Synthesis And Electrochemical Properties Of Nitrogen Doped Carbon Materials

Lithium-ion batteries?LIBs?have been widely used in various portable electronic devices because of their superior performance.However,with the development of electric vehicles and energy storage market,the capacity of commercial LIBs cannot meet the market demand any more.Therefore,an urgent improvement is needed for the performance of the LIBs.Nitrogen doping is one effective method to improve the lithium storage performance of carbon anode materials.In this thesis,we have conducted the morphology and structure characterization,electrochemical performance testing of the as-prepared nitrogen-doped carbon materials to study the effect of the nitrogen doping on the lithium storage performance and the possible mechanisms.The main research contents are as follows:?1?Glucose and melamine were used as carbon and nitrogen sources separately to synthesize nitrogen-doped carbon materials?CNC?by pyrolysis,and zinc chloride was added as a reaction additive to investigate the effect of zinc ions on the microstructure of the reaction products.We found that the nitrogen content of the prepared nitrogen-doped carbon material was as high as 26.56wt%and the nanocrystal size was¹ nm.The addition of zinc chloride can not only inhibit the formation of graphite-nitrogen which is unstable in the electrochemical lithium insertion reaction,but also adjust the ratio of pyrrolic-N/pyridinic-N in the carbon material.?2?The CNC material has a high specific capacity of about 1353 mAhg^-1 at a current density of 1 Ag^-1 when used as anode materials for LIBs.After 100 cycles,a specific capacity of 1155mAhg^-1 was maintained,implying its good cycle stability.According to the new calculation method proposed by S.Freunberger,we calculated the mass specific capacity and volume specific capacity of CNC electrode to be 970 mAhg^-1 and 951 mAhcm^-3,respectively.Moreover,the specific capacity of CNC electrode is comparable with Si and outperforms all other reported carbon based electrodes.?3?Preparation of vanadium oxide and carbon-nitrogen composites by using ZIF-8 as the precursor and further combining with vanadium oxide.vanadium oxide particles can promote the decomposition part of SEI at a large current density and form stable film,which increases the lithium storage performance.At 5 Ag^-11 current density,the vanadium oxide and carbon-nitrogen composites maintain a reversible capacity of 220 mAhg^-1 after 100 cycles.