The implementation of all-solid-state batteries (ASSBs) is regarded as an important step toward next-generation energy storage systems, in particular for electric vehicles and portable electronics. This may be achieved through application of layered Ni-rich oxide cathode materials such as Li 1+x (Ni 1−y−z Co y Mn z ) 1−x O 2 (NCM) with high specific capacity and thiophosphate-based solid electrolytes. Here, the profound effect that the secondary particle size of the cathode active material has on the capacity of ASSB cells comprising NCM622 (60% Ni), β-Li 3 PS 4 , and In anode is demonstrated. We show the benefits of using small particles (d ≪ 10 μm), allowing virtually full charge capacity. This finding is rationalized through galvanostatic charge−discharge tests and complementary ex situ and operando X-ray diffraction experiments combined with Rietveld refinement analysis. Our results indicate the importance of considering and avoiding electrochemically inactive electrode material in bulk-type ASSBs, which we show using charge transport measurements is due to poor electronic contact (in carbon-free cathode composites).

Bulk-type all-solid-state batteries (SSBs) are receiving much attention as next-generation energy storage technology with potentially improved safety and higher power and energy densities (over a wider operating temperature range) compared to conventional Li-ion batteries (LIBs). However, practical implementation of SSBs faces a number of hurdles, such as issues related to interfacial stability between the solid electrolyte (SE) and other active and inactive electrode constituents. One approach to effectively prevent or mitigate side reactions at the positive electrode is through surface coating of the cathode material with a dielectric material. In this article, we report on the preparation of Li 2 CO 3 -and Li 2 CO 3 /LiNbO 3 -coated NCM622 (60% Ni) for application in pelletized SSB cells using β-Li 3 PS 4 as the SE. Specifically, we demonstrate that in contrast to state-of-the-art LIBs, the presence of surface carbonate contaminants helps improve the cell cyclability, and the combination of carbonate and niobate species in a kind of hybrid or solid-solution coating is particularly beneficial for achieving stable performance of Ni-rich NCM composite cathodes of practical loading (91% capacity retention after 100 cycles at a C/10 rate and 25 °C). This is in part because of the formation of robust interfaces in the cathode layer, strongly suppressing CO 2 evolution (because of decomposition of the relevant carbonate species) and the accompanied SO 2 formation and release during cycling operation.

Large-scale industrial application of all-solid-state-batteries (ASSBs) is currently hindered by numerous problems. Regarding thiophosphate-based ASSBs, interfacial reactions with the solid electrolyte are considered a major reason for capacity fading. On the positive electrode side, cathode active material coating addresses these issues and improves the ASSB performance. Yet, the working principle of the coating often remains unclear, and protection concepts on the way to long-term stable ASSBs remain empirical. In this work, we characterize the influence of a Li2CO3/LiNbO3 cathode active material coating on the battery performance and cathode degradation reactions of a Li4Ti5O12/Li6PS5Cl/Super C65|Li6PS5Cl|LiNi0.6Co0.2Mn0.2O2/Li6PS5Cl/Super C65 cell. The coating microstructure is characterized comprehensively using a combination of focused ion beam scanning electron microscopy (FIB-SEM), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Based on this knowledge, we demonstrate and discuss the positive effect of the coating on the ASSB performance. Finally, we present an in-depth post-mortem analysis of composite cathodes by combining XPS depth profiling with ToF-SIMS. The Li2CO3/LiNbO3 coating suppresses the interfacial reaction at the cathode active material/solid electrolyte interface, in particular, the formation of oxygenated phosphorous and sulfur compounds such as phosphates and sulfates/sulfites, leading to a significantly enhanced ASSB performance.

The formation of gaseous side products in liquid electrolyte-based lithium-ion batteries has been intensively studied in recent years and identified as being one of the sources of degradation (an indication of electrolyte and electrode instabilities). Herein, we demonstrate, to our knowledge for the first time, that gassing can also arise in all-solid-state battery cells made of Ni-rich layered oxide cathode materials and thiophosphate-based solid electrolytes. Combining isotopic labeling, titration for quantitative carbonate determination, and operando gas analysis, our findings reveal the evolution of CO2 stemming from carbonate species on the cathode surface as well as O2 from the bulk of the oxide cathode at potentials above 4.5 V with respect to Li+/Li, among others.

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.