(Digital Presentation) Electrochemical Impedance Analysis of Three-Electrode Cell with Solid Electrolyte/Liquid Electrolyte Interface
Authors: Suzuki Tatsumi , Zhong Chengchao , Shimoda Keiji , Okazaki Ken'ichi , Orikasa Yuki 
Published: February 2024

Mechanical contact loss at the solid electrolyte/electrode interface in all-solid-state batteries, a type of next-generation battery, has been reported as a major issue for ion transport in all-solid-state batteries[1]. To improve this contact problem, it has been proposed to add a small amount of liquid electrolyte to the solid electrolyte/electrode interface[2]. However, the reported ion transport analysis at the solid electrolyte/liquid electrolyte interface is limited in semi-solid-state system using symmetrical cells with lithium metal as the working electrode[3]. In this study, charge transfer reactions at the solid electrolyte/liquid electrolyte interface were analyzed by impedance (EIS) measurements in a three-electrode cell with a solid/liquid electrolyte interface using a composite electrode containing a cathode active material as the working electrode.

A composite electrode prepared by mixing LiCoO2:acetylene black:polyvinylidene fluoride in a weight ratio of 8:1:1, coating Al foil, drying and pressing was used as the working electrode, while lithium metal was used as the counter and reference electrodes. A NASICON-type solid electrolyte Li1+x+y
Al
x
(Ti2−y
Ge
y
)P3−z
Si
z
O12 was constructed between the working electrode and the counter electrode, and a three-electrode cell prepared by filling the liquid electrolyte 1 M LiClO4/PC between the solid electrolyte and both electrodes. The reference electrode was placed between the solid electrolyte and the counter electrode, as the solid electrolyte/liquid electrolyte interface charge transfer is not observed in EIS measurements when the reference electrode is placed between the working electrode and the solid electrolyte. After two cycles of constant current charge/discharge measurements (current rate: 0.1 C rate, cut-off potential: 3.2 V - 4.2 V vs. Li/Li+), the solid electrolyte/liquid electrolyte interface charge transfer was analyzed by performing EIS measurements. To identify the semicircle associated with the solid electrolyte/liquid electrolyte interface resistance, measurements were also performed in a cell without a solid electrolyte and the resistance components corresponding to each semicircle were assigned.

The temperature dependence of the observed semicircles was analyzed. A comparison of the activation energies calculated from the slopes of the Arrhenius plots confirmed a particularly large activation barrier at the solid electrolyte/liquid electrolyte interface and the working electrode/liquid electrolyte interface charge transfer.

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[2] C. Wanga, Q. Suna, Y. Liua, Y. Zhaoa, X. Lia, X. Lina, M.N. Banisa, M. Lia, W. Lia, K.R. Adaira, D. Wanga, J. Lianga, R. Lia, L. Zhangb, R. Yangb, S. Lub and X. Suna, Nano Energy, 48, 35-43 (2018).

[3] T. Abe, H. Fukuda, Y. Iriyama, Z. Ogumi, J. Electrochem. Soc., 151, A1120-A1123 (2004).