Controllable Preparation Of Porous Carbon Materials By Template Method And Their Electrochemical Energy Storage

To overcome the crisis of resource shortage and environmental pollution along the utilization of fossil energy sources,a series of green and renewable energy sources have been developed,such as wind energy,solar energy,tidal energy,etc.So far,these energy sources have become hotspots in the field of energy research,due to their inexhaustible and clean advantages.However,it is necessary to realize grid-connected transmission that large-scale energy storage equipment with excellent conversion and storage performance could address the problems of intermittency and instability.Therefore,it is urgent to develop energy storage devices which can meet these demands.In addition,the rapid development of advanced electronic equipment and electric vehicles increasingly relies on reliable energy storage devices.Meanwhile,more new requirements are put forward for energy storage devices by these rapid development of equipment.For example,special electronic devices need power sources with high current output and high cycle stability,and electric vehicles need power batteries with low cost,high energy density and high safety.Additionally,the emerging flexible wearable electronics need flexible and bendable energy storage devices.Nevertheless,these special needs are difficult to be satisfied by current existing energy storage devices.At present,the development of carrying equipment and portable electronics has seriously restricted,owing to the lagging development of energy storage devices.With the inherent advantages of high power density and energy density,supercapacitors and lithium sulfur batteries are considered as important secondary power devices.By further improving the performance of super capacitors and lithium sulfur batteries to meet specific needs,it will effectively promote the practical application of energy storage devices in clean energy,electronic equipment,electric vehicles and other fields.Aiming at solving the problem of limited storage capacity of traditional carbon-based electrodes in supercapacitors and lithium sulfur batteries,the present dissertation concentrates on to realize energy storage devices with high energy density and power density by developing optimized porous carbon materials.The main results,including synthesis method,design of micro-nano structure,reaction mechanism and electrochemical performance,are summarized as follows:（1）ZnO nanofibers were synthesized by electrospinning,and the surface was coated with a ultrathin carbon layer converted by ethanol.Then,ZnO template was removed by reduction-evaporation in H₂/Ar atmosphere.Finally,the nanofiber network membrane constructed by ultra-thin carbon bubbles was formed.The self-supporting carbon nanofiber network membrane can be directly used as a flexible electrode in flexible supercapacitors.The electrode exhibites long cycling stability and excellent rate performance.Under three-electrode condition,the capacitance retention rate is still 94.1%at 10 A g^-1 after 35,000 cycles.When the current density was increased from 0.5 to 35 A g^-1,the capacitance retention was increased to 81.4%.The capacitive properties of flexible symmetric devices are almost unchanged under different bending conditions,demonstrating the excellent mechanical flexibility.These outstanding electrochemical properties are mainly attributed to the closely interconnected hollow carbon bubbles in the carbon nanofiber network,which not only provide fast electron and ion transport channels,but also possess high specific surface area to provide rich reactive sites.（2）ZIF-8-derived carbon"welded"separation of carbon nanofibers into an integrated nanofiber network membrane was proposed and realized,resulting in a significant increase in electrical conductivity.In addition,ZIF-8 derived carbon formed a special"spider-web"surface micro-nano structure,which substantially enhanced the infiltration of carbon membrane.Compared with the unwelded carbon nanofiber network,the capacitance of 36.5%was increased.More prominently,the integrated carbon membrane still held a capacitance retention of 75.5%after the current density is increased 70 times.And at 10 A g^-1,the capacitance remained 98.8%after 100,000cycles.The flexible quasi-solid supercapacitor showed a stable electrochemical performance under severe mechanical bending,fully proving the application prospect of the integrated carbon membrane in the flexible energy storage device.（3）The pore structure of porous carbon materials was constructed through simple template method and reduction-evaporation method.By comparing and analyzing the pore structure and electrochemical properties of different porous carbon materials,the relationship between pore structure and electrochemical properties of carbon materials was revealed.The experimental results showed that the pore structure of carbon material has a profound effect on capacitive performance.This work will provide some reference for the structural design of carbon electrodes in carbon-based supercapacitors.（4）Based on the combustion method and template method,the ultra-light carbon foam with ultra-high pore volume was constructed.The wall thickness of carbon foam can be precisely regulated by reaction conditions.The effect of different carbon wall thickness on the performance of lithium sulfur batteries was compared.The sulfur content of sulfur-carbon nanocomposites is increased to 96 wt%via optimized carbon foams.Even at a high sulfur content,the soft-pack pouch cells still exhibit an excellent electrochemical performance.When the sulfur content is 93 wt%and the sulfur loading is 6.9 mg cm^-2,the initial discharge specific capacity of soft-pack pouch cells was 1162mA h g^-1 and the energy density was 382 Wh kg^-1.After 40 cycles,the specific capacity was still as high as 975 mA h g^-1.