The insulator-metal transition upon lithium deintercalation from LiCoO2: electronic properties and 7Li NMR study

Ménétrier, Michel; Saadoune, Ismae͏̈l; Levasseur, Stéphane; Delmas, Claude

doi:10.1039/a900016j

Cited by 474 publications

(527 citation statements)

References 13 publications

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“…Sample D with a single spinel MgCo 2 O 4 phase shows an excellent electrical conductivity of the order 10 À2 Scm À1 in comparison with Sample A, B, and C. Furthermore, it is emphasized here that the electrical conductivity of MgCo 2 O 4 (Sample D) is comparable to that of LiCoO 2 and sufficiently high for use as an electrode of batteries. 12) Thus, by substituting Mg for Co, the electrical conductivity of spinel (Mg, Co) 3 O 4 is found to be markedly enhanced. The reason is now under investigation from the viewpoint of the electronic structure of the spinel phase.…”

Section: Discussionmentioning

confidence: 99%

Synthesis of Spinel-Type Magnesium Cobalt Oxide and Its Electrical Conductivity

et al. 2008

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This work devotes to investigate synthesis and electrical properties of spinel MgCo 2 O 4 that is considered as a candidate of the cathode materials of magnesium-ion batteries in future. Samples were synthesized by two types of techniques: solid-state reaction and wet process. The crystal structures of the samples were analyzed by X-ray diffraction, and their electrical conductivities were obtained through the dc resistance and ac impedance measurements. By solid-state reaction, sample of a single MgCo 2 O 4 phase was not obtained; a sample synthesized at 800 C for 24 h after milling of Co 3 O 4 and MgO powder was comprised of dual phases of spinel-type and rocksalt-type structures, and samples synthesized at temperatures higher than 880 C showed a single rocksalt-type phase without electrical conductance. The former sample showed p-type semiconducting behavior as well as spinel-type Co 3 O 4 , but its electrical conductivity around room temperature was shown to exceed that of Co 3 O 4 . In contrast, a sample consisting of a single spinel-type phase was successfully synthesized by wet process, which exhibited an electrical conductivity of the order 10 À2 Scm À1 , being much higher than those of the samples synthesized by solid-state reaction. Thus, substitution of Co 2þ in Co 3 O 4 with Mg 2þ is found to enhance the electrical conductivity of the spinel-type phase.

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Section: Discussionmentioning

confidence: 99%

Synthesis of Spinel-Type Magnesium Cobalt Oxide and Its Electrical Conductivity

et al. 2008

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“…Structural relaxations with U have little impact on the electronic structure. Note that we do not explore U > 5 eV since in this regime we find DFT+U predicts a high-spin state for LiCoO 2 26 in con- tradiction with experimental observation 69,70 . CoO 2 is semimetallic at lower values of U with the A 1g and E g states both partially occupied.…”

Section: 79mentioning

confidence: 99%

Compositional phase stability of strongly correlated electron materials within DFT+ U

Isaacs

Marianetti

2017

Phys. Rev. B

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Predicting the compositional phase stability of strongly correlated electron materials is an outstanding challenge in condensed matter physics. In this work, we employ the density functional theory plus U (DFT+U ) formalism to address the effects of local correlations due to transition metal d electrons on compositional phase stability in the prototype phase stable and separating materials LixCoO2 and olivine LixFePO4, respectively. We exploit a new spectral decomposition of the DFT+U total energy, revealing the distinct roles of the filling and ordering of the d orbital correlated subspace. The on-site interaction U drives both of these very different materials systems towards phase separation, stemming from enhanced ordering of the d orbital occupancies in the x = 0 and x = 1 species, whereas changes in the overall filling of the d shell contribute negligibly. We show that DFT+U formation energies are qualitatively consistent with experiments for phase stable LixCoO2, phase separating LixFePO4, and phase stable LixCoPO4. However, we find that charge ordering plays a critical role in the energetics at intermediate x, strongly dampening the tendency for the Hubbard U to drive phase separation. Most relevantly, the phase stability of Li 1/2 CoO2 within DFT+U is qualitatively incorrect without allowing charge ordering, which is problematic given that neither charge ordering nor the band gap that it induces are observed in experiment. We demonstrate that charge ordering arises from the correlated subspace interaction energy as opposed to the double counting. Additionally, we predict the Li order-disorder transition temperature for Li 1/2 CoO2, demonstrating that the unphysical charge ordering within DFT+U renders the method problematic, often producing unrealistically large results. Our findings motivate the need for other advanced techniques, such as DFT plus dynamical mean-field theory, for total energies in strongly correlated materials.

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“…15 In contrast, in the partially oxidized but unheated two-phase xLiFeP04/(l-x)FeP04 crystals, the end members are located in stripes alternating along the a direction with phase boundaries in the be plane. 15 Magic angle spinning nuclear magnetic resonance (MAS NMR) has proven to be a very useful technique to study short range ordering schemes that are not detectable by diffraction techniques in positive electrode materials 16 such as LiMn2C»4- 17 " 21 and LiMCV type (M=Mn 22 ' 23 , Co 24 and/or Ni 25 " 32 ) phases, both in pristine and in charged/discharged samples. When experiments at different temperatures are combined, additional information regarding the diffusion of lithium and/or electron hopping can also be obtained.f ' ' ' ] Since the intermediate Li x FeP04 phases necessarily contain lithium vacancies and mixed Fe /Fe states, ' Li and P NMR experiments were conducted in this study in order to search for vacancy/charge ordering and enhanced ion/electron mobility in these phases.…”

Section: Introductionmentioning

confidence: 99%

MAS NMR Study of the Metastable Solid Solutions Found in the LiFePO₄/FePO₄ System

et al. 2010

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6 ' 7 Li and 3I P NMR experiments were conducted on a series of single-or twophase samples in the LiFePCvFePCM system with different overall lithium contents, and containing the two end-members and/or two metastable solid solution phases, Lio.6FeP04 or Lio.34FeP04. These experiments were carried out at different temperatures in order to search for vacancy/charge ordering and ion/electron mobility in the metastable phases.Evidence for Li + -Fe 2+ interactions was observed for both Lio.6FeP04 and Lio.34FePC>4.The strength of this interaction leads to the formation of LiFePCvlike clusters in the latter, as shown by the room temperature data. Different motional processes are proposed to exist as the temperature is increased and various scenarios are discussed. While concerted lithium-electron hopping and/or correlations explains the data below 125°C, evidence for some uncorrelated motion is found at higher temperatures, together with the onset of phase mixing.2

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The insulator-metal transition upon lithium deintercalation from LiCoO2: electronic properties and 7Li NMR study

Cited by 474 publications

References 13 publications

Synthesis of Spinel-Type Magnesium Cobalt Oxide and Its Electrical Conductivity

Synthesis of Spinel-Type Magnesium Cobalt Oxide and Its Electrical Conductivity

Compositional phase stability of strongly correlated electron materials within DFT+ U

MAS NMR Study of the Metastable Solid Solutions Found in the LiFePO₄/FePO₄ System

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The insulator-metal transition upon lithium deintercalation from LiCoO2: electronic properties and 7Li NMR study

Cited by 474 publications

References 13 publications

Synthesis of Spinel-Type Magnesium Cobalt Oxide and Its Electrical Conductivity

Synthesis of Spinel-Type Magnesium Cobalt Oxide and Its Electrical Conductivity

Compositional phase stability of strongly correlated electron materials within DFT+ U

MAS NMR Study of the Metastable Solid Solutions Found in the LiFePO4/FePO4 System

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MAS NMR Study of the Metastable Solid Solutions Found in the LiFePO₄/FePO₄ System