Studies On Preparation And Electrochemical Performance Of Conductive Polymer Composites

With the rapid development of technology and society,the market has put forward a higher specific energy demand for energy conversion storage devices.Electrode material is the key to determining the performance of energy storage equipment.Therefore,the research and development of advanced electrode materials is very important in the field of energy storage science.Conductive polymers have great application potential in energy storage devices due to their unique physical and chemical properties,and have been developed for use in supercapacitor electrode materials and lithium-sulfur battery cathode materials for new generation energy storage devices.Supercapacitors based on conductive polymer materials have a high theoretical specific capacitance.However,due to the limited reactive sites,the actual specific capacitance needs to be improved.On the other hand,the conductive polymer is used as a cathode material for lithium-sulfur batteries after high-temperature vulcanization,and realizes the"solid-solid conversion"charge and discharge mechanism in the carbonate electrolyte,which theoretically can avoid the"shuttle effect".However,the sulfur content of this type of material is usually low,making the specific discharge capacity of the battery unsatisfactory.At the same time,the reaction kinetics of this type of material is slow.Therefore,it is of practical significance to improve the electrochemical performance of conductive polymer composites and promote their applications in lithium-sulfur batteries and supercapacitors.In this thesis,we paid attention to the conductive polymers polyaniline（PANI）and pyrolytic polyacrylonitrile（PAN）.Research has been carried out on the synthesis of materials,the optimization of vulcanization conditions and the improvement of electrochemical performance.The main conclusions are summarized as follows.（1）The PANI/Ba Ti O₃ composite material was prepared by in-situ oxidative polymerization method,and the electrochemical behavior of PANI/Ba Ti O₃ material with different composite ratios was investigated by three-electrode test.Research showed that the electrode material with a PANI/Ba Ti O₃ composite ratio of 75/25（w/w）has the smallest R_ctand higher specific capacitance,which fully demonstrates the synergy between the ferroelectric materials Ba Ti O₃ and PANI.（2）The SPAN composite materials were synthesized by vulcanizing polyacrylonitrile（PAN）（as a matrix）and elemental sulfur（S₈）at high temperature according to a certain mass ratio.The vulcanization conditions are optimized to obtain SPAN composites with excellent electrochemical performance.Based on the results of electrochemical tests,The SPAN composite material obtained by vulcanizing a mixture of PAN and S₈ at a mass ratio of 1:2at 350 ^oC for 10 hours as the cathode material for preparation of the Li-S coin cell demonstrated excellent electrochemical performance.After cycling 100 cycles（except for the first cycle）at 0.5 A·g^-1,the capacity still retained 585 m Ah·g^-1（calculated on the SPAN）and the capacity retention was 88%.（3）A small amount of metal sulfide tin disulfide（Sn S₂）with a layered structure was added to the SPAN composite obtained under the above-mentioned optimal vulcanization conditions to prepare a Sn S₂/SPAN composite.The results show that Sn S₂/SPAN composite doped with Sn S₂ has faster reaction kinetics and lower charge transfer resistance.The lithium-sulfur battery with Sn S₂/SPAN composite material as the cathode material maintains a reversible discharge specific capacity of 505 m Ah·g^-1（calculated on the SPAN）after 200cycles at a test current density of 1.0 A·g^-1.The capacity retention was 82.4%（except for the first cycle）.