Bio-based Activated Carbon Microspheres With High Specific Surface Areas For Electrochemical Capacitors

Electrochemical capacitors,also called supercapacitors,due to their unique properties of high power density,rapid charging speed,ultra-long cycle life and wide operating temperatures,have attracted tremendous attention in many important application areas,such as consumer electronics,electric vehicles or buses,uninterruptible power supplies,smart grid,load-levelling equipments and so on.However,compared with batteries,the much lower energy densities of supercapacitors limit their application as primary power sources.The supercapacitors mainly consists of the electrical double-layer capacitors?EDLCs?and the pseudocapacitors according to the energy storage mechanism.The energy storage of EDLCs depends on the electrical double-layer adsorbed on the carbon electrode/electrolyte interface,without any redox reaction.Porous carbons,due to their high surface area,great cycle stability,and easy production in large quantities,have been the most widely used electrode materials for commercial supercapacitors.In order to meet the market demand,economic and environmentally freindly precursors have been selected to prepare porous carbon materials with high performance.Investigating the effects of porous carbon microstructures,pore sizes and distributions,surface chemistry and electrode sizes on the electrochemical performance of supercapcacitors,thus further improving their energy densities,is very important to push the applications of supercapacitors.In this project,the research is focused on designing the suitable architechtures of porous carbon electrodes,increasing the effective specific surface area?SSA?of porous carbons,improving the ionic diffusion and transportation.On the one hand,three-dimensional porous hollow microspheres of activated carbon are fabricated by utilizing various pollens and spores as carbon precursors and self-templates through a facile,green and low-cost route.The abundant and easily available carbon sources allow for mass production of activated carbon microspheres?ACMs?,which almost ideally inherit the distinctive nano-architectures of pollens and spores,presenting superhigh surface areas(up to 2620 m² g^-13053 m² g^-1),and hierarchical porous structure.Such ACM electrodes show remarkable electrical double-layer storage performances,such as high specific capacitance(308 F g^-1 in organic eletrolyte),ultrafast rate capability and good cycling stability,thus leading to a high energy density(57 Wh kg^-1)and superior power density(17 kW kg^-1).On the other hand,nano-sized?300 nm in diameter?porous ACMs are synthesized from nature glucose and the SSA reaches 2534 m² g^-1.By using the ACMs as electrode material,and optimizing the electrode structure to interdigital,all-solid-state flexible supercapacitors are fabricated.The electrochemical performance of the devices are evaluated,and the specific capacitance can reach 38.4 mF cm^-2 with good mechanical and cycling stability.The proposed technic demonstrates a great potential for fabrication of intergrated supercapacitors with practical and commercial prospects.