Application Of Organic Conjugated Molecules In Sodium / Potassium-ion Batteries

With the development of mobile electronic equipment,electric vehicles and large-scale energy storage in recent years,there is an increasing demand for clean and efficient energy storage technology.Although lithium-ion batteries（LIBs）are widely used as efficient energy storage technology,with its specific capacity gradually approaching the theoretical specific capacity and environmental protection requirements,it is difficult for traditional LIBs to make a·great breakthrough in energy density and environmental protection.In addition,the uneven distribution and limitation of lithium mineral resources also limit the development of LIBs industry.So more and more researcher pay attention to sodium-ion batteries（SIBs）and potassium-ion batteries（PIBs）,because of more abundant reserves of sodium and potassium.Compared with traditional inorganic electrode materials,organic electrode materials have many advantages such as rich resources,friendly environment and large specific capacity.Organic materials are very promising to become the next generation of energy storage materials.However,the application of organic electrodes still faces great challenges.One of the most important problems is that organic materials have high solubility in traditional electrolyte system.Which will lead to the rapid deterioration the electrochemical performance of the batteries.Therefore,designing and developing organic electrode materials with high energy density and reducing the solubility of organic materials in electrolyte in order to achieve excellent electrochemical performance of organic electrode materials have great scientific significance and application value.This dissertation aimed to solve these problems in the application of small-molecular organic materials in batteries.Research was carried out on quinone-based materials with conjugated structure to screen appropriate organic molecules.The solubility of organic electrode materials in electrolyte was reduced by oligomerization,polyanion salinization and polymerization.The relationship between the electrochemical properties of several materials and the parameters such as molecular type,morphology and structure change was systematically studied.In addition,the commercialization of organic electrodes has been explored through the study of SIBs with high active substance loading and the study of SIBs and PIBs full cells.The specific contents include the following parts:（1）In order to solve the problem of high solubility of small molecular quinone-based materials,the solubility of organic electrode materials was reduced by oligomerization based on the principle of increasing molecular weight to reducing solubility.This work selected the dimers of 9,10-phenanthraquinone（PQ）and9,10-anthraquinone（AQ）,namely 3,3’-（1,4-phenyl）bis（phenanthrene-9,10-dione）（DPQ）and 6,15-dihydrodiphenylpyridazine-5,9,14,18-tetraone（DAQ）as the organic cathode materials.Its half cells performance in LIBs,SIBs and PIBs were studied.Electrochemical test,scanning electron microscope（SEM）and ex-situ fourier transform infrared spectrum（FT-IR）showed that dimers have better cyclic stability and structural stability.After 50 cycles at low current density(100 m A·g^-1),the discharge specific capacities of PQ/AQ in SIBs half cells were only 30/36 m Ah·g^-1,the DPQ/DAQ have reisen to 145/110 m Ah·g^-1.After cycling,the microstructure of DPQ and DAQ electrodes were relatively stable,and the change of their molecular structure during electrochemical process was reversible;（2）In order to further improve the batteries stability of small-molecule organics,polyanionic salinization was used to reduce the solubility of small anthraquinone molecules.A polyanion salt derivative of AQ namely sodium9,10-anthraquinone-2,6-disulfonate（Na₂AQ26DS）was selected as the cathode material.The characterization of Na₂AQ26DS by electrochemical performance test,ex-situ FT-IR and X-ray diffraction（XRD）test confirmed its good cycle stability in SIBs half cells.At the same time,Na₂AQ26DS has fast ion transport behavior in the electrochemical process,and it has a stable molecular structure.Therefore,Na₂AQ26DS shows good rate performance;（3）In view of the low solubility of polymer materials,PQ-based polymer poly（9,10-phenanthraquinone-alt-benzene）（PPQ）was synthesized as cathode material.In the following work,the electrochemical properties of PPQ in SIBs and PIBs half cells were studied.The electrochemical test,FT-IR and X-ray photoelectron spectroscopy（XPS）test show that PPQ has good cycle stability in SIBs.The specific discharge capacity of PPQ does not decay significantly compared with the peak specific discharge capacity during 300 cycles.Moreover,PPQ molecule has partial structural reversibility in the redox process.Compared with PQ,the actual specific capacity and rate performance of SIBs and PIBs have been significantly improved;（4）Finally,using Na₂AQ26DS and PPQ as cathode,graphite,1,4-benzenedicarboxylic acid sodium salt（Na₂TP）and bismuth（Bi）as anode to assemble the SIBs and PIBs full cells for electrochemical performance test.It is very important for the full cells to select the appropriate anode material.Under low current density,compared with the Na₂AQ26DS II graphite PIBs full ceslls,the coulombic efficiency of Na₂AQ26DS II Na₃Bi PIBs full cells were significantly improved（from～60%to 99%）.Compared with the PPQ II Na₃Bi SIBs full cells,the cycle stability and rate performance of PPQ II Na₄TP SIBs full cells were significantly increased.