Multistage Hole Carbon - Based Materials And Their Application In Electrochemical Capacitors

In recent years, supercapacitors have attracted great attentions due to its fast charging/discharging rate, high specific power density, long cycling life and wide working temperature range. However, its energy density is much lower than that of conventional batteries, e.g. lithium-ion battery (LIB), which has restricted its further applications. It is well known that the energy of a supercapacitor can be calculated according to the equation:E=1/2CV2. Thus, there are two effective approaches to improve its energy density:One is to improve the specific capacitance of the electrode materials (C) and the other is to promote the output voltage of the capacitor (V). In this thesis, three major works were studied to enhance the specific capacitance of the carbon materials for supercapacitors:Firstly, the effect of the ratio of micropore to mesopore was extensively studied to increase the specific capacitance and rate capability. Secondly, functionalities with pseudo-capacitive effects originated from faradic interactions were introduced into the carbon matrix. Thirdly, these modified carbons were further constructed with a three-dimensional ordered architecture to reduce its resistance for the promotion of working voltage.1. Synthesis and application for superpacitors of disordered mesoporous/microporous carbons derived from titanium carbide/carbon composites by chlorination.In this work, micropores were introduced into the bulk of disordered mesoporous activated carbon (AC) to improve the capacitance. Mesoporous/microporous carbons with different proportion of micropores were derived from titanium carbide/carbon composites with different TiC content by chlorination. An optimal material was obtained with a high specific surface area of1853m2/g and a miropore content of48.6%. It shows a higher capacitance of136F/g than AC (120F/g) in1M (C2H5)4NBF4/PC electrolyte. It keeps a capacitance retention of65%at a current density of10A/g vs.0.5A/g. The incorporation of micropores into the matrix of carbon has enhanced the surface utilizing thus increase the capacitance efficiently. 2. Synthesis and optimization of ordered mesoporous/microporous carbon for supercapacitor applicationActivated carbon with a high surface area is widely used in supercapacitors, but the disordered pore connectivity, the existence of abundant closed pores and a wide pore size distribution have restricted its surface utilizing for capacitor applications. Ordered mesoporous carbons with a better rate capability were identified as alternative materials owing to their narrow pore size distributions and connected pore channels. In this work, a series of ordered mesoporous/microporous carbon materials (OMMCX) was prepared from the chlorination of Ti species in TiC/C composites which were obtained by a soft-templating self-assembly method. The influence of Ti content on the porous structures and electrochemical performances were investigated. An optimal mesoporous/microporous carbon with moderate micropores (52.4%in volume) was obtained. It has a high surface area (1698m2/g) and a large pore volume (1.17cm3/g), with mesopore size centered at4.4nm and micropore size of ca.1nm.It exhibits a high capacitance of132F/g at a current density of500mA/g and good rate capability with capacitance retention of79%at scan rate of2000vs.20mV/s in nonaqueous electrolyte. It also shows a good cycling stability with a capacitance retention of84%over5000cycles. The micropores drilled on the mesopore walls contribute to a high capacitance. The ordered mesoporous channel provides a favorable ion-path for electrolyte penetration and transportation, leading to a good rate capability.3. Three dimensional ordered mesoporous/microporous carbon sphere array and its electrochemical performance in supercapacitorThe capacitive performance of carbon material is not only dependent on its microstructure but also related to its morphology. It is proved that electrode materials with confined architectural morphologies usually deliver better electrochemical performances with lower resistance. In this work, a three dimensional ordered mesoporous/microporous carbon sphere array was prepared from the chlorination of mesoporous TiC/C composite which was prepared by a soft-templating self-assembly approach using a macroporous silicon skeleton as hard template. The obtained carbon material has a high surface area (1464.4m2/g) and a large pore volume (1.48cm2/g), with mesopore size centered at about8.5nm, micropore size of0.69and1.51nm, and an interconnected window size of about60nm. It exhibits a high capacitance of134 F/g in nonaqueous electrolyte and good cycling stability with capacitance retention of84%over5000cycles. The unique mesoporous structure and sphere arrays morphology provide a more favorable path for electrolyte penetration and transportation and lower electrode resistance to achieve promising rate capability performance, while the micropores drilled on the mesopore-walls highly enhanced the specific capacitance.4. Nitrogen-enriched ordered mesoporous carbon with controllable nitrogen contentApart from the high surface area, appropriate pore size and ordered architectural morphology, introducing functionalities on the surface of the electrode material has been considered another effective way to improve the capacitance. The pseudocapacitance originated from faradic interactions can contribute to an enhanced capacity. In this work, a series of N-doped ordered mesoporous carbons (ONMC) with various N contents was prepared by using dicyandiamide (DCDA) as a nitrogen source via an evaporation-induced self-assembly process. The effect of nitrogen-containing precursor content and the preparation condition on its porous structure as well as the electrochemical performance was investigated. Under optimal preparation condition, an ordered mesoporous carbon with a moderate nitrogen content of8.0%was obtained at a pyrolysis temperature of750℃. It has a specific surface area of676m2/g with mesopore size of8.3nm. The ONMC delivers a specific capacitance as large as259F/g in1M H2SO4electrolyte due to the incorporation of nitrogen functionalities. It also shows a good rate capability with capacitance retention of71.8%at10A/g vs.0.5A/g. The generally ordered mesopores provide a favorable path for ion transportation and penetration.5. Nitrogen-enriched ordered mesoporous carbon nanofiber array and its application for supercapacitors.In this work, a nitrogen-doped ordered mesoporous carbon nanofiber array (N-MCNFA) with hierarchical porous structure was prepared by a soft-templating method combined with a hard-templating approach. A crab shell with well-aligned mesoporous structure (100nm in mean pore size) was used as a hard-templat. The obtained N-enriched mesoporous carbon nanofiber array with a nitrogen content of6.7wt%has a high surface area of1030m2/g and uniform mesopores located at15.0 nm. It shows a high capacitance of264F/g in1.0M H2SO4electrolyte and a good rate capability with capacitance retention of85.6%at10A/gvs.0.5A/g. It also exhibits a good cycling stability without capacitance fading over10000cycles. The construction of confined architectural morphology was proved to have a positive effect on the electrochemical performance for supercapacitor.