Investigation On Construction And Performances Of Electrodes For Flexible Solid-state Capacitors

Owing to their advantages including miniaturization and functionality,flexible solid-state capacitors have shown significant potential in energy storage devices,power electronics,etc.,and have become one of the research hotspots in current industry and academia.The existing studies have demonstrated that developing high-performance,ease of processing,lightweight,flexible electrode materials has become a core task in the development of flexible solid-state capacitors.Therefore,the goal is to construct advanced electrodes with novel structure and excellent performance.The research content involves the application background of supercapacitors and dielectric capacitors.The main research works and results are as follows:First,in order to improve effective heat dissipation of all-solid-state supercapcitor devices,it is urgently need to develop highly thermal conductive and high-performance electrode materials.Thus,we manifest a facile strategy to in situ synthesize flower-like ternary cobalt nickel sulfide?CoNi₂S₄,CNS?on graphite foil?GF?by one-step electrodeposition as binder-free supercapacitor electrode materials?GF/CNS?.The direct growth of active materials on graphite foil forms conductive pathways that not only promote charge transportation,but also minimize the interfacial thermal resistance between substrate and active materials for heat transfer.The integrated GF/CNS electrode shows an outstanding thermal thermal conductivity of 620.1 W m^-1K^-1and an excellent specific capacitance of 881 F g^-1with 5 mA cm^-2,as well as favorable rate capability and cycling stability.As a consequence,through in situ measurement,the all-solid-state symmetric device employing the advanced electrodes exhibits remarkable heat dissipation ability as compared to that of traditional slurry electrodes during the GCD cycles,especially in high current.This facile approach affords a new platform to construct advanced electrodes for the thermal management of energy storage devices.Second,in order to improve effective electron collection and transportation of all-solid-state supercapcitors,the hierarchical conductive interconnection is well structured for supercapacitor electrodes in this work.We shows a facile synthesis of conductive and alternate layered structured?-Ni?OH?₂/graphene?Ni-GS?film electrode by solution processable filtration.To further enhance the conductivity of supercapacitor electrode,a novel flexible current collector is fabricated on the surface of Ni-GS film by screen printing.As integrated electrode,it presents excellent thinness and flexibility.On account of the rational hierarchical conductive structure,the graphene serves as flexible framework in the composite electrode,rendering conductive pathways for?-Ni?OH?₂.Meanwhile,the conductive interconnected current collector effectively enhances the electron collection and transportation capabilities of the entire device?electrode?.Ultimately,the all-solid-state symmetric supercapacitor based on these electrodes has been assembled,the areal capacitances are significantly increased,which demonstrates that a great areal capacitance of 61.7mF cm^-2with 5 mA cm^-2 is 3.7 folds higher than that of the common assembled device.This simple and effective work contributes a new idea for the development of high-performance supercapacitors.Third,based on the study of aforesaid chapter,in this work,we report a facile strategy to fabricate 3D porous Ni arrays on flexible conductive cloth?CC?with high electrical conductivity and large surface area as flexible current collector?3D Ni/CC?.Furthermore,NiCo-LDH nanosheets were electrochemically grown over the 3D architectured current collector as binder-free integrated electrode?3D Ni/LDH?for supercapacitors.Benefiting from the hierarchical structure of 3D Ni/CC current collector,the mass loading of active materials is significantly enhanced.Meanwhile,the 3D porous Ni arrays provide effective electronic transmission network.The integrated NiCo-LDH@3D Ni/CC electrode exhibits a high mass capacitance of 2248F g^-1and a high areal capacitance of 3260 mF cm^-2at 5 mA cm^-2,as well as good cycling stability.A remarkably flexible all-solid-state symmetric supercapacitor assembled with the advanced electrodes manifests an excellent areal capacitance of116.7 mF cm^-2at 5 mA cm^-2and attains outstanding cycling stability with a high capacitance retention of 105%after 10 000 cycles at 10 mA cm^-2.This facile and cost-effective strategy of building hierarchical structured electrode may be an economical way for flexible energy storage applications.Fourth,in order to improve the breakdown strength and energy density of dielectric capacitors,in this system,the core-shell structured BaTiO₃@graphene oxide?BT@GO?hybrids were facilely synthesized and incorporated into dielectric polymer composites for enhanced energy density.The high dielectric constant,low dielectric loss,and high breakdown strength are achieved,leading to highly improved maximum energy density in the as-fabricated BT@GO/PVDF composites.For instance,the the introduction of 20 wt%BT@GO into composites exhibits a dielectric constant of 14and dielectric loss of 0.04 at 1 kHz while maintaining a satisfactory breakdown strength of 210 MV/m.Finally,the maximum energy density of 3.88 J/cm³,which is around 2.1 and 1.6 folds higher than the values of neat PVDF and BT/PVDF composites with the equivalent mass fraction,respectively.The novel structured BT@GO hybrids with synergistic contribution of the two fillers leads to the tunable properties of these composites,in which the cores of BT improve the dielectric constant,and the shells of GO as buffer layers effectively relieve local electric field concentration for breakdown strength.Located at the interface structured engineering,it provides a potential design idea for the development of high energy density dielectric polymer composites.