| Recently,the research of metal lithium-ion batteries has reached a bottleneck,and toxic metal salt electrode will cause damage to the environment and are not conducive to the concept of sustainable development.Therefore,it is imperative to develop new energy-storage electrode materials that are rich in resources and eco-friendly.The rise of organic electrode materials has brought dawn to researchers.Today,the most representative of organic electrode materials are carbonyl compounds and conductive polymers,which have been used as electrode materials for decades.Each of them has advantages and disadvantages.In the lithium-ion battery system,the carbonyl polymer stores energy through a reversible redox reaction,which guarantees the capacitance of the lithium-ion battery.However,its carbon-oxygen anions are unstable and needs to be connected with a stable functional group.The conductive polymer conjugated system ensures fast and efficient charge transfer of lithium ion batteries,but its reactivity and energy storage capacity are insufficient,which is embarrassing and unuseful.In this work,we have studied the lithium-ion battery performance of pyrrolopyrrole-based polymer that has both carbonyl group and conjugated conductive polymer system,which takes advantage of poor solubility of polymer in organic solvents.Then,the lithium ion battery anode material with more stability and capacity performance is prepared by doping the pyrrolopyrrole-dione polymers with the graphene material.The details are as follows:1.Synthesis of pyrrolopyrrole-based polymers and their applications in lithium-ion batteries: Four pyrrolopyrrole-based polymers containing hexyl or tert-butyl acetate groups at the N position and 1-octylnonylcarbazole or dioctylfluorenyl groups at both ends of thiophene were prepared by Suzuki reaction,respectively named PCTDPPBA(containing carbazolyl and t-butyl ester groups),PFTDPPBA(containing fluorenyl and t-butyl ester groups),PCTDPPDO(containing carbazolyl and hexyl groups)and PFTDPPDO(containing fluorenyl and hexyl groups).Under the same conditions,PCTDPPBA electrode has the best capacitance performance at 100 m A/g.After 500 cycles,its discharge specific capacitance is still 357 m Ah/g,and its capacitance retention rate is up to 82 %.It is ascribed to the carbazole and isobutyl acetate groups providing lithium-ion intercalation and reaction sites for the polymer electrode to improve the capacitance performance of polymer electrode.The PFTDPPDO electrode has the best cycle stability.After 500 cycles at 100 m A / g,its cycle stability is as high as 92 %.It is ascribed to the hexyl and fluorene groups which regulate its band gap and electrical conductivity and make it have excellent electrical conductivity.By comparing the electrochemical performance of these polymer electrodes,we find that the PCTDPPBA electrode is more suitable as a negative electrode for lithium-ion batteries.At a current density of 1000 m A/g for1000 cycles,its discharge specific capacitance is still 203.6 m Ah/g and cycle stability is as high as 88.8 %,while its energy density and power density are 98 Wh/kg and 247.6 W/kg,respectively.This method of designing pyrrolopyrrole-based polymers to obtain promising electrode materials paves a new way to improve the performance of lithium ion batteries.2.Preparation of pyrrolopyrrole-based polymer/reduced graphene oxide composite electrodes and their application in lithium-ion battery: PCTDPPBA and PFTDPPBA electrodes have better redox capabilities among the above four polymer electrode materials,but their poor cycle stability and electrical conductivity restrict their further applications.The reduced graphene oxide is often used in the doping of polymer electrode materials because of its excellent conductivity and stable conjugated structure.Through experiments,PCTDPPC/RGO electrode has better electrochemical performance,which has a specific capacitance of 1583 m Ah/g at 100 m A/g for 500 cycles and its capacitance retention rate is up to 91 %.It is much higher than those of the polymer PCTDPPBA(specific capacitance is 357 m Ah/g and the cycle stability is 82 %).For the PFTDPPC/RGO composite electrode material,its specific capacity is 787 m Ah/g at current density of 100 m A/g for 500 cycles,and its cycle stability is 78 %,thus its performance is much higher than those of the polymer PFTDPPBA(specific capacity is 298 m Ah/g,cycle stability is 70 %).This is mainly due to the good charge transfer property of graphene materials,which provides an efficient reaction platform.Meanwhile,the carboxyl functional group has certain bond-valence relationship with graphene oxide,which makes the capacitance performance of composite electrodes higher than that of graphene(theoretical capacity is 744 m Ah/g).In addition,the PCTDPPC/RGO composite electrode has a specific capacity of 856 m Ah/g at current density of 1000 m A/g for 1000 cycles and its cycle stability that compared to the initial specific capacitance is 83 %.At the moment,its energy density and power density are respectively 558 Wh/kg and 356.2 W/kg.Therefore,negative electrode materials composed of pyrrolopyrrole-based polymers and graphene oxide have a great potential applied in lithium-ion battery. |
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