Preparation And Application Of Porous Carbons For High Performance Supercapacitors

Supercapacitors,a novel type of capacitors,charge/discharge on the interface between electrolyte and high specific surface area electrodes of porous carbon,metal oxides or other materials.They follow the same basic principle of energy storage as conventional capacitors and are ideally suitable for fast storage and release of energy.Supercapacitors have a wide range of applications in the field of energy storage with their advantages of high power density,high charge/discharge speed,long cycle life,strong weatherability,high safety and environment-friendly nature.However,the energy density of a supercapacitor is lower than that of a battery,which becomes a factor restricting its widespread use.According to the energy equation E= 1/2 CV2,the energy density of a supercapacitor mainly depends on the capacitance of the active materials and the voltage window of the device.In order to increase the energy density of a supercapacitor,the electric double layer capacitance of the active materials should be improved,for instance,by optimizing the porosity of carbon materials through activation,or by introducing the pseudocapacity.On the other hand,the energy density can also be improved effectively by widening the operating voltage window of the capacitor.The general research strategy is to use organic electrolytes or ionic liquids instead of aqueous electrolytes.At present,the research for supercapacitors mainly focuses on improving existing active electrode materials and developing new materials.Most processes for preparing domestic supercapacitive carbon are currently complicated,and difficult to achieve mass production and application with optimized performance and reasonable cost.In this context,facile preparation of porous carbon materials with high supercapacitive performance is of both theoretical and practical importance.The main results of this thesis are summarized as follows:(1)The hierarchical porous carbon was prepared by a simple carbonation method using sucrose as precursor and ZnCl2 as activator.The surface morphology and pore structure of activated carbon were characterized by SEM,XRD,N2 adsorption and desorption analysis.The results show that the porous carbon has a high specific surface area up to 1688 m2 g-1.It is an amorphous carbon with coexistence of micropores,mesopores and macropores,indicating that this method can successfully prepare porous carbon with high specific surface area.The use of this porous carbon as an electrode material in an organic supercapacitor shows good electrochemical performance.The specific capacitance reached 130 F g-1 at a current density of 1 A g-1.The capacitance also exhibited 120 F g-1 at a high current density of 20 A g-1.In addition,the energy density was up to 55 Wh kg-1 at a high voltage of 3V.The capacitance retains 85%of its initial capacitance after 10,000 cycles at a current density of 5 A g-1,demonstrating good cycling performance.(2)The porous carbon was prepared using pine cone as precursor with different impregnation ratios of ZnCl2 by high temperature carbonization at 800? in a nitrogen atmosphere.The porous carbon prepared at the impregnation ratio of 5:1 possessed a high specific surface area of 1579 m2 g-1 and showed an amorphous structure,and the material consisted of only two elements C and O without other inorganic impurities.The capacitance of this material showed 114 F g-1 at a current density of 1 A g-1.The capacitance still maintained 116 F g-1,demonstrating its excellent rate performance.The energy density could reach 16.1 Wh kg-1 at the potential of 2 V,indicating good electrochemical energy storage performance.