Study On Novel Composite Conductive Polymer Electrode Materials For Flexible Lithium Ion Batteries

Lithium ion batteries have been widely used among electronic devices for a long time because of their high energy density,specific power and stable discharge process.Compared with the inorganic materials,the polymer electrode materials not only have the advantages of easy synthesis and environment friendliness,but also have high theoretical specific capacity and good comprehensive properties which can be obtained by the modification,which makes it become another important development field.Among these polymers,polypyrrole（PPy）and poly-2,2,6,6-tetramethyl-1-piperidinyloxy-4-methyl acrylate（PTMA）have received much attention.PPy has a wide application prospect because of its fast reaction kinetics,good flexibility and environmental friendliness.And PTMA is also an ideal cathode material for lithium ion battery due to its advantages in reaction kinetics and theoretical specific capacity.However,the common drawback is that their conductivity is often poor when they are in the eigenstate,so the actual specific capacity is low.According to the characteristics of the reaction mechanism,the PPy and PTMA composite conductive polymer electrode materials were prepared by double doping modification and double conductive agent combination,respectively,and their application in lithium ion batteries was studied.In order to make the PPy conductive and improve the specific capacity of the system,PPy was doped with anthraquinone-2-sulfonate（AQS）and reductive graphene oxide（r-GO）.The introduction of AQS provided an additional charge storage capacity,and graphene made a substantial increase in the conductivity.In addition,the synergistic effect of the two dopants made the composite electrode material form a three-dimensional porous micro-morphology,which helped full contact between the active material and the electrolyte and effective transmission of the carriers.The experimental results showed that the discharge capacity of the composite electrode material increased to 127 m Ah g^-1.In addition,the effect of the doping ratio was investigated.Under the given conditions,when the r-GO content was 0.5 mg m L-1,the formed porous three-dimensional structure had larger specific surface area and it made the conductivity of the system best.The discharge capacity of the electrode material could reach 132.52 m Ah g^-1 at this time.In order to further verify the rationality of the double doping system and try to meet the working environment at high output voltage,we used phenanthrenequinone-2-sulfonate（PQS）in palce of AQS to be the dopant.The results showed that the sequential addition of the two dopants lead to the transition from the lamellar structure to the cauliflower-like structure and eventually became the ideal three-dimensional porous structure.And the combination of PPy and PQS made the redox response of the electrode more obvious in the high potential range and the further introduction of r-GO solved the problem that the resistance value of the system in the low potential range was too high.Similarly,the discharge capacity of the composite electrode was gradually increased from 75 m Ah g^-1 to more than 120 m Ah g^-1.In order to further enhance the capacity of the composite polymer electrode material,the nitroxide radical polymer-PTMA with higher theoretical specific capacity was used as the active material.To discuss the limiting factor-conductivity,the effects of different conductive agents（acetylene black（AB）,carbon fiber（CF）,carbon nanotubes（CNT）and reductive graphene（r-GO））on the microscopic morphology and electrochemical performance of PTMA composite electrode materials were investigated.The results showed that the single conductive agent-carbon nanotubes were uniform Ly attached to the surface of the PTMA particles,which greatly promoted the conductivity.The corresponding PTMA electrode owned the highest first-cycle discharge capacity(129.6 m Ah g^-1)and rate performance(capacity of 100.2 m Ah g^-1 at 10 C),comparing with the control samples with acetylene black and carbon fiber as the single conductive agent.On the basis of this,the double conductive agent system-CNT/r-GO provided an excellent conductive network by the introduction of r-GO,which made electron transfer easier and the discharge capacity of the composite electrode could be increased to 137 m Ah g^-1.