Synthesis Of Multi-stage Porous Carbon Materials And Their Application In Battery Energy Storage

With the development of today’s society and the continuous advancement of science and technology,energy consumption and environmental issues are becoming increasingly prominent,and the development and utilization of new renewable energy sources is imminent.In the 1990s,Sony developed lithium-ion batteries,which are widely used in many electronic devices such as mobile phones,notebook telegraphs,electric vehicles,and large-scale smart grids.Today,lithium-ion batteries have become an indispensable part of people’s lives.The traditional anode material of lithium-ion batteries is mainly graphite.The specific capacity of such materials is about 372 mAh g-1.As scientists continue to explore and research,their energy density is close to the theoretical limit and cannot meet the growing market demand.The porous carbon material has a high specific surface area,a large pore volume,good electrical conductivity and excellent mechanical properties.As a negative electrode of a lithium-ion battery,it not only has a specific capacity exceeding that of conventional graphite,but also has good cycle stability.At the same time,lithium-sulfur batteries with elemental sulfur and metallic lithium as the positive and negative electrodes attract more and more attention.Lithium-sulfur batteries have a theoretical specific energy of up to 2600 Wh kg-1 and a theoretical specific capacity of 1675 mAh g-1.Low sulfur toxicity,large reserves,and low prices,but elemental sulfur is an electronic insulator when used as an active material in lithium-sulfur batteries,and polysulfide shuttle effects and volume changes will occur during charging and discharging,which will lead to problems such as the collapse of the electrode structure and so on.The porous carbon material,because of its pore structure and excellent conductivity,is used as a sulfur carrier,which can effectively alleviate the shuttle of polysulfides and the insulation of elemental sulfur.Therefore,in this thesis,porous carbon is the research object,with the purpose of improving the capacity,rate performance and cycle life of the anode of the lithium battery and the cathode of the lithium-sulfur battery,a porous carbon material with excellent performance has been prepared.The specific research contents are as follows:(1)Using non-traditional carbon source halogen polymer polyvinylidene chloride(PVDC),dehalogenation reaction with KOH at room temperature can obtain high-quality carbon nanomaterials,in which KOH acts as a dehalogenating agent and pore-forming agent.The dual role of the carbon source after the removal of the functional group has a high reactivity.In the presence of the dopant thiourea,N and S doping atoms can be effectively introduced on the surface of the material to increase the interplanar spacing of the carbon material.,The obtained high-quality carbon nanomaterials(CHPC)were characterized by SEM,Raman,BET,XRD,XPS,etc.,and used as the negative electrode material of the lithium ion battery to test the electrochemical performance of the battery at a current of 0.1 A g-1 under the density,the specific capacity of the first cycle reaches 1351.21 mAh g-1,which is much higher than the specific capacity of traditional graphite.After 100 cycles,the specific capacity can be kept at 948.92 mAh g-1.(2)Because the synthesized N and S double-doped porous carbon nanomaterials(CHPC)are rich in microporous structure and large specific surface area(742.01 m2 g-1),their porous structure and good conductivity can be effectively alleviated.The elemental sulfur has poor conductivity and the "shuttle effect" problem,and the N and S elements can also enhance the chemical adsorption of polysulfides by carbon materials,so they are used as sulfur carriers to prepare carbon-sulfur composite materials by melt diffusion method.(CHPC@S),TGA characterization of the composite material and use it as the positive electrode of the lithium-sulfur battery to test the electrochemical performance of the battery.At a current density of 0.1 C,the specific capacity of the first lap reaches 1227.45 mAh g-1.After 100 cycles,the specific capacity remained at 844.15 mAh g-1.