Three-Electrode Setups for Lithium-Ion Batteries

Abstract

Material and degradation effects in lithium-ion batteries are studied in three-electrode cells using electrochemical impedance spectroscopy. But half-cell impedance spectra are often superimposed by distortions caused by the individual cell arrangement. Finite Element Method simulations of the three-electrode cell were applied to identify and quantify these contributions. This study identified two basic mechanisms: (I) a radially inhomogeneous current distribution originating from geometric asymmetry of the electrodes; and (II) a frequency-dependent inhomogeneous current distribution in the electrolyte caused by an electrochemical asymmetry. Mechanism II is caused by different electrode materials, and enhanced when the electrolyte diameter exceeds those of both working and counter electrode. With the help of the FEM model, we evaluated three-electrode cells featuring different reference electrode geometries: (a) point-like, (b) wire and (c) mesh reference electrode. The results of these FEM simulations are shown as half-cell and full-cell impedance data, disclosing the magnitude of distortions and artifacts for each type of reference electrode geometry. The mesh reference electrode, proposed in literature but not widely adopted, showed the largest potential for error-free impedance spectra. The FEM simulations were supported by experiments, comparing a point-like with a mesh reference electrode in a three-electrode cell (see part II).

The Effect of Electrode-Electrolyte Interface on the Electrochemical Impedance Spectra for Positive Electrode in Li-Ion Battery

“…"spiral" behavior on Nyquist plots with Li rod reference electrode). 25,26,30,31 Mesh reference electrode also enables us to avoid blocking ion-flow/migration between positive and negative electrodes. In addition, loading density of Li 4 Ti 5 O 12 on mesh reference electrode is kept relatively low (∼1.0 mg/cm 2 ) to avoid impedance contribution from reference electrode.…”

Revealing electrolyte oxidation via carbonate dehydrogenation on Ni-based oxides in Li-ion batteries by in situ Fourier transform infrared spectroscopy

“…''spiral'' behavior on Nyquist plots with Li rod reference electrode). 104,[113][114][115][116] Galvanostatic and potentiostatic charge and EIS tests were performed using VMP3 (potentiostat with frequency response analyzer, Biologic) with thermally equilibrated by thermostat chamber (SU-241, Espec) at 25 1C. After cell assembly, Li 4 Ti 5 O 12 mesh reference electrode was electrochemically lithiated (negatively polarized at constant current of 500 mA against Li metal counter electrode with cut-off voltage of 1.3 V Li ) and got stable reference electrode potential at 1.56 V Li .…”

A Reference Electrode for In Situ Impedance Measurements in Sodium-Ion Batteries

“…[9][10][11][12][13][14][15] However, the measurement of cell impedance data does not allow for the deconvolution of cathode and anode impedances, and for in situ impedance analysis of individual electrodes a reference electrode (RE) is required. 9,[16][17][18] Without a RE, the only possibility to independently quantify the anode and/or cathode impedance is the disassembly of multiple cells and the recombination of identical anode or cathode pairs in symmetrical cells. 13,[19][20][21][22] In the latter case, monitoring the evolution of the electrode impedance as a function of state-of-charge (SOC) and/or over extended cycling requires dis-and reassembly of numerous cells, so that artefacts due to cell opening and electrode transfer may be introduced.…”

“…On the other hand, when using μ-REs, the design and placement of the μ-RE with respect to working (WE) and counter electrode (CE) in a three-electrode setup is crucial in order to obtain artefact-free impedance spectra. 9,16,17,23 The μ-RE has to fulfill the following requirements: a) its potential has to be stable within the measuring duration of the impedance spectrum (typically <20 min); b) it has to be located centrally between anode and cathode, where the electric field is homogeneous; and, c) its cross-sectional dimensions have to be small compared to the distance between the electrodes in order to minimize the potential gradient across the diameter of the μ-RE. In general, it is advantageous to use μ-REs with a well-defined reference potential, as simple metal wire pseudo-REs frequently exhibit too large potential drifts, as was shown by Dollé et al for copper and silver wires; 24 in some cases, however, the potential of pseudo-REs is sufficiently stable to enable EIS analysis down to frequencies of ≈0.1 Hz.…”