| Organic batteries based on organic electrode materials are regarded as an important direction for future green batteries.Organic small molecules can be easily synthesized,processed and recovered on a large scale,which is conducive to their further commercialization.Among various organic electrode materials,small molecule conjugated diketones have attracted considerable attention owing to high theoretical specific capacity,high discharge voltage and fast reaction kinetics.However,the notorious dissolution problem of small molecule conjugated diketones in organic electrolytes and the ambiguous ion storage mechanism hinders their further development.Therefore,hydrogen bonding donor amino or imino groups are introduced to the conjugated diketone small molecules for strengthening intermolecular interactions,and the impact mechanism of amino or imino groups on the electrochemical properties of various conjugated diketone small molecules is systematically investigated.The research contents of this thesis are as follows:(1)For the extremely unstable conjugated 1,3-diketone molecule,amino groups are introduced to construct hydrogen bonds with carbon-oxygen double bonds,and thus an air-stable small molecule conjugated 1,3-diketone of 4,6-diamino-1,3-diketonebenzene(DADKB)is obtained.A series of characterizations of the chemical structure as well as the magnetic characterizations and theoretical calculations demonstrate that the chemical state of DADKB is zwitterion.Due to the coexistence of hydrogen bonding and ionic-ionic interactions,the solubility of DADKB in the electrolyte is effectively inhibited,and the DADKB electrode thus exhibits favorable cycling stability.Meanwhile,the highly dissociable lithium salts,the solvents with large polarity,and high-concentration lithium salts in the electrolyte can destroy DADKB intermolecular interactions,resulting in DADKB electrodes exhibiting poor cycling stability.Finally,the special chemical state of zwitterion allows the DADKB molecule reversibly store one lithium ion.(2)The impact of amino groups on the different physical state and electrochemical properties of a conjugated 1,4-diketone molecule is studied by using the2,3,5,6-tetraamino-1,4-benzoquinone(TABQ)as a model.The introduction of amino groups facilitates the formation of hydrogen bonds,which enhances of intermolecular interaction and makes TABQ crystal very stable in air.However,once the TABQ solution(without intermolecular interaction)is exposed to air,the amino groups will readiy undergo a process of deprotonation and oxidation,and then trigger the transformation of TABQ molecules into TABQ dimer.Although the conjugated 1,4-diketone group in TABQ or TABQ dimer can undergo a two-electron-transfer redox reaction,TABQ dimers possess abundant hydrogen bonds and stronger intermolecular interactions,and thus exhit high discharge capacity,excellent cycling stability and rate performance.(3)Based on the above-mentioned small molecule conjugated 1,4-diketone compound,imino groups and conjugated 1,2-diketone groups were further introduced.On the one hand,the introduction of imino groups is beneficial to enhancing the intermolecular interaction,and thus improving the cycling stability of active molecule in the cell.On the other hand,the electron-donating effect of the imino group significantly reduces the redox potential of the conjugated 1,2-diketone.Upon extending the discharge cut-off voltage,these conjugated1,2-diketone small molecules display higher discharging capacities,but their chemical structures will easily decompose owning to the cleavage of the C-N bonds and the intermolecular interaction will thus be destroyed,leading to the rapid capacity decay.(4)In order to solve the above decomposition problem of conjugated 1,2-diketone structure,a quinone-fused phenazine small molecule(QAPs)is designed and synthesized by introducing a larger conjugated 1,2-diketone structure of o-benzoquinone and replacing the imino groups with amino groups.The amino groups is beneficial to forming hydrogen bonds and effectively enhancing the stability of QAPs.Meanwhile,the adjacent hydroxyl groups can experience an ion-exchange process during the cycling process,and then transform into conjugated 1,2-diketone moieties.Benefitting from the strong chelating effect of the conjugated 1,2-diketone moieties,the strong ionic-dipole interaction always exists in the QAPs electrode.Finally,the QAPs electrode adequately exerts the redox activity of the conjugated 1,4-diketone groups and conjugated 1,2-diketone groups,and thus exhibits a stable five-electron-transfer reversible discharge capacity. |
