| Gel polymer electrolyte(GPE)is the suitable electrolyte for assembling of solid-state supercapacitor.As a new type of energy storage device solid-state supercapacitor has wide application in the field of power battery,thin electronic device and flexible energy storage device due to good cycle stability and safety performance.The performance of supercapacitor has a close relationship with the performance of GPE.Improvement has been made in GPE,in view of the problem that the low ionic conductivity and the poor diffusion ability of the GPE,combining the characteristics of the electrochemical double electric layer and the Faraday pseudo-capacitor.With the goal of increasing the capacity of the supercapacitor,reducing the internal resistance and improving the rate capability,PVA-H3PO4 and PVA-H2SO4 were electroactive modified by PMo12 and KI respectively,in addition,GO was used to modify structure of PVA-Na2SO4.The electroactive modified gel electrolyte can introduce the Faradaic reaction at the electrode|electrolyte interface,which improved the pseudo-capacitance characteristic of the supercapacitor and increased the capacity of the device.The GPE modified by GO can construct the channel which facilitate ion transport,thus the ionic conductivity of GPE was improved.As a result,the device’s internal resistance was reduced and the rate performance and power output efficiency were improved.Specifically,PVA-H3PO4-PMo12,PVA-H2SO4-KI,PVA-Na2SO4-GO were applied into electric double layer capacitors and Pseudo-supercapacitors.1.Application of PVA-H3PO4-PMO12 in carbon based symmetrical solid-state supercapacitor.PVA-H3PO4-PMO12 was fabricated by sol-gel method When the addition rate of PVA to KI is 1:0.5,PVA-H3PO4-PMO12 has the highest ion conductivity and capacitance performance.The supercapacitor was constructed by using PVA-H3PO4-PMO12 GPE and two electrodes of carbon paper.Specific capacitance of 28.65 mF cm-2(698.8 mF cm-3),specific energy of 20.37 μWh cm-2,specific power of 0.32 mW cm-2 at a current density of 0.2 mA cm-2(4.9 mA cm-3)were achieved.Compared with the specific capacitance of traditional PVA-H3PO4 system(12.16 mF cm-2,296.6 mF cm-3),the specific capacitance increased by 135.6%and the equivalent series resistance decreased from 313 Ω cm2 to 275.3 Ω cm2.When the current density increased from 0.2 mA cm-2 to 2 mA cm-2,the specific capacitance decreased by 58%,which was lower than that of PVA-H3PO4 electrolyte system(78.6%).The supercapacitor can light up the LED(rated voltage 1.8V).The PMO12 modified PVA-H3PO4 GPE,has improved the specific capacitance of carbon-based supercapacitor,which shows a good practical application.But the cycle performance needs to be improved.2.Application of PVA-H2SO4-KI in carbon based symmetrical solid-state supercapacitor and PAN I based supercapacitorPVA-H2SO4-KI GPE was fabricated by sol-gel method,the optimized addition rate of PVA to KI is 1:0.166.under this circumstance high ion conductivity and improved capacity can be achieved.The symmetrical solid-state supercapacitor was constructed by using CP electrode and PVA-H2SO4-KI GPE,the specific capacitance of the supercapacitor was 24.75 mF cm-2 at the current density of 0.25 mA cm 2.Compared with the specific capacity of PVA-H2SO4 system(12.93 mF cm-2),it increased by 91.4%.When the current density increased to 2 mA cm-2,the specific capacity of the supercapacitor was 11.28 mF cm-2,and the specific capacitance loss rate was 54.4%while that of the PVA-H2SO4-based device was 84.4%.Those results indicated that KI improved the charging and discharging performance of the supercapacitor at high current.The supercapacitor,when assembled by using the GPE modified by KI has the lower equivalent series resistance(71.6 Ω cm-2).A symmetrical supercapacitor was assembled with PVA-H2SO4-KI as the electrolyte and PANI/CP as the electrode.The areal capacitance was 163.5 mF cm-2 at a current density of 0.5 mA cm-2,which increased by 31.25%compared with the device using PVA-H2SO4 as electrolyte.The capacitance of supercapacitor underwent almost no loss after 2000 cycles at the current density of 1mA cm-2,indicating outstanding cycle stability.The symmetrical solid-state supercapacitor was assembled by using PANI/GS/CP electrode and PVA-H2SO4-KI GPE.It possesses the high specific capacitance of 219.5 mF cm 2,the energy density of 39.02 μWh cm-2 and the power density of 0.8 mW cm-2 at the current density of 1mA cm-2 and the voltage window of 0.8 V.When the current density increased to 5 mA cm-2,the specific capacitance and the capacity retention rate were 169.9 mF cm-2 and 77.4%,respectively.When the voltage window is 1.6V,the specific capacitance,specific energy and specific power of the supercapacitor were 113.5 mF cm-2,80.71 μWh cm-2,1.6 mW cm-2 at the current density of 1 mA cm-2.When the current density increased to 5 mA cm-2,the specific capacitance was 105.3 mF cm-2 and the capacitance retention was 78.9%.PVA-H2SO4-KI GPE can maintained the stability of PANI/GS/CP porous structure,contributing to high current charge and discharge characteristics.The PVA-H2SO4 GPE modified by KI can improve the specific capacity of the carbon-based supercapacitor,and also play a good role in the pseudo-supercapacitor,so it can be widely used in acidic electrolyte system solid-state supercapacitor.3.Application of PVA-Na2S04-GO in carbon based symmetrical solid-state supercapacitor and Manganese oxide based supercapacitorPVA-Na2S04-GO was fabricated by solution casting method.GO can be compatible well with PVA-Na2SO4 GPE.The ionic conductivity of the modified GPE was increased from 1.6 mS cm-1 to 3.90 mS cm-1.The PVA-Na2S04-GO GPE can be used as the solid-state electrolyte and the separator at the same time,which simplifies device assembly.When GO modified PVA-Na2S04 was used in carbon based supercapacitor,the equivalent series resistance of supercapacitor was reduced from 438.8 e cm2 to 370.8 G cm2 at the current density of 0.2 mA cm-2.The AC impedance displays that resistance of devlce was reduced after using PVA-Na2SO4-GO GPEThe equivalent equivalent series resistance of NaxMnO2/CP based supercapacitor was reduced from 293.2 Ω cm2 reduced to 221 Ω cm2 at the current density of 0.5 mA cm-2 after PVA-Na2SO4 GPE was modified by GO.Obviously,the addition of GO reduced the internal resistance of GPE.When the current density increased to 5 mA cm-2,the capacitance retention rate was 26.3%,higher than that of supercapacitor(16.4%)based on PVA-Na2SO4 system.In the AC impedance,after GPE was modified by GO,the Ro(Ω)reduced from 5.2 Ωto 3.998 Ω and the Wo reduced from 81.4 Ω to 61.1 Ω.In addition,the three-dimensional structure of PVA-Na2SO4-GO contributed to good water storage ability.The increment of internal resistance of supercapacitor based on PVA-Na2S04-GO system after 500 cycles was relatively lower.When using PVA-Na2SO4-GO,The solid-state supercapacitor with NaxMnO2/TiN as electrodes,has good electrochemical performance under the potential window of 1.6 V.Regarding to the PVA-Na2SO4 system and PVA-Na2SO4-GO system supercapacitor,the areal capacitance of was 16.13 mF cm-2 and 22.41 mF cm-2 at the current density of 0.5 mA cm-2,respectively.The equivalent series resistance is 109 Ω cm2 and 40 Ω cm2,respectively.PVA-Na2SO4 GPE modified by GO improved the specific capacitance and reduces the inte11al resistance of supercapacitor.When the current density increased to 5 mA cm-2,the specific capacitance of PVA-Na2SO4 supercapacitor and PVA-Na2SO4-GO were 4.65 mF cm-2 and 9.62 mF cm-2,separately.The capacitance retention rates are 25.1%and 42.9%,respectively.PVA-Na2SO4-GO GPE improved the rate performance of the supercapacitor.The AC impedance shows that the Ro of the supercapacitor reduced from 10.14 Ω to 5.576 Ω,indicating the significant decrease of the internal resistance of the supercapacitor.The Wo declined from 941.5 Ω to 3.379 Ω,showing the improvement of ion diffusion resistance.The characteristic time constant(to)was shortened from 1s to 0.56s,indicating that the resistance characteristic of supercapacitor was easily converted to the capacitance characteristic and in turn the output power efficiency is improved.The PVA-Na2SO4 system and PVA-Na2SO4-GO system supercapacitor were measured at 1mA cm-2 after two days.The supercapacitor using the modified GPE still maintain small equivalent series resistance,indicating that PVA-Na2SO4-GO GPE has potential application value to improve the electrochemical performance of solid-state supercapacitor. |
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