Mrs Bulletin最新文献

Global demand for batteries is increasing at a rapid pace, precipitating the equally rapid generation of hazardous battery waste. Recycling, which holds high potential for both mitigating this waste and recovering raw materials for subsequent battery manufacture, is often recognized as a necessary component of the battery life cycle. A critical step in many battery recycling schemes is the use of solvent to recover valuable metals such as lithium, cobalt, manganese, nickel, and others. This recovery typically involves the use of harsh mineral acids and peroxides, which pose their own environmental and safety hazards. The use of more benign organic acids and other organic compounds has emerged as a promising means to mitigate the hazards posed by purely inorganic solvents. In this article, we review recent research on organics-based metal recovery for battery recycling and provide our perspective on the extant challenges and opportunities in the field.

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Increasing demand for electric vehicles (EVs) is increasing demand for the permanent magnets that drive their motors, as approximately 80% of modern EV drivetrains rely on high-performance permanent magnets to convert electricity into torque. In turn, these high-performance permanent magnets rely on rare earth elements for their magnetic properties. These elements are “critical” (i.e., at risk of limiting the growth of renewable energy technologies such as EVs), which motivates an exploration for alternative materials. In this article, we overview the relevant fundamentals of permanent magnets, describe commercialized and emerging materials, and add perspective on future areas of research. Currently, the leading magnetic material for EV motors is Nd₂Fe₁₄B, with samarium-cobalt compounds (SmCo₅ and Sm₂Co₁₇) providing the only high-performing commercialized alternative. Emerging materials that address criticality concerns include Sm₂Fe₁₇N₃, Fe₁₆N₂, and the L1₀ structure of FeNi, which use lower cost elements that produce similar magnetic properties. However, these temperature-sensitive materials are incompatible with current metallurgical processing techniques. We provide perspective on how advances in low-temperature synthesis and processing science could unlock new classes of high-performing magnetic materials for a paradigm shift beyond rare earth-based magnets. In doing so, we explore the question: What magnetic materials will drive future EVs?

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Abstract

An oblique helicoidal state of a cholesteric liquid crystal (Ch_OH) is capable of continuous change of the pitch (P) in response to an applied electric field. Such a structure reflects 50% of the unpolarized light incident along the Ch_OH axis in the electrically tunable band determined by (P)/2. Here, we demonstrate that at an oblique incidence of light, Ch_OH reflects 100% of light of any polarization. This singlet band of total reflection is associated with the full pitch (P). We also describe the satellite (P/2), (P/3), and (P/4) bands. The (P/2) and (P/4) bands are triplets, whereas (P/3) band is a singlet caused by multiple scatterings at (P) and (P/2). A single Ch_OH cell acted upon by an electric field tunes all these bands in a very broad spectral range, from ultraviolet to infrared and beyond, thus representing a structural color device with enormous potential for optical and photonic applications.

Impact statement

Pigments, inks, and dyes produce colors by partially consuming the energy of light. In contrast, structural colors caused by interference and diffraction of light scattered at submicrometer length scales do not involve energy losses, which explains their widespread in Nature and the interest of researchers to develop mimicking materials. The grand challenge is to produce materials in which the structural colors could be dynamically tuned. Among the oldest known materials producing structural colors are cholesteric liquid crystals. Light causes coloration by selective Bragg reflection at the periodic helicoidal structure formed by cholesteric molecules. The cholesteric pitch and thus the color can be altered by chemical composition or by temperature, but, unfortunately, dynamic tuning by electromagnetic field has been elusive. Here, we demonstrate that a cholesteric material in a new oblique helicoidal Ch_OH state could produce total reflection of an obliquely incident light of any polarization. The material reflects 100% of light within a band that is continuously tunable by the electric field through the entire visible spectrum while preserving its maximum efficiency. Broad electric tunability of total reflection makes the Ch_OH material suitable for applications in energy-saving smart windows, transparent displays, communications, lasers, multispectral imaging, and virtual and augmented reality.

Graphical Abstract