Construction And Research Electrochemical Performances Of Positive And Negative Electrode Materials For Supercapacitor

Supercapacitors have huge potential applications in energy storage,energy buses,and portable electronic communications due to their good rate performance,low cost,and environmental friendliness.However,the energy density grows slowly restricts the progress of supercapacitor commercial application.Designing the composition and structure of electrode materials and effectively constructing functional interfaces are the most important methods to develop high-performance supercapacitors.Improving electrode surface activity,shortening ion diffusion distance,increasing the contact area between electrode material/electrolyte and forming a potential barrier facilitates electron transport are useful ways to achieve high energy density supercapacitor.In addition,there are new challenges that develop a simple and practical strategy to further increase electrode materials electrochemical performance and general achieve the increasement of supercapacitor energy density.Therefore,the starting point of this paper is to obtain positive and negative electrode materials(transition metal composites and carbon materials)with large electrochemical activity specific area,high electrical conductivity and stable structure for high-performance supercapacitors.Electrode materials with optimized structure,controllable morphology,and multi-component composite synergy with three-dimensional structure are designed and prepared.The electrochemical performances and energy storage mechanism of electrode materials and supercapacitors are deeply studied and revealed through structural characterization,DFT calculation,and electrochemical analysis.The influences of electrolyte wettability,conductivity and supercapacitor specific capacitance with external magnetic field are proposed.The mechanism of magnetic field is discussed and analyzed in detail.The obtained results are as following:1.Herein,3D Ni Co Fe alloy framework covered with Ni Co Fe-OH nanosheets hybrid architecture is constructed via solid-state-grinding and subsequent glycerol solvothermal treatment methodes.High conductive Ni Co Fe alloy as core and high capacity Ni Co Fe-OH nanosheets with abundant active sites as shell,such structure accelerates ions transport and increases the electrode contact area with KOH electrolyte.Moreover,the abundance of existing interfaces between the Ni Co Fe and Ni Co Fe-OH structures produces more electrochemical activity and presents further improvement to the electrical conductivity.The constructed 3D space structure also makes the electrode material have more pores and suitable pore size,which is more conducive to the rapid transport of ions.The assembled Ni Co Fe/Ni Co Fe-OH//activated carbon(AC)asymmetric supercapacitor(ASC)exhibits ultra-high cycling stability,even after 20,000 cycles the capacitance retention still remain89.3%.2.The AC,CNTs and rGO perfectly mixed via the intrinsic van der Waals forces and the?–?stacking interactions to form three-dimensional(3D)structure composite electrode material during the stirring process at room temperature.1D CNTs and 2D r GO are interwoven into a 3D porous and flexible framework,which provides support for further anchoring of AC particles.The suspending AC particles anchor into a mass of ultrathin graphene oxide and wrapped by the CNTs not only improved it conductivity but also in order to further prevent the aggregation of r GO and CNTs.Therefore,the synergistic effect between AC,CNTs and r GO makes GCA composites have a larger specific surface area and a suitable pore structure,further endows all components contribute to the electrode specific capacitance.As aspect,the GCA composite presents the largest specific capacitance(277 F g^-1)and exhibits 52.2%capacitance retention at 30 A g^-1better rate performance.Consequently,the as-assembled symmetrical supercapacitor(SSC)based on this GCA composite as electrodes displays a considerable energy density of 11.2 Wh kg^-1 at a power density of 861.6 k W kg^-1.The same as the anode material and the Ni Co Fe/Ni Co Fe-OH cathode material we synthesized before to assemble an asymmetric supercapacitor,resulting in an energy density of 50.6 Wh kg^-1 at a power density of 812.2 W kg^-1.3.The Fe₃O₄@NiS/Co₃S₄ flexible positive and negative electrode material is constructed with tuning different amounts of NiS/Co₃S₄ nanosheets covered on Fe₃O₄nanorods by electrodeposition method.Since the two electrode materials have the same composition,they have no repulsion,thus the mass matching process of anode and cathode for ASC assembly is omitted.By experimental observation and theoretical calculation,it is confirmed that Fe₃O₄@NiS/Co₃S₄core-shell structure forms a heterostructure interface between Fe₃O₄and Co₃S₄,which can hold and adsorb more ions.Thereby,the flexible all-solid state ASC device shows high energy density(77.6 Wh kg^-1)and power density(828.3 W kg^-1)as well as long cycle stability(91.7%of capacitance retention after 10 000cycles).As a flexible energy storage device,it can be bent and twisted,also showing consistent electrochemical performances.Moreover,just one single ASC can lighten up fifteen LED bubbles till three minutes due to its large voltage window.It may bring a new idea to fabricate high-performance electrode materials.4.The effect of external magnetic field on the performance of supercapacitors was studied.The Lorentz force generated by coupling with the external magnetic field and the internal electric field,which promotes the transport of ions in electrolyte,improves the efficiency of ion insertion/intercalation in electrode material,and increases the contact area between ions in electrolyte and electrode surface.Thereby,they affect the comprehensive electrochemical performance of supercapacitors.Meanwhile,the magnetic field also enhances the electrode material electrolyte wetting ability.The experimental results show that the energy density of symmetrical supercapacitors assembled with GCA electrode has also been significantly improved and increased about 62%under the magnetic field condition(GCA//GCA SSC:from 11.2 to 18.1 Wh kg^-1).Moreover,the other electrochemical properties of SSC and ASC are also improved to a certain extent.The energy density of Ni Co Fe/Ni Co Fe-OH//GCA increased from 50.6 Wh kg^-1 to 61.4 Wh kg^-1.The energy density of Fe₃O₄@NiS/Co₃S₄-5c//Fe₃O₄@NiS/Co₃S₄-3c increased from 74.8 Wh kg^-1to 77.4 Wh kg^-1.