The prospect of aqueous processing of Li-Ni x Mn y Co z O 2 (NMC) cathodes has significant appeal to battery manufacturers for the reduction in materials cost, toxicological risk, and environmental impact compared to conventional N-methyl-2pyrrolidone (NMP)-based processing. However, the effects of aqueous processing of NMC powders at industrial timescales are not well studied, with prior studies mostly focusing on relatively brief water washing processes. In this work, we investigate the bulk and surface impacts of extended aqueous processing of polycrystalline NMC powders with different compositions. We demonstrate that at timescales of several hours, polycrystalline NMC is susceptible to intergranular fracture, with the severity of fracture scaling with the NMC nickel content. While bulk crystallinity and composition are unchanged, surface sensitive techniques such as X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) indicate that the exposure of water leads to a level of delithiation, nickel reduction, and reconstruction from the layered to rock-salt structure at the surface of individual grains. Dynamic single NMC microparticle compression testing suggests that the resulting mechanical stresses weaken the integrity of the polycrystalline particle and increases susceptibility of intergranular fracture. The initially degraded surfaces along with the increased surface area lead to faster capacity fade and impedance growth during electrochemical cycling. From this work, it is demonstrated that NMC powders require surface or grain boundary modifications to make industrial-scale aqueous cathode processing viable, especially for next-generation nickel-rich NMC chemistries.
Combination of CuI and tetrahydrothiophene (THT) in MeCN or neat THT produces various phases depending upon experimental conditions. Green luminescent product (CuI)4(THT)2 (1) consists of Cu4I4 cubane units knit into a 3-D network by 2-THT ligands. Yellow luminescent (CuI)10(THT)7(MeCN) (2) contains {[Cu4I4(THT)](2-THT)2(Cu2I2)(2-THT)2[Cu4I4(NCMe)]} "rungs" linked into 1-D ladders by pairs of 2-THT ligands. Two molecular (CuI)4(THT)4 phases were found: 2 orange luminescent 3a and dull yellow luminescent 3b. Triclinic 3b is the more stable phase at 25 °C, but undergoes endothermic transformation to monoclinic 3a at 38 °C. 3a transforms to a triclinic phase (3a') that retains orange emission at −60 °C. Non-emissive (CuI)3(THT)3•MeCN (4) is a 2-D sheet structure in which Cu3(THT)3 rings are linked in trigonal directions by rhomboid Cu2I2 dimer units. The previously reported (CuI)2(THT)4 (5) is a molecular dimer. Temperature and mixing ratio domains for the formation of the CuI-THT phases from MeCN are presented. Luminescence in 1, 2, 3a, and 3b is rationalized based on varying degrees of halide-to-metal charge transfer (XMCT) and metal-centered (MC) behavior. Low temperature spectra reveal reversible changes, including modest red shifts for 1 and 2, and splitting into two excitation/emission band pairs for 3a and 3b.
Cold gas-dynamic spray is a solid-state materials consolidation technology that has experienced successful adoption within the coatings, remanufacturing and repair sectors of the advanced manufacturing community. As of late, cold spray has also emerged as a high deposition rate metal additive manufacturing method for structural and nonstructural applications. As cold spray enjoys wider recognition and adoption, the demand for versatile, high-throughput and significant methods of particulate feedstock as well consolidated materials characterization has also become more notable. In order to address the interest for such an instrument, nanoindentation is presented herein as a viable means of achieving the desired mechanical characterization abilities. In this work, conventionally static nanoindentation testing using both Berkovich and spherical indenter tips, as well as nanoindentation using the continuous stiffness measurement mode of testing, will be applied to a range of powder-based feedstocks and cold sprayed materials.
The role of high strain rate and severe plastic deformation, microstructure, electrochemical behavior, surface chemistry and surface roughness were characterized for two copper cold spray material consolidations, which were produced from conventionally gas-atomized copper powder as well as spray-dried copper feedstock, during the course of this work. The motivation underpinning this work centers upon the development of a more robust understanding of the microstructural features and properties of the conventional copper and nanostructured copper coatings as they relate to antipathogenic contact killing and inactivation applications. Prior work has demonstrated greater antipathogenic efficacy with respect to the nanostructured coating versus the conventional coating. Thus, microstructural analysis was performed in order to establish differences between the two coatings that their respective pathogen kill rates could be attributed to. Results from advanced laser-induced projectile impact testing, X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, scanning transmission microscopy, nanoindentation, energy-dispersive X-ray spectroscopy, nanoindentation, confocal microscopy, atomic force microscopy, linear polarization, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy and copper ion release assaying were performed during the course of this research.
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