| The rapid development of social economy is related to the sustainable utilization of resources.With the depletion of fossil energy and the deterioration of environment,there is an urge to develop new energy storage devices to deal with the energy crisis caused by the depletion of primary energy.Among many energy storage devices,supercapacitors are considered to be one of the most potential energy storage devices due to their advantages of high power density,fast charging speed,long cycle life and so on.Nowadays,inorganic materials like carbon materials or transition metal oxides/hydroxides are mainly used as electrodes for commercial supercapacitors.However,their obstacles consist of high cost,mechanical brittleness,and environmental pollution,hamper the further development of supercapacitor toward flexible and sustainable concerns.Compared with the traditional inorganic compounds,the redox active organic polymers with conjugated structures have the advantages of stable structures,flexible design,low cost and strong sustainability,showing great potential in the field of supercapacitor applications.Based on this,a series of redox active poly(imine-anthraquinone)(AQP)electrode materials were designed and synthesized in this work.The electrochemcial performances of as-prepared polyimide anthraquinones have been adjusted by introducing active functional groups.In addition,via combining as-prepared poly(imine-anthraquinone)with graphene and further designing different-types supercapacitor devices,we achieve a huge improvement in electrochemical properties.The specific content is as follows:(1)A series of AQP supercapacitor electrode materials with pseudocapacitive behaviors were prepared by one-step thermal reflux method based on the Schiff-base reaction between the aminoquinone-contained units and the aldehyde-contained units under the same experimental conditions.Three-types of AQP electrode materials with different electrochemically active sites were constructed by changing the amount of hydroxyl substituents on monomers,which were 1,5-poly(imine-anthraquinone)(1,5-AQP)without hydroxyl group,1,5-AQPOH with two hydroxyl groups and 1,5-AQPOH2 with four hydroxyl groups,respectively.The effects of substituents on the structural composition and microstructures as well as the electrochemcial properties of the materials prepared were analyzed.It turned out that the introduction of active functionalities enables 1,5-AQPOH2with the hihgest specific capacitance of 184 F g-1at 0.5 A g-1superior to 1,5-AQP and1,5-AQPOH,which is as the result of the rich active functional groups for more pseudocapacitance contribution.In addition,by tuning the amino positions within amino-contained monomers,we prepared two-kinds of polyiminanthraquinone isomerides(i.e.,1,5-AQP and 2,6-poly(imine-anthraquinone)(2,6-AQP)).It was found that,as comparision to 1,5-AQP,2,6-AQP demonstrated better thermal stability,larger specific surface area,faster ion diffusion,and higher specific capacitance.All of these were benefited from the better regularity in 2,6-AQP molecular structure.In this work,the electrochemical behavior of the poly(imine-anthraquinone)electrode is regulated by either introducing substituents or changing the reaction site,which provides a new idea for developing high-performance organic materials for energy storage applications.(2)Regarding to the poor intrinsic conductivity of organic materials leading a slow electron transfer and the agglomerated microstructures restricting ion transport and active site exposure.Based on the results of(1),the graphene/poly(imine-anthraquinone)composite electrode material was prepared by combining 2,6-AQP with reduced oxide graphene via the one-step thermal reflux method.Morphology and structure of the research showed the uniform growth of 2,6-AQP on the surface of graphene,due to the?-?interaction between the graphene and polyiminanthraquinone,that contributes more active sites within 2,6-AQP exposed for electrolyte accessibility,and facilitates electron transfer and ions transportation throughout the whole composite structures.Ascribing to these synergistic effect,the resultant composite electrodes showed a huge improvement in capacitive properties.In addition,the energy storage capability of the composite electrode materials were further optimized by increasing the graphene loading.It was confirmed that,for the composite loaded with 20 wt%graphene theoretically,the specific capacitances were as high as 212 and 154 F g-1at 0.5 and20 A g-1respectively,much higher than those of graphene,2,6-AQP,and composite loaded with 10 wt%graphene.The retention of initial capacitance was 94%after 10000 cycles,showing an excellent cycling stability.(3)Based on the results of(1)and(2),in this work,a poly(imine-anthraquinone)polymer(AQPOH)with rich active sites and regular chain structure was prepared by reasonably selecting the reaction units.The graphene/poly(imine-anthraquinone)composite electrode material(Gr/AQPOH)was prepared by the one-step thermal reflux method.In order to further improve the energy storage capacity,the composite electrodes were assembled into different types of supercapacitors.It turned out that,for symmetrical supercapacitor(Gr/AQPOH//Gr/AQPOH),the device shows a energy density of 9.3 Wh kg-1at the power density of 100 W kg-1.When assembling Gr/AQPOH into an asymmetric supercapacitor with active carbon(Gr/AQPOH//AC),the device turns out a higher energy density of 20.3 Wh kg-1at a power density is 350.2 W kg-1.While for a lithium-ion capacitor based on Gr/AQPOH,when the power density is 360 W kg-1,the energy density of this device is up to 107.3 Wh kg-1.It is confirmed that the construction of lithium-ion supercapacitors can effectively improve the electrochemical performance of electrodes,which provides a alternative direction into developing high-performance energy storage devices. |
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