel method. The samples were characterized on the structure and morphology, and electrochemical properties of Na₀.44MnO₂ were researched. In optimal potential range（0-1.5V）, the optimal sample（Na₀.44MnO₂/AC） calcined at 900℃ displayed energy density and power density as high as 9.4 Wh/kg and 208.6 W/kg at the current density of 1A/g. Na₀.44 MnO₂/AC demonstrated that it retained up to 80% of the initial capacitance after 200 cycles.