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.
This article is titled “Moisture Stability of Sulfide Solid Electrolytes: Systematic Comparison and Mechanistic Insight” by Dr. Yusuke Morino et al. selected as an Editor’s Choice for the 71st Special Feature, “New Progress of Batteries and Fuel Cells” recommended jointly by the guest editors from The Committee of Battery Technology and the editorial board. In this article, the authors systematically investigate the moisture stability of various sulfide solid electrolytes (SEs) and elucidate distinct mechanisms responsible for the degradation of lithium ionic conductivity upon exposure to moisture. A quantitative comparison was conducted for SEs with different crystal structures, including Li6PS5Cl, Li3PS4, and Li4SnS4, in order to offer a more comprehensive understanding of their respective degradation behaviors. This comparative study revealed that the SEs undergo two different degradation pathways: hydrolysis and hydration. Notably, both Li3PS4 and Li4SnS4 exhibited a comparable decline in lithium ionic conductivity to that of Li6PS5Cl, despite generating significantly less H2S gas. This observation suggests that the underlying deterioration mechanisms differ among the materials.
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.
“Chemical Composition-Driven Machine Learning Models for Predicting Ionic Conductivity in Lithium-Containing Oxides” by Yudai Iwamizu et al. selected as an Editor’s Choice for the 71st Special Feature, “New Progress of Batteries and Fuel Cells” recommended jointly by the guest editors from The Committee of Battery Technology and the editorial board. In this article, the authors present machine learning models that predict the ionic conductivity of lithium-ion conductive solid oxide electrolytes based solely on their chemical composition. High ionic conductivity is essential for the development of high-performance all-solid-state batteries (ASSBs), making solid electrolytes a critical component. The proposed models, trained on over 2,200 data entries, significantly outperform previous approaches. Notably, configurational entropy emerged as a key feature in predicting ionic conductivity. The models also generalize well to previously unseen systems, facilitating the efficient discovery of promising solid electrolytes for ASSBs.
To extend the lifetime of lithium-ion batteries, determining the side-reaction current (ISR) is essential because capacity fading is mainly caused by the state-of-charge imbalances of positive and negative electrodes. Among the three types of ISR (intrinsic, additional, and actual), the additional ISR 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 ISR was examined by measuring the three types of ISR in Li[Li1/3Ti5/3]O4/Li[Li0.1Al0.1Mn1.8]O4 cells with different capacity ratios of the positive and negative electrodes. The results indicate that additional ISR correlates with the weight of the opposing electrode, whereas intrinsic ISR depends on the weight of each electrode. These findings suggest that additional ISR is closely related to the amounts of side-reaction products generated at the opposing electrode owing to the intrinsic ISR. 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 ISR.
“Measurement of Side-Reaction Currents in Lithium-Ion Batteries with Different Capacity Ratios” by Prof. Kingo Ariyoshi et al. selected as an Editor’s Choice for the 71st Special Feature, “New Progress of Batteries and Fuel Cells” recommended jointly by the guest editors from The Committee of Battery Technology and the editorial board. The side-reaction current (ISR) significantly contributes to capacity fading, primarily due to state-of-charge imbalances between the positive and negative electrodes in lithium-ion batteries. In this study, the authors conducted a detailed analysis of three types of ISR based on electrochemical behavior, using electrodes with different loadings and varying positive/negative capacity ratios. The results revealed that an additional ISR, caused by internal crosstalk within the battery, depends on the concentration of side-reaction products. Controlling this ISR by adjusting its magnitude is essential for extending battery life. This study provides valuable insights into strategies for improving the longevity of lithium-ion batteries.
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.
“Mechanistic Insights into Electrooxidative Allylation of a Carbamate in the Presence of Solid-Supported Acids” by Ms Haruka Homma et al. as an Editor’s Choice. In this work, the authors successfully demonstrated electrooxidative carbon–carbon bond formation of a carbamate with allyltrimethylsilane, aided by in-situ generated HBF4 species. Electrochemical oxidation of organic compounds is a highly promising strategy for generating reactive and versatile carbocations in organic synthesis. To effectively control subsequent nucleophilic reactions with these carbocations, the authors introduced a solid-supported acid, which generated HBF4 and promoted the desired C–C bond formation. Detailed mechanistic analysis revealed that in-situ generated HBF4 plays a crucial role in enabling carbon-carbon bond formation of a carbamate with allyltrimethylsilane.
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