Halogen compounds are capable of playing an important role in the manipulation of nanoparticle shapes and properties. In a new approach, we examined the shape evolution of CdSe nanorods to hexagonal pyramids in a hotinjection synthesis under the influence of halogenated additives in the form of organic chlorine, bromine and iodine compounds. Supported by DFT calculations, this shape evolution is explained as a result of X-type ligand coordination to sloped and flat Cd-rich facets and an equilibrium shape strongly influenced by halides. Synchrotron XPS measurements and TXRF results show that the shape evolution is accompanied by a modification in the chemical composition of the ligand sphere. Our experimental results suggest that the molecular structure of the halogenated compound is related to the degree of the effect on both rod growth and further shape evolution. This presents a new degree of freedom in nanoparticle shape control and highlights the role of additives in nanoparticle synthesis and their possible in situ formation of ligands.

No abstract

No abstract

The high-voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) spinel is a promising material for high-energy battery applications, despite problems of capacity fade. This is due in part to transition metal leaching that produces chemical and morphological inhomogeneities. Using fast micro-X-ray fluorescence spectroscopy to scan the sample at medium spatial resolution (500 nm) over millimeter ranges, effects of cycling rate and state-of-charge on the elemental distribution (Ni and Mn) for LiNi 0.5 Mn 1.5 O 4 /carbon composite electrodes in LNMO/Li cells are visualized. Charge distribution is imaged by mapping the Ni oxidation state by acquisition of a stack of elemental maps in the vicinity of the Ni K edge. Our results show significant effects on morphology and elemental distribution, such as formation of elemental hot-spots and material erosion, becoming more pronounced at higher cycling rates. In nickel hot-spots, we observed hampered oxidation of nickel during charging. ■ INTRODUCTIONThe high-voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) spinel is a promising material for high-energy battery applications because of its high operation potential of ∼4.7 V versus Li + /Li 0 . However, this high potential lies outside the thermodynamic window of stability for conventional electrolyte solutions used in Li-ion batteries, and therefore presents a critical hurdle toward application. 1 As one result, oxidation of the electrolyte by the active material produces passivating products, causing reduced cycle life and capacity fade of the material. 2−4 Furthermore, Mn-containing phases such as the LiMn 2 O 4 spinel and also the LiNi 0.5 Mn 1.5 O 4 spinel are known to be susceptible to leaching of Mn 2+ and Ni 2+ to the electrolyte, 5 possibly as a consequence of the parasitic reactions with the electrolyte, 6,7 thereby causing elemental inhomogeneities in the electrodes. Formation of hydrofluoric acid, caused by trace amounts of water in the electrolyte, is regarded as one origin for this cathode corrosion. 8,9 The effect on capacity fade is especially pronounced in LNMO/graphite full cells, because of the detrimental contribution of the deposited 3d metals on the anode impacting the solid-electrolyte-interphase (SEI) growth on its surface. 2,10−13 The interplay between Ni and Mn cations leads to complex ordering effects, formation of secondary rock-salt structures, variable Mn 3+ content, and oxygen vacancies that all significantly influence electrochemical performance and are determined by the synthesis conditions. 6,14−16 Detailed investigations of the composition−structure relationship in LNMO spinel showed systematic deviations from the theoretical stoichiometry involving an excess of Mn. To compensate for the formation of excess Mn 3+ , formation of a rock-salt-type structure with a lower Mn/Ni ratio was observed. 17 A systematic study by Choi and Manthiram 5 on manganese dissolution into the electrolyte revealed a correlation with the Mn oxidation state, with samples containing initially more Mn 3+ being prone to the disproportionation reaction...

The characteristics of dried residues of picodroplets of single-, two-, and three-element aqueous solutions, which qualify these as reference materials in the direct analysis of single particles, single cells, and other microscopic objects using, e.g., laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOF-MS) and micro-X-ray fluorescence (MXRF), were evaluated. Different single-, two-, and three-element solutions (0.01-1 g/L) were prepared in picoliter volume (around 130 pL) with a thermal inkjet printing technique. An achievable dosing precision of 4-15% was calculated by total reflection X-ray fluorescence (TXRF) determination of the transferred elemental mass of an array of 100 droplets. The size of the dried residues was determined by optical microscopy to be 5-20 microm in diameter depending on the concentration and the surface material. The elemental distribution of the dried residues was determined with synchrotron micro-X-ray fluorescence (SR-MXRF) analyses. The MXRF results show high uniformity for element deposition of every single droplet with an RSTD of 4-6% depending on the concentration of spotted solution. The shape and height profile of dried residues from picoliter droplets were studied using atomic force microscopy (AFM). It was found that these dry to give symmetrical spherical segments with maximum heights of 1.7 microm. The potential of this technique for direct LA-ICP-TOF-MS analysis is shown.

No abstract

Lithium aluminum oxide has previously been identified to be a suitable compound to recover lithium (Li) from Li-ion battery recycling slags. Its formation is hampered in the presence of high concentrations of manganese (9 wt.% MnO2). In this study, mock-up slags of the system Li2O-CaO-SiO2-Al2O3-MgO-MnOx with up to 17 mol% MnO2-content were prepared. The manganese (Mn)-bearing phases were characterized with inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), electron probe microanalysis (EPMA), and X-ray absorption near edge structure analysis (XANES). The XRD results confirm the decrease of LiAlO2 phases from Mn-poor slags (7 mol% MnO2) to Mn-rich slags (17 mol% MnO2). The Mn-rich grains are predominantly present as idiomorphic and relatively large (>50 µm) crystals. XRD, EPMA and XANES suggest that manganese is present in the form of a spinel solid solution. The absence of light elements besides Li and O allowed to estimate the Li content in the Mn-rich grain, and to determine a generic stoichiometry of the spinel solid solution, i.e., (Li(2x)Mn2+(1−x))1+x(Al(2−z),Mn3+z)O4. The coefficients x and z were determined at several locations of the grain. It is shown that the aluminum concentration decreases, while the manganese concentration increases from the start (x: 0.27; z: 0.54) to the end (x: 0.34; z: 1.55) of the crystallization.

Synchrotron-radiation-induced total reflection x-ray fluorescence (SR-TXRF) analysis was used for x-ray absorption near edge structure (XANES) measurements for the speciation of arsenic in cucumber (Cucumis sativus L.) xylem sap. The objective of the presented work was to exploit the advantages of the TXRF geometry for XANES analysis. Measurements were accomplished at the bending magnet beamline L of HASYLAB, Hamburg, Germany, using a Si(111) double crystal monochromator and a silicon drift detector (SDD). Experiments were performed by growing cucumber plants in hydroponics containing arsenite [As(III)] or arsenate [As(V)] in order to identify the arsenic species of the collected xylem saps by K-edge SR-TXRF XANES. Cucumber xylem saps, as well as nutrient solutions containing arsenic in the two above-mentioned species, were analyzed and compared with arsenate and arsenite standard solutions. Arsenic speciation in xylem sap down to 30 ng/ml (30 ppb) was achieved, and no alteration of the oxidation state was observed during the measurements. Analysis of xylem saps showed that As(V) taken up from the nutrient solution was reduced to As(III). As(III) contained in the nutrient solutions was found to be partially oxidized to As(V). These results confirmed the preliminary measurements obtained with flow injection analysis (FIA) and high-performance liquid chromatography-high resolution inductively coupled plasma mass spectrometry (HPLC-HR-ICP-MS) and showed the competitive capability of SR-TXRF XANES analysis for this application.