Sulfonated silk fibroin gel as interface modification layer for aqueous zinc electrode and preparation method thereof

Abstract

The application discloses sulfonated silk protein gel as an interface modification layer of a water-based zinc electrode and a preparation method thereof, and belongs to the technical field of negative electrode materials of zinc ion batteries. The sulfonated silk protein gel is prepared by using natural silk, raw materials are widely sourced, and the sulfonated silk protein gel is green and environment-friendly. The prepared sulfonated silk protein gel contains rich functional groups (‑OH, ‑NH‑, ‑C=O, ‑SO3H and the like), can cover the entire zinc electrode surface, forms a gel-like transition zone at the interface, and provides basic protection for the zinc electrode. In addition, the gel layer optimizes the electric field, improves the interface compatibility, can guarantee uniformity in the nucleation and growth process, plays an obvious role in controlling the dendrite growth, effectively prolongs the service life of the zinc ion battery, and improves the cycle stability of the zinc ion battery.

Description

Technical Field

[0001] This invention belongs to the technical field of zinc-ion battery anode materials, and more specifically relates to a sulfonated silk protein gel as an interface modification layer for aqueous zinc electrodes and its preparation method. Background Technology

[0002] The zinc metal anode has a high theoretical volumetric capacity (5854 mAh / cm³). 3 Due to their inherently safe aqueous solutions as the primary electrolyte solvent, aqueous zinc batteries are considered promising candidates for energy storage devices and flexible devices, thanks to their low redox potential (-0.762V vs. SHE), low cost, and abundant resources. However, traditional zinc anode materials still face significant challenges, such as uncontrollable dendrite growth and corrosion. Inhomogeneity during nucleation and growth often leads to the formation and growth of zinc dendrites, increasing the electrode surface area, worsening parasitic reactions on Zn, and increasing the potential threat of short circuits. Hydrogen evolution reactions and the formation of byproducts result in short cycle life, poor reversibility, and rapid capacity decay during charge-discharge cycles, significantly impacting the commercial application of aqueous zinc batteries.

[0003] Therefore, it is of great significance to develop a method that can effectively solve the problems of uneven deposition and poor stability on the surface of zinc anodes. Summary of the Invention

[0004] The purpose of this invention is to provide a sulfonated silk protein gel as an interface modification layer for aqueous zinc electrodes and its preparation method, so as to solve the problems existing in the prior art, extend the service life of zinc-ion batteries, and improve the cycle stability of zinc-ion batteries.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of this invention is to provide a method for preparing sulfonated silk fibroin gel, comprising the following steps:

[0007] Natural silk is degummed to obtain degummed silk;

[0008] The degummed filaments were subjected to dialysis in a lithium bromide solution to obtain silk protein powder.

[0009] The silk protein powder was dissolved in a mixture of pyridine and chlorosulfonic acid and subjected to a sulfonation reaction to obtain sulfonated silk protein powder.

[0010] The sulfonated silk protein powder was diluted and allowed to stand to obtain the sulfonated silk protein gel.

[0011] Preferably, the degumming process includes: mixing natural silk and sodium carbonate solution and then performing a degumming process; the degumming process is carried out at a temperature of 100°C for a time of 30–60 min; the ratio of natural silk to sodium carbonate solution is 0.5–1.5 g: 8–12 mL; and the concentration of sodium carbonate solution is 0.01–0.03 M.

[0012] Preferably, the concentration of the lithium bromide solution is 9–9.5 M; the dialysis treatment time is 2–3 days; and the molecular weight cutoff of the dialysis bag used for the dialysis treatment is 3000–4000 Da.

[0013] Preferably, the dialysis treatment further includes a post-treatment step; the post-treatment includes: allowing the dialysis product to stand for the first time, then diluting it with water to a mass fraction of 1.5-2.5%, and finally allowing it to stand for the second time; the temperature of the first and second standing is 50-70°C and the time is 20-24h.

[0014] Preferably, the ratio of silk protein powder, pyridine, and chlorosulfonic acid is 0.5–1.5 g: 50–70 mL: 8–12 mL; the sulfonation reaction is carried out at a temperature of 70–85 °C for 1–2 h.

[0015] Preferably, the sulfonation reaction is further complicated by steps of removing impurities, dialysis and drying the product.

[0016] Preferably, the reagent used to dilute the sulfonated silk protein powder includes formic acid.

[0017] Furthermore, during the preparation of the sulfonated silk protein gel, degummed silk fibers are obtained. 、 Both silk protein powder and sulfonated silk protein powder require conventional drying methods (freeze drying, oven drying, etc.) to dry the products obtained from each treatment. In addition, the present invention does not impose special limitations on the drying method and parameters, only ensuring that a solid product can be obtained after drying.

[0018] The second technical solution of the present invention is to provide sulfonated silk protein gel prepared by the above preparation method.

[0019] The third technical solution of the present invention provides the application of the sulfonated silk protein gel as an interface modification layer for aqueous zinc electrodes in zinc-ion batteries, wherein the zinc-ion batteries include zinc-ion symmetric batteries and / or zinc-ion full batteries.

[0020] Fourth technical solution of the present invention: Provides a zinc-ion battery, wherein the zinc-ion battery includes a zinc-ion symmetric battery and / or a zinc-ion full battery;

[0021] The zinc-ion symmetric battery includes a zinc negative electrode coated with sulfonated silk protein gel, a zinc positive electrode coated with sulfonated silk protein gel, a separator, and an electrolyte.

[0022] The zinc-ion full battery includes a zinc negative electrode, a positive electrode, a separator, and an electrolyte coated with sulfonated silk protein gel.

[0023] The coating thickness of the sulfonated silk protein gel in the zinc anode and zinc cathode coated with the sulfonated silk protein gel is independently 2–10 μm.

[0024] The technical mechanism of this invention is as follows: Silk fibroin, a naturally occurring protein, is mainly composed of glycine, alanine, and serine, and also contains various other amino acids such as proline and tyrosine. These amino acids are linked by peptide bonds to form stable polypeptide chains. This invention, by controlling relevant parameters in the preparation process of sulfonated silk fibroin gel, more efficiently utilizes the sulfonation reaction to replace hydrogen atoms in the silk fibroin molecule with sulfonic acid groups. This ensures that the prepared sulfonated silk fibroin gel contains abundant polar functional groups (-OH, -NH-, -C=O, -SO3H, etc.), which can effectively improve the wettability of the electrolyte at the negative electrode, enhance the hydrophilicity of the zinc interface, promote the uniform distribution of zinc ions on the negative electrode surface, and improve the cycle stability of the battery. Simultaneously, the sulfonated silk fibroin gel prepared by this invention has a rich, porous, cross-linked fiber network structure. This fiber network structure can integrate ion channels, ensuring a uniform distribution of zinc ions at the electrode-electrolyte interface, thereby inhibiting the formation of zinc dendrites. It also maintains structural stability. The excellent network structure allows the gel to withstand certain volume changes and stresses on the zinc electrode during battery charging and discharging, maintaining its structural integrity and preventing breakage or deformation. This ensures the continuity of its modification and protection of the zinc electrode, improving the battery's cycle stability. Furthermore, compared to zinc electrodes without sulfonated silk protein gel protection, this invention's sulfonated silk protein gel protection ensures that the zinc deposited on the electrode surface exhibits a planar growth trend, forming closely parallel crystal planes. This prevents dendrite formation and growth, effectively extending the lifespan of the zinc-ion battery.

[0025] The present invention discloses the following technical effects:

[0026] This invention utilizes natural silkworm silk to prepare sulfonated silk protein gel. The raw materials used are widely available and environmentally friendly. The prepared sulfonated silk protein gel contains abundant functional groups (-OH, -NH-, -C=O, -SO3H, etc.), which can cover the entire electrode surface and form a gel-like transition zone at the interface, providing basic protection for the zinc electrode. Furthermore, the gel layer optimizes the electric field, improves interfacial compatibility, and ensures uniformity during nucleation and growth. It plays a significant role in controlling dendrite growth, effectively extending the lifespan of the zinc-ion battery and improving its cycle stability. Attached Figure Description

[0027] Figure 1 The infrared spectrum of the sulfonated silk protein gel film prepared in Example 1;

[0028] Figure 2 SEM images of the surface and cross-section of the sulfonated silk protein gel film prepared in Example 1, where a is the surface SEM image and b is the cross-sectional SEM image;

[0029] Figure 3 The image shows a comparison of the wettability of the zinc electrode sheets described in Comparative Example 1 and Example 1 to the electrolyte, where a is the zinc electrode sheet described in Comparative Example 1 and b is the zinc electrode sheet described in Example 1.

[0030] Figure 4 SEM images of the deposition morphology of the zinc electrode sheets described in Comparative Example 1 and Example 1 after 10 cycles, where a is the zinc electrode sheet described in Comparative Example 1 and b is the zinc electrode sheet described in Example 1.

[0031] Figure 5 The zinc-ion coin cells prepared for Comparative Example 1 and Example 1 operate at 1 mA / cm². 2 1mAh / cm 2 Comparison of cyclic voltage curves under the given conditions.

[0032] Figure 6 This is a schematic diagram of the structure of the zinc-ion coin cell symmetric battery prepared according to the present invention;

[0033] Figure 7 The zinc-ion coin cells prepared in Examples 6 and 7 operate at 1 mA / cm². 2 1mAh / cm 2 The cyclic voltage curves under the given conditions are shown in Figure 6 and Figure 7, where a represents Example 6 and b represents Example 7. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0037] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0038] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0039] The structure of the zinc-ion coin cell symmetric battery prepared by the technical solution described in this invention is as follows: Figure 6 As shown in the figure. This invention utilizes the abundant polar functional groups (-OH, -NH-, -C=O, -SO3H, etc.) in the prepared sulfonated silk protein gel, which effectively improves the wettability of the electrolyte to the zinc electrode, enhances the hydrophilicity of the zinc interface, promotes the uniform distribution of zinc ions on the negative electrode surface, and improves the cycle stability of the battery. Furthermore, compared to zinc electrodes without sulfonated silk protein gel protection, this invention ensures that the zinc deposited on the electrode surface exhibits a planar growth trend, forming closely parallel crystal planes, avoiding dendrite formation and growth, and effectively extending the service life of the zinc-ion battery.

[0040] Unless otherwise specified, all raw materials used in the following embodiments, comparative examples, and performance tests of this invention are commercially available products, and the source of these commercially available products does not affect the final results.

[0041] Example 1

[0042] (1) Preparation of sulfonated silk fibroin gel: 10g of chopped silkworm cocoons were placed in 100mL of 0.02M sodium carbonate aqueous solution and boiled (100℃) for 30min to degummify. After washing and drying, the degummed filaments were added to 9.3M lithium bromide aqueous solution until completely dissolved. Dialysis was performed in ultrapure water using a dialysis bag with a molecular weight cutoff of 3500Da for 3 days until the solution was transparent. After centrifugation to remove impurities, the obtained solution was allowed to stand at 60℃ for 24h, diluted with ultrapure water to a mass fraction of 2%, and then allowed to stand at 60℃ for 24h to complete the self-assembly of filament nanofibers, obtaining a silk fibroin solution. After freeze-drying, silk fibroin powder was obtained. 1g of silk fibroin powder was soaked in 60mL of pyridine and placed in an ice bath. Then, 10mL of chlorosulfonic acid solution was added and stirred until homogeneous. The mixture was then placed in a water bath at 80℃ for sulfonation for 1 hour. After cooling to room temperature, 200mL of ultrapure water and NaOH solution were added to neutralize the pH to 7. Insoluble matter was removed by vacuum filtration, and the remaining soluble matter was precipitated with 500mL of ethanol. The precipitate was collected by centrifugation, dissolved in ultrapure water, and dialyzed using a dialysis bag with a molecular weight cutoff of 3500 Da for 3 days. After freeze-drying, sulfonated silk fibroin powder was obtained. The sulfonated silk fibroin powder was dissolved in formic acid and coated onto a smooth platform. After standing, a sulfonated silk fibroin gel film, denoted as SSF, was obtained.

[0043] (2) Preparation of zinc electrode sheet: The prepared sulfonated silk protein gel was coated on the surface of a zinc electrode with a diameter of 12 mm and a coating thickness of 10 μm, denoted as SSF / Zn.

[0044] (3) Preparation of zinc-ion button symmetric cells: Glass fiber was selected as the separator, 2M ZnSO4 as the electrolyte, and SSF / Zn prepared in step (2) as the positive and negative electrodes. The above materials were then processed according to... Figure 6 The structure shown is assembled to obtain a zinc-ion coin cell.

[0045] Example 2

[0046] (1) Preparation of sulfonated silk fibroin gel: 15g of chopped silkworm cocoons were placed in 120mL of 0.02M sodium carbonate aqueous solution and boiled (100℃) for degumming treatment for 40min. After washing and drying, the degummed filaments were added to 9.3M lithium bromide aqueous solution until completely dissolved. Dialysis was performed in ultrapure water using a dialysis bag with a molecular weight cutoff of 3800Da for 3 days until the solution was transparent. After centrifugation to remove impurities, the obtained solution was allowed to stand at 65℃ for 24h, diluted with ultrapure water to a mass fraction of 2%, and then allowed to stand at 60℃ for 24h to complete the self-assembly of filament nanofibers, obtaining a silk fibroin solution. After freeze-drying, silk fibroin powder was obtained. 1.5g of silk fibroin powder was soaked in 60mL of pyridine and placed in an ice bath. Then, 10mL of chlorosulfonic acid solution was added, and the mixture was stirred until homogeneous. The solution was then placed in a water bath at 80℃ for sulfonation for 1 hour. After cooling to room temperature, 200mL of ultrapure water and NaOH solution were added to neutralize the pH to 7. Insoluble matter was removed by vacuum filtration, and the remaining soluble matter was precipitated with 500mL of ethanol. The precipitate was collected by centrifugation, dissolved in ultrapure water, and dialyzed using a dialysis bag with a molecular weight cutoff of 3800 Da for 3 days. After freeze-drying, sulfonated silk fibroin powder was obtained. The sulfonated silk fibroin powder was dissolved in formic acid and coated onto a smooth platform, allowing it to stand to obtain a sulfonated silk fibroin gel film.

[0047] (2) Preparation of zinc electrode sheet: The prepared sulfonated silk protein gel was coated on the surface of the zinc electrode with a diameter of 12 mm and the coating thickness was 5 μm.

[0048] (3) Preparation of zinc-ion button symmetrical cells: Glass fiber was selected as the separator, 2M ZnSO4 as the electrolyte, and the zinc electrode sheets prepared in step (2) were used as the positive and negative electrodes. The above materials were then processed according to... Figure 6 The structure shown is assembled to obtain a zinc-ion coin cell.

[0049] Example 3

[0050] The difference from Example 1 is that the battery preparation steps are different. Specifically, glass fiber is used as the separator, 2MZnSO4 as the electrolyte, manganese dioxide as the positive electrode, and SSF / Zn prepared in step (2) as the negative electrode. The above materials are assembled to obtain a zinc-ion full cell. Other aspects are the same as in Example 1.

[0051] Comparative Example 1

[0052] (1) Prepare zinc electrode plates: Prepare two zinc electrodes with a diameter of 12 mm that are not coated with sulfonated silk protein gel, denoted as Bare Zn.

[0053] (2) Preparation of zinc-ion button symmetric battery: Glass fiber was selected as the separator, 2M ZnSO4 as the electrolyte, and two zinc electrodes with a diameter of 12mm without sulfonated silk protein gel were used as the positive electrode and negative electrode. The above materials were assembled to obtain zinc-ion button symmetric battery.

[0054] Comparative Example 2

[0055] The difference from Example 1 is that the amount of chlorosulfonic acid used is adjusted to 20 mL. Everything else is the same as in Example 1.

[0056] Comparative Example 3

[0057] The difference from Example 1 is that the amount of chlorosulfonic acid used is adjusted to 4 mL. Everything else is the same as in Example 1.

[0058] Comparative Example 4

[0059] The difference from Example 1 is that the sulfonation reaction temperature was adjusted to 105°C. Everything else is the same as in Example 1.

[0060] Comparative Example 5

[0061] The difference from Example 1 is that the sulfonation reaction temperature was adjusted to 50°C. Everything else is the same as in Example 1.

[0062] Comparative Example 6

[0063] The difference from Example 1 is that the coating thickness of the sulfonated silk protein gel was adjusted to 30 μm. Everything else is the same as in Example 1.

[0064] Comparative Example 7

[0065] The difference from Example 1 is that the coating thickness of the sulfonated silk protein gel was adjusted to 1 μm. Everything else is the same as in Example 1.

[0066] Performance testing:

[0067] 1. Characterization of sulfonated silk protein gel films:

[0068] (1) Characterization:

[0069] The infrared spectrum of the sulfonated silk protein gel film prepared in Example 1 is shown below. Figure 1 As shown.

[0070] Figure 1 This proves that the reaction between silk protein powder and chlorosulfonic acid successfully incorporates sulfonic acid groups into the silk protein molecules. Figure 1 The display shows 1600-1700cm -1 A strong peak in the amide I band (C=O) indicates the integrity of the protein backbone. (1500–1600 cm⁻¹) -1 The presence of the amide II band (NH / CN) confirms the peptide bond structure. (1200–1350 cm⁻¹)-1 Amide III bands (CN / NH) further support protein secondary structures (such as β-sheets).

[0071] (2) Surface morphology:

[0072] The surface and cross-sectional morphology of the sulfonated silk protein gel film prepared in Example 1 were observed, and the results are as follows: Figure 2 As shown.

[0073] Figure 2 SEM images of the surface and cross-section of the sulfonated silk protein gel film prepared in Example 1 are shown, where a is the surface SEM image and b is the cross-sectional SEM image. Figure 2 As can be seen, the sulfonated silk protein gel film prepared in Example 1 has a rich, porous, cross-linked fiber network structure. This fiber network structure can integrate ion channels, ensuring a uniform distribution of zinc ions at the electrode-electrolyte interface, thereby suppressing the formation of zinc dendrites. Simultaneously, it maintains structural stability. This favorable network structure allows the gel to withstand certain volume changes and stresses on the zinc electrode during battery charging and discharging, maintaining its structural integrity and preventing breakage or deformation. This ensures the continuity of its modification and protection effect on the zinc electrode, improving the battery's cycle stability.

[0074] 2. Wetting properties:

[0075] The wettability of the zinc electrode sheets described in Comparative Example 1 and Example 1 to the 2M ZnSO4 electrolyte was verified, and the results are as follows: Figure 3 As shown.

[0076] Figure 3 This is a comparison diagram of the wettability of the zinc electrode sheets described in Comparative Example 1 and Example 1 to the electrolyte, where a is the zinc electrode sheet described in Comparative Example 1, and b is the zinc electrode sheet described in Example 1. Figure 3 It is evident that the zinc electrode coated with sulfonated silk protein gel exhibits significantly better wettability to the electrolyte than the zinc electrode without sulfonated silk protein gel coating. The sulfonated silk protein gel, with its abundant polar groups, effectively enhances the wettability of the electrolyte at the negative electrode, increases the hydrophilicity of the zinc interface, promotes the uniform distribution of zinc ions on the negative electrode surface, and improves the cycle stability of the battery.

[0077] 3. Surface morphology of zinc electrode sheets after zinc deposition:

[0078] The zinc electrode plates described in Comparative Example 1 and Example 1 are subjected to a fixed current density of 1 mA / cm². 2 Under the condition of 1 hour of charge / discharge cycle and 10 cycles, the surface morphology of zinc deposition was observed, and the results are as follows. Figure 4 As shown.

[0079] Figure 4SEM images showing the deposition morphology of the zinc electrode sheets described in Comparative Example 1 and Example 1 after 10 cycles, where a is the zinc electrode sheet described in Comparative Example 1 and b is the zinc electrode sheet described in Example 1. Figure 4 It can be seen that during the cycling process, the exposed Zn surface, which is not covered by sulfonated silk protein gel, exhibits disordered Zn deposition accompanied by a dendritic structure. Furthermore, due to the uneven deposition, these crystal planes are not tightly packed, exhibiting many loose structures. In contrast, Zn deposited on the SSF / Zn surface shows a planar growth trend, forming closely parallel crystal planes.

[0080] 4. Cyclic stability and lifespan testing:

[0081] At a current density of 1 mA / cm 2 The surface capacity is 1mAh / cm². 2 The cycle voltages of the zinc-ion coin cells prepared in Comparative Example 1 and Example 1 were tested under the specified conditions, and the results are as follows: Figure 5 As shown.

[0082] Figure 5 The zinc-ion coin cells prepared for Comparative Example 1 and Example 1 operate at 1 mA / cm². 2 1mAh / cm 2 A comparison of cyclic voltage curves under the given conditions. (From...) Figure 5 It can be seen that when the current density is 1 mA / cm² 2 The surface capacity is 1mAh / cm². 2 At that time, the bare zinc battery (the zinc-ion coin cell prepared in Comparative Example 1) failed rapidly after 100 hours, with a sudden drop in the overpotential curve. Rapid failure indicates rapid accumulation of byproducts and dendrite growth. In contrast, the zinc-ion coin cell prepared in Example 1 showed a significantly longer lifespan under the same conditions, achieving stable cycling for 900 hours. Furthermore, the cycling voltage curve of the zinc-ion coin cell prepared in Example 1 maintained a high overpotential without significant non-uniform polarization fluctuations. The flat, high overpotential facilitates uniform particle deposition, resulting in a uniform and dense deposited Zn layer.

[0083] 5. The effect of sulfonated silk protein gel coating thickness on the cycle stability and lifespan of zinc-ion coin cells:

[0084] At a current density of 1 mA / cm 2 The surface capacity is 1mAh / cm². 2 The cycle voltage of the zinc-ion coin cells prepared in Examples 6 and 7 was tested under the specified conditions, and the results are as follows: Figure 7 As shown.

[0085] Figure 7The zinc-ion coin cells prepared in Examples 6 and 7 operate at 1 mA / cm². 2 1mAh / cm 2 The cyclic voltage curves under the given conditions are shown in Figure 6 and Figure 7, where a represents Example 6 and b represents Example 7.

[0086] contrast Figure 5 and Figure 7 It is known that an excessively thick modification layer increases ion transport resistance: zinc ions must travel a longer path to pass through the protective layer, resulting in a slower ion transport rate, decreased battery charge / discharge performance, and exacerbated polarization. It also reduces battery energy density: occupying too much space and mass relatively reduces the proportion of zinc metal and electrolyte, lowering both volumetric and gravimetric energy densities, thus affecting overall battery performance and application range. Conversely, an excessively thin modification layer cannot effectively isolate and protect the battery, failing to completely cover defects and active sites on the zinc anode surface. It also makes it difficult to achieve a uniform electric field and regulate ion deposition, easily leading to excessive zinc ion deposition in localized areas, reducing battery cycle stability and lifespan.

[0087] In addition, since the sulfonated silk protein gels obtained from Comparative Examples 2 to 5 could not be prepared to a satisfactory degree, their coating performance was relatively poor, and some could not even be coated. Therefore, the performance test data of the zinc-ion coin cells obtained from Comparative Examples 2 to 5 were not recorded.

[0088] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0089] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing sulfonated silk protein gel, characterized in that, Includes the following steps: Natural silk is degummed to obtain degummed silk; The degummed filaments were subjected to dialysis in a lithium bromide solution to obtain silk protein powder. The silk protein powder was dissolved in a mixture of pyridine and chlorosulfonic acid and subjected to a sulfonation reaction to obtain sulfonated silk protein powder. The sulfonated silk protein powder was diluted and allowed to stand to obtain the sulfonated silk protein gel.

2. The preparation method according to claim 1, characterized in that, The degumming process includes: mixing natural silk and sodium carbonate solution and then performing a degumming process; the degumming process is carried out at a temperature of 100°C for a time of 30–60 min; and / or, the ratio of natural silk to sodium carbonate solution is 0.5–1.5 g: 8–12 mL; and / or, the concentration of sodium carbonate solution is 0.01–0.03 M.

3. The preparation method according to claim 1, characterized in that, The concentration of the lithium bromide solution is 9–9.5 M; and / or the dialysis treatment time is 2–3 days; the molecular weight cutoff of the dialysis bag used for the dialysis treatment is 3000–4000 Da.

4. The preparation method according to claim 1, characterized in that, The dialysis process also includes a post-processing step; the post-processing includes: first allowing the dialysis product to stand for the first time, then diluting it with water to a mass fraction of 1.5-2.5%, and finally allowing it to stand for the second time; the temperature of the first and second standing is 50-70°C and the time is 20-24h.

5. The preparation method according to claim 1, characterized in that, The ratio of silk protein powder, pyridine, and chlorosulfonic acid is 0.5–1.5 g: 50–70 mL: 8–12 mL; and / or, the sulfonation reaction is carried out at a temperature of 70–85 °C for 1–2 h.

6. The preparation method according to claim 1, characterized in that, The sulfonation reaction is completed after the product is purified, dialyzed and dried.

7. The preparation method according to claim 1, characterized in that, The reagents used to dilute the sulfonated silk protein powder include formic acid.

8. The sulfonated silk protein gel prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the sulfonated silk protein gel according to claim 8 as an interface modification layer for an aqueous zinc electrode in a zinc-ion battery, characterized in that, The zinc-ion battery includes zinc-ion symmetric cells and / or zinc-ion full cells.

10. A zinc-ion battery, characterized in that, The zinc-ion battery includes a zinc-ion symmetric battery and / or a zinc-ion full battery; The zinc-ion symmetric battery includes a zinc negative electrode coated with sulfonated silk protein gel, a zinc positive electrode coated with sulfonated silk protein gel, a separator, and an electrolyte. The zinc-ion full battery includes a zinc negative electrode, a positive electrode, a separator, and an electrolyte coated with sulfonated silk protein gel. The coating thickness of the sulfonated silk protein gel in the zinc anode and zinc cathode coated with the sulfonated silk protein gel is independently 2–10 μm.

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