Study On Supercapacitor Performance Based On Carbon-based Composite Electrode Material

With the advancement of the natural sciences and the shortage of energy,the collection and storage of energy has become the focus of attention.Among them,the efficiency of energy collection and storage is crucial.In terms of electrical energy storage,supercapacitors have attracted extensive research by scientists due to their long cycle life and specific capacitance.Interestingly,the nano-scale layered porous electrode material contributes to an increase in the contact area of the electrolyte and has been extensively studied as an electrode material for a supercapacitor.However,the drawback is that the energy density is not high.Therefore,it is an inevitable trend of commercialization to study the hybrid supercapacitor（SSC）to improve the energy storage rate.In this paper,the carbon based composite electrode materials prepared by hydrothermal and electrochemical methods have the advantages of good stability,excellent catalytic performance and low production cost.They exhibit excellent capacitance stability in the supercapacitor devices assembled by polyvinyl alcohol（PVA）quasi solid gel electrolyte,and significantly improve their voltage window and comprehensive electrochemical performance.The specific research contents of this paper are as follows:（1）MoS₂ nanosheet multi-walled carbon nanotubes（MS|MWCNT）composites were prepared by hydrothermal method.The optimum amount of MWCNTs doping was investigated by varying the amount of MWCNTs added（0 mg,18 mg,36 mg,and 72 mg）.The SEM topography test,Raman characteristic spectrum and XRD structure characterization showed that the MoS₂ nanosheets were successfully synthesized and attached to the surface and end active sites of MWCNTs.When the amount of MWCNTs added was 36 mg,the prepared molybdenum sulfide and carbon nanotube composites（MS|MWCNT）had relatively better capacitance properties,and the order of MWCNTs also increased.At 1 A/g,the specific capacitance is up to 255.8 F/g.After 1000 cycles,MS|MWCNT exhibits excellent cycle stability（91.36%capacity retention）.Its excellent capacitance performance is attributed to the excellent electrical conductivity of the MWCNTs skeleton and the good ionic conductivity of MoS₂.Using MS|MWCNT as the electrode,the symmetric supercapacitor prepared with the neutral PVA-Na₂SO₄ gel electrolyte exhibited lower solution internal resistance（R_s）and charge transfer internal resistance(R_ct).（2）PANI|MWCNTs composite electrode materials were prepared by in-situ chemical polymerization.Morphology testing and phase characterization indicated that polyaniline was successfully synthesized and deposited well on MWCNTs.We explored better polymerization schemes by changing the polymerization time（2 h,4 h,6 h,8 h,10 h）.When the polymerization time is 8 h,the prepared composite electrode material（PM.t8）has a relatively good capacitance characteristic.At 1 A/g,the specific capacitance is 331.52 F/g.After 1000 cycles,PM.t8 exhibits excellent cycle stability（97.94%capacity retention）.Symmetric supercapacitors（PM//PM SSC）and asymmetric supercapacitors（PM//MM ASC）were prepared from PANI|MWCNTs and MS|MWCNT composites using PVA-Na₂SO₄ gel electrolyte as medium.The PM//MM ASC has a specific capacitance of 45.56 F/g at a voltage window of 0.7 V,and a specific capacitance of 94.31 F/g when the voltage window is increased to 1.5 V.Also,at a power density of 243.62 W/kg,PM//PM SSC exhibits an energy density of 3.78 Wh/kg,while MM//PM ASC exhibits an energy of 25.67 Wh/kg at a power density of 233.33 W/kg.density.The comparison shows that ASC has a larger voltage window in terms of increasing energy density.（3）Carbon fiber and polyaniline（CF|PANI）composites were prepared by electrochemical polymerization.The Raman test results show that PANI was successfully synthesized and better covered on CF.We explored better electrodeposition cycles（times）by changing the period of electrochemical deposition（200,300,400,and 500 cycles）.When the electrodeposition period is 300 cycles,the prepared CF|PANI electrode material has a better specific capacitance of 231.63 F/g at 1 A/g and higher rate performance（from 0.5 A/g to 20 A/g,with a 98.14%retention rate）,and excellent cycle stability（only 0.96%capacity loss after 1000 cycles）.This is because without the addition of a binder,the internal resistance is significantly reduced.Therefore,at higher current densities,its higher operating potential and good pseudo-capacitance performance are maintained.Moreover,this approach is more conducive to the diffusion and transfer of ions in the electrode surface and bulk phase.The symmetrical supercapacitors （CP//CP SSC）based on CF|PANI electrode materials were connected by acidic PVA-H₂SO₄ gel electrolyte.The asymmetric supercapacitors（MM//CP ASC）based on MS|MWCNT and CF|PANI electrode materials were connected by neutral PVA-Na₂SO₄ gel electrolytes.At a power density of 564.37 W/kg,the CP//CP SSC exhibits an energy density of 6.55 Wh/kg,while the MM//CP ASC has an energy density of 16.12 Wh/kg at a power density of 525.03 W/kg.This result indicates that the lower internal resistance contributes to the higher energy density of SSC and ASC at high current density and high power density,which is of great significance for its practical application.