Micro/nano Structure Construction And Sodium Storage Performance Of Biomass-based Hard Carbon For Anode Material Of Sodium Ion Battery

In the sodium ion battery system,the exploitation of anode materials with high capacity,long cycle life and excellent rate performance is the key to the practical application of sodium ion batteries.Biomass hard carbon material has certain economic benefits because of its wide source,simple synthesis process,environment friendly and renewable,is a high quality carbon source as sodium ion battery anode material.Therefore,the preparation of micro/nano multi-level hard carbon from rice husks,palm leaves biomass materials.The derived hard carbon materials and nitrogen-doped carbon materials are used as active negative electrode materials for sodium ion batteries.X-ray diffractometer,Raman spectroscopy,N₂ adsorption apparatus,X-ray photoelectron spectroscopy,scanning electron microscope and transmission electron microscope are used as the characterization methods to analyze the biomass types,carbonization conditions,material structure and nitrogen atom doping on sodium storage performance Impact.Rice husk can be used as a carbon source and a natural micro/nanopore template.A high-surface-area hierarchical porous carbon material can be obtained by removing inorganic SiO₂ part with NaOH solution,and it is used for reversible sodium storage.Compared with the other samples,the hard carbon materials prepared at 800°C from rice husk?RHPC-800?can deliver a high reversible capacity of 274mAh g^-11 at a current density of 100mA g^-1,maintaining the capacity of approximately 260mAh g^-1,and after500 cycles retaining 92.7%of its capacity.The RHPC-800 carbon material with excellent electrochemical performance is attributed to the material's high specific surface area and low charge transfer resistance.Based on the above 800?calcination temperature of the best performance,the porous carbon anode material of sodium ion battery was prepared by hydrothermal method and calcination temperature of 800?with different concentrations of KOH solution as activator.The results show that the porous carbon material?RHPC-1-2?synthesized with 2mol L^-1 of KOH exhibits excellent electrochemical performance.It has a high specific area of 37.6336m² g^-1 and a large number of micropores and mesopores.The intial reversible capacity is 204mAh g^-1,the capacity is still 200mAh g^-1 with almost no attenuation for 100 cycles at a current density of 100mA g^-1.Hard carbon materials?PLHCs?are prepared using palm leaves as carbon sources,and the effects of the structure of the materials on the sodium storage performance at different carbonization temperatures are studied.As the carbonization temperature is higher,the value of I_D/I_G is smaller,indicating that the degree of disordering decreases and the degree of graphitization increases.Its first electrochemical curves also show that its capacity has increased in the plateau region?<0.1V?,and its mechanism is mainly the sodium ion insertion.When the temperature is 1000°C,the electrochemical performance of PLHC-1000 is optimal.At a current density of 50mA g^-1,the reversible capacity still achieves 292mAh g^-1 after the 200th cycle,and the capacity is still202mAh g^-1 after 1000 cycles at the high current density of 200mA g^-1,which shows that it has high capacity and excellent cycle and rate performance.The graphitization degree of PLHC-1000 material is in the middle,which also reflects that the sodium storage capacity in hard carbon materials is provided by the adsorption capacity and the insertion capacity.Pre-carbonized palm leaves are added during aniline solution polymerization,and nitrogen-doped hard carbon materials are successfully prepared by in-situ polymerization and pyrolysis.Compared with the PLHCs samples,the PLHC-Ns materials have higher defects and a larger interlayer spacing of the graphite crystal region,so there are more sodium ions to be adsorbed and inserted into active sites.PLHC-N-1000 nitrogen-doped electrode material shows more excellent cycle stability performance and rate performance.When the current density is 50mA g^-1,the reversible capacity of 321mAh g^-1 can be supplied.After 200 cycles,the capacity of 314mAh g^-1can be maintained with the about 97.8%capacity retention.It is worth mentioning that the PLHC-N-1000 electrode material also maintains good rate and cycle stability performance at a high current density of 200mA g^-1.It has a reversible specific capacity of 245mAh g^-1,after 1000 cycles,it maintains a capacity of 221mAh g^-1 with a capacity retention rate of 90.2%.This is mainly due to N electronegativity and the defects caused by it,which can attract many sodium ions as well as the insertion and desorption of sodium ions,so that the capacity of sodium ion battery has been improved.