Preparation Of Rice Husk-based Porous Carbon Materials By Thermal Decomposition And Study Of Sodium Storage Properties

At the moment,global warming and natural resource scarcity issues are causing a gradual increase in energy demand while also posing challenges in its production,storage,and distribution.To address these issues,scientists are developing renewable,efficient,and green energy systems.Among them,lithium-ion batteries are considered to be an important high-energy density energy storage device.And with the expanding market for new energy vehicles and the rapid development of the electronics industry in China,the demand for lithium-ion batteries is rapidly increasing.However,the limited lithium resources and increasing production costs have seriously hindered its large-scale application.In the search for replacement batteries for lithium-ion batteries,sodium-ion batteries have received special attention from researchers in recent years because of their abundant sodium metal reserves,environmental friendliness,and similar physical and chemical properties to lithium,and as a supplement to lithium-ion batteries,they have very promising prospects for practical applications in large-scale energy storage devices.Nonetheless,sodium-ion battery technology is still in its early stages,with the primary obstacles being the selection and design of high-performance electrode materials.Among them,hard carbon anode materials stand out among the many anode materials due to their low cost,high specific surface area and large layer spacing.And hard carbon anode materials derived from biomass materials are a potential ideal candidate with the advantages of high capacity,good cycling stability and low voltage plateau.In this paper,the conversion of rice husk waste into high performance porous hard carbon anode material for sodium ion batteries is mainly done with the help of hydrothermal assistance:（1）First,the rice husk-based anode material was treated by a two-step low temperature-high temperature carbonized method to modulate its microstructure and explore the optimum sintering temperature during the high-temperature carbonized treatment.When the temperature was increased to 1100°C,the hard carbon material exhibited the best layer spacing,with a discharge specific capacity of 244 m Ah g^-1 and a charge/discharge specific capacity retention rate of 99%after 50 cycles.（2）On the basis of the above experimental temperatures,the effects of different types and concentrations of activators on the morphological structure and related electrochemical properties of the rice husk materials were investigated.After treatment by three activators,KOH,Na OH and K₂CO₃,the materials activated by KOH were found to have more structural stability and excellent electrochemical properties,when the concentration of KOH was 1 M,the discharge specific capacity was 212 m Ah g^-1for the first cycle at a current density of 50 m A g^-1 and 209 m Ah g^-1 after 50 cycles,with almost no capacity degradation.（3）In conjunction with the above study,heteroatom doping was used to select urea as the nitrogen source and to explore the appropriate doping ratio to further improve the multiplicative performance of the rice husk-based material and the reversibility of the material’s charge and discharge.The experimental results show that at a 4:1 mixing ratio of rice husk to urea material mass,the material has a higher degree of defects and a more suitable graphite layer spacing,which is more conducive to the embedding and detachment of sodium ions.A reversible specific capacity of 333 m Ah g^-1 can be provided at a current density of 25 m A g^-1 and still has a capacity of 306 m Ah g^-1 after200 cycles,with a capacity retention rate of 94.5%.