Research On The Performance Of Flexible Supercapacitors Based On MoS₂ And NiCo₂S₄ Composite Materials

With the increasing development of wearable smart technology,higher requirements are put forward for the mechanical flexibility of energy storage devices.Flexible supercapacitors have a wide range of applications in the field of wearable devices due to their high power density and excellent cycle stability,but owing to its inherent low energy density,poor rate performance and other issues limit its development.This thesis addresses the problems of large interface impedance and small reaction specific surface area of flexible supercapacitors.Optimizing the energy storage performance of flexible supercapacitors through reasonable design of electrode material structure and composite carbon material strategy.Self-assembly of MoS₂and NiCo₂S₄nanosheet arrays on the surface of carbon cloth(CC)by in-situ growth method,and the use of hydrothermal and electrodeposition methods to composite nitrogen-doped graphene quantum dots(N-GQDs)and spiral carbon nanotubes(HCNT),using synergy to improve the conductivity and pseudocapacitance performance of electrode materials,the edge effect and size effect of N-GQDs are used to improve the wettability and redox activity of electrode materials.Simultaneously,the special tubular structure and high conductivity of HCNT can improve the flexibility and conductivity of electrode materials.The specific research content is as follows:(1)The MoS₂nanosheets array were uniformly grown on the CC surface by hydrothermal self-assembly method,and the MoS₂nanosheet was used as the longitudinal frame support.Meanwhile,it also provides a larger reaction surface area for the electrode,effectively increasing the electrode material and electrolyte Solid-liquid contact area.The results showed that a high specific capacitance of 1162m F cm^-2can be achieved at a current density of 6 m A cm^-2.After 2500 cycles of constant current charging and discharging,the capacitance retention rate was 81%.(2)Using MoS₂nanosheets as the substrate,N-GQDs and HCNT were introduced to construct a vertical layered heterostructure on the CC surface.In this vertical layered structure,N-GQDs are embedded between MoS₂nanosheets.Due to its edge effect,more active sites were induced and exposed for the composite electrode,resulting in pseudocapacitance contribution.Meanwhile,HCNT acts as a conductive bridge between MoS₂and nanosheets,providing a fast transport channel for ions/electrons.The results showed that,compared with MoS₂@CC electrode,the electrochemical performance of MoS₂/HCNT/N-GQDs@CC composite electrode was significantly improved.It had a high specific capacitance of 3360 m F cm^-2.In addition,the assembled solid flexible supercapacitor still had a high specific capacitance of 2097 m F cm^-2and energy density of 673?Wh cm^-2.After 2500 cycles,the capacitance retention rate was 85%,and the capacity remains stable under different bending test angles.(3)NiCo₂S₄had a more flexible valence state change,which makes it had more excellent pseudocapacitance performance.By growed NiCo₂S₄nanosheets in situ on the CC framework,the honeycomb nanosheets further increase the reaction specific surface area of the electrode material.N-GQDs were deposited on NiCo₂S₄honeycomb nanosheets by two-electrode electrodeposition,and the rich edge effects of N-GQDs can be used to give full play to the pseudocapacitance performance of the NiCo₂S₄/N-GQDs@CC composite electrode.The results showed that the specific capacitance of NiCo₂S₄/N-GQDs@CC composite was 3870 m F cm^-2.The assembled ASSC device had a maximum energy density of 126?Wh cm^-2,and the capacitance retention rate was 83%after 2500 cycles of charging and discharging.