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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Exploring Lithium-Cobalt-Nickel Oxide Spinel Electrodes for ≥3.5 V Li-Ion Cells

Recent reports have indicated that a manganese oxide spinel component, when embedded in a relatively small concentration in layered xLi2MnO3(1-x)LiMO2 (M=Ni, Mn, Co) electrode systems, can act as a stabilizer that increases their capacity, rate capability, cycle life, and first-cycle efficiency. These findings prompted us to explore the possibility of exploiting lithiated cobalt oxide spinel stabilizers by taking advantage of (1) the low mobility of cobalt ions relative to manganese and nickel ions in close-packed oxides and (2) their higher potential (~3.6 V vs. Li0) relative to manganese oxide spinels (~2.9 V vs. Li0) for the spinel-to-lithiated spinel electrochemical reaction. In particular, we have revisited the structural and electrochemical properties of lithiated spinels in the LiCo1-xNixO2 (0x0.2) system, first reported almost 25 years ago, by means of high-resolution (synchrotron) X-ray diffraction, transmission electron microscopy, nuclear magnetic resonance spectroscopy, electrochemical cell tests, and theoretical calculations. The results provide a deeper understanding of the complexity of intergrown layered/lithiated spinel LiCo1-xNixO2 structures, when prepared in air between 400 and 800 C, and the impact of structural variations on their electrochemical behavior. These structures, when used in low concentration, offer the possibility of improving the cycling stability, energy, and power of high energy (≥3.5 V) lithium-ion cells.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2019

Unified View of the Local Cation-Ordered State in Inverse Spinel Oxides

Cation ordering/disordering in spinel oxides plays a necessary role in the rich physical and chemical properties which are hallmarks of the structural archetype. A variety of cation-ordering motifs have been reported for spinel oxides with multiple cations residing on the octahedral site (or B-site). This has attracted tremendous attention from both experimental and theoretical communities in the last few decades. Yet, no unified view has been reached, presumably due to the richness of cation species and corresponding complex arrangements emergent in this large family of compounds. Here, local cation-ordered ground states of (inverse) spinel oxides with two different cations on the octahedral site have been thoroughly investigated using neutron and X-ray total scattering, and a comprehensive theory has been proposed to explain the commonly observed cation-ordered polymorphs. It is found that a cation-zigzag-ordered structure (space group P4122) is the ground state for inverse spinel oxides with a pure or strong ionic lattice, while a cation-linear-ordered arrangement (space group Imma) emerges when one of the B-site cations forms very strong directional covalent bonds with lattice oxygen. The degree and length scale of cation ordering is strongly correlated with the charge and ionic radius difference between the two octahedral site cations. More complicated cation ordering schemes can be formed when there is a concomitant charge and orbital ordering which fall on a similar energy scale. This can lead to the formation of orbital-driven cation clusters or the broad concept of “molecules” in solid- state compounds. It is anticipated these findings will help to better understand the observed physical properties of spinel oxides and thus facilitate design strategies for improved functional materials.

25 ENERGY STORAGE↗
DOE OSTI2017

Surface enrichment of Pt in stable Pt-Ir nano-alloy particles on MgAl 2 O 4 spinel in oxidizing atmosphere

With the capability of MgAl2O4 spinel {111} nano-facets in stabilizing small Rh, Ir and Pt particles, bimetallic Ir-Pt catalysts on the same support were investigated, aiming at further lowering the catalyst cost by substituting expensive Pt with cheaper Ir in the bulk. Small Pt-Ir nano-alloy particles (< 2nm) were successfully stabilized on the spinel {111} nano-facets as expected. Interestingly, methanol oxidative dehydrogenation (ODH) rate on the surface Pt atoms increases with oxidizing aging but decreases upon reducing treatment, where Ir is almost inactive under the same reaction conditions. Up to three times enhancement in Pt exposure was achieved when the sample was oxidized at 800 °C in air for 1 week and subsequently reduced by H2 for 2 h, demonstrating successful surface enrichment of Pt on Pt-Ir nano-alloy particles. A dynamic stabilization mechanism involving wetting\nucleation seems to be responsible for the evolution of surface compositions upon cyclic oxidizing and reducing ther-mal treatments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Topotactic Phase Transformation of Lithiated Spinel to Layered LiMn0.5Ni0.5O2: The Interaction of 3-D and 2-D Li-ion Diffusion

This study investigates the structural evolution of LiMn0.5Ni0.5O2 cathode materials for Li-ion batteries as a function of synthesis temperature and its effect on electrochemical performance. It is demonstrated that, as the synthesis temperature increases from 400 to 900 ?C, a gradual topotactic transformation occurs between a lithiated spinel structure, denoted herein as “lithium-excess spinel” LxS-LiMn0.5Ni0.5O2 (or LxS-LMNO), and the well-known layered LiMn0.5Ni0.5O2 structure prepared at high temperature, HT-LiMn0.5Ni0.5O2 (HT-LMNO). The electrochemical capacity of the LiMn0.5Ni0.5O2 electrodes follows a parabolic trend with increasing synthesis temperature, which is attributed primarily to the gradual transformation of 3-dimensional (3-D) to 2-dimensional (2-D) diffusion pathways for the Li ions. When synthesized at 400 °C, LxS-LiMn0.5Ni0.5O2 electrodes perform well, benefitting from the 3-D network of channels within the LxS structure. By contrast, when prepared at 500-700 °C, LiMn0.5Ni0.5O2 electrodes operate poorly, which is attributed to the formation of locally disordered structural arrangements that impede Li-ion diffusion. Such an increase in local disorder in the mid-temperature synthesis range is attributed to the structural frustration between the lithium-excess spinal and layered end-members. The transformation from the locally disordered to more ordered layered components between 700 °C and 900 °C enhances electrochemical performance. The study opens new avenues for designing next-generation Mn-rich cathode materials by fine-tuning the synthesis conditions as well as the composition and structure of LxS-LMNO electrodes.

energy storage↗
DOE OSTI2016

Spinel and post-spinel phase assemblages in Zn 2 TiO 4 : an experimental and theoretical study

Zn2TiO4 spinel (Zn2TiO4-Sp) was synthesized by a solid-state reaction method (1573 K, room P and 72 h) and quasi-hydrostatically compressed to ~24 GPa using a DAC coupled with a synchrotron X-ray radiation (ambient T). We found that the Zn2TiO4-Sp was stable up to ~21 GPa and transformed to another phase at higher P. With some theoretical simulations, we revealed that this high-P phase adopted the CaTi2O4-type structure (Zn2TiO4-CT). Additionally, the isothermal bulk modulus (KT) of the Zn2TiO4-Sp was experimentally obtained as 156.0(44) GPa and theoretically obtained as 159.1(4) GPa, with its first pressure derivative K'TKT' as 3.8(6) and 4.37(4), respectively. The volumetric and axial isothermal bulk moduli of the Zn2TiO4-CT were theoretically obtained as KT = 150(2) GPa (K'TKT' = 5.4(2); for the volume), KT-a = 173(2) GPa (K'T-aKT-a' = 3.9(1); for the a-axis), KT-b = 74(2) GPa (K'T-bKT-b' = 7.0(2); for the b-axis), and KT-c = 365(8) GPa (K'T-cKT-c' = 1.5(4); for the c-axis), indicating a strong elastic anisotropy. The Zn2TiO4-CT was found as ~10.0 % denser than the Zn2TiO4-Sp at ambient conditions. The spinel and post-spinel phase assemblages for the Zn2TiO4 composition at high T have been deduced as Zn2TiO4-Sp, ZnTiO3-ilmenite + ZnO-wurtzite, ZnTiO3-ilmenite + ZnO-rock salt, ZnTiO3-perovskite + ZnO-rock salt, and Zn2TiO4-CT as P increases, which presumably implies a potential stability field for a CT-type Mg2SiO4 at very high P.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Liquidus temperature in the spinel primary phase field: A comparison between optical and crystal fraction methods

Liquidus temperature (TL) was measured for simulated high-level waste borosilicate glasses covering a Hanford composition region, using an optical method and a crystal-fraction extrapolation method with X-ray diffraction data from isothermal heat treatments. The 38 glasses encompassed a one-component-at-a-time variation of a 16-component matrix. The TL values ranged from 1006°C to 1603°C. First-order polynomial models were fitted to data to obtain coefficients in terms of the effect of 1 mass% component addition on the TL: TL-increasing oxides Cr2O3 (264°C), “Others” (minor components, 163°C), oxides of noble metals (137°C), NiO (91°C), Al2O3 and Fe2O3 (~19–21°C); TL-decreasing oxides K2O (-26°C), Na2O (-41°C), and Li2O (-68°C); oxides of little effect MnO, P2O5, ZrO2, F, Bi2O3, SiO2, B2O3, and CaO (9 to -12°C). Also presented are temperatures (T1%) at which glasses contain 1 vol% of spinel as these values are considered relevant to the Hanford Tank Waste Treatment and Immobilization Plant. The measured and estimated values are compared and contrasted and the effect of TL and T1% on glass formulation is discussed.

crystal fraction↗