| Lithium-ion batteries with outstanding energy density and supercapacitors specializing in power density have been the masters of the energy storage field for decades.However,with the ever-increasing double demand for energy and power of new large-scale energy-consuming devices,neither lithium-ion batteries nor supercapacitors can shoulder such a heavy task alone.Metal-ion hybrid capacitors,burgeoning energy storage devices that theoretically provide power density and cyclability comparable to supercapacitors without sacrificing energy density,are expected to bridge the gap between lithium-ion batteries and supercapacitors.Among them,sodium/potassium-ion hybrid capacitors have attracted tremendous attention due to the low reduction potential of Na+/K+,profuse natural abundance and optimistic economic prospects.However,due to the immaturity exploit and design strategies of electrode materials,and the imbalance of anode and cathode kinetics of the device system,further in-depth research is still needed bofore the promotion and application of high-performance sodium/potassium-ion hybrid capacitors.This thesis is based on phenolic resin-derived porous carbon and cucurbit[6]uril-derived porous carbon,and is dedicated to research from the perspective of sodium/potassium-ion hybrid capacitor architecture.Through the targeted design of the structure of anode and cathode materials and the rational selection of auxiliary components that match the electrode materials,the energy storage mechanism of the porous carbon anode and cathode electrodes has been revealed,the bonding mechanism of different binders has been clarified,and the relationship between the electrochemical performances of sodium/potassium-ion hybrid capacitors and the microstructure of electrodes has been unveiled.The innovative results as follows:(1)We have clarified the relationship between the performances and the structure of sodium-ion hybrid capacitors porous carbon electrode,and revealed the construction principles of high-performance dual-carbon sodium-ion hybrid capacitors.Using phenolic resin-derived porous hollow carbon spheres and hollow carbon bowls based on in-situ silica template as reference anode and cathode materials,systematic electrochemical tests were carried out in sodium-ion half-cells.Benefiting from the interconnected hierarchical porous structure,amorphous carbon framework and ion-permeable shell,the hollow carbon spheres anode exhibits a reversible specific capacity of 728 mA hg-1 at 0.1 A g-1,maintains 133.3 mA hg-1 at 20 A g-1,and displays almost no specific capacity attenuation after 5000 cycles at 5 A g-1.Due to the large-size micropores dominated hierarchical porous structure,the reversible specific capacity of hollow carbon bowls cathode is up to 198.7 F g-1.As a consequence,the dual-carbon sodium-ion hybrid capacitors constructed with hollow carbon spheres anode and hollow carbon bowls cathode exhibit the ultimate energy density and power density of 128.5 Wh kg-1 and 11.9 kW kg-1,and a lifespan of up to 4500 cycles,showing bright application potential.(2)We have systematically clarified the relationship between the binder and the performances of potassium-ion hybrid capacitors porous carbon anode,unveiled the bonding mechanism of binder,and revealed the construction principles of dual-carbon potassium-ion hybrid capacitors.Using phenolic resin-derived nitrogen-doped porous hollow carbon spheres as the reference anode material,the effect of the binder on the performances of porous carbon anode was systematically studied in potassium-ion half-cell.Among them,the anode bonded with sodium alginate exhibits the highest reversible specific capacity(322 mA hg-1 at 0.1C),the optimal rate capability(134 mA hg-1 at 20C),the strongest durability and considerable initial Coulombic efficiency(37.1%).Further characterization showed that the chemical interaction between sodium alginate and porous carbon anode and the special structure of its own molecular chain endow sodium alginate excellent bonding properties.As expected,the dual-carbon potassium-ion hybrid capacitors constructed with nitrogen-doped porous hollow carbon spheres anode,KOH-activated hollow carbon spheres cathode and sodium alginate binder demonstrate excellent comprehensive performance indicators.The successful construction of high-performance potassium-ion hybrid capacitors opens a new avenue for the development and application of potassium-ion hybrid capacitors in the future.(3)We have proposed a universal strategy to optimize the electrochemical performances of potassium-ion hybrid capacitors porous carbon anode,and clarified the energy storage mechanism and nitrogen action mechanism of the nitrogen-doped porous carbon anode.The cucurbit[6]uril-derived porous carbon with an ultrahigh nitrogen doping level of 15.5 at.%was dispersed in the graphene framework with the aid of ultrasound to form a pomegranate-like composite.The potassium-ion half-cell test results show that the potassium storage performance of the composite has been improved in all aspects compared to cucurbit[6]uril-derived porous carbon.In-situ electrochemical Raman,in-situ EIS,and ex-situ XPS revealed the energy storage mechanism of the reversible conversion of amorphous carbon and K-C compounds of composite;in-depth XPS and HRTEM clarified that the SEI film of the composite is mainly composed of K2CO3,K2O and K-containing organics;theoretical calculations proved that the N-6 dominated N configuration is beneficial to the potassium storage performance of the porous carbon anode.Consequently,potassium-ion hybrid capacitors constructed with composite anode and KOH-activated cucurbit[6]uril-derived porous carbon cathode demonstrate ultrahigh energy/power density(172 Wh kg-1/22 kW kg-1)and extraordinary cyclability(81.5%capacity retention for 5000 cycles at 5 A g-1),the comprehensive indexes of energy density,power density,and cycling stability of this device are superior to most of the reported potassium-ion hybrid capacitors.(4)We elucidated the relationship between the pore structure and electrochemical performance of the potassium-ion hybrid capacitors porous carbon cathode,and established a new evaluation standard for the electrochemical performance of porous carbon based on the pore structure.Based on the aforementioned cucurbit[6]uril-derived porous carbon,a series of hierarchical porous carbons with narrow pore size distribution of 0.5-4 nm were synthesized by precise adjusting KOH dosage,and symmetrical supercapacitors were assembled based on these hierarchical porous carbons to evaluate the relationship between the pore structure and the electrochemical performance of porous carbon.Systematic Trasatti theoretical calculations and linear fitting analysis show that the reversible specific capacity of symmetrical supercapacitors and the ion-accessible pore volume of hierarchical porous carbon are generally linearly positively correlated in different electrolyte systems,which provides a theoretical basis for elucidating the relationship between electrochemical performance and pore structure of the carbon-based supercapacitors. |
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