Electronic structure of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>Li</mml:mtext></mml:mrow><mml:mi>x</mml:mi></mml:msub><mml:msub><mml:mrow><mml:mtext>CoO</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>studied by photoemission spectroscopy and unrestricted Hartree-Fock calculations

Ikedo, Kazumichi; Wakisaka, Yuki; Mizokawa, T.; Iwai, C.; Miyoshi, Kiyotaka; Takeuchi, Jun

doi:10.1103/physrevb.82.075126

Cited by 22 publications

(8 citation statements)

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“…Such dual behavior with itinerancy and localization of the Co 3d and O 2p states is consistent with the photoemission results on Li x CoO 2 [26,27] in the wide range of x. Since the O 2p contribution in the Co 4þ e g state is much larger than that in the Co 3þ e g state, the e g component of the O 2p holes tend to be localized as indicated by the present XAS results at 20 K. The photoemission results on the same system [27] show that the localized nature does not change appreciably up to 300 K. The present Hartree-Fock calculation for Co 3þ =Co 4þ charge ordering can describe the overall features of the O 1s XAS spectra dominated by the localized part whereas it fails to describe the metallic a 1g state. The interplay between the localized e g and itinerant a 1g components can provide the dual nature of Li x CoO 2 .…”

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confidence: 89%

Role of Oxygen Holes inLixCoO2Revealed by Soft X-Ray Spectroscopy

et al. 2013

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The fundamental electronic structure of the widely used battery material Li(x)CoO(2) still remains a mystery. Soft x-ray absorption spectroscopy of Li(x)CoO(2) reveals that holes with strong O 2p character play an essential role in the electronic conductivity of the Co(3+)/Co(4+) mixed valence CoO(2) layer. The oxygen holes are bound to the Co(4+) sites and the Li-ion vacancy, suggesting that the Li-ion flow can be stabilized by oxygen hole back flow. Such an oxygen hole state of Li(x)CoO(2) is unique among the various oxide-based battery materials and is one of the key ingredients to improving their electronic and Li-ion conductivities.

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confidence: 89%

Role of Oxygen Holes inLixCoO2Revealed by Soft X-Ray Spectroscopy

et al. 2013

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“…Li + extraction from the host material is accompanied by the removal of an electron from (add a hole to) the occupied states to satisfy charge neutrality of the material. In LCO, a valence electron is removed, at first, from the occupied t 2g state which is close to E F (see Figure ), which results in the chemical potential shift to low energies shown recently on a single crystal LCO by photoemission experiments . Changes in the valence band spectra measured as a function of the charging state of our thin films are shown in Figure a.…”

Section: Results and Discussionsupporting

confidence: 51%

Nonrigid Band Behavior of the Electronic Structure of LiCoO₂ Thin Film during Electrochemical Li Deintercalation

et al. 2014

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In this study, a comprehensive experimental in situ analysis of the evolution of the occupied and unoccupied density of states as a function of the charging state of the Li x≤1CoO2 films has been done by using synchrotron X-ray photoelectron spectroscopy (SXPS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and O K- and Co L 3,2-edges XANES. Our experimental data demonstrate the change of the Fermi level position and the Co3d–O2p hybridization under the Li+ removal and provide the evidence for the involvement of the oxygen states in the charge compensation. Thus, the rigid band model fails to describe the observed changes of the electronic structure. The Co site is involved in a Co3+ → Co4+ oxidation at the period of the Li deintercalation (x ∼ 0.5), while the electronic configuration at the oxygen site is stable up to 4.2 V. Further lowering of the Fermi level promoted by Li+ extraction leads to a deviation of the electronic density of states due to structural distortions, and the top of the O2p bands overlaps the Co3d state which is accompanied by a hole transfer to the O2p states. The intrinsic voltage limit of LiCoO2 has been determined, and the energy band diagram of Li x≤1CoO2 vs the evolution of the Fermi level has been built. It was concluded that Li x CoO2 cannot be stabilized at the deep Li deintercalation even with chemically compatible solid electrolytes.

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“…Without the renormalization effect, the a 1g band is almost flat for k x < 0.5Å −1 and becomes steep for k x > 0.5Å −1 . Therefore, for x < 0.6 with k F > 0.5 A −1 , the large chemical potential shift is consistent with the bare band dispersion before the renormalization [31] while the a 1g band is strongly renormalized with renormalization factor of 3-4. The shoulder structure at ∼ -0.3 eV can be assigned to the bottom of a 1g band and the top of e ′ g band.…”

Section: Introductionsupporting

confidence: 64%

“…[23][24][25][26] By removing the Li ions using an electrochemical reaction, Li x CoO 2 exhibits an insulator-to-metal transition at around x=0.95 by hole doping in the t 2g band. [27,28] Single crystals of Li x CoO 2 were successfully synthesized by Miyoshi et al [29,30] and their electronic structure has been studied by photoemission spectroscopy, [31] x-ray absorption spectroscopy, [32] and hard x-ray absorption and emission spectroscopy. [33] In particular, the x-ray absorption study has revealed that the a 1g band with strong mixture of O 2p accommodates the doped holes and that the O 2p hole plays an important role for the Li-ion motion in Li x CoO 2 .…”

Section: Introductionmentioning

confidence: 99%

Electronic structure and polar catastrophe at the surface of LixCoO2 studied by angle-resolved photoemission spectroscopy

et al. 2017

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We report an angle-resolved photoemission spectroscopy (ARPES) study of Li x CoO 2 single crystals which have a hole-doped CoO 2 triangular lattice. Similar to Na x CoO 2 , the Co 3d a 1g band crosses the Fermi level with strongly renormalized band dispersion while the Co 3d e ′ g bands are fully occupied in Li x CoO 2 (x=0.46 and 0.71). At x=0.46, the Fermi surface area is consistent with the bulk hole concentration indicating that the ARPES result represents the bulk electronic structure. On the other hand, at x=0.71, the Fermi surface area is larger than the expectation which can be associated to the inhomogeneous distribution of Li reported in the previous scanning tunneling microscopy study by Iwaya et al. [Phys. Rev. Lett. 111, 126104 (2013)]. However, the Co 3d peak is systematically shifted towards the Fermi level with hole doping excluding phase separation between hole rich and hole poor regions in the bulk. Therefore, the deviation of the Fermi surface area at x=0.71 can be attributed to hole redistribution at the surface avoiding polar catastrophe. The bulk Fermi surface of Co 3d a 1g is very robust around x=0.5 even in the topmost CoO 2 layer due to the absence of the polar catastrophe.

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Electronic structure ofLixCoO2studied by photoemission spectroscopy and unrestricted Hartree-Fock calculations

Cited by 22 publications

References 42 publications

Role of Oxygen Holes inLixCoO2Revealed by Soft X-Ray Spectroscopy

Role of Oxygen Holes inLixCoO2Revealed by Soft X-Ray Spectroscopy

Nonrigid Band Behavior of the Electronic Structure of LiCoO₂ Thin Film during Electrochemical Li Deintercalation

Electronic structure and polar catastrophe at the surface of LixCoO2 studied by angle-resolved photoemission spectroscopy

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Electronic structure ofLixCoO2studied by photoemission spectroscopy and unrestricted Hartree-Fock calculations

Cited by 22 publications

References 42 publications

Role of Oxygen Holes inLixCoO2Revealed by Soft X-Ray Spectroscopy

Role of Oxygen Holes inLixCoO2Revealed by Soft X-Ray Spectroscopy

Nonrigid Band Behavior of the Electronic Structure of LiCoO2 Thin Film during Electrochemical Li Deintercalation

Electronic structure and polar catastrophe at the surface of LixCoO2 studied by angle-resolved photoemission spectroscopy

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Nonrigid Band Behavior of the Electronic Structure of LiCoO₂ Thin Film during Electrochemical Li Deintercalation