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Unocic, Raymond R

Publications and source records attributed to Unocic, Raymond R.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Sodium manganese oxide thin films as cathodes for Na-ion batteries

This paper presents the fabrication and characterization of sodium manganese oxide cathode thin films for rechargeable Na-ion batteries. Layered oxide compounds of nominal compositions Na0.6MnO2 and Na1.0MnO2 have been prepared by radio frequency magnetron sputtering and post-annealing at high temperatures under various conditions. The Na0.6MnO2 thin films possess either a hexagonal or orthorhombic structure while the Na1.0MnO2 films crystallize in a monoclinic structure, as shown by X-ray diffraction and X-ray absorption spectroscopy results. The potential profiles of the film cathodes are characterized by features similar to those measured for the powders and exhibit reversible storage capacities in the range of 50-60 Ah cm-2 m-1, which correspond to about 120-140 mAh g-1, and are maintained over 80 cycles.

Baggetto, Loic↗
DOE OSTI2014

In situ formation of micron-scale Li-metal anodes with high cyclability

Scanning probe microscopy methods have been used to fabricate and cycle micron-scale Li anodes deposited electrochemically under nanofabricated Au current collectors. An average Li volume of 5 10^8 nm3 was deposited and cycled with 100 % coulombic efficiency for ~ 160 cycles. Integrated charge/discharge values agree with before/after topography, as well as in situ dilatometry, suggesting this is a reliable method to study solid-state electrochemical processes. In this work we illustrate the possibility to deposit highly cyclable nanometer thick Li electrodes by mature SPM and nanofab techniques which can pave the way for inexpensive nanoscale battery arrays.

Arruda, Thomas M↗
DOE OSTI2014

Cr, N-Codoped TiO2 Mesoporous Microspheres for Li-ion Rechargeable Batteries with Enhanced Electrochemical Performance

Cr,N-codoped TiO2 mesoporous microspheres synthesized using hydrothermal and subsequent nitridation treatment, exhibited higher solubility of nitrogen, and improved electrical conductivity than N-doped TiO2, as anode for Lithium-ion rechargeable batteries, which led to improving charge-discharge capacity at 0.1 C and twice higher rate capability compared to that of nitrogen-doped TiO2 mesoporous microsphere at 10 C

Bi, Zhonghe↗
DOE OSTI2013

Defect chemistry of phospho-olivine nanoparticles synthesized by a microwave-assisted solvothermal process

Nanocrystalline LiFePO{sub 4} powders synthesized by a microwave-assisted solvothermal (MW-ST) process have been structurally characterized with a combination of high resolution powder neutron diffraction, synchrotron X-ray diffraction, and aberration-corrected HAADF STEM imaging. A significant level of defects has been found in the samples prepared at 255 and 275 °C. These temperatures are significantly higher than what has previously been suggested to be the maximum temperature for defect formation in LiFePO{sub 4}, so the presence of defects is likely related to the rapid MW-ST synthesis involving a short reaction time (∼5 min). A defect model has been tentatively proposed, though it has been shown that powder diffraction data alone cannot conclusively determine the precise defect distribution in LiFePO{sub 4} samples. The model is consistent with other literature reports on nanopowders synthesized at low temperatures, in which the unit cell volume is significantly reduced relative to defect-free, micron-sized LiFePO{sub 4} powders. - Graphical abstract: Temperature-dependent antisite defect formation has been observed in nanocrystalline LiFePO{sub 4} powders synthesized by a microwave solvothermal process, using high resolution diffraction and STEM imaging. Display Omitted - Highlights: • LiFePO{sub 4} nanopowders synthesized by a microwave-assisted solvothermal process. • Defects directly observed by aberration-corrected HAADF STEM imaging. • Antisite defects present from synthesis at 255 and 275 °C. • Defects present from higher temperature synthesis than previously reported. • Powder diffraction data have been analyzed in detail for various defect models.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Mesoporous TiO2 spheres with a nitridated conducting layer

Nitridated TiO2 mesoporous spheres have been synthesized by hydrothermal processing followed by post-nitridation with NH3. Characterization data reveal a nitridated conducting layer, in addition to a mesoporous, and nanosized building-block morphology resulting in a large surface area. The samples have an average pore size and surface area of, respectively, 10 nm and 87 m2/g. The nitridated TiO2 mesoporous spheres exhibit a high capacity of > 200 mAh/g with good cyclability and high rate capability, as the nitridated conducting layer and favorable morphology of nanosized spheres provides good electrical contact, accommodates cycling induced strain smoothly, and facilitates lithium-ion diffusion.

anode↗
DOE OSTI2013

Characterization of Sodium Ion Electrochemical Reaction with Tin Anodes: Experiment and Theory

Tin anodes show a rich structure and reaction chemistry which we have investigated in detail. Upon discharge five plateaus are observed corresponding to -Sn, an unidentified phase (Na/Sn = 0.6), an amorphous phase (Na/Sn = 1.2), a hexagonal R-3m Na5Sn2, and fully sodiated Na15Sn 4. With charging there are six plateaus, which are related to the formation of Na5Sn2 followed by the formation of amorphous phases and -Sn. Upon cycling the formation of metastable Na5Sn2 seems to be suppressed, leading to a single charge plateau at 0.2 V. Theoretical voltages calculated from existing crystal structures using DFT provide a good match with constant current measurements, however, the voltage is more negative compared to quasi-equilibrium measurements (GITT). Search for additional (meta)stable phases using cluster-expansion method predicts many phases lower in energy than the convex hull, including the R-3m Na5Sn2 phase characterized experimentally. The presence of multiple phases in varying lattices with very similar formation energy suggests why the reaction mechanism is non-reversible. Interpretation of M ssbauer spectroscopy data is not yet elucidated due to the very low recoil-free fraction of the materials. The electrode surface is terminated with a SEI layer rich in carbonates such as Na2CO3 and Na alkyl carbonates as evidenced by XPS. After a full charge at 2V, strong evidence for the formation of oxidized Sn4+ is obtained. Subjecting the electrode to a rest after a full charge at 2 V reveals that aging in the electrolyte reduces the oxidized Sn4+ into Sn2+ and Sn0, and concomitantly suppresses the electrolyte decomposition represented by an anomalous discharge plateau at 1.2 V. Thereby, the catalytic decomposition of the electrolyte during discharge is caused by nanosized Sn particles covered by oxidized Sn4+ and not by pure metallic Sn.

Na5Sn2 metastable phase (XRD)↗
DOE OSTI2013

Extremely fast reaction kinetics of Mo3Sb7 thin films as anodes for Li- and Na-ion batteries

Mo3Sb7 thin films prepared by magnetron sputtering are evaluated as an anode material for Li- and Na-ion batteries. The as deposited films are amorphous and composed of small agglomerated domains with an overall Sb/Mo ratio of 2.34 that is almost identical to the ratio measured for the starting powder and the expected nominal ratio of 2.33. When cycled with Li and Na, the films show large storage capacities of around 430 and 330 mAh g-1, respectively, with good capacity retention. In addition, micron thick films retain large capacities of about 310 and 280 mAh g-1 at very high rates of 100 and 30 C-rate currents for Li and Na, respectively. The XRD study of the changes in the structure of the electrode material reveals that Li3Sb forms at full discharge whereas the electrode at full charge is amorphous. For the reaction with Na, the electrode material remains amorphous. Analysis of the surface chemistry characterized by XPS suggests the formation of an inorganic layer (LiF, LixPOyFz) covered by organic products (carbonates, esters, ethers) in the case of Li and the formation of an organic layer only (carbonates) in the case of Na. The electrode surface is visible at full charge for Na, thereby indicating that the SEI layer is thinner when cycling with Na compared to that with Li. Overall, the results highlight the very good potential of Mo3Sb7 as an anode for Li- and Na-ion batteries.

Baggetto, Loic↗