All-solid-state lithium batteries have the potential to provide increased energy and power density compared to conventional lithium-ion batteries with a liquid electrolyte. The charge transport within solid electrolyte-based composite cathodes determines the C-rate capability and ultimately the overall performance of a solid-state cell, making it one of the key remaining challenges. In this study, the charge transport in composite cathodes composed of Li6PS5Cl and NCM-622 is analyzed and characterized in terms of the effective ionic and electronic partial conductivities. The correlations between these effective conductivities, the microstructure of the composite cathodes, and the all-solid-state cell performance are revealed. By quantifying these correlations, bottlenecks for charge transport in composite cathodes are identified and strategies to optimize the cell performance are developed. The optimization potential of these strategies is demonstrated exemplarily by tuning electronic and ionic charge transport pathways using high active material loadings and an adjusted solid electrolyte particle size, respectively. The results will help to further increase energy and power density of all-solid-state batteries.

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CAM) in its lithiated form, that is, as present in a discharged cell. In its delithiated form, when the cell is charged, it is the only cell component that is contributing to storing energy (in conjunction with a hypothetical in situ lithiumplated anode formed during charging), thus making it the material required to be present in large quantity to achieve a high-performing cell. All other components, which may be required for large scale processing, only decrease the specific energy of the cell and are, therefore, engineered to minimize their content without affecting the function of the cell. This is evident in the research efforts made to increase the CAM content in the cathode layer, decrease the separator thickness as much as possible, and the pursuit to plate lithium metal in situ (in "anode-free" cells, which are more correctly described as "zero excess lithium metal" cells) without the use of an anode active material. [4] Thus, the CAM type and content in the cell ultimately determine the maximum specific energy that the system can provide.Moreover, the CAM contributes a significant proportion to the overall cell costs, [5] hence the necessity of steady tailoring toward reduced costs and higher energy density. So far, CAM development has mainly targeted performance optimization with LEs in LIBs. For instance, cathode electrolyte interface (CEI) formation, [6] Solid-state batteries (SSBs) currently attract great attention as a potentially safe electrochemical high-energy storage concept. However, several issues still prevent SSBs from outperforming today's lithium-ion batteries based on liquid electrolytes. One major challenge is related to the design of cathode active materials (CAMs) that are compatible with the superionic solid electrolytes (SEs) of interest. This perspective, gives a brief overview of the required properties and possible challenges for inorganic CAMs employed in SSBs, and describes stateof-the art solutions. In particular, the issue of tailoring CAMs is structured into challenges arising on the cathode-, particle-, and interface-level, related to microstructural, (chemo-)mechanical, and (electro-)chemical interplay of CAMs with SEs, and finally guidelines for future CAM development for SSBs are proposed.

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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Solid‐state batteries with a lithium metal anode (LMA) are promising candidates for the next generation of energy storage systems with high energy and power density. However, successful implementation of the LMA requires deeper insight into the lithium metal–solid electrolyte (Li|SE) interface. Since lithium is highly reactive, reaction products form when it comes into contact with most solid electrolytes (SEs) and the resulting interphase can have detrimental effects on cell performance. To better understand the formation of interphases, Li|SE interfaces are studied with time‐of‐flight secondary‐ion mass spectrometry (ToF‐SIMS), which provides chemical information with high sensitivity in 2D as well as 3D and is a valuable complement to commonly used techniques. To investigate the interphase, lithium is deposited in situ on SE pellets either through lithium vapor deposition or electrochemical lithium plating. Subsequent depth profiling provides information about the stability of the Li|SE interface and about the microstructure of the formed interphase. At the Li|Li6PS5Cl interface of lithium metal with argyrodite‐type Li6PS5Cl, an apparently covering Li2S‐rich layer is found as major part of the interphase. Independent of the deposition method, a combination of ToF‐SIMS and atomic force microscopy indicates a thickness of about 250 nm for the Li2S‐rich interlayer.

Although tungsten trioxide (WO3) has been extensively studied since its electrochromic properties were first discovered, the mechanism responsible for the coloration or bleaching effect is still disputed. New insights into the coloration mechanism of electrochromic, nanocrystalline WO3 are provided in this paper by studying thin WO3 films combining the electrochemical and spectroscopic techniques. By employing in situ UV-Vis transmission spectroscopy at a fixed spectral band pass during electrochemical experiments, such as cyclic voltammetry, a two-step insertion process for both protons and lithium ions is identified, of which one step exhibits a significantly higher coloration efficiency than the other. To obtain a better understanding of the insertion process AxWO3 (A = H, Li,…) thin films were studied at different stages of intercalation using UV-Vis and X-ray photoelectron spectroscopy. The results show that the first step of the intercalation process represents the reduction from initial W(6+) to W(5+) and the second step the reduction of W(5+) to W(4+). We found that the blue coloration of this nanocrystalline tungsten trioxide is mainly due to the presence of W(4+) rather than that of W(5+).