Carbon Nanotubes/Phthalocyanine Composites And Their Applications As Cathodes For Lithium Sulfur Batteries

The theoretical specific energy of lithium-sulfur battery reaches 2600 Wh·kg-1,which is a new secondary battery with great application prospectshas and has attracted wide attention from researchers at home and abroad.However,Sulfur and sulfide have lower conductivity,in the Li intercalation and deintercalation process,sulfur will produce huge volume changes,lithium polysulfide of electrochemical reaction intermediate has a "shuttle effect",these problems hinder the business application.Multi-walled carbon nanotubes have the advantages of high aspect ratio,specific surface area and can be produced in large quantities,which has become a hotspot of lithium-sulfur battery cathode materials.Based on the catalytic principle of metal phthalocyanine complexes,phthalocyanines are loaded in multi-walled carbon nanotubes in different physicochemical methods,this paper aims to develop a positive electrode material for lithium-sulfur batteries with excellent performance to reduce the "shuttle effect".The main research contents are as follows:Multi-walled carbon nanotubes were used as the matrix material,70 wt.%of elemental sulfur was loaded(the sulfur content was loaded according to this value in the subsequent experiments),and the materials were heating at 155? to assemble simplest carbon-sulfur composite material(MWCNT/S70).Accrording to the experimental results,hydrophobic carbon paper was most suitable as a current collector(the current collectors were selected these in the subsequent experiments),and then characterizing composite materials and testing the electrochemical performance of batteries.It was proved that the porous structure of multi-walled carbon nanotubes fixes sulfur well and has good activity.,but the battery performance still needs to be improved.Application of phthalocyanine complex in catalysis of batteries such as Li/SOCl2 batteries,adding 30 wt.%and 50 wt.%of cobalt phthalocyanine,nickel phthalocyanine and phthalocyanine to multi-walled carbon nanotubes in ball milling method,then preparing sulfur electrodes to assemble the batteries finally The composite cathode materials were characterized by SEM and TEM,it was proved that the phthalocyanine complexes mostly existed in the interior of the multi-walled carbon nanotubes with the form of fine particles.Sulfur can be uniformly loaded on the surface of the material in this mechanical mixing method.This uniformly coated structure lays a good structural foundation for sulfur to play its role.The electrochemical test results show that cobalt phthalocyanine and nickel phthalocyanine with 30 wt.%can exert the best catalytic effect,their initial gram capacity has been greatly improved compared with the control group.Multi-walled carbon nanotubes were sonicated in toluene solution at room temperature,and then added 30 wt.%of cobalt phthalocyanine and nickel phthalocyanine to mixture to return flow agitation at 60?,finally preparing sulfur electrodes to assemble the batteries.The composite cathode materials were characterized by SEM and TEM,it was proved that the phthalocyanine complexes were uniformly mixed with the multi-walled carbon nanotubes,and the materials'agglomeration was not so obvious.It shows that the initial gram capacity of the battery has increased and the battery also has good rate recovery performance.Nickel tetraaminophthalocyanine synthesized by solution method was chemically bonded to fluorinated carbon nanotubes,finally preparing sulfur electrodes to assemble the batteries.The composite cathode materials were characterized by SEM,TEM and XPS proved that the nickel-aminophthalocyanine-modified multi-walled carbon nanotubes can support elemental sulfur well.The electrochemical test results show that the battery has good electrochemical performance.