Controllable Synthesis Of Porous Carbon Based Capacitor Energy Storage Materials

Supercapacitors,are considered as one of the most potential candidates among energy-storage systems due to their various applications in portable devices,electric vehicles,and stationary energy storage systems.Compared with other energy storage systems such as batteries and conventional capacitors,supercapacitors mainly have three major advantages:ultrahigh power density,long cycle life and fast charge/discharge processes within seconds.At the same time,lithium ion capacitors have been used as a new energy storage device of lithium ion battery and electric double layer supercapacitor"internal hybrid",due to its high energy density,high power density,wide operating voltage range,high safety factor,etc.Activated carbon,the main electrode material of supercapacitor,is a carbon material dominated by microporous structure,which can not adapt to the situation of high current and organic electrolyte.Therefore,the pore structure should be optimized to improve the capacitance performance of electrode material.Therefore,the development of high specific surface area carbon materials with hierarchical porous structure is an effective way to achieve higher capacity and better rate performance of supercapacitors.For lithium ion capacitors,graphite is the main electrode material for the anode electrode,but the theoretical capacity of graphite is limited,and the rate performance is poor.Therefore,it is necessary to prepare a kind of porous carbon material which can achieve high capacity and high rate performance of lithium ion capacitors.In view of the existing problems,the following two aspects of work have been carried out.（1）The hierarchically porous hollow-carbon spheres（HPHCSs）are synthesized by activating the hollow-carbon spheres（HCSs）derived from the template-directing method using Si O₂ spheres and waste tire pyrolysis oil（WTPO）as templates and carbon precursor,respectively.The developed template-directing coupled with post-activation methodology can not only adjust the pore structure of HPHCSs,but also can not destroy the hollow-sphere-like micromorphology.HPHCSs with a relative-intact hollow sphere microarchitecture and abundant micro-mesoporous structure possess the outstanding hydrophilcity and electrical conductivity.As the capacitive energy-storage electrode,HPHCSs electrode presents excellent rate capability,high capacitance retention and good durability in aqueous and organic electrolytes,exhibiting a good compatibility to different kind of electrolyte ions.Besides,the increased ratio of IR drop of HPHCSs electrode is relatively small among the contrast samples possessing different pore structures with the decrease of the test temperature,exhibiting its exceptional low-temperature performance.The favorable combination of template-directing and post-activation is able to realize the controllability of the pore structure of HPHCSs electrode with high capacitive storage behavior.（2）Porous carbon spheres derived from the facile hydrothermal treatment associated with the calcination process exhibit the good spherical morphology and unique porous structure.For the Li-based half-cell test,porous carbon spheres electrode not only exhibits larger reversible capacities and better compatibility as compared to the widely-used graphite,but also provides stable delithiation plateaus under different current density.Additionally,the delithiation ratio below 1 V almost accounts for a constant value（around 70%）with the increase of current density,evidencing that Li intercalation storage is the dominant model and Li insertion/extraction processes are propitious.The lithium ion hybrid capacitor configured with S-doped mesoporous graphene and porous carbon spheres as cathode and anode,delivers satisfied energy and power densities(up to 177 Wh kg^-1 and 12,303 W kg^-1,respectively)as well as long-term cyclability,which is superior to the corresponding S-doped mesoporous graphene//graphite and activated carbon//porous carbon spheres.