Fabrication And Electrochemical Performance Test Of Using Coconut Shell Carbon/Graphene Composites Electrode

Supercapacitors has been widely concerned with its characteristics of large capacity,high energy storage density,high charge and discharge efficiency and long cycle life as a new type of energy storage component.Electrode material quality is one of the key factors determining the performance of supercapacitors.As the electrode material of supercapacitor,activated carbon has low cost,high specific surface area and good chemical stability,but its specific capacitance is lower when it is used as a supercapacitor electrode.It is believed that activated carbon prepared from biomass materials has high strength and extremely fine micropores,and is the best raw material for preparing activated carbon.Beside,because of its high mechanical strength(E=1.0TPa)and large specific surface area(about 2630m~2/g),graphene is often used in lithium-ion batteries and lead-carbon batteries which is one of the most promising supercapacitor electrode materials.But the single graphene as the electrode material has a relatively small capacitance value,which affects its capacitance performance.Aiming at the problems of poor conductivity of single coconut shell charcoal and small single graphene capacitance,it is important to develop a new composite material with high specific surface and good electrical conductivity,which is important for the synergy of two components.The main research work and results are as follows:(1)The coconut shell activated carbon was prepared by a two-step carbonization and activation method using coconut shell as a raw material and potassium hydroxide as an activator.The physical properties and chemical characterization of coconut shell activated carbon for the performance of supercapacitor were studied at a carbonization and activation temperature of 900°C and 750°C,a ratio of KOH to carbonized material of 4:1,and different activation times of 2h and 4h.The results showed that the capacitance value and capacity retention rate of coconut shell activated carbon(csc2h)activated for 2h were 70F/g and 85%higher than that of coconut shell activated carbon(csc4h)activated for 4h 68F/g and 64%respectively,indicating that csc2h has better capacitance performance.(2)The coconut shell carbon/graphene composite was prepared by in-situ composite method.The low-cost coconut shell carbon and high-dispersion graphene were combined in situ(coconut carbon and graphene ratio of 7:1),and coconut shell carbon/graphene composites were prepared at different activation times.In this experiment,commercial cola activated carbon was used as a comparative sample.The prepared coconut shell carbon,coconut shell carbon/graphene composite material and commercial cola liquid activated carbon(csc2h,csc4h,csc2h+G,csc4h+G,cola)are activated under different conditions to ensure the same conditions.At the time,the five samples were compared and analyzed by physical characterization and chemical characterization,and their capacitance performance in the capacitor was explored.(3)The experimental results show that the five samples have a carbonization temperature of 900°C and an activation temperature of 750°C,a ratio of KOH to carbonized material of 4:1,and different activation times of 2h and 4h,csc2h,csc2h+G and cola have higher good capacitance performance,and csc2h+G has the best capacitance performance,the order of capacitance performance is csc2h+G>cola>csc2h>csc4h+G>csc4h.After the addition of graphene,the csc2h+G material has higher rate performance than the unadded,which fully demonstrates that the conductivity of graphene plays a role in the composite.After 500 cycles,the capacity retention rate of coconut shell carbon plus graphene(csc2h+G)was 93%higher than that of coconut shell carbon(csc2h),and the cycle efficiency of coconut shell carbon plus graphene remained at sbout 100%.The capacitance of coconut shell carbon plus graphene is as high as 75F/g,which exceeds the value of commercial cola carbon capacitor(72F/g).The results show that the composite material has better electrochemical performance than pure coconut shell carbon material.