JP2021136192A - Lithium-rich antiperovskite compound, solid electrolyte for lithium ion secondary battery, and lithium ion solid secondary battery - Google Patents

Abstract

To provide a lithium compound for a solid electrolyte, which is superior in ion conductivity, charge/discharge stability, and thermodynamic stability.SOLUTION: A compound for a lithium ion secondary battery comprises one or more compounds of a lithium-rich antiperovskite structure, represented by the following formulas: Li24Se2Br6Cl2O6; Li24S6Br4Cl4O2; Li24I2Cl6O8; Li32Te8I8Cl8; Li24Se6I6Cl2O2; Li24Se4I8O4; Li32Br8Cl8O8; Li24Br2Cl6O8; Li32I4Br12O8; and Li24Se6S2I6Cl2.SELECTED DRAWING: Figure 2

Description

The present invention relates to a lithium-rich antiperovskite compound, a solid electrolyte for a lithium ion secondary battery, and a lithium ion solid secondary battery.

Lithium-ion secondary batteries are used in a wide range of fields from personal use to industrial use as batteries for hybrid and EV automobiles, mobile terminals such as smartphones, power supplies for PCs, and photovoltaic power storage. And the market is expanding rapidly.

Lithium-ion secondary batteries are used in such a wide range of fields, but further improvement in electric capacity and charge / discharge characteristics is required. Furthermore, the current lithium-ion secondary batteries mainly use liquids as electrolytes, and there are problems in handling and countermeasures against liquid leakage, and there is a strong demand for lithium secondary batteries with solid electrolytes. There is.
There, a solid electrolyte of a lithium ion secondary battery is required to have high ionic conductivity (Non-Patent Document 1), excellent charge / discharge characteristics, and high stability against heat, moisture, and the like.

Against this background, various studies have been made as a solid electrolyte for lithium ion secondary batteries. For example, mention may be made of Patent Document 1 as its efforts, in _{which, Li 3-x ClO 1-} x Hal x, Li 3-y-x M y O 1-x Hal x Cl (Hal is F, Cl, Br or I, M is Na, K, Rb or Cs, and 0 <x <1, 0 <y <2) and the like have been studied. However, ionic conductivity, charge / discharge stability, and thermodynamic stability did not always meet the requirements.

Special Table 2019-513687

Braga et al. , J. Mater. Chem. , 2014, 2, 5470-5480 A. P. Guerreiro et al. , Evolutionary Computation, 2016, 24 (3), 521-544 R. Jalem et al. , Sci. Tech. Adv. Mater. , 2018, 19, 231-242 R. Jalem et al. , Sci. Rep. , 2018, 8, 5845

An object of the present invention is to provide a compound for a solid electrolyte having excellent thermodynamic stability such as ionic conductivity, charge / discharge stability and hydration.
Furthermore, it is an object of the present invention to provide a solid electrolyte for a lithium secondary battery and a lithium solid secondary battery having excellent stability including ionic conductivity and charge / discharge using the compound.

The configuration of the present invention is shown below.
(Structure 1)
A compound for a lithium ion secondary battery having one or more compounds having a lithium-rich antiperovskite structure represented by Formulas 1 to 10 below.
[Formula 1]
Li ₂₄ Se ₂ Br ₆ Cl ₂ O ₆
[Formula 2]
Li ₂₄ S ₆ Br ₄ Cl ₄ O ₂
[Formula 3]
Li ₂₄ I ₂ Cl ₆ O ₈
[Formula 4]
Li ₃₂ Te ₈ I ₈ Cl ₈
[Formula 5]
Li ₂₄ Se ₆ I ₆ Cl ₂ O ₂
[Formula 6]
Li ₂₄ Se ₄ I ₈ O ₄
[Formula 7]
Li ₃₂ Br ₈ Cl ₈ O ₈
[Formula 8]
Li ₂₄ Br ₂ Cl ₆ O ₈
[Formula 9]
Li ₃₂ I ₄ Br ₁₂ O ₈
[Formula 10]
Li ₂₄ Se ₆ S ₂ I ₆ Cl ₂
(Structure 2)
The compound according to composition 1, which has a lithium-rich antiperovskite structure represented by 1 selected from the group consisting of the formula 4, the formula 5, the formula 7, the formula 8 and the formula 10.
(Structure 3)
The compound according to composition 1, which has a lithium-rich antiperovskite structure represented by Formula 1.
(Structure 4)
The compound according to composition 1, which has a lithium-rich antiperovskite structure represented by the formula 6.
(Structure 5)
The compound according to composition 1, which has a lithium-rich antiperovskite structure represented by the formula 7.
(Structure 6)
A solid electrolyte for a lithium ion secondary battery containing at least one compound having a lithium-rich antiperovskite structure represented by Formulas 1 to 10 below.
[Formula 1]
Li ₂₄ Se ₂ Br ₆ Cl ₂ O ₆
[Formula 2]
Li ₂₄ S ₆ Br ₄ Cl ₄ O ₂
[Formula 3]
Li ₂₄ I ₂ Cl ₆ O ₈
[Formula 4]
Li ₃₂ Te ₈ I ₈ Cl ₈
[Formula 5]
Li ₂₄ Se ₆ I ₆ Cl ₂ O ₂
[Formula 6]
Li ₂₄ Se ₄ I ₈ O ₄
[Formula 7]
Li ₃₂ Br ₈ Cl ₈ O ₈
[Formula 8]
Li ₂₄ Br ₂ Cl ₆ O ₈
[Formula 9]
Li ₃₂ I ₄ Br ₁₂ O ₈
[Formula 10]
Li ₂₄ Se ₆ S ₂ I ₆ Cl ₂
(Structure 7)
The lithium ion 2 according to composition 6, which contains one or more compounds having a lithium-rich antiperovskite structure represented by 1 selected from the group consisting of the formula 4, the formula 5, the formula 7, the formula 8 and the formula 10. Solid electrolyte for next battery.
(Structure 8)
The solid electrolyte for a lithium ion secondary battery according to composition 6, which contains a compound having a lithium-rich antiperovskite structure represented by Formula 1.
(Structure 9)
The solid electrolyte for a lithium ion secondary battery according to composition 6, which contains a compound having a lithium-rich antiperovskite structure represented by the formula 6.
(Structure 10)
The solid electrolyte for a lithium ion secondary battery according to composition 6, which contains a compound having a lithium-rich antiperovskite structure represented by the formula 7.
(Structure 11)
A lithium ion solid secondary battery having the solid electrolyte for a lithium ion secondary battery according to any one of configurations 6 to 10.

INDUSTRIAL APPLICABILITY The present invention provides a compound for a solid electrolyte having excellent thermodynamic stability such as ionic conductivity, charge / discharge stability and hydration.
Further, it becomes possible to provide a solid electrolyte for a lithium secondary battery and a lithium solid secondary battery having excellent stability including ionic conductivity and charge / discharge.

It is a structural drawing which shows the antiperovskite compound. It is a structural diagram which shows the basic structure of the searched antiperovskite compound. It is explanatory drawing which shows the material search process.

Hereinafter, the present invention will be described in detail. The detailed description of the present invention described below may be based on representative embodiments, embodiments, and examples, but these are examples, and the present invention describes such embodiments, embodiments, and the like. And is not limited to the examples.

(Embodiment 1)
In the first embodiment, the outline of the material search method will be described.

FIG. 1 is a structural formula showing a basic antiperovskite, where 1 is a Z site, 2 is an A site, 3 is an X site, and Li (lithium) is contained in the Z site as the base of the object of the present invention. It has become.
As shown in FIG. 2, the basic structure of the antiperovskite compound searched for in the present invention basically consists of five types of FIGS. 2 (a) to 2 (e).
First, as shown in FIG. 3, any one of the five types of FIGS. 2 (a) to 2 (e) is used as the host structure, and the A site is O (oxygen), S (sulfur), Se (selenium), and so on. Any of Te (tellurium), OS, OS, O-Te, S-Se, S-Te, Se-Te, X-site is F (fluorine), Cl (chlorine), Br (bromine), I (fluorine), F-Cl, F-Br, FI, Cl-Br, Cl-I, Br-I, and the ratio is 0.0,0.25,0.5,0. Assuming 5-level swing compounds of 75 and 1.0, further optimizing their positions in terms of stable electron density is performed using Density Function Theory (DFT) to extract formula candidates. Here, for example, OS means that O and S are included. The ratio is the ratio of the above five levels. For example, when the ratio is 0.0, only O is arranged, when 1.0, only S is arranged, and when 0.5, it means that the same number of O and S are arranged.

After that, the decomposition energy (Decomposition Energy) is calculated based on the first-principles calculation, and the process proceeds to the next step only when the decomposition energy is 0.1 eV or less. Here, the standard of decomposition energy of 0.1 eV is an empirical value derived from the experience of material synthesis. That is, it is based on the experience that material synthesis is difficult when the decomposition energy exceeds 0.1 eV.

Thereafter, water-reactive energy _{(H 2 O Reaction energy),} Li -ion conductivity (Li ionic conductivity), the band gap (Band gap) and scores that reflect these items, for example, by the method described in Example 1 From the ones with the highest scores and the ones with the highest scores, those with particularly excellent water reaction energy, Li ion conductivity, and bandgap are extracted.

Those with high water reaction energy have high stability to water and thermodynamic stability, those with high Li ion conductivity contribute to reduction of internal resistance and improvement of current characteristics, and those with high bandgap. Excellent charge / discharge stability.
Therefore, the extracted antiperovskite formula is suitable for a solid electrolyte for a lithium secondary battery, which has excellent stability including ionic conductivity and charge / discharge.

(Embodiment 2)
The second embodiment describes a lithium ion solid secondary battery using the formula selected in the first embodiment.
The lithium ion solid secondary battery mainly comprises a positive electrode, a negative electrode, and a solid electrolyte, and the formula selected in the first embodiment is used as the solid electrolyte among them. Here, examples of the positive electrode include LiCoO _{2 , LiFePO 4, and the} like, and examples of the negative electrode include C (carbon), Li metal, LiSi, and the like.
By using the formula selected in the first embodiment as the solid electrolyte, it is excellent in stability including ionic conductivity and charge / discharge, and because it is a solid-state battery, it is easy to handle, safe, and leak-free. It will be possible to supply a lithium-ion solid-state secondary battery that has all the characteristics.
In particular, when Li ₂₄ Se ₂ Br ₆ Cl ₂ O ₆ is used as the solid electrolyte, it becomes possible to supply a lithium ion solid secondary battery having excellent ionic conductivity, low internal resistance, and high output current. When Li ₃₂ Br ₈ Cl ₈ O ₈ is used as the solid electrolyte, it becomes possible to supply a lithium ion solid secondary battery having excellent stability of charge / discharge characteristics, and Li ₂₄ Se ₄ I ₈ O as the solid electrolyte. _{When No. 4} is used, it becomes possible to supply a lithium ion solid secondary battery that is stable against water and has excellent thermodynamic stability.

The present invention is not limited to the above-described embodiment, and the above-described embodiment is an example for explaining the present invention, and is substantially the same as the technical idea described in the claims of the present invention. Anything having the same configuration and exhibiting the same effect and effect is included in the technical scope of the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example 1)
In Example 1, the following simulation is carried out to show the result of searching for a suitable material from the three viewpoints of Li ion conductivity, hydration energy and bandgap energy. These three elements are particularly important elements for improving the performance of the lithium ion solid secondary battery.

1. 1. Density Functional Theory (DFT) Setting Using the projector-enhanced wave (PAW) format of ion-electron interactions, the function of the exchange correlation energy is a generalized gradient approximation parameterized by Perdew, Burke and Ernzerhof (PBE) (PBE). GGA) was used.
As the Li pseudopotential, a semi-core state was used as the valence state, and a standard pseudopotential was used for other atomic types.
Here, the kinetic energy cutoff was set to 520 eV.
As meshes, at least 1000 k-point meshes were assigned in the Monkhorst-Pack grid scheme.
All calculations were performed under spin polarization conditions and the optimized convergence was set to less than 1 meV / atom for energy and less than 0.001 eV / nm for residual force.

2. Inorganic crystal structure data As the inorganic crystal structure data, the crystal structure data of the inorganic crystal structure database (ICSD) was used.

3. 3. Ion Substitution Scheme The ion substitution scheme is the relationship between crystal symmetry groups and subgroups at a special site concentration ratio (0,0.25,0.33,0.5,0.67,0.75,1.0). Was simulated based on.

4. Thermodynamic calculation (4-1)
Based on thermodynamics, the Gibbs free energy (G) at a specific temperature (T) and pressure (P) is G (T, P, N _Li , N _x , N _z ) = H (T, P, N). It was calculated using the formula _Li , N _x , N _z ) + PV (T, P, NN _Li , N _x , N _z ) -TS (T, P, N _Li , N _x , N _z).
Here, H is enthalpy, V is volume, and S is entropy. The PV and TS terms were negligible and were set to zero in the 0K condensed phase.
(4-2)
For the predicted compounds and their competing phases, the convex hull approach was used to determine the ground state phase.
(4-3)
For the chemical potential, the reference chemical potential used based on the standard state of the element was used as shown below. That is, here, (μ _Na ⁰ ) from Li metal, O (μ ₀ ⁰ ) from 1 / 2O ₂ gas, S (μ _S ⁰ ) from S solid, Br (μ) from 1 / 2Br _{2 gas. Br} ⁰ ), Cl from 1 / 2Cl ₂ gas (μ _Cl ⁰ ), F from 1 / 2F ₂ gas (μ _F ⁰ ), I from 1 / 2I ₂ gas (μ _I ⁰ ), from Se metal Se (μ _Se ⁰ ) and Te (μ _Te ⁰ ) from Te metal were used.
(4-4)
Chemical stability with water was calculated based on the following LiOH formation: Li _a X _b Z _c + H ₂ O = Li _a HX _b Z _c + LiOH. Here, a, b, and c are the atomic numbers of the supercell model.

5. Calculation of ionic conductivity The ionic conductivity was estimated from the molecular dynamics calculation (MD) at the target temperature T = 400K. Here, a supercell model of at least 100 atoms was used for Li orbital sampling by MD.
Specifically, the step size of MD execution was set to 1 fs, and equilibration of 10 ps (10000 MD steps) was performed under NPT ensemble conditions before 50 ps (50,000 MD steps) MD trajectory sampling under NPT ensemble conditions.
The Li diffusion rate at T = 400K was determined by the following equation from the gradient of the time ensemble average root mean square displacement (MSD) plot.
MSD = <[r _v (t + τ) -r _v (t)] ² >
Here, r _v (t) is the position (vector) of the atom at time t, and τ is the delay time between the _{two positions r v} (t + τ) and r _{v (t).}
The diffusion coefficient (D) of Na was calculated based on the Einstein-Smoluchowski equation. That is, the calculation was performed using the following formula (1). Here, d is the number of grid dimensions in the diffusion process.

Ionic conductivity at T = 400K (σ) is, Nernst - Einstein relation, i.e. sigma ⁼ calculated based on (ze 2 D) / (kT ). Here, z is the charge carrier density, e is the elementary charge, and k is the Boltzmann constant.

6. Multipurpose Bayesian Optimization (MOBO) Algorithm Three batteries: Li ion conductivity, electrochemical window using band gap energy (DFT electron band gap energy), and hydration energy, which is an indicator of the chemical stability of lithium ion batteries. Important properties were simultaneously optimized at the same ratio with no weight difference. This method conforms to the method described in Non-References 2 and 3.
The MOBO algorithm finds a solution by a Gaussian (GP) process model, but here, three objective functions (f ₁ : Li ion conductivity, f ₂ : electrochemical window using DFT electron band gap energy, f ₃ : Chemical stability to water) was applied.
The GP model has an addition structure having the following six subkernels (k) defined from a histogram of six general material properties of each compound. k ₁ : Electronegativity of the elements of the compound, k ₂ : A subset of the actual values from the boronoite serrations of the atomic pair coordinates (cation-cation, cation-anion, and anion-anion pairs), k ₃ : Atomic pair coordinates Partial radiative distribution function of a subset (cation-cation, cation-anion, and anion-anion pair), and product kernel k ₄ = k ₁ × k ₂ , k ₅ = k ₁ × k ₃ , and k ₆ = K ₂ x k ₃ . This handling is in accordance with Non-Patent Document 4.
The MOBO parameters were updated in all MOBO steps, and the batch sampling size was set to 10 compounds in all MOBO steps. The MOBO step was set to 7 steps in view of convergence.
In addition, the acquisition function was formulated at each MOBO step based on the upper limit confidence limit (GP-UCB) based on the hypervolume from the GP prediction.

The above simulation was performed on a total of 10500 lithium-rich antiperovskite. Then, the object was narrowed down to about 1000 according to the decomposition energy standard of 0.1 eV or less, and further narrowed down to 200 from among them by optimization. On that basis, the ones with the highest scores and the ones with excellent performance were selected in consideration of the values of reaction energy, ionic conductivity, and bandgap.

As a result, the formulas of the selected high-ranking antiperovskite compounds are shown in Table 1. _{In addition, Table 1 also applies the method described in Example 1 to Li 24} O ₈ Br ₈ known as a solid electrolyte for a lithium secondary battery, and applies decomposition energy, water reaction energy, and ion conduction. The results of calculating the rate, band gap and score are also posted.

Li ₂₄ Se ₂ Br ₆ Cl ₂ O ₆ , Li ₂₄ S ₆ Br ₄ Cl ₄ O ₂ , Li ₂₄ I ₂ Cl ₆ O ₈ , Li ₃₂ Te ₈ I ₈ Cl ₈ , Li ₂₄ Se ₆ I ₆ Cl ₂ O ₂ , Li ₂₄ Se ₄ I ₈ O ₄ , Li ₃₂ Br ₈ Cl ₈ O ₈ , Li ₂₄ Br ₂ Cl ₆ O ₈ , Li ₃₂ I ₄ Br ₁₂ O ₈ and Li ₂₄ Se ₆ S ₂ I ₆ Cl ₂ has high levels of water reaction energy, ionic conductivity, and band gap, among which Li ₃₂ Te ₈ I ₈ Cl ₈ , Li described in Nos. 4, 5, 7, 8 and 10 ₂₄ Se ₆ I ₆ Cl ₂ O ₂ , Li ₃₂ Br ₈ Cl ₈ O ₈ , Li ₂₄ Br ₂ Cl ₆ O ₈ and Li ₂₄ Se ₆ S ₂ I ₆ Cl ₂ have water reaction energy, ionic conductivity, and band gap. It was at a particularly high level.

Li ₂₄ Se ₂ Br ₆ Cl ₂ O ₆ has an ionic conductivity of 0.7823 S / cm, which is about 90 times as high as 0.0086 S / cm of _{Li 24} O ₈ Br _{8 which is a comparative example.} Indicated.
Li ₂₄ Se ₄ I ₈ O ₄ is characterized by a water reaction energy of about 38 KJ / mol and particularly high stability with respect to water. On the other hand, Li ₂₄ O ₈ Br ₈ which is a comparative example has a negative value of about −39 KJ / mol in which the reaction proceeds with water.
The _{bandgap of Li 32} Br ₈ Cl ₈ O ₈ is 4.5431 eV, which is about 8% higher than that of 4.1935 eV of _{Li 24} O ₈ Br ₈ which is a comparative example, which is a value when used as a secondary battery. It means that the charge / discharge stability is high.

_{Therefore, Li 24} Se ₂ Br ₆ Cl ₂ O ₆ , Li ₂₄ S ₆ Br ₄ Cl ₄ O ₂ , Li ₂₄ I ₂ Cl ₆ O ₈ , Li ₃₂ Te ₈ I ₈ Cl ₈ , Li listed in Table 1. ₂₄ Se ₆ I ₆ Cl ₂ O ₂ , Li ₂₄ Se ₄ I ₈ O ₄ , Li ₃₂ Br ₈ Cl ₈ O ₈ , Li ₂₄ Br ₂ Cl ₆ O ₈ , Li ₃₂ I ₄ Br ₁₂ O ₈ and Li ₂₄ Se ₆ S ₂ I ₆ Cl ₂ has high performance as an electrolyte for Li solid secondary batteries, and in particular, Li ₃₂ Te ₈ I ₈ Cl ₈ , Li ₂₄ Se ₆ I ₆ Cl ₂ O ₂ , Li ₃₂ Br ₈ Cl ₈ O. ₈ , Li ₂₄ Br ₂ Cl ₆ O ₈ and Li ₂₄ Se ₆ S ₂ I ₆ Cl ₂ had particularly high performance as electrolytes for Li solid secondary batteries. _{Also, Li 24 Se 2 Br 6 Cl} 2 O 6 ion _{conductivity, Li 24 Se 4 I 8 O} 4 is water stable, and _Li 32 _{Br 8 Cl} 8 _O 8 is perforated excellent properties charge and discharge stability Was.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a compound for a solid electrolyte for a secondary battery and a solid electrolyte that are easy to handle and have excellent current characteristics, high stability against charge / discharge and moisture, and no fear of liquid leakage. Further, a solid secondary battery using the compound as an electrolyte has excellent current characteristics, is highly stable against charge / discharge and moisture, and is easy to handle without fear of liquid leakage.
In a smart society such as hybrid and electric vehicles, high-performance housing, and mobile terminals such as smartphones, there is a strong demand for secondary batteries that support large currents, are highly stable, and are easy to handle. Therefore, the present invention includes personal applications. We believe that it will contribute to the development of industry and society.

1: Z site (Li)
2: A site 3: X site

Claims (11)

A compound for a lithium ion secondary battery having one or more compounds having a lithium-rich antiperovskite structure represented by Formulas 1 to 10 below.
[Formula 1]
Li ₂₄ Se ₂ Br ₆ Cl ₂ O ₆
[Formula 2]
Li ₂₄ S ₆ Br ₄ Cl ₄ O ₂
[Formula 3]
Li ₂₄ I ₂ Cl ₆ O ₈
[Formula 4]
Li ₃₂ Te ₈ I ₈ Cl ₈
[Formula 5]
Li ₂₄ Se ₆ I ₆ Cl ₂ O ₂
[Formula 6]
Li ₂₄ Se ₄ I ₈ O ₄
[Formula 7]
Li ₃₂ Br ₈ Cl ₈ O ₈
[Formula 8]
Li ₂₄ Br ₂ Cl ₆ O ₈
[Formula 9]
Li ₃₂ I ₄ Br ₁₂ O ₈
[Formula 10]
Li ₂₄ Se ₆ S ₂ I ₆ Cl ₂ The compound according to claim 1, which has a lithium-rich antiperovskite structure represented by 1 selected from the group consisting of the formula 4, the formula 5, the formula 7, the formula 8 and the formula 10. The compound according to claim 1, which has a lithium-rich antiperovskite structure represented by Formula 1. The compound according to claim 1, which has a lithium-rich antiperovskite structure represented by the formula 6. The compound according to claim 1, which has a lithium-rich antiperovskite structure represented by the formula 7. A solid electrolyte for a lithium ion secondary battery containing at least one compound having a lithium-rich antiperovskite structure represented by Formulas 1 to 10 below.
[Formula 1]
Li ₂₄ Se ₂ Br ₆ Cl ₂ O ₆
[Formula 2]
Li ₂₄ S ₆ Br ₄ Cl ₄ O ₂
[Formula 3]
Li ₂₄ I ₂ Cl ₆ O ₈
[Formula 4]
Li ₃₂ Te ₈ I ₈ Cl ₈
[Formula 5]
Li ₂₄ Se ₆ I ₆ Cl ₂ O ₂
[Formula 6]
Li ₂₄ Se ₄ I ₈ O ₄
[Formula 7]
Li ₃₂ Br ₈ Cl ₈ O ₈
[Formula 8]
Li ₂₄ Br ₂ Cl ₆ O ₈
[Formula 9]
Li ₃₂ I ₄ Br ₁₂ O ₈
[Formula 10]
Li ₂₄ Se ₆ S ₂ I ₆ Cl ₂ The lithium ion according to claim 6, wherein the lithium ion according to claim 6 contains one or more compounds having a lithium-rich antiperovskite structure represented by 1 selected from the group consisting of the formula 4, the formula 5, the formula 7, the formula 8 and the formula 10. Solid electrolyte for secondary batteries. The solid electrolyte for a lithium ion secondary battery according to claim 6, which contains a compound having a lithium-rich antiperovskite structure represented by Formula 1. The solid electrolyte for a lithium ion secondary battery according to claim 6, which contains a compound having a lithium-rich antiperovskite structure represented by the formula 6. The solid electrolyte for a lithium ion secondary battery according to claim 6, which contains a compound having a lithium-rich antiperovskite structure represented by the formula 7. A lithium ion solid secondary battery having the solid electrolyte for a lithium ion secondary battery according to any one of claims 6 to 10.

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