Synthesis Of Phenazine-based Multi-electron Battery Cathode Materials And Investigation On Their Electrochemical Properties

The development of renewable energy sources is necessary for the sustainable development of modern society.Due to the intermittent property of renewable energy sources,electrical energy storage systems especially batteries are regarded as promising candidates in large-scale energy storage.Moreover,as the ever-increasing environmental awareness from the public,the batteries should be made from nontoxic yet abundant materials.In this regard,the redox-active organic materials may play a key role in developing rechargeable batteries with better sustainability than the inorganic counterparts that have been currently used in commercialized batteries.The redox-active organic materials also bear attractive features such as tailorable structures,compatibility with variable guesting ions.However,some organic electrode materials have ploblems of voltage gap or relatively low theoretical specific capacity.The main contents are as follow:(1)Redox-active organics based on a multi-electron mechanism are of great interest in battery electrode materials as they are capable of delivering high capacity per molecular weight.However,most of such organics shows huge voltage gap that is inherited from their stepwise redox reactions occurring in the same conjugated redox moiety.This study focuses on the voltage tailoring of polymeric dihydrophenazine derivative which shows high specific capacity as a cathode electrode material and decent cycling stability,but suffers huge voltage gap of ca.0.8 V.We demonstrate through theoretical calculation based on density-functional theory that the substitute site and types of functional groups are of great importance in voltage tailoring as well as structural stability of the dihydrophenazine derivatives.Based on the calculation results,we demonstrate a strategy to modify the voltage gap of dihydrophenazine derivatives through the incorporation of functional groups with different electron affinity near the redox moiety.The as-designed dihydrophenazine derivatives are further copolymerized to yield a polymeric material with significantly smoothened charge-discharge profiles and good capacity retention.1(2)In this part,we demonstrate a new strategy that using molecules containing redox centers as linkes to improve the theoretical specific capacity as well as smoothen the discharge curve of polymer materials.We synthesized a new type of ?-conjugated redox polymer based on phenazine and phenothizine derivatives.This new strategy enables the as-prepared material with a high therotical capacity of 168 mAh g'1.What's more,the electrode features defined discharge plateaus at 4.1,3.8 and 3.1 V(vs.Li/Li+),giving rise to a high energy density of ca.400 Wh kg-1.In addition,the ?-conjugated structure enables good structure stability of the electrode during the cycling which is attributed to the better electron delocalization through conjugate effect,87%of the initial capacity is retained after 500 cycles at 1 C.This conjugated copolymer design strategy can be used in the development of other organic materials with high specific capacity.