All-solid-state Li-ion batteries (ASSBs), considered to be potential next-generation energy storage devices, require solid electrolytes (SEs). Thiophosphate-based materials are popular, but these sulfides exhibit poor anodic stability and require specialty coatings on lithium metal oxide cathodes. Moreover, electrode designs aimed at high energy density are limited by their narrow electrochemical stability window. Here, we report new mixed-metal halide Li3–x M1–x Zr x Cl6 (M = Y, Er) SEs with high ionic conductivityup to 1.4 mS cm–1 at 25 °Cthat are stable to high voltage. Substitution of M (M = Y, Er) by Zr is accompanied by a trigonal-to-orthorhombic phase transition, and structure solution using combined neutron and single-crystal X-ray diffraction methods reveal a new framework. The employment of >4 V-class cathode materials without any protective coating is enabled by the high electrochemical oxidation stability of these halides. An ASSB showcasing their electrolyte properties exhibits very promising cycling stability up to 4.5 V at room temperature.
We report on a new family of argyrodite lithium superionic conductors, as solid solutions Li 6+x M x Sb 1−x S 5 I (M = Si, Ge, Sn), that exhibit superionic conductivity. These represent the first antimony argyrodites to date. Exploration of the series using a combination of single crystal X-ray and synchrotron/neutron powder diffraction, combined with impedance spectroscopy, reveals that an optimal degree of substitution (x), and substituent induces slight S 2− /I − anion site disorderbut more importantly drives Li + cation site disorder. The additional, delocalized Li-ion density is located in new high energy lattice sites that provide intermediate interstitial positions (local minima) for Li + diffusion and activate concerted ion migration, leading to a low activation energy of 0.25 eV. Excellent room temperature ionic conductivity of 14.8 mS•cm −1 is exhibited for cold-pressed pelletsup to 24 mS•cm −1 for sintered pelletsamong the highest values reported to date. This enables all-solid-state battery prototypes that exhibit promising properties. Furthermore, even at −78 °C, suitable bulk ionic conductivity of the electrolyte is retained (0.25 mS•cm −1 ). Selected thioantimonate iodides demonstrate good compatibility with Li metal, sustaining over 1000 h of Li stripping/plating at current densities up to 0.6 mA•cm −2 . The significantly enhanced Li ion conduction and lowered activation energy barrier with increasing site disorder reveals an important strategy toward the development of superionic conductors.
A new disordered chlorospinel superionic conductor, Li2Sc2/3Cl4, enables high-voltage all solid state batteries up to 4.6 V vs. Li+/Li.
Glyme-based electrolytes were studied for the use in lithium-air batteries because of their greater stability towards oxygen reduction reaction intermediates (e.g., superoxide anion radicals (O2˙(-))) produced upon discharge at the cathode compared to previously employed carbonate-based electrolytes. However, contradictory results of glyme stability tests employing KO2 as an O2˙(-) source were reported in the literature. For clarification, we investigated the reaction of KO2 with glymes of various chain lengths qualitatively using (1)H NMR and FTIR spectroscopy as well as more quantitatively using UV-Vis spectroscopy. During our experiments we found a huge impact of small quantities of impurities on the stability of the solvents. Therefore, we studied further the influence of impurities in the glymes on the cycling behavior of Li-O2 cells, demonstrating the large effect of electrolyte impurities on Li-O2 cell performance.
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.
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