40 September/October 2023 | E-Mobility Engineering particle size, and according to the lightscattering theory, the polarisation state of the scattered light is related to the particle shape. By calculating the spatial correlation of two consecutive scattering images in the 0o polarisation direction, the rate of intensity fluctuations in the scattered light can be determined, giving the particle size. Continuous measurements can provide multiple particle size measurement results, including the average value and the dispersion. By analysing the intensity of scattered light from four polarisation images in the 0, 45, 90 and 135o polarisation directions taken at the same time, the degree of linear polarisation – or optical sphericity – is obtained that gives the degree of approximation of particles to a sphere. A value of 1 indicates a perfect sphere, while a smaller value indicates a deviation from a sphere. Continuous measurements can provide the optical sphericity of the nanoparticles, giving the statistical shape distribution. This technique has been tested on spherical, octahedral, flat, rod-shaped, and filamentous nanoparticles. The results of particle size, morphology and distributions obtained from the PIDLS method were consistent with those obtained from electron microscopy. Cryo-EM Researchers in the US have used a technique from biological imaging to determine the structure of lithium crystals. Metallic lithium reacts so easily with chemicals that, under normal conditions, corrosion forms almost immediately while the metal is being laid down on a surface such as an electrode. Without that layer, lithium atoms assemble into a surprising shape — a 12-sided figure known as a rhombic dodecahedron. Many papers on lithium metal describe its crystal structure as ‘chunky’ or ‘column-like’, but looking at the true shape of the lithium crystals suggests that the explosion risk for lithium metal batteries can be reduced as the atoms accumulate in an orderly form. The researchers have developed a new technique for depositing lithium faster than corrosion forms. They ran current through a much smaller electrode without creating dendrite filaments, laying down lithium on surfaces using four different electrolytes, then comparing the results using cryoelectron microscopy, or cryo-EM. This technique uses electron beam imaging through frozen samples in order to show details down to the atomic level while inhibiting damage to the samples. It has been widely used to determine the structure of proteins and viruses, and several cryo-EM instruments have been customised to accommodate the types of samples used in materials research. Laser scribing Laser pulses have been used to modify the structure of a 2D material called MXene to boost its energy capacity for use as a battery material. MXenes are a fast-growing family of 2D transition metal carbides/nitrides, and hold promise for electronics and energy storage applications. Mo2CTx MXene in particular has demonstrated a higher capacity than other MXenes as an anode for lithiumion batteries. Graphite contains flat layers of carbon atoms, and during battery charging, lithium atoms are stored between these layers in a process called intercalation. MXenes also contain layers that can accommodate lithium, but these are made of transition metals such as titanium or molybdenum bonded to carbon or nitrogen atoms, which make the material highly conducting. The surfaces of the layers also feature additional atoms such as oxygen or fluorine. MXenes based on molybdenum carbide have particularly good lithium storage capacity, but their performance soon degrades after repeated chargedischarge cycles. This degradation is caused by a chemical change that Focus | Battery surface analysis Surface analysis was critical for developing a dry anode process (Courtesy of Oak Ridge National Laboratory)
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