An asymmetric hydrogel-based electrolyte, its preparation method and application in zinc ion batteries

Abstract

The application discloses an electrolyte based on asymmetric hydrogel and application thereof in a zinc ion battery. First, an acrylic monomer containing a hydrophilic group and an acrylic monomer containing a hydrophobic group are obtained through a strategy of regulating a polymerization mold to obtain asymmetric hydrogel. The asymmetric hydrogel has the performance of being hydrophilic on one side and hydrophobic on the other side. The application has simple and easy-to-operate experimental process, wide test range, and the performance of being hydrophilic on one side and hydrophobic on the other side of the asymmetric hydrogel. The hydrophobic group reduces the water content and the generation of branch crystals and the corrosion problem of the negative electrode at the negative electrode. Meanwhile, the hydrophilic group provides sufficient water molecules at the positive electrode, so that the zinc ion and the hydrogen ion realize the effective utilization of the positive electrode material through the co-intercalation of the positive electrode. The asymmetric hydrogel electrolyte simultaneously solves the problems of the zinc negative electrode branch crystal and the efficient utilization of the positive electrode, and provides a new idea for the popularization and application of the aqueous zinc ion battery.

Description

Technical Field

[0001] The invention belongs to the field of electrochemistry, and particularly relates to an electrolyte based on an asymmetric hydrogel and application thereof in a zinc ion battery. Background Art

[0002] Aqueous zinc-ion batteries stand out from many batteries due to their suitable redox potential, high theoretical specific capacity, high crustal abundance and low cost, and have great application prospects in future fields such as large-scale energy storage and green energy.

[0003] However, in aqueous zinc-ion batteries, interactions between zinc ions and water molecules, such as the formation of water and zinc ions, and the interaction between the large amount of free water in the aqueous electrolyte and dissolved oxygen molecules, can lead to corrosion on the zinc anode, hydrogen evolution side reactions, uncontrollable electrochemical side reactions, and dendrite formation due to uneven zinc ion deposition. Dendrite growth can lead to short circuits in zinc-ion batteries. To address these issues, researchers have prepared a large number of gel electrolytes. Gel electrolytes possess a stable three-dimensional network structure, excellent ion conductivity, and a certain viscosity, which improves the interfacial contact between the zinc anode and the electrolyte. Compared with traditional separators, they can achieve uniform zinc ion deposition and reduce dendrite formation. The hydrogels used in current research contain a large number of hydrophilic groups and a high water content. Water-induced side reactions remain to be addressed, so it is necessary to reduce the water content in the hydrogel to reduce zinc corrosion, hydrogen evolution, and dendrite formation. For cathode materials, hydrogen ion intercalation and water molecule lubrication play a crucial role in improving the utilization of cathode active materials, increasing battery capacity, and achieving battery cycle stability. Therefore, a relatively high water content is required on the cathode side. The gel electrolyte currently under research has a symmetrical structure, and either too high or too low a water content will limit the capacity and long-term cycle stability of zinc-ion batteries.

[0004] Therefore, there is an urgent need to develop an asymmetric gel electrolyte that can weaken the active water molecules on the zinc negative electrode while providing sufficient water molecules on the positive electrode side to improve the battery capacity and long-term cycle stability. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention aims to provide an electrolyte based on an asymmetric hydrogel and its application in zinc ion batteries.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for preparing an electrolyte based on an asymmetric hydrogel, and the process is as follows:

[0008] A hydrophobic acrylic monomer, a hydrophilic acrylic monomer, a diacrylic crosslinker, an initiator, a catalyst, and a zinc salt are dissolved in water and stirred at 10-40°C for 5-30 minutes under a protective atmosphere. The mixture is then placed in a mold with one hydrophobic and one hydrophilic side, and polymerized at 20-70°C for 2-36 hours to produce the asymmetric hydrogel electrolyte. The molar ratio of the hydrophobic acrylic monomer, the hydrophilic acrylic monomer, and the acrylic salt is (1-50):(50-99), and the molar fraction of the zinc salt in the solution is 0.1-2 mol / L.

[0009] Furthermore, in the above technical solution, the hydrophobic group-containing acrylic monomer is one or a mixture of two or more of N-isopropylacrylamide, N,N-diethylacrylamide, and N,N-dimethylacrylamide in any proportion.

[0010] Furthermore, in the above technical solution, the hydrophilic group-containing acrylic monomer is one or a mixture of two or more of acrylamide, acrylic acid, 2-hydroxyethyl acrylate and zinc acrylate in any proportion.

[0011] Furthermore, in the above technical solution, the diacrylate cross-linking agent is N,N'-methylenebisacrylamide, polyethylene glycol diacrylate or tetraethylene glycol diacrylate.

[0012] Furthermore, in the above technical solution, the initiator is ammonium persulfate, potassium persulfate and dibenzoyl peroxide.

[0013] Furthermore, in the above technical solution, the zinc salt is zinc sulfate, zinc carbonate, zinc chloride and zinc trifluoromethanesulfonate.

[0014] Furthermore, in the above technical solution, the polymer mold with one hydrophobic side and the other hydrophilic side has the hydrophilic side made of glass and the hydrophobic side made of polytetrafluoroethylene or acrylic plate.

[0015] The present invention provides an asymmetric hydrogel-based electrolyte prepared by the above method.

[0016] The present invention provides an application of the electrolyte in a zinc ion battery.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) The present invention prepares a gel electrolyte by free radical copolymerization of an acrylic monomer containing a hydrophilic group and an acrylic monomer containing a hydrophobic group. The preparation method is simple and can be easily expanded on a large scale.

[0019] (2) The present invention prepares an electrolyte based on an asymmetric hydrogel by using a mold with one side being hydrophobic and the other side being hydrophilic. The preparation method is simple and easy, with a wide range of options, and has the possibility of industrial promotion and application.

[0020] (3) The asymmetric hydrogel-based electrolyte prepared by the present invention reduces the water molecules in the zinc negative electrode while ensuring a higher water content on the positive electrode side, thereby improving the capacity and cycle stability of the zinc ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The contact angles of the upper and lower surfaces of the asymmetric hydrogels prepared in Examples 1-3 and Comparative Example 1;

[0022] Figure 2 The contact angles of the upper and lower surfaces of the asymmetric hydrogel prepared in Comparative Example 2-3;

[0023] Figure 3 The full battery with the hydrogel prepared in Example 2 and Comparative Examples 2-3 as the electrolyte was tested at 0.5Ag. -1 Cyclic stability test curve under ;

[0024] Figure 4 The full battery with the hydrogel prepared in Example 2 and Comparative Examples 2-3 as the electrolyte was tested at 0.5 A g -1 XRD curve of the negative electrode after 100 cycles;

[0025] Figure 5 The full battery with the hydrogel prepared in Example 2 and Comparative Examples 2-3 as the electrolyte was tested at 0.5 A g -1 XRD curve of the positive electrode after 100 cycles. DETAILED DESCRIPTION

[0026] The following examples further illustrate an asymmetric hydrogel-based electrolyte and its application in zinc ion batteries. The examples are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0027] Example 1

[0028] An electrolyte based on an asymmetric hydrogel and a preparation method thereof, comprising the following steps:

[0029] Acrylamide, N-isopropylacrylamide, zinc acrylate, N,N'-methylenebisacrylamide and zinc sulfate were dissolved in deionized water, wherein the molar ratio of acrylamide, N-isopropylacrylamide, zinc acrylate and N,N'-methylenebisacrylamide was 89.97:5:5:0.3. Subsequently, ammonium persulfate and N,N,N',N'-tetramethylethylenediamine were added. The reaction system was evacuated and protected by inert gas. Finally, the system was poured into a mold with one glass and one polytetrafluoroethylene, and polymerization reaction was carried out at 60°C for 2 hours.

[0030] The prepared asymmetric hydrogel-based electrolyte was combined with zinc foil, (NH4)2V 10 O 25 Assemble the full battery with 8H2O positive electrode sheet and test the battery performance.

[0031] Example 2

[0032] An electrolyte based on an asymmetric hydrogel and a preparation method thereof, comprising the following steps:

[0033] Acrylamide, N-isopropylacrylamide, zinc acrylate, N,N'-methylenebisacrylamide and zinc sulfate were dissolved in deionized water, wherein the molar ratio of acrylamide, N-isopropylacrylamide, zinc acrylate and N,N'-methylenebisacrylamide was 79.97:15:5:0.3. Subsequently, ammonium persulfate and N,N,N',N'-tetramethylethylenediamine were added. The reaction system was evacuated and protected by inert gas. Finally, the system was poured into a mold with one glass and one polytetrafluoroethylene, and polymerization reaction was carried out at 60°C for 2 hours.

[0034] The prepared asymmetric hydrogel-based electrolyte was combined with zinc foil, (NH4)2V 10 O 25 Assemble the full battery with 8H2O positive electrode sheet and test the battery performance.

[0035] Example 3

[0036] An electrolyte based on an asymmetric hydrogel and a preparation method thereof, comprising the following steps:

[0037] Acrylamide, N-isopropylacrylamide, zinc acrylate, N,N'-methylenebisacrylamide and zinc sulfate were dissolved in deionized water, wherein the molar ratio of acrylamide, N-isopropylacrylamide, zinc acrylate and N,N'-methylenebisacrylamide was 69.97:25:5:0.3. Subsequently, ammonium persulfate and N,N,N',N'-tetramethylethylenediamine were added. The reaction system was evacuated and protected by inert gas. Finally, the system was poured into a mold with one glass and one polytetrafluoroethylene, and polymerization reaction was carried out at 60°C for 2 hours.

[0038] The prepared asymmetric hydrogel-based electrolyte was combined with zinc foil, (NH4)2V 10 O 25 Assemble the full battery with 8H2O positive electrode sheet and test the battery performance.

[0039] Comparative Example 1

[0040] An electrolyte based on an asymmetric hydrogel and a preparation method thereof, comprising the following steps:

[0041] Acrylamide, N-isopropylacrylamide, zinc acrylate, N,N'-methylenebisacrylamide and zinc sulfate were dissolved in deionized water, wherein the molar ratio of acrylamide, N-isopropylacrylamide, zinc acrylate and N,N'-methylenebisacrylamide was 94.97:0:5:0.3. Subsequently, ammonium persulfate and N,N,N',N'-tetramethylethylenediamine were added. The reaction system was evacuated and protected by inert gas. Finally, the mixture was poured into a mold with one glass and one polytetrafluoroethylene, and polymerization reaction was carried out at 60°C for 2 hours.

[0042] The prepared asymmetric hydrogel-based electrolyte was combined with zinc foil, (NH4)2V 10 O 25 Assemble the full battery with 8H2O positive electrode sheet and test the battery performance.

[0043] The contact angles of the upper and lower surfaces of the asymmetric hydrogels prepared in Examples 1-3 and Comparative Example 1 are shown in FIG. Figure 1 As can be seen from the results, the contact angles of the upper surfaces of the asymmetric hydrogels prepared in Examples 1-3 when in contact with the polytetrafluoroethylene plate are greater than the contact angles of the lower surfaces when in contact with the glass plate. Comparative Example 1 does not contain the hydrophobic monomer N-isopropylacrylamide, so the contact angles of the upper surfaces of the hydrogels prepared in Comparative Example 1 when in contact with the polytetrafluoroethylene plate and the lower surfaces when in contact with the glass plate are similar.

[0044] Comparative Example 2

[0045] A symmetrical hydrogel-based electrolyte and a preparation method thereof, comprising the following steps:

[0046] Acrylamide, N-isopropylacrylamide, zinc acrylate, N,N'-methylenebisacrylamide and zinc sulfate were dissolved in deionized water, wherein the molar ratio of acrylamide, N-isopropylacrylamide, zinc acrylate and N,N'-methylenebisacrylamide was 79.97:15:5:0.3. Subsequently, ammonium persulfate and N,N,N',N'-tetramethylethylenediamine were added. The reaction system was evacuated and protected by inert gas. Finally, the mixture was poured into a mold with polytetrafluoroethylene on both sides and polymerized at 60°C for 2 hours.

[0047] The prepared symmetric hydrogel-based electrolyte was mixed with zinc foil, (NH4)2V10 O 25 Assemble the full battery with 8H2O positive electrode sheet and test the battery performance.

[0048] Comparative Example 3

[0049] A symmetrical hydrogel-based electrolyte and a preparation method thereof, comprising the following steps:

[0050] Acrylamide, N-isopropylacrylamide, zinc acrylate, N,N'-methylenebisacrylamide and zinc sulfate were dissolved in deionized water, wherein the molar ratio of acrylamide, N-isopropylacrylamide, zinc acrylate and N,N'-methylenebisacrylamide was 79.97:15:5:0.3. Subsequently, ammonium persulfate and N,N,N',N'-tetramethylethylenediamine were added. The reaction system was evacuated and protected by inert gas. Finally, the mixture was poured into a mold with two glass surfaces and polymerized at 60°C for 2 hours.

[0051] The prepared symmetric hydrogel-based electrolyte was mixed with zinc foil, (NH4)2V 10 O 25 Assemble the full battery with 8H2O positive electrode sheet and test the battery performance.

[0052] The contact angles of the symmetrical hydrogels prepared in Comparative Examples 2 and 3 are shown in Table 2. Figure 2 In Comparative Example 2, the mold's upper and lower surfaces were both hydrophobic polytetrafluoroethylene plates. The hydrophobic monomers in the gel had a strong affinity for the polytetrafluoroethylene plates, resulting in relatively large contact angles of 49.2° and 52.5° for the symmetrical hydrogel prepared in Comparative Example 2. In Comparative Example 3, the mold's upper and lower surfaces were both hydrophilic glass plates. The hydrophilic monomers acrylamide and zinc acrylate in the gel had a strong affinity for glass. Therefore, the symmetrical hydrogel prepared in Comparative Example 3 had relatively small contact angles of 38.6° and 37.4° for the upper and lower surfaces, respectively.

[0053] The asymmetric hydrogel electrolyte prepared in Example 2, Comparative Example 2 and Comparative Example 3 was mixed with zinc foil, (NH4)2V 10 O 25 The charge and discharge results of the full battery assembled with 8H2O positive electrode sheet after 100 cycles at 0.5A / g are shown in Figure 3 It can be seen that the performance of the full battery with the asymmetric hydrogel prepared in Example 2 as the electrolyte is better than the performance of the full battery with the symmetric hydrogel in Comparative Examples 2 and 3 as the electrolyte.

[0054] The hydrogel electrolyte prepared in Example 2, Comparative Example 2 and Comparative Example 3 was mixed with zinc foil, (NH4)2V 10 O 25 The XRD curve of the negative electrode zinc foil of the full battery assembled with 8H2O positive electrode sheet after 100 cycles at 0.5A / g is shown in Figure 4 It can be seen that in Example 2 and Comparative Example 2, the hydrophobic surface of the asymmetric gel and the hydrophobic surface of the symmetric gel are in contact with the zinc foil, the active water content is low, and almost no by-product (Zn(OH)2)3(ZnSO4)(H2O)5 is generated. In Comparative Example 3, the hydrophilic surface of the symmetric gel is in contact with the zinc foil, and the active water content is very high, so a large amount of by-product (Zn(OH)2)3(ZnSO4)(H2O)5 is generated.

[0055] The asymmetric hydrogel electrolyte prepared in Example 2, Comparative Example 2 and Comparative Example 3 was mixed with zinc foil, (NH4)2V 10 O 25 The full battery assembled with 8H2O positive electrode contains (NH4)2V after 100 cycles at 0.5A / g 10 O 25 · The XRD curve of the positive electrode of 8H2O is shown in Figure 5 As can be seen from the above, in Example 2 and Comparative Example 3, the hydrophilic surfaces of the asymmetric and symmetric gels contacted the positive electrode sheet, respectively. Sufficient water molecules were present on the positive electrode side, and effective utilization of the positive electrode material was achieved through co-intercalation of zinc ions and hydrogen ions in the positive electrode. Therefore, almost no byproduct Zn3(OH)2(V2O7)(H2O)2 was generated in the positive electrode sheets in Example 2 and Comparative Example 3. In Comparative Example 2, the hydrophobic surface of the symmetric gel contacted the positive electrode sheet, and a large amount of byproduct Zn3(OH)2(V2O7)(H2O)2 was generated after cycling.

Claims

1. A method for preparing an electrolyte based on an asymmetric hydrogel, characterized in that: An acrylic monomer containing a hydrophobic group, an acrylic monomer containing a hydrophilic group, a diacrylic crosslinking agent, an initiator, a catalyst, and a zinc salt are dissolved in water, stirred and mixed at 10-40° C. for 5-30 minutes under a protective atmosphere, and then placed in a mold with one hydrophobic and the other hydrophilic. The mixture is polymerized at 20-70° C. for 2-36 hours to obtain the asymmetric hydrogel electrolyte. The molar ratio of the hydrophobic group-containing acrylic monomer to the hydrophilic group-containing acrylic monomer is (1-50):(50-99), and the molar fraction of the zinc salt in the solution is 0.1-2 mol / L.

2. The preparation method according to claim 1, characterized in that The acrylic monomer containing a hydrophobic group is one of N-isopropyl acrylamide, N,N-diethyl acrylamide, and N,N-dimethyl acrylamide, or a mixture of two or more of them in any proportion.

3. The preparation method according to claim 1, characterized in that The acrylic monomer containing a hydrophilic group is one or a mixture of two or more of acrylamide, acrylic acid, 2-hydroxyethyl acrylate and zinc acrylate in any proportion.

4. The preparation method according to claim 1, characterized in that The bisacrylic acid cross-linking agent is N,N'-methylenebisacrylamide, polyethylene glycol diacrylate or tetraethylene glycol diacrylate.

5. The preparation method according to claim 1, characterized in that The initiator is ammonium persulfate, potassium persulfate or dibenzoyl peroxide.

6. The preparation method according to claim 1, characterized in that The zinc salts are zinc sulfate, zinc carbonate, zinc chloride and zinc trifluoromethanesulfonate.

7. The preparation method according to claim 1, characterized in that The polymer mold with one hydrophobic side and the other hydrophilic side has a hydrophilic side made of glass and a hydrophobic side made of polytetrafluoroethylene or acrylic plate.

8. An asymmetric hydrogel-based electrolyte prepared by the method according to any one of claims 1 to 7.

9. Use of the electrolyte according to claim 8 in a zinc ion battery.

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