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Title: Structure and electron density analysis of electrochemically and chemically delithiated LiCoO{sub 2} single crystals

Abstract

Single crystals of Li{sub 0.68}CoO{sub 2}, Li{sub 0.48}CoO{sub 2}, and Li{sub 0.35}CoO{sub 2} were successfully synthesized for the first time by means of electrochemical and chemical delithiation processes using LiCoO{sub 2} single crystals as a parent compound. A single-crystal X-ray diffraction study confirmed the trigonal R3-barm space group and the hexagonal lattice parameters a=2.8107(5) A, c=14.2235(6) A, and c/a=5.060 for Li{sub 0.68}CoO{sub 2}; a=2.8090(15) A, c=14.3890(17) A, and c/a=5.122 for Li{sub 0.48}CoO{sub 2}; and a=2.8070(12) A, c=14.4359(14) A, and c/a=5.143 for Li{sub 0.35}CoO{sub 2}. The crystal structures were refined to the conventional values R=1.99% and wR=1.88% for Li{sub 0.68}CoO{sub 2}; R=2.40% and wR=2.58% for Li{sub 0.48}CoO{sub 2}; and R=2.63% and wR=2.56% for Li{sub 0.35}CoO{sub 2}. The oxygen-oxygen contact distance in the CoO{sub 6} octahedron was determined to be shortened by the delithiation from 2.6180(9) A in LiCoO{sub 2} to 2.5385(15) A in Li{sub 0.35}CoO{sub 2}. The electron density distributions of these Li {sub x} CoO{sub 2} crystals were analyzed by the maximum entropy method (MEM) using the present single-crystal X-ray diffraction data at 300 K. From the results of the single-crystal MEM, strong covalent bonding was clearly visible between the Co and O atoms, while no bonding was found aroundmore » the Li atoms in these compounds. The gradual decrease in the electron density at the Li site upon delithiation could be precisely analyzed. - Graphical abstract: Three-dimensional electron density distribution of the electrochemically delithiated Li{sub 0.68}CoO{sub 2} obtained by the maximum entropy method (MEM) using single-crystal X-ray diffraction data.« less

Authors:
 [1];  [1];  [2];  [2];  [2];  [3]
  1. National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8565 (Japan)
  2. Graduate School of Engineering, Tohoku University, Aramaki-Aoba, Aoba-ku, Sendai 980-8579 (Japan)
  3. National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8565 (Japan), E-mail: j.akimoto@aist.go.jp
Publication Date:
OSTI Identifier:
21015653
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 180; Journal Issue: 1; Other Information: DOI: 10.1016/j.jssc.2006.10.018; PII: S0022-4596(06)00552-4; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CALCULATION METHODS; COBALT OXIDES; COVALENCE; ELECTROCHEMISTRY; ELECTROMECHANICS; ELECTRON DENSITY; ENTROPY; HEXAGONAL LATTICES; LITHIUM OXIDES; MICROSTRUCTURE; MONOCRYSTALS; SPACE GROUPS; TRIGONAL LATTICES; X-RAY DIFFRACTION

Citation Formats

Takahashi, Yasuhiko, Kijima, Norihito, Dokko, Kaoru, Nishizawa, Matsuhiko, Uchida, Isamu, and Akimoto, Junji. Structure and electron density analysis of electrochemically and chemically delithiated LiCoO{sub 2} single crystals. United States: N. p., 2007. Web. doi:10.1016/j.jssc.2006.10.018.
Takahashi, Yasuhiko, Kijima, Norihito, Dokko, Kaoru, Nishizawa, Matsuhiko, Uchida, Isamu, & Akimoto, Junji. Structure and electron density analysis of electrochemically and chemically delithiated LiCoO{sub 2} single crystals. United States. doi:10.1016/j.jssc.2006.10.018.
Takahashi, Yasuhiko, Kijima, Norihito, Dokko, Kaoru, Nishizawa, Matsuhiko, Uchida, Isamu, and Akimoto, Junji. Mon . "Structure and electron density analysis of electrochemically and chemically delithiated LiCoO{sub 2} single crystals". United States. doi:10.1016/j.jssc.2006.10.018.
@article{osti_21015653,
title = {Structure and electron density analysis of electrochemically and chemically delithiated LiCoO{sub 2} single crystals},
author = {Takahashi, Yasuhiko and Kijima, Norihito and Dokko, Kaoru and Nishizawa, Matsuhiko and Uchida, Isamu and Akimoto, Junji},
abstractNote = {Single crystals of Li{sub 0.68}CoO{sub 2}, Li{sub 0.48}CoO{sub 2}, and Li{sub 0.35}CoO{sub 2} were successfully synthesized for the first time by means of electrochemical and chemical delithiation processes using LiCoO{sub 2} single crystals as a parent compound. A single-crystal X-ray diffraction study confirmed the trigonal R3-barm space group and the hexagonal lattice parameters a=2.8107(5) A, c=14.2235(6) A, and c/a=5.060 for Li{sub 0.68}CoO{sub 2}; a=2.8090(15) A, c=14.3890(17) A, and c/a=5.122 for Li{sub 0.48}CoO{sub 2}; and a=2.8070(12) A, c=14.4359(14) A, and c/a=5.143 for Li{sub 0.35}CoO{sub 2}. The crystal structures were refined to the conventional values R=1.99% and wR=1.88% for Li{sub 0.68}CoO{sub 2}; R=2.40% and wR=2.58% for Li{sub 0.48}CoO{sub 2}; and R=2.63% and wR=2.56% for Li{sub 0.35}CoO{sub 2}. The oxygen-oxygen contact distance in the CoO{sub 6} octahedron was determined to be shortened by the delithiation from 2.6180(9) A in LiCoO{sub 2} to 2.5385(15) A in Li{sub 0.35}CoO{sub 2}. The electron density distributions of these Li {sub x} CoO{sub 2} crystals were analyzed by the maximum entropy method (MEM) using the present single-crystal X-ray diffraction data at 300 K. From the results of the single-crystal MEM, strong covalent bonding was clearly visible between the Co and O atoms, while no bonding was found around the Li atoms in these compounds. The gradual decrease in the electron density at the Li site upon delithiation could be precisely analyzed. - Graphical abstract: Three-dimensional electron density distribution of the electrochemically delithiated Li{sub 0.68}CoO{sub 2} obtained by the maximum entropy method (MEM) using single-crystal X-ray diffraction data.},
doi = {10.1016/j.jssc.2006.10.018},
journal = {Journal of Solid State Chemistry},
number = 1,
volume = 180,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • X-ray diffraction and transmission electron microscopy were used to study the structural features of low-temperature LiCoO{sub 2} (LT-LiCoO{sub 2}) samples prepared at 400 C either by a simple solid-state reaction or via a sol-gel process. Single-crystal electron diffraction analysis showed that both a lithiated-spinel Li{sub 2} [Co{sub 2}]O{sub 4} (Fd3m) and a layered-type structure (R{bar 3}m) were present in LT-LiCoO{sub 2} samples but that the lithiated-spinel structure was the major phase. Electron diffraction analysis also indicated that some crystallites in the LT-LiCoO{sub 2} samples had a cation distribution in the spinel notation, {l_brace}(Li{sub 16{minus}4x}){sub 16c}[Li{sub 4x}]{sub 16d}{r_brace}{sub layer1} between themore » ideal layered (x = 1) and ideal lithiated-spinel (x = 0) structures. Electron diffraction confirmed that acid-delithiation of LT-LiCoO{sub 2} resulted in a lithium-deficient spinel, Li{sub 0.8}[Co{sub 2}]O{sub 4}, with lithium ions on the tetrahedral sites of the spinel structure. The structural features of LT-LiCoO{sub 2} and the acid-delithiated Li{sub 0.4}CoO{sub 2} products provide reasons for the poor electrochemical properties of Li/LT-LiCoO{sub 2} cells and are consistent with earlier studies.« less
  • Single crystals of the LiCoO{sub 2}-LiAlO{sub 2} solid solution compounds LiAl{sub 0.32}Co{sub 0.68}O{sub 2} and LiAl{sub 0.71}Co{sub 0.29}O{sub 2} were synthesized by a flux method using alumina crucibles. A single-crystal X-ray diffraction study confirmed the trigonal R3-bar m space group and the lattice parameters a=2.8056(11)A, c=14.1079(15)A, and c/a=5.028 for LiAl{sub 0.32}Co{sub 0.68}O{sub 2}, and a=2.8023(7)A, c=14.184(4)A, and c/a=5.061 for LiAl{sub 0.71}Co{sub 0.29}O{sub 2}. The crystal structures have been refined to the conventional values R=3.2% and wR=2.4% for LiAl{sub 0.32}Co{sub 0.68}O{sub 2}, and R=3.6% and wR=3.5% for LiAl{sub 0.71}Co{sub 0.29}O{sub 2}. The evidence of the location of Al atoms in themore » pseudotetragonal coordination (6c site), reported previously in LiAl{sub 0.2}Co{sub 0.8}O{sub 2}, could not be observed in the present electron density distribution maps in both LiAl{sub 0.32}Co{sub 0.68}O{sub 2} and LiAl{sub 0.71}Co{sub 0.29}O{sub 2}. The octahedral distortion analysis indicated that the Al-substitution strongly affected the distortion of the LiO{sub 6} octahedron in this solid-solution compound system, but hardly affected that of the (Al.Co)O{sub 6} octahedron.« less
  • Stoichiometric and excess-lithium spinels, Li(Li{sub x}Mn{sub 2{minus}x})O{sub 4} (x = 0.0, 0.1, 0.2), were treated with diluted H{sub 2}SO{sub 4}. The resulting products retained the spinel structure at reduced lithium content; those with lowest lithium content underwent exothermic phase transitions, observed as peaks in differential scanning calorimetry (DSC) curves between 250 and 300 C at heating rates of 10 C/m. The phase transition of the delithiated stoichiometric spinel was followed by powder X-ray diffraction of heat-treated samples. The structural analysis shows that the oxygen atoms rearrange first (from cubic to hexagonal packing), leaving the manganese atoms in disordered positions. Itmore » is this rearrangement of oxygen atoms that releases most of the heat observed in DSC measurements. Eventually the manganese atoms took their expected positions in the rutile or {beta}-form of MnO{sub 2}. The metastability of the delithiated compounds turned out not to be the origin of the capacity fade in electrochemical cells using stoichiometric spinel as the cathode.« less
  • Magnetism for the Li{sub x}Mn{sub 2}O{sub 4} samples with 0.07{<=}x{<=}1, which are prepared by a chemical reaction in HNO{sub 3} solution, is investigated by direct current susceptibility ({chi}) and muon-spin rotation/relaxation ({mu}SR) measurements. The effective magnetic moment ({mu}{sub eff}) of Mn ions decreases monotonically with decreasing x, indicating that Mn{sup 3+} ions with S=2 (t{sub 2g}{sup 3}e{sub g}{sup 1}) are oxidized to Mn{sup 4+} ions with S=3/2 (t{sub 2g}{sup 3}) with decreasing x. On the other hand, as x decreases from 1 to 0.6, the Curie-Weiss temperature ({Theta}{sub p}) increases monotonically from {approx}-260 to -100 K, and then levels offmore » to -100 K with further decreasing x. This indicates that the antiferromagnetic interaction is dominant in the whole x range. For the x=0.48 sample, the temperature dependence of {chi} in field-cooling mode clearly deviates from that in zero-field-cooling mode below {approx}63 K (=T{sub m}). Furthermore, the hysteresis loop is observed in the magnetization vs. field curve at 5 K. Since the zero-field {mu}SR spectrum is well fitted by a strongly damped oscillation function, the Mn moments for the x=0.48 sample are in a highly disordered fashion down to the lowest temperature measured. -- Graphical abstract: Magnetic phase diagram of the chemically delithiated spinel Li{sub x}Mn{sub 2}O{sub 4} determined by magnetic susceptibility ({chi}) and muon spin rotation/relaxation ({mu}SR) measurements. Display Omitted Highlights: {yields} Magnetic properties of the chemically delithiated Li{sub x}Mn{sub 2}O{sub 4} samples are investigated. {yields} The antiferromagnetic interaction is dominant in the whole x range. {yields} All the Li{sub x}Mn{sub 2}O{sub 4} samples show a magnetic transition below T{sub m}. {yields} The remanent magnetization vs. x curve exhibits a maximum at x=0.48. {yields} The x=0.48 sample is in a highly disordered magnetic state even at 1.8 K.« less
  • The layered LiMO{sub 2} (M = Co, Ni) compounds, which are of potential interest for Li-ion batteries, were synthesized at low temperatures by treatment under hydrothermal conditions of LiOH{center_dot}H{sub 2}O aqueous solutions containing powdered H{sub x}MO{sub 2} phases. The authors studied the reaction mechanism and the influence of temperature, pressure, water dilution, and precursor ratio on the degree of progress of the ion exchange process. Single-phase LiMO{sub 2} can be obtained in 48 h at 160 C under an air pressure of 60 bars from an MOOH/LiOH{center_dot}H{sub 2}O/H{sub 2}O mixture. The degree of advancement of the exchange reaction for Mmore » = Co was monitored in situ using an autoclave which allows the withdrawal of samples in the course of the reaction. From transmission electron microscopy coupled with x-ray diffraction studies the authors conclude that the reaction occurs by surface H{sup +}/Li{sup +} exchange and is accompanied by a progressive breaking of the particles due to an interfacial collapse phenomenon. Infrared studies indicate that the LiCoO{sub 2} and LiNiO{sub 2} phases obtained are contaminated by carbonates that can more easily be eliminated in the case of LiCoO{sub 2} by water washing and post-heating treatments under primary vacuum at 200 C for 2 days. Once the ion-exchange parameters are controlled, the LiMO{sub 2} products exhibit electrochemical performances comparable to those of high-temperature made phases.« less