Electrochemical Properties Of Bipolar Phenazine Derivatives In Lithium-ion Batteries

At present,commercial lithium-ion batteries are mainly based on inorganic materials,and their representative cathode materials are mainly Li Co O2,Li(Ni Co Mn)O2,etc.Recent research had mainly focused on doping modification of the materials to achieve improved battery performance,and the development of their performance was almost extreme due to the limitations of the materials themselves,making it increasingly challenging to further improve the energy density.Lithium-ion batteries were relatively expensive due to the presence of transition metals,while organic cathode materials were considered to be one of the extremely promising candidates for electrodes due to their abundant sources,environmental friendliness and structural design flexibility.However,most of the organic materials reported so far were N-type materials,which have low redox potentials.And they were very easy to dissolve in the electrolyte and maked their cycling performance too poor,so this work focuses on the electrochemical performance of bipolar phenazine derivatives in lithium-ion batteries.Firstly,quinone organic small molecules containing nitrogen radicals,N,N’-bis(2-anthraquinone)-dihydrophenazine(N,N’-bis(2-anthraquinone)-dihydrophenazine,DAQ-),were synthesized by Buchwald-Hartwig reaction.DPZ).By introducing a more stable phenazine moiety and a higher potential of nitrogen-containing radicals,the gain or loss of electrons mainly relies on nitrogen radicals and does not produce bond breakage and generation,thus improving its own stability;its peak specific capacity can reach 272 m Ah/g at a current density of 200 m A/g,which has an energy density of 764 Wh/kg.Next,the polymer is obtained by polymerization without the introduction of inert groups,which greatly increases its theoretical specific capacity and solves the problem of high solubility of DAQ-DPZ in electrolyte.It was shown that the polymer with high specific capacity and high potential,namely poly[anthraquinone-alt-dihydrophenazine](PAQDPZ),has a peak discharge capacity of 250 m Ah/g at a current density of 100 m A/g,a median voltage of 2.85 V,and a corresponding energy density of 713 Wh/kg.Finally,the PAQDPZ||graphite full cell was constructed and its electrochemical performance was tested.After 10,000 cycles,the full cell still had a capacity of 69 m Ah/g,demonstrating a good long lifetime;based on the bipolar material characteristics,the untreated electrode sheet was directly used to assemble the PAQDPZ||PAQDPZ symmetric full cell in order to simplify the assembly process,and after 800 cycles,the symmetric cell still had a specific capacity of 84 m Ah/g remaining,compared to its peak capacity of 104 m Ah/g,with a capacity retention rate of 81% after cycling.