| As two typical efficient and clean electric energy storage devices,supercapacitors and alkali-metal secondary batteries have been widely studied and reported in the past decade.However,according to the energy storage mechanism of the two systems,it is difficult to meet the practical requirements with both high energy density and high power density,which severely limits their practical application space.Therefore,novel energy storage devices with high energy and high power have come into a hot spot.Hybrid capacitors(HSCs),composed of battery-type materials and capacitive double-layer electrode materials,are regarded as a promising energy storage device because they can get the properties of high power and high energy at the same time.Although hybrid capacitors inherit the advantages of supercapacitors and alkaline-secondary batteries,their further improvement is still restricted by the capability and design of anode and cathode materials.The narrow valence band and band gap of transition metal selenides give them higher electronic conductivity,which is conducive to fundamentally improving the charge transfer rate of battery-type electrode materials,thus solving the defect of low power density.At present,studies on transition metal selenide(TMSe)mainly focus on single metal selenides,while reports on bimetal selenides with higher electrical conductivity are still few or unitary.Carbon materials with high electrical conductivity have been widely used as battery type and capacitive electrode materials due to stable chemical properties,controllable morphologies and wide sources.However,the low theoretical capacity and the slow kinetics when used as battery electrode materials are the biggest obstacles to the application of carbon materials.And the current research also focuses on the electrode material,ignoring its practical application.In this paper,firstly,a series of nickel-cobalt selenides with different crystalline structures and morphologies were prepared by using low-cost metal alcohols as precursors.They were studied on the influences of the temperature,time and Ni/Co ratios on the final product Ni-Co selenides.The electrochemical properties of Ni-Co selenides as the electrode materials of aqueous HSCs were investigated.The electrochemical properties of Ni-Co selenides as electrode materials for water aqueous HSCs were investigated.Secondly,the phytic acid doped polypyrrole precursor was directly pyrolyzed and carbonized or activated by KOH to prepare carbon materials with high defects,rich heteroatoms and wide layer spacing and the graded porous carbon materials with controllable pore size,respectively.The relationship between their chemical composition,structural characteristics and electrochemical energy storage behavior was studied in detail.The electrochemical performance of water system mixed capacitor,symmetrical supercapacitor and potassium ion mixed capacitor and other energy storage devices constructed by the three electrode materials were studied comprehensively.The research results are as follows:A hollow bimetallic perselenide with Ni-CO biphase(named N2C4Se)is reported.Its structure is designed and regulated to accelerate ion diffusion and promote electron transfer,thus achieving high energy density and excellent power density in HSCs.To be specific,a hollow biphasic N2C4Se composed of highly conductive marcasite-type CoSe2 and highly capacitive pyrite-type NiCoSe4 was successfully synthesized by using solvothermal method with metal alcoxides as precursor and changing the formation of marcasite and pyrite-type phases by adjusting the Ni/Co ratios.Due to the enhanced electron conductivity and shortened ion/electron transfer distance,the specific capacitance of N2C4Se electrode(1008 F g-1 at 0.5 A g-1)is about 3 times and 1.5 times that of CoSe2 and NiCoSe4,respectively.When the current density expands 40 times,there is still 85%available capacity.The carbon materials with high defects,abundant heteroatoms and wide layer spacing were successfully prepared by direct pyrolysis and carbonization of polypyrrole precursor doped with phytic acid in different proportions.It is found that the introduction of P can not only widen the layer spacing(0.381 nm),but also induce the distortion of nitrogen-rich carbon electronic structure to achieve more defects and edge positions.Compared with non-P-doped nitrogen-enriched carbon,the active N content of P-doped N-enriched carbon increased from 80.4%to 85.8%.The increase of active nitrogen content can effectively increase the adsorption of potassium ion.In addition,the electrical conductivity of carbon altered by P atoms can ben ameliorated.The anode(NCP1)delivers specific capacity of 310 mAh g-1 at 25 mA g-1.Even if the current density increased to 200 times,the specific capacity is still 47 percent for the initial.The hierarchical porous carbon(HPC)with high effective micropore(81.82%total micropore with more than 0.7 nm,79.84%micropore with more than 0.8 nm),high mesoporous content and high oxygen-rich heteroatoms were prepared by using phytic acid-doped polypyrrole as the precursor,carbonized at low temperature(400?)and activated by KOH at high temperature(600??900?).The fractional porous carbon with high specific surface area(3208 m2 g-1),high mesoporous content(61.67%)and rich nitrogen oxygen heteroatoms(1.10 at%nitrogen and 7.86 at%oxygen)was prepared at 900?.High specific surface area can provide enough charge storage space for electrolyte ions,thus contributing more capacity;the high proportion of mesoporous is conducive to the rapid ion transfer of electrolyte and improves the capacity and multiplier performance of HPC.When used as anode and cathode material to assemble symmetrical supercapacitor,(SSCs)showed excellent electrochemical performance in aqueous electrolyte.Aqueous HSCs composed of HPC-900 and Nickel-cobalt selenide(N2C4Se)delivers excellent energy(34.8 Wh kg-1).Potassium ion HSCs consisted of NPC1 and HPC-900 output outstanding energy density of 103Wh kg-1 with power density of 6106.2 W kg-1. |
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