Three-Electrode Setups for Lithium-Ion Batteries

An approach to increase the autonomy of batteries developed for transportation applications, without changing currently-used positive and negative active materials, is to increase the battery energy density by increasing the active material loading (mg.cm −2 ) of the electrodes. A direct consequence of a higher loading is the increase of mass transport-related issues across the electrode porosity. Therefore, the optimization of the porous electrode structure is mandatory to facilitate the access of lithium ions to the whole electrode volume. In this regard, pore tortuosity is a key parameter whose determination is not so straightforward. Although tomography techniques and corresponding analyses are promising methods to acquire precise geometrical information about porous electrode, they hardly can be used as a routine technique. In this work, a transmission-line-model analysis of the electrochemical impedance diagram of symmetric cells containing porous electrodes in blocking condition, i.e. without any charge transfer reaction, is proposed in order to readily derive pore tortuosity. The method is applied to a set of graphite electrodes composed of anisotropic particles. Lithium-ion technology is the leading contender for transportation applications such as plug-in, hybrid, and electric vehicles.1,2 It offers the highest energy density among the different existing battery technologies such as nickel metal hydride (NiMH), nickel cadmium (NiCd), and lead acid.3 Additionally, Li-ion batteries exhibit good electrochemical and thermal stability, 4,5 long life, low self-discharge rate and good charge/discharge rate capability.6-10 Nevertheless, today's electric vehicle performance still need improvement in terms of autonomy, recharge time, and cost, in order to approach internalcombustion-engine-vehicle capabilities.9,11 Increasing electrode loading is one of the most straightforward way to increase energy density and thereby the vehicle range. However, high-loading electrodes will suffer larger power limitations, which might be a problem, in particular during fast charging of the battery pack. Power limitations will mostly arise because of lithium-ion transport limitations across the electrode porosity and are known to increase with the electrode thickness or with a decrease of the porosity.To predict power limitations of an actual electrode design, accurate modeling of mass transport is desired. Nowadays, the most popular and efficient battery model is the so-called Newman's model that relies on the porous electrode theory.12 The porous electrode is described as the superposition of the liquid and solid phases that are defined by their respective volume fraction and interfacial surface area. Electrode properties are averaged over volume elements which are small compared to the overall dimension of the system but large compared to the pore details. Therefore, the pore detail is neglected and the electrode geometry is fully described by its thickness, the interfacial area per unit volume of electrode, and volume fract...

Section: E3330mentioning

confidence: 99%

Determination of Tortuosity Using Impedance Spectra Analysis of Symmetric Cell

Malifarge

Delobel

Delacourt

2017

“…[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.…”

mentioning

confidence: 99%

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

Linsenmann

Pritzl

Gasteiger

2019

In this work, we introduce a newly developed micro-reference electrode (μ-RE) for sodium-ion batteries (SIBs). This μ-RE is based on a 50 μm-sized tin-coated copper wire, manually insulated using polyurethane (PU) spray, such that only the cross-sectional area of the wire tip is in contact with the electrolyte. The tin-coating allows for facile in situ electrochemical sodiation, resulting in a stable potential of the wire that enables in situ Electrochemical Impedance Spectroscopy (EIS). We will show that reliable singleelectrode impedance data from SIB cells can be obtained with this new tin wire μ-RE (μ-TWRE) concept, validated by comparing μ-RE-based single-electrode impedance data with those acquired by a symmetrical cell approach. As hard carbons are currently the most promising anode material for SIBs, we evaluate the impedance evolution of a hard carbon anode over extended charge/discharge cycles in a half-cell vs. sodium metal, comparing its impedance measured at the same state-of-charge (SOC) over 50 cycles. Thus, we demonstrate that EIS using a μ-TWRE can be used as a convenient tool to quantify the impedance evolution of SIB anodes and cathodes.

“…However, a reliable 3-electrode setup can be experimentally challenging, considering cell design and referenceelectrode positioning. [31][32][33][34] Hence, the purpose of this section is to assess the error made by using 2-electrode data as an input for a 3-electrode based model analysis by fitting 2-electrode surrogate data simulated from the P2D model with the basecase 3-electrode P2D model. The difference between the two models is that the WE potential is either referred to the CE or the RE.…”

Section: Resultsmentioning

confidence: 99%

Guidelines for the Analysis of Data from the Potentiostatic Intermittent Titration Technique on Battery Electrodes

Malifarge

Delobel

Delacourt

2017

The Li-ion battery (LIB) modeling community needs to rely on a vast bank of measured Li-ion cell parameters. Most of them are determined by routine experiments but some can solely be estimated by fitting a model to a well-designed experiment. For instance, the determination of the lithium chemical diffusion coefficient has been the focus of numerous studies. Specific techniques have been proposed for its estimation, e.g., the potentiostatic intermittent titration technique (PITT), the galvanostatic intermittent titration technique (GITT), the cyclic voltammetry (CV), and the electrochemical impedance spectroscopy (EIS). Our study focuses on the PITT so as to provide guidelines for experimental measurements and corresponding data analysis. The validity of underlying assumptions of published analytic solutions used to fit PITT data is assessed using a pseudo-2D (P2D) model. Among the tested assumptions are the drop of the porous-electrode effect, of the particle size distribution and of the finite kinetics of Li insertion/de-insertion. Tests are also conducted to assess the error made on the chemical diffusion coefficient and reaction-rate constant determination by fitting 2-electrode simulated data with a 3-electrode P2D model. Lithium-ion battery (LIB) cell energy density has been greatly enhanced over the years owing to research in new materials and electrode engineering.1 Further improvement of LIB energy density is possible by packing more active material within the electrodes. However, doing this usually trades off with a power decrease as lithium-ion transport in the liquid phase becomes a major issue in thick and/or dense porous electrodes.2 Nonetheless, a compromise is still achievable through engineering of the electrode fabrication process, i.e., by tuning the electrode microstructure to optimize the ion and electron transport paths. This would decrease electrode nonuniformities that appear during cell operation, e.g., in terms of state of charge, liquidphase salt concentration, and solid/liquid-phase potentials.3 On this matter, LIB physical models prove an efficient tool to shed light on phenomena such as the development of concentration/potential gradients across the cell. Moreover, LIB models are tunable to the studied physics and cost effective compared to an experimental trial-and-error process, which makes them well-suited to determine parameters that optimize the porous-electrode design depending on the application. It also helps to assess the possible occurrence of unwanted phenomena such as Li metal plating. Among these models, the pseudo-2D (P2D) one introduced by Newman group in the early nineties is a widely used continuum model. 4,5 It relies on porous-electrode and concentrated-solution theories. In this model, the porous electrode is described as the superposition of the liquid and solid phases that are defined by their respective volume fractions and the interfacial surface area. Electrode properties are averaged over volume elements that are small compared to the overall dimension of t...