The pixel size in the SEM image can be as low as 5 nm, which determines the achievable resolution in the image, whereas the resolution through the thickness is determined by the FIB-milling depth. In the current study, we take high-resolution SEM images using the so-called electron immersion mode where electrons are caged in the imaging region. To enhance contrast, the polymer structure was stained with osmium tetroxide and then filled with epoxy. performed FIB-SEM on soft polymer MIP at the nano-scale 23.
Most previous studies investigated micro-scale pore structures. Furthermore, the pores in the SBE are very small, ranging from a few to hundreds of nanometers. In general, artifacts induced by FIB milling on such specimens are more conspicuous and can be compensated for in the analysis. These features cause issues such as curtaining, charging, and low contrast of images 19, 20, 21, 22, 23. However, FIB-SEM has not yet been applied to the SBE, which is more challenging since the SBE is a soft and non-conductive material. This technique has been successfully used in studies of different porous structures 16, 17, 18, 19, 20. Different phases are separated, and 3D voxel models are generated for the different phases. The obtained 2D image sequences are stacked in 3D space. High-resolution 2D images are then taken by SEM.
1 d battery serial#
Serial milling using FIB can be performed at the nanometer scale to expose the underlying microstructure. FIB-SEM is nowadays a well-established technique to obtain high-resolution 3D data. Instead, combined focused ion beam and scanning electron microscopy (FIB-SEM) is utilized. Its spatial resolution can be down to 50 nm, which is not sufficient to accurately capture the nano-scale pores in the SBE 15. X-ray computed tomography is a popular non-destructive method to obtain 3D structure information. Instead, a three-dimensional (3D) model is required to analyze the mechanical properties and ionic conductivity of the porous network via numerical simulations.
For a porous structure, traditional two-dimensional (2D) images from scanning electron microscopy (SEM) are not sufficient. This SBE structure offers a good compromise between ionic conductivity (~2 × 10 −4 S cm −1) and mechanical properties (elastic modulus of 540 MPa).įurther development of the SBE requires a deep understanding of its structure and an accompanying structure-property relationship analysis. The solid polymer backbone ensures the integrity of the entire structure, whereas the liquid electrolyte, which occupies the porous network structure, allows the transport of lithium ions. Its porous structure is formed by polymerization-induced phase separation (PIPS) reaction 14. In the recent structural battery, a bi-continuous polymer structural battery electrolyte (SBE) is used 4. Solid polymer electrolytes and gel electrolytes are not well fit in structural battery either, since their mechanical and electrochemical properties are highly antagonistic 13. However, their poor interfacial properties and fragility cause difficulties in practical use. Solid inorganic electrolytes have high ionic conductivity (>10 −4 S cm −1) and high elastic modulus (>1 GPa) 12. For the same reason, the liquid electrolyte in conventional lithium-ion batteries cannot be used and must be replaced by a mechanically robust, at least partly solid, electrolyte system. In the positive electrode, active material, e.g., lithium iron phosphate is coated on the carbon fiber that acts as a current collector and reinforcement 10, 11. In the negative electrode, carbon fibers are used as active material, i.e., host of lithium, current collector, and reinforcement 6, 9. Structural electrodes are generally utilizing carbon fibers 2, 8. In order to carry mechanical loads, the structural batteries must be of high stiffness. Replacing parts of the structural components in various applications, such as electric vehicles, the weight of the whole system is reduced 6, 7. With its combined energy storage and structural functions, the structural battery provides massless energy storage. The structural battery possesses an elastic modulus of 25 GPa and strength of 300 MPa and holds an energy density of 24 Wh kg −1. 4 and its integration in a multi-cell composite laminate 5. A successful example is a recently reported structural battery by Asp et al. Since carbon fiber is an excellent lightweight structural reinforcement material the structural battery composite inherits high mechanical properties 3. Structural battery composites are one type of lithium-ion batteries that employs carbon fiber as the negative electrode 2. Among them, the lithium-ion battery has rapidly developed into an important component of electric vehicles 1. Energy storage materials have gained wider attention in the past few years.
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