Abstract
Dendrite formation, which could cause a battery short circuit, occurs in batteries that contain lithium metal anodes. In order to suppress dendrite growth, the use of electrolytes with a ...high shear modulus is suggested as an ionic conductive separator in batteries. One promising candidate for this application is Li
7
La
3
Zr
2
O
12
(LLZO) because it has excellent mechanical properties and chemical stability. In this work, in situ scanning electron microscopy (SEM) technique was employed to monitor the interface behavior between lithium metal and LLZO electrolyte during cycling with pressure. Using the obtained SEM images, videos were created that show the inhomogeneous dissolution and deposition of lithium, which induce dendrite growth. The energy dispersive spectroscopy analyses of dendrites indicate the presence of Li, C, and O elements. Moreover, the cross-section mapping comparison of the LLZO shows the inhomogeneous distribution of La, Zr, and C after cycling that was caused by lithium loss near the Li electrode and possible side reactions. This work demonstrates the morphological and chemical evolution that occurs during cycling in a symmetrical Li–Li cell that contains LLZO. Although the superior mechanical properties of LLZO make it an excellent electrolyte candidate for batteries, the further improvement of the electrochemical stabilization of the garnet–lithium metal interface is suggested.
► Mg–1% Mn (M1) and M1–1.6% Sr (M1–1.6Sr) alloys were extruded at 300, 350 and 400°C. ► Extrusion at 300°C develops weaker texture in alloy M1 whereas extrusion at 350 and 400°C gives basal fiber ...texture in M1. ► Sr addition to alloy M1 results in randomization of texture due to particle stimulated nucleation (PSN) at all extrusion temperatures.
Alloys Mg–1% Mn (M1) and Mg–1% Mn–1.6Sr (M1–1.6Sr) were subjected to three extrusion temperatures of 300, 350 and 400°C at 8mm/s ram speed in order to investigate the texture evolution and recrystallization mechanisms. M1 alloy exhibits weaker texture after extrusion at 300°C, but develops strong basal texture at 350 and 400°C. The weaker texture of M1 at 300°C is partially due to random orientations created by CDRX mechanism. M1–1.6Sr alloy develops weaker textures at all extrusion temperatures as a result of particle stimulated nucleation promoted by Mg–Sr intermetallics which forms grains with random orientations.
•Effect of multiple femtosecond laser scans on stainless steel.•Ellipsoidal cones, columnar and chaotic structures observed on irradiated surface.•Chemical, crystallographic, and topographical ...analyses of ellipsoidal cones.•Developed mechanism for formation and growth of ellipsoidal cones.
The majority of studies performed on the formation of surface features by femtosecond laser radiation focuses on single scan procedures, i.e. manipulating the laser beam once over the target area to fabricate different surface topographies. In this work, the effect of scanning stainless steel 304 multiple times with femtosecond laser pulses is thoroughly investigated over a wide range of fluences. The resultant laser-induced surface topographies can be categorized into two different regimes. In the low fluence regime (FΣline,max<130J/cm2), ellipsoidal cones (randomly distributed surface protrusions covered by several layers of nanoparticles) are formed. Based on chemical, crystallographic, and topographical analyses, we conclude that these ellipsoidal cones are composed of unablated steel whose conical geometry offers a significant degree of fluence reduction (35–52%). Therefore, the rest of the irradiated area is preferentially ablated at a higher rate than the ellipsoidal cones. The second, or high fluence regime (FΣline,max>130J/cm2) consists of laser-induced surface patterns such as columnar and chaotic structures. Here, the surface topography showed little to no change even when the target was scanned repeatedly. This is in contrast to the ellipsoidal cones, which evolve and grow continuously as more laser passes are applied.
The structural evolution of carbon nanotubes (CNTs) during mechanical milling was investigated using SEM, TEM, XRD, XPS and Raman spectroscopy. The study showed that milling of the CNTs alone ...introduces defects but preserves the tubular structure. When milling the CNTs with aluminum (Al) powder in order to produce a composite, Raman spectroscopy has shown that most of the nanotubes are destroyed. During sintering of the CNT/Al milled mixture, the carbon atoms available from the destruction of the nanotubes react with the Al to form aluminum carbide (Al
4C
3). The effect of milling on the Al matrix was also studied.
Li-ion storage electrodes are manufactured through the conventional cast process involving the use of a toxic solvent (n-methyl-2- pyrrolidone, NMP) and the binder polyvinylidene fluoride (PVDF). ...This process can be problematic for nanosized materials as they form viscous suspensions that prevent the formation of uniformly dense coatings. Additionally, the NMP solvent is very hazardous. Herein lies the viability of using electrophoretic deposition (EPD) as an alternative manufacturing process that would both eliminate the need for a toxic solvent and improve electrode properties is presented. In particular, it is shown that styrene- butadiene rubber (SBR) enables the assembly of carbon-coated LTO and carbon nanoparticles into bridged hetero-aggregates that render themselves to fast growth of adherent highly performing LIB electrodes. The electrodes are built by suspending C-coated LTO, carbon, and SBR at 80/10/10 wt% ratio in a medium consisting of 90/10 vol% acetonitrile and water, performing 3–5 stages of 15-s constant current deposition cycles followed by pressing at 4 MPa and drying in a vacuum oven. Raman spectroscopy, thermogravimetric analysis (TGA), and energy-dispersive X-ray spectroscopy (EDS) with SEM were performed to examine carbon/LTO composite film homogeneity and compared to conventional PVDF-based electrodes. More importantly, photoemission electron microscopy (PEEM) and X-ray absorption near edge structure (XANES) were used to probe the presence/distribution of the SBR binder in the coating. The EPD-based electrode exhibits superior rate capability when compared to the PVDF-based electrodes. The conductivity, as shown by EIS, of the pressed EPD electrodes was 15 times higher than that of the pressed PVDF electrodes demonstrating the superiority of EPD in fabricating highly conductive electrodes for high-power LIB application.
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•Benign NMP-free electrode fabrication by electrophoretic deposition.•Non-toxic SBR binder enabling of C-coated LTO/Carbon Black bridged hetero-aggregates.•EDS-SEM and PEEM/XANES show excellent electrode film homogeneity.•EPD-built electrode's conductivity 15 times higher than that of conventional electrode.
Abstract
Lithium metal is a favorable anode material in all-solid Li-polymer batteries because of its high energy density. However, dendrite formation on lithium metal causes safety concerns. Here we ...obtain images of the Li-metal anode surface during cycling using in situ scanning electron microscopy. Constructing videos from the images enables us to monitor the failure mechanism of the battery. Our results show the formation of dendrites on the edge of the anode and isles of decomposed lithium bis(trifluoromethanesulfonyl)imide on the grain boundaries. Cycling at high rates results in the opening of the grain boundaries and depletion of lithium in the vicinity of the isles. We also observe changes in the surface morphology of the polymer close to the anode edge. Extrusion of lithium from these regions could be evidence of polymer reduction due to a local increase in temperature and thermal runaway assisting in dendrite formation.
Crack-free Hastelloy X fabricated through laser powder bed fusion (LPBF) from powder with a standard chemical composition is reported. Electron backscatter diffraction (EBSD) analysis evidenced ...columnar grains parallel to the building direction. The typical LPBF columnar dendrite microstructure was found to be finer than reported elsewhere. Mo-enriched carbides (~50 nm), presumed to play an important role in the cracking behavior of the alloy, were confirmed along interdendritic regions. Crack-free condition was maintained after heat treatment at 1177 °C for 1 h followed by water quenching, and the resulting microstructure was analyzed.
Scanning electron microscopy is widespread in field of material science and research, especially because of its high surface sensitivity due to the increased interactions of electrons with the target ...material’s atoms compared to X-ray-oriented methods. Among the available techniques in scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) is used to gather information regarding the crystallinity and the chemistry of crystalline and amorphous regions of a specimen. When post-processing the diffraction patterns or the image captured by the EBSD detector screen which was obtained in this manner, specific imaging contrasts are generated and can be used to understand some of the mechanisms involved in several imaging modes. In this manuscript, we reviewed the benefits of this procedure regarding topographic, compositional, diffraction, and magnetic domain contrasts. This work shows preliminary and encouraging results regarding the non-conventional use of the EBSD detector. The method is becoming viable with the advent of new EBSD camera technologies, allowing acquisition speed close to imaging rates. This method, named dark-field electron backscatter diffraction imaging, is described in detail, and several application examples are given in reflection as well as in transmission modes.
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