Preparation And Lithium-Storage Properties Of High-Performance Conjugated Organic Anode Materials

Due to the advantages of abundant resources,environmentally friend,designable structure,high capacity,system safety and mild preparation method,organic materials have attracted widely attention.Although they show widely application prospect,as the solubleness in the electrolyte and poor electrical conductivity,their practical applications are greatly limited.Therefore,the development of a new organic electrode materials to overcome these issues has become a hot research topic.Hetero-atom is beneficial to the embedding of lithium ions,and the conjugate structure of organic materials have a high capacity performance.Therefore,the conjugated polymer containing abundant hetero-atoms are the first choice for preparing high-performance organic battery materials.In this thesis,several strategies are applied to modify the organic electrodes and enhance their battery performance.（1）Design organic electrodes from conjugate polymers with different hetero-atoms;and improve the performance via increasing the conductivity by adding conductivity fillers.（2）Design the electrode with novel self-adhesive structure and excellent distribution to improve the utilization and the capacitance.（3）Introduce pores into 1D nanofibers to improve the wetting behavior between electrode and electrolyte and further enhance the electrochemical performance.（4）Organic/inorganic composite can not only improve the conductivity but also enhance the capacity by combining the advantages of organic and inorganic materials.To achieve super-lithiation,conductive fillers（such as carbon nanotubes and reduced graphene oxide）are also added to prepare excellent active materials for the lithium ion batteries with good battery performance.The specific researches are described as follows:（1）Based on 1,4,5,8-Naphthalenetetracarboxylic acid-3,3’-Diaminobenzidine（NTCA-DAB）monomers,and polyvinylpyrrolidone（PVP）used as spinning assistant,CNTs used as conductive filler,the polypyrron-carbon nanotubes（BBB-CNTs）composite nanofibers were prepared by electrospinning and solid phase reaction and applied as cathode material of lithium ion battery.In this work,the processing issue of BBB due to the insolubility and infusion was solved.In addition,the electrochemical property of BBB-CNTs was studied on the influence of the CNTs content.The results show that the optimum amount of CNTs in BBB is10%（BBB-CNTs-10%）,and the capacity of BBB-CNTs-10%can still retain 660mAh g^-1at 0.1 A g^-1after 100 cycles,which increases 106%compared with pure BBB,showing that the superlization has been realized.By this method,the processing issue of BBB due to the insolubility and infusion was solved,and the addition of CNTs into BBB nanofiber can improve the conductivity of BBB,achieving organic anode materials with high-performances.（2）Polyamic acid@graphene oxide（PAA@GO）and polyamic acid@carbon nanotubes（PAA@CNTs）solution were prepared by in-situ polymerization,GO coated by PI nanosheets（PI@GO）was obtained by chemical imidization.Then a novel self-adhesive PI@RGO/PI@CNTs hierarchically porous electrode was prepared due to the intrinsic viscosity of PAA.The results show that the PI@RGO/PI@CNTs self-adhesive electrode could achieve a maximized electroactive materials utilization of 100%.The intial discharge-charge capacity of PI@RGO/PI@CNTs can reach 2263 mAh g^-1and 1291 mAh g^-1at 0.1 A g^-1,respectively.It can retain a high reversible specific capacity of 790 mAh g^-1after 200cycles,which is significantly higher than the capacity of PI/PI@CNTs(420 mAh g^-1).The improvement of performance may be due to these:（1）.RGO and CNTs can be dispersed uniformly in the electrodes as the in-situ polymerization,and polymer combined with carbon substrate tighter;（2）.2D/1D network structure was formed by RGO and CNTs,which achieved better conductivity with less carbon material;（3）.due to the intrinsic viscosity of PAA,the PI@RGO/PI@CNTs electrode could be directly obtained without any conventional extra binders and achieve a superhigh utilization of active materials.（3）Polyacrylonitrile（PAN）-derived conjugated ladder structures（CLSP）was prepared under different temperatures（300～600℃）by using conventional emulsion polymerization and heat treatment process.And the electrochemical performance was studied on the influence of treat temperature when it applied in lithium ion battery.The results confirm that PAN-derived CLSP was organic material in the temperature range of 300～600℃,and CLSP presents a high capacitance property.The CLSP under heat treatment at 600℃（CLSP-600）possesses the best electrochemical performance.The capacity of CLSP-600 can maintain 480 mAh g^-1at the current density of 0.1 A g^-1,which is significantly higher than theoretical specific capacity of graphite materials(372 mAh g^-1).（4）Using RGO as additive of conductive material,and cellulose acetate（CA）as the pore-forming agent,PAN as electrospinning solution.PAN-derived（CLSP/RGO@CA）nanofibers with the different pore structures were prepared by facile electrospinning and heat treatment processes.The pore structures and electrochemical performance of CLSP/RGO@CA with different amounts of CA was studied.The results show that the optimum ratio of CA/PAN is 1:1 by weight（CLSP/RGO@CA-100）.The intial charge-discharge capacity of CLSP/RGO@CA-100 can reach 1677 mAh g^-1and 1220 mAh g^-1at 0.1 A g^-1,respectively.It can still retain 740 mAh g^-1and 640 mAh g^-1at 0.1 A g^-1and 0.2 A g^-1after 100 cycles,respectively,showing high capacity properties,excellent rate performance and high-low temperature performance.In this method,GO was reduced to RGO to improve the conductivity,and abundant pores was formed by the pyrolysis of CA,which is beneficial to the infiltration of electrolyte.The capacity performance and rate performance were improved due to the shortened the transport distance of lithium ion.（5）Using nickel acetylacetonate as raw material,Ni（NiO）nanoparticle loaded CLSP nanofiber（CLSP/Ni）were prepared via simple electrospinning and heat treatment processes.The effect of the amount of Ni on electrochemical performance of CLSP/Ni was studied.The results show that Ni nanoparticles are monodisperse in the nanofibers,which is composed of Ni@NiO dominated by Ni element.The addition of Ni not only improved the conductivity of CLSP/Ni,but also provided the capacity for composite.Electrochemical result shows that CLSP/Ni-100 is optimum while the amount of nickel acetylacetonate is 100%relative to PAN.And the capacity of CLSP/Ni-100 can keep 800 mAh g^-1after 100 cycles at the current density of 0.1 A g^-1.