PEO基固态聚合物电解质交流阻抗谱的研究

【作者】 赵悠曼；

【导师】 潘春跃；

【作者基本信息】 中南大学 ， 有机化学， 2009， 硕士

【摘要】 用交流阻抗谱法测定固体聚合物电解质的电导率时,对于同一固体聚合物电解质而言,同样的测试条件常会出现不同的测试结果,即数据重现性不高,这与电极/固体聚合物电解质界面双电层的形成有很大关系。目前有很多关于电极/固体聚合物电解质界面双电层的研究,但仍未见深入的、全面的研究。因而,对于双电层的进一步探究还是很有必要。为此,本文从固体聚合物电解质/电极界面双电层角度出发,探讨了交流阻抗谱法测定聚合物电解质电导率时的若干问题。本文首先以聚环氧乙烷（PEO）为基质,加入LiClO₄、丁二腈（SN）和无机粒子SiO₂后,分别制得了PEO/LiClO₄,PEO/LiClO₄/SN,PEO/LiClO₄/SN/SiO₂三种固体聚合物电解质溶液,再采用溶液浇铸法制备了相应的电解质膜。采用交流阻抗谱法研究了聚合物电解质本体电阻测定时存在的一些问题以及聚合物电解质/阻塞电极体系界面双电层的性质。主要研究结果如下:（1）对聚合物电解质本体电阻（R_b）与膜厚（L）关系的研究表明,实验测得的聚合物电解质本体电阻（R_b）与膜厚（L）的关系并非为经过原点的一条直线而是与纵轴正向有一定的截距,因而从交流阻抗谱中直接读取的R_b（高频半圆与低频斜线交点对应的实轴截距）不是单指聚合物电解质的本体电阻。通过不同电极的测试,得知从阻抗谱中读取的R_b可能含有一定的界面阻抗。从古依-恰帕门-斯特恩双电层模型中进一步证明了R_b中含有界面阻抗。（2）改变初始直流电压的交流阻抗测试表明,随直流电压增大,交流阻抗谱中对应的R_b值减小。从古依-恰帕门-斯特恩双电层模型中得知,惰性电极与电解质之间的界面阻抗随直流电压的增大而减小,由于R_b中含有一定的界面阻抗,界面阻抗随电压的减小导致了阻抗谱中读取的R_b值减小。（3）等效电路分析表明,代表界面双电层电容值的CPE1-T值随直流电压增大而增大,界面阻抗相应减小,从阻抗谱中读取的R_b值也随之减小。（4）直流电压影响交流阻抗谱低频部分斜线斜率的研究表明,直流电压从0V升高到3V时,交流阻抗谱低频部分斜线斜率随之减小。当直流电压增大到1.5V时斜线部分开始出现半圆,且当电压增大到2V时半圆明显呈现,随着电压继续增大,圆弧范围增大。这是由于聚合物电解质中的阴阳离子在直流电压的影响下,分别在正负极富集,改变了电极界面双电层性质引起的。同时,离子在电极表面吸附使得界面离子扩散阻抗增加,导致了低频部分弧形增大。（5）研究电池陈放时间对交流阻抗谱的影响表明,随陈放时间的延长,交流阻抗谱低频部分斜线斜率先减小后增大。出现这种现象的原因是由于陷于钢片表面沟壑部分的聚合物电解质中的阴阳离子在一定初始直流电压以及陈放时间的影响下,分别吸附于正负两电极形成紧密的吸附单层,该吸附单层的侧压力造成的弥散电容以及随陈放时间的延长聚合物电解质缓慢的表面应力弛豫作用所造成的弥散电容导致了低频部分斜线斜率的改变。（6）研究阻塞电极种类对交流阻抗谱的影响表明,由于电极表面粗糙程度的不同,造成了以不锈钢为电极的交流阻抗谱图低频部分斜线的斜率最小,铜箔电极次之,铝箔电极最大。更多还原

【Abstract】 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.更多还原