Aqueous zinc ion battery diaphragm as well as preparation method and application thereof

Abstract

The invention discloses an aqueous zinc ion battery diaphragm as well as a preparation method and application thereof. The battery diaphragm comprises a base material and a Nus-6 layer arranged on the surface of the base material. According to the invention, the Nus-6 layer is used for carrying out coating modification on the diaphragm, and the modified diaphragm can selectively allow zinc ions to pass through and block some impurity ions or solvent molecules which may cause side reactions, so that the occurrence of the side reactions is reduced. The porous structure of the Nus-6 layer can provide an additional channel for ion transmission. Meanwhile, Nus-6 is relatively stable at high temperature and in a water system environment, and can be applied to a water system zinc ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a separator for aqueous zinc-ion batteries, a preparation method thereof, and an application thereof. Background Art

[0002] Aqueous zinc-ion batteries have emerged as a promising candidate to replace lithium-ion batteries due to their high safety, low cost, and environmental friendliness. Aqueous zinc-ion batteries have many theoretical advantages, but their commercialization process still faces many challenges. The zinc anode is prone to corrosion and dendrite formation during charge and discharge, and these dendrites may cause battery short circuits and reduce the cycle life of the battery. At the same time, the by-products generated by the hydrogen evolution reaction also affect the performance and stability of the battery. To overcome these challenges, researchers are actively exploring various strategies, including optimizing the electrolyte formulation, improving the electrode material and structure design, and developing new separator technologies.

[0003] Constructing an interfacial layer in aqueous zinc-ion batteries and modifying the surface with organic or inorganic materials is an important method to inhibit dendrite growth and improve the cycle stability of aqueous zinc-ion batteries. The interfacial protection layer strategy is simple to operate, has a wide variety of protection layer materials, and has good controllability. To date, various types of artificial interfacial layers have been reported, including metal oxides and their compounds, metals and their alloys, carbon-based coatings, polymer materials, inorganic salts, metal-organic framework (MOF) materials, covalent organic framework (COF) materials, and biopolymer materials.

[0004] The crystal structures of some MOF materials may change during the charge and discharge process of the battery, resulting in a decline in their performance. For example, during the insertion and extraction of zinc ions in some MOF materials, their framework structures may deform or collapse, thus affecting the cycle life and performance of the battery. On the other hand, MOF materials are usually sensitive to water and are prone to structural damage or performance decline in a humid environment or aqueous electrolyte. The commonly used aqueous electrolyte in zinc-ion batteries will affect the stability of MOF materials, limiting their application in zinc-ion batteries. Summary of the Invention

[0005] The present invention aims to at least solve one of the above technical problems existing in the prior art. To this end, the object of the present invention is to provide a separator for aqueous zinc-ion batteries, a preparation method thereof, and an application thereof.

[0006] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0007] In a first aspect of the present invention, there is provided a separator for aqueous zinc-ion batteries, comprising a substrate and an Nus-6 layer provided on the surface of the substrate.

[0008] In the present invention, Nus-6 has a unique hierarchical porous structure with coexisting micropores and mesopores. On the one hand, this porous structure can reduce the ion transport resistance and improve the ionic conductivity. On the other hand, it can selectively allow zinc ions to pass through while blocking some impurity ions or solvent molecules that may cause side reactions. This ion sieving function is similar to an intelligent filter, which helps to purify the ionic transport environment at the electrode / electrolyte interface, thereby reducing the occurrence of side reactions, which is conducive to maintaining the stability of the internal structure of the battery. During the charge and discharge process of the battery, a stable internal environment can prevent safety hazards such as overheating and short-circuiting of the battery, thereby improving the overall safety of the battery. The Nus-6 layer can also form chemical bonds or physical adsorption with the separator substrate, enhancing the strength and toughness of the battery separator, improving its mechanical properties, and preventing the separator from rupturing during the charge and discharge process of the battery.

[0009] In some embodiments of the present invention, the Nus-6 layer comprises Nus-6 powder and an adhesive; the Nus-6 layer is disposed on the surface of the substrate through the adhesive.

[0010] In some embodiments of the present invention, the mass ratio of the Nus-6 powder to the adhesive is 7-11:1; such as 8-10:1, 9:1.

[0011] In some embodiments of the present invention, the average particle size of the Nus-6 powder is 0.8-1.2 μm, such as 1.0 μm.

[0012] In some embodiments of the present invention, there are micropores and mesopores in the Nus-6 powder; the ratio of the pore volume of the micropores to the total pore volume is at least 90%, such as 90%-98%, 90%-95%; the pore diameter of the micropores in the Nus-6 is 0.4-1.5 nm; the pore diameter of the mesopores is 3-5 nm.

[0013] In the present invention, the diameter corresponding to zinc ions is about 0.148 nm, and the radius of hexahydrate zinc ions is about 0.86 nm. Zinc ions can easily pass through the channels in Nus-6, while hexahydrate zinc ions are not easy to pass through, so that the desolvation process can be realized. At the same time, Nus-6 is relatively stable in both high-temperature and aqueous environments and can be applied in aqueous zinc-ion batteries.

[0014] In some embodiments of the present invention, in the Nus-6 powder, the pore diameter volume distribution of the micropores is D10≤0.5 μm, D50 = 0.8-1.2 μm, D90≥2.5 μm.

[0015] In some embodiments of the present invention, the substrate comprises at least one of a polyethylene separator, a polypropylene separator, a polyethylene film-polypropylene film composite separator, glass fiber, and a porous ceramic fiber-based membrane.

[0016] In some embodiments of the present invention, the binder includes polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE).

[0017] In some embodiments of the present invention, the thickness of the Nus-6 layer is 40 μm to 150 μm; such as 40 to 100 μm, 40 to 70 μm.

[0018] In some embodiments of the present invention, the thickness of the substrate is 25 μm to 500 μm.

[0019] In some embodiments of the present invention, the thickness of the aqueous zinc ion battery separator is 65 μm to 650 μm, such as 100 μm, 200 μm, 300 μm, 400 μm.

[0020] The second aspect of the present invention provides a method for preparing the aqueous zinc ion battery separator described above, comprising the following steps:

[0021] Coat the Nus-6 layer on the surface of the substrate to obtain the aqueous zinc ion battery separator described above.

[0022] In some embodiments of the present invention, disperse Nus-6 powder and a binder in an organic solvent to obtain a slurry; coat the slurry on both sides of the substrate to obtain the aqueous zinc ion battery separator described above.

[0023] In some embodiments of the present invention, disperse Nus-6 powder and a binder in an organic solvent to obtain a slurry; coat the slurry on both sides of the substrate, and after drying, obtain the aqueous zinc ion battery separator described above.

[0024] In some embodiments of the present invention, the organic solvent includes at least one of N-methyl-2-pyrrolidone (NMP), ethanol, and acetone.

[0025] In some embodiments of the present invention, the mass concentration of the slurry is 0.8 to 2.5 g / mL, such as 1.0 to 2.0 g / mL.

[0026] In some embodiments of the present invention, the drying can remove the organic solvent; the temperature of the drying is 70 to 100 °C; the time is 8 to 20 h.

[0027] In some embodiments of the present invention, the Nus-6 powder can be obtained commercially; it can also be prepared according to the following preparation method of the present invention.

[0028] In some embodiments of the present invention, the preparation method of the Nus-6 powder includes the following steps: Dissolve sodium 2-sulfoterephthalate and a zirconium salt in a water-alcohol mixed solvent for reaction to obtain the Nus-6 powder.

[0029] In some embodiments of the present invention, the molar ratio of sodium 2-sulphoisophthalate to the zirconium salt is 1:(1-2).

[0030] In some embodiments of the present invention, the zirconium salt includes ZrCl4 and / or Zr(SO4)2.

[0031] In some embodiments of the present invention, the mixed solvent includes water-methanol, water-ethanol solvents, and the volume ratio of water to alcohol is 2-5:2.

[0032] In some embodiments of the present invention, the temperature of the reaction is 70-100 °C, and the reaction time is 12-48 h.

[0033] In some embodiments of the present invention, the method for preparing the Nus-6 powder further includes purifying the reaction product. The purification treatment includes washing with water, extraction, precipitation, and drying. The specific operation of the purification treatment includes washing the reaction product with water, soaking and extracting with methanol, precipitating, and drying at 120-180 °C for 12-48 h to obtain the Nus-6 powder.

[0034] The third aspect of the present invention provides an aqueous zinc-ion battery, including the aqueous zinc-ion battery separator described above.

[0035] In some embodiments of the present invention, the aqueous zinc-ion battery further includes a positive electrode, a zinc metal negative electrode, and an electrolyte.

[0036] In some embodiments of the present invention, the aqueous zinc-ion battery separator is located between the zinc metal negative electrode and the positive electrode, and the electrolyte is filled in the battery.

[0037] In some embodiments of the present invention, the zinc metal negative electrode includes at least one of zinc sheets, zinc foils, zinc blocks, zinc tapes, zinc powders, and zinc alloys.

[0038] In some embodiments of the present invention, the electrolyte includes aqueous solutions of zinc salts such as ZnCl2, ZnF2, Zn(NO3)2, ZnSO4, Zn(CF3SO3)2, Zn(TFSI)2, Zn(CH3COO)2, Zn(ClO4)2, etc.

[0039] In some embodiments of the present invention, the aqueous zinc-ion battery includes a symmetric battery, a half-cell, or a full cell.

[0040] The beneficial effects of the present invention are:

[0041] In the present invention, the separator is coated and modified with the Nus-6 layer. The modified separator can selectively allow zinc ions to pass through, while blocking some impurity ions or solvent molecules that may cause side reactions, reducing the occurrence of side reactions. The porous structure of the Nus-6 layer can provide additional channels for ion transport. At the same time, Nus-6 is relatively stable in both high-temperature and aqueous environments and can be applied in aqueous zinc-ion batteries.

[0042] When the separator modified with the Nus-6 layer is applied to a zinc-ion battery, it can improve its cycle life and electrochemical performance, and the improvement effect is significant. Compared with the electrolyte of an unmodified aqueous zinc-ion battery, the Zn||Zn symmetric battery assembled with the modified separator has a cycle life increased from 250 h to more than 4500 h at a current density of 1 mA / cm 2 . Description of the Drawings

[0043] Figure 1 It is the SEM image of the Nus-6 powder of the present invention.

[0044] Figure 2 It is the SEM image of the surface appearance of the copper electrode on the stripping side after 20 cycles of the Zn||Cu asymmetric battery with glass fiber as the battery separator in Example 6 of the present invention.

[0045] Figure 3 It is the SEM image of the surface appearance of the copper electrode on the deposition side after 20 cycles of the Zn||Cu asymmetric battery with glass fiber as the battery separator in Example 6 of the present invention.

[0046] Figure 4 It is the SEM image of the surface appearance of the copper electrode on the stripping side after 20 cycles of the Zn||Cu asymmetric battery with the glass fiber modified with the Nus-6 layer as the battery separator in Example 6 of the present invention.

[0047] Figure 5 It is the SEM image of the surface appearance of the copper electrode on the deposition side after 20 cycles of the Zn||Cu asymmetric battery with the glass fiber modified with the Nus-6 layer as the battery separator in Example 6 of the present invention.

[0048] Figure 6 It is the constant current charge-discharge test result of the Zn||Zn symmetric battery in Example 4 of the present invention.

[0049] Figure 7 It is the constant current charge-discharge test result of the Zn||Zn symmetric battery in Example 5 of the present invention.

[0050] Figure 8 It is the cycle charge-discharge test result of the Zn||PANI full battery in Example 3 of the present invention.

[0051] Figure 9This is the test result of the specific capacity of the Zn||PANI full battery in Example 3 of the present invention. Detailed implementation manners

[0052] The content of the present invention will be further described in detail through specific embodiments below. Unless otherwise specified, the raw materials, reagents or devices used in the examples and comparative examples can be obtained from conventional commercial channels or can be obtained by existing technical methods. Unless otherwise specified, the test or measurement methods are all conventional methods in the art.

[0053] In the following examples or comparative examples, the preparation method of Nus-6 powder is as follows:

[0054] Sodium 2-sulfoterephthalate monohydrate (BDC-S03Na) (1.3 g, 4.8 mmol) and ZrCl4 (1.2 g, 5.2 mmol) dissolved in 50 mL of a water / acetic acid (30 / 20, v / v) mixed solvent were loaded into a flask and heated at 80 °C for 24 h to obtain the active product of Nus-6. The product was washed three times with water and soaked in anhydrous methanol at room temperature for 3 days. During this period, the extraction was decanted and fresh methanol was added every day. After removing the methanol by precipitation, the sample was dried under dynamic vacuum at 150 °C for 24 h to obtain the final product.

[0055] The SEM image of the prepared Nus-6 powder is as Figure 1 shown. It can be seen that in terms of structure, Nus-6 has a unique hierarchical porous structure with the coexistence of micropores and mesopores. According to non-local density functional theory calculations, the micropore diameters in Nus-6 are 0.5 nm, 0.7 nm, and 1.4 nm, and the mesopore diameter is about 4 nm.

[0056] Example 1

[0057] In this example, a zinc-ion battery separator was prepared. The specific process was as follows:

[0058] Nus-6 powder and the binder PVDF were mixed at a mass ratio of 9:1, and 2 mL of N-methyl-2-pyrrolidone (NMP) was added to form a uniform slurry with a concentration of 0.45 g / mL. The slurry was stirred to make it uniformly mixed. A 5 cm × 10 cm glass fiber (GF) separator was taken and fixed on a flat substrate. The prepared slurry was evenly coated on both sides of the separator using a 200 μm doctor blade. The coated separator was placed in a vacuum drying oven and dried at a drying temperature of 80 °C for 12 hours to remove the organic solvent, obtaining a battery separator, and a circular piece with a diameter of 16 mm was made using a cutting machine. Among them, the thickness of the Nus-6 layer was 40-70 μm.

[0059] Example 2

[0060] In this example, a zinc-ion battery separator was prepared. The specific process is as follows:

[0061] Mix Nus-6 powder and binder PVDF in a mass ratio of 9:1, add 1 mL of N-methyl-2-pyrrolidone (NMP) to form a homogeneous slurry with a concentration of 0.9 g / mL. Stir the slurry to make it well mixed. Take a 5 cm × 10 cm glass fiber (GF) separator and fix it on a flat substrate. Use a 200 μm doctor blade to evenly coat the prepared slurry on both sides of the separator. Place the coated separator in a vacuum drying oven for drying at a temperature of 80 °C for 12 hours to remove the organic solvent, obtaining the battery separator, and use a cutting machine to cut it into a disc with a diameter of 16 mm. Among them, the thickness of the Nus-6 layer is 100 - 150 μm.

[0062] Example 3

[0063] In this example, a Zn||PANI full battery was prepared. The specific process is as follows:

[0064] (1) Electrolyte: Take 5.7512 g of zinc sulfate heptahydrate and add deionized water, make up the volume to 10 mL of solution, and perform magnetic stirring on it at room temperature until completely dissolved to obtain 10 mL of 2 mol / L zinc sulfate electrolyte;

[0065] (2) Positive electrode sheet: Use a chi660e electrochemical workstation to electroplate polyaniline on a carbon nanotube film in a three-electrode system to obtain a PANI positive electrode sheet;

[0066] (3) Zn||PANI full battery: Use the above-prepared PANI positive electrode sheet as the positive electrode, zinc foil as the negative electrode, and glass fiber or the zinc-ion battery separator prepared in Example 1 as the battery separator. Take 130 μL of electrolyte and assemble it in a 2032-type button cell case in the corresponding order: positive electrode case, positive electrode sheet, zinc-ion battery separator, electrolyte, zinc negative electrode sheet, gasket, spring piece, and negative electrode case. Pressurize and seal the assembled battery to assemble a CR2032-type button cell.

[0067] Example 4

[0068] In this example, a Zn||Zn symmetric battery was prepared. The specific process is as follows:

[0069] (1) Electrolyte: Take 5.7512 g of zinc sulfate heptahydrate and add deionized water, make up the volume to 10 mL of solution, and perform magnetic stirring on it at room temperature until completely dissolved to obtain 10 mL of 2 mol / L zinc sulfate electrolyte;

[0070] (2) Zn||Zn symmetric battery: Using zinc foil as the positive and negative electrodes, and using glass fiber or the zinc-ion battery separator prepared in Example 1 as the battery separator, take 130 μL of the above-mentioned obtained electrolyte to assemble a CR2032-type coin cell.

[0071] Example 5

[0072] In this example, a Zn||Zn symmetric battery was prepared. The specific process is as follows:

[0073] (1) Electrolyte: Take 5.7512 g of zinc sulfate heptahydrate and add deionized water, make up the volume to 10 mL of solution, and carry out magnetic stirring at room temperature until completely dissolved to obtain 10 mL of 2 mol / L zinc sulfate electrolyte;

[0074] (2) Zn||Zn symmetric battery: Using zinc foil as the positive and negative electrodes, and using glass fiber or the zinc-ion battery separator prepared in Example 2 as the battery separator, take 130 μL of the above-mentioned obtained electrolyte to assemble a CR2032-type coin cell.

[0075] Example 6

[0076] In this example, a Zn||Cu asymmetric battery was prepared. The specific process is as follows:

[0077] (1) Electrolyte: Take 5.7512 g of zinc sulfate heptahydrate and add deionized water, make up the volume to 10 mL of solution, and carry out magnetic stirring at room temperature until completely dissolved to obtain 10 mL of 2 mol / L zinc sulfate electrolyte;

[0078] (2) Zn||Cu asymmetric battery: Using copper foil as the positive electrode and zinc foil as the negative electrode, and using glass fiber or the zinc-ion battery separator prepared in Example 1 as the battery separator, take 130 μL of the above-mentioned obtained electrolyte to assemble a CR2032-type coin cell.

[0079] Test Example

[0080] In this test example, the performance of the Zn||Cu asymmetric battery was tested. The specific process is as follows:

[0081] Using the Zn||Cu asymmetric battery prepared in Example 6, perform 20 constant current charge and discharge cycles on a blue battery test system, with a current density of 1 mA / cm 2 , and the areal capacity is 1 mAh / cm 2 . Conduct scanning electron microscope detection, and obtain the SEM images of the surface morphology of the copper electrode after cycling of the zinc-ion battery with the zinc-ion battery separator of Example 1 and glass fiber as the battery separator as shown in Figures 2 to 5 shown.

[0082] From Figures 2 to 5It can be seen that for the asymmetric battery using only glass fiber as the battery separator, severe zinc dendrite growth occurs at the zinc negative electrode, which may lead to battery short - circuit. After modification with the Nus - 6 layer, the zinc dendrite particles on the zinc negative electrode are significantly smaller after 20 cycles of the battery. The surface of the zinc negative electrode is smoother, and the deposited side of the zinc electrode presents a typical (002) plane morphology, indicating that the modified separator can significantly inhibit dendrite growth.

[0083] This test example also conducts performance tests on the Zn||Zn symmetric battery. The specific process is as follows:

[0084] The Zn||Zn symmetric battery prepared in Example 4 was subjected to a constant - current charge - discharge test at room temperature with a current density of 0.5 mA / cm 2 , and the areal capacity was 0.25 mAh / cm 2 . The test results are as Figure 6 shown. The Zn||Zn symmetric battery prepared in Example 5 was subjected to a constant - current charge - discharge test at room temperature with a current density of 1 mA / cm 2 , and the areal capacity was 1 mAh / cm 2 . The test results are as Figure 7 shown.

[0085] It can be seen that the symmetric battery using only glass fiber as the battery separator short - circuited after 250 h of cycling, indicating severe dendrite growth and resulting in battery damage. Compared with the aqueous zinc - ion battery electrolyte using only glass fiber as the battery separator, for the Zn||Zn symmetric battery assembled with the Nus - 6 layer modified separator prepared in Example 2 in Example 5, at a current density of 1 mA / cm 2 , the cycle life was increased from 250 h to more than 1200 h, indicating that after modification with the Nus - 6 layer, the separator can significantly extend the battery life and greatly improve the long - cycle stability of the zinc negative electrode. For the Zn||Zn symmetric battery assembled with the Nus - 6 layer modified separator prepared in Example 1 in Example 4, at a current density of 0.5 mA / cm 2 , the cycle life was increased from 250 h to more than 5000 h, indicating that the thinner separator has better cycle performance at low current densities. This may be because at low current densities, the thinner separator has relatively less resistance to ion transport and can more efficiently maintain the charge balance inside the battery.

[0086] This test example also conducts performance tests on the Zn||PANI full battery. The specific process is as follows:

[0087] The Zn||PANI full battery prepared in Example 3 was subjected to cyclic charge - discharge tests on a blue - power battery test system at a current density of 1 A / g. The test results are as Figure 8 、 Figure 9 shown.

[0088] It can be seen that the maximum discharge specific capacity of the Zn||PANI full cell prepared in Example 3 is about 117.14 mAh / g, and the average specific capacity is 107.66 mAh / g. After 4000 cycles, the capacity retention rate is 93.55%, and the average Coulombic efficiency is 99.79%. The average specific capacity of the Zn||PANI full cell using only glass fiber as the battery separator is 78.63 mAh / g, and the capacity decays to 49.57 mAh / g after 100 cycles. This shows that during the cycling process of the full cell, the Nus-6 layer modified separator can reduce the battery capacity loss, improve the reversibility of zinc deposition and stripping reactions, effectively extend the cycle life of the aqueous zinc ion battery, and improve the Coulombic efficiency, effectively slowing down the attenuation process of the battery specific capacity.

[0089] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. An aqueous zinc ion battery separator, characterized in that: The invention comprises a substrate and a Nus-6 layer arranged on the surface of the substrate.

2. The aqueous zinc ion battery separator according to claim 1, characterized in that: The Nus-6 layer comprises Nus-6 powder and an adhesive; the Nus-6 layer is arranged on the surface of the substrate through the adhesive.

3. The aqueous zinc ion battery separator according to claim 2, characterized in that: There are micropores and mesopores in the Nus-6 powder; the ratio of the pore volume of the micropores to the total pore volume is at least 90%; preferably, the pore diameter of the micropores in the Nus-6 is 0.4 to 1.5 nm; the pore diameter of the mesopores is 3 to 5 nm.

4. The aqueous zinc ion battery separator according to claim 2, characterized in that: The mass ratio of the Nus-6 powder to the adhesive is 7 to 11:

1.

5. The aqueous zinc ion battery separator according to claim 1, characterized in that: The thickness of the Nus-6 layer is 40 μm to 150 μm.

6. A method for preparing an aqueous zinc ion battery separator according to any one of claims 1 to 5, characterized in that: The following steps are involved: The Nus-6 layer is coated on the surface of the substrate to obtain the aqueous zinc ion battery separator.

7. The method for preparing an aqueous zinc ion battery separator according to claim 6, wherein: Dispersing Nus-6 powder and a binder in an organic solvent to obtain a slurry; coating the slurry on both sides of a substrate to obtain the aqueous zinc ion battery separator; preferably, the preparation method of the Nus-6 powder comprises the following steps: dissolving monosodium 2-sulfonate terephthalate and a zirconium salt in a water-alcohol mixed solvent for reaction to obtain Nus-6 powder.

8. An aqueous zinc ion battery, characterized in that: The invention comprises the aqueous zinc ion battery separator according to any one of claims 1 to 5.

9. The aqueous zinc ion battery according to claim 8, characterized in that: The aqueous zinc ion battery also includes a positive electrode, a zinc metal negative electrode, and an electrolyte; the aqueous zinc ion battery separator is located between the zinc metal negative electrode and the positive electrode, and the electrolyte is filled in the battery.

10. The aqueous zinc ion battery according to claim 8, characterized in that: The aqueous zinc ion battery includes a symmetrical battery, a half-cell or a full battery.

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