Preparation Of High-Performance Peanut Shell-Based Anode Materials Lithium/Sodium Storage Performance

As global energy demand continues to grow,the development of efficient and cost-effective anode materials for lithium/sodium ion batteries,a typical electrochemical energy storage technology,is crucial for further improvements in electrochemical energy storage technology.In lithium/sodium batteries,the anode material is a key component and has a significant impact on the electrochemical performance and cost of the battery.The most common commercial anode material for Li-ion batteries is still graphite,but its low theoretical capacity limits the application.Also,as the radius of sodium is larger than that of lithium,often resulting in a lower diffusion coefficient,graphite is not suitable for sodium embedding and exfoliation due to its small interlayer distance,while hard carbon materials are considered suitable anode materials for sodium ion batteries due to their larger layer spacing.Improving the electrochemical performance of batteries through heteroatom doping and structural optimization is also an effective approach.However,the current process of producing heteroatom-doped hard carbon is not yet mature and can lead to an increase in the price of lithium/sodium ion batteries.In this thesis,anode materials for lithium/sodium ion batteries were prepared using cheap and common peanut shells as the carbon source,with a view to solving the key technical problems that currently exist and investigating their electrochemical properties,providing some practical basis and theoretical background for the application of low-cost,high-performance biomass carbon composites.The main research elements of this thesis are as follows:（1）Peanut shells were used as the carbon source,and chitosan and phytic acid were used as the nitrogen and phosphorus sources,respectively,to obtain peanut shell based nitrogen-phosphorus-doped porous carbon anode materials by activation,hydrothermal and carbonization treatments.It is shown that the N/P-doped porous carbon anode material has excellent sodium storage capacity at a carbonization temperature of 800℃,maintaining a high specific capacity of 242.8 m A h g^-1 after 100 cycles of charge and discharge at 25 m A g^-1 and a stable capacity after 200 cycles of charge and discharge at 500 m A g^-1.The nitrogen-phosphorus doped composites exhibit excellent performance,partly due to the fact that peanut shells,being hard carbon,have a large number of structural defects of their own,and partly due to the introduction of nitrogen and phosphorus atoms,which can generate more exogenous defects and active sites,and can effectively increase the interlayer distance,which in turn promotes Na⁺insertion/deinsertion and improves the capacity and electrochemical performance of the material.（2）Peanut shell based graphene（PSHC）composites were prepared by hydrothermal and pyrolysis using peanut shells as the carbon source.Some characterization and electrochemical tests were carried out on the PSHC-x series.The results show that PSHC-900 has excellent performance as an anode material for sodium ion batteries,maintaining a capacity of 248.8m A h g^-1 after 120 cycles at 25 m A g^-1 and around 140.3 m A h g^-1 after 400 charge/discharge cycles at 500 m A g^-1.This excellent performance is mainly due to the large interlayer distance as well as the abundance of structural defects in the prepared hard carbon material,which not only increases the active sites for Na⁺adsorption on the surface and accelerates the transport of sodium ions,but also facilitates easier Na⁺insertion/deinsertion.（3）Fe₂O₃@C composites were obtained by stepwise hydrothermal carbonization at low temperatures using peanut shells as the carbon source.The material was subjected to a series of physical characterization and the lithium storage performance of the material was tested by assembling half-cells.Fe₂O₃@C as an anode material for LIBs can still reach a reversible capacity of 1000.8 m A h g^-1 after 100 charge/discharge cycles at 200 m A g^-1;it can still maintain a capacity of 573.5 m A h g^-1 at a high charge/discharge flow of 1 A g^-1.The excellent electrochemical performance of the Fe₂O₃@C composite is due to the loading of Fe₂O₃nanoparticles in this porous carbon matrix,which can effectively mitigate the occurrence of volume changes and agglomeration of Fe₂O₃ nanoparticles during the charge/discharge process,and can facilitate the diffusion and electron transport of LIBs.