Preparation Of Biomass Based Carbon Materials And Its Application To Lithium-ion Batteries

Lithium ion batteries?LIBs?are considered to be the most promising electrochemical energy storage devices due to their high energy density,high output voltage,no memory effect and environmental friendliness."Graphite-type"carbon materials?graphene,carbon nanotubes,and amorphous carbon,etc.?are widely used in lithium ion batteries electrode materials because of their advantages such as easy availability of materials,non-toxicity and high chemical stability.However,the lower theoretical capacity?372 mA h/g?and poor rate performance make it unable to meet the requirements for high energy and high rate performance of LIBs.Biomass carbon materials have the characteristics of large specific surface area and high electrical conductivity.Therefore,in recent years,researchers have focused on the research of the application of biomass carbon materials in LIBs.In summary,in order to further postgraduate material carbon materials and their applications in lithium-ion battery electrodes,this thesis focuses on the preparation of biomass-based carbon materials and electrochemical performance research,and has carried out the following three work studies:?1?Biomass waste pine needles were used as raw materials,KCl is used as an activator,and carbonized pine needles?CPNs?with a three-dimensional multi-stage pore structure are prepared by calcination at high temperature.In this experiment,CPNs and acetylene black?AB?were used as composite binary conductive additives for the first time,and their effects on the electrochemical performance of commercial anode material lithium titanate?LTO?were investigated.The experimental results show that the binary conductive additive can significantly improve the electrochemical performance of the active material LTO.Among them,when the mass ratio of CPNs/AB is 2/8,the capacity retention rate after 300 cycles at a current density of 30 C can reach 97.2 wt.%.The reason can be attributed to the application of the binary composite conductive additive is beneficial to disperse and support the active material,and improve the cycle performance and rate performance of the electrode material.The study of binary conductive additives provides a research basis for the future research of composite conductive additives.?2?Using silk as a biomass material and KCl as an activator,the effects of ultrasonic and pressure treatments on pore formation under constant temperature conditions are discussed.The analysis of the structure and performance of the material shows that the carbonized silk?CS?prepared after ultrasonic treatment has a more uniform pore distribution and a larger specific surface area.Meanwhile,comparing the electrochemical performance of CS prepared by different methods,the results show that CS prepared by KCl activation has higher electrochemical performance than CS without KCl activation.Among them,CS negative electrode material was prepared by sonication and KCl activation.The capacity was 648.99 mA h/g at a current density of 0.1 A/g,and the capacity retention rate after 500 cycles at a current density of 1 A/g could reach 82.54 wt.%.The reason can be attributed to the fact that ultrasonic treatment is beneficial for K⁺to disperse in silk materials,the pore distribution of the prepared material is more uniform,and the specific surface area is larger,which is conducive to lithium ion storage to increase reversible capacity.This part of the study provides a new method for the preparation and research of porous carbon materials in the future.?3?Manganese oxide/nitrogen-doped carbon composite materials?MnO/N-C?and manganese carbide/manganese oxide/nitrogen-doped carbon composite materials?Mn₇C₃/MnO/N-C?.Through the analysis of the material structure,the results show that has a"sandwich structure",which is beneficial to the structural stability of the material during the charge and discharge process.By comparing the electrochemical properties of MnO/N-C and Mn₇C₃/MnO/N-C,the results show that the introduction of Mn₇C₃ into the composite material is beneficial to improve the conductivity of the material,and then improve the electrochemical performance of the material.In this part of the study,the carbon material/metal compound diversity combination is achieved through a simple synthesis method,which provides a low-cost and environmentally friendly synthesis method for the preparation of high-performance lithium-ion battery anode materials.