Influence of a silver salt on the nanostructure of a Au(111)/ionic liquid interface: an atomic force microscopy study and theoretical concepts

In this article, we derive and discuss a physics-based model for impedance spectroscopy of lithium batteries. Our model for electrochemical cells with planar electrodes takes into account the solid-electrolyte interphase (SEI) as porous surface film. We present two improvements over standard impedance models. Firstly, our model is based on a consistent description of lithium transport through electrolyte and SEI. We use welldefined transport parameters, e.g., transference numbers, and consider convection of the center-of-mass. Secondly, we solve our model equations analytically and state the full transport parameter dependence of the impedance signals. Our consistent model results in an analytic expression for the cell impedance including bulk and surface processes. The impedance signals due to concentration polarizations highlight the importance of electrolyte convection in concentrated electrolytes. We simplify our expression for the complex impedance and compare it to common equivalent circuit models. Such simplified models are good approximations in concise parameter ranges. Finally, we compare our model with experiments of lithium metal electrodes and find large transference numbers for lithium ions. This analysis reveals that lithium-ion transport through the SEI has solid electrolyte character.

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“…(23), considering eqs. (16) and (18), and dividing by I. We find that Z is the sum of three distinct contributions…”

Section: Impedancementioning

confidence: 92%

Theory of Impedance Spectroscopy for Lithium Batteries

2019

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“…Eventually, at concentrations above 500 µM AgTFSA, the ordered structure collapses into a simple double layer. The developed thermodynamic continuum model, which treats the ionic liquid as being composed of hard spheres, could be successfully applied to describe the interfacial structure under the influence of Ag additives and to simulate the force-separation curves [119]. To summarize the investigations of metal additives in different ionic liquids, it can be concluded that, in general, the structured interface layer becomes distorted at high metal concentrations; however, at low and intermediate concentrations, a complex interplay with the metallic species and ionic liquid takes place such that each specific combination of additives and liquids must be considered independently.…”

Section: Addition Of Metallic Solvatesmentioning

confidence: 99%

Atomic Force Spectroscopy on Ionic Liquids

2019

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Ionic liquids have become of significant relevance in chemistry, as they can serve as environmentally-friendly solvents, electrolytes, and lubricants with bespoke properties. In particular for electrochemical applications, an understanding of the interface structure between the ionic liquid and an electrified interface is needed to model and optimize the reactions taking place on the solid surface. As with ionic liquids, the interplay between electrostatic forces and steric effects leads to an intrinsic heterogeneity, as the structure of the ionic liquid above an electrified interface cannot be described by the classical electrical double layer model. Instead, a layered solvation layer is present with a structure that depends on the material combination of the ionic liquid and substrate. In order to experimentally monitor this structure, atomic force spectroscopy (AFS) has become the method of choice. By measuring the force acting on a sharp microfabricated tip while approaching the surface in an ionic liquid, it has become possible to map the solvation layers with sub-nanometer resolution. In this review, we provide an overview of the AFS studies on ionic liquids published in recent years that illustrate how the interface is formed and how it can be modified by applying electrical potential or by adding impurities and solvents.

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“…The interfacial nanostructures were demonstrated to link to electrochemical performance of an IL/metal anode systems 21,22,23 ; the IL cation and anion chemistry was also found to have a dramatic effect on interfacial layering near the electrode surface 9,10,21,24,25 . The effect of salt concentration on interfacial nanostructures was also considered but with a focus on low to moderate salt concentration range 26,27,28 . From several recent studies 29,30,31,32 , we know that dendrite free metal anode cycling is possible in so-called 'superconcentrated' IL electrolytes (e.g.…”

mentioning

confidence: 99%

Engineering High Energy Density Sodium Battery Anodes for Improved Cycling with Superconcentrated Ionic Liquid Electrolytes

Rakov¹,

Chen²,

Ferdousi³

et al. 2020

Preprint

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<div> <div> <div> <p>Non-uniform metal deposition and dendrite formation in high density energy storage devices reduces the efficiency, safety, and life of batteries with metal anodes. Superconcentrated ionic liquid (IL) electrolytes (e.g. 1:1 IL:alkali ion) coupled with anode preconditioning at more negative potentials can completely mitigate these issues, and therefore revolutionize high density energy storage devices. However, the mechanisms by which very high salt concentration and preconditioning potential enable uniform metal deposition and prevent dendrite formation at the metal anode during cycling are poorly understood, and therefore not optimized. Here, we use </p> </div> </div> </div> <div> <div> <div> <p>atomic-force microscopy and molecular dynamics simulations to unravel the influence of these factors on the interface chemistry in a sodium electrolyte, demonstrating how a molten salt like structure at the electrode surface results in dendrite free metal cycling at higher rates. Such a structure will support the formation of a more favorable solid electrolyte interphase (SEI) accepted as being a critical factor in stable battery cycling. This new understanding will enable engineering of efficient anode electrodes by tuning interfacial nanostructure via salt concentration and high voltage preconditioning. </p> </div> </div> </div>

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Influence of a silver salt on the nanostructure of a Au(111)/ionic liquid interface: an atomic force microscopy study and theoretical concepts

Cited by 37 publications

References 61 publications

Theory of Impedance Spectroscopy for Lithium Batteries

Theory of Impedance Spectroscopy for Lithium Batteries

Atomic Force Spectroscopy on Ionic Liquids

Engineering High Energy Density Sodium Battery Anodes for Improved Cycling with Superconcentrated Ionic Liquid Electrolytes

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