Lithium-based batteries are a class of electrochemical energy storage devices where the potentiality of electrochemical impedance spectroscopy (EIS) for understanding the battery charge storage mechanisms is still to be fully exploited. Generally considered as an ancillary technique, the application of EIS should be promoted focusing on improved experimental design of experiments and advanced data analysis using physics-based models. Electrochemical impedance spectroscopy is a key technique for understanding Li-based battery processes. Here, the authors discuss the current state of the art, advantages and challenges of this technique, also giving an outlook for future developments.

Li insertion electrodes are made by pressing a mixture of active material and additives on a metallic substrate. Here we estimate how various interphase contacts affect the electrode kinetics. We apply variable external mechanical pressure onto different cathodes and measure their impedance response. Similar experiments are performed on dry composites in contact with: Al or Cu foil, or Ag paste. Most surprisingly, we find that the high-frequency impedance arc is due to the contact impedance between the metal and the electrode material. This is in fundamental contradiction with previous interpretations. We propose an equivalent circuit explaining the observed phenomena.

This review addresses concepts, approaches, tools, and outcomes of multiscale modeling used to design and optimize the current and next generation rechargeable battery cells. Different kinds of multiscale models are discussed and demystified with a particular emphasis on methodological aspects. The outcome is compared both to results of other modeling strategies as well as to the vast pool of experimental data available. Finally, the main challenges remaining and future developments are discussed.

Water electrolysis powered by renewables is regarded as the feasible route for the production of hydrogen, obtained at the cathode side through electrochemical hydrogen evolution reaction (HER). Herein, we present a rational strategy to improve the overall HER catalytic performance of Pt, which is known as the best monometallic catalyst for this reaction, by supporting it on a conductive titanium oxynitride (TiON _x ) dispersed over reduced graphene oxide nanoribbons. Characterization of the Pt/TiON _x composite revealed the presence of small Pt particles with diameters between 2 and 3 nm, which are well dispersed over the TiON _x support. The Pt/TiON _x nanocomposite exhibited improved HER activity and stability with respect to the Pt/C benchmark in an acid electrolyte, which was ascribed to the strong metal-support interaction (SMSI) triggered between the TiON _x support and grafted Pt nanoparticles. SMSI between TiON _x and Pt was evidenced by X-ray photoelectron spectroscopy (XPS) through a shift of the binding energies of the characteristic Pt 4f photoelectron lines with respect to Pt/C. Density functional theory (DFT) calculations confirmed the strong interaction between Pt nanoparticles and the TiON _x support. This strong interaction improves the stability of Pt nanoparticles and weakens the binding of chemisorbed H atoms thereon. Both of these effects may result in enhanced HER activity.

In the literature, the interpretation of electrochemical impedance spectra measured on insertion cathode materials is far from being unique. In most cases, various arbitrarily selected equivalent circuits have been used for analysis of spectra whereby the criterion of merit has mainly been the quality of fit. Herein, we propose a different approach. We try to explain the main features such as the high and medium frequency arcs and the low frequency diffusional tail using convenient (simplified) equivalent circuits derived from a quite general description of impedance due to a particulate (porous) system. The proposed models have a clear physical background. The meaning of selected circuit parameters is experimentally verified using carefully modeled experiments on and materials. In particular, we discuss the effects of state of charge, external pressure, electrode mass (thickness), and electrolyte concentration on the measured and simulated equivalent circuits. In the last part, we discuss in certain depth the complications arising from poor electronic or ionic contacting (wiring) between different phases constituting electrodes.