The Study On Biomass Derived Carbon-based Material As Anode For Lithium-ion Batteries

All countries all over the world have devoted all their efforts to develop new energy storage devices as the energy crisis and environmental pollution problems have become more and more seriously.Lithium-ion batteries?LIBs?have been intensively studied in recent years owing to their numerous merits such as high energy density,high operating voltage,low self-discharge rate,no memory effect,long cycle life,and environmental friendliness and so on.However,the low energy density of commercial graphite anode materials limits its further application.Development of energy devices with higher energy density,lower costs is highly desirable.Biomass,as a kind of waste resources,possesses the advantageous of low-cost,easy to access and environmental friendly.The as-obtained biomass can be easily activated and further carbonized to produce biomass-derived carbon materials which have large specific surface area,stable structure,excellent conductivity,and good electrochemical performance.In view of the above advantageous,biomass has been studied by many scientific researchers and has shown great potential in the application of lithium ion battery anode materials.The aim of this thesis is to fabricate easily synthesized,less costly and high-performanced biomass derived carbon-based material as anode material for LIBs,which improves the capacity,cycling stability and rate capability of the material and makes the biomass derived carbon-based materials can be used commericially.The main research contents are listed as follows:?1?Soybean as both carbon and nitrogen source with KOH as activator was utilized to obtain the required N-doped carbon materials at different pyrolyzing temperatures.The SPC pyrolyzed at 700?C showed excellent morphology and good reversible capacity of 360 mA h g^-1 in the 100^th at 0.5 C,and excellent cycling performance(320 mA h g^-1 in the 500^th at 2 C and 275 mA h g^-1 at 4 C after 1000cycles).The lithium storage mechanism is studied and discussed through the pseudocapacitance.The result shows that the pseudocapacitance contributes to the storage of lithium ions not only as a simple lithium ion diffusion control.The good electrochemical performance could be ascribed to the unique honeycomb-like structure,interconnected porosity and more importantly,capacitive contributions from its nitrogen doping and distortional graphite nanocrystals.?2?By furtherly optimizing,the prepared soybean derived carbon?NC?has better conductivity,higher specific surface area and higher nitrogen content,and it was composited with SnCl₂ by hydrothermal method.The SnO₂@NC materials exhibited much lithium storage capacity than NC,at current density of 200 mA g^-1,the capacity was maintained at 586.7 mA h g^-1 after 100 cycles,and 420 mA h g^-1 in the 200^th at500 mA g^-1.The reason is mainly attributed to the fact that the excellent conductivity,larger specific surface area and more pore diameters of NC materials are beneficial to improve the conductivity of SnO₂ and contact with electrolyte.?3?TiO₂ nanoparticles with uniform spheres were prepared by sol-gel method using tetrabutyl titanate as raw material,and then hydrothermally compounded with NC to obtain TiO₂@NC material.The prepared composite showed outstanding cycle performance with reversible capacity of 282.2 mA h g^-1 in the 100^th at 1 C,and excellent rate performance(155 mA h g^-1 in the 200^th at 5 C).CV and EIS tests were performed to explain the excellent electrochemical performance.Therefore,the selection of N-doping biomass-derived carbon and its composites with metal oxides are potential anode materials.