| Nitrogen doping is one of the effective means to enhance the lithium storage performance of carbon anode materials.Therefore,it is of significance to study the effect of nitrogen doping on carbon anode materials.In this thesis,to study the effect of the nitrogen doping on the lithium storage performance and the mechanism of carbon materials,morphology and structure characterization,electrochemical performance testing of the as-prepared nitrogen-doped carbon materials were conducted.The main research contents are as follows:?1?The poly?acrylonitrile?was carbonized into nitrogen-doped carbon and named CPAN.The poly?acrylonitrile?-ionic liquid copolymer was carbonized into nitrogen-doped carbon and named CPAN-PIL.Through comparing these two nitrogen-doped carbon materials,it was found that the nitrogen content increased from2.32%?CPAN?to 6.80%?CPAN-PIL?.In order to characteristic the benefits of the using of ionic liquid materials,CPAN-PIL carbon materials was used as anode materials to fabricated lithium-ion half cells.The reversible capacity of CPAN-PIL is404m Ah·g-1 after 50 cycles at current density of 0.1C,obviously higher than the reversible capacity of CPAN(309m Ah·g-1).This is mainly due to the employment of ionic liquids effectively improved the nitrogen-doped content.Higher nitrogen content increased the conductivity of CPAN-PIL,and generated a large number of active sites,contributing to the improvement of the electrochemical performance of CPAN-PIL carbon materials.The above results prove that the ionic liquid copolymer is an excellent nitrogen-doped carbon material precursor..?2?The poly?acrylonitrile?-ionic liquid copolymer were prepared with different weight ratio of acrylonitrile and ionic liquids.Through studying,it is found that the ionic liquids content had a significant influence on the lithium storage performance and the nitrogen configuration of nitrogen-doped carbon.With the increase of the ratio of ionic liquid monomers?0%,5%,10%,15%?,the reversible capacity of nitrogen-doped carbon materials were maintained at 309,360,388 and 404 m Ah·g-11 at current density of 0.1C,respectively.This result contributes to the increase of pyridinic-N and pyrrolic-N content promoted the electrochemical performances of the nitrogen-doped carbon.However,the initial coulombic efficiency showed a downward trend,and the impedance solid electrolyte interface shown an increasing trend with the increase of graphitic-N.This is mainly due to the fact that the adsorption energy of graphitic-N and Li is lower than the cohesive energy of Li dimer,which means that it is easier to form lithium clusters.The formation of lithium clusters is not conducive to the improvement of the initial coulombic efficiency has a negative effect on the lithium storage capacity of the electrode material.Therefore,excessive graphite nitrogen may be unfavorable for the lithium storage performance of nitrogen-doped carbon.?3?The prepared nitrogen-doped carbon materials were further compounded with cobalt.Co particles embedded on the surface of carbon materials could greatly improve the conductivity of the as-prepared composites.Moreover,the Co particles can promote the decomposition part of SEI at a large current density and form stable thin SEI film,which increases the lithium storage performance.The reversible capacity of the as-prepared composites was 487m Ah·g-1 at current density of 2C.Besides,the nitrogen-doped carbon materials were activated by KOH to prepare porous carbon materials.The electrochemical performance of the active carbon materials were greatly improved,and the reversible capacity can reach to 766m Ah·g-1 at the current density of 0.5C.By comparing porous carbons of two pore diameter,it was found that the larger polar solvents in the polymerization process can form nitrogen doped carbon materials with smaller pore size,thereby improving its lithium storage performance. |
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