FIGURE 3 - uploaded by Manuel Dillenz
Content may be subject to copyright.
| Isosurfaces of the charge density difference of MgSc 2 Se 4 structures in side view with the charge carrier (A) Li, (C) Al in octahedral coordination and (B) Li, (D) Al in tetrahedral coordination. Areas of charge depletion are shown in blue and areas of charge accumulation are shown in red.

| Isosurfaces of the charge density difference of MgSc 2 Se 4 structures in side view with the charge carrier (A) Li, (C) Al in octahedral coordination and (B) Li, (D) Al in tetrahedral coordination. Areas of charge depletion are shown in blue and areas of charge accumulation are shown in red.

Source publication
Article
Full-text available
Periodic density functional theory calculations have been performed to study the migration of various charge carriers in spinel‐type MgSc2Se4. This compound exhibits low barriers for Mg ion diffusion, making it a potential candidate for solid electrolytes in Mg-ion batteries. In order to elucidate the decisive factors for the ion mobility in spinel...

Contexts in source publication

Context 1
... latter ones are obtained by subtracting both, the charge density of the isolated host structure and of the selected charge carrier from the charge density of the combined system. In order to illustrate the charge density differences, we have plotted isosurfaces for selected octahedral and tetrahedral environments in Figure 3. Moreover, Figure 4 depicts contour plots of the octahedrally coordinated sites, showing the plane connecting four atoms of the Se octahedron, as illustrated in panel A. Only the most stable sites at high charge carrier concentration are considered, i.e., the tetrahedral and octahedral sites. ...
Context 2
... should be noted that the appearance of the isosurface plots depends strongly on the selected isosurface level (see Supplementary Figure S1). To allow for comparison, the same isosurface value was chosen for all panels in Figure 3. The charge densities are slightly distorted and do not show the full octahedral symmetry. ...
Context 3
... is a consequence of the trigonal distortion of the MgSc 2 Se 4 spinel which slightly displaces the Se atoms in front of and behind the plane depicted in Figure 4A. Li is known to show mostly ionic interaction in the spinel structure, as can be inferred from Figures 3A,B, 4B. Furthermore, the other alkaline metals show charge density differences very similar to the one of Li (Supplementary Figures S2, S3), with the charge density difference for K being even further smeared out. ...
Context 4
... charge density difference plots show mostly ionic bonding for the alkaline metals at the octahedral site, however, with a possibly increasing covalent character for the larger and softer ions. These findings are essentially the same for the tetrahedral site, as shown for the case of Li in Figure 3B. ...
Context 5
... the charge depletion areas are less pronounced in the plane depicted in the contour plot, such that only a slight charge depletion is visible inside the octahedron, shown in light blue in Figure 4E. For Al, even more pronounced charge depletion is present (see Figures 3C, D, 4D). The charge depletion in the vicinity of the octahedron center, as observed for the multivalent ions, may be associated with the formation of an ionic bond and a greater interaction strength with the host lattice. ...
Context 6
... contrast to the multivalent charge carriers, the alkaline metals hardly polarize the charge distribution of the Sc-Se bond, and therefore, at the transition metal. This is best seen when comparing the 3D plots for Li and Al (see Figure 3). In the case of multivalent ions, the charge distribution at the transition metal is strongly changed when moving from octahedral to tetrahedral coordination (see Figures 3C, D), and the charge depletion distributes over the twelve Sc atoms neighboring the tetrahedral site. ...
Context 7
... is best seen when comparing the 3D plots for Li and Al (see Figure 3). In the case of multivalent ions, the charge distribution at the transition metal is strongly changed when moving from octahedral to tetrahedral coordination (see Figures 3C, D), and the charge depletion distributes over the twelve Sc atoms neighboring the tetrahedral site. For Al, an additional charge depletion between each Se atom of the tetrahedron and its three neighboring Sc atoms is observed. ...

Similar publications

Article
Full-text available
In this work, a magnesium ion rechargeable battery with twin‐graphene based anode material has been proposed and studied for its feasibility as a suitable option to replace the commercially available lithium‐ion rechargeable batteries. The adsorption of magnesium ion is tested at different sites on the substrate and adsorption at the trigonal sites...

Citations

... ARjats.cls April 1, 2022 15:19 structure (125) and in turn the Mg motion in the spinel, as highlighted by higher barriers in some tellurides (e.g., MgSc 2 Te 4 ; Figure 9) compared with the corresponding selenide (e.g., MgSc 2 Se 4 ). 2. Rong, Liu, and colleagues (22,122) have also indicated that a reduction of E m for Mg can be attained by selecting anion frameworks where the stable site for Mg displays an unfavorable coordination (i.e., a higher-energy stable site) and the transition state has a more favorable coordination (i.e., a lower-energy transition site). ...
Article
The development of inexpensive batteries based on magnesium (Mg) chemistry will contribute remarkably toward developing high-energy-density storage systems that can be used worldwide. Significant challenges remain in developing practical Mg batteries, the chief of which is designing materials that can provide facile transport of Mg. In this review, we cover the experimental and theoretical methods that can be used to quantify Mg mobility in a variety of host frameworks, the specific transport quantities that each technique is designed to measure or calculate, and some practical examples of their applications. We then list the unique challenges faced by different experimental and computational techniques in probing Mg ion transport in materials. This review concludes with an outlook on the directions that the scientific community could soon pursue as we strive to construct a pragmatic Mg battery. Expected final online publication date for the Annual Review of Materials Research, Volume 52 is July 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... These post-Li-ion batteries, in particular those based on multivalent ions, can compete with existing Li-ion batteries or even outperform them, as far as energy density and safety are concerned, 14,15 the latter in particular with respect to their lower tendency for dendrite growth. 16−20 Furthermore, as liquid electrolytes are prone to corrosion processes and often represent fire hazards because of their flammability, all-solid-state batteries with higher safety and better electrochemical stability 21 based on materials such as inorganic oxides, 22,23 hydrides, 24−26 and chalcogenides 27,28 have been intensely studied for all possible charge carriers. ...
... In fact, also with respect to ion mobility in solids, a number of possible descriptors have been proposed on the basis of, e.g., the lattice volume and ionic size, 28,29 the choice of the anion sublattice, 29,40 the lattice dynamics, 29,41,42 or the preferred crystal insertion site. 30 However, many of the identified descriptors are restricted to some particular crystal structure. ...
... Motivated by the goal to identify the fundamental factors determining ion mobility in solids, in a previous study 28 we had derived the activation barriers for the diffusion of a number of ions of varying size and charge in the same host lattice, a chalcogenide spinel. We obtained the expected results: namely, that the size and the charge of the diffusing ion matter. ...
Article
Full-text available
Ion mobility is a critical performance parameter not only in electrochemical energy storage and conversion but also in other electrochemical devices. On the basis of first-principles electronic structure calculations, we have derived a descriptor for the ion mobility in battery electrodes and solid electrolytes. This descriptor is entirely composed of observables that are easily accessible: ionic radii, oxidation states, and the Pauling electronegativities of the involved species. Within a particular class of materials, the migration barriers are connected to this descriptor through linear scaling relations upon the variation of either the cation chemistry of the charge carriers or the anion chemistry of the host lattice. The validity of these scaling relations indicates that a purely ionic view falls short of capturing all factors influencing ion mobility in solids. The identification of these scaling relations has the potential to significantly accelerate the discovery of materials with desired mobility properties.
... In order to illustrate the charge rearrangement and thus the nature of the interaction [49] between ions and the solvent molecules, we have determined charge density differences ...
Preprint
Full-text available
Density functional theory calculations together with ab initio molecular dynamics (AIMD) simulations have been used to study the solvation, diffusion and transformation of Li+ and LiO2 upon O2 reduction in three organic electrolytes. These processes are critical for the performance of Li-air batteries. Apart from studying the structure of the solvation shells in detail, AIMD simulations have been used to derive the diffusivity and together with the Blue Moon ensemble approach to explore LiO2 formation from Li+ and O2- and the subsequent disproportionation of 2LiO2 into Li2O2 + O2. By comparing the results of the simulations to gas phase calculations the impact of electrolytes on these reactions is assessed which turns out to be more pronounced for the ionic species involved in these reactions.
... A promising research field with great potential for improvement are multivalent ion batteries, in particular due to their high volumetric capacities as compared to lithium. [6][7][8] However, of course there are also certain drawbacks: Multivalent batteries suffer from mobility issues due to the higher ionic charge 5,[9][10][11][12] and also typically exhibit lower operating voltages than LIBs. 7 Additionally, new battery chemistries typically also require the identification and/or development of suitable electrolytes and electrode materials. ...
Preprint
Full-text available
While the Mo6S8 chevrel phase is frequently used as cathode material in Mg--ion batteries, theoretical studies on this material are comparatively scarce. The particular structure of the Mo6S8 phase, with rather loosely connected cluster entities, points to the important role of dispersion forces in this material. However, so far this aspect has been completely neglected in the discussion of Mo6S8 as cathode material for mono- and multivalent-ion batteries. In this work we therefore have studied the impact of dispersion forces on stability and kinetics of Mo6S8 intercalation compounds. For this purpose, a series of charge carriers (Li, Na, K, Mg, Ca, Zn, Al) has been investigated. Interestingly, dispersion forces are observed to only slightly affect the lattice spacing of the chevrel phase, nevertheless having a significant impact on insertion voltage and in particular on the charge carrier mobility in the material. Moreover, upon varying the charge carriers in the chevrel phase, their diffusion barriers are observed to scale linearly with the ion size, almost independent of the charge of the considered ions. This indicates a rather unique and geometry dominated diffusion mechanism in the chevrel phase. The consequences of these findings for the ion mobility in the chevrel phase will be carefully discussed.
... These post-Li-ion batteries, in particular those based on multivalent ions, can compete with existing Li-ion batteries or even outperform them, as far as energy density and safety are concerned, 14,15 the latter in particular with respect to their lower tendency for dendrite growth. [16][17][18][19][20] Furthermore, as liquid electrolytes are prone to corrosion processes and often represent fire hazards because of their flammability, all solid-state batteries with higher safety and better electrochemical stability 21 based on materials such as inorganic oxides, 22,23 hydrides, [24][25][26] and chalcogenides 27,28 have been intensively studied for all possible charge carriers. ...
... Such an minimum energy path can be determined by automatic search routines. 43 In the present work, we have used the nudged elastic band method (NEB) 44 in the DFT calcu- Motivated by the goal to identify the fundamental factors determining ion mobility in solids, in a previous study 28 we had derived the activation barriers for diffusion of a number of ions of varying size and charge in the same host lattice, a chalcogenide spinel. We obtained the expected results, namely that the size and the charge of the diffusing ion matter. ...
... Indeed these findings confirm that the oxidation states reflecting the charge of the atoms, the ion radii and the electronegativity differences are the determining factors for the migration barriers. Interestingly, the unit cell volume V which has been shown to substantially influence the ionic mobility in some structural families 28,29 does not show up in these statistically derived descriptors. However, note that the functional dependencies found by the SISSO operators do not allow for a straightforward interpretation of the physico-chemical factors underlying the migration process. ...
Preprint
Full-text available
Ion mobility is a critical performance parameter in electrochemical energy storage and conversion, but also in other electrochemical devices. Based on first-principles electronic structure calculations, we have derived a descriptor for the ion mobility in battery electrodes and solid electrolytes. This descriptor is entirely composed of observables that are easily accessible: ionic radii, oxidation states and the Pauling electronegativities of the involved species. Within a particular class of materials, the migration barriers are connected to this descriptor through linear scaling relations upon the variation of either the cation chemistry of the charge carriers or the anion chemistry of the host lattice. The validity of these scaling relations indicates that a purely ionic view falls short of capturing all factors influencing ion mobility in solids.The identification of these scaling relations has the potential to significantly accelerate the discovery of materials with desired mobility properties.
Article
Magnesium (Mg) batteries are promising candidates for lithium-ion batteries owing to their high theoretical capacity and the rich natural abundance of Mg. However, the development of Mg metal batteries, especially in an attractive solid-state configuration, is hampered by sluggish Mg²⁺ migration. Here, we discover that by incorporating oxygen vacancies on the surface of metal oxide nanopowders, the Mg²⁺ ion conductivity (σi) at room temperature in Mg(BH4)2•1.5NH3 is dramatically improved on the order of 10⁻⁴ S cm⁻¹, e.g., 2.96 × 10⁻⁴ S cm⁻¹, by the addition of 60 wt.% TiO2. Theoretical simulations indicate that the high σi is due to the “coordination-unlock” phenomenon at the interface, where the coordination sheath of Mg(BH4)2•1.5NH3 is unlocked by oxygen vacancies and coordination-deficient Mg transfers on the surface through interactions with oxygen sites. The strategy involving the assistance of oxygen vacancies could create a new path for designing new divalent cation conductors.
Article
While the Mo 6 S 8 chevrel phase is frequently used as cathode material in Mg–ion batteries, theoretical studies on this material are comparatively scarce. The particular structure of the Mo 6 S 8 phase, with rather loosely connected cluster entities, points to the important role of dispersion forces in this material. However, so far this aspect has been completely neglected in the discussion of Mo 6 S 8 as cathode material for mono– and multivalent–ion batteries. In this work we therefore have studied the impact of dispersion forces on stability and kinetics of Mo 6 S 8 intercalation compounds. For this purpose, a series of charge carriers (Li, Na, K, Mg, Ca, Zn, Al) has been investigated. Interestingly, dispersion forces are observed to only slightly affect the lattice spacing of the chevrel phase, nevertheless having a significant impact on insertion voltage and in particular on the charge carrier mobility in the material. Moreover, upon varying the charge carriers in the chevrel phase, their diffusion barriers are observed to scale linearly with the ion size, almost independent of the charge of the considered ions. This indicates a rather unique and geometry dominated diffusion mechanism in the chevrel phase. The consequences of these findings for the ion mobility in the chevrel phase will be carefully discussed.
Article
Full-text available
Batteries based on multivalent ions such as magnesium have been attracting considerable attention due to their potential for high energy densities, but their low ion mobility remains an obstacle. Herein, ionic conductivity in spinel host materials, which represent a promising class of cathode and solid‐electrolyte materials in batteries, is addressed. Based on periodic density functional theory calculations, the important parameters that determine the mobility and insertion of ions are identified. In particular, the critical role that trigonal distortions of the spinel structure play for the ion mobility is highlighted. It is shown that it is the competition between coordination and bond length that governs the Mg site preference in spinel compounds upon trigonal distortions. This can only be understood by also taking covalent interactions into account. This reveals that purely ionic concepts are not sufficient to understand mobility in crystalline battery materials. Furthermore, the calculations suggest that anionic redox plays a much more important role in sulfide and selenide spinels than in oxide spinels. The findings shed light on the fundamentional mechanisms underlying ionic conductivity in solid hosts and thus may contribute to improvement of ion transport in battery electrodes. Ion mobility in electrodes and electrolytes is a critical performance parameter for batteries. Herein, using first‐principles electronic structure calculations, the factors underlying the migration and site preference of ions in spinel chalcogenides are determined. It is demonstrated that a purely ionic picture of the interaction in crystalline battery materials falls short of providing a complete understanding of ionic conductivity.
Preprint
Full-text available
In the area of sustainable energy storage, batteries based on multivalent ions such as magnesium have been attracting considerable attention due to their potential for high energy densities. Furthermore, they are typically also more abundant than, e.g., lithium. However, as a challenge their low ion mobility in electrode materials remains. This study addresses the ionic conductivity in spinel host materials which represent a promising class of cathode and solid-electrolyte materials in Mg-ion batteries. Based on periodic density functional theory calculations, we identify the critical parameters which determine the mobility and insertion of ions. We will in particular highlight the critical role that trigonal distortions of the spinel structure play for the ion mobility. In detail, we will show that it is the competition between coordination and bond length that governs the Mg site preference in ternary spinel compounds upon trigonal distortions. This can only be understood by also taking covalent interactions into account. Furthermore, our calculations suggest that anionic redox plays a much more important role in sulfide and selenide spinels than in oxide spinels. Based on our theoretical study, we rationalize the impact of the metal distribution in the host material and the ion concentration on the diffusion process. Furthermore, cathode-related challenges for practical devices will be addressed. Our findings shed light on the fundamentional mechanisms underlying ionic conductivity in solid hosts and thus may contribute to improve ion transport in battery electrodes.
Article
Recently, post Li batteries have been intensively researched due to high cost and localization of Li sources, especially for large-scale applications. Concurrently, ceramic electrolytes for post Li batteries also gain much attention to develop all-solid-state post Li batteries. The most intensively researched post Li battery is Na battery because of chemical and electrochemical similarities between Li and Na elements. Many good review papers about Na battery have been published including Na-ion conductive ceramic electrolytes. Contrary, ceramic electrolytes for other post Li batteries like K, Mg, Ca, Zn and Al batteries are hardly summarized. In this review, research on ceramic electrolytes for K, Mg, Ca, Zn and Al batteries is analyzed based on latest papers published since 2019 and suggested future research direction of ceramic electrolytes for post-Li batteries.