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All-solid-state sodium batteries (ASSSBs) are promising candidates for grid-scale energy storage. However, there are no commercialized ASSSBs yet, in part due to the lack of a low-cost, simple-to-fabricate solid electrolyte (SE) with electrochemical stability towards Na metal. In this work, we report a family of oxysulfide glass SEs (Na3PS4-xOx, where 0

Surface lattice reconstruction is commonly observed in nickel-rich layered oxide battery cathode materials, causing unsatisfactory high-voltage cycling performance. However, the interplay of the surface chemistry and the bulk microstructure remains largely unexplored due to the intrinsic structural complexity and the lack of integrated diagnostic tools for a thorough investigation at complementary length scales. Herein, by combining nano-resolution X-ray probes in both soft and hard X-ray regimes, we demonstrate correlative surface chemical mapping and bulk microstructure imaging over a single charged LiNi0.8Mn0.1Co0.1O2 (NMC811) secondary particle. We reveal that the sub-particle regions with more micro cracks are associated with more severe surface degradation. A mechanism of mutual modulation between the surface chemistry and the bulk microstructure is formulated based on our experimental observations and finite element modeling. Such a surface-to-bulk reaction coupling effect is fundamentally important for the design of the next generation battery cathode materials.

Background: To address some challenges that the large lecture-focused courses have faced in higher education, the flipped classroom model was implemented in mechanical engineering. The purpose of the study was to investigate mechanical engineering undergraduate students' performance in the flipped classroom. A comprehensive analysis was conducted to investigate the pedagogical benefits of active learning in the flipped classroom from a self-determination theory perspective. To evaluate the effectiveness of the flipped classroom, students' academic achievements in the flipped classroom were compared with the ones in the traditional lecture format. Moreover, to explore in-depth students' learning experiences and their perceptions about the flipped classroom, students' open-ended surveys were analyzed. Results: Results demonstrated that students in the flipped classroom performed better and favored the new model, feeling that flipped classroom was useful and helpful in preparing for the course. The qualitative findings showed that students felt that they benefited from the pre-week online lectures in the flipped classroom to prepare for the course. Conclusions: The current study shows that the flipped classroom model has the potential to create an autonomy-supportive learning environment and provide beneficial learning experiences. This study highlights the benefits of and future direction for implementing the flipped classroom in traditional mechanical engineering courses.

While Li ion batteries are intended to be operated within a mild temperature window, their structural and chemical complexity could lead to unanticipated local electrochemical events that could cause extreme temperature spikes, which, in turn, could trigger more undesired and sophisticated reactions in the system. Visualizing and understanding the response of battery electrode materials to thermal abuse conditions could potentially offer a knowledge basis for the prevention and mitigation of the safety hazards. Here we show a comprehensive investigation of thermally driven chemomechanical interplay in a Li0.5Ni0.6Mn0.2Co0.2O2 (charged NMC622) cathode material. We report that, at the early stage of the thermal abuse, oxygen release and internal Li migration occur concurrently, and are accompanied by mechanical disintegration at the mesoscale. At the later stage, Li protrusions are observed on the secondary particle surface due to the limited lithium solubility in non-layered lattices. The extraction of both oxygen and lithium from the host material at elevated temperature could influence the chemistry and safety at the cell level via rearrangement of the electron and ion diffusion pathways, reduction of the coulombic efficiency, and/or causing an internal short circuit that could provoke a thermal runaway.

Chemical and mechanical properties interplay on the nanometric scale and collectively govern the functionalities of battery materials. Understanding the relationship between the two can inform the design of battery materials with optimal chemomechanical properties for long-life lithium batteries. Herein, we report a mechanism of nanoscale mechanical breakdown in layered oxide cathode materials, originating from oxygen release at high states of charge under thermal abuse conditions. We observe that the mechanical breakdown of charged Li1- xNi0.4Mn0.4Co0.2O2 materials proceeds via a two-step pathway involving intergranular and intragranular crack formation. Owing to the oxygen release, sporadic phase transformations from the layered structure to the spinel and/or rocksalt structures introduce local stress, which initiates microcracks along grain boundaries and ultimately leads to the detachment of primary particles, i.e., intergranular crack formation. Furthermore, intragranular cracks (pores and exfoliations) form, likely due to the accumulation of oxygen vacancies and continuous phase transformations at the surfaces of primary particles. Finally, finite element modeling confirms our experimental observation that the crack formation is attributable to the formation of oxygen vacancies, oxygen release, and phase transformations. This study is designed to directly observe the chemomechanical behavior of layered oxide cathode materials and provides a chemical basis for strengthening primary and secondary particles by stabilizing the oxygen anions in the lattice.

It is of great importance to do research on the preparation and applications of the MgSi film as an ecological friendly semiconducting material. Semiconducting MgSi films were prepared by electron beam evaporation deposition of Mg film onto Si substrate and subsequent heat treatment. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize and analyse the obtained MgSi films. Effects of heat treatment temperature (300-700 °C) under Ar gas pressure (200 Pa) on the crystal structure and surface morphologies of MgSi films were investigated. The XRD results show that heat treatment at 400-500 °C for 4-5 h is the optimal heat treatment condition to prepare MgSi films by the diffusion between the Mg atoms and Si atoms, and high temperature treatment above 600 °C causes the decomposition of MgSi and the formation of MgO. The SEM images show that the surfaces of obtained films become smooth and compact with the increase in heat treatment temperature. However, significant differences on the surface of the films occur when heat temperature is above 600 °C because of the decomposition of MgSi phase and the formation of MgO phase. These experimental results are beneficial to the development of optoelectronic devices based on the MgSi films. [ABSTRACT FROM AUTHOR]

Abstract: Mg2Si films have been prepared by magnetron sputter deposition and thermal process. Metal Mg films of about 380 nm thickness were deposited first on Si (111) substrates by radio frequency (RF) magnetron sputtering at various sputtering powers, and subsequent annealing was performed in an argon atmosphere. The formation of Mg2Si films was clarified using X-ray diffraction (XRD), and the surface microstructure of the prepared Mg2Si films was characterized by scanning electron microscopy (SEM). The results showed that the strongest diffraction peaks of all the Mg2Si films prepared on Si (111) substrates were observed at 40.12°. When the RF sputtering power increased, there was a significant increase in the intensity of the diffraction peak. However, increasing the sputtering power further to 110W failed to yield further improvement in the intensity of the different peak. The optimal sputtering power is 100W for the preparation of the Mg2Si films under the present preparation conditions. SEM results indicted that the grain sizes increased with the increasing of the sputtering power. [Copyright &y& Elsevier]