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Doeff, Marca

Publications and source records attributed to Doeff, Marca.

32 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Crystal Chemistry and Electrochemistry of Li x Mn 1.5 Ni 0.5 O 4 Solid Solution Cathode Materials

For ordered high-voltage spinel LiMn 1.5 Ni 0.5 O 4 (LMNO) with the P4 3 2 1 symmetry, the two consecutive two-phase transformations at ~4.7 V (vs Li + /Li), involving three cubic phases of LMNO, Li 0.5 Mn 1.5 Ni 0.5 O 4 (L 0.5 MNO), and Mn 1.5 Ni 0.5 O 4 (MNO), have been well-established. Such a mechanism is traditionally associated with poor kinetics due to the slow movement of the phase boundaries and the large mechanical strain resulting from the volume changes among the phases, yet ordered LMNO has been shown to have excellent rate capability. In this paper, we show the ability of the phases to dissolve into each other and determine their solubility limit. We characterized the properties of the formed solid solutions and investigated the role of non-equilibrium single-phase redox processes during the charge and discharge of LMNO. Finally, by using an array of advanced analytical techniques, such as soft and hard X-ray spectroscopy, transmission X-ray microscopy, and neutron/X-ray diffraction, as well as bond valence sum analysis, the present study examines the metastable nature of solid-solution phases and provides new insights in enabling cathode materials that are thermodynamically unstable.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Effects of the particle properties on electrochemical performance of nanocrystalline LiAl 0.1 Cu 0.1 Mn 1.8 O 4 cathode materials prepared by ultrasonic spray pyrolysis

LiAl 0.1 Cu 0.1 Mn 1.8 O 4 particles were prepared by the ultrasonic spray pyrolysis using nitrate salts at 800 °C in air atmosphere. The effects of ultrasonic frequency (120 kHz and 2.4 MHz) of the atomizer on the particle properties were investigated by X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive spectroscopy. In addition, cyclic voltammetry and galvanostatic tests were performed to study the influence of the particle structure on the electrochemical behavior in Li-ion battery half-cell. Particle characterization studies reveal that the LiAl 0.1 Cu 0.1 Mn 1.8 O 4 particles have a nanocrystalline spinel structure. The secondary particles have a spherical morphology and the average particle size of the samples decreases with increase in frequency from 3.5 μm to 770 nm. Both samples have porous and partly hollow structure. The initial discharge capacities of LiAl 0.1 Cu 0.1 Mn 1.8 O 4 particles produced using 120 kHz and 2.4 MHz atomizers are 82 and 75 mAh·g -1 , respectively, between 3.0 and 4.8 V at 0.1C rate. Discharge capacities at the 4 V potential region drop to 85% of the initial values for both samples after 110 cycles. Although the micron-sized LiAl 0.1 Cu 0.1 Mn 1.8 O 4 particles exhibit higher capacity at 0.1C than the finer particles, the cathode prepared from the submicron particles has a better rate capability with a retention of the discharge capacity that is 3 times higher at 4C rate.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Enhanced lithium ion transport in garnet-type solid state electrolytes

Al-substituted Li 7 La 3 Zr 2 O 12 samples processed under argon show enhanced Li-ion transport and interfacial properties in symmetrical cells with lithium electrodes, compared to those prepared in air. In particular, the samples prepared under argon have higher ionic conductivities and lower interfacial impedances in symmetrical lithium cells, and show better DC cycling characteristics. The electronic conductivities are also somewhat higher. Pellets subjected to thermal treatment under the two types of atmospheres have different colors but exhibit similar microstructures. X-ray diffraction experiments suggest that there are slight structural differences between the two types of samples, but few dissimilarities were observed in elemental composition, distribution of ions, oxidation states, or bond lengths using laser-induced breakdown spectroscopy (LIBS), x-ray photoelectron spectroscopy (XPS), and extended x-ray absorption fine structure spectroscopy (EXAFS) to analyze the materials. Additionally, there was no evidence that La or Zr were reduced during the processing under Ar. Possible explanations for the improved electrochemical properties of the sample prepared under Ar compared to the one prepared in air include differences in grain boundary chemistries and conductivities and/or a small concentration of oxygen vacancies in the former.

25 ENERGY STORAGE↗
DOE OSTI2016

Experimental and Computational Investigation of Lepidocrocite Anodes for Sodium-Ion Batteries

In this work, we investigated several titanates with lepidocrocite-type structures (general formula A x Ti1- y M y O 4 , with A = Na and M = Li or Mg), having potential utility as anode materials for sodium-ion batteries. First-principles calculations were used to determine key battery metrics, including potential profiles, structural changes during sodiation, and sodium diffusion energy barriers for several compositions, and were compared to experimental results. Site limitations were found to be critical determinants of the gravimetric capacities, which are also affected both by the stacking arrangement of the corrugated layers and the identity of M (Li or Mg). To explain the experimentally observed lattice parameter changes observed as a function of the state of charge, it was necessary to assume the participation of water/solvent during the sodium intercalation process. Here, sodium diffusion barriers were also found to vary as a function of state of charge and diffusion direction, with a spread of 0.06-1.3 eV at low sodium contents, narrowing to 0.3-0.5 eV at higher sodium contents. Based on these results, strategies for selecting and improving the performance of these electrode materials are suggested.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Electrochemical Properties of Electrodes Derived from NaTi 3 O 6 OH·2H 2 O in Sodium and Lithium Cells

Materials derived from the layered compound NaTi 3 O 6 OH·2H 2 O, also known as “sodium nonatitanate” or NNT, have recently been found to undergo reversible sodium or lithium intercalation processes at very low potentials. While practical discharge capacities in lithium cells can be above 200 mAh/g, making them of interest for high-energy applications, the presence of mobile sodium in the materials complicates the cycling behavior. A simple ion-exchange process prior to incorporation in electrochemical cells removes all sodium ions, producing the lithiated form of the material. The lithiated material (LNT) performs similarly to NNT in lithium cells, although coulombic inefficiencies are somewhat higher. A comparison is made between the behavior of NNT in sodium cells and that of NNT and the lithiated analog in lithium cells.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Structural and electrochemical Investigation of Li(Ni0.4Co0.2-yAlyMn0.4)O2 Cathode Material

Li(Ni{sub 0.4}Co{sub 0.15}Al{sub 0.05}Mn{sub 0.4})O{sub 2} was investigated to understand the effect of replacement of the cobalt by aluminum on the structural and electrochemical properties. In situ X-ray absorption spectroscopy (XAS) was performed, utilizing a novel in situ electrochemical cell, specifically designed for long-term X-ray experiments. The cell was cycled at a moderate rate through a typical Li-ion battery operating voltage range. (1.0-4.7 V) XAS measurements were performed at different states of charge (SOC) during cycling, at the Ni, Co, and the Mn edges, revealing details about the response of the cathode to Li insertion and extraction processes. The extended X-ray absorption fine structure (EXAFS) region of the spectra revealed the changes of bond distance and coordination number of Ni, Co, and Mn absorbers as a function of the SOC of the material. The oxidation states of the transition metals in the system are Ni{sup 2+}, Co{sup 3+}, and Mn{sup 4+} in the as-made material (fully discharged), while during charging the Ni{sup 2+} is oxidized to Ni{sup 4+} through an intermediate stage of Ni{sup 3+}, Co{sup 3+} is oxidized toward Co{sup 4+}, and Mn was found to be electrochemically inactive and remained as Mn{sup 4+}. The EXAFS results during cycling show that the Ni-O changes the most, followed by Co-O, and Mn-O varies the least. These measurements on this cathode material confirmed that the material retains its symmetry and good structural short-range order leading to the superior cycling reported earlier.

25 ENERGY STORAGE↗