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Polyethylene oxide (PEO)-based solid polymer electrolytes (SPEs) have good ionic conductivity and flexibility, and is a key component of all-solid-state lithium batteries (ASSLBs). Therefore, the mechanical integrity of PEO-based SPEs during cell operation needs to be urgently evaluated. Here, we conducted a series of tensile and shear adhesion performance tests on PEO16–LiTFSI electrolyte and LiFePO4 electrode adhesion samples at various temperatures and quenching rates. Based on the interface performance data and the elastic–viscoplastic material model of the PEO–LiTFSI electrolyte, a comprehensive electrochemical–mechanical model was established to analyze the stress in the cell and evaluate the mechanical integrity of the PEO16–LiTFSI electrolyte and SPE/cathode interface. The experimental results show that the adhesion strength of the SPE and cathode decreases significantly with increasing operating temperature and quenching rate. The simulation study indicates that the mechanical properties of the SPE can be fully utilized to a certain extent by increasing the quenching rate. In addition, appropriately increasing the operating temperature helps maintain the mechanical integrity of the SPE during cell operation. However, increasing the quenching rate and operating temperature will reduce the interface bonding properties between the SPE and the cathode, resulting in an increased probability of mechanical failure at the SPE/cathode interface. To suppress this negative effect, a design scheme to maintain the structural integrity of the PEO-based polymer electrolyte is proposed by using the C-rate and the SPE thickness as control parameters, which can assist in engineering design and safe operation of Li/PEO16–LiTFSI/LiFePO4 for ASSLBs. [ABSTRACT FROM AUTHOR]

The natural fibrous sepiolite is introduced into emulsion polymer isocyanate (EPI) consisting of aqueous vinyl acetate copolymer-based main component (MC) and polymeric methylene diisocyanate (pMDI) for the first time to prepare a high-performance, environmentally friendly, and cost-effective timber adhesive. We have studied the effect of the sepiolite content on the tensile stress-strain curves, dynamical mechanical properties, essential work of fracture of the cured glue layer, and the EPI bonding properties. In addition, we have also investigated the chemical group, fractional free volume, and morphology of EPI polymers with various sepiolite contents. The results indicate that adding sepiolite can significantly increase the tensile strength, elastic modulus, dynamic stiffness, and fracture toughness of cured EPI films. Remarkably, EPI-bonded structures exhibit superior resistance to compressive shear damage upon ageing in boiling water. For MC with 6.0–9.0 wt% sepiolite, only the addition of 10.0 wt% general pMDI crosslinker is required to achieve the JIS K6806 structural adhesive. The underlying enhancement mechanism is the significant hydrogen-bonding coupled chemical reaction capability of sepiolite for the available groups in the EPI system. [ABSTRACT FROM AUTHOR]

A novel method of combination of wavelet‐based boundary element method (WBEM) with frequency‐independent fundamental solutions is proposed to determine the band structures of fluid–solid phononic crystals (PCs) with square and triangular lattices. Integral equations established are based on the frequency‐independent fundamental solutions, which can avoid nonlinear eigenvalue problems and reduce computing time. Domain integral terms arising from the use of frequency‐independent fundamental solutions are handled with the radial integration method (RIM) and dual reciprocity method (DRM), respectively. The results show the lower precision in high frequency domain of using RIM to handle domain integral terms than that of using DRM, which can be solved by increasing Gauss point. The B‐spline wavelet on the interval and wavelet coefficients are applied to approximate the physical boundary conditions. It is proved that coupling conditions between matrix and scatterers and Bloch theorem are also applicable to wavelet coefficients. Some small matrix entries generated by wavelet vanishing moment characteristics are truncated by the provided matrix compression technique, and the influence of compressed matrices on the results is studied. Furthermore, the final Eigen equations constructed are modified to avoid numerical instability. Some examples are provided to demonstrate the accuracy and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

The drying rate would significantly affect the quality of the composite electrode after solidification. In order to clarify the underlying effect mechanism of ingredient heterogeneity in the electrode caused by the drying process on the mechanical integrity of lithium secondary batteries in service, an integrated analysis approach is developed to determine the mechanical properties and lithium diffusion-induced stress of the composite electrode with gradient distributed binder and conductive agent. A faster solidification is found to broaden the inhomogeneous extent of inactive components in the electrode coating across its thickness, markedly. As a result, it will not only enlarge the tensile stress in the brittle electrode upon electrochemical operation due to the increased effective modulus of composite near the surface, but will also impair the interfacial strength between the active layer and current collector. Moreover, a two-stage drying protocol (initially fast, followed by slow evaporation of solvent) is found to be greatly beneficial to boosting the resistance to cohesion failure and surface damage of the composite electrode, and the optimized processing parameters are proposed to obtain a robust production with high efficiency. [ABSTRACT FROM AUTHOR]

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]