A hierarchical porous membrane with different Ag content on the front and back surface, a preparation method thereof and application in negative side separator of aqueous zinc ion battery

Abstract

The application discloses a hierarchical porous membrane with Ag content difference on both sides, a preparation method thereof and application of the hierarchical porous membrane in a negative side separator of a water-based zinc ion battery. By combining a chemical plating process and a phase inversion process to change a solvent exchange rate, the content of Ag particles on both sides of the membrane is regulated in a film forming process, and the hierarchical porous membrane with intrinsic potential difference is prepared by one-step method. The membrane is used as an interlayer with hierarchical porous structure, which is beneficial to guiding zinc ions to disperse in the complex porous structure. The potential difference caused by the gradient distribution of the Ag concentration induces the further transmission of the zinc ions downward and reduces the nucleation energy barrier of the zinc ions, which is beneficial to the redispersion and deposition of the zinc ions, so that the zinc dendrites are inhibited. The prepared water-based zinc ion battery has excellent zinc dendrite inhibition capacity, and can be stably cycled for more than 1000 h under the condition of 1 mA cm ‑2 , 0.5 mAh cm ‑2 . The assembled full battery can be stably cycled for more than 5000 cycles under the current density of 5 Ag ‑1 .

Description

Technical Field

[0001] This invention belongs to the technical field of negative electrode side separators for aqueous zinc-ion batteries, and relates to a hierarchical porous membrane with a difference in Ag content on the front and back sides, its preparation method, and its application in the negative electrode side separator of aqueous zinc-ion batteries. Specifically, the hierarchical porous membrane relates to a hierarchical porous membrane constructed by loading Ag onto carbon nanotubes and polyacrylonitrile. Background Technology

[0002] New energy storage technologies are crucial for achieving the goal of "carbon peaking and carbon neutrality," but existing technologies still face challenges such as weak safety and limited resources. Therefore, there is an urgent need to develop new rechargeable battery systems. Aqueous zinc-ion batteries, with their low cost, high safety, and high power, represent a highly promising green battery system. An aqueous zinc-ion battery consists of a negative electrode of metallic zinc, a separator, a positive electrode active material, and an aqueous electrolyte. During discharge, zinc metal loses electrons to form Zn. 2+ Zn 2+ The Zn electrode material is embedded in the positive electrode material through the separator from the negative electrode. During charging, the positive electrode material releases Zn. 2+ It is then returned to the negative electrode to be deposited as metallic zinc. During the deposition process, the morphology of metallic zinc deposition is regulated by crystal thermodynamics and kinetics. It needs to overcome the nucleation energy barrier to form a solid phase through heterogeneous nucleation, and finally complete the energy storage.

[0003] Among the many solutions for addressing zinc dendrite formation in aqueous zinc-ion batteries, the design of highly functionalized separators has attracted widespread attention. As an emerging strategy, separator design also faces several challenges. For example, the introduction of separators increases interfacial contact within the battery, which increases the resistance to internal operation. Furthermore, most existing design methods are very complex and expensive for large-scale manufacturing. Therefore, it is necessary to design and propose a simple method to prepare a solution that can disperse and guide Zn. 2+ Highly efficient deposition of the interlayer. Therefore, how to design and optimize the interlayer structure and strengthen its interaction with Zn is crucial. 2+ Affinity, co-dispersibility of Zn 2+ Simultaneous regulation of Zn 2+ The deposition process suppresses zinc dendrite formation, which has guiding significance for the practical application of aqueous zinc-ion batteries. Summary of the Invention

[0004] To address the above problems, this invention proposes a hierarchical porous membrane with a difference in Ag content on its front and back sides, its preparation method, and its application in the negative electrode separator membrane of an aqueous zinc-ion battery. By combining chemical plating and phase inversion processes, the polar functional groups on the membrane material surface adsorb metal cations, thus reducing the metal cations to metals in situ on the membrane framework during the phase inversion process and loading them onto the membrane framework. By controlling the solvent exchange rate during the phase inversion process, the difference in metal content on the front and back sides of the membrane is achieved, constructing a functionalized membrane with different metal content on both sides, denoted as a CNT / PAN / Ag membrane. The hierarchical porous structure constructed due to the phase inversion characteristics not only effectively disperses the zinc ion flow, but the macroporous structure also promotes the storage of electrolyte and excess Zn, thereby homogenizing the zinc ion flow at the deposition interface. Simultaneously, the difference in metal content on the front and back sides of the membrane creates a certain potential difference, thereby inducing Zn... 2+ The downward transfer and deposition process suppresses zinc dendrite formation, improving the cycle stability and rate performance of the battery. The CNT / PAN / Ag membrane is prepared using carbon nanotubes and polyacrylonitrile as raw materials. Silver trifluoroacetate is pre-mixed in the membrane solution, utilizing the polar functional groups -COOH and carbon-nitrogen triple bonds on the surfaces of carbon nanotubes and polyacrylonitrile to adsorb metallic silver ions. Subsequently, the membrane solution is scraped and subjected to phase inversion in an aqueous solution of dimethylamine borane. During this phase inversion, the adsorbed silver ions are reduced to metallic Ag upon contact with dimethylamine borane and loaded onto the membrane framework, preparing a hierarchical porous membrane with Ag loading and a difference in Ag content between the front and back sides. This membrane is used as the negative electrode separator in an aqueous zinc-ion battery, effectively controlling the deposition of Zn. 2+ Redispersing and lowering its nucleation energy barrier induces Zn 2+ Uniform deposition suppresses zinc dendrite formation. Aqueous zinc-ion batteries exhibit excellent cycle stability and rate performance.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A hierarchical porous membrane with a difference in Ag content on its front and back sides is provided. The membrane is constructed using carbon nanotubes (CNTs) and polyacrylonitrile (PAN) as the hierarchical porous membranes, and Ag metal particles are loaded onto the hierarchical porous membranes. The content of Ag metal in the hierarchical porous membranes is 5%-30%, and the Ag content on the front and back sides of the hierarchical porous membranes increases in a gradient.

[0006] The present invention also provides a method for preparing a hierarchical porous membrane with a difference in Ag content on its front and back sides, comprising the following steps: 1) Add solvent, polyacrylonitrile, carbon nanotubes and silver trifluoroacetate to a blue-capped screw-top bottle, and stir magnetically at 60-80 °C for 10-48 h to obtain a black viscous membrane solution; the mass ratio of polyacrylonitrile to solvent in the membrane solution is 1:8-1:20; the solvent is N,N-dimethylformamide or N-methylpyrrolidone; 2) Using a film scraper, the black film solution prepared above is scraped onto a glass plate to form a gel phase membrane with a thickness of 100-500 μm; 3) Dissolve dimethylamine borane in water to prepare an antisolvent. Immerse the gel phase membrane obtained in step 2) completely in the antisolvent for in-situ reduction phase transformation. After the reaction is completed, vacuum dry the obtained membrane material to obtain a hierarchical porous membrane with a difference in Ag content on the front and back sides, denoted as CNT / PAN / Ag membrane.

[0007] Furthermore, in step 1), the mass ratio of the polyacrylonitrile to the solvent is 1:5 to 1:30.

[0008] Furthermore, in step 1), the mass ratio of the carbon nanotubes to polyacrylonitrile is 1:2 to 1:5.

[0009] Furthermore, in step 1), the mass ratio of silver trifluoroacetate to polyacrylonitrile is 1:1 to 1:10.

[0010] Furthermore, in step 3), the mass ratio of dimethylamine borane to water is 1:200 to 1:1000.

[0011] Furthermore, in step 3), the thickness of the film obtained by the in-situ reduction phase transformation is 20-50 μm.

[0012] Furthermore, the vacuum drying conditions described in step 3) are: drying temperature 50-80 ℃, drying time 8-24h.

[0013] Furthermore, step 3) also includes cutting the CNT / PAN / Ag film into 12-16 mm discs.

[0014] The present invention also provides a negative electrode side separator for an aqueous zinc-ion battery, which uses a hierarchical porous membrane with a difference in Ag content on the front and back sides as the side separator.

[0015] The beneficial effects of this invention include: This invention combines chemical plating and phase inversion methods to prepare an Ag-supported hierarchical porous membrane through in-situ reduction phase inversion of a membrane solution composed of carbon nanotubes, polyacrylonitrile, and silver trifluoroacetate. The Ag content differs between the front and back sides of the membrane. This membrane exhibits a hierarchical porous structure resulting from the phase inversion. As a separator, it facilitates the guidance of Zn.2+ Redispersed, uniformly deposited Zn at the interface 2+ The concentration of Ag on the membrane backbone can effectively reduce Zn concentration. 2+ Nucleation energy barrier, inducing Zn 2+ Uniform deposition suppresses zinc dendrite formation and improves battery cycle stability. This material, applied to aqueous zinc-ion batteries, effectively solves the severe zinc dendrite formation problem in these batteries, improving cycle stability and rate performance, and exhibiting excellent electrochemical performance. The effect of suppressing zinc dendrite formation was tested in assembled zinc-symmetric cells at 1 mA cm⁻¹. -2 0.5 mAh cm -2 Under these conditions, batteries using CNT / PAN / Ag films as the negative electrode separator can cycle stably for over 1200 hours. However, batteries using CNT / PAN films as intercalation layers and those without intercalation layers showed significant zinc dendrite formation after 430 and 220 hours of cycling, respectively, leading to short circuits. In full-cell testing, at 5 Ag... -1 After 5000 cycles at a current density, the battery using a CNT / PAN / Ag film as the negative electrode separator still maintained 74.7 mA hg. -1 The specific capacity of the CNT / PAN membrane and the unprotected full cell decreased to 56.4 and 35.1 mA hg after 5000 cycles. -1 This demonstrates that the CNT / PAN / Ag membrane is effective in improving battery cycle stability. Attached Figure Description

[0016] Figure 1 The image shows a cross-sectional scanning electron microscope (SEM) image of the negative electrode side separator of an aqueous zinc-ion battery with a difference in Ag content on the front and back sides, as prepared in Example 1.

[0017] Figure 2 The surface scanning electron microscope image of the negative electrode side separator of an aqueous zinc-ion battery with a difference in Ag content on the front and back sides, as shown in Example 1.

[0018] Figure 3 The reverse scanning electron microscope image of the separator on the negative electrode side of an aqueous zinc-ion battery with a difference in Ag content on the front and back sides, as shown in Example 1.

[0019] Figure 4 This is a pore size distribution diagram of the membrane in Example 1.

[0020] Figure 5 This is a diagram of the zinc symmetric cycle test assembled in Example 1.

[0021] Figure 6 This is a cycle test diagram of the full battery assembled in Example 1. Detailed Implementation

[0022] The experimental scheme of the present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments. Unless otherwise specified, the methods described are conventional methods. Unless otherwise specified, the raw materials or instruments can be obtained commercially available.

[0023] Example 1 1. Preparation of negative electrode side separator electrode material for aqueous zinc-ion batteries 1) 0.5 g of carbon nanotubes, 1 g of polyacrylonitrile, 0.5 g of silver trifluoroacetate and a certain amount of N,N-dimethylformamide were added sequentially to a blue-capped sieve. The sieve was magnetically stirred at 60 °C for 12 h to obtain a black viscous membrane solution. The mass ratio of polyacrylonitrile to N,N-dimethylformamide in the membrane solution was 1:12. 2) Using a film scraper, the black film solution prepared above is scraped onto a glass plate to form a 500-micrometer-thick gel phase film; 3) Dissolve 3 g of dimethylamine borane in 2 L of water to prepare an antisolvent. Completely immerse the gel phase membrane obtained in step 2) in the antisolvent for in-situ reduction phase transformation. After the reaction, dry the resulting membrane material under vacuum for 12 h at 60 °C to obtain CNT / PAN / Ag (CPA). 0.5 M) membranes, as shown in Figures 1, 2, 3, 4 and Table 1.

[0024] Table 1 CPA 0.5 Ag content distribution on both sides of M <![CDATA[CPA 0.5 M surface]]> 12.52 1.61 <![CDATA[CPA 0.5 M (reverse side) 15.05 1.99 2. Preparation of CNT / PAN membrane (not part of this invention) 1) 1 g of carbon nanotubes, 1 g of polyacrylonitrile and a certain amount of N,N-dimethylformamide were added sequentially to a blue-capped sieve. The sieve was magnetically stirred at 60°C for 12 h to obtain a black viscous membrane solution. The mass ratio of polyacrylonitrile to solvent in the membrane solution was 1:12. 2) Using a film scraper, the black film solution prepared above is scraped onto a glass plate to form a 500-micrometer-thick gel phase film; 3) The gel phase membrane obtained in step 2) is completely immersed in water for phase transformation. After the reaction is completed, the membrane material is dried under vacuum for 12 hours at a temperature of 60°C to obtain the CNT / PAN (CPM) membrane.

[0025] 3. Fabrication of aqueous zinc-ion batteries using CNT / PAN / Ag membrane separator materials 10 mg of polyvinylidene fluoride was dissolved in 700 μL of N-methylpyrrolidone, and then 90 mg of calcium vanadate was added and stirred to obtain a calcium vanadate composite slurry. The calcium vanadate composite slurry was coated on one side of an aluminum foil (a 12 mm diameter disc), vacuum dried, and used as the positive electrode of an aqueous zinc-ion battery. Subsequent battery assembly involved using a zinc foil as the negative electrode, a CNT / PAN / Ag membrane as a separator placed between the negative electrode and a glass fiber separator, and a 2 M ZnSO4 aqueous solution as the electrolyte.

[0026] 4. Fabrication of lithium-sulfur batteries using CNT / PAN films as separators With other conditions remaining unchanged, the CNT / PAN membrane was used as the separator to replace the CNT / PAN / Ag membrane.

[0027] 5. Performance testing of CNT / PAN / Ag and CNT / PAN separator batteries After the battery was left to stand for 12 hours, constant current constant time cycle performance test and constant current charge-discharge cycle performance test were completed using the Blue Electric test system. The test voltage window for the constant current charge-discharge cycle performance test was 0.2-1.6 V. Figure 5 For the zinc dendrite prevention test (constant current constant time cycle performance test) of aqueous zinc-ion batteries with different separators and without separators assembled in Example 1, at 1 mA cm⁻¹ -2 0.5 mAh cm -2 Under these conditions, the voltage of an aqueous zinc-ion battery without a separator began to increase after 220 hours of cycling, indicating the presence of zinc dendrites. However, aqueous zinc-ion batteries using a CNT / PAN membrane as a separator could develop zinc dendrites after more than 400 hours of cycling. Aqueous zinc-ion batteries using a CNT / PAN / Ag membrane as a separator remained stable for over 1200 hours without the appearance of zinc dendrites. Figure 6 This is a performance test chart of the assembled full cell, at 5 A g. -1 At the specified current density, the batteries can stably cycle for 5000 cycles, but the specific capacity decreases to 74.7 mA hg. -1 56.4 mA hg -1 and 35.1 mA hg -1 .

[0028] Finally, it should be noted that the above embodiments are merely one specific implementation of the present invention. Although the descriptions are detailed and specific, they should not be construed as limiting the scope of the present invention. Those skilled in the art should understand that any equivalent substitutions or modifications made to the present invention without departing from its technical scope are considered to have remained within the scope of protection of the present invention.

Claims

1. A method for preparing a hierarchical porous membrane with a difference in Ag content on its front and back sides, characterized in that: A hierarchical porous membrane is constructed using carbon nanotubes and polyacrylonitrile, with Ag metal particles loaded on the membrane. The Ag metal content in the hierarchical porous membrane ranges from 5% to 30%, and the Ag content increases gradually on the front and back sides of the membrane. The preparation method includes the following steps: 1) Add carbon nanotubes, polyacrylonitrile, solvent, and silver trifluoroacetate to a blue-capped swivel bottle, and incubate the swivel bottle at 60-80°C. o After magnetic stirring at C for 10-48 hours, a black viscous membrane solution was obtained; the mass ratio of polyacrylonitrile to solvent in the membrane solution was 1:8-1:20; the solvent was N,N-dimethylformamide or N-methylpyrrolidone. The mass ratio of carbon nanotubes to polyacrylonitrile is 1:2-1:5; the mass ratio of silver trifluoroacetate to polyacrylonitrile is 1:1-1:

10. 2) Using a film scraper, the black viscous film solution prepared above is scraped onto a glass plate to form a gel phase film with a thickness of 100-500 μm; 3) Dissolve dimethylamine borane in water to prepare an antisolvent. Immerse the gel phase membrane obtained in step 2) completely in the antisolvent for in-situ reduction phase transformation. After the reaction is completed, vacuum dry the obtained membrane material to obtain a hierarchical porous membrane with a difference in Ag content on the front and back sides, denoted as CNT / PAN / Ag membrane.

2. The method for preparing a hierarchical porous membrane with a difference in Ag content on its front and back sides as described in claim 1, characterized in that: In step 1), the mass ratio of polyacrylonitrile to solvent is 1:5-1:

30.

3. The method for preparing a hierarchical porous membrane with a difference in Ag content on its front and back sides as described in claim 1, characterized in that: In step 3), the mass ratio of dimethylamine borane to water is 1:200-1:1000.

4. The method for preparing a hierarchical porous membrane with a difference in Ag content on its front and back sides as described in claim 1, characterized in that: In step 3), the thickness of the film obtained by the in-situ reduction phase transformation is 20-50 μm.

5. The method for preparing a hierarchical porous membrane with a difference in Ag content on its front and back sides as described in claim 1, characterized in that: The vacuum drying conditions described in step 3) are: drying temperature 50-80°C. o C, drying time 8-24h.

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