Hydrothermal Synthesis And Electrochemical Properties Of Bio-based Carbon Microspheres For Lithium-ion Batteries

With the environmental pollution and energy shortage,the development and application of new clean energy have become the most important issue.The effective way to reduce exhaust emissions and the consumption of petroleum resources is to develop electric-driven vehicles.Lithium-ion batteries are the core components of electric vehicles.Besides,the discharge curve of hard carbon materials shows gradually falling,which is suitable for the application of hybrid vehicles,so it is reasonable to find a negative electrode material with low cost,high volume energy density and high mass energy density,and high efficiency for the first time.Biomass resources are rich in resource and have a wide range of sources,making them a promising alternative.This thesis uses the cheapest and most abundant cotton pulp cellulose in nature and the safe and low-cost N-rich chitosan as the carbon sources,respectively.The micron-sized carbon microspheres were prepared by mild hydrothermal synthesis.After carbonization at 600-700℃,the electrochemical performances of the carbon sphere anode materials for lithium ion battery were investigated on the basis of morphological and structural characterizations.The results show that the addition of citric acid to prepare cellulose-based carbon microspheres reduces the hydrothermal temperature and improves the dispersion of carbon spheres.Most of the particle size distribution is 4-10μm.Under the conditions of 230℃,10h,and 1.5g citric acid,the carbon microspheres with an average particle diameter of 6.30μm and good spherical morphology were prepared.When the chitosan was used as the carbon source,water or 4.5%acetic acid solution as the medium,the products were non-spherical under the hydrothermal condition of 200℃ for 10h.The addition of hydrochloric acid accelerated the degradation of chitosan,and N was stably doped in carbon structure.Carbon spheres with the particle size distribution of 1-6μm were prepared at a lower temperature of 160-180℃ and for a shorter period of time.The hydrothermal reaction is a chemical process.The as-grown carbon microspheres by hydrothermal synthesis are distinguished from the raw materials of the crystalline structure and are amorphous carbon,which undergoes dehydration polymerization and aromatic cyclization.At the optimum carbonization temperature of 700℃,both cellulose-based hard carbon spheres(HCS-Cel)and chitosan-based hard carbon spheres(HCS-Chi)exhibit high specific capacity and rate performance.The first reversible capacity of HCS-Cel and HCS-Chi at a current density of 50mA/g are 570mAh/g and 503mAh/g respectively.After HCS-Chi was cycled 500 times at a current density of 500mA/g,the specific capacity decreased from 214.9 to 174.2mAh/g,and the specific capacity retained 81%of the initial value.The cycle stability was good and may be related to the doping of N.