High pressure metal-silicate partitioning of Ni, Co, V, Cr, Si, and O, Geochimica et Cosmochimica Acta (2015), doi: http://dx.High pressure metal-silicate partitioning of Ni, Co, V, Cr, Si, and O AbstractThe distributions of major and minor elements in Earth's core and mantle were primarily established by high pressure, high temperature metal-silicate partitioning during core segregation. The partitioning behaviors of moderately siderophile elements can be used to constrain the pressure-temperature conditions of core formation and the 2 core's composition. We performed experiments to study the partitioning of Ni, Co, V, Cr, Si, and O between silicate melt and Fe-rich metallic melt in a multianvil press and diamond anvil cell, up to 100 GPa and 5700 K. Combining our new results with data from 18 previous studies, we parameterized the effects of pressure, temperature, and metallic melt composition on partitioning. Ni and Co partitioning are insensitive to composition. At low pressures, these elements become less siderophile with increasing temperature, with this trend reversing above ~45 GPa. V and Cr partitioning are much more sensitive to metallic melt composition and less sensitive to pressure. Partitioning of Si and O are insensitive to pressure, but with strong and moderate temperature dependences, respectively. Our new parameterizations of Ni and Co partitioning suggest that the Earth's distributions of these elements can be matched by single-stage coremantle equilibration at 54 ± 5 GPa and 3300-3400 K. These conditions would result in 8.5 ± 1.4 wt% Si and 1.6 ± 0.3 wt% O in the core, compatible with the core's measured density. However, this single-stage model matches the Earth's V and Cr distributions less well. We also incorporated our parameterizations into models of multi-stage core formation over evolving pressure-temperature-oxygen fugacity conditions, reproducing the Earth's Ni and Co distributions while simultaneously producing a core whose light element composition is consistent with its density.

The intercalation of solvated sodium ions into graphite from ether electrolytes was recently discovered to be a surprisingly reversible process. The mechanisms of this “cointercalation reaction” are poorly understood and commonly accepted design criteria for graphite intercalation electrodes do not seem to apply. The excellent reversibility despite the large volume expansion, the small polarization and the puzzling role of the solid electrolyte interphase (SEI) are particularly striking. Here, in situ electrochemical dilatometry, online electrochemical mass spectrometry (OEMS), a variety of other methods among scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) as well as theory to advance the understanding of this peculiar electrode reaction are used. The electrode periodically “breathes” by about 70–100% during cycling yet excellent reversibility is maintained. This is because the graphite particles exfoliate to crystalline platelets but do not delaminate. The speed at which the electrode breathes strongly depends on the state of discharge/charge. Below 0.5 V versus Na+/Na, the reaction behaves more pseudocapacitive than Faradaic. Despite the large volume changes, OEMS gas analysis shows that electrolyte decomposition is largely restricted to the first cycle only. Combined with TEM analysis and the electrochemical results, this suggests that the reaction is likely the first example of a SEI‐free graphite anode.

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Until now, descriptions of intracellular biomineralization of amorphous inclusions involving alkaline-earth metal (AEM) carbonates other than calcium have been confined exclusively to cyanobacteria (Couradeau et al., 2012). Here, we report the first evidence of the presence of intracellular amorphous granules of AEM carbonates (calcium, strontium, and barium) in unicellular eukaryotes. These inclusions, which we have named micropearls, show concentric and oscillatory zoning on a nanometric scale. They are widespread in certain eukaryote phytoplankters of Lake Geneva (Switzerland) and represent a previously unknown type of non-skeletal biomineralization, revealing an unexpected pathway in the geochemical cycle of AEMs. We have identified Tetraselmis cf. cordiformis (Chlorophyta, Prasinophyceae) as being responsible for the formation of one micropearl type containing strontium ([Ca,Sr]CO ), which we also found in a cultured strain of Tetraselmis cordiformis. A different flagellated eukaryotic cell forms barium-rich micropearls [(Ca,Ba)CO ]. The strontium and barium concentrations of both micropearl types are extremely high compared with the undersaturated water of Lake Geneva (the Ba/Ca ratio of the micropearls is up to 800,000 times higher than in the water). This can only be explained by a high biological pre-concentration of these elements. The particular characteristics of the micropearls, along with the presence of organic sulfur-containing compounds-associated with and surrounding the micropearls-strongly suggest the existence of a yet-unreported intracellular biomineralization pathway in eukaryotic micro-organisms.

This work reports the facile synthesis of a Sn-P composite combined with nitrogen doped hard carbon (NHC) obtained by ball-milling and its use as electrode material for sodium ion batteries (SIBs). The "Sn 4 P 3 "/NHC electrode (with nominal composition "Sn 4 P 3 ":NHC = 75:25 wt%) when coupled with a diglyme-based electrolyte rather than the most commonly employed carbonatebased systems, exhibits a reversible capacity of 550 mAh g electrode −1 at 50 mA g −1 and 440 mAh g electrode −1 over 500 cycles (83% capacity retention). Morphology and solid electrolyte interphase formation of cycled "Sn 4 P 3 "/NHC electrodes is studied via electron microscopy and X-ray photoelectron spectroscopy. The expansion of the electrode upon sodiation (300 mAh g electrode −1) is only about 12-14% as determined by in situ electrochemical dilatometry, giving a reasonable explanation for the excellent cycle life despite the conversion-type storage mechanism. In situ X-ray diffraction shows that the discharge product is Na 15 Sn 4. The formation of mostly amorphous Na 3 P is derived from the overall (electro)chemical reactions. Upon charge the formation of Sn is observed while amorphous P is derived, which are reversibly alloying with Na in the subsequent cycles. However, the formation of Sn 4 P 3 can be certainly excluded.

The electrode behavior of exfoliated MoS2 is studied in an all-solid-state lithium-ion battery. MoS2 nanosheets with a crystallite thickness of about 6 nm are synthesized by chemical exfoliation of bulk MoS2 and characterized by XRD, SEM, and TEM. MoS2 composite electrodes are obtained by uniaxial cold-pressing at 3 tons and contain 60 wt % MoS2, 30 wt % β-Li3PS4 solid electrolyte, and 10 wt % carbon black. Solid-state lithium-ion batteries are assembled using β-Li3PS4 as the solid electrolyte and a Li–In alloy as the counter electrode. The electrode performance is well above state-of-the-art with an initial specific capacity of about 439 mAh g–1 when discharged at 67 mA g–1 (C/10) in the potential range of 0.01–3.0 V. The initial irreversible capacity is only 9%. The specific capacity retention is excellent with 312 mAh g–1 obtained after 500 cycles. In view of the theoretical capacity of MoS2 (q th = 670 mAh g–1), the solid-state reaction in the cell is incomplete; yet the end phases of the conversion reaction after discharge (Mo and Li2S) are confirmed by XRD. We also studied the behavior of bulk MoS2 (same mass loading) and found that the performance is inferior as compared to MoS2 nanosheets. The initial discharge capacity of bulk MoS2 is only 259 mAh g–1, and the initial irreversible capacity is as large as 26%. Overall, the study shows that MoS2 can be effectively cycled in all-solid-state batteries with β-Li3PS4 as solid electrolyte and that the electrode performance can be significantly improved by nanostructuring.