Layered-structure nanoribbons with efficient electron transport and short lithium ion insertion lengths are promising candidates for Li battery applications. Here we studied at the single nanostructure level the chemical, structural, and electrical transformations of V2O5 nanoribbons. We found that transformation of V2O5 into the omega-Li3V2O5 phase depends not only on the width but also the thickness of the nanoribbons. Transformation can take place within 10 s in thin nanoribbons, suggesting a Li diffusion constant 3 orders of magnitude faster than in bulk materials, resulting in a significant increase in battery power density (360 C power rate). For the first time, complete delithiation of omega-Li3V2O5 back to the single-crystalline, pristine V2O5 nanoribbon was observed, indicating a 30% higher energy density. These new observations are attributed to the ability of facile strain relaxation and phase transformation at the nanoscale. In addition, efficient electronic transport can be maintained to charge a Li3V2O5 nanoribbon within less than 5 s. These exciting nanosize effects can be exploited to fabricate high-performance Li batteries for applications in electric and hybrid electric vehicles.

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We demonstrate that electrochemically etched, hydrogen capped Si n H x clusters with n larger than 20 are obtained within a family of discrete sizes. These sizes are 1.0 (Si 29 ), 1.67 (Si 123 ), 2.15, 2.9, and 3.7 nm in diameter. We characterize the particles via direct electron imaging, excitation and emission optical spectroscopy, and colloidal crystallization. The band gaps and emission bands are measured. The smallest four are ultrabright blue, green, yellow and red luminescent particles. The availability of discrete sizes and distinct emission in the red, green and blue ͑RGB͒ range is useful for biomedical tagging, RGB displays, and flash memories.

Structural and electronic investigations were conducted on lithium nickel oxide-based particles used in positive electrodes of 18650-type high-power Li-ion cells. K-edge X-ray absorption spectroscopy ͑XAS͒ revealed trivalent Ni and Co ions in the bulk LiNi 0.8 Co 0.2 O 2 powder used to prepare the high power electrode laminates. Using oxygen K-edge XAS, high resolution electron microscopy, nanoprobe diffraction, and electron energy-loss spectroscopy, we identified a Ͻ5 nm thick modified layer on the surface of the oxide particles, which results from the loss of Ni and Li ordering in the layered R3 m structure. This structural change was accompanied by oxygen loss and a lowering of the Ni-and Co-oxidation states in the surface layer. Growth of this surface layer may contribute to the impedance rise observed during accelerated aging of these Li-ion cells.The Li x Ni 1Ϫx O solid solutions form over a lithium concentration range of 0 р x р 0.5. 1-3 When lithium is added to NiO (x ϭ 0), conventional wisdom states that the Li ϩ charge compensation is achieved through the creation of Ni ϩ3 ions. The crystal structure of these solid solutions changes with x. For low x (0 р x р 0.3), lithium cations substitute randomly for nickel cations in the NiO lattice ͑NaCl-type structure͒. For x Ͼ 0.3, ordering of the Li and Ni ions starts in alternating cubic ͑111͒ planes culminating at x ϭ 0.5 in layered LiNiO 2 (␣-NaFeO 2 structure͒. The oxidation state of Ni has long been believed to be ϩ3 in LiNiO 2 -based compounds.Recent electronic structure investigations have, however, sparked a debate on the Ni oxidation states. Several spectroscopic and theoretical studies have concluded that hole states in Li x Ni 1Ϫx O compounds are localized predominantly at oxygen rather than at nickel, and that the charge compensating states are better described as O Ϫ rather than Ni ϩ3 ; that is, the nickel ions retain their ϩ2 character for all values of x. [4][5][6][7][8] In contrast, other researchers have affirmed the traditional view that Ni ϩ3 is present in LiNiO 2 -based compounds. 9-13 The charge-compensation debate achieves additional complexity when lithium is intercalated and deintercalated from these compounds. Several theoretical and ex situ experimental studies have indicated that the majority of the electron charge is accommodated by the oxygen anions during Li-ion cell cycling, [14][15][16][17][18][19] whereas other in situ experimental studies have indicated that the charge compensation occurs predominantly at the nickel sites. [11][12][13] An understanding of nickel oxidation states and electron charge compensation processes is critical for determining mechanisms that limit the calendar life and thermal abuse characteristics of high power Li-ion cells being developed for hybrid electric vehicle ͑HEV͒ applications as part of the Advanced Technology Development program in the United States. [20][21][22][23][24][25] In this program, the capacity and pulse power capabilities of ϳ1 Ah capacity, 18650-type ͑18 mm diam, 65 mm long͒ cells,...

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In this letter, we report an electron diffraction determination of chiral vectors (n,m) of individual single-wall carbon nanotubes (SWNTs). Electron diffraction patterns from individual SWNTs were recorded on imaging plates using a parallel electron beam over a section of tube of ∼50 nm long. Using two tubes of 1.39 and 3.77 nm in diameter, we show that the details of electron diffuse scattering can be detected for both the small and large tubes. The quality of diffraction patterns allows the accurate measurement of both the diameters and chiral angles of SWNTs for a direct determination of chiral vectors. The electron diffraction technique is general and applicable to other forms of individual nanostructures.

Frataxin is a conserved mitochondrial protein required for iron homeostasis. We showed previously that in the presence of ferrous iron recombinant yeast frataxin (mYfh1p) assembles into a regular multimer of approximately 1.1 MDa storing approximately 3000 iron atoms. Here, we further demonstrate that mYfh1p and iron form a stable hydrophilic complex that can be detected by either protein or iron staining on nondenaturing polyacrylamide gels, and by either interference or absorbance measurements at sedimentation equilibrium. The molecular mass of this complex has been refined to 840 kDa corresponding to 48 protein subunits and 2400 iron atoms. Solution density measurements have determined a partial specific volume of 0.58 cm(3)/g, consistent with the amino acid composition of mYfh1p and the presence of 50 Fe-O equivalents per subunit. By dynamic light scattering, we show that the complex has a radius of approximately 11 nm and assembles within 2 min at 30 degrees C when ferrous iron, not ferric iron or other divalent cations, is added to mYfh1p monomer at pH between 6 and 8. Iron-rich granules with diameter of 2-4 nm are detected in the complex by scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. These findings support the hypothesis that frataxin is an iron storage protein, which could explain the mitochondrial iron accumulation and oxidative damage associated with frataxin defects in yeast, mouse, and humans.

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