Study On The Preparation Of High Performance Activated Carbon For Supercapacitor

As a new energy storage device with excellent performance,supercapacitor has been widely applied in various fields of the national economy due to its high power density,fast charge-discharge ability and long cycle life.The electrode material is the most important factor affecting the performance of supercapacitor.Therefore,high performance electrode material has attracted much attention in this research area.Activated carbon?AC?has been shown to be the most attractive electrode material for supercapacitor.However,there are still some challenges in activated carbon limiting its electrochemical performance.Therefore,in this paper,activated carbon with high specific surface area and developed pore structure was prepared by making a systematic study of its activation process;the purification process of removing potassium ions from activated carbon was also investigated by means of H₂O₂ oxidation-ultrasound treatment to achieve a high purity activated carbon.Based on the study above,activated carbon was then modified by NiCo₂O₄ to form NiCo₂O₄/AC composite material,aiming to greatly improve its electrochemical performance.The main research contents and results are summarized as follows:?1?Preparation and capacitance performance of coconut shell-based activated carbonActivated carbon for supercapacitor was prepared from coconut shell carbide by KOH activation.The effects of the ratio of KOH/carbon,activation temperature and activation time on the specific surface area and pore structure of activated carbon were investigated.The influences of pore structure of activated carbon on the specific capacitance of electrode material were also studied.The results showed that with the increasing of the ratio of KOH/carbon,activation temperature and activation time,the specific surface area,total pore volume and mesopore ratio displayed a trend of first increase and then decrease.And the ratio of KOH/carbon and activation temperature were two key factors influencing the porosity of activated carbon.The electrochemical performance of activated carbon was characterized by galvanostatic charge-discharge.It was found that the specific surface area,pore volume and pore size distribution had a significant influence on the performances of supercapacitor.Larger surface area,higher pore volume and 2-4 nm pore size were favorable for activated carbon electrode material to achieve a higher specific capacitance.In addition,the results demonstrated that high quality activated carbon with the best pore structure parameters and capacitance properties was prepared under the condition of ratio of KOH/carbon was 4,activation temperature was 800°C and activation time was 60 min,which specific surface area was 2 891 m²/g,total pore volume was 1.488 cm³/g,mesopore ratio was 73.6% and specific capacitance was 235 F/g.?2?Effect of removing potassium ions from activated carbon on its electrochemical performanceActivated carbon prepared under the optimized condition was purified using HCl treatment and H₂O₂ oxidation-ultrasound treatment to deeply remove the K+.The effects of mass fraction and treatment time of HCl solution,mass fraction of H₂O₂ solution,ultrasonic reaction temperature and reaction time on the K+ content of activated carbon were investigated.The results showed that most of the KOH agents remained inside activated carbon could be removed by HCl treatment,and H₂O₂ oxidation-ultrasound treatment could further deeply remove the K+ from activated carbon based on HCl washing.And 1.0% HCl,treatment time of 120 min,0.6% H₂O₂,ultrasonic reaction temperature of 60°C and reaction time of 8 h were considered as the optimum conditions to achieve a high purity activated carbon with a low K+ content of 46 mg/kg.Moreover,the physical properties and electrochemical performances of the activated carbons before and after purification were characterized.SEM analysis showed that the surface of the activated carbon treated by H₂O₂ oxidation-ultrasound process was very clean and smooth,almost no residues remaining on the surface;N₂ adsorption test showed that the activated carbon which had been deeply purified possessed a significantly increased surface area,total pore volume,mesopore ratio of 3 299 m²/g,1.798 cm³/g,86.4% and an average pore size of 2.228 nm,respectively.Electrochemical performances test showed that the as-prepared activated carbon displayed a specific capacitance of 316 F/g and a capacitance retention of 96% after 5 000 cycles.?3?Preparation and electrochemical performance of NiCo₂O₄/AC composite materialNiCo₂O₄/AC composite materials were prepared through a hydrothermal method with high purity activated carbon as a support.XRD,SEM and TEM analysis showed that spinel NiCo₂O₄ was uniformly coated on the activated carbon;N₂ adsorption test showed that the NiCo₂O₄ caused a decrease in specific surface area and pore volume to a certain extent.The influence of NiCo₂O₄ content on the capacitance performance of NiCo₂O₄/AC composite electrode was investigated.It was found that the specific capacitance of composite electrode increased first and then started to drop as NiCo₂O₄ content kept increasing.When 15% of NiCo₂O₄ was added,the NiCo₂O₄/AC composite electrode exhibited the optimal specific capacitance of 509 F/g,which increased by 61% compared with pure activated carbon electrode.At last,the electrochemical performance of the 15% NiCo₂O₄/AC for supercapacitor was evaluated.The results showed that the NiCo₂O₄/AC composite electrode still had a good impedance characteristic,rate capability and cycling performance?92.7% retention?in 3 mol/L KOH electrolyte,suggesting a promising electrode material for high performance supercapacitor.