The very high ionic conductivity of Li10GeP2S12 (LGPS) makes it a potential solid electrolyte for lithium all-solid-state batteries. Besides the high ionic conductivity, another key requirement is the stability of the solid electrolyte against degradation reactions with the electrodes; here, we analyze the reaction of LGPS with lithium metal. In situ X-ray photoelectron spectroscopy (XPS), in combination with time-resolved electrochemical measurements offers detailed information on the chemical reactions at the Li/LGPS interface. The decomposition of Li10GeP2S12 leads to the formation of an interphase composed of Li3P, Li2S, and Li–Ge alloy, which is in perfect agreement with theoretical predictions, and an increase of the interfacial resistance. These results highlight the necessity to perform long-term, time-resolved electrochemical measurements when evaluating potential new solid electrolytes for solid-state batteries. The kinetics of this interphase growthcomparable to SEI formation on lithium anodes in liquid electrolytesseems to be governed by diffusion across the interphase, as a square root time dependence is observed.

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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.

A detailed structural characterization is performed on β-Li3PS4 using 6Li and 31P magic-angle spinning NMR spectroscopy in combination with X-ray and neutron diffraction. High-temperature synchrotron X-ray diffraction was used to determine the phase stability and observe phase transitions. In addition, we investigated the Li+-ion dynamics by temperature-dependent 7Li NMR lineshape analysis, 7Li NMR relaxometry, and 7Li pulsed field-gradient (PFG) NMR measurements. A good agreement is obtained between the local hopping observed by T 1 relaxation time measurements and the long-range transport investigated by PFG NMR with a Li+ diffusion coefficient of 9 × 10–14 m2/s at 298 K and an activation energy of 0.24 eV. From this, a Li+ conductivity of 1.0 × 10–4 S/cm is estimated, which corresponds well with impedance measurements on β-Li3PS4 pellets.

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.