Research On Electrochemical Performance And Device Construction Of 3D Nanoelectrode Materials Based On Flexible Supercapacitors

As the demand for portable electronic equipment continues to grow,flexible,wearable,foldable,and compact electronic products have emerged one after another,and the storage devices that provide energy for them are developing in light,thin,and flexible directions.In addition,the deteriorating energy and global warming issues urgently require the development of clean and high-performance energy storage devices.Among those energy storage devices,supercapacitors,especially flexible solid-state supercapacitors with fast charge and discharge,high power density,long cycle life,safety and environmental protection,and excellent mechanical properties that can maintain good electrochemical performance in any deformation have attracted wide attention.Increasing the energy density of devices and enhancing the ability to bear flexible deformations are very important research directions for flexible supercapacitors.The energy density can be improved by increasing the specific capacitance of the electrode material and designing an asymmetric supercapacitor.Moreover,the improvement of the devices’flexible deformation ability requires optimization of the electrode structure and device structure.As an important part of supercapacitors,electrode materials are responsible for energy storage and multiple functions of flexible and wearable devices.Their structural and morphological design have a very significant impact on their capacitive performance.Based on the above analysis,graphene paper was first used as a flexible substrate and current collector to synthesize binderless and flexible electrodes.The flexible graphene paper（GP）porous Ni-Co-N nanosheets was synthesized by simple electrodeposition and ammonia annealing method.The prepared hybrid porous electrode has higher electronic conductivity and larger specific surface area,which is beneficial to ion diffusion and electrochemical reaction.Compared with NiCo₂O₄/GP,Ni₃N/GP and CoN/GP,Ni-Co-N/GP exhibits excellent performance,with the specific capacitance of 960 F g^-1 at a current density of 4 A g^-1.After5000 charge and discharge cycles,the capacitance retention rate is 95%.In addition,graphene oxide paper with more defects and oxygen functional groups was prepared by electrochemical oxidation as a cathode and Ni-Co-N/GP assembled into a paper-based solid asymmetric supercapacitor.The device shows an energy density of 4.78 mWh cm^-3 at the power density of0.15 W cm^-3.After 8000 cycles,the retention rate of specific capacitance is 89%.The device also exhibits excellent flexibility and cutability,with little capacitance loss after bending at different angles,and the cut portion can continue to work normally.Generally speaking,carbon materials have a relatively high specific surface area,but the specific capacitance of carbon materials is much lower than that of batteries and pseudocapacitive materials.Combining the advantages of carbon materials and pseudocapacitive materials to prepare high-performance electrodes is an important research direction of supercapacitors.This paper proposes a feasible strategy to synthesize MoC/Ni@NCNTs/CC multifunctional flexible supercapacitor electrodes,whose structure is composed of Ni nanoparticles embedded in N-doped carbon nanotubes,MoC nanoclusters and the interface composition of MoC nanoparticles between Ni@NCNTs and CC.As an anode,thanks to the high electrical conductivity,high surface area,nickel coated by the carbon layer and the synergistic effect of the various components,the electrode shows a high specific capacitance of1210 mF cm^-2 at 5 mV s^-1.After 8000 consecutive cycles,it has a stability of 91.7%of the initial capacitance.In addition,as a cathode,this electrode has an enhanced specific capacitance(338 mF cm^-2 at 10 mV s^-1),rate performance(262 mF cm^-1 at 200 mV s^-1),after 8000 cycles After charging and discharging,the capacitor still maintains 95.3%of the initial value).The solid supercapacitor consists of two MoC/Ni@NCNTs/CC.The test results show that the flexible supercapacitor has high energy density(78.7μWh cm^-2 when the power density is 2.4mW cm^-2)and excellent cycle stability（after 8000 cycles,the capacity retention rate is about91%）.In addition,MoC/Ni@NCNTs/CC is also a very good electric heating material.It only needs a DC voltage of 3 V and the material is heated to 170°C within 5 s.the solid flexible supercapacitor and MoC/Ni@NCNTs/CC electrodes are combined together to become a self-heating flexible device to keep the human body warm.