In-situ Electropolymerization Preparation And Performance Research Of Organic Cathodes For Lithium-ion Batteries

Organic cathode materials have attracted extensive attention because of their diverse molecular structures,facile synthesis,and environmental friendliness.However,they often suffer from low capacity utilization and insufficient cycling stability caused by the good dissolution and poor conductivity,which bring great challenges to subsequent development.In this thesis,in-situ electropolymerization was developed to stabilize and enhance organic cathodes for lithium-ion batteries.The research content mainly includes the following two aspects:（1）4,4’,4’’-triscarbazol triphenylamine was employed because carbazole groups can be polymerized under an electric field at a high voltage,which in-situ prepare the organic cathode with high voltage,high rate performance,and stable cycling performance.In-situ electropolymerization can not only effectively alleviate the dissolution of the organic cathode in the electrolyte,but the extended conjugated system also improved the kinetics of the organic cathode.4,4’,4’’-triscarbazol triphenylamine demonstrated a high discharge voltage of 3.95 V.After 5000 cycles at a current density of 1 A g^-1,the capacity retention was 60%with the highest specific capacity was 80 m Ah g^-1.Even at a high current density of 5 A g^-1,the cathode material can still provide a specific capacity of 75 m Ah g^-1.This work provides a novel strategy to address the dissolution issue and provides a new direction for improving the electrochemical performance of organic electrode materials in the following research.（2）N,N’-Bis-（4-indole-1-phenyl）-1,4,5,8-naphthalenetetracarboximide with two electrochemically active groups was synthesized through a three-step high conversion reaction.By utilizing the in-situ electropolymerization of indole groups,the organic cathode material was prepared with excellent electrochemical properties due to the suppressed dissolution process.After 300 cycles at a current density of 1 A g^-1,the cathode can provide a reversible specific capacity of 140 m Ah g^-1 without any significant decay.At a high current density of 5 A g^-1,the specific capacity of the cathode can still reach 106 m Ah g^-1.Molecular structure simulations showed that the bi-active groups do not interfere with each other while they perform electrochemical energy storage and exhibit good reversibility.This work confirmed the feasibility of introducing electropolymerization reactive groups to improve the electrochemical performance and broadened the molecular design purposes of organic electrode materials.