| Lithium-ion batteries(LIBs)have been commercialized on a large scale in the field of smart grids and electric vehicles due to their advantages such as high energy density,long service life,and good charge/discharge efficiency.The current commercial electrode materials mainly include phosphate(Li Fe PO4),transition metal lithium oxide(Li Co O2)and graphite,because that these inorganic materials based on intercalation mechanism have higher specific capacity and cycling stability.However,the safety of LIBs has been seriously threatened due to the large amount of heat generated by the collapse of the layered structure for inorganic materials.Besides,the limited sources of most inorganic electrode materials have cannot meet the demand of large-scale popularization of LIBs.At the same time,inorganic materials also suffer from the shortcomings of limited energy density and sluggish kinetics.Therefore,exploring advanced electrode materials with excellent performance,environmental friendliness,safety and stability is crucial to the further development of new energy storage devices.Organic molecules are most likely to replace traditional inorganic electrode materials due to their structural designability,processability,variety,rich sources,and environmental friendliness.Among various organic electrodes,polyimide has good thermal stability and designable molecular structure,while polyquinones possess higher theoretical capacity,good reaction reversibility and higher resource utilization.Therefore,poly(anthraquinone-imide)s combining the advantages of two polymers has been considered to be the most promising candidate for LIBs electrode materials.However,the low discharge voltage for organic cathode,poor conductivity,and high solubility in organic electrolytes have seriously restricted the practical application of organic materials.Based on this background,this thesis has carried out the following work from the aspects of structural designing,conductive carbon composite and full battery assembling:(1)Three kinds of muti-carbonyl poly(anthraquinone-imide)s(PI)were synthesized by traditional reflux thermal amine method: high benzene-type non-bridged polyimide(PMAQ),biphenyl-type bridged polyimide(BPAQ),carbonyl group-bridged polyimide(BTAQ).PMAQ shows porous structure consisted by irregular nanoparticles.In contrast,BPAQ exhibites tightly stacked structure with limited the exposure of electrochemically active sites.BTAQ presents a spherical layered structure composed of regular nanosheets.Nitrogen adsorption/desorption tests showed that the three polymers have micropores,mesopores and macropores at the same time.This hierarchical porous structure is beneficial to ion transport and charge storage.The electrochemical testes showed that PMAQ has the most excellent rate performance and stable cycle performance whether used as cathode or anode.This is mainly due to the excellent electronic conduction of the non-bridged chain strutcure,and the porous structure is conducive to the full exposure of active sites,electrolyte infiltration and rapid lithium-ion transport.(2)In view of the poor conductivity and low utilization of electrochemical active sites for polymer electrodes polyimide/CNTs composites(PMAQ@CNT)with different morphologies were synthesized through in-situ thermal amine method.The effect of reaction time and organic solvents on the structure and morphology of the product has been explored.The results show that carbon nanotubes can not only increase the electronic conductivity,but also serve as nucleation sites for the growth of PMAQ.The growth of PMAQ on the surface of carbon nanotubes changed from the surface coating based on homogeneous nucleation to nanosheet array formed by heterogeneous nucleation with the increase of reaction time.The electrochemical tests showed that PMAQ@CNT with nanosheet array exhibits the largest initial discharge specific capacity(238 m Ah g-1),the best rate performance(the retention rate is up to 80%)and good cycle stability(the capacity still remains 171 m Ah g-1 after 1000 cycles at 1.0 A g-1)compared with pure PMAQ and PMAQ@CNT without array structure.On the one hand,carbon nanotubes can significantly improve the electronic conductivity of polyimide.On the other hand,the polyimide nanosheet arrays has abundant active site exposure,which is conducive to the full infiltration of the electrolyte and can greatly improve the lithium-ion transportation.(3)Based on the lithium storage activity on active groups C=O and C=C in different voltage ranges for PMAQ@CNT,a symmetrical polymer-based full battery(PMAQ@CNT/PMAQ@CNT)with high power density has been designed and constructed.By matching the capacity and quality of the positive and negative electrodes,a symmetrical polymer-based full battery was successfully assembled.The discharge capacity of the full battery is as high as 235 m Ah g-1 at a current density of 0.02 A g-1.When the current density increases to 0.1 A g-1,the full battery still maintains a high reversible capacity of 109 m Ah g-1.And the reversible capacity can be maintained at 101 m Ah g-1 after 50 cycles at 0.1 A g-1.The symmetrical polymer-based full battery exhibits excellent power density(3818 W kg-1)and good application(powering LED bulbs),which lays a foundation for the development of organic electrode materials and the next generation wearable flexible energy storage devices. |
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