Study On Preparation And Electrochemical Performance Of Graphitized And Nitrogen-doped Biochar

Green and clean energy sources such as photovoltaics and wind power from nature are intermittent and random,and must be collected and transported using energy storage equipment.Electrochemical energy storage is convenient and efficient,making it an ideal energy storage method.Biochar has excellent electrochemical properties and is an ideal renewable green material for a variety of energy storage components.However,electrochemical devices assembled with biochar materials as key components generally have problems such as low capacitance,low coulombic efficiency in the first week,and poor rate performance at high currents.In order to find a biochar electrochemical material with excellent performance,three forestry non-wood fiber materials,namely Eucommia ulmoides bark,lacquer seed bark and Acer truncatum seed husk,were pre-carbonized at 400℃,and then co-catalyzed by Co/Ni or potassium ferricyanide activated biochar materials.Prepared biochar materials with different structures.Various methods were used to characterize the microstructure of biochar,and potassium ion batteries and supercapacitors were assembled.The electrochemical properties of biochar materials were analyzed,and the following research results were obtained.Eucommia ulmoides bark biochar obviously changes from amorphous to graphite in the process of Co/Ni co-catalysis.The catalytic graphitization effect at 900 ^oC is the best,and the X-ray diffraction pattern shows that the graphitization characteristic peak intensity of the Eucommia ulmoides bark biochar catalyzed at 900 ^oC is significantly higher than that of other materials.At a constant current density of 0.05 A g^-1,the specific capacity of a potassium-ion battery assembled with it as the negative electrode reaches 180 m Ah g^-1.At this current density,there is almost no capacity degradation after 300 cycles.The material was charged and discharged 10 times under 0.05,0.1,0.2,0.5,1.0 A g^-1,and the obtained discharge capacity was 180,150,105,90,70 m Ah g^-1,and the rate performance was good.The microporous Acer truncatum seed husk charcoal prepared by pre-carbonizing the seed husk of Acer truncatum and then activated by potassium ferricyanide at high temperature.Scanning electron microscopy and transmission electron microscopy showed that the biochar materials prepared by activation at 650℃and 800℃produced intertwined pore structures,and the pore distribution was mainly microporous.The specific surface area of the latter reached 1220 m²/g.Its I_G/I_D value is 1.10,indicating that higher temperature is beneficial to catalyze graphitization reaction and pore formation reaction.It shows excellent electrochemical indicators under the three-electrode system.The specific capacitance reaches more than 200 m Ah g^-1 at a current density of 0.02 A g^-1,and the rate performance is good.Nitrogen-doped mesoporous lacquer seed fiber charcoal prepared by dewaxing,pre-carbonization,and high temperature activation of potassium ferricyanide.The specific surface area of the biochar prepared by activation at 650℃is 311 m²/g,and the pores are mainly composed of mesopores.X-ray photoelectron spectroscopy analysis shows that the material is doped with a large amount of N element.At a current density of 0.2 A/g,the specific capacitance of the supercapacitor prepared with nitrogen-doped mesoporous varnish seed fiber carbon as the negative electrode reaches 324 F/g.After 3000 charge-discharge cycles,the capacitance retention rate reaches over 97%,and it has good charge-discharge performance.Dynamic analysis of the charging and discharging process found that its energy storage capacity is mainly played by the surface control behavior.In this study,three inexpensive forest fiber materials were used to prepare electrochemical energy storage devices with good performance.It was found that nitrogen-doped mesoporous varnished fiber carbon had excellent electrochemical performance,which enriched the source of raw materials for electrochemical materials.The application of forestry resources in energy storage devices provides a practical reference.