Preparation And Electrochemical Performances Of Biomass-derived Carbon Materials

Lithium-ion batteries have the advantages of green pollution-free,high power density and long cycle life,and widely used in mobile phones,notebook computers,digital cameras and electric vehicles.Because the low theoretical capacity characteristics of conventional commercial graphite anodes are difficult to meet the requirements of various electronic products for the growing high-energy and high-power devices of lithium-ion batteries,biomass is inexpensive,widely distributed,and environmentally friendly.It has a very large advantage as a carbon material precursor.However,due to the diversity of biomass,unique material design is required to make biochar materials play a more promising role.The treatment methods of the carbon materials used herein include:hetero atom doping,structure nanostructures,and compounding with high-capacity transition metal materials.The innovation of this paper is to use different biomass materials as precursors of carbon materials to prepare biomass carbon materials and their composite materials through ingenious treatment methods.Moreover,a variety of testing methods are used to characterize and analyze the morphology,structure and composition of biomass carbon materials and their composite materials.This paper focuses on the electrochemical performance of bio-carbon materials as negative electrodes for lithium-ion batteries,and explores the effects of the composition and structure of carbon materials on electrochemical performance.The main research contents and conclusions of this paper are as follows:（1）Preparation and electrochemical properties of heteroatoms self-doped biomass carbon materialsHeterogeneous egg-containing egg whites are used as precursors of biomass carbon materials to prepare a variety of heteroatom self-doped biomass carbon materials by simple one-step carbonization method.（Doping of heteroatoms can improve the electron conduction of materials.Sexuality can also bring a rich active site to the electrode material）.This chapter focuses on the effects of different treatment temperatures on the doping amount and doping type of various heteroatoms（O,N and S）of biomass carbon materials,and the influence of electrochemical properties.The study found that biomass carbon materials obtained by carbonization at 600 ^oC have the best lithium ion storage performance.It mainly includes high reversible capacity(807.5 mA h g-1 for 100 cycles at 100 mA g^-1)and excellent capacity retention（104.8%）.Moreover,this temperature-treated biochar material also has excellent sodium ion storage performance(reversible capacity of 226.8 mA h g^-1 at 100 mA g^-1).（2）Preparation and electrochemical properties of two-dimensional biomass porous carbon nanosheetsUsing natural dried loofah as a precursor of biomass carbon material,on the basis of high temperature pre-carbonization,two-dimensional biomass porous carbon nanosheets are prepared by air-annealing shearing and stripping,and the obtained porous carbon nanosheets are obtained.The surface area is 20 times or more that is not air treated.In addition,a large number of oxygen-containing functional groups are introduced during the air-induced activation process,resulting in a certain amount of tantalum capacitance contribution.The results show that the biomass carbon material obtained by 350°C air annealing activation treatment has an ultra-high specific surface area and pore volume and an excellent hierarchical porous structure.The biomass carbon material treated in this way not only provides a large number of fast transport channels for ions and electrons,but also improves the charge transfer efficiency,and has extraordinary lithium ion storage performance(100 mA g^-1 after 100 cycles maintain 742.8 mA h g^-1)and good capacity retention.（3）Preparation and electrochemical properties of flexible biomass carbon-based MC/NiCo2O4 compositesThe plant fiber mask was used as the precursor of the biomass carbon material,and the stability of the mask was improved by pre-oxidation treatment,and then carbonized at a high temperature to investigate the influence of the carbonization temperature on the flexible biomass carbon material（MC）.A flexible MC/NiCo2O4 composite was obtained by using a mask-derived flexible carbon material as a substrate,hydrothermal and annealing to obtain two-dimensional nickel cobaltate nanosheets.The effect of hydrothermal time on the morphology and distribution of nickel cobaltate nanosheets on the substrate of biomass carbon was studied.The results show that the MC/NiCo2O4 composite with a hydrothermal time of8 hours not only has good flexibility,but also the two-dimensional nickel cobaltate nanosheets grow uniformly and densely,forming a stable three-dimensional interpenetrating network structure,which brings excellent Lithium-ion storage performance(reversible capacity of1130 mA h g^-1 maintained after 80 cycles at 100 mA g^-1).（4）Preparation and electrochemical properties of flexible flower-like biomass carbon-based MC/MoS2 compositesA carbonized plant fiber mask was used as a flexible substrate to hydrothermally grow two-dimensional molybdenum disulfide nanosheets to obtain a flexible MC/MoS2 composite.The effects of hydrothermal time on the growth and distribution of molybdenum disulfide nanosheets and the phase transition（1T to 2H）of molybdenum disulfide in hydrothermal processes were investigated.The results show that the MC/MoS2 composite with a hydrothermal time of 9 hours has good flexibility and the molybdenum disulfide nanosheet has the most growth and is a composite phase of 1T/2H.The MC/MoS2 composite is used as the negative electrode of lithium ion battery.Excellent electrochemical performance(stable reversible capacity of 4.03 mA h cm^-2 at 100 mA g^-1).