Controllable Synthesis Of Doped Carbon Materials And Their Supercapacitors Applications

Carbon materials are chemically stable with good corrosion resistance and electrical and thermal conductivity.As a typical supercapacitor electrode material,they exhibit ultra-high power density and excellent cycle stability.However,carbon materials are used for energy storage in supercapacitors.Compared with battery energy storage,their specific capacity and specific energy are lower.Therefore developing high-performance carbon materials with high specific capacity and specific energy has broad application prospects and great challenges.Based on this,this work focuses on two important influencing factors in capacitor energy storage:two porous functional carbon materials with large surface area and high amount of doping are developed.Experiments show that these two materials have large specific surface area,excellent conductivity and a certain level of doping of hetero elements.They are applied to supercapacitor energy storage to obtain larger supercapacitor specific capacity and larger energy.The specific content is as follows:(1)Porous carbon materials with rich porosity are prepared from calcium carbonate(CaC2)treated with mild molten alkali.Carbon carbide represents a typical porous carbon material,which has a wide range of uses,but the synthesis of this porous carbide requires harmful chlorine to achieve the conversion to carbides.In this study,by using low-toxic KOH to react with CaC2 and optimizing the synthesis conditions,the obtained porous carbon material showed a large specific surface area(about 839 m2 g-1)and specific capacitance(at current density of 0.5 A g-1,a specific capacity of 403.00 F g-1 is obtained).At the same time,it can also obtain excellent rate performance,maintain a capacitance of more than 63%at high current density of 5.0 A g-1,and excellent cycle performance(Only about 5%attenuation after 5000 cycles at high current density of 5.0 A g-1).The research proposes a simple and effective method to utilize CaC2 as a carbon source and may have a wide range of applications,such as adsorbents,anode materials for lithium/sodium ion batteries.(2)Based on the strategy of dehalogenation to carbon,using polyvinylidene chloride as a carbon source and subjecting it to room temperature ball milling and dehalogenation carbonization to obtain the doped carbon material precursor.Then roasting them at different temperatures(600℃/700℃/800℃).Then three kinds of nitrogen-phosphorus(N,P)co-doped carbon materials were obtained.The study finds that N,P co-doped carbon materials calcined at 700℃ have high nitrogen and phosphorus content(N:1.32 at.%,P:6.29 at.%)and large specific surface area(942.89 m2 g-1).The material has optimal electrochemical performance ii both acidic and alkaline conditions.Three-electrode electrochemical tests show that using alkaline electrolyte its specific capacity can reach 367.5 F g-1 at low current density of 0.5 A g-1.And at high current of 50.0 A g-1 the specific capacity is 285.0 F g-1;using an acidic electrolyte at low current density of 0.5 A g-1 the specific capacity can be up to 332.4 F g-1.And at high current density of 50.0 A g-1,the specific capacity is 187.5 F g-1.In addition,the sample also has excellent cycle stability(in alkaline conditions at high current densities of 5.0 A g-1 and 10.0 A g-1,respectively the capacity retention rates are 87.36%and 89.45%after 5,000 cycles).Assembled into a symmetrical button capacitor in alkaline medium,when the current density is 0.5 A g-1,the specific capacity is 50.2 F g-1,which also has excellent cycle stability.At high current densities of 5.0 A g-1 and 10.0 A g-1,respectively the capacity retention rates after 5,000 cycles are 96.18%and 94.76%.