All-solid-state batteries (ASSBs) present a promising route towards safe and high power battery systems in order to meet the future demands in the consumer and automotive market. Composite cathodes are one way to boost the energy density of ASSBs compared to thin-film configurations. In this manuscript we investigate composites consisting of β-Li 3 PS 4 (β-LPS) solid electrolyte and high energy Li( Ni 0.6 Mn 0.2 Co 0.2 )O 2 (NMC622). The fabricated cells show a good cycle life with a satisfactory capacity retention. Still, the cathode utilization is below the values reported in the literature for systems with liquid electrolytes. Common understanding is that interface processes between the active material and solid electrolyte are responsible for the reduced performance. In order to throw some light on this topic, we perform 3D microstructureresolved simulations on virtual samples obtained via X-ray tomography. Through this approach we are able to correlate the composite microstructure with electrode performance and impedance. We identify the low electronic conductivity in the fully lithiated NMC622 as material inherent restriction preventing high cathode utilization. Moreover, we find that geometrical properties and morphological changes of the microstructure interact with the internal and external interfaces, significantly affecting the capacity retention at higher currents.

All-solid-state batteries promise to enable lithium metal anodes and outperform state-of-the-art lithium-ion battery technology. To achieve high battery capacity, utilization of the active material in the cathode must be maximized. Carbon-based conductive additives are known to improve the capacity and rate performance of electrode composites. However, their influence on cathode composites in all-solid-state batteries is yet not fully understood. Here, we study the influence of several carbon additives with different morphologies and surface areas on the performance of an all-solid-state battery cell Li|β-Li 3 PS 4 | Li(Ni 0.6 Co 0.2 Mn 0.2 )O 2 /β-Li 3 PS 4 /carbon. Cycling tests and microstructure-resolved simulations show that higher utilization of the cathode active material can be achieved using fiber-shaped vapor-grown carbon additives, whereas particle-shaped carbons show a minor influence. Unfortunately, carbon additives generally lead to an accelerated capacity loss during cycling and an enhanced formation of solid electrolyte decomposition products. The latter was studied in more detail using cyclic voltammetry, X-ray photoelectron spectroscopy, and cycling experiments. The results show that carbon additives with a small surface area and a fiber-like morphology result in the lowest degree of decomposition. To completely overcome electrolyte degradation caused by the use of carbon additives, a protection concept is developed. A thin alumina coating with a few nanometers thickness was deposited on the carbon fibers by atomic layer deposition, which successfully prevents decomposition reactions, reduces long-term capacity fading, and leads to an enhanced overall all-solid-state battery performance.

Lithium metal anodes are vital enablers for high-energy all-solid-state batteries (ASSBs). To promote ASSBs in practical applications, performance limitations such as the high lithium interface resistance and the grain boundary resistance in the solid electrolyte (SE) need to be understood and reduced by optimization of the cell design. In this work, we use our 3D microstructure-resolved simulation approach combined with a modified grain boundary transport model for the SE to shed some light on the aforementioned limitations in garnet ASSBs. Using high-resolution volume images of the SE electrode sample, we are able to reconstruct the SE microstructure. Using a grain segmentation algorithm, we further distinguish individual grains and account for the influence of the SE grain size and grain boundaries. We focus our simulation work on the trilayer cell architecture, consisting of two porous SE electrodes separated by a dense layer. Even though the highly porous SE electrodes reduce the lithium interface resistance by providing a higher active surface area, the increased electrode tortuosity also reduces the effective ionic conductivity in the SE. We confirm via impedance simulation studies and validation against experimental results that with increasing SE electrode porosity, the lithium transport becomes limited by grain boundaries. We also correlate the area-specific resistance to different lithium infiltration stages in the trilayer cell by spatially resolving the current density distribution. This analysis allows us to suggest a plausible deposition mechanism, and moreover, we identify current density hot spots in the proximity of the dense layer. These hot spots might lead to dendrite formation and long-term cell failure. The joint theoretical and experimental study gives guidelines for cell design and optimization which allow further improvement of the trilayer architecture.

Solid‐state batteries (SSBs) are promising candidates to significantly exceed the energy densities of today's state‐of‐the‐art technology, lithium‐ion batteries (LIBs). To enable this advancement, optimizing the solid electrolyte (SE) is the key. β‐Li3PS4 (β‐LPS) is the most studied member of the Li2S‐P2S5 family, offering promising properties for implementation in electric vehicles. In this work, the microstructure of this SE and how it influences the electrochemical performance are systematically investigated. To figure this out, four batches of β‐LPS electrolyte with different particle size, shape, and porosity are investigated in detail. It is found that differences in pellet porosities mostly originate from single‐particle intrinsic features and less from interparticle voids. Surprisingly, the β‐LPS electrolyte pellets with the highest porosity and larger particle size not only show the highest ionic conductivity (up to 0.049 mS cm–1 at RT), but also the most stable cycling performance in symmetrical Li cells. This behavior is traced back to the grain boundary resistance. Larger SE particles seem to be more attractive, as their grain boundary contribution is lower than that of denser pellets prepared using smaller β‐LPS particles.

All‐solid‐state batteries promise higher energy and power densities as well as increased safety compared to lithium‐ion batteries by using non‐flammable solid electrolytes and metallic lithium as the anode. Ensuring permanent and close contact between the components and individual particles is crucial for long‐term operation of a solid‐state cell. This study investigates the particle size dependent compression mechanics and ionic conductivity of the mechanically soft thiophosphate solid electrolyte tetragonal Li7SiPS8 (t‐LiSiPS) under pressure. The effect of stack and pelletizing pressure is demonstrated as a powerful tool to influence the microstructure and, hence, ionic conductivity of t‐LiSiPS. Heckel analysis for granular powder compression reveals distinct pressure regimes, which differently impact the Li ion conductivity. The pelletizing process is simulated using the discrete element method followed by finite volume analysis to disentangle the effects of pressure‐dependent microstructure evolution from atomistic activation volume effects. Furthermore, it is found that the relative density of a tablet is a weaker descriptor for the sample's impedance compared to the particle size distribution. The multiscale experimental and theoretical study thus captures both atomistic and microstructural effects of pressure on the ionic conductivity, thus emphasizing the importance of microstructure, particle size distribution and pressure control in solid electrolytes.

All-solid-state batteries promise higher energy and power densities as well as increased safety compared to lithium ion batteries, by using non-flammable solid electrolytes and metallic lithium as the anode. As the liquid electrolyte is replaced by a solid electrolyte, ensuring permanent and close contact between the various components as well as between the individual particles is key for the long-term operation of a solid-state cell. Currently, there are few studies on how a solid-state electrolyte behaves when compressed by external pressure. Here we present a study in which the compression mechanics and ionic conductivity evolution of the fast solid-state conductor Li7SiPS8 were investigated under pressure on two samples with different particle sizes. In operando electrochemical impedance spectroscopy under pressure allows the determination of the activation volume of Li7SiPS8. In addition to the experiments under pressure, we show that the determined ionic conductivity additionally depends on the contact pressure. Furthermore, we simulate pelletizing using the discrete element method followed by finite volume analysis, where the effect of the pressure dependent microstructure can be distinguished from the atomistic effect of the activation volume. We conclude not only that the pelletizing pressure is an important parameter for describing the ionic conductivity of a solid, but also the particle size and morphology as well as the contact pressure during the measurement affect the impedance of a solid tablet. Furthermore, the relative density of a tablet is a weaker descriptor for the sample's impedance, compared to the particle size distribution.

All-solid-state batteries (ASSB) are candidates for the next generation of high power- and energy storage systems. To reach their full potential, limiting factors like high interfacial resistances or decomposition of the electrolyte require further understanding and optimization. Porous 3D electrolyte networks, like the oxidic trilayer structures prepared by the authors, provide a much higher specific contact area between the electrolyte and the active materials [1]. The fabrication via a tape casting process allows for control of the porosity and sample thickness and is scalable to industrial production levels [2]. It was demonstrated that such a system allows for much higher current densities compared to a planar setup. Nevertheless, the critical influences of grain and grain boundaries on the cell performance and the lithium transport in these porous oxidic systems are still under investigation and not fully resolved. In this contribution, we investigate the lithium transport in porous garnet-type 3D electrolyte network consisting of Li7La2.75Ca0.25Zr1.75Nb0.25O12. The focus of our study is on the influence of grain and grain boundary effects. Our multi-scale approach consists of 3D microstructure-resolved simulations, which are supplemented by a thermodynamically consistent modeling framework [3,4]. The modeling framework enables us to provide additional microscopic interface- and bulk properties such as space charge layer effects, which are transferred as theory-based input parameters to our 3D microstructure-resolved simulations. The 3D simulations are performed directly on virtual microstructures reconstructed from FIB-SEM tomography measurements. In our study, we investigate samples with different porosity, thereby, our approach inherently incorporates the morphological features of the porous solid electrolyte. Moreover, we perform impedance simulations on the porous polycrystalline 3D electrolyte network. The simulations reproduce the experimental data and allow us to identify features in the corresponding impedance spectra. This approach enables us to analyze the correlation between grain size and garnet porosity on the cell impedance. In the final step, we virtually fill the porous electrolyte networks with metallic lithium corresponding to different state of charges during operation. Based on the impedance analysis, we evaluate the area specific resistance in our simulations and validate the results against experimental data. The current density distribution analysis allows identifying flux hot spots, which can serve as an indicator for dendrite growth [5]. The comparison between simulations and experiments demonstrates the importance of interfacial processes at the grain boundaries and gives directions for optimizing future oxide-based ASSBs. Acknowledgment This work was conducted as part of the US-German joint collaboration on "Interfaces and Interphases In Rechargeable Li-metal based Batteries” supported by the US Department of Energy (DOE) and German Federal Ministry of Education and Research (BMBF). Financial support was provided by BMBF under grant number 03XP0223E and DOE under grant number DEEE0008858. Reference s : [1] T. Hamann et al., Adv. Funct. Mater. 30 (2020) 1910362. [2] T. Hitz et al., Materials Today 22 (2019) 50-57. [3] A. Latz and J. Zausch, J. Power Sources 196 (2011) 3296-3302. [4] S. Braun et al., J. Phys. Chem. C 119 (2015) 22281-22288. [5] C.Tsai et al., ACS Appl. Mater. Interfaces 8 (2016) 10617-10626.

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