CN115692858A - Local high-concentration electrolyte suitable for potassium ion battery and application thereof - Google Patents

Abstract

The invention discloses a local high-concentration electrolyte suitable for a potassium ion battery, which consists of a high-concentration ether electrolyte and a functional fluorinated diluent, wherein the high-concentration ether electrolyte preferably consists of potassium bis (fluorosulfonyl) imide and ethylene glycol dimethyl ether, the concentration of the high-concentration ether electrolyte is 3-6 mol/L, the functional fluorinated diluent preferably consists of 1, 2-tetrafluoroethyl-2, 3-tetrafluoropropyl ether, and the volume ratio of the two is (2). The specific combination not only can obviously improve the viscosity and the fluidity of the high-concentration ether electrolyte and the electrode wettability, but also can change the solvation structure and the molecular energy level of potassium ions in the electrolyte, effectively regulate and control the formation of a solid electrolyte layer on the surface of the phosphorus/carbon cathode and improve the electrochemical reversibility, the circulation stability and the rate capability in the potassium storage process. The local high-concentration electrolyte is further applied to a potassium ion full battery consisting of a phosphorus/carbon cathode and a purified 3,4,9, 10-perylene tetracarboxylic dianhydride anode, so that long cycle life and high coulombic efficiency can be realized.

Description

A local high-concentration electrolyte suitable for potassium-ion batteries and its application

technical field

The invention belongs to the technical field of metal battery liquid electrolyte, and in particular relates to a local high-concentration electrolyte of a potassium ion battery and an application method thereof.

Background technique

Potassium-ion batteries, due to the abundant reserves of potassium resources, low cost and the similarity of basic physical and chemical properties of potassium and lithium/sodium elements, have gradually attracted the attention of the field of electrochemical energy research. As a cheap negative electrode material, phosphorus can alloy with multiple potassium ions, so it has extremely high theoretical capacity and energy density, but its electrochemical performance is still limited by its low electrical conductivity and potassium storage process. Larger volume change rate in the medium. Although the combination with highly conductive/highly flexible carbon materials can buffer its huge volume change during the potassium storage process to a certain extent, the prepared phosphorus/carbon (P/C) anode materials still face severe internal structure collapse and violent Interfacial side reactions and rapid electrochemical performance decay and other issues. As a by-product of the interfacial reaction during the discharge process, the solid electrolyte interface (SEI) layer directly determines the basic electrochemical properties of P/C anode materials.

In the current study, the composition of the electrolyte is generally considered to be able to effectively regulate the formation process of the SEI layer of the anode material of the potassium-ion battery, and at the same time significantly improve its cycle stability. As the main components of the electrolyte of potassium-ion batteries, potassium salts and solvents directly determine the formation and electrochemical performance of the negative electrode material SEI layer. From the perspective of potassium salts, potassium bisfluorosulfonimide (KFSI) with high solubility and low lowest unoccupied molecular orbital (LUMO) energy level (-2.062eV) is compared with low solubility and high LUMO energy level (- 1.988eV) of potassium hexafluorophosphate (KPF ₆ ), can form an SEI layer with more uniform coating, more complete structure, better flexibility and thinner thickness on the surface of the negative electrode material, thereby significantly improving its performance in the potassium storage process. Electrochemical reversibility and cycle stability. From the perspective of the solvent, the ether (Ether) electrolyte with a higher dielectric constant can effectively promote the dissociation of the potassium salt in the solvent and increase the solubility of the potassium salt without significantly increasing the viscosity of the electrolyte. On this basis, increasing the concentration of KFSI in the organic solvent (>3M) was found to effectively reduce the LUMO energy level of the electrolyte, further enhance the dominant role of KFSI in the SEI formation process, reduce free solvent molecules, and thus improve the performance of the electrolyte at high capacity. A SEI layer with firm structure and excellent flexibility is formed on the surface of the negative electrode material, and the electrochemical reversibility and stability of the high-capacity negative electrode material are significantly improved.

Chinese patent CN201810551120.9 reports a concentrated electrolyte system suitable for potassium-ion batteries. Its potassium salt concentration is greater than or equal to 2mol/L, which can make battery electrode materials exhibit excellent electrochemical performance and can be successfully applied to bismuth negative electrodes. Or a potassium ion battery assembled with p-benzoquinone organic negative electrode and Prussian white positive electrode. Chinese patent CN201910675748.4 reports a high-concentration potassium ion battery electrolyte, which uses bisfluorosulfonimide potassium salt (KFSI) as the solute, and the potassium salt concentration is 3 to 5 mol/L, which can form a stable electrolyte on the surface of the graphite negative electrode. SEI layer, and significantly improve its potassium storage performance and cycle life.

However, the high viscosity, low fluidity, low ion conductivity and poor electrode wettability of the high-concentration electrolyte itself will directly weaken the rate performance of the negative electrode material at high current density, and its high production cost will further hinder it. Commercialization of potassium-ion batteries. On the other hand, the widespread use of flammable and volatile active solvents in traditional organic electrolytes also casts a huge shadow on the safety of potassium-ion batteries.

In view of the above deficiencies, it is very necessary to provide an electrolyte that can efficiently regulate potassium ion batteries.

Contents of the invention

The present invention aims at defects such as high viscosity, low fluidity, low ion conductivity and poor electrode wettability presented by high-concentration electrolytes, and introduces functional fluorinated solvents as diluents into high-concentration ether electrolytes for potassium-ion batteries , so as to form a local high-concentration electrolyte that has both the solvation characteristics of the high-concentration electrolyte and the fluidization characteristics of the conventional electrolyte, and precisely build a structurally complete, flexible and thin SEI layer on the surface of the P/C negative electrode material. And then significantly improve its reversible capacity, cycle life and rate performance in potassium ion batteries.

The purpose of the present invention is achieved through the following technical solutions.

A partial high-concentration electrolyte solution for a potassium ion battery, including a functional fluorinated solvent and a high-concentration ether electrolyte solution. First, a certain concentration of potassium salt is dissolved in an ether solvent and stirred thoroughly for several hours to prepare a high-concentration ether electrolyte. Then add the functional fluorinated solvent into the high-concentration ether electrolyte according to a certain volume percentage, and stir thoroughly for several hours to prepare a local high-concentration electrolyte.

Further, the high-concentration ether electrolyte is mainly composed of ether solvent and potassium salt, and its concentration is 3-6 mol/L.

Further, the volume ratio of the functional fluorinated solvent to the high concentration ether electrolyte is 2:1, 1:1, 1:2, 1:3, 1:4, 1:8.

Further, the stirring time of the high-concentration ether electrolyte is 24-72 hours, the stirring time of the partial high-concentration electrolyte is 48-96 hours, and the stirring speed is 400-800 rpm.

Further, the functional fluorinated solvents include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) Ether, tris(trifluoroethoxy)methane, tris(2,2,2-trifluoroethyl)phosphite, 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether , 1-(2,2,2-trifluoroethoxy)-1,1,2,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethyl-2,2,2-tri Fluoroethyl ether, fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether. Preference is given to 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

Further, ether solvents include ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and 1,3-dioxolane.

Further, potassium salts include potassium bisfluorosulfonyl imide, potassium bis(trifluoromethylsulfonyl)imide, potassium hexafluorophosphate, potassium perchlorate, and potassium trifluoromethanesulfonate. Potassium bisfluorosulfonimide is preferred.

Provided is a potassium ion half battery, comprising a P/C composite electrode, a composite diaphragm, a potassium metal negative electrode and a local high-concentration electrolyte.

A potassium ion full battery is provided, comprising a pre-potassiized P/C composite negative electrode, a composite separator, a pre-potassiized 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) positive electrode and a local high-concentration electrolyte.

Further, the raw material of 3,4,9,10-perylenetetracarboxylic dianhydride is first treated under an argon atmosphere at 300-500°C for 3-6 hours to obtain purified 3,4,9,10-perylenetetracarboxylic acid Dianhydride cathode material.

Further, the 3,4,9,10-perylenetetracarboxylic dianhydride positive electrode is purified from 60-80wt.% 3,4,9,10-perylenetetracarboxylic dianhydride positive electrode material, 10-20wt.% acetylene black, 10 ~20wt.% polyvinylidene fluoride composition. Each component is first dissolved in a certain amount of N-methylpyrrolidone, and then evenly coated on the aluminum foil, and after vacuuming at 70-100°C for 12-36 hours, the 3,4,9,10-perylene can be prepared Tetraformic dianhydride positive electrode.

Further, the active material mass ratio of the P/C negative electrode to the 3,4,9,10-perylenetetracarboxylic dianhydride positive electrode is 1:2˜1:6, preferably 1:4.

Composite diaphragms consist of a conventional polymer diaphragm and a fiberglass diaphragm.

In the pre-potassiation process, the P/C electrode and the PTCDA electrode are pre-activated 3 to 5 times in the potassium ion half-cell, and then the electrodes are discharged to realize the pre-potassiation, wherein the P/C electrode and the PTCDA electrode pre-activate the current The densities are 100-400 and 25-100 mA g ^-1 , respectively.

Compared with prior art, the present invention has following advantage:

The present invention successfully builds a firm, flexible and thin SEI layer on the surface of a high-capacity P/C negative electrode by preparing a local high-concentration electrolyte with good fluidity and a unique solvation structure, so as to improve its The structural/interfacial stability in the potassium storage process can significantly improve its electrochemical reversibility and cycle stability, and realize the long cycle life of potassium-ion full batteries. This method has the advantages of low cost, simple operation, strong adaptability, etc., and has very broad application prospects.

Description of drawings

The charge-discharge curve of the P/C negative electrode of the local high-concentration electrolyte B prepared in Fig. 1 embodiment 2 under different current densities;

The potassium ion half-cell charge-discharge curve of the PTCDA positive electrode and the P/C negative electrode of prepared local high concentration electrolyte B in Fig. 2 embodiment 2;

The cycle performance of the potassium ion full battery formed by the PTCDA positive electrode and the P/C negative electrode of the prepared local high concentration electrolyte B in Fig. 3 embodiment 2;

The rate performance of the potassium ion full battery formed by the PTCDA positive electrode and the P/C negative electrode of the prepared local high concentration electrolyte B in Fig. 4 embodiment 2;

Detailed ways

The present invention will be further described in detail below in conjunction with specific examples, but the embodiments of the present invention are not limited thereto, and for process parameters not specifically indicated, conventional techniques can be referred to.

Preparation of P/C composite materials: P/C composite materials are mainly prepared by high-energy ball milling. First, red phosphorus and commercial porous carbon black are added to a stainless steel ball mill tank in a certain proportion, and an appropriate amount of stainless steel ball mill beads is added. After the assembly in the box is completed, high-energy ball milling with gradient speed is carried out, and finally sieved, collected and stored in an argon atmosphere glove box.

The mass ratio of phosphorus to carbon is 7:3. Stainless steel ball milling beads are composed of ball milling beads with a diameter of 2, 3, and 5mm, and their mass ratio is 1:1:1. The mass ratio of P/C material to stainless steel ball milling beads is 1:20.

Gradient speed high-energy ball milling is mainly to carry out planetary ball milling sequentially at different speeds to realize the uniform compounding of phosphorus and carbon on the nanometer scale. Carry out high-energy planetary ball milling at 200, 300, and 400 rpm in turn for 12 hours, and repeat this process twice.

Preparation of high-performance P/C negative electrode for potassium ion battery: First, disperse the above-mentioned P/C composite material, acetylene black, and sodium alginate in a certain amount of deionized water according to a certain mass ratio to prepare an electrode slurry, and evenly coat it on copper The surface of the foil can be vacuum-dried at a certain temperature for a certain period of time.

The mass ratio of P/C composite material, acetylene black, and sodium alginate is 7:1.5:1.5. The vacuum drying temperature of the P/C negative electrode is 60° C., and the drying time is 12 hours. The active material loading of the P/C anode is 1.0 mg cm ^-2 .

Example 1

First, the potassium salt of bisfluorosulfonimide was dissolved in ethylene glycol dimethyl ether solvent, and fully stirred at 600 rpm for 48 hours to prepare a high-concentration ether electrolyte, and the potassium salt concentration in the electrolyte was 6 mol/L. Then add 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether into the high-concentration ether electrolyte, in which 1,1,2,2-tetrafluoroethyl- The volume ratio of 2,2,3,3-tetrafluoropropyl ether to the high-concentration ether electrolyte is 1:2. After fully stirring at 600rpm for 72 hours, the local high-concentration electrolyte A can be obtained.

Example 2

Using the same method as in Example 1, the difference is that the volume ratio of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether to high-concentration ether electrolyte is 1:3, A local high-concentration electrolyte B is obtained.

Example 3

Using the same method as in Example 1, the difference is that the volume ratio of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether to high-concentration ether electrolyte is 1:4, A local high-concentration electrolyte C is obtained.

Example 4

Using the same method as in Example 1, the difference is that the functional fluorinated solvent is 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether to obtain a partial high-concentration electrolyte D.

Example 5

Using the same method as in Example 1, the difference is that the potassium salt is potassium hexafluorophosphate, to obtain a local high-concentration electrolyte E.

Comparative example 1

First, dissolve the potassium salt of bisfluorosulfonimide in the solvent of ethylene glycol dimethyl ether, and fully stir it at 600rpm for 48 hours to prepare a high-concentration ether electrolyte F. The concentration of potassium salt in the electrolyte is 6mol/L .

Comparative example 2

First, dissolve the potassium salt of bisfluorosulfonyl imide in the solvent of ethylene glycol dimethyl ether, and fully stir it at 600rpm for 48 hours to prepare the low-concentration ether electrolyte G. The concentration of potassium salt in the electrolyte is 3mol/L .

Example 6

A potassium ion full battery was assembled by prepotassium P/C composite negative electrode, composite separator, prepotassium PTCDA positive electrode and local high-concentration electrolyte B in Example 2. PTCDA was first treated at 450°C under an argon atmosphere for 4 hours. The PTCDA positive electrode is composed of 80wt.% purified PTCDA positive electrode material, 10wt.% acetylene black, and 10wt.% polyvinylidene fluoride. Each component is firstly dissolved in a certain amount of N-methylpyrrolidone, and then evenly coated on aluminum foil, and after vacuuming at 90°C for 24 hours, 3,4,9,10-perylenetetracarboxylic dianhydride can be prepared positive electrode. The active material mass ratio of the P/C negative electrode to the PTCDA positive electrode is 1:4. The composite diaphragm consists of a layer of celgard 2400 diaphragm and a layer of glass fiber diaphragm. In the pre-potassiation process, the P/C electrode and the PTCDA electrode were pre-activated 5 times in the potassium ion half-cell, and then the electrodes were discharged to achieve pre-potassiation. The pre-activation current densities of the P/C electrode and the PTCDA electrode were 200 and 50mA g ^-1 .

The potassium ion conductivities and transfer numbers of different electrolytes prepared in Examples 1-5 and Comparative Examples 1-2 were further compared.

Potassium ion conductivity and transfer number of prepared different electrolytes in Table 1 embodiment 1-3 and comparative example 1-2

Table 1 further compares the potassium ion conductivities and transfer numbers of different electrolytes prepared in Examples 1-5 and Comparative Examples 1-2. Among them, the low-concentration electrolyte G exhibits a higher potassium ion conductivity (3.74mS cm ^-1 ), while the high-concentration electrolyte F exhibits a lower potassium ion conductivity (1.88mS cm ^-1 ), and a certain amount of specific function The addition of non-toxic fluorinated ether diluents can effectively improve the viscosity and fluidity of the high-concentration electrolyte, and then increase the AD potassium ion conductivity of the local high-concentration electrolyte to 1.96, 1.94, 1.92, and 1.90. However, after replacing the specific functional fluorinated ether diluent, the potassium ion conductivity of the local high-concentration electrolyte E will drop to 1.65mS cm ^-1 . Meanwhile, the potassium ion migration number of the low-concentration electrolyte F is 0.42, while that of the high-concentration electrolyte is 0.28. When a certain amount of functional fluorinated ether diluent is introduced into the high-concentration electrolyte, the potassium ion migration numbers of the local high-concentration electrolyte AD will be significantly increased to 0.73, 0.75, 0.56, and 0.52. After replacing the specific functional fluorinated ether diluent, the potassium ion migration number of the local high-concentration electrolyte E was 0.48. The comparison of relevant parameters in Table 1 further shows the excellent electrochemical properties of the local high-concentration electrolyte of the potassium-ion battery.

Use embodiment 1-5 and comparative example 1-2 in the P/C negative electrode of different electrolytic solutions prepared in comparative example 1-2, the potassium ion half-cell cycle performance under 200mA ^g current density is systematically compared, and experimental data is as shown in table 2:

The cycle performance of the potassium ion half-cell at a current density of 800mA g ^-1 was further systematically compared with the P/C negative electrodes prepared in Examples 1-5 and Comparative Examples 1-2 with different electrolytes. The experimental data are shown in Table 3

For further investigation, the charging specific capacity of the P/C negative electrodes with different electrolytes prepared in Examples 1-5 and Comparative Examples 1-2 after the 5th cycle at different current densities, the specific data are shown in Table 4

The experimental data from Table 2-Table 4 show that the P/C negative electrode using the local high-concentration electrolyte B of Example 2 presents the most excellent electrochemical performance. Fig. 1 further compares the potassium ion half-cell charge-discharge curves of the P/C negative electrode using the local high-concentration electrolyte B prepared in Example 2 at different current densities, and finds that the P/C negative electrode material is uniform under different current densities. It shows obvious alloying/dealloying reaction process and relatively small electrochemical polarization phenomenon. Fig. 2 is the charge-discharge curve of the PTCDA positive electrode and the P/C negative electrode using the partial high-concentration electrolyte B prepared in Example 2. Among them, the PTCDA positive electrode has a discharge specific capacity of 138mAh g ^-1 at a current density of 50mAg ^-1 , while the P/C negative electrode has a charge specific capacity of 728mAh g ^-1 at a current density of 200mA g ^-1 . Figure 3 is the cycle performance of the potassium ion full battery composed of the PTCDA positive electrode and the P/C negative electrode of the local high-concentration electrolyte B prepared in Example 2, wherein the current density and specific capacity are calculated based on the mass of the active material of the positive electrode material . The assembled PTCDA//P/C full battery has a discharge specific capacity of 138mAh g ^-1 for the first time, and after 400 cycles at a current of 50mA g ^-1 , the discharge specific capacity is 47mAh g ^-1 , and the coulombic efficiency is still as high as 98%. Figure 4 is the rate performance of a potassium ion full battery composed of the PTCDA positive electrode and the P/C negative electrode of the local high-concentration electrolyte B prepared in Example 2, wherein the current density and specific capacity are calculated based on the mass of the active material of the positive electrode material . When cycled at current densities of 50, 100, 200, and 400 mA g ^-1 , the assembled PTCDA//P/C full cells can exhibit specific discharge capacities of 123, 100, 85, and 69 mAh g ^-1 , respectively. Even when cycled at a current density of 800mA g ^-1 , it can still maintain a specific discharge capacity of 39mAh g ^-1 .

It can be seen that the local high-concentration electrolyte of the present invention can controllably construct a SEI layer with firm structure, good flexibility and thin thickness on the surface of the high-capacity P/C negative electrode to improve its structure/interface stability in the process of potassium storage, Thereby, its electrochemical reversibility and cycle stability are significantly improved, and the long cycle life of the potassium-ion full battery is realized. In particular, the specific ratio of the electrolyte in Example 2 and the combination of specific functional functional fluorinated solvents and potassium salts can make the P/C negative electrode material have optimal electrochemical performance.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limit the protection scope of the present invention, so they are used as the main embodiments, but although the present invention has been described in detail with reference to the preferred embodiments, the present invention Those of ordinary skill in the art should understand that the technical method of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical method of the present invention.

Claims (10)

1. A local high-concentration electrolyte suitable for potassium ion batteries, characterized in that: it includes a functional fluorinated solvent and a high-concentration ether electrolyte, wherein the high-concentration ether electrolyte is composed of an ether solvent and a potassium salt, The potassium salt concentration is 3-6mol/L, and the volume ratio of the functional fluorinated solvent to the high-concentration ether electrolyte is 2:1-1:8. 2. The electrolyte solution according to claim 1, wherein the functional fluorinated solvent is selected from 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, Bis(2,2,2-trifluoroethyl)ether, tris(trifluoroethoxy)methane, tris(2,2,2-trifluoroethyl)phosphite, 1H,1H,5H-octafluoro Amyl 1,1,2,2-tetrafluoroethyl ether, 1-(2,2,2-trifluoroethoxy)-1,1,2,2-tetrafluoroethane, 1,1,2,2 -Tetrafluoroethyl-2,2,2-trifluoroethyl ether, one or more of fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether; The ether solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and 1,3-dioxolane. 3. The electrolyte solution according to claim 1, wherein the potassium salt is selected from potassium difluorosulfonyl imide, potassium bis(trifluoromethylsulfonyl)imide, potassium hexafluorophosphate, potassium perchlorate, trifluoro One or more of potassium methanesulfonate. 4. A method for preparing a local high-concentration electrolyte for a potassium-ion battery as described in any one of claims 1-3, characterized in that: a certain concentration of potassium salt is dissolved in an ether solvent and fully stirred for several hours , to prepare a high-concentration ether electrolyte, and then add a functional fluorinated solvent into the high-concentration ether electrolyte according to a certain volume percentage, and stir thoroughly for several hours to prepare a local high-concentration electrolyte. 5. The preparation method according to claim 4, characterized in that: the stirring time of the high-concentration ether electrolyte is 24-72 hours, the stirring time of the partial high-concentration electrolyte is 48-96 hours, and the stirring speed is 400-800 rpm. 6. A lithium ion half battery, characterized in that: the battery comprises a P/C composite electrode, a composite diaphragm, a potassium metal negative electrode and the local high-concentration electrolyte according to any one of claims 1-4. 7. A potassium ion full battery, characterized in that: said battery comprises a pre-potassiized P/C composite negative pole, a composite separator, a pre-potassiized 3,4,9,10-perylenetetracarboxylic dianhydride positive pole and claim 1 -3 Any one of the local high concentration electrolytes. 8. The potassium ion full battery according to claim 7, characterized in that: 3,4,9,10-perylenetetracarboxylic dianhydride positive electrode is purified from 60-80wt.% of 3,4,9,10-perylenetetracarboxylic acid The dianhydride positive electrode material is composed of 10-20wt.% acetylene black and 10-20wt.% polyvinylidene fluoride. Each component is first dissolved in a certain amount of N-methylpyrrolidone, and then evenly coated on the aluminum foil. The positive electrode of 3,4,9,10-perylenetetracarboxylic dianhydride can be prepared after vacuuming at 70-100°C for 12-36 hours. 9. The potassium ion full battery according to claim 7, characterized in that: the active material mass ratio of the P/C negative electrode to the 3,4,9,10-perylenetetracarboxylic dianhydride positive electrode is 1:2 to 1:6, Preferably 1:4. 10. According to the described potassium ion full battery of claim 7, it is characterized in that: the pre-potassiation process is first to pre-potassium the P/C electrode and the 3,4,9,10-perylenetetracarboxylic dianhydride electrode in the potassium ion half-cell. Activation for 3 to 5 times, and then discharge the electrode to achieve pre-potassiation, where the pre-activation current densities of the P/C electrode and the 3,4,9,10-perylenetetracarboxylic dianhydride electrode are 100-400mAg ^-1 and 25 ~100 mA g ⁻¹ .

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