CoO2, The End Member of the Li x CoO2 Solid Solution

Amatucci, Glenn G.; Tarascon, J. M.; Klein, Lisa C.

doi:10.1149/1.1836594

Cited by 980 publications

(913 citation statements)

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“…The Na concentration versus chemical potential is characterized by plateaus at x = 1 3 , 1 2 , 5 7 , 3 4 , comparable to those appearing in electrochemical cells [4]. The the 1 2 -plateau corresponds to an {a'=2a-b, b'=2b} ordered structure with equal occupation of Na 1 and Na 2 sites in perfect agreement with ED spectra [2].…”

supporting

confidence: 70%

On the Ordering of Na+ Ions in NaxCoO2

Roger¹,

Morris²,

Tennant³

et al. 2006

AIP Conference Proceedings

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Abstract. The influence of electrostatic interactions on the ordering of sodium ions in Na x CoO 2 is studied theoretically through Monte-Carlo simulations. For large x small di-or tri-vacancy clusters are stable with respect to isolated Na vacancies. At commensurate fillings these small clusters order in triangular superstructures. These results agree with recent electron diffraction data at x = 1/2 and 3/4. We have performed neutron Laüe diffraction experiments at higher x, which confirm the predictions of this simple model. The consequences on the properties of the electronic charges in the Co layers are discussed.In the past decade, Na x CoO 2 has emerged as a system of fundamental interest because of its high thermoelectric power, unusual magnetic properties and possibility, when hydrated, to superconduct [1]. The density x of intercalated sodium atoms tunes directly the density of states of quasi-particles in the metallic CoO 2 sheets. For simple fractional fıllings, electron diffraction (ED) experiments [2,3] provide evidence for the ordering of Na + ions at room temperature. This non-trivial order is generally believed to be the consequence of intricate interactions between Na + ions, mobile electrons, and phonons. We show here that the dominant process driving this ordering is simply the Coulomb potential between Na + ions. Sodium ions can occupy sites between oxygen atoms, which form two interpenetrating triangular lattices denoted Na 1 and Na 2 . Cobalt ions lie above and below Na 1 sites, resulting in an extra energy cost ∆ = ∆ c + ∆ sr relative to an Na 2 site (∆ c in the long-range Coulomb part and ∆ sr a short range repulsion between Na and Co ions shells). Na ions are bigger than the distance between nearest Na 1 and Na 2 sites, forbidding simultaneous occupancy of nearest-neighboring sites and that makes Coulomb energy minimization highly nontrivial. Our model Hamiltonian includes: (i) a long-range Coulomb potential, e/(4πεε 0 r) (the dielectric constant, taken as isotropic, is fıxed at ε = 6 to account quantitatively for the variations of the chemical potential, in terms of x, measured in cell devices [4]); (ii) Na-Na ionshell repulsion V=0.04eV for neighbors on the same sublattice; and (iii) on-site energy ∆ sr = 0.01eV. A system of two sheets of Na ions, each containing a maximum number of 1176 ions, intercalated between two CoO 2 layers (with periodic boundary conditions in 3 dimensions) is simulated at fınite temperature and fıxed chemical potential µ through a Grand-Canonical Monte-Carlo method. The hexagonal cell parameters a=2.84Å and c=10.87Å are fıxed to those measured in the x = 0.75 phase, and elastic deformations are neglected. We maintain neutrality at each step by varying the charges in the Co layers assuming a uniform spreading.The organization of Na ions is driven by the spontaneous formation of multivacancy clusters, as illustrated in Figure 1. At large distance d, the repulsion energy between two vacancies decreases as 1/d. However neighboring vacancies can reduce their energy...

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supporting

confidence: 70%

On the Ordering of Na+ Ions in NaxCoO2

Roger¹,

Morris²,

Tennant³

et al. 2006

AIP Conference Proceedings

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“…After complete delithiation, the MO 2 layers are weakly bound by van der Waals forces. 38 The layered oxides have been extensively studied both experimentally 5,39 and theoretically. [40][41][42][43] Because the layered dichalcogenide, LiTiS 2 , was once considered as a positive electrode material, 1 we have included this material in our investigations to ascertain if a different anion would modify the differences between the lithium vs sodium intercalation properties.…”

Section: Structure Selectionmentioning

confidence: 99%

Voltage, stability and diffusion barrier differences between sodium-ion and lithium-ion intercalation materials

Ong

Chevrier

Hautier

et al. 2011

Energy Environ. Sci.

1,309

1,046

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To evaluate the potential of Na-ion batteries, we contrast in this work the difference between Na-ion and Li-ion based intercalation chemistries in terms of three key battery properties -voltage, phase stability and diffusion barriers. The compounds investigated comprise the layered AMO 2 and AMS 2 structures, the olivine and maricite AMPO 4 structures, and the NA-SICON A 3 V 2 (PO 4 ) 3 structures. The calculated Na voltages for the compounds investigated are 0.18-0.57 V lower than that of the corresponding Li voltages, in agreement with previous experimental data. We believe the observed lower voltages for Na compounds are predominantly a cathodic effect related to the much smaller energy gain from inserting Na into the host structure compared to inserting Li. We also found a relatively strong dependence of battery properties with structural features. In general, the difference between the Na and Li voltage of the same compound, ∆V Na-Li , is less negative for the maricite structures preferred by Na, and * To whom correspondence should be addressed 1 more negative for the olivine structures preferred by Li. The layered compounds have the most negative ∆V Na-Li . In terms of phase stability, we found that open structures, such as the layered and NASICON structures that are better able to accommodate the larger Na + ion generally have both Na and Li versions of the same compound. For the close-packed AMPO 4 structures, our results show that Na generally prefers the maricite structure, while Li prefers the olivine structure, in agreement with previous experimental work. We also found surprising evidence that the barriers for Na + migration can potentially be lower than that for Li + migration in the layered structures. Overall, our findings indicate that Na-ion systems can be competitive with Li-ion systems.

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“…This method is highly informative in the study of surface properties of energy storage, lithium-ion batteries, capacitors, etc. For example, SPM allows to notice a change in the lattice parameter of the cathode material Li x CоO 2 along the normal to the surface on the magnitude of 40 pm in the process of charging/discharging of Li-ion power source [4].…”

Section: #8 / 70 / 2016mentioning

confidence: 99%

“…Этот метод является весьма информатив-ным при изучении свойств поверхности энергона-копителей, литий-ионных батарей, конденсаторов и пр. Например, СПМ позволяет заметить измене-ние параметра решетки катодного материала Li x CоO 2 вдоль нормали к поверхности на величину в 40 пм в процессе зарядки / разрядки литий-ионного источ-ника тока [4].…”

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