Preparation And Lithium/Sodium Storage Of High Performance Rice Husk-based Anode Materials

With the continuous expansion of the new energy vehicle market,lithium（sodium）ion batteries are expected to have lower cost and higher energy density.At present,graphite shows excellent cycling performance which is commonly used in commercial lithium-ion batteries,but its low theoretical capacity limits its wide application.Although silicon-based anode materials with high theoretical capacity have been produced in small batches,but the complex preparation process and high production cost cannot meet the social requirements for low-cost batteries.In addition,due to the lack of lithium resources and the difficulty of recycling,the cost of lithium-ion batteries is also increasing.The sodium element,which is in the same main group as lithium,not only has similar chemical properties to lithium,but also it is cheap and abundant.Sodium-ion batteries have great competitive advantages for large-scale energy storage devices.Hard carbon materials are suitable anode materials for Sodium-ion batteries,which can be attributed to their large interlayer spacing that allows Na⁺intercalation and deintercalation.However,the current commercial hard carbons are immature and expensive to produce and generate toxic substances during the production process.In view of the urgent scientific questions that need to be addressed in the current negative electrode materials for lithium-ion batteries and sodium-ion batteries,this thesis uses cheap and abundant biomass rice husks as silicon and carbon sources to prepare silicon-based and hard carbon anode materials,respectively.The electrochemical properties of these materials were explored,which provided a practical and theoretical basis for the industrial production of low-cost,high-capacity LIBs silicon-based anode materials and the preparation of low-cost SIBs hard carbon anode materials.The main research contents of this thesis are as follows:（1）First,Rice husks were used as silicon source to prepare the SiO_xnanoparticles by the processes such as alkali extraction,acid precipitation,and aluminothermic reduction.Then,the porous graphene aerogel matrix was further loaded to construct a SiO_x@graphene aerogel（SGA）composite materials.The physical properties of the SGA series of materials were characterized by XRD,SEM,etc.,and the lithium storage performance of the materials was evaluated by assembling CR2032 half-cells.The co-transport of electrons and ions in the composites and the effect of the amount of graphene aerogel on the electrochemical performance were systematically studied.As the negative electrode of LIBs,SGA-1 still maintains a high capacity of 994.7 m Ah g^-1after 200 charge-discharge cycles at 200 m A g^-1,even after 400 charge-discharge cycles at 1 A g^-1,it also maintains a capacity of 937.1 m Ah g^-1,which is much higher than that of current commercial graphite.The excellent electrochemical performance of SGA-1 is mainly due to the fact that SGA-1 is a three-dimensional high-porosity framework interconnected by highly conductive graphene sheets.This special porous structure can not only facilitate the penetration of electrolytes,but also accelerate transfer of electrons.（2）Rice husks were used as silicon and carbon sources to prepare rice husk-based silicon/carbon（RH-Si）composite anode materials by carbonization,aluminothermic reduction and etching method.A series of physical properties and electrochemical performance tests were carried out on RH-Si.As the LIBs anode,RH-Si has a charge capacity of 640.2 m Ah g^-1after 200 cycles at a charge-discharge current of 200 m A g^-1,which is much higher than that of graphite.The excellent electrochemical performance of the material is attributed to the natural in-situ conductive carbon-based network of rice husks.This three-dimensional network can completely encapsulate silicon.On the one hand,it alleviates the volume change of silicon during during Li⁺insertion/extraction.On the other hand,it can enhance the conductivity of the material and improve the rate performance.In addition,the three-dimensional structure formed after carbonization can accelerate the penetration of the electrolyte and shorten the migration path of ions,which is beneficial to the improvement of the rate performance of RH-Si.（3）Rice husk-based hard carbon materials were obtained by alkali extraction,filtration and carbonization treatment with rice husk as carbon source.The effect of calcination temperature on the morphology,structure and sodium storage ability of RH-x series hard carbons was explored.The RH-1200 electrode exhibited excellent sodium storage capacity as an advanced SIBs anode material.It still has a high specific capacity of 324.8 m Ah g^-1after 100 charge-discharge cycles at 25 m A g^-1.The capacity remains stable even after 400charge-discharge cycles at 100 m A g^-1.The excellent performance is mainly attributed to the high specific surface area and abundant defects,which can not only accelerate the infiltration of the electrolyte,but also increases the active sites for Na⁺surface adsorption.In addition,the larger interlayer spacing can also allow Na⁺to intercalate and deintercalate in the material.