An asymmetric hydrogel electrolyte and a method of preparing the same

Abstract

The application provides an asymmetric hydrogel electrolyte and a preparation method thereof, and belongs to the technical field of gel electrolytes.The asymmetric hydrogel electrolyte with the advantages of two kinds of hydrogels is obtained by constructing two hydrogel electrolyte layers with high and low polymer network densities, wherein the hydrogel electrolyte layer with the high polymer network density can provide good mechanical properties, reduce the activity of water molecules in the electrolyte, help the desolvation of hydrated zinc ions and uniformize the zinc ion flux; and the hydrogel electrolyte layer with the low polymer network density can maintain high ionic conductivity.The asymmetric hydrogel electrolyte can effectively inhibit the dendrite growth and side reactions of the zinc negative electrode of a zinc ion battery, thereby improving the cycle service life of the zinc ion battery, and the zinc ion battery can also maintain fast reaction kinetics, thereby exhibiting excellent electrochemical energy storage performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gel electrolyte, in particular to an asymmetric hydrogel electrolyte and a preparation method thereof. BACKGROUND

[0002] With the consumption of non-renewable energy such as oil, coal, natural gas and the worsening of environmental pollution, renewable clean energy (such as wind energy, solar energy, geothermal energy, tidal energy, etc.) has become the focus of subsequent development. Due to the instability of power generation by these clean energy sources, and the large difference between the power generation curve and the power consumption curve, it is urgent to develop a low-cost, high-safety, high-efficiency and environmentally friendly energy storage system for power storage. Lithium ion batteries have a high energy density, a small volume and a long cycle life, and therefore occupy the dominant position in the global electrochemical energy storage market. However, lithium ion batteries have the shortcomings of high cost, shortage of lithium mineral resources and low safety, which restrict their application in the field of large-scale energy storage.

[0003] In recent years, aqueous zinc ion batteries have attracted widespread attention as a new type of energy storage system. They have the advantages of simple preparation, low cost, large theoretical capacity, high safety and environmental friendliness, and are expected to replace lithium ion batteries as the main energy storage system for large-scale power grids in the future. However, during charging and discharging, zinc dendrites are easily formed on the surface of the zinc metal anode and side reactions occur, which leads to a decrease in the energy storage efficiency and service life of the zinc ion battery.

[0004] Developing a new type of hydrogel electrolyte to replace aqueous electrolyte is an effective strategy to stabilize the zinc anode, and has received increasing attention in recent years. The cross-linked three-dimensional polymer network in the hydrogel electrolyte can provide good mechanical properties, reduce the activity of water molecules in the electrolyte, help the desolvation of hydrated zinc ions and uniformize the zinc ion flux, thereby effectively inhibiting the growth of zinc dendrites and the occurrence of side reactions, and stabilizing the zinc ion battery anode. However, compared with traditional aqueous electrolytes, the tight three-dimensional polymer network of the hydrogel electrolyte will inevitably reduce the transmission rate of zinc ions. Therefore, how to obtain a hydrogel electrolyte that can both stabilize the zinc anode and maintain high ionic conductivity is still a difficulty in the field of gel electrolyte technology. SUMMARY

[0005] In view of the shortcomings of the prior art, the present application provides an asymmetric hydrogel electrolyte and a preparation method thereof. The general idea of the present application is as follows: a double-layer asymmetric hydrogel electrolyte is prepared, and the two hydrogel layers have high and low polymer network densities. The hydrogel electrolyte layer with high polymer network density can provide good mechanical properties, reduce the activity of water molecules in the electrolyte, help the desolvation of hydrated zinc ions and uniformize the zinc ion flux; and the hydrogel electrolyte layer with low polymer network density can maintain a high ionic conductivity.

[0006] To achieve the above object, the specific technical solutions of the present application are as follows:

[0007] In a first aspect, the present application provides a preparation method of an asymmetric hydrogel electrolyte, comprising the following steps: constructing a low-polymer network density hydrogel layer on the surface of a high-polymer network density hydrogel layer to obtain an asymmetric hydrogel; soaking the asymmetric hydrogel in an aqueous electrolyte to obtain an asymmetric hydrogel electrolyte; the solid content of the high-polymer network density hydrogel layer is 15% to 50%, and the solid content of the low-polymer network density hydrogel layer is 2% to 8%.

[0008] Preferably, the raw materials of the hydrogel layer include a matrix material and / or a functional material.

[0009] Further preferably, the matrix material includes but is not limited to one or more of polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, polyurethane, cellulose, chitin, chitosan, gelatin, hyaluronic acid, and sodium alginate.

[0010] Further preferably, the functional material includes but is not limited to one or more of graphene oxide, carbon nanotubes, silver nanowires, MXene, MOF, COF, and cellulose derivatives.

[0011] Preferably, the thickness of the high-polymer network density hydrogel layer is 1 to 500 μm, and the thickness of the low-polymer network density hydrogel layer is 10 to 1500 μm.

[0012] Further preferably, the thickness of the high-polymer network density hydrogel layer is 200 μm, and the thickness of the low-polymer network density hydrogel layer is 800 μm.

[0013] Preferably, the gelation method of the hydrogel includes but is not limited to one of cyclic freezing, photo-induced crosslinking, thermal-induced crosslinking, ionic crosslinking, and electrodeposition.

[0014] Preferably, the aqueous electrolyte includes but is not limited to one or more of ZnSO4, ZnCl2, Zn(NO3)2, Zn(Ac)2, Zn(OTf)2, MnSO4, MnCl2, and Mn(Ac)2.

[0015] Preferably, the soaking time of the asymmetric hydrogel in the aqueous electrolyte is 2 to 72 h.

[0016] Further preferably, the soaking time of the asymmetric hydrogel in the aqueous electrolyte is 24 h.

[0017] In a second aspect, the present application provides an asymmetric hydrogel electrolyte prepared by the method.

[0018] In a third aspect, the present application provides an application of the asymmetric hydrogel electrolyte in a zinc ion battery, wherein the high-polymer network density hydrogel layer of the asymmetric hydrogel electrolyte is on the negative electrode side, and the low-polymer network density hydrogel layer is on the positive electrode side.

[0019] Compared with the prior art, the present application has the advantages of:

[0020] Through structural design, the present application obtains an asymmetric hydrogel electrolyte with the advantages of both high-polymer network density hydrogel electrolyte and low-polymer network density hydrogel electrolyte. The asymmetric hydrogel electrolyte of the present application can stabilize the negative electrode of the zinc ion battery while maintaining a high ion transmission rate, thereby maintaining fast reaction kinetics. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a schematic diagram of the preparation process of the asymmetric hydrogel electrolyte.

[0022] Figure 2 It is a physical picture of the asymmetric hydrogel electrolyte prepared in Example 1.

[0023] Figure 3 It is a tensile and twist physical picture of the asymmetric hydrogel electrolyte prepared in Example 1.

[0024] Figure 4 It is an SEM picture of the hydrogel electrolyte of Comparative Examples 1, 2, 3 and Examples 1, 2 after drying treatment; wherein, Figure 4 a is an SEM picture of the hydrogel electrolyte of Comparative Example 1 after drying treatment; Figure 4 b is an SEM picture of the hydrogel electrolyte of Comparative Example 2 after drying treatment; Figure 4 c is an SEM picture of the hydrogel electrolyte of Comparative Example 3 after drying treatment; Figure 4 d is an SEM picture of the hydrogel electrolyte of Example 1 after drying treatment; Figure 4 e is an SEM picture of the hydrogel electrolyte of Example 2 after drying treatment;

[0025] Figure 5 It is a mechanical property of the hydrogel electrolyte of Examples 1, 2 and Comparative Examples 1, 2, 3; wherein, Figure 5 a is a tensile strain and tensile stress relationship diagram of the hydrogel electrolyte of Examples 1, 2 and Comparative Examples 1, 2, 3, Figure 5 b is a tensile strength comparison diagram of the hydrogel electrolyte of Examples 1, 2 and Comparative Examples 1, 2, 3;

[0026] Figure 6The ionic conductivity of the hydrogel electrolyte of Comparative Examples 1, 2, 3 and Examples 1, 2;

[0027] Figure 7 The cycle stability test results of the zinc symmetric cell assembled by using the hydrogel electrolyte of Comparative Example 2, Examples 1, 2 respectively and the surface SEM images of the zinc electrode after the cycle test; wherein, Figure 7 a is the cycle stability test results of the zinc symmetric cell assembled by using the hydrogel electrolyte of Comparative Example 2; Figure 7 b is the cycle stability test results of the zinc symmetric cell assembled by using the hydrogel electrolyte of Example 2; Figure 7 c is the cycle stability test results of the zinc symmetric cell assembled by using the hydrogel electrolyte of Example 1; Figure 7 d is the SEM image of the zinc sheet of the zinc symmetric cell assembled by using the hydrogel electrolyte of Comparative Example 2; Figure 7 e is the SEM image of the zinc sheet of the zinc symmetric cell assembled by using the hydrogel electrolyte of Example 2; Figure 7 f is the SEM image of the zinc sheet of the zinc symmetric cell assembled by using the hydrogel electrolyte of Example 1;

[0028] Figure 8 The chronoamperometric test results of the zinc symmetric cell assembled by using Comparative Example 2 and Examples 1, 2;

[0029] Figure 9 The electrochemical performance of the zinc-manganese full cell assembled by using Comparative Example 2 and Examples 1, 2; wherein, Figure 9 a is the EIS curve of the full cell; Figure 9 b is the rate cycle performance results of the full cell; Figure 9 c is the charge-discharge cycle performance results. DETAILED DESCRIPTION

[0030] The technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0031] The present application provides a preparation method of an asymmetric hydrogel electrolyte, comprising the following steps: constructing a low-polymer network density hydrogel layer on the surface of a high-polymer network density hydrogel layer to obtain an asymmetric hydrogel; soaking the asymmetric hydrogel in an aqueous electrolyte to obtain an asymmetric hydrogel electrolyte; the solid content of the high-polymer network density hydrogel layer is 15% to 50%, and the solid content of the low-polymer network density hydrogel layer is 2% to 8%. Figure 1 It is a preparation flowchart of the asymmetric hydrogel electrolyte.

[0032] In some examples, the raw material of the hydrogel layer comprises a base material and / or a functional material.

[0033] In some examples, the base material comprises one or more of, but not limited to, polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, polyurethane, cellulose, chitin, chitosan, gelatin, hyaluronic acid, sodium alginate.

[0034] In some examples, the functional material comprises one or more of, but not limited to, graphene oxide, carbon nanotube, silver nanowire, MXene, MOF, COF, cellulose derivative.

[0035] In some examples, the thickness of the hydrogel layer with high polymer network density is 1-500 μm; the thickness of the hydrogel layer with low polymer network density is 10-1500 μm.

[0036] In some examples, the gelation method of the hydrogel comprises one or more of, but not limited to, cyclic freezing, photo-initiated crosslinking, thermal-initiated crosslinking, ionic crosslinking, electrodeposition.

[0037] In some examples, the aqueous electrolyte comprises one or more of, but not limited to, ZnSO4, ZnCl2, Zn(NO3)2, Zn(Ac)2, Zn(OTf)2, MnSO4, MnCl2, Mn(Ac)2.

[0038] In some examples, the soaking time of the asymmetric hydrogel in the aqueous electrolyte is 2-72 h.

[0039] In the following specific examples, unless otherwise specified, the polyvinyl alcohol used is type 1799, purchased from Shanghai Aldrich Biochemical Technology Co., Ltd.

[0040] Example 1

[0041] An asymmetric hydrogel electrolyte, the preparation steps are as follows:

[0042] (1) Take 2 mL of cellulose nanofiber (CNF) aqueous suspension (10 mg / mL) and 2 mL of graphene oxide (GO) aqueous suspension (10 mg / mL) and add them to 1.6 mL of polyvinyl alcohol (PVA) aqueous solution (100 mg / mL) and stir (400 r / min) at 100 ℃ until 2 mL of the mixture remains. Pour the obtained PVA / CNF / GO mixture into a 10 cm x 10 cm x 0.1 cm mold and place it in a refrigerator for 8 h (-20 ℃). Then take it out and thaw it at room temperature for 4 h. After three freezing / thawing cycles, a PVA / CNF / GO hydrogel layer with high polymer network density is obtained;

[0043] (2) Take 2 mL of CNF aqueous suspension (10 mg / mL) and 4.2 mL of water and add them to 1.8 mL of PVA aqueous solution (100 mg / mL) and stir (400 r / min) at room temperature for 1 h until complete mixing. Pour the obtained PVA / CNF aqueous solution onto the surface of the PVA / CNF / GO hydrogel layer with high polymer network density in the mold of step 1, place it in a refrigerator for 8 h (-20 ℃), and then take it out and thaw it at room temperature for 4 h. After three freezing / thawing cycles, a PVA / CNF / GO-PVA / CNF asymmetric hydrogel is obtained after demolding;

[0044] (3) Soak the prepared hydrogel in a 2 M ZnSO4 aqueous electrolyte for 24 h, and then take it out to obtain a PVA / CNF / GO-PVA / CNF asymmetric hydrogel electrolyte. The physical diagram of the PVA / CNF / GO-PVA / CNF asymmetric hydrogel electrolyte is shown in Figure 2 The stretching and twisting tests of the PVA / CNF / GO-PVA / CNF asymmetric hydrogel electrolyte are shown in Figure 4 The results show that the hydrogel electrolyte can still maintain its shape and integrity without being broken during stretching and twisting, exhibiting excellent mechanical properties.

[0045] Example 2

[0046] An asymmetric hydrogel electrolyte is prepared according to the following steps:

[0047] (1) Take 2 mL of CNF water suspension (10 mg / mL) and add it to 1.8 mL of PVA aqueous solution (100 mg / mL) and stir at 100°C (400 r / min) until the mixture is left with 2 mL. Pour the obtained PVA / CNF mixture into a 10 cm x 10 cm x 0.1 cm mold and place it in a refrigerator for 8 h (-20°C). Then take it out and thaw at room temperature for 4 h. After three freezing / thawing cycles, a PVA / CNF hydrogel layer with high polymer network density is obtained;

[0048] (2) Take 2 mL of CNF water suspension (10 mg / mL) and 4.2 mL of water and add them to 1.8 mL of PVA aqueous solution (100 mg / mL) and stir at room temperature for 1 h until complete mixing (400 r / min). Pour the obtained PVA / CNF aqueous solution onto the surface of the PVA / CNF hydrogel layer with high polymer network density in the mold of step 1 and place it in a refrigerator for 8 h (-20°C). Then take it out and thaw at room temperature for 4 h. After three freezing / thawing cycles, a PVA / CNF-PVA / CNF asymmetric hydrogel is obtained after demolding;

[0049] (3) Soak the prepared asymmetric hydrogel in 2 M ZnSO4 aqueous electrolyte for 24 h. After taking it out, a PVA / CNF-PVA / CNF asymmetric hydrogel electrolyte is obtained.

[0050] Example 3

[0051] An asymmetric hydrogel electrolyte is prepared according to the following steps:

[0052] (1) Take 4 mL of GO water suspension (10 mg / mL) and add it to 3.6 mL of PVA aqueous solution (100 mg / mL) and stir at 100°C (400 r / min) until the mixture is left with 4 mL. Pour the obtained PVA / CNF mixture into a 10 cm x 10 cm x 0.2 cm mold and place it in a refrigerator for 8 h (-20°C). Then take it out and thaw at room temperature for 4 h. After three freezing / thawing cycles, a PVA / GO hydrogel layer with high polymer network density is obtained;

[0053] (2) Take 16 mL of PVA aqueous solution (25 mg / mL) and pour it onto the surface of the PVA / GO hydrogel layer with high polymer network density in the mold of step 1. Place it in a refrigerator for 8 h (-20°C). Then take it out and thaw at room temperature for 4 h. After three freezing / thawing cycles, a PVA / GO-PVA asymmetric hydrogel is obtained after demolding;

[0054] (3) The prepared asymmetric hydrogel was immersed in 2 M ZnS04aqueous electrolyte for 24 h, and the PVA / GO-PVA asymmetric hydrogel electrolyte was obtained after taking out.

[0055] Example 4

[0056] An asymmetric hydrogel electrolyte was prepared by the following steps:

[0057] (1) 2 mL of PVA aqueous solution (100 mg / mL) was taken into a 10 cm x 10 cm x 0.1 cm mold, and then placed in a refrigerator for freezing for 8 h (-20 °C), and then taken out and thawed at room temperature for 4 h. After three freezing / thawing cycles, a PVA hydrogel layer with high polymer network density was obtained;

[0058] (2) 16 mL of PVA aqueous solution (50 mg / mL) was poured onto the surface of the high polymer network density PVA hydrogel layer in the mold of step 1, and then placed in a refrigerator for freezing for 8 h (-20 °C), and then taken out and thawed at room temperature for 4 h. After three freezing / thawing cycles, the PVA-PVA asymmetric hydrogel was obtained after demolding.

[0059] (3) The prepared asymmetric hydrogel was immersed in 2 M ZnS04aqueous electrolyte for 24 h, and the PVA-PVA asymmetric hydrogel electrolyte was obtained after taking out.

[0060] Example 5

[0061] An asymmetric hydrogel electrolyte was prepared by the following steps:

[0062] (1) 2 mL of cellulose nanofiber (CNF) aqueous suspension (10 mg / mL) and 2 mL of graphene oxide (GO) aqueous suspension (10 mg / mL) were added to 1.6 mL of polyvinyl alcohol (PVA) aqueous solution (100 mg / mL), and stirred (400 r / min) at 100 °C until 2 mL of the mixture remained. The obtained PVA / CNF / GO mixture was poured into a 10 cm x 10 cm x 0.1 cm mold, and then placed in a refrigerator for freezing for 8 h (-20 °C), and then taken out and thawed at room temperature for 4 h. After three freezing / thawing cycles, a PVA / CNF / GO hydrogel layer with high polymer network density was obtained.

[0063] (2) Take 2 mL of CNF water suspension (10 mg / mL) and 4.2 mL of water into 1.8 mL of PVA aqueous solution (100 mg / mL), stir at room temperature for 1 h to complete mixing (400 r / min), pour the obtained PVA / CNF aqueous solution onto the surface of the high polymer network density PVA / CNF / GO hydrogel layer in the mold of step 1, put it into the refrigerator and freeze for 8 h (-20 ℃), then take it out and thaw at room temperature for 4 h, after three freeze / thaw cycles, the PVA / CNF / GO-PVA / CNF asymmetric hydrogel is obtained after demolding;

[0064] (3) The prepared hydrogel is soaked in a mixed aqueous electrolyte of 2 M ZnSO4 and 0.1 M MnSO4 for 24 h, and the PVA / CNF / GO-PVA / CNF asymmetric hydrogel electrolyte is obtained after taking out.

[0065] Example 6

[0066] An asymmetric hydrogel electrolyte, the preparation steps are as follows:

[0067] (1) Take 2 mL of CNF water suspension (10 mg / mL) into 1.8 mL of PVA aqueous solution (100 mg / mL), stir at 100 ℃ (400 r / min) until 2 mL of the mixed solution remains, pour the obtained PVA / CNF mixed solution into a 10 cm×10 cm×0.1 cm mold, put it into the refrigerator and freeze for 8 h (-20 ℃), then take it out and thaw at room temperature for 4 h, after three freeze / thaw cycles, a PVA / CNF hydrogel layer with high polymer network density is obtained;

[0068] (2) Take 2 mL of CNF water suspension (10 mg / mL) and 4.2 mL of water into 1.8 mL of PVA aqueous solution (100 mg / mL), stir at room temperature for 1 h to complete mixing (400 r / min), pour the obtained PVA / CNF aqueous solution onto the surface of the high polymer network density PVA / CNF hydrogel layer in the mold of step 1, put it into the refrigerator and freeze for 8 h (-20 ℃), then take it out and thaw at room temperature for 4 h, after three freeze / thaw cycles, the PVA / CNF-PVA / CNF asymmetric hydrogel is obtained after demolding;

[0069] (3) The prepared asymmetric hydrogel is soaked in a mixed aqueous electrolyte of 2 M ZnSO4 and 0.1 M MnSO4 for 24 h, and the PVA / CNF-PVA / CNF asymmetric hydrogel electrolyte is obtained after taking out.

[0070] Example 7

[0071] An asymmetric hydrogel electrolyte is prepared by the following steps:

[0072] (1) 2 mL of PVA aqueous solution (100 mg / mL) is poured into a 10 cm x 10 cm x 0.1 cm mold, and then placed in a refrigerator for freezing for 8 h (-20 °C), and then taken out and thawed at room temperature for 4 h. After three freezing / thawing cycles, a PVA hydrogel layer with high polymer network density is obtained;

[0073] (2) 16 mL of PVA aqueous solution (25 mg / mL) is poured onto the surface of the high polymer network density PVA hydrogel layer in the mold of step 1, and then placed in a refrigerator for freezing for 8 h (-20 °C), and then taken out and thawed at room temperature for 4 h. After three freezing / thawing cycles, a PVA-PVA asymmetric hydrogel is obtained after demolding;

[0074] (3) The prepared asymmetric hydrogel is soaked in 2 M ZnSO4 aqueous electrolyte for 24 h, and then taken out to obtain a PVA-PVA asymmetric hydrogel electrolyte.

[0075] Comparative Example 1

[0076] A conventional hydrogel electrolyte is prepared by the following steps:

[0077] (1) 2.5 mL of CNF aqueous suspension (10 mg / mL) and 5.25 mL of water are added to 2.25 mL of PVA aqueous solution (100 mg / mL), and then stirred at room temperature for 1 h to complete mixing (400 r / min). The obtained PVA / CNF aqueous solution is poured into a 10 cm x 10 cm x 0.1 cm mold, and then placed in a refrigerator for freezing for 8 h (-20 °C), and then taken out and thawed at room temperature for 4 h. After three freezing / thawing cycles, a PVA / CNF hydrogel is obtained after demolding;

[0078] (2) The prepared hydrogel is soaked in 2 M ZnSO4 aqueous electrolyte for 24 h, and then taken out to obtain a PVA / CNF hydrogel electrolyte.

[0079] Comparative Example 2

[0080] A conventional hydrogel electrolyte is prepared by the following steps:

[0081] (1) 5 mL of CNF aqueous suspension (10 mg / mL) and 0.5 mL of water were added to 4.5 mL of PVA aqueous solution (100 mg / mL) and stirred at room temperature for 1 h until complete mixing (400 r / min). The obtained PVA / CNF aqueous solution was poured into a mold of 10 cm x 10 cm x 0.1 cm, and placed in a refrigerator for freezing for 8 h (-20 °C), and then taken out and thawed at room temperature for 4 h. After three freezing / thawing cycles, the PVA / CNF hydrogel was obtained after demolding.

[0082] (2) The prepared hydrogel was soaked in 2 M ZnSO4 aqueous electrolyte for 24 h, and the PVA / CNF hydrogel electrolyte was obtained after taking out.

[0083] Comparative Example 3

[0084] A conventional hydrogel electrolyte was prepared by the following steps:

[0085] (1) 10 mL of CNF aqueous suspension (10 mg / mL) was added to 9 mL of PVA aqueous solution (100 mg / mL) and stirred at 100 °C (400 r / min) until 10 mL of the mixed solution remained. The obtained PVA / CNF aqueous solution was poured into a mold of 10 cm x 10 cm x 0.1 cm, and placed in a refrigerator for freezing for 8 h (-20 °C), and then taken out and thawed at room temperature for 4 h. After three freezing / thawing cycles, the PVA / CNF hydrogel was obtained after demolding.

[0086] (2) The prepared hydrogel was soaked in 2 M ZnSO4 aqueous electrolyte for 24 h, and the PVA / CNF hydrogel electrolyte was obtained after taking out.

[0087] Comparative Example 4

[0088] A conventional hydrogel electrolyte was prepared by the following steps:

[0089] (1) 5 mL of CNF aqueous suspension (10 mg / mL) and 0.5 mL of water were added to 4.5 mL of PVA aqueous solution (100 mg / mL) and stirred at room temperature for 1 h until complete mixing (400 r / min). The obtained PVA / CNF aqueous solution was poured into a mold of 10 cm x 10 cm x 0.1 cm, and placed in a refrigerator for freezing for 8 h (-20 °C), and then taken out and thawed at room temperature for 4 h. After three freezing / thawing cycles, the PVA / CNF hydrogel was obtained after demolding.

[0090] (2) The prepared hydrogel was immersed in a mixed aqueous electrolyte of 2 M ZnSO4 and 0.1 M M MnSO4 for 24 h, and then PVA / CNF hydrogel electrolyte was obtained.

[0091] The hydrogel electrolytes of Examples 1 and 2 and Comparative Examples 1, 2 and 3 were freeze-dried, and the morphology of the freeze-dried hydrogel electrolytes was characterized by SEM. The results are as follows: Figure 4 As shown, where, Figure 4 a is a SEM image of the hydrogel electrolyte of Comparative Example 1 after drying; Figure 4 b is a SEM image of the hydrogel electrolyte of Comparative Example 2 after drying. Figure 4 c is a SEM image of the hydrogel electrolyte of Comparative Example 3 after drying. Figure 4 d is a SEM image of the hydrogel electrolyte of Example 1 after drying. Figure 4 e is a SEM image of the hydrogel electrolyte from Example 2 after drying. Figure 4 As can be seen, the conventional hydrogel electrolyte in the comparative example has a uniform porous structure. As the polymer network density increases, the pore structure of the hydrogel becomes more compact, while the hydrogel of the present invention has a significant asymmetric pore structure.

[0092] Tensile tests were performed on the hydrogel electrolytes of Examples 1 and 2 and Comparative Examples 1, 2 and 3 using a universal testing machine. The test results are as follows: Figure 5 As shown, where, Figure 5 a is a graph showing the tensile strain and tensile stress relationship of the hydrogel electrolytes in Examples 1 and 2 and Comparative Examples 1, 2 and 3. Figure 5 b is a comparison graph showing the tensile strength of the hydrogel electrolytes in Examples 1 and 2 and Comparative Examples 1, 2, and 3. From Figure 5 As can be seen, the tensile strengths of the hydrogel electrolytes in Comparative Examples 1, 2, and 3 are 0.17 MPa, 0.47 MPa, and 0.74 MPa, respectively, indicating that the tensile strength of the hydrogel electrolytes increases significantly with the increase of polymer network density. The tensile strengths of the asymmetric hydrogel electrolytes in Examples 1 and 2 are 0.43 MPa and 0.37 MPa, respectively. This is because the asymmetric hydrogel electrolytes in Examples 1 and 2 have a high polymer network density layer with high tensile strength. Therefore, the asymmetric hydrogel electrolytes in Examples 1 and 2 can still maintain good mechanical properties.

[0093] Electrochemical performance testing

[0094] (1) Ionic conductivity test

[0095] The ionic conductivity of the hydrogel electrolytes in Examples 1 and 2 and Comparative Examples 1, 2, and 3 was tested and calculated. The test results are as follows:Figure 6 As shown. From Figure 6 It can be seen that the ionic conductivity of the hydrogel electrolytes in Comparative Examples 1, 2, and 3 is 23.2 mS / cm, respectively. -1 10.1 mS cm -1 4.3 mS cm -1 This indicates that the ionic conductivity of the hydrogel electrolyte decreases significantly with increasing polymer network density; the ionic conductivity of the asymmetric hydrogel electrolytes in Examples 1 and 2 is 16.2 mS / cm. -1 and 11.8 mS cm -1 This is because the asymmetric hydrogel electrolytes in Examples 1 and 2 have a low polymer network density layer, thus the asymmetric hydrogel electrolytes in Examples 1 and 2 can still maintain a high ionic conductivity.

[0096] (2) Activation energy test

[0097] Zinc symmetric cells were assembled using hydrogel electrolytes from Examples 1 and 2 and Comparative Examples 1, 2 and 3. The activation energy was tested and calculated to characterize the desolvation ability of hydrated zinc ions in the hydrogel electrolyte. The test results are shown in Table 1.

[0098] Table 1: Activation Energy Test Results

[0099]

[0100] As shown in Table 1, the activation energies of comparative examples 1, 2, and 3 are 28.1 kJ / mol. -1 22.7 kJ mol -1 16.7 KJ mol -1 This indicates that the desolvation ability of hydrated zinc ions in the hydrogel electrolyte is significantly improved with increasing polymer network density; the activation energies of Examples 1 and 2 are 19.2 kJ / mol, respectively. -1 and 21.0 KJ mol -1 This is because the asymmetric hydrogel electrolytes in Examples 1 and 2 have a high polymer network density layer, thus the asymmetric hydrogel electrolytes in Examples 1 and 2 can still maintain excellent desolvation ability.

[0101] (3) Corrosion current test

[0102] Zinc symmetric cells were assembled using hydrogel electrolytes from Examples 1 and 2 and Comparative Examples 1, 2 and 3. Tafel curve tests were performed, and the corresponding corrosion currents were calculated to characterize the corrosion resistance of the zinc anode in the hydrogel electrolyte. The test results are shown in Table 2.

[0103] Table 2: Corrosion Current Test Results

[0104]

[0105] From Table 2, the corrosion current of Comparative Examples 1, 2 and 3 is 0.60 mA cm -2 , 0.41 mA cm -2 , 0.15 mA cm -2 , respectively, indicating that the corrosion resistance of the zinc negative electrode is significantly improved as the polymer network density increases; the activation energy of Example 1 and Example 2 is 0.27 mA cm -2 and 0.33 mA cm -2 , respectively, because the high polymer network density layer in the asymmetric hydrogel electrolyte in Example 1 and Example 2 is in direct contact with the zinc negative electrode, and therefore, the zinc negative electrode in Example 1 and Example 2 both maintain excellent corrosion resistance.

[0106] (4) Zinc symmetric battery cycle performance test

[0107] Zinc symmetric batteries were assembled using the hydrogel electrolytes of Example 1, Example 2 and Comparative Example 2 to test the zinc symmetric performance, and to characterize the cycle stability of the zinc negative electrode in the hydrogel electrolyte. The test results are shown in Table 3 and Figure 7 a~7c.

[0108] Table 3: Zinc symmetric battery cycle performance test results

[0109]

[0110] From Table 3 and Figure 7 a, it can be seen that the stability of the zinc negative electrode using the traditional hydrogel electrolyte of Comparative Example 2 is poor, and the cycle time is short; while the cycle life of the zinc negative electrode using the asymmetric hydrogel electrolyte of Example 1 and Example 2 is significantly improved, indicating that the asymmetric structure design of the hydrogel electrolyte can significantly improve the stability of the zinc negative electrode.

[0111] SEM was used to characterize the morphology of the zinc sheet in the zinc symmetric battery after 100 cycles, and the results are shown in Figure 7 d~7f, wherein, Figure 7 d is the SEM image of the zinc sheet of the zinc symmetric battery assembled using the hydrogel electrolyte of Comparative Example 2; Figure 7 e is the SEM image of the zinc sheet of the zinc symmetric battery assembled using the hydrogel electrolyte of Example 2; Figure 7 f is the SEM image of the zinc sheet of the zinc symmetric battery assembled using the hydrogel electrolyte of Example 1. From Figure 7 d~7f, it can be seen that the surface structure of the zinc sheet corresponding to Comparative Example 2 is not uniform, and there are obvious zinc dendrites; while the surface of the zinc sheet corresponding to Example 1 and Example 2 is relatively flat, indicating that the asymmetric structure of the hydrogel electrolyte can significantly inhibit the growth of zinc dendrites on the surface of the zinc negative electrode.

[0112] (5) Chronoamperometry test

[0113] The zinc symmetric batteries were assembled using the hydrogel electrolytes of Examples 1, 2 and Comparative Example 2, and chronoamperometry test was performed at overpotential of -150 mV to characterize the diffusion behavior of zinc ions in the hydrogel electrolytes, and the test results are shown in Figure 8 It can be seen from Figure 8 that the current of the battery assembled using the hydrogel electrolyte of Comparative Example 2 continuously increased, indicating that the zinc ions mainly diffused in two dimensions in the hydrogel electrolyte; while the current of the batteries assembled using the hydrogel electrolytes of Examples 1, 2 remained stable after a short increase, indicating that the zinc ions mainly diffused in three dimensions in the asymmetric hydrogel electrolyte, further indicating that the use of asymmetric hydrogel electrolyte can homogenize the zinc ion flux and inhibit uneven two-dimensional diffusion.

[0114] (6) Zinc-manganese full battery performance test

[0115] The zinc-manganese full batteries were assembled using manganese dioxide as the positive electrode material, zinc sheet as the negative electrode material, and the hydrogel electrolytes of Examples 1, 2 and Comparative Example 2 as the electrolyte and separator, and electrochemical energy storage performance test was performed to characterize the influence of the hydrogel electrolyte on the energy storage performance of the zinc ion battery, and the test results are shown in Figure 9 , wherein, Figure 9 a is the EIS curve of the full battery, Figure 9 b is the rate cycling performance result of the full battery, Figure 9 c is the charge-discharge cycling performance result. From Figure 9 a, it can be seen that the diameter of the semicircular ring in the EIS curve of the full battery corresponding to Examples 1, 2 is smaller than that of Comparative Example 2, corresponding to a lower charge transfer resistance, indicating that the battery using asymmetric hydrogel electrolyte has faster reaction kinetics; from Figure 9 b, it can be seen that the full batteries corresponding to Examples 1, 2 have higher capacity and more excellent rate performance. In addition, the charge-discharge cycling performance of the full battery was also tested, and from Figure 9 c, it can be seen that the full batteries corresponding to Examples 1, 2 can still maintain 89.4% and 65.5% of the initial capacity after 800 charge-discharge cycles, showing good cycle stability, while the capacity retention rate of the battery corresponding to Comparative Example 2 is only 34.6%, indicating that the use of asymmetric hydrogel electrolyte can significantly improve the cycle stability of the zinc ion battery.

[0116] In summary, the asymmetric hydrogel electrolyte of the present application is prepared by step-by-step construction of two hydrogel electrolyte layers with high and low polymer network densities, and has the advantages of both the two hydrogels. The hydrogel electrolyte layer with high polymer network density can provide good mechanical properties, reduce the activity of water molecules in the electrolyte, help the desolvation of hydrated zinc ions and uniform the zinc ion flux. The hydrogel electrolyte layer with low polymer network density can maintain high ionic conductivity. The asymmetric hydrogel electrolyte of the present application can effectively inhibit the dendrite growth and side reactions of the zinc anode of the zinc ion battery, thereby improving the cycle life of the zinc ion battery. At the same time, the zinc ion battery can also maintain fast reaction kinetics, thereby exhibiting excellent electrochemical energy storage performance.

[0117] The above detailed description of the embodiments of the present application, but the present application is not limited to the specific details of the above embodiments. Within the scope of the claims and technical concepts of the present application, various simple modifications and changes can be made to the technical solutions of the present application, and these simple modifications all belong to the protection scope of the present application.

Claims

1. A method for preparing an asymmetric hydrogel electrolyte, characterized in that, The process includes the following steps: constructing a low polymer network density hydrogel layer on the surface of a high polymer network density hydrogel layer to obtain an asymmetric hydrogel; immersing the asymmetric hydrogel in an aqueous electrolyte to obtain an asymmetric hydrogel electrolyte; wherein the solid content of the high polymer network density hydrogel layer is 15%~50%, and the solid content of the low polymer network density hydrogel layer is 2%~8%; The raw material of the hydrogel layer includes a matrix material, or the raw material of the hydrogel layer includes a matrix material and a functional material; The matrix material includes one or more of the following: polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, polyurethane, cellulose, chitin, chitosan, gelatin, hyaluronic acid, and sodium alginate. The functional materials include one or more of graphene oxide, carbon nanotubes, silver nanowires, MXene, MOF, COF, and cellulose derivatives.

2. The method for preparing an asymmetric hydrogel electrolyte according to claim 1, characterized in that, The thickness of the high polymer network density hydrogel layer is 1–500 μm; the thickness of the low polymer network density hydrogel layer is 10–1500 μm.

3. The method for preparing an asymmetric hydrogel electrolyte according to claim 1, characterized in that, The gelation method of the hydrogel includes one of the following: cyclic freezing, photo-initiated crosslinking, thermally initiated crosslinking, ionic crosslinking, and electrodeposition.

4. The method for preparing an asymmetric hydrogel electrolyte according to claim 1, characterized in that, The aqueous electrolyte includes one or more of ZnSO4, ZnCl2, Zn(NO3)2, Zn(Ac)2, Zn(OTf)2, MnSO4, MnCl2, and Mn(Ac)2.

5. The method for preparing an asymmetric hydrogel electrolyte according to claim 1, characterized in that, The asymmetric hydrogel was immersed in an aqueous electrolyte for 2 to 72 hours.

6. An asymmetric hydrogel electrolyte prepared by the method described in any one of claims 1 to 5.

7. The application of an asymmetric hydrogel electrolyte prepared by the method according to any one of claims 1 to 5 in a zinc-ion battery, characterized in that, In the asymmetric hydrogel electrolyte, the hydrogel layer with high polymer network density is on the zinc negative electrode side, and the hydrogel layer with low polymer network density is on the positive electrode side.

Images