Thermodynamics and kinetics of defects in Li2S

Moradabadi, Ashkan; Kaghazchi, Payam

doi:10.1063/1.4952434

Cited by 18 publications

(30 citation statements)

References 37 publications

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“…Understanding the transport properties of the S and Li 2 S REMs is a prerequisite for the development of rational strategies to improve the capacity, efficiency, and cycle life of Li-S batteries. Nevertheless, transport mechanisms in these compounds have not been widely studied, especially in the case of S. [38][39][40][41] While a few studies exist for Li 2 S, consensus regarding the dominant charge-carrying species has been slow to emerge. For example, Kang et al reported that the dominant charge carriers in Li 2 S are negative Li and positive S vacancies, based on calculations performed at the hybrid functional level of theory.…”

Section: Introductionmentioning

confidence: 99%

“…41 Moradabadi and co-workers found that the dominant charge carriers were Li vacancies and Li interstitials, based on calculations employing a semi-local functional. 39 (Li interstitials were not considered in Refs. 27 and 41 .)…”

Section: Introductionmentioning

confidence: 99%

“…Moradabadi et al calculated a Li + interstital migration barrier of 0.47eV using the PBE-GGA functional. 39 For V Li migration, there is only one symmetry-distinct Li vacancy site and only one migration pathway between nearest-neighbor sites was considered. The calculated barrier for V Li migration, 0.32 eV, is 0.2 eV smaller than that for Li interstitials.…”

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Adiabatic and Nonadiabatic Charge Transport in Li-S Batteries

Siegel¹

2018

Meet. Abstr.

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The insulating nature of the redox end members in Li-S batteries, -S and Li 2 S, has the potential to limit the capacity and efficiency of this emerging energy storage system. Nevertheless, the mechanisms responsible for ionic and electronic transport in these materials remain a matter of debate. The present study clarifies these mechanisms -in both the adiabatic and nonadiabatic charge transfer regimes -by employing a combination of hybrid-functional-based and constrained density functional theory calculations. Charge transfer in Li 2 S is predicted to be adiabatic, and thus is well described by conventional DFT methodologies. In sulfur, however, transitions between S 8 rings are nonadiabatic. In this case, conventional DFT overestimates charge transfer rates by up to 2 orders of magnitude. Delocalized holes, and to a lesser extent, localized electron polarons, are predicted to be the most mobile electronic charge carriers in -S; in Li 2 S hole polarons dominate. Although all carriers exhibit extremely low equilibrium concentrations, and thus yield negligible contributions to the conductivity, their mobilities are sufficient to enable the sulfur loading targets necessary for high energy densities. Our results highlight the value of methods capable of capturing nonadiabadicty, such as constrained DFT. These techniques are especially important for molecular crystals such as -S, where longer-range charge transfer events are expected. Combining the present computational results with prior experimental studies, we conclude that low equilibrium carrier concentrations are responsible for sluggish charge transport in -S and Li 2 S. Thus, a potential strategy for improving the performance of Li-S batteries is to increase the concentrations of holes in these redox end members.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Adiabatic and Nonadiabatic Charge Transport in Li-S Batteries

Siegel¹

2018

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“…This coupling is most relevant in Li-ion batteries, where due to charging/discharging processes, bulk and interfacial as well as thermal strains can occur. The fact that induced stresses, which raise during intercalation, could weaken the interface between electrode/electrolyte and finally degrade the battery performance has been extensively discussed in the past [16][17][18][19][20][21][22][23][24][25][26][27]. Much less is known, however, about the coupling of strain fields to the formation and migration of Li vacancies in the bulk part of the material.…”

Section: Introductionmentioning

confidence: 99%

Influence of elastic strain on the thermodynamics and kinetics of lithium vacancy in bulkLiCoO2

Moradabadi

Kaghazchi

Rohrer

et al. 2018

Phys. Rev. Materials

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The influence of elastic strain on the lithium vacancy formation and migration in bulk LiCoO 2 is evaluated by means of first-principles calculations within density functional theory (DFT). Strain dependent energies are determined directly from defective cells and also within linear elasticity theory from the elastic dipole tensor (G i j ) for ground state and saddle point configurations. We analyze finite size-effects in the calculation of G i j , compare the predictions of the linear elastic model with those obtained from direct calculations of defective cells under strain and discuss the differences. Based on our data, we calculate the variations in vacancy concentration and mobility due to the presence of external strain in bulk LiCoO 2 cathodes. Our results reveal that elastic in-plane and out-of-plane strains can significantly change the ionic conductivity of bulk LiCoO 2 by an order of magnitude and thus strongly affect the performance of Li-secondary batteries.

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“…[10] Theoretical simulations, in particular based on density functional theory (DFT) calculations, have been successfully applied to evaluate diffusion barriers [11,12,14] andf ormation energies. [12,13,15,16] The formation of Schottky pairs consisting of Li + and F À vacancies for av oltage range of 0-4 Vh as been con-firmed for the rock-salt LiF crystal using DFT calculations and thermodynamic considerations. [12] Shi, et.…”

Section: Introductionmentioning

confidence: 99%

Dependence of Ion Transport on the Electronegativity of the Constituting Atoms in Ionic Crystals

Zhang

Kaghazchi

2017

ChemPhysChem

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Ion transport in electrode and electrolyte materials is a key process in Li-based batteries. In this work, we study the mechanism and activation energy of ion transport (Ea ) in rock-salt Li-based LiX (X=Cl, Br, and I) materials. It is found that Ea at low external voltages, where Li-X Schottky pairs are the most favorable defect types, is about 0.42 times the Gibbs energy of formation of LiX compound (ΔGf ). The value of 0.42 is the slope of the electronegativity of anions of binary Li-based materials as a function of ΔGf . At high voltages, where the Fermi level is located very close to the valence band maximum (VBM), electrons can be excited from the VB to Li vacancy-induced states close to the Fermi level. Under this condition, the formation of Li vacancies that are compensated by holes is energetically more favorable than that of Li-X Schottky pairs, and therefore, the activation energies are lower in the former case. The wide range of reported experimental values of activation energies lies between calculated values at low and high voltage regimes. This work motivates further studies on the relation between the activation energy for ionic conductivity in solid materials and the intrinsic ground-state properties of their free atoms.

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Thermodynamics and kinetics of defects in Li2S

Cited by 18 publications

References 37 publications

Adiabatic and Nonadiabatic Charge Transport in Li-S Batteries

Adiabatic and Nonadiabatic Charge Transport in Li-S Batteries

Influence of elastic strain on the thermodynamics and kinetics of lithium vacancy in bulkLiCoO2

Dependence of Ion Transport on the Electronegativity of the Constituting Atoms in Ionic Crystals

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