Preparation Of Biomorphic Porous Carbon Electrodes And Their Energy Storage Properties

With the development of electronic equipment and electric automobile,the demand of energy storage equipment with high energy density is becoming more and more urgent.Electrode materials have become the focus of research which is an important part of energy storage equipment.The biomorphic carbon materials have attracted people’s attention because of its rich raw material resources and excellent hierarchical structures.Recently,biomorphic carbon materials exhibit good electrochemical performance as anodes for potassium,sodium and lithium ion batteries.In this paper,the electrochemical properties of biomorphic carbon electrodes derived from corn husk and walnut septum are studied:Firstly,the biomorphic carbon derived from corn husk with porous structure and different specific surface area is used as anode of the potassium ion battery.The results show that the unactivated carbon materials with low specific surface area have higher electrochemical properties.The initial charge and discharge capacity at the current density of 0.1 A g-1 were 231.0 and 396.2 mAh g-1,respectively.The initial coulombic efficiency was 58.3%,and the reversible capacity was still 205.8 mAh g-1 after 100 cycles.One of the important reason is that the unactivated carbon materials have higher structurals stability,which is beneficial to the transport of K-ion,thus improving the charge-discharge performance and cycle stability of the anode materials.The low specific surface area also gives the anode a higher first coulomb efficiency.Secondly,N-doped biomorhic carbon material by using walnut septum as raw material and urea as nitrogen source was prepared as anode of potassium ion battery.The results show that the electrochemical properties of biomorphic carbon materials with 5.45 at%nitrogen are obviously increased.Specifically,the first charge and discharge capacity is 263.6 and 478.4 mAh g-1 at the current density of 0.1 A g-1.There is little loss of capacity after the 50th cycle.After 200 cycles,the reversible capacity of the anodes is 242.5 mAh g-1,and the capacity retention rate is 92.0%.At the high current density of 1 A g-1,the capacity of the anodes is still 119.9 mAh g-1 after 1000 cycles.The main reason is that the nitrogen atom and the carbon atom in the carbon material form N-5,N-6 and N-Q,which increases the diffusion rate of the K-ion and the conductivity of the carbon materials.The existence of nitrogen also increased the internal defect of the carbon materials,more active sites are provided for the storage of the potassium ions.Thirdly,the effect of carbonization temperature on the anode materials of potassium ion battery was studied by pyrolyzing walnut septum at different temperatures.The results show that the anode materials carbonized at 1000℃ has the best electrochemical performance,which has excellent electrochemical stability and high reversible capacity at the high current density of 1 A g-1 especially.The biomorphic carbon by carbonized at low temperature has many defects,which stores potassium ion by absorption on the surface.The graphitization degree of the materials and the diffusion intercalation potassium storage both increases by the increasing of temperature.But the interlayer spacing decreases with the further increasing of graphitization.So the large radius of potassium ions leads to the diffusion difficulty and the specific capacity decreases.Finally,a critical point is formed at 1000℃.Finally,supercapacitor electrode materials were prepared by carbonization and activation with walnut septum as raw material and potassium hydroxide as activating agent.High specific surface area electrode materials with high porosity exhibit excellent electrochemical stability and specific capacitance in supercapacitors.For rate performance,the specific capacitance of the electrode is 255.3 F g-1 at a current density of 0.5 A g-1,210.9 F g-1 at the current density of 8 A g-1,which capacity retention rate is up to 82.6%.And there are no loss of the specific capacitance at a high current density of 8 A g-1 for 5000 cycles.