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On the interfacial charge transfer between solid and liquid Li+ electrolytes

Abstract

The Li+ ion transfer between a solid and a liquid Li+ electrolyte has been investigated by DC polarisation techniques. The current density i is measured as a function of the electrochemical potential drop ΔμLi+ at the interface, using a liquid electrolyte with different Li+ concentrations. Subject of this experimental study is the interface between the solid electrolyte Ta-substituted lithium lanthanum zirconate (Li6.6La3Zr1.6Ta0.4O12) and a liquid electrolyte consisting of LiPF6 dissolved in in ethylen carbonate/dimethyl carbonate (1:1). The functional course of i vs. ΔμLi+ can be described by a serial connection between a constant ohmic resistance Rslei and a current dependent thermally activated ion transfer process. For the present solid-liquid electrolyte interface the areal resistance Rslei of the surface layer is independent of the Li+ concentration in the liquid electrolyte. At room temperature a value of about 300 Ω cm2 is found. The constant ohmic resistance Rslei can be attributed to a surface layer on the solid electrolyte with a (relatively) low conductivity (solid-liquid electrolyte interphase). The low conducting surface layer is formed by degradation reactions with the liquid electrolyte. Rslei is considerably increased if small amounts (ppm) of water is added to the liquid electrolyte. The thermally activated ionic transfer process obeys a Butler-Volmer-like behaviour, resulting in an exchange current density i0 depending on the Li+ concentration in the liquid electrolyte by a power-law. At a Li+ concentration of 1 mol l-1 a value of 53.1 μA cm-2 is found. A charge transfer coefficient α of ∼0.44 is measured. The finding of a superposed constant ohmic resistance, due to a solid-liquid electrolyte interphase, and a current dependent thermally activated ion transfer process is confirmed by the results of two former experimental studies from literature, performing AC measurements/EIS.

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Publication details

The article was accepted on 07 Sep 2017 and first published on 07 Sep 2017


Article type: Paper
DOI: 10.1039/C7CP05213H
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    On the interfacial charge transfer between solid and liquid Li+ electrolytes

    M. Schleutker, J. Bahner, C. Tsai, D. Stolten and C. Korte, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP05213H

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