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1.
ACS Appl Mater Interfaces ; 16(14): 18222-18235, 2024 Apr 10.
Artículo en Inglés | MEDLINE | ID: mdl-38547370

RESUMEN

The requirements for suitable electrolyte materials in solid-state batteries are diverse and vary greatly depending on their role as separator or as part of the composite cathode. Hybrid cell concepts that incorporate different types of solid electrolytes are considered a promising solution to overcome the limitations of single material classes. However, the kinetics at the heteroionic interface (i.e., charge transfer) substantially affects the cell performance. Moreover, non-ideal physical contacts hinder detailed electrochemical characterization of the interface properties. Thus, we use microstructure-resolved electric network computations to explore how the impedance response of a homogeneous bilayer system is influenced by the interface morphology and the material parameters of the single solid electrolyte layers. Porous interfaces and the resulting current constriction effects give rise to signatures in the impedance spectrum that resemble that of actual migration processes. This hinders unequivocal identification of the origin of the impedance contributions. The resistance and capacitance of this geometric interface signal depend strongly on the contact area and its spatial distribution, the pore capacitance, and the local conductivities around the interface. An experimental case study of an oxide-sulfide multilayer is considered to highlight the challenges in impedance analysis and the assessment of reliable material parameters. These findings are universal and apply to any heterojunction.

2.
ACS Appl Mater Interfaces ; 16(40): 54847-54863, 2024 Oct 09.
Artículo en Inglés | MEDLINE | ID: mdl-39316658

RESUMEN

Developing solid-state batteries (SSB) with a lithium metal electrode (LME) using only one type of solid electrolyte (SE) is a significant challenge since no SE fits all the requirements imposed by both electrodes. A possible solution is using multilayer SSBs with an LME where the drawbacks of each SE are overcome by using layers of different SEs. However, research on inorganic SE1|SE2 heteroionic interfaces is still quite preliminary, especially regarding oxide|sulfide heteroionic interfaces. This work reports the electrochemical investigation of the heteroionic interface between Li6.25Al0.25La3Zr2O12 (Al-LLZO) and two representative materials for sulfide-based SEs: argyrodite-based Li6PS5Cl (LPSCl) and glass-like Li7P3S11 (LPS711). Through in-depth temperature- and pressure-dependent impedance analyses of multilayer symmetric cells at equilibrium (i.e., no current load), the electrical properties of the heteroionic interfaces are assessed. The pressure-dependent kinetic of the Al-LLZO|LPSCl pair is interpreted with the concept of geometric constriction resistance and show that its resistance is lower than for the Al-LLZO|LPS711 pair. Furthermore, the effect of Al-LLZO surface treatment on the electrical properties of the Al-LLZO|LPSCl heteroionic interface is evaluated. Such investigation shows that the value of the interface activation energy decreases when the Al-LLZO surface is heat treated, revealing a significant influence of the carbonate/hydroxide passivation layer on the heteroionic interface. Additionally, by cycling the symmetric cell for 900 h at 1.0 mAh·cm-2, it is revealed that the Al-LLZO|LPSCl interface has a lower impedance increase than the Al-LLZO|LPS711 interface, especially if the Al-LLZO is heat treated. With this work, we highlight that the oxide|argyrodite combination can be a promising candidate for multilayer SSBs with an LME. However, we show that an optimized LLZO surface treatment and chemical analysis of the interface are recommended for future research.

3.
ACS Appl Mater Interfaces ; 16(33): 44236-44248, 2024 Aug 21.
Artículo en Inglés | MEDLINE | ID: mdl-39121451

RESUMEN

Hybrid battery cells that combine a garnet-type Li7La3Zr2O12 (LLZO) solid electrolyte with other solid, polymer or liquid electrolytes are increasingly investigated. In such cells with layered electrolytes, ensuring a low-resistive heteroionic interface between neighboring electrolytes is crucial for preventing major additional overpotentials during operation. Electrochemical impedance spectroscopy is frequently used to extract such parameters, usually on multilayer symmetrical model cells that contain the different electrolytes stacked in series. Unfortunately, the impedance contributions of the heteroionic interfaces often overlap with those of the electrolyte|electrode interfaces, necessitating the use of sophisticated four-point cells that probe the electrochemical potential away from the polarization source. In this work, an alternative solution to this problem is demonstrated by taking advantage of the inherent fast charge transfer kinetics of LLZO with its parent metal electrode. The "resistance-free" nature of a reversible Li|LLZO interface enables a precise evaluation of the heteroionic interface impedance in symmetric two-point cells of the type Li|LLZO|electrolyte|LLZO|Li with negligible electrode contribution. This is exemplified for symmetric multilayer cells containing tantalum-doped LLZO and a poly(ethylene oxide) (PEO)-based dry polymer electrolyte. Validation and comparison of impedance data with results from symmetric four-point cells and two-point cells with ion-blocking electrodes demonstrate the advantage of the proposed method. Overall, this study presents a simple and reliable method for studying heteroionic interface impedances in LLZO-containing multilayer cells.

4.
ACS Appl Mater Interfaces ; 15(29): 35332-35341, 2023 Jul 26.
Artículo en Inglés | MEDLINE | ID: mdl-37439760

RESUMEN

The unique architecture of ordered mesoporous oxides makes them a promising class of materials for various electrochemical applications, such as gas sensing or energy storage and conversion. The high accessibility of the internal surface allows tailoring of their electrochemical properties, e.g., by adjusting the pore size or surface functionalization, resulting in superior device performance compared to nanoparticles or disordered mesoporous counterparts. However, optimization of the mesoporous architecture requires reliable electrochemical characterization of the system. Unfortunately, the interplay between nanocrystalline grains, grain boundaries, and the open pore framework hinders a simple estimation of material-specific transport quantities by using impedance spectroscopy. Here, we use a 3D electric network model to elucidate the impact of the pore structure on the electrical transport properties of mesoporous thin films. It is demonstrated that the impedance response is dominated only by the geometric current constriction effect arising from the regular pore network. Estimating the effective conductivity from the total resistance and the electrode geometry, thus, differs by more than 1 order of magnitude from the material-specific conductivity of the solid mesoporous framework. A detailed analysis of computed impedances for varying pore size allows for the correlation of the effective conductivity with the material-specific conductivity. We derive an empirical expression that accounts for the porous structure of the thin films and allows a reliable determination of the material-specific conductivity with an error of less than 8%.

5.
ACS Appl Mater Interfaces ; 15(40): 47260-47277, 2023 Oct 11.
Artículo en Inglés | MEDLINE | ID: mdl-37751537

RESUMEN

Variants of garnet-type Li7La3Zr2O12 are being intensively studied as separator materials in solid-state battery research. The material-specific transport properties, such as bulk and grain boundary conductivity, are of prime interest and are mostly investigated by impedance spectroscopy. Data evaluation is usually based on the one-dimensional (1D) brick layer model, which assumes a homogeneous microstructure of identical grains. Real samples show microstructural inhomogeneities in grain size and porosity due to the complex behavior of grain growth in garnets that is very sensitive to the sintering protocol. However, the true microstructure is often omitted in impedance data analysis, hindering the interlaboratory reproducibility and comparability of results reported in the literature. Here, we use a combinatorial approach of structural analysis and three-dimensional (3D) transport modeling to explore the effects of microstructure on the derived material-specific properties of garnet-type ceramics. For this purpose, Al-doped Li7La3Zr2O12 pellets with different microstructures are fabricated and electrochemically characterized. A machine learning-assisted image segmentation approach is used for statistical analysis and quantification of the microstructural changes during sintering. A detailed analysis of transport through statistically modeled twin microstructures demonstrates that the transport parameters derived from a 1D brick layer model approach show uncertainties up to 150%, only due to variations in grain size. These uncertainties can be even larger in the presence of porosity. This study helps to better understand the role of the microstructure of polycrystalline electroceramics and its influence on experimental results.

6.
ACS Appl Mater Interfaces ; 14(31): 35545-35554, 2022 Aug 10.
Artículo en Inglés | MEDLINE | ID: mdl-35878322

RESUMEN

In an all-solid-state battery, the electrical contact between its individual components is of key relevance in addition to the electrochemical stability of its interfaces. Impedance spectroscopy is particularly suited for the non-destructive investigation of interfaces and of their stability under load. Establishing a valid correlation between microscopic processes and the macroscopic impedance signal, however, is challenging and prone to errors. Here, we use a 3D electric network model to systematically investigate the effect of various electrode/sample interface morphologies on the impedance spectrum. It is demonstrated that the interface impedance generally results from a charge transfer step and a geometric constriction contribution. The weights of both signals depend strongly on the material parameters as well as on the interface morphology. Dynamic constriction results from a non-ideal local contact, e.g., from pores or voids, which reduce the electrochemical active surface area only in a certain frequency range. Constriction effects dominate the interface behavior for systems with small charge transfer resistance like garnet-type solid electrolytes in contact with a lithium metal electrode. An in-depth analysis of the origin and the characteristics of the constriction phenomenon and their dependence on the interface morphology is conducted. The discussion of the constriction effect provides further insight into the processes at the microscopic level, which are, e.g., relevant in the case of reversible metal anodes.

7.
J Phys Condens Matter ; 34(32)2022 Jun 10.
Artículo en Inglés | MEDLINE | ID: mdl-35640589

RESUMEN

Disorder effects in alloys are usually modeled by averaging various supercell calculations considering different positions of the alloy atoms. This approach, however, is only possible as long as the portion of the individual components of the alloy is sufficiently large. Herein, we present anab initiostudy considering the lithium insertion material Li1-x[Ni0.33Co0.33Mn0.33]O2as model system to demonstrate the power of the coherent potential approximation within the Korringa-Kohn-Rostoker Green's function method. This approach enables the description of disorder effects within alloy systems of any composition. It is applied in this study to describe the (de-)intercalation of arbitrary amounts of lithium from the cathode active material. Moreover, we highlight that using either fully optimized structures or experimental lattice parameters and atomic positions both lead to comparable results. Our findings suggest that this approach is also suitable for modeling the electronic structure of state-of-the-art materials such as high-nickel alloys.

8.
ACS Appl Mater Interfaces ; 14(37): 42757-42769, 2022 Sep 21.
Artículo en Inglés | MEDLINE | ID: mdl-36075055

RESUMEN

A non-ideal contact at the electrode/solid electrolyte interface of a solid-state battery arising due to pores (voids) or inclusions results in a geometric constriction effect that severely deteriorates the electric transport properties of the battery cell. The lack of understanding of this phenomenon hinders the optimization process of novel components, such as reversible and high-rate metal anodes. Deeper insight into the constriction phenomenon is necessary to correctly monitor interface degradation and to accelerate the successful use of metal anodes in solid-state batteries. Here, we use a 3D electric network model to study the fundamentals of the constriction effect. Our findings suggest that dynamic constriction as a non-local effect cannot be captured by conventional 1D equivalent circuit models and that its electric behavior is not ad hoc predictable. It strongly depends on the interplay of the geometry of the interface causing the constriction and the microscopic transport processes in the adjacent phases. In the presence of constriction, the contribution from the non-ideal electrode/solid electrolyte interface to the impedance spectrum may exhibit two signals that cannot be explained when the porous interface is described by a physical-based (effective medium theory) 1D equivalent circuit model. In consequence, the widespread assumption of a single interface contribution to the experimental impedance spectrum may be entirely misleading and can cause serious misinterpretation.

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