All-solid-state batteries with sulfide solid electrolytes are promising next-generation energy storage devices owing to their longer lifetimes compared with liquid-type lithium-ion batteries. However, their practical application is hindered by low moisture stability. Few studies have quantitatively compared their moisture stability and underlying mechanisms among electrolyte species. This study systematically evaluates the moisture stability of sulfide solid electrolytes by standardizing particle size and varying electrolyte species, moisture content (dew point), and atmospheric conditions. Sulfide solid electrolytes with different crystal structures, such as Li₆PS₅Cl, Li₃PS₄, and Li₄SnS₄, were exposed to Ar gas flows with dew points from −30 to 0 °C (H₂O concentrations: 0.45–4.8 g m⁻³). H₂S generation followed the order: Li₆PS₅Cl ≫ Li₃PS₄ > Li₄SnS₄. At 0 °C dew point, H₂S gas release was ∼22.7 ml g⁻¹ for Li₆PS₅Cl, ∼0.44 ml g⁻¹ for Li₃PS₄, and ∼0.17 ml g⁻¹ for Li₄SnS₄. Despite variations in H₂S generation, lithium ionic conductivity retention was similar. X-ray photoelectron spectroscopy showed surface hydrolytic decomposition species were observed on Li₆PS₅Cl, whereas Li₃PS₄ and Li₄SnS₄ showed minimal changes. Thermogravimetric analysis revealed clearer hydration in Li₃PS₄ and Li₄SnS₄, causing lower ionic conductivity without H₂S generation. Differences in conductivity reduction are attributed to sulfide unit structures.

A machine learning model that can predict the ionic conductivity of lithium-containing oxides using chemical composition and ionic conductivity data was previously developed. However, this model revealed several limitations, leading to less-than-ideal prediction accuracy. Thus, new models demonstrating improved prediction ability must be developed. This study presents the development of machine learning models for the accurate prediction of ionic conductivity in lithium-containing materials based solely on their chemical composition. The models constructed using the NGBoost and LightGBM algorithms show high compatibility with the training and test data, resulting in high predictive accuracy. The constructed models identify “entropy,” which is considered a key factor in developing ionic conductors, as an important feature. This finding highlights the potential utility of this property from a solid-state chemistry perspective. The developed models demonstrate high predictive accuracy even for previously reported lithium superionic conductor-type materials that were not included in the training dataset. The established models are expected to facilitate efficient material discovery for the development of all-solid-state lithium batteries.

To extend the lifetime of lithium-ion batteries, determining the side-reaction current (I_SR) is essential because capacity fading is mainly caused by the state-of-charge imbalances of positive and negative electrodes. Among the three types of I_SR (intrinsic, additional, and actual), the additional I_SR resulting from crosstalk reactions exhibits complex behavior owing to its dependence on the opposing electrode. In this study, the effect of the opposing electrode on additional I_SR was examined by measuring the three types of I_SR in Li[Li_1/3Ti_5/3]O₄/Li[Li_0.1Al_0.1Mn_1.8]O₄ cells with different capacity ratios of the positive and negative electrodes. The results indicate that additional I_SR correlates with the weight of the opposing electrode, whereas intrinsic I_SR depends on the weight of each electrode. These findings suggest that additional I_SR is closely related to the amounts of side-reaction products generated at the opposing electrode owing to the intrinsic I_SR. The dependence of crosstalk reactions on the concentration of side-reaction products indicates that these concentrations must be considered to extend battery life by adjusting the actual I_SR.

The electrooxidative allylation of a carbamate was successfully demonstrated using 3-propylsulfonic acid-functionalized silica gel (Si-SCX-2). It was shown that the electrochemical oxidation of the carbamate as a first step yields the corresponding N-acyliminium ion equivalent at room temperature, and the reaction of the N-acyliminium ion equivalent with allyltrimethylsilane as a next step leads to allylation without the use of Lewis acids. It was also found that the HBF₄ generated by the cation exchange reaction between the Si-SCX-2 and the supporting electrolyte plays an important role in this reaction system.