Determination of Transport Properties for Solid Electrolytes from the Impedance of Thin Layer Cells

Abstract

A mathematical model has been developed that describes the transport of species across amorphous and single-crystal solid electrolytes during ac impedance experiments. The analysis is based on the multicomponent transport equation, and it includes not only the effects of ion-pairing reactions but also the possibility that a second, nonconducting phase is distributed through the electrolyte. Transient and steady-periodic equations for the low-frequency impedance are derived for concentrated binary and ternary electrolytes sandwiched between electrodes at which an electrochemical reaction takes place. General analytic expressions are presented which relate the characteristics of the impedance response to the diffusion coefficient(s) and transference number(s) representative of the solid ionic conductor. The results show that transient effects are usually small but that species interactions and activity coefficient corrections can significantly influence the steady-periodic impedance. Accurate information on reaction stoichiometries and the nature of the mobile species is a prerequisite for meaningful interpretation of the transport properties. With the model, consistency tests are established that help distinguish between dilute and concentrated electrolytes and also that indicate when the material should be treated as a four-species system rather than as a binary electrolyte. The utility of the approach is illustrated by comparing theoretical results with available experimental data for two solid polymer electrolytes.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 129.170.195.149 Downloaded on 2015-01-02 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 129.170.195.149 Downloaded on 2015-01-02 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 129.170.195.149 Downloaded on 2015-01-02 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 129.170.195.149 Downloaded on 2015-01-02 to IP

Transport Properties of Solid Polymer Electrolytes Prepared from Oligomeric Fluorosulfonimide Lithium Salts Dissolved in High Molecular Weight Poly(ethylene oxide)

“…Measurements were made using blocking electrodes for the anion and reversible nonblocking electrodes for the lithium cation, so that the experimental cell had the form Li|(polymer) n LiX|Li. For this case, the complex impedance spectrum at ambient temperature consisted of three arcs , that, using the equivalent Randles circuit theory for a SPE with nonblocking electrodes, could be attributed to the various physical/chemical phenomena taking place. The highest frequency semicircle is due to the bulk capacitance of the host polymer ( C b ) plus the parallel bulk resistance of the electrolyte ( R b ).…”

“…At intermediate frequencies, the second arc is associated with the parallel circuit of the double-layer capacitance ( C dl ) and the charge-transfer resistance ( R ct ). At low frequencies, the amount of charge transferred during a half-cycle produces salt concentration gradients in the electrolyte that can be modeled by a Warburg impedance ( Z d ). ,, This gives rise to a linear response with a phase angle of approximately 45° in the spectrum that reflects the diffusion-controlled nature of Z d . , At still lower frequencies, the impedance may deviate from the Warburg impedance and return to the real axis (forming a skewed semicircle). This effect may be attributed either to a finite diffusion layer thickness at steady state or to a finite electrolyte thickness .…”

Parameterising continuum level Li-ion battery models & the LiionDB database

“…This is often done with an electrolyte soaked porous separator between electrodes and can be used to calculate the effective conductivity, based on the high frequency bulk resistance intercept on a Nyquist plot [197,173,198]. The low-frequency impedance response can also determine contributions from the ionic diffusion coefficient, D e (c e ), and transference number, t 0 + (c e ) [197,199]. This approach is akin to a frequency-domain analysis of repeated polarisation-relaxation experiments, discussed in the following section.…”

Solid-state sodium batteries using polymer electrolytes and sodium intercalation electrode materials

“…studied materials are -lithium-intercalating titanium disulfide, vanadium oxides, manganese oxides, 10-15 and cobalt and nickel oxides 16-20 for lithium cells, and the sodium analogues of these for sodium cells. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] Lithium and sodium batteries are attractive not only for their potential high energy density but also because a battery assembly that is completely solid state is possible using solid-state lithium or-sodium ion conducting electrolytes. Solid-state polymer electrolytes were proposed by Armand in 1979 for lithium battery use, 37 and have attracted great attention since then.…”