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Solid electrolyte interphase (SEI) is known to be heterogeneous which comprises inorganic and organic decomposition products. To assess the effects of heterogeneity on the stability of the SEI, we establish a mathematical model in simulating the stress of heterogeneous SEI. Comparing with the analytical solution of stress in the homogeneous film, the heterogeneity of SEI is identified to be essential in the stress calculation of the inorganic layer, which is proven decisive for the stability of SEI. Further, the peak tensile stress within the inorganic layer is found in the bilayer SEI. It generates at the interface between the active material and the inorganic layer when the battery is fully charged. In addition, the impacts of the interface parameter, modulus, Poisson's ratio, thickness of SEI and lithiation properties of active material on SEI stress are systematically investigated. Based on the simulation results, this work provides insights into the stress analysis of the heterogeneous SEI, as well as suggestions in pursuing a well-designed SEI, i.e., a functional gradient heterogeneous SEI in which the inner layer close to the active material provides sufficient mechanical performance while the outer layer near the electrolyte performs good chemical and electrochemical behaviors, to enhance the battery performance. [ABSTRACT FROM AUTHOR]

Abstract: Mesoporous silicas and Fe–SiO2 with worm-like structures have been synthesized using a room temperature ionic liquid, 1-hexadecane-3-methylimidazolium bromide, as a template at a high aging temperature (150–190°C) with the assistance of NaF. The hydrothermal stability of mesoporous silica was effectively improved by increasing the aging temperature and adding NaF to the synthesis gel. High hydrothermally stable mesoporous silica was obtained after being aged at 190°C in the presence of NaF, which endured the hydrothermal treatment in boiling water at least for 10d or steam treatment at 600°C for 6h. The ultra hydrothermal stability could be attributed to its high degree of polymerization of silicate. Furthermore, highly hydrothermal stable mesoporous Fe–SiO2 has been synthesized, which still remained its mesostructure after being hydrothermally treated at 100°C for 12d or steam-treated at 600°C for 6h. [Copyright &y& Elsevier]