Electrochemical impedance spectroscopy allows access to the complete set of kinetic characteristics of electrochemical systems, such as rate constants, diffusion coefficients, and so on, in single variable‐load experiment. It is restricted to characteristics that describe system behavior in linear range of electrical excitation, for example, when it can be approximated by linear differential equations. It can be contrasted with other methods where explicitly nonlinear properties are investigated, such as cyclic voltammetry (see Chapter Cyclic Voltammetry ). A common example of linear conditions is voltage excitation below 25 mV, where V ( I ) dependency can be approximated as linear. Some of the parameters remain constant over a wide range of conditions, and once found under linear conditions can also be applied to model much wider ranges. An example of such parameters would be ohmic resistance of electrolyte or thickness of passivating film on the electrode. Although impedance spectroscopy is sharing the variable‐load experimental method with many other linear excitation electrochemical techniques, its analysis method is distinct, where a time‐domain signal and response are converted to the frequency domain and their relation is found in the form of complex impedance. Complex impedance values over a range of frequencies form an impedance spectrum. Further analysis strives to derive system parameters from the impedance spectrum, typically by developing a model function connecting the impedance spectrum with system parameters and optimizing parameters to obtain a best fit to the impedance spectrum. This article covers the basics of the experimental implementation of this technique, as well as background and mathematical approaches for developing model functions for most common systems and analysis of the experimental data to obtain system parameters.

A three-electrode cell can be a useful tool for measuring electrode-level and cell-level electrochemical characteristics, such as the impedance response and potential variations in lithium-ion cells. In this paper, a reliable three-electrode coin cell setup is introduced, which improves the stability and accuracy of electrochemical measurements by modifying the electrode alignment and employing Li 4 Ti 5 O 12 as a reference electrode. An important highlight is the ability to obtain impedance evolution characteristics at different depth of discharge (DOD) for an individual electrode and the full cell based on both the frequency response analysis and the carrier function Laplace transform characteristics. The reliability of the proposed modified three-electrode coin cell setup has been validated by analyzing the impedance response of symmetric and full cells, and the voltage profiles of the full cell along with the positive/negative electrode contributions. The importance of the resistance contributions from the negative and positive electrodes to the full cell impedance evolution at different DOD is highlighted. Lithium-ion batteries (LIBs) are popular candidates for use in electric vehicles and in the application of portable electronic devices due to their favorable energy density and power capability.1-4 The wide usage of LIBs, in recent years, has raised interest in the observation of their performance and degradation phenomena. The typical configuration of battery cells, which only have anode and cathode, is suitable when the whole cell is the objective of the analysis. However, the typical cell configuration is limited when the interest is in separately studying the electrochemical characteristic of each electrode. To study the electrochemical characteristics of anode and cathode separately during the charging and discharging processes, a three-electrode cell, which includes a reference electrode (RE), working electrode (WE), and counter electrode (CE), has been introduced. By investigating the electrochemical impedance spectroscopy (EIS) and potential from three-electrode cell, the influence of the cathode and anode on the cell performance and degradation phenomena can be separately analyzed and characterized. 5-9The three-electrode cell can be setup with the configuration of plastic pouch cell, 10-12 steel cell housing, 13 or Swagelok cell. 14,15 These previous setups have the disadvantage of having a large size and high cost. To overcome these disadvantages, the three-electrode coin cell setup was selected due to its advantage of being well-sealed, portable, and low cost. To the best of the authors' knowledge, few of these three-electrode coin cell setups have been implemented to study the EIS and full cell performance (electrode potential). Delacourt et al. 16 developed a T-cell-like three-electrode coin cell setup. In this T-celllike setup, the distortion in the EIS measurement, especially in the low frequency region, can be attributed primarily to the alignment and uneven separation of the RE, CE, and ...

In operando detection and quantification of lithium plating is critical toward understanding the deleterious consequences under operational extremes in Li-ion batteries.

Lithium metal anodes are an attractive option for next-generation batteries because of high gravimetric and volumetric energy densities. The formation of dendritic morphology of electrodeposition during charging, however, poses safety concerns, which, in particular, have been a focus of intense research. The formation of “dead lithium” with successive cycling, on the other hand, has been relatively unexplored as the deterioration in performance is gradual. Dead lithium is the fragment of lithium that is detached from the lithium electrode during electrodissolution or stripping. In this study, the mesoscale underpinnings of dead lithium formation via a synergistic computational and experimental approach are presented. The mechanistic focus centers on the morphological evolution of the lithium electrode–electrolyte interface and the relative quantification of dead lithium formation under a range of operating temperatures and currents. This study reveals that the amount of dead lithium formed during stripping increases with decreasing current and increasing temperatures. This finding is in direct contrast to the operating conditions that lead to dendritic deposition during charging, i.e., at higher currents and lower temperatures. During stripping, more dead lithium is formed when the interface has thin narrow structures. The ionic diffusion and self-diffusion of lithium at the interface play a key role in the evolution of narrow structures at the interface. Therefore, more dead lithium is formed when diffusive processes are facilitated compared to the oxidative reaction at the interface.