Research And Development Of High-performance Supercapacitors Based On Nanocarbon Composites

Supercapacitors are considered as one of the most promising energy storage devices due to their high power density,long cyclic life,fast charge-discharge rate and environmentally friendliness.Unfortunately,the practical application of commercial supercapacitors is limited because of their low energy density,poor volume performance,low power density and safety.Therefore,it is of great importance to research and develop high performance supercapacitors with high specific energy,high power density,long cycle life,high safety and reliability.In order to address the shortcomings of current supercapacitors,the core components of supercapacitors including electrode,current collector and electrolyte have been systematically studied to develop high-performance supercapacitors in this thesis.Based on the above conception,the major works of the present thesis include the following aspects:1.Commercial activated carbon(AC)and conductive additive(CB)were incorporated with multi-component carbon nanomaterials(CNT and CNF)through a simple slurry process to synthesize novel high-performance activated carbon/carbon nanomaterial 3D nanocomposite.Thanks to the synergistic effects of 3D conductive network formed by the interweave of CB,CNT and CNF and the 3D hierarchical pore structure constructed by these multiple carbon nanomaterials,along with the effects of"particle-mixing-interaction",the optimized novel 3D nanocomposite electrode(AC/CB/CNT/CNF,NCE-3)shows a high packing density(0.63 g cm^-3),a high rate capability(capacitance retains 77.5%at 80 A g^-1 vs.0.5 A g^-1),a high energy and power density of 23.5 Wh kg^-1(29.6 Wh L^-1)and 80.7 k W kg^-1(101.7 k W L^-1),and outstanding cycle stability(capacitance retains 91.4%after charging/discharging at 10 A g^-1 for 30000 cycles),significantly exceeding those of conventional AC electrode.2.An innovative in-situ wrapping synthesis method was proposed,in which the AC/reduced graphene oxide(AC@r GO)composite was synthesized by in-situ compositing r GO with AC during the preparation of r GO.A simple slurry method was then used to combine the AC@r GO with CNF and CB to develop a high-power graphene based 3D nanocomposite electrode.Due to the improvement in conductive mode of compositing electrode system from the simple"point-to-point"mode to a more efficient 3D"point-line-plane"mode enabled by the introduction of CNF and r GO,along with the synergistic effects and interaction of CB,CNF and r GO,the resultant AC@r GO/CB/CNF nanocomposite possesses an efficient 3D conductive network and hierarchical pore structure,as well as a higher electrode packing efficiency,so as to achieve higher packing density(0.63 g cm^-3)and specific capacitance(106.2 F g^-1,66.9 F cm^-3),excellent rate performance(83.13%capacity retention at 80 A g^-1),higher energy density(21.1 Wh kg^-1,26.5 Wh L^-1)and power density(84.7 k W kg^-1,106.8k W L^-1),and long cycle life(capacitance retains 91.25%after 15000 cycles at 10 A g^-1).3.By using a simple synthesis process of conductive coating slurry and convenient conductive coating preparation method,commercial multiple carbon nanomaterials(such as graphene,CNF,CNT,and CB)were adopted as hybrid conductive coating on the surface of etched aluminum foil current collector to develop a multi-component nanocarbon coated aluminum foil.The special structure and conductive mode of multiple carbon nanomaterials and their strong adhesion on the surface of the collector,as well as their persistent protection to the corrosion of aluminum foil during the long-term cycling make the multi-component nanocarbon coated aluminum foil to exhibit significantly improved interface roughness and contact area,enhanced interface adhesion and lower interface impedance,thus greatly improving the power performance and cycling stability of capacitors.Among them,the maximum power density of the capacitor based on CB/CNT/CNF carbon coated aluminum foil can reach 90.84 k W kg^-1,and the energy density at the maximum power density can also achieve 15.63 Wh kg^-1.After 20000 cycles at a current density of 10 A g^-1,the capacity retention and columbic efficiency are as high as 90.82%and 96.99%,respectively.4.A new type of highvoltage electrolyte with wide electrochemical stability window(8.3V),high conductivity(18.58 m S cm^-1 at room temperature)and excellent temperature adaptability was developed by combining SBP-BF₄ with a solvent with an excellent electrochemical stability and high dielectric constant(?-GBL).The prepared novel electrolyte was incorporated with the NCE-3 electrode to develop a high energy supercapacitor.Owing to the excellent conductivity and high packing density of NCE-3 and the high withstand voltage window and conductivity of SBP-BF₄/GBL,the developed high energy supercapacitor can work stably at a high voltage of 3.2 V and show excellent energy and power performances,as well as an outstanding cycling stability.The energy and power density are as high as 37.73Wh kg^-1(47.54 Wh L^-1)and 52.08 k W kg^-1(65.62 k W L^-1),respectively,and a high capacity retention of 71.31%after 20000 charge/discharge cycles at 10 A g^-1,which significantly outperforms the current commercial supercapacitor technology.In this thesis,high-performance supercapacitors with high energy and power density,long cycle life and high safety have been developed by innovative experimental conception and comprehensive system analysis.The commercial availability of the materials used,the convenience of the proposed preparation method,and the superiority of the new materials and new devices developed have made the present work to show good commercial application prospects.In addition,the new methods,new technologies and novel materials of this work can be used to develop other high performance energy storage devices(such as lithium-ion batteries,fuel cells and solar cells).