The Study On P-Type Polymer Cathode Materials Based On Heteroaromatics

Organic electrode materials composed of naturally abundant elements have merits of resource sustainability,tunable redox properties and environmental friendliness,which become promising candidates for next generation of green batteries.Because of the anion doping/dedoping mechanism and relatively higher redox potential,p-type organic electrode materials are important cathode materials for the study of dual-ion batteries.The most well-known p-type organic cathode materials are conducting polymers and nitroxyl radical polymers.In recent years,researchers’interest also shifts to polymers based on various electroactive heteroaromatics,including N-substituted phenazine,phenothiazine,phenoxazine,and thianthrene.A merit of these heteroaromatic units is that they are potentially able to deliver two electrons and thus achieve attractive capacity above 200 m Ah g^–1.However,the structure and synthesis of these materials are relatively complex.Herein,two heteroaromatic polymers were synthesized by simple methods,and their electrochemical performances and reaction mechanisms as cathode materials for rechargeable lithium batteries were studied.The main contents in this dissertation are as follows:1.Polyphenothiazine（PPTZ）cathode materialPPTZ was synthesized by a facile one-step oxidation polymerization from the phenothiazine（PTZ）monomer.As a novel p-type polymer,PPTZ achieved a high reversible capacity of 157 m Ah g^–1 within 2.5–4.3 V vs.Li⁺/Li with an average discharge voltage of 3.5 V,and a high capacity retention of 77%after 500 cycles under a current density of 200 m A g^–1.Furthermore,the redox mechanism of PPTZ was detailedly investigated by ex-situ FT-IR,XPS characterizations,and DFT calculations.The facile polymerization method and excellent electrochemical performance of PPTZ are of great significance for the study of other p-type polymer electrode materials.2.Poly（thianthrene sulfide）（PTAS）cathode materialThianthrene active centers can exhibit very high redox potentials（>4.0 V vs.Li⁺/Li）.We synthesized PTAS by linking thianthrene units with thioether bond,and studied its electrochemical performances.The results showed that PTAS achieved a reversible capacity of 103 m Ah g^–1 with an average discharge voltage of 4.0 V vs.Li⁺/Li,making it a potential candidate cathode material for dual-ion batteries.In addition,we investigated the redox mechanism of PTAS by the ex-situ FT-IR characterization.Due to the low degree of polymerization and limited electrochemical window of the aprotic electrolyte,the electrochemical performance of PTAS needs to be further improved.