High-voltage Organic Battery Cathode Materials Based On Oligomer Of Phenazine Derivatives

As one of the most effective electrochemical energy storage techniques,Li-ion batteries possess several desirable features,including high energy density,high round-trip effiency and long cycle life.The large-scale use of conventional inorganic materials was restricted by the limited resources,but organic materials are promising candidates for the energy storage system,due to their elemental aboundance,structure diversity and flexibility.However,there are a few problems with organic materials,including the limited structure stability and the dissolution problem in the electrolyte.To solve the problems above,organic cathode materials based on phenazine derivatives were designd and synthesized.The main contents are as follows:1.N,N'-diphenyl-5,10-dihydrophenazine(p-DPPZ)was synthesized via a Buchwald-Hartwig coupling reaction and used in Li-ion batteries.By manipulation of conjugation to stabilize N redox-active centres,two successive one-electron transfer reactions have been reversibly achieved.p-DPPZ exhibits high redox potentials of 4.1 V and 3.3 V(vs.Li+/Li),an energy density up to 530 Wh kg-1,and good cycling stability.DFT calculation exibited that,the skeleton of dihydrophenazine unit maintained good structure stability due to effective positive charge delocalization in the conjugated structure.2.An alternative strategy was introduced by using quaternary nitrogen redox center for the design of stable organic battery materials.In such a strategy,the redox center is stabilized through conjugation without chemical bond rearrangement.The oligomer of 5,10-diphenyl-dihydrophenazine(p-DPPZS)was synthesized by connecting phenyl sulfide and dihydrophenazine.The electrochemical performance of p-DPPZS|Li cell demonstrates high specific energy/power density of 441 W h kg-1/9114 W kg-1,stable cycling performance with capacity retention over 90%and Coulombic efficiency over 99.5%in 1000 charge/discharge cycles.The test exhibited that the quaternary redox center possessed good structure steability.This strategy may applicable to further consolidate the family of organic battery materials using quaternary redox center from the III/V elements of the main group in the periodic table.