Study On Electrochemical Performance Of Modified Redox Gel Polymer Electrolyte

Supercapacitor(SC)is an efficient energy storage device.The electrolyte is an important component of SC,which affects the energy storage performance of SC.Gel polymer electrolyte(GPE)has two advantages.Compared with liquid electrolyte,GPE is not easy to leak;compared with solid electrolyte,GPE can show higher conductivity performance,so it is a vital electrolyte for SC with significant advantages.However,at the same time,GPE still has problems such as low ionic conductivity,low capacitance performance,poor electrochemical stability and poor matching with electrode materials.Therefore,in response to the above problems,this research designed symmetrical and asymmetrical redox gel polymer electrolyte supercapacitor(Redox-GPE SC),using redox active substances to modify GPE,introducing inorganic nanomaterials to build GPE ion transport channels and matching the redox active electrode strategy to improve the electrochemical performance of GPE supercapacitors.Also,density functional theory(DFT)simulation calculations and electrochemical performance testing methods were utilized to study the energy storage mechanism of GPE systems.This paper mainly completed the following tasks:(1)Electrochemical performance research of PVA-H₃PO₄-KI-PMo₁₂ Redox Gel Polymer ElectrolyteDesign and synthesize polyvinyl alcohol-phosphoric acid-potassium iodide-phosphomolybdic acid(PVA-H₃PO₄-KI-PMo₁₂,PPIP)redox gel polymer electrolyte(Redox-GPE).The Redox-GPE was based on dual active substances KI and PMo₁₂ modified simultaneously.Then Match polyaniline/carbon paper(PANI/CP),phosphomolybdic acid/polyaniline/carbon paper(PMo₁₂/PANI/CP)redox active electrodes to construct a symmetrical Redox-GPE SC.DFT calculations are used to study the interaction mechanism between the dual active material Redox-GPE and the electrode interface.Based on KI and PMo₁₂ in GPE and PMo₁₂ and PANI in the electrode material,the performance of Faradic capacitance is improved by synergistic redox reactions.When the mass ratio of optimized PVA:H₃PO₄:PMo₁₂:KI is 10:20:5:1,the ion conductivity of PPIP reaches 41.41 m S cm^-1,which is higher than PVA-H₃PO₄-KI(PPI,22.99 m S cm^-1)and PVA-H₃PO₄-PMo₁₂(PPP,17.32 m S cm^-1).When the output voltage is 1.2 V and the current density is 0.5 m A cm^-2,the specific capacitance and energy density of PPIP//CP supercapacitor are 228.12 m F cm^-2 and456.25 m Wh m^-2,respectively,which are better than PPI//CP(138.30 m F cm^-2,276.60 m Wh m^-2)and PPP//CP(82.30 m F cm^-2,164.06 m Wh m^-2).The specific capacitance and energy density of PPIP//PMo₁₂/PANI/CP are increased to 1063.75 m F cm^-2 and 2127.5 m Wh m^-2.Therefore,the specific capacitance performance of the symmetric Redox-GPE SC system with KI and PMo₁₂ dual active material simultaneously modified PPIP is significantly better than that of the Redox-GPE SC system with a single active material.Also,matching the redox active electrode can further improve its capacitance performance.(2)Electrochemical performance research of CNTs-PVA-H₃PO₄-KI Redox Gel Polymer ElectrolytePrepare and synthesize carbon nanotubes(CNTs)modified polyvinyl alcohol-phosphoric acid-potassium iodide(CNTs-PVA-H₃PO₄-KI,CNTs-PPI)Redox-GPE modified simultaneously.The Redox-GPE was based on active material KI and two-dimensional nanomaterial CNTs.Then Match polyaniline/carbon paper(PANI/CP)and phosphomolybdic acid/polyaniline/carbon paper(PMo₁₂/PANI/CP)redox active electrodes to construct a symmetrical Redox-GPE SC.DFT calculations are used to study the interaction mechanism between the CNTs and KI modified Redox-GPE and the electrode interface.Based on CNTs,it can expand ion transmission channels and strengthen polymer molecular structure to improve ion conductivity and electrochemical stability of GPE.Based on KI in GPE and PMo₁₂ and PANI in electrode materials,the performance of Faradic capacitance is improved by synergistic redox reactions.When the mass ratio of optimized PVA:H₃PO₄:KI:CNTs is 250:500:25:1,the ion conductivity of CNTs-PPI reaches 41.41 m S cm^-1,which is higher than PPI(22.99 m S cm^-1).When the output voltage is 1.2 V and the current density is 0.5 m A cm^-2,the specific capacitance and energy density of CNTs-PPI//CP supercapacitor are 247.54 m F cm^-2 and 495.08 m Wh m^-2,respectively,which are better than PPI//CP(138.30 m F cm^-2 and 276.60 m Wh m^-2).The specific capacitance retention rate of 2000 cycles of charging and discharging is 80.9%,which is also better than 71.2%of PPI//CP.The specific capacitance and energy density of CNTs-PPI//PMo₁₂/PANI/CP are increased to 1475.80 m F cm^-2 and 2951.60 m Wh m^-2.Therefore,the ionic conductivity,specific capacitance and electrochemical stability performance of the symmetric Redox-GPE SC system with active substance KI and two-dimensional nanomaterial CNTs simultaneously modified CNTs-PPI is significantly better than that of the Redox-GPE SC system with a single active material.Also,matching the redox active electrode can further improve its capacitance performance.(3)Electrochemical performance research of PVA-H₃PO₄-PMo₁₂|PVA-H₃PO₄-Na₂Mo O₄Asymmetric Redox Gel Polymer Electrolyte SystemDesign and synthesize polyvinyl alcohol-phosphoric acid-phosphomolybdic acid(PVA-H₃PO₄-PMo₁₂,PPP)and polyvinyl alcohol-phosphoric acid-sodium molybdate(PVA-H₃PO₄-Na₂Mo O₄,PPM)Redox-GPE.PPP and PPM are respectively coated on CP electrode to assemble into PPP|PPM asymmetric GPE-SC.DFT calculations are used to study the interaction mechanism between the single active substance Redox-GPE and the electrode interface.The Faradic capacitance is introduced based on the synergetic redox reactions between the active material PMo₁₂ and Na₂Mo O₄.The asymmetric Redox-GPE system based on active materials PMo₁₂ and Na₂Mo O₄ improves the performance of electrochemical capacitance through independent redox reactions.The asymmetric Redox-GPE system modified based on the active substances PMo₁₂ and Na₂Mo O₄respectively improves the performance of Faradic capacitance through independently optimized redox reactions.When the mass ratio of optimized PVA:H₃PO₄:PMo₁₂:Na₂Mo O₄is 10:20:5:1,the ion conductivity of PPP|PPM reaches 36.43 m S cm^-1,which is higher than PPP(17.14 m S cm^-1)and PPM(12.38 m S cm^-1)GPE.When the output voltage is 1.0 V and the current density is 0.5 m A cm^-2,the specific capacitance and energy density of PPP|PPM//CP are 170.03 m F cm^-2 and 236.15 m Wh m^-2,respectively,which are better than PPM//CP(58.85 m F cm^-2?81.74 m Wh m^-2)and PPP//CP(76.75 m F cm^-2?106.60 m Wh m^-2).Therefore,the ionic conductivity and specific capacitance performance of the asymmetric Redox-GPE SC system with Na₂Mo O₄ and PMo₁₂ dual active material modified PPP|PPM is significantly better than that of the Redox-GPE SC system with a single active material modified PPP and PPM.