| In recent years,supercapacitors have attracted wide attention and have been rapidly applied in many fields due to its high power density,excellent cycle stability,low maintenance cost and rapid speed of charge and discharge.However,low energy density is one of the bottlenecks to development of supercapacitors,while it depends on the performance of electrode materials.Therefore,design and preparation of the electrode materials with excellent capacitive properties has become the key to improve the performance of supercapacitors.Transition metal sulfide electrode materials have excellent capacitive properties due to its high conductivity and abundant redox sites.However,compared with other electrode materials,the specific capacity and rate performance of transition metal sulfide need to be improved and aggregation phenomenon often occurs in preparation.In this thesis,two effective strategies of both constructing transition metal sulfide electrode materials with hierarchical structure and designing transition metal sulfide based composite materials are adopted to improve the electrochemical performance of the as-prepared electrode materials.The whole thesis consisted of five chapters.The classification,composition,working principle,performance,superiority and defects,and the developing trend of supercapacitor and electrode material were reviewed in detail.And the structure,property,preparation and research progress of molybdenum disulfide,manganese sulfide and binary and ternary nickel cobalt sulfide were disscussed in Chapter 1.Chapter 2,Chapter 3 and Chapter 4 were the experimental parts and result discussion.?-MnS@MoS2 and CoNi2S4/CNT composite electrode material with hierarchical structure were prepared by hydrothermal method and electrodeposition method,respectively.CoNi2S4/CNT//Fe2O3/CNT asymmetric supercapacitors with excellent mechanical flexibility and capacitance performance were assembled by using CoNi2S4/CNT sponge as positive electrode and Fe2O3/CNT sponge as negative electrode.The conclusion of this thesis was given in Chapter 5.The main research works were as follows:(1)?-MnS@MoS2 microcubes with hierarchical core-shell structure were prepared by one-step hydrothermal method at 200 ? for 24 h without template assistance.By adjusting the type of manganese source and the amount of molybdenum source in the reaction system,the crystal phase and morphology of composite products can be controlled.The experimental results showed that ?-MnO2 nanowires and Na2MoO4·2H20 of 0.248 mmol were the optimizated manganese source and addition.The phase transition behavior of ?-MnS@MoS2 microcubes with hierarchical core-shell structure was studied by adjusting the hydrothermal temperature and time of the reaction system.The growth process consistsed of four stages,they were the ultralong ?-MnO2 nanowires were transformed into Mn3O4 nanocrystals,then converted to ?-MnS hexagonal prisms and followed to ?-MnS,and finally?-MnS@MoS2 microcubes were formed.At a current density of 1 A g-1,?-MnS@MoS2 electrode showed specific capacitance of 26 F g-1 in the three-electrode system.By selecting transition metal and adjusting the amount of sulfur source,transition metal sulfide with novel hierarchical core-shell structure and morphology could be prepared by one-step hydrothermal method without template.(2)CoNi2S4/CNT composite sponge electrode materials were prepared by one-step depositing CoNi2S4 nanoparticles on the functional carbon nanotube sponge.CoNi2S4/CNT composite sponge electrode materials with different mass loading were prepared by adjusting the time of electrochemical deposition.The average size of CoNi2S4 nanoparticles was about 10?15 nm and there was no obvious aggregation phenomenon on the surface of carbon nanotubes.These electrode materials with different mass loading were tested in the three-electrode system.The experimental results showed that the CoNi2S4/CNT composite sponge with 15 electrodeposition cycles showed the optimal capacitive property,and the mass specific capacitance was up to 1530 F g-1 at a current density of 1 A g-1,and the capacitance retention was 88%.The mechanical properties of the composite sponge were also investigated under different compression conditions.CoNi2S4/CNT sponge could return to its original state after the loading exceeded 100 kPa and the strain reached 90%.In addition,the electrochemical property of the composite sponge electrode under different compression conditions was also studied.With the increasing of stain,electrode materials could not maintain origin specific capacitance and have big resistance at higher current density.Three-dimensional structure of carbon nanotube in CoNi2S4/CNT composite sponge and the morphology of CoNi2S4 nanoparticles played a key role in structural stability and high mass loading.The method provides a new idea for preparating transition metal sulfide composite electrode with ultrahigh compressibility and excellent electrochemical performance.(3)By using CoNi2S4/CNT composite sponge as positive electrode and Fe2O3/CNT composite sponge as negative electrode,and 2.0 M KOH as electrolyte,CoNi2S4/CNT//Fe2O3/CNT asymmetric supercapacitors with ultrahigh compressibility and excellent electrochemical performance were successfully assembled.The assembled device with ultrahigh compressibility and excellent electrochemical performance showed maximum energy density and power density of 50 Wh kg-1 and 24 kW kg-1,respectively.After 1000 compression cycles,the area of CV curve of the assembled device at 20 mV s-1 only changed slightly.Even at a strain of 85%,about 75%of its initial capacitance was retained after 10000 consecutive cycles at a current density of 2 A g-1,showing that the CoNi2S4/CNT//Fe2O3/CNT asymmetric supercapacitors had excellent mechanical properties and electrochemical stability.The assembled compressible supercapacitors showed a broad application prospect in the energy storage field of the compressible and high-performance electronic devices. |
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