All-solid-state lithium-ion batteries (ASSBs) are expected to represent a future alternative compared to conventional lithium-ion batteries with liquid electrolytes (LIBs). The excellent performance of today's LIBs relies to a large extent on the development of liquid electrolytes that form stable, or at least slowly degrading, interfaces (interphases) with both anodes and cathodes. This has not yet been achieved in ASSBs, and degradation of anode and cathode interfaces of solid electrolytes (SE) is one of the key issues to be solved. Unlike investigations of liquid/solid interfaces, the degradation of interfaces between the solid electrodes and the SE is challenging since (i) solid/solid interfaces are less easily accessed analytically, (ii) interface compounds may contribute only in very low concentrations to spectroscopic or spectrometric data, and (iii) a high spatial resolution is required to determine the local component distribution. Typically, solid/solid interface investigations are primarily based on electrochemical experiments, diffraction studies, electron microscopy, or on theoretical calculations to obtain sufficient information. Interestingly, the prospects of recent advanced analytical tools such as time-of-flight secondary-ion mass spectrometry (ToF-SIMS) are not fully exploited yet; therefore, we demonstrate in this paper that ToF-SIMS can provide valuable insights into the interphase composition and microstructure of ASSBs. For this purpose, we combine local compositional information from ToF-SIMS and complementary X-ray photoelectron spectroscopy measurements to characterize and visualize the degradation mechanism in the LiNi 0.6 Co 0.2 Mn 0.2 O 2 /Li 6 PS 5 Cl-composite cathode of an ASSB. Our results indicate that sulfates and phosphates play an important role in the formation of a solid electrolyte interface (SEI), whereas transition-metal chlorides, phosphides, and sulfides can be neglected. Furthermore, to the best of our knowledge, we show for the first time the local structure and morphology of the SEI layer on the basis of information about the chemical composition using ToF-SIMS analysis.

On the way to a large-scale industrial application of allsolid-state batteries (ASSBs) it is necessary to overcome a number of challenges. An important task is to maximize the utilization of active material in the cathode composite to achieve high capacities. Carbonbased conductive additives are common in cathode composites for conventional lithium-ion batteries based on liquid electrolytes. In allsolid-state batteries, the beneficial effect of carbon additives is often not maintained over a sufficient number of charge/discharge cycles. Thus, ASSB cells often suffer from an increased long-term capacity loss with an enhanced formation of decomposition products. So far, these effects have not been analyzed in depth and are not fully understood because of the complexity of the composite cathode structure. Together with overlap of the occurring degradation paths, this makes a separation of the individual decomposition processes challenging. In this work, we investigate the influence of vapor-grown carbon fibers as carbon-based conductive additives on the degradation of a LiNi 0.6 Co 0.2 Mn 0.2 O 2 /β-Li 3 PS 4 composite cathode. We use a combination of X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS) and combine surface and bulk analyses to separate the overlapping decomposition processes from each other. The results show an initially higher capacity by using vapor-grown carbon fibers due to higher utilization of the active material and an additional capacity contribution caused by redox-active decomposition reactions. The observed capacity fading is associated with the formation of sulfates/sulfites, phosphates, and polysulfides, which are detected directly in LiNi 0.6 Co 0.2 Mn 0.2 O 2 /β-Li 3 PS 4 composite cathodes with ToF-SIMS for the first time. Overall, the results extend the knowledge and understanding of degradation phenomena in thiophosphate-based composite cathodes considerably, which is an essential step to develop protection concepts more efficiently on the way to long-term stable ASSBs.

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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 first objective was to investigate new bone formation in a critical-size metaphyseal defect in the femur of ovariectomized rats filled with a strontium modified calcium phosphate cement (SrCPC) compared to calcium phosphate cement (CPC) and empty defects. Second, detection of strontium release from the materials as well as calcium and collagen mass distribution in the fracture defect should be targeted by time of flight secondary ion mass spectrometry (TOF-SIMS). 45 female Sprague-Dawley rats were randomly assigned to three different treatment groups: (1) SrCPC (n = 15), (2) CPC (n = 15), and (3) empty defect (n = 15). Bilateral ovariectomy was performed and three months after multi-deficient diet, the left femur of all animals underwent a 4 mm wedge-shaped metaphyseal osteotomy that was internally fixed with a T-shaped plate. The defect was then either filled with SrCPC or CPC or was left empty. After 6 weeks, histomorphometric analysis showed a statistically significant increase in bone formation of SrCPC compared to CPC (p = 0.005) and the empty defect (p = 0.002) in the former fracture defect zone. Furthermore, there was a statistically significant higher bone formation at the tissue-implant interface in the SrCPC group compared to the CPC group (p < 0.0001). These data were confirmed by immunohistochemistry revealing an increase in bone-morphogenic protein 2, osteocalcin and osteoprotegerin expression and a statistically significant higher gene expression of alkaline phosphatase, collagen10a1 and osteocalcin in the SrCPC group compared to CPC. TOF-SIMS analysis showed a high release of Sr from the SrCPC into the interface region in this area compared to CPC suggesting that improved bone formation is attributable to the released Sr from the SrCPC.