Preparation And Research Of Electrochemical Properties On PVA-based Polymer Electrolyte Membranes

Supercapacitors have become a hot research field recently due to its advantages such as high power and energy density,short charging time,wide range of working temperature and no leakage etc.They are widely applied to various fields like electric cars,consumer electronic products,power generation of new energy,biological sensors etc.Electrolyte is one of the key components of the supercapacitor.Polyvinyl alcohol?PVA?based polymer electrolyte membrane holds high conductivity and good mechanical performance.It is a good candidata of the flexible supercapacitor and solid-state supercapacitor.This thesis presents three different kinds of PVA-based polymer electrolyte membrane.By Utilizing X-ray diffraction?XRD?,fourier transform infrared spectroscopy?FT-IR?,thermogravimetric analysis?TGA?,the composition,structure and thermal stability of polymer electrolyte membrane were characterized.Ac impedance,cyclic voltammetry and constant current charge and discharge were applied for electrochemical performance test of polymer electrolyte membrane.In the paper,the impact of changes of relative humidity in the environment on the proton conductivity of polymer electrolyte membrane were also studied.The results were briefly described as follows:?1?The polyvinyl alcohol?PVA?-silicotungstic acid?STA?polymer electrolyte membranes were prepared by solution casting,in which PVA was taken as substrate and Keggin heteropoly acid were used as proton sources.XRD,FT-IR characterization results confirmed that the STA doped into PVA matrix.The thermal stability of electrolyte membrane were enhanced with doping of STA into PVA.When m?PVA?: m?STA?= 1:8,the conductivity of PVA-STA polymer electrolyte reached 2.7×10^-2S/cm at room temperature.Under the same scanning speed,its specific capacity also reaches maximum as 43.9?F/cm2.The electrolyte membrane has good electrochemical stability.The change of relative humidity has a considerable influence on the conductivity of the electrolyte membrane.?2?The PVA-H₃PO₄-STA polymer electrolyte membrane were also prepared and studied.The paper examined the effects of H₃PO₄ content on the proton conductivity of PVA-H₃PO₄-STA polymer electrolyte membrane.When the STA content is constant,with the increase of H₃PO₄ content,the conductivity of the electrolyte membrane first increases and then decreases;When m?PVA?: m?H₃PO₄?: m?STA?= 1:4:8,the conductivity reached its maximum as 5.5×10^-2S/cm at room temperature.At the same scanning speed,its specific capacity is also the largest as 68.8?F/cm2.Under the constant current density of 0.05mA/cm2,constant current charge and discharge tests were carried out on the four different polymer electrolytes of PVA-H₃PO₄-STA?1:2:8?,PVA-H₃PO₄-STA?1:3:8?,PVA-H₃PO₄-STA?1:4:8?and PVA-H₃PO₄-STA?1:5:8?.The corresponding IR drop were 0.25 V,0.24 V,0.20 V and 0.23 V,respectively.It was shown that the higher the proton conductivity of the electrolyte membrane is,the lower IR drop is.According to the cyclic voltammograms test of PVA-H₃PO₄-STA?1:4:8?polymer electrolyte membrane,it has good electrochemical stability.?3?The glutaraldehyde was used as cross-linking agent to obtain cross-linked PVA-H₃PO₄-chitosan?CS?polymer electrolyte membrane.XRD,FT-IR,TGA were used to characterize the electrolyte membrane.Its proton conductivity was tested as 9.1×10^-2S/cm at room temperature.Cyclic voltammetry tests show that the electrolyte membrane has good electrochemical stability.Charge-discharge test of the electrolyte membrane revealed that its IR drop was as small as 0.12 V.The relative humidity changes have little impact on the proton conductivity of the electrolyte membrane.