Formation Of Space Charge Layer Research Articles

Stabilizing of Lithium-Solid-Electrolyte Interfaces by Atomic Layer Deposition Prepared Nano-Interlayers for a Model All-Solid-State Battery

To understand the electrochemistry of all-solid-state batteries (ASSBs), the use of electrochemical equivalent circuits with a physical meaning is essential. A model battery is needed whose characterization is independent of the influence of the complex battery assembly.Therefore, LICGC©, a model solid electrolyte is chosen that shows stability in air, but on the other hand is also well-known for its instability against metallic lithium upon direct contact. As a first step towards a model ASSB, the interface between lithium and the solid electrolyte (SE) is stabilized with thin (5 nm and 10 nm) coatings of titanium oxide (TO). Impedance data shows that symmetric cells with the TO coatings are protected from rapid SE surface degradation due to reducing lithium. Titanium oxide nano-interlayers can hence serve as a protective interlayer on the anode side of a model ASSB. Additionally, the formation of space charge layers (SCLs), which have been already documented for LICGC alone, appear once again at the interface between metal oxide interlayer and the solid electrolyte. The observed SCL thickness can reach up to ∼ 5 µm (cf. figure). Figure 1

Which Interfaces Matter Most? Variability in Grain Boundary Defect Chemistry and Conductivity in a Concentrated Solid Electrolyte

Inorganic solid electrolytes with fast ionic conductivity are critical components of fuel/electrolysis cells, all-solid-state batteries, membrane and separation reactors, sensors and other electrochemical devices. For example, solid oxygen ion (O2-) conductors are used in solid oxide fuel/electrolysis cells (SOFCs/SOECs) for high-efficiency conversion between chemical and electrical energy and chemical production from CO2. One major challenge in engineering such materials is the diminished grain boundary (GB) conductivity in polycrystalline oxide ceramics. This phenomenon, which was initially accredited to highly resistive silica-based glassy impurity phases, is attributed to the formation of intrinsic space charge layers (SCLs) directly adjacent to GB cores. The positive potential at the GB core (due to large concentrations of oxygen vacancies) results in a depletion of oxygen vacancies in the space charge layer as well as the segregation of charge-compensating acceptor solutes from grain interiors which ultimately reduces GB conductivity. Several strategies have been explored to improve GB conductivity by understanding and mitigating the SCL effects. While the standard Poisson–Boltzmann approach models the near-grain boundary defect behavior in dilute solid solutions and recent models by Mebane et al [1] and Virkant et al [2] incorporate the effects of defect-defect interactions (in concentrated solid solutions) and chemomechanical stress, respectively, there is yet to be a model developed that can predict individual GB conductivities in concentrated solid solutions based on direct experimental measurements of near-GB defect chemistry.Here, we present an experimental-computational framework that predicts which GBs in a polycrystalline electrolyte likely facilitate ionic conductivity. We developed a thermodynamic phase-field modeling framework and applied it to a model oxygen electrolyte Gd0.25Ce0.75O2-δ, wherein the GB-to-GB variability in defect concentrations (Gd3+ solutes, electrons localized at Ce3+, and oxygen vacancies) was measured microscopically using scanning transmission electron microscopy electron energy-loss spectroscopy (STEM EELS). These data were used to predict the GB-to-GB variability in cross-GB ionic conduction using a unique model, which prioritizes reproducing microscopically observed GB defect concentrations and considers defect-defect interactions in highly concentrated solid solutions, making the framework applicable to other technologically relevant solid electrolytes. Across the GBs studied, we revealed a non-monotonic relationship between depletion and GB conductivity, with the highest conductivity predicted for intermediate depletion amounts. This work lays the foundation for future experimental-computational research and advanced data-driven design of solid electrolytes needed for functional and energy storage/conversion devices.[1] D. S. Mebane, R. A. D. Souza, Energy & Environmental Science, 2015.[2] K. S. N. Vikrant, R. Edwin García, Energy & Environmental Science, 2018.[3] H. Vahidi, W.J. Bowman (Submitted). Acknowledgments HV and WJB acknowledge primary support from the UCI new faculty startup funding. This research was partially supported by the National Science Foundation Materials Research Science and Engineering Center program through the UC Irvine Center for Complex and Active Materials (DMR-2011967). We acknowledge the use of facilities and instrumentation at the UC Irvine Materials Research Institute (IMRI) supported in part by the same NSF MRSEC (DMR-2011967). AM, DM, and AC acknowledge funding from the NSF [WB1] [hv2] and the WVU MAE research department for the use of the Thorny Flat HPC Cluster for the numerical modeling work and computational resources.

Utilizing Data-Driven Optimization to Automate the Parametrization of Kinetic Monte Carlo Models.

Kinetic Monte Carlo (kMC) simulations are a popular tool to investigate the dynamic behavior of stochastic systems. However, one major limitation is their relatively high computational costs. In the last three decades, significant effort has been put into developing methodologies to make kMC more efficient, resulting in an enhanced runtime efficiency. Nevertheless, kMC models remain computationally expensive. This is in particular an issue in complex systems with several unknown input parameters where often most of the simulation time is required for finding a suitable parametrization. A potential route for automating the parametrization of kinetic Monte Carlo models arises from coupling kMC with a data-driven approach. In this work, we equip kinetic Monte Carlo simulations with a feedback loop consisting of Gaussian Processes (GPs) and Bayesian optimization (BO) to enable a systematic and data-efficient input parametrization. We utilize the results from fast-converging kMC simulations to construct a database for training a cheap-to-evaluate surrogate model based on Gaussian processes. Combining the surrogate model with a system-specific acquisition function enables us to apply Bayesian optimization for the guided prediction of suitable input parameters. Thus, the amount of trial simulation runs can be considerably reduced facilitating an efficient utilization of arbitrary kMC models. We showcase the effectiveness of our methodology for a physical process of growing industrial relevance: the space-charge layer formation in solid-state electrolytes as it occurs in all-solid-state batteries. Our data-driven approach requires only 1-2 iterations to reconstruct the input parameters from different baseline simulations within the training data set. Moreover, we show that the methodology is even capable of accurately extrapolating into regions outside the training data set which are computationally expensive for direct kMC simulation. Concluding, we demonstrate the high accuracy of the underlying surrogate model via a full parameter space investigation eventually making the original kMC simulation obsolete.

Interface Design Considering Intrinsic Properties of Dielectric Materials to Minimize Space‐Charge Layer Effect between Oxide Cathode and Sulfide Solid Electrolyte in All‐Solid‐State Batteries (Adv. Energy Mater. 37/2022)

All-Solid-State Batteries In article number 2201208, Woosuk Cho, Ki Jae Kim, and co-workers reveal the action mechanism of dielectric materials on the space-charge-layer (SCL) in sulfide-based all-solid-state batteries (ASSBs). The proposed paraelectric materials successfully mitigate SCL formation and accelerate lithium-ion transport, thereby allowing for the superior performances of the ASSBs and offering guidelines for enhancing the performance of electric vehicles.

Interface Design Considering Intrinsic Properties of Dielectric Materials to Minimize Space‐Charge Layer Effect between Oxide Cathode and Sulfide Solid Electrolyte in All‐Solid‐State Batteries

AbstractIntroducing dielectric materials is a promising approach to mitigate space‐charge‐layer (SCL) formation, which negatively affects the electrochemical performance of sulfide‐based all‐solid‐state batteries (ASSBs). Most previous studies have focused on mitigating SCL formation by introducing dielectric materials, overlooking the fact that significant dielectric properties such as the dipole moment direction and the magnitude of the dielectric constant can influence SCL formation. To clarify the unclear mechanism of dielectric materials mitigating SCL formation, paraelectricity, ferroelectricity, and the magnitude of the dielectric constant are investigated to determine their effect on SCL formation. Paraelectric materials possessing no permanent dipole moment can effectively mitigate the SCL formation better than ferroelectric material with strong permanent dipole moment because of the intrinsic characteristics of the paraelectric material, in which the dipole moment can be aligned along the direction of the electric field applied inside of ASSB. Furthermore, paraelectric materials with a larger dielectric constant have a greater effect in mitigating SCL effect than paraelectric materials with a smaller dielectric constant. Thus, these properties should be considered in cathode‐solid‐electrolyte interface design. This study considers relevant dielectric material characteristics that had not been considered previously, suggesting a new paradigm for optimizing the interfacial resistance of sulfide‐based ASSBs originating from SCL formation.

Effect of O/N doping in CNT aerogel film on their nucleic acid hybridization detection ability as electrochemical impedance biosensor

An emerging material CNT aerogel, mitigating nano-level properties of CNT into macro level, has been synthesized using scalable floating catalyst chemical vapor deposition and doped with oxygen/nitrogen via plasma treatment. The dopant leads to formation of a strong space charge layer due to the high surface wetting effect, which is unfavorable for DNA hybridization detection. Bare CNT aerogel showed best sequence selectivity for the detection of DNA hybridization. The present study showed existence of a critical trade-off between doping and presence of huge hydrophilic functional groups on CNT aerogel surface is detrimental for electrochemical impedance bio sensing performance.

Interfacial challenges in all-solid-state lithium batteries

This mini-review provides a current opinion on interfacial challenges in solid-state batteries (SSBs). We focus our discussion on the effects of mechanical instability, chemical instability, electrochemical instability, and space charge layer formation on the interfacial resistance of SSBs. We highlight that the resulting interfacial resistance of SSBs arises from the coupling of all these effects. Quantifying the exact contribution of each effect to the overall interfacial resistance can be very difficult, if not impossible, because all these effects occur simultaneously during battery operation, but the dominant source, which varies with different electrode/electrolyte combinations, will need to be determined for future development of SSBs.

Li+ Conductivity of Space Charge Layers Formed at Electrified Interfaces Between a Model Solid-State Electrolyte and Blocking Au-Electrodes.

The formation of space charge layers in solid-state ion conductors has been investigated as early as the 1980s. With the advent of all-solid-state batteries as an alternative to traditional Li-ion batteries, possibly improving performance and safety, the phenomenon of space charge formation caught the attention of researchers as a possible origin for the observed high interfacial resistance. Following classical space charge theory, such high resistances result from the formation of the depletion layers. These layers of up to hundreds of nanometers in thickness are almost free of mobile cations. With the prediction of a Debye-like screening effect, the thickness of the depletion layer is expected to scale with the square root of the absolute temperature. In this work, we studied the temperature dependence of the depletion layer properties in model solid Ohara LICGC Li+ conducting electrolytes using electrochemical impedance spectroscopy. We show that the activation energy inside the depletion layer increases to ca 0.42 eV compared to ca 0.39 eV in the bulk electrolyte. Moreover, the proportionality between temperature and depletion layer thickness, correlating to the Debye length, is tested and validated.

Investigation of the interaction of dense noble gas plasmas with cold cathodes: I—Experimental setup and application to Al, Cu, Ti, and graphite cathodes

AbstractThe formation of arc spots on cold cathodes, called arcing, is an interference factor in all kinds of plasma technical devices. It is investigated by igniting an arc in a clean atmospheric pressure Ar or Kr filling of a stainless steel vessel. It is brought into interaction by a magnetic blast field with a negatively biased commutation electrode (CE), formed by a rod with a diameter of 2 mm consisting of pure Al, Cu, Ti, or graphite; its end face is polished with diamond grinding powder. The arc commutation is observed by short‐time photography, streak camera records, and temporally highly resolved optical spectroscopy for different applied voltages. The emission of ion lines of the filling gas and of vaporized electrode material by the plasma in front of the cathode is indicating the formation of a positive space charge layer in front of its surface. It provides the ions, which induce secondary electron emission of the cathode surface and with it, the arc commutation. The commutation time tc elapsing between a signal generated by the arc plasma in front of the CE and the beginning of a current flow through the electrode increases for low voltages with increasing permittivity of a surface layer formed by electrically insulating metal oxide and decreases with increasing electrical conductivity of the layer. It is lowest for graphite without an oxide layer. On scanning electron microscope pictures, taken of the end face of the electrode after arc commutation, craters with diameters of less than 1 μm are visible.

Excellent Cathode Interfaces Achieved by Atomic/Molecualr Layer Depositions for Sulfide-Based All-Solid-State Batteries

All-solid-state Lithium batteries (ASSLBs) are attracting a large amount of attention due to the improved safety and high energy density compared with conventional liquid electrolyte-based Li-ion batteries (LIBs). Sulfide-based solid-state electrolytes (SSEs) exhibit ultrahigh ionic conductivity up to 10-2 S cm-1 at room temperature (RT). [1] However, the interface between sulfide SSEs and oxide cathode materials is considered unstable. The reason of the poor cathode interface stability is originated form the low oxidation potential of sulfide SSEs. This causes big chemical-potential gap between sulfides and oxide cathode materials, which would cause the formation of space-charge layer and increase the interfacial impedance. [1] Additionally, the low oxidation limit of sulfides leads to severe decomposition of SSEs at the cathode interface, thus affecting the interfacial Li+ transport. Designing coating materials for cathode particles is the most common strategy to alleviate the cathode interface problems. [2]Atomic/molecular layer deposition (ALD/MLD) is an advanced film fabricating technique, capable of tuning the interface property with atomic-level thickness control at relatively low temperature (< 400 oC). Compared with the conventional wet chemical method (e.g., sol-gel method), the ALD/MLD method can not only show the ability of developing Li-containing ternary oxides and organic coatings with uniform and conformal features, but also completely avoid the negative effects of using solvents and high-temperature treatments. [2-4] In our work, we employed ALD/MLD to elaborately design LiNbOx, LiZrOx, LiPOx, and PEDOT coating materials to solve the interface problem between sulfide SSEs and oxide cathode materials. [5-8] Ion-conducting and electron-insulating ALD coating layers can prevent the interfacial side reactions and improve the Li+ transport, while the semiconductor MLD layer can suppress the interfacial degradation. Therefore, excellent performance of sulfide-based ASSLBs was obtained. Ex/in-situ synchrotron X-ray characterizations (XANES, EXAFS, STXM) were used to analyze the local structure of ALD/MLD coatings and reveal the working mechanism of designed interfaces. The flexible design of functional cathode interface realized by ALD/MLD coatings paves the way to achieve advanced sulfide-based ASSLBs. Re ferences C. Yu, F. Zhao, X. Sun*, et al. Recent Development of lithium argyrodite solid-state electrolytes for solid-state batteries: synthesis, structure, stability and dynamics. Nano Energy 2021, 83, 105858.Y. Zhao, F. Zhao, X. Sun*, et al. Atomic/molecular layer deposition for energy storage and conversion. Chem. Soc. Rev., 2021, 50, 3889-3956.Y. Zhao, X. Sun*, et al. Addressing interfacial issues in liquid-based and solid-state batteries by atomic and molecular layer deposition, Joule 2018, 2, 2583-2604.Y. Zhao, X. Sun*. Molecular Layer Deposition for Energy Conversion and Storage, ACS Energy Lett. 2018, 3, 899-914.F. Zhao, X. Sun*, et al. Tuning bifunctional interface for advanced sulfide-based all-solid-state batteries. Energy Storage Mater. 2020, 33, 139-146.C. Wang, F. Zhao, X. Sun* et al. Manipulating Interfacial Nanostructure to Achieve High-Performance All-Solid-State Lithium-Ion Batteries, Small M e thods, 2019, 3, 1900261.S. Deng, X. Sun*, et al. Dual-functional interfaces for highly stable Ni-rich layered cathodes in sulfide all-solid-state batteries Energy Storage Mater. 2020, 27, 117-123.S. Deng, X. Sun*, et al. Eliminating the Detrimental Effects of Conductive Agents in Sulfide-Based Solid-State Batteries, ACS Energy Lett. 2020, 5, 1243-1251.

Structural Design of Composite Polymer Electrolytes for Solid‐state Lithium Metal Batteries

AbstractComposite polymer electrolytes with good safety and improved electrochemical performance have attracted widespread attention. However, the ion conduction ability at room temperature and interface compatibility between the electrolyte and electrode still face huge challenges, which greatly hinders the overall performance of solid‐state batteries. Therefore, the focus of this review is on the impact of the composite electrolyte structure on its ion conduction ability and interfacial compatibility, including physical contact of the electrolyte with electrodes, formation of lithium dendrites and space charge layer, adapting to high‐voltage cathode, as well as corresponding solving strategies. Moreover, the structural design‐based ion transport mechanism is highlighted, and the inorganic component with 0D, 1D, 2D, 3D and vertical structure are summarized. The purpose here is to outline the problems and challenges in structural design of composite electrolytes and their interfacial compatibility with various electrodes, allowing for target‐oriented research for high performance solid‐state lithium metal batteries.

Properties of the Space Charge Layers Formed in Li-Ion Conducting Glass Ceramics.

For years, the space charge layer formation in Li-conducting solid electrolytes and its relevance to so-called all solid-state batteries have been controversially discussed from experimental and theoretical perspectives. In this work, we observe the phenomenon of space charge layer formation using impedance spectroscopy at different electrode polarizations. We analyze the properties of these space charge layers using a physical equivalent circuit describing the response of the solid electrolytes and solid/solid electrified interfaces under blocking conditions. The elements corresponding to the interfacial layers are identified and analyzed with different electrode metals and applied biases. The effective thickness of the space charge layer was calculated to be ∼60 nm at a bias potential of 1 V. In addition, it was possible to estimate the relative permittivity of the electrolytes, specific resistance of the space charge layer, and the effective thickness of the electric double layer (∼0.7 nm).

In-situ visualization of the space-charge-layer effect on interfacial lithium-ion transport in all-solid-state batteries

The space charge layer (SCL) is generally considered one of the origins of the sluggish interfacial lithium-ion transport in all-solid-state lithium-ion batteries (ASSLIBs). However, in-situ visualization of the SCL effect on the interfacial lithium-ion transport in sulfide-based ASSLIBs is still a great challenge. Here, we directly observe the electrode/electrolyte interface lithium-ion accumulation resulting from the SCL by investigating the net-charge-density distribution across the high-voltage LiCoO2/argyrodite Li6PS5Cl interface using the in-situ differential phase contrast scanning transmission electron microscopy (DPC-STEM) technique. Moreover, we further demonstrate a built-in electric field and chemical potential coupling strategy to reduce the SCL formation and boost lithium-ion transport across the electrode/electrolyte interface by the in-situ DPC-STEM technique and finite element method simulations. Our findings will strikingly advance the fundamental scientific understanding of the SCL mechanism in ASSLIBs and shed light on rational electrode/electrolyte interface design for high-rate performance ASSLIBs.

A new perspective of co-doping and Nd segregation effect on proton stability and transportation in Y and Nd co-doped BaCeO3

Bulk and surface properties of proton stability and transportation in Y and Nd co-doped BaCeO3 (BCYN), especially the effect of Nd segregation, were investigated by first-principles calculations. Since the structure of doped BaCeO3 at the operating temperature of proton-conducting has been unclear for a long time, we have summarized the latest experimental results and calculated the structure of the asymmetric BCYN for the first time. The results show that compared with Y, Nd doping promotes oxygen vacancy formation, however reduces proton stability. Our calculation can also provide a possible explanation for the formation of space charge layer at the grain boundary of doped BaCeO3 in experiment. Unlike the stable Y in BCYN, Nd is calculated to be easily segregated, which can facilitate both proton hydration and proton transportation near the surface. Moreover, Nd segregation at the grain boundary is predicted to be beneficial for proton transportation between grains.

Accelerates High Temperature Oxidation due to the Change of Schottky’s Barrier Height of Cr2O3 Layer in Humid Condition

Development of the new generation of Ultra Supercritical (USC) power plant that has successfully achieved the targeted working temperature of 970 K. Nonetheless, increasing the operating temperature will further accelerate the high temperature oxidation of ferritic alloys of the boiler. Furthermore, water vapour in humid environment will make it easier for the alloy to further oxidize at high temperature. It is hypothesized that water vapour provides hydrogen that dissolves into the ferritic alloy susbstrate, hence altering their electronic state at the metal-semiconductor (oxide) interface. This study aims to measure Schottky Barrier Height (SBH) in dry and wet environment and relates it with acclerated oxidation behaviour. The Schottky Barrier was prepared by sputtering Cr2O3 onto the T91 boiler tube in high vacuum condition of 0.4 Pa, RF power 150W for an hour. The existance of Cr2O3 / Fe junction was confirmed by XRD analysis. The junction was then connected with platinum wire to act as the electrode for the current-voltage, I-V and capacitance-voltage, C-V test at high temperature. From the I-V graph, the reversed saturated current, Io was estimated and the SBH was calculated from the results. The SBH increased as the conductivity increased with the increment of temperature. From the C-V plots the value of Vbi was determined and used to calculate the SBH. The SBH increased with the increased of built in voltage. The result obtained from the two method agrees with one another. SBH value in wet condition is higher than that in dry condition. This is explained by the formation of space charge layer at metal/oxide interface due to dissolved hydrogen in metal, thus may change the transport property and accelerate the oxidation rate in water vapor.

AC conductivity, electrochemical and magnetic studies of CoWO4/PbWO4 nanocomposites

Structural, AC conductivity, electrochemical and magnetic properties of CoWO4 and CoWO4/PbWO4 nanocomposites are reported in the present manuscript. Structural characterization and HRTEM images of the nanocomposites confirm interface formation. Room temperature (RT) DC conductivity (σdc) calculated from Jonscher power law, carrier concentration (N) and carrier mobility (μ) of the interfaced sample with maximum agglomeration (P2) are 6.7 times, 3 orders and 4 orders higher than that of CoWO4 sample respectively. Enhanced AC conductivity is also observed for P2 sample. These enhanced properties of P2 sample are due to the space charge layer (SCL) formation at the interface. Conduction models for all the samples are explained in detail. The specific capacitance (calculated from GCD curve) of the CoWO4 sample is 2.1 times larger than the CoWO4/PbWO4 nanocomposite for 1 A/g of current density. Paramagnetic behaviour at (RT) and antiferromagnetic nature below the transition temperature (TN) are observed for all the samples.

Materials Informatics Screening of Li‐Rich Layered Oxide Cathode Materials with Enhanced Characteristics Using Synthesis Data

AbstractLithium‐ion batteries (LIBs) are the objects of active research and attract interest as important elements of near‐term energy storage technologies. The ever‐growing requirements for cathode materials of next‐generation LIBs impel the need to screen the materials with high energy and power densities, cycling stability, rate capability, safety and compatibility with other battery elements. This study is focused on Li‐rich layered oxide cathode materials as the materials candidates that are characterized by high energy density and large capacity and are therefore attractive as the potential solution for next‐generation LIBs whereas moderate structural stability hinders their commercialization. Machine learning‐assisted analysis of the collected experimental data has been performed for assessing the contribution of lattice doping, composition of compounds, the method and details of synthesis in the electrochemical characteristics. The possibility to relate parameters with the formation of a certain structure type (composite or solid solution), conceivable phase transformations and space charge layer formation are discussed. From this analysis, the features most probably amenable for electrochemical characteristics enhancement are distinguished and the focus area for further research is defined.

Multiscale modeling of the ionic conductivity of acceptor doped ceria

The ionic conductivity of acceptor doped ceria is strongly influenced by grain boundaries and interfaces, with most experiments showing a conductivity decrease in these regions. Classical models explain this observation by the formation of space charge layers, that are depleted of mobile ionic charge carriers. However, some experiments demonstrate an increase in ionic conductivity and recent models show that the space charge layers can also be enriched in mobile ionic species. Because of these discrepancies, it is still not certain whether nanocrystalline or thin film ceria can offer superior ionic conductivity or not. Recently, we have demonstrated by means of Monte Carlo simulations that the ionic conductivity in space charge layers can indeed exceed the bulk value. In this work, we combine these Monte Carlo simulations with a continuum model to predict charge carrier concentration profiles. This multiscale approach allows for a realistic prediction of the grain boundary ionic conductivity.

Electro-chemo-mechanical modeling of solid-state batteries

Solid-state batteries (SSBs) have recently been proposed as promising alternatives to conventional Li-ion batteries because of their high level of safety and power density. The engineering of SSBs requires comprehensive modeling of their physics and electrochemistry with an emphasis on the interfacial processes, including electrochemical stability and mechanical stresses. In this article, continuum-scale simulations are chosen as the modeling framework to study such properties. A comprehensive continuum model is constructed for the simulation of the electro-chemo-mechanical (ECM) response of an SSB that resolves the bulk transportation of charged species and their interfacial transfer kinetics. It also studies the formation of space charge layers (SCLs) at interfaces and the development of interfacial stresses. The results suggest that the SCLs and the charge transfer kinetics are intertwined. The emergence of the SCLs and the depletion of reactants increases the charge transfer overpotential. We have also studied the coupling between electrochemistry and mechanics at interfaces, the results of which indicate that the strong electric fields originating at interfaces yield significant stresses. We, thereby, highlight the necessity of considering the ECM coupling in the SCLs when modeling an SSB.

Investigating the Grain Boundary Transport and Resulting Effective Bulk Properties for Polycrystalline Solid Electrolytes

All-solid-state batteries (ASSB) are candidates for the next-generation of safe and high energy density storage systems. In order to reach the full potential in terms of energy and power density the current limiting processes on the microscopic interface level as well as the macroscopic cell level need to be overcome. In this contribution, we explore the working principle of ASSBs and their interfaces in a multi-scale approach. We combine our 3D microstructure-resolved simulation tool BEST [1,2] with a supplementary thermodynamically consistent modelling framework [3] to capture the electrochemical performance and gain insight on - homogeneous solid-solid interface processes. Through this combined approach we are able to provide additional microscopic interface and bulk properties which are transferred as theory-based input parameters to our 3D microstructure-resolved simulations. Our focus lies on the transport limiting phenomena occurring at the homogeneous solid-solid interface e.g. grain boundary resistance in the polycrystalline electrolyte. On the microscopic level we resolve the formation of space charge layers in the solid electrolyte under the influence of grains and grain boundaries. This local electrostatic perturbation of the system through the additional polarization of the crystal grain boundaries is approximated by a mean-field approach to derive an effective dielectric constant for the polycrystalline bulk solid electrolyte. The new effective material parameter depends on the magnitude of the induced polarization and therefore relies on the material specific parameters e.g. grain size, grain width, grain volume fraction. This approach provides a link between microscopic material parameters and macroscopic electrochemical transport phenomena on cell level. Besides the effective material parameter estimation of the system, the three dimensional resolved transport through the granular solid electrolyte e.g., the grain and grain boundary transport is of special interest. In order to account for the lithium ion hopping probability between two neighbouring particles we introduce a modified interface flux at the grain interfaces. By explicit modelling of the polycrystalline electrolyte, the experimentally observed impedance characteristics are reproduced and identified. In an extended study for oxidic garnet type systems the correlation between grain size and grain impedance as well as the varying transport properties between boundary and core phase are presented. The comparison between simulations and experiments demonstrates the importance of interfacial processes and gives directions for the development of future ASSBs.