Of Peo-based Solid Polymer Electrolyte Electrochemical Impedance Spectroscopy Study

The conductivity of solid polymer electrolyte was not consistent for the same electrolyte by using electrochemical impedance spectroscopy(EIS) under the same testing conditions when test it for many times.And it has a great relationship of electric double layer between interface of electrode and solid polymer electrode.In recent years,there were so many researches on electric double layer of electrode/solid polymer electrolyte interface,but they were not embedded and general.It was so necessary for a further research of electric double layer.Therefor,in this paper,it was discussed many problems of testing conductivity of solid polymer electrolyte by using electrochemical impedance spectroscopy from the point of view about electric double-layer.Three kinds of polymer electrolytes were prepared by a solution cast technique base on PEO,such as PEO/LiClO₄,PEO/LiClO₄/SN, PEO/LiClO₄/SN/SiO₂.It was studied many problems of the blocking resistance testing of polymer electrolyte by using electrochemical impedance spectroscopy.(1) The relationship between R_b and the thickness(L) of the polymer film was studied,it was found that the R_b obtained from the Nyquist plots maybe not only contain the bulk resistance but also has some other resistance because the straight line R_b～L didn't pass through the origin.It was found that Rb maybe contained interface resistance by testing with different electrodes,and this was proved by using Gouy-Chapman-Stem theory.(2) By using electrochemical impedance spectroscopy,it was found that R_b obtained from the Nyquist plots was step-down with the increase of dc voltage.One can see the interface resistance of the blocing electrode/SPE was step-down with the increase of dc voltage from the Gouy-Chapman-Stern theory,and then R_b was decreased for it had some interface resistance.(3) Equivalent circuit analysis showed that the CPE1-T which represents the value of capacitance of the electric double-layer was increased with the increase of dc voltage,and then interface resistance was decreased;R_b obtained from the Nyquist plots was step-down correspondingly.(4) Study on dc voltage influencing the slope of straight line in low-frequency shows that the bias' slope decreased with the increasing of dc voltage from 0v to 3v.A semicircle appeared instead of the straight line in low-frequency when dc voltage increased to 1.5v,and the circular arc appeared in focus and augment with the increasing of dc voltage. Anions and cations in the polymer electrolyte congregated at two poles under the influence of dc voltage,and then electric double-layer of blocking electrode/SPE interface changed.Meanwhile,ions adsorptions in the electrode cause the increasing of diffuse impedance,and leading the augment of circular arc.(5) Deposit time of battery could influence the Nyquist plots.Slope of the straight line in low-frequency first decreased then increased.At potentials,anions and cations in the polymer electrolyte which was immersed in the donga of steel interface adsorbed at anode and cathode separately,and then formed a compact monolayer.The lateral compression of the adsorption layer leaded to capacitance dispersion,the slow relaxation of surface stress of polymer electrolyte could lead to capacitance dispersion.This capacitance dispersion caused the changing of straight line's slope in the low-frequency.(6) The kind of blocking electrode could also influence the Nyquist plots.For the roughness of the blocking electrodes were different,which leaded to the straight line's slope in the low-frequency with stainless steels electrode was the least,the slope of copper foil electrode took second place,and the aluminum foil electrode was the biggest.