Gradient hydrophilic-hydrophobic separator for aqueous zinc-ion battery and preparation method thereof, and aqueous zinc-ion battery

Abstract

The application provides a gradient hydrophilic-hydrophobic diaphragm for an aqueous zinc ion battery, which comprises a hydrophilic layer, a first hydrophobic layer and a second hydrophobic layer, the hydrophilic layer is located between the first hydrophobic layer and the second hydrophobic layer, thereby forming a gradient hydrophilic-hydrophobic diaphragm with hydrophobic and hydrophilic layers alternating; wherein the hydrophilic diaphragm layer is prepared by using an electrospinning process, and a mixed solution of 4,4'-diamino diphenyl ether (ODA) and pyromellitic dianhydride (PMDA) is used as a hydrophilic precursor; the hydrophobic diaphragm layer is prepared by using an electrospinning process, and a mixed solution of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) is used as a hydrophobic precursor. The gradient hydrophilic-hydrophobic diaphragm can reduce the desolvation barrier to inhibit the occurrence of side reactions, inhibit the disordered growth of zinc negative electrode dendrites while keeping the electrochemical performance of the zinc ion battery unchanged, and improve the cycle performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aqueous zinc-ion batteries, in particular to a gradient hydrophilic-hydrophobic separator for aqueous zinc-ion batteries, a preparation method thereof and an aqueous zinc-ion battery. BACKGROUND

[0002] Aqueous zinc-ion batteries (AZIBs) are increasingly becoming a low-cost energy storage solution due to their excellent safety performance, rapid charging and discharging speed, and high energy density. However, the commercialization of AZIBs still faces many obstacles, especially the problem of unordered growth of zinc negative electrode surface dendrites. These dendrites can pierce the separator, causing short circuit risk, which seriously threatens the safety of the battery. In addition, the release of hydrogen and the intensification of corrosion-related side reactions also accelerate the aging speed of the battery and shorten its cycle life. At the same time, the dissolution problem of the cathode material cannot be ignored, because it directly leads to the gradual decay of the battery capacity. The root cause of these problems lies in the complex interaction between the electrode-electrolyte interface and the electrolyte-separator interface, therefore, optimizing the characteristics of these interfaces is crucial for improving the performance of AZIBs and overcoming existing difficulties.

[0003] Researchers have made efforts to explore and implement various innovative strategies to enhance the stability between the electrode and the electrolyte interface, aiming to significantly extend the cycle life of AZIBs. These carefully designed strategies cover positive electrode modification, negative electrode modification, and fine adjustment of electrolyte composition, each of which plays a key role in improving battery performance. For example, in the exploration of positive electrode modification, using Sr(NO3)2 to coat the surface of vanadium oxide positive electrode, it will react with the components in the electrolyte to form a dense CEI film, which can tightly adhere to the surface of the positive electrode material, effectively isolating the direct contact between the electrode and the electrolyte. The formation of the CEI film significantly reduces the contact between the positive electrode material and active water, thereby reducing unnecessary side reactions between the positive electrode material and the electrolyte, which often leads to corrosion of the electrode material, decomposition of the electrolyte, and decline in battery performance. By inhibiting these side reactions, the CEI film helps to extend the service life of the battery.

[0004] In terms of negative electrode modification, for example, using Nano-CaCO3 and dopamine polymer as a protective coating for zinc anode, these coatings will react with the components in the electrolyte to form a dense SEI film, which not only isolates the contact between active water and zinc negative electrode to inhibit the occurrence of a large number of side reactions, but also guides the uniform deposition of zinc dendrites, further improving the stability and safety of the anode.

[0005] In addition, a large number of attempts have also been made in the aspect of electrolyte regulation, using a variety of materials including carboxymethyl cellulose (CMC), silk fibroin, borate, polyacrylamide (PAM), and various gel electrolytes, to fine-tune the interaction between the single electrode and the electrolyte interface to optimize the ion transport path, reduce the active water reaching the electrode surface to inhibit the occurrence of side reactions, and to some extent, alleviate the dissolution of the electrode material and the deposition of the alkaline salt.

[0006] Although the adjustment of the negative electrode / electrolyte interface has effectively inhibited the growth of dendrites, anode corrosion, and the evolution of hydrogen, and the adjustment of the positive electrode / electrolyte interface has significantly reduced the evolution of hydrogen / oxygen, the deposition of alkaline salt, and the dissolution of the positive electrode material, etc. However, how to simultaneously solve the challenges faced by the negative electrode and the positive electrode in the same battery system remains a technical problem that needs to be overcome.

[0007] Both the negative electrode and the positive electrode are closely related to their respective electrochemical interfaces, and the separator directly contacts the negative electrode and the positive electrode, therefore, separator modification is an effective and practical method to control the anode and cathode interfaces. Many studies focus on modifying glass fibers with graphene, MXene, melamine and cyanuric acid, metal organic framework (MOF) and UIO-66, etc. to form Janus separators. These modifications provide uniform pore size distribution, strong mechanical strength, and strong zinc ion transmission efficiency, but only inhibit the disordered growth of zinc dendrites and reduce the contact of active water with the zinc anode. However, few studies can simultaneously improve the performance of the negative electrode and the positive electrode in the complete battery system. In addition, glass fiber separators are usually too thick (about 200 microns) and lack sufficient mechanical strength, which cannot be practically applied in AZIBs.

[0008] In order to overcome the above-mentioned defects, the prior art uses an electrostatic spinning process to prepare a PI@PMIA nanofiber membrane with high porosity, large specific surface area and rough structure to improve the problems of poor mechanical performance, short service life and uneven ion transmission of existing separators. There are also composite fiber separators with hydrophilic and hydrophobic properties prepared by mixing different fiber slurries in proportion to inhibit the disordered growth of zinc dendrites. There are also simple composite double-layer or multi-layer anti-dendrite separators and hydrophilic separators using low-melting-point network binders to solve the problems of dendrite growth of zinc anode in aqueous zinc ion batteries and large demand for positive electrolyte. Although these separators improve the electrochemical performance of zinc ion batteries to some extent, the performance of zinc ion batteries is still limited due to the limited reduction of the solvation barrier, making it difficult to break through the barriers.

[0009] Prior art documents:

[0010] Chinese patent: CN115275506

[0011] Chinese patent: CN117855747

[0012] Chinese patent: CN119361969 SUMMARY

[0013] The present application aims at the deficiencies of the prior art, and provides a gradient hydrophilic-hydrophobic separator for aqueous zinc ion batteries and a preparation method thereof.

[0014] According to a first aspect of the present application, a gradient hydrophilic-hydrophobic separator for aqueous zinc ion batteries is provided, comprising a hydrophilic layer, a first hydrophobic layer and a second hydrophobic layer, the hydrophilic layer being located between the first hydrophobic layer and the second hydrophobic layer, thereby forming a gradient hydrophilic-hydrophobic separator with alternating hydrophobic and hydrophilic layers.

[0015] The hydrophilic layer is prepared by electrospinning process using a mixed solution of 4,4'-diamino diphenyl ether (ODA) and pyromellitic dianhydride (PMDA) as the hydrophilic precursor.

[0016] The first hydrophobic layer and the second hydrophobic layer are prepared by electrospinning process using a mixed solution of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) as the hydrophobic precursor.

[0017] As an optional embodiment, the thickness T of the gradient hydrophilic-hydrophobic separator ranges from 0.1 mm to less than 0.3 mm.

[0018] As an optional embodiment, the first hydrophobic layer and the second hydrophobic layer are symmetrically arranged around the hydrophilic layer.

[0019] As an optional embodiment, the thickness ratio of the first hydrophobic layer, the hydrophilic layer and the second hydrophobic layer is (0.4-0.5):(1-1.1):(0.4-0.5).

[0020] According to a second aspect of the present application, a preparation method of the aforementioned gradient hydrophilic-hydrophobic separator for aqueous zinc ion batteries is provided, comprising the following steps:

[0021] Polyacrylonitrile and polyvinylidene fluoride are dissolved in N,N-dimethylformamide respectively and then mixed to obtain a first mixed solution;

[0022] 4,4'-diamino diphenyl ether and pyromellitic dianhydride are dissolved in N,N-dimethylformamide in an inert gas-filled environment, and a second mixed solution is obtained by stirring and reacting;

[0023] The first mixed solution is used to prepare the first hydrophobic layer by electrospinning, the second mixed solution is used to stack the hydrophilic layer on one side surface of the first hydrophobic layer by electrospinning, then the first mixed solution is used to stack the second hydrophobic layer on the hydrophilic layer by electrospinning, and finally the membrane after spinning is dried to obtain the gradient hydrophilic-hydrophobic membrane.

[0024] As an optional embodiment, the mass ratio of polyacrylonitrile, polyvinylidene fluoride and N,N-dimethylformamide is (0.95-1.05):(1-1.05):10.

[0025] As an optional embodiment, the mass ratio of 4,4'-diamino diphenyl ether, pyromellitic dianhydride and N,N-dimethylformamide is (0.95-1):(1-1.05):10.

[0026] As an optional embodiment, the process conditions of electrospinning when preparing the first hydrophobic layer and the second hydrophobic layer include:

[0027] The concentration of the spinning solution is 10%-12%, the jet voltage is-8KV--9KV and 12KV-14KV, the receiving distance is 120mm-150mm, the solution advancing speed is 0.03mm / min-0.05mm / min, the needle head diameter is 0.86mm-0.95mm, the temperature is 35℃, and the humidity is 40%.

[0028] As an optional embodiment, the process conditions of electrospinning when preparing the hydrophilic layer include:

[0029] The concentration of the solution is 19%-21%, the jet voltage is-8KV--9KV and 12KV-14KV, the receiving distance is 120mm-150mm, the solution advancing speed is 0.035mm / min-0.05mm / min, the needle head diameter is 0.86mm-0.95mm, the temperature is 35℃, and the humidity is 40%.

[0030] According to a third aspect of the object of the present application, a water-based zinc ion battery is provided, which comprises the aforementioned gradient hydrophilic-hydrophobic membrane for water-based zinc ion batteries.

[0031] The gradient hydrophilic-hydrophobic separator for the aqueous zinc ion battery of the application is prepared by using a mixed solution of 4,4'-diamino diphenyl ether and pyromellitic dianhydride to form a polyamic acid solution as a hydrophilic precursor for electrospinning, using a mixed solution of polyacrylonitrile and polyvinylidene fluoride as a hydrophobic precursor for electrospinning, first electrospinning the hydrophobic precursor to obtain a first layer of the separator (a first hydrophobic layer), then electrospinning the hydrophilic precursor on the first layer of the separator to prepare a second layer of the separator (a hydrophilic layer), and finally electrospinning the hydrophobic precursor on the second layer of the separator to prepare a third layer of the separator (a second hydrophobic layer), and drying the separator in a vacuum oven to obtain the gradient hydrophilic-hydrophobic separator.

[0032] The separator of the application has a hydrophilic layer in the middle that retains sufficient aqueous electrolyte to ensure high ionic conductivity, and the hydrophobic layers on both sides repel the adsorption of hydrated ions (H + and OH - are both hydrophilic ions and exist in the form of hydrated ions in the aqueous electrolyte), and selectively transmit only the hydrophobic ions in the electrolyte, such as bis(trifluoromethanesulfonyl) imide anions (TFSI - ) and trifluoromethanesulfonate anions (OTF - ), thereby minimizing the desolvation barrier, which on the one hand can effectively reduce the nucleation overpotential of zinc deposition, enhance the interface charge transfer kinetics, and inhibit the disordered growth of zinc dendrites, and on the other hand prevent water-induced side reactions, thereby simultaneously optimizing the performance of the negative electrode and the positive electrode in the same battery system and improving the performance of the battery.

[0033] The preparation method of the application is simple, low in cost, and does not produce pollution, and has certain environmental friendliness. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a structural schematic diagram of the gradient hydrophilic-hydrophobic separator for the aqueous zinc ion battery of the application.

[0035] Figure 2 is an SEM diagram of the gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) prepared in Example 1 of the application; wherein a is an SEM diagram of the fiber of the hydrophilic layer of the gradient hydrophilic-hydrophobic separator, and b is an SEM diagram of the fiber of the hydrophobic layer of the gradient hydrophilic-hydrophobic separator.

[0036] Figure 3 is the contact angle of the gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) and the glass fiber separator prepared in Example 1 of the application; wherein a is the contact angle of the fiber of the hydrophilic layer of the gradient hydrophilic-hydrophobic separator, b is the contact angle of the fiber of the hydrophobic layer of the gradient hydrophilic-hydrophobic separator, and c is the contact angle of the glass fiber separator.

[0037] Figure 4are the battery performance test figures of zinc ion batteries of embodiment 1 and comparative example 3 of the application; wherein a is the zinc ion battery using gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) and glass fiber separator (GF) at 0.1A g -1 Current density under 100 cycles of cycle performance comparison figure, b is the GCD curve figure of zinc ion battery using gradient hydrophilic-hydrophobic separator under 100 cycles of cycle, c is the GCD curve figure of zinc ion battery using glass fiber separator under 100 cycles of cycle.

[0038] Figure 5 are the battery performance test figures of zinc ion batteries of embodiment 1, comparative example 1 and comparative example 2 of the application; wherein a is the zinc ion battery using gradient hydrophilic-hydrophobic separator of different thickness at 0.1A g -1 Current density under 100 cycles of cycle performance comparison figure, b is the GCD curve figure of zinc ion battery using gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) under 100 cycles of cycle, c is the GCD curve figure of zinc ion battery using gradient hydrophilic-hydrophobic separator (P-F / A 0.3mm) under 100 cycles of cycle, d is the GCD curve figure of zinc ion battery using gradient hydrophilic-hydrophobic separator (P-F / A 0.1mm) under 100 cycles of cycle.

[0039] Figure 6 are the rate performance test figures of zinc ion batteries of embodiment 1 and comparative example 3 of the application; wherein a is the battery rate performance comparison figure using gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) and glass fiber separator, b-c is the GCD curve figure of zinc ion battery using different electrolyte at 0.1Ag -1 , 0.2Ag -1 , 0.5Ag -1 , 1.0Ag -1 , 2.0Ag -1 , 5.0Ag -1 Current density under 100 cycles of cycle performance comparison figure: b gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm); c glass fiber separator.

[0040] Figure 7 are the ion conductivity tests of zinc ion batteries of embodiment 1, comparative example 1, comparative example 2 and comparative example 3 of the application; wherein a is the electrochemical impedance spectrum of four different separators of gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm), gradient hydrophilic-hydrophobic separator (P-F / A 0.3mm), gradient hydrophilic-hydrophobic separator (P-F / A 0.1mm) and glass fiber separator, b is the ion conductivity comparison of zinc ion battery using four different separators.

[0041] Figure 8Impedance plots of zinc ion batteries of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of the present application at 0.01 Hz to 105 Hz.

[0042] Figure 9 Scanning electron microscope (SEM) images of zinc anodes after cycling for zinc ion batteries of Example 1 and Comparative Example 3 of the present application; wherein a is the SEM image of zinc anode after cycling using gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm), b is the SEM image of zinc anode after cycling using glass fiber separator.

[0043] Figure 10 Electrochemical stability of gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and glass fiber separator was evaluated on non-active stainless steel electrode using linear sweep voltammetry (LSV).

[0044] Figure 11 Electrochemical stability of gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and glass fiber separator was evaluated on Zn / / Zn symmetric cell using TAFEL.

[0045] Figure 12 Raman test of V2O5 electrode after cycling using gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and glass fiber separator. DETAILED DESCRIPTION

[0046] For a more complete understanding of the technical content of the present application, specific embodiments are described below with reference to the accompanying drawings.

[0047] Aspects of the present application are described in the disclosure by reference to the accompanying drawings, in which a number of illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to include all aspects of the present application. It should be understood that a variety of concepts and embodiments as introduced above and as described in more detail below can be implemented in any of numerous ways, as the skilled artisan will appreciate.

[0048] Combination Figure 1 As shown, the exemplary gradient hydrophilic-hydrophobic separator for aqueous zinc ion batteries of the present application comprises a hydrophilic layer 1, a first hydrophobic layer 2 and a second hydrophobic layer 3, wherein the hydrophilic layer 1 is located between the first hydrophobic layer 2 and the second hydrophobic layer 3, thereby forming a gradient hydrophilic-hydrophobic separator with alternating hydrophilic and hydrophobic layers.

[0049] The hydrophilic layer 1 is prepared by electrospinning process using a mixed solution of 4,4'-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA) as the hydrophilic precursor.

[0050] The first hydrophobic layer 2 and the second hydrophobic layer 3 are prepared by using an electrostatic spinning process with a mixed solution of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) as a hydrophobic precursor.

[0051] As an optional example, the thickness T of the aforementioned gradient hydrophilic-hydrophobic separator ranges from 0.1 mm to less than 0.3 mm, and is particularly preferably about 0.2 mm.

[0052] The thickness of the separator needs to be maintained within a reasonable range. A thinner separator tends to have lower mechanical strength and is easily damaged during battery assembly or use. The damaged separator may not effectively isolate the positive and negative electrodes, leading to internal short circuit of the battery and thus causing safety problems. In addition, one important function of the separator is to screen ions, allowing only specific ions to pass through. A too thin separator may not effectively screen ions, leading to a decrease in battery performance, such as capacity decay and poor cycle stability. At the same time, a thinner separator is more likely to be penetrated by zinc dendrites, leading to internal short circuit of the battery and even causing battery explosion and other safety problems. A too thin separator may also have insufficient surface area or structural defects, resulting in insufficient electrolyte wettability and thus affecting battery performance.

[0053] A too thick separator will increase the transmission distance of zinc ions within the battery, thereby increasing the internal resistance of the battery. The increase in internal resistance may lead to the generation of more heat during the charging and discharging process of the battery, affecting the thermal stability and safety of the battery. During the battery cycling process, a large amount of ions need to be quickly transported, and a thicker separator will hinder this process, leading to a decrease in ion conductivity and the charging and discharging rate of the battery, affecting the performance and response speed of the battery. A thicker separator may also be unfavorable for the uniform deposition and stripping of zinc ions, thereby increasing the likelihood of zinc dendrite formation, which may lead to the penetration of the dendrites into the separator and thus damage the battery.

[0054] As an optional example, the first hydrophobic layer 2 and the second hydrophobic layer 3 are symmetrically arranged around the hydrophilic layer 1.

[0055] In a more specific example, the thickness of the first hydrophobic layer 2 and the second hydrophobic layer 3 is equal, so that the first hydrophobic layer 2 and the second hydrophobic layer 3 are symmetrically distributed around the hydrophilic layer 1.

[0056] As an optional example, the thickness of the first hydrophobic layer 2 and the second hydrophobic layer 3 is less than the thickness of the hydrophilic layer 1.

[0057] In a more specific example, the thickness ratio of the first hydrophobic layer 2, the hydrophilic layer 1 and the second hydrophobic layer 3 is (0.4-0.5):(1-1.1):(0.4-0.5).

[0058] As an optional example, the hydrophilic separator layer is composed of fibers of polyamide acid (PAA) obtained by polymerization reaction of ODA and PMDA, and the diameter of the fibers is 90 nm to 120 nm, and the size is uniform.

[0059] As an optional example, the hydrophobic separator layer is composed of fibers of PAN and PVDF, and the average diameter of the fibers is 90 nm to 120 nm, and the size is uniform.

[0060] In another exemplary embodiment of the present application, a preparation method of the gradient hydrophilic-hydrophobic separator for the aqueous zinc ion battery is also provided, comprising the following steps:

[0061] After polyacrylonitrile and polyvinylidene fluoride are respectively dissolved in N,N-dimethylformamide and then mixed, a first mixed solution is obtained by stirring uniformly;

[0062] 4,4'-diamino diphenyl ether and pyromellitic dianhydride are dissolved in N,N-dimethylformamide in an inert gas filled environment, and a second mixed solution is obtained by stirring reaction;

[0063] The first mixed solution is prepared into a first hydrophobic layer by electrospinning, and then the second mixed solution is stacked on one side surface of the first hydrophobic layer by electrospinning to form a hydrophilic layer, and then the first mixed solution is stacked on the hydrophilic layer by electrospinning to form a second hydrophobic layer, and finally the completed separator is dried to obtain the gradient hydrophilic-hydrophobic separator.

[0064] In an optional example, when the second mixed solution is prepared, 4,4'-diamino diphenyl ether is first dissolved in N,N-dimethylformamide until it is completely dissolved, and then pyromellitic dianhydride is added in batches until pyromellitic dianhydride is completely dissolved, and then a polyamide acid (PAA) solution, i.e. the second mixed solution, is obtained by stirring reaction.

[0065] As an optional example, the mass ratio of polyacrylonitrile, polyvinylidene fluoride and N,N-dimethylformamide is (0.95-1.05):(1-1.05):10, and 1:1:10 is particularly preferred.

[0066] As an optional example, the mass ratio of 4,4'-diamino diphenyl ether, pyromellitic dianhydride and N,N-dimethylformamide is (0.95-1):(1-1.05):10.

[0067] As an optional example, when the first hydrophobic layer and the second hydrophobic layer are prepared, the process conditions of electrospinning include:

[0068] The concentration of the spinning solution is 10% to 12%, the jet voltage is -8KV to -9KV and 12KV to 14KV (a positive voltage is applied at the end of the container containing the solution and a negative voltage is applied at the end of the receiver to form an electric field), the receiving distance is 120mm to 150mm, the solution advancing speed is 0.03mm / min to 0.05mm / min, the head diameter is 0.86mm to 0.95mm, the temperature is 35℃, and the humidity is 40%.

[0069] As an optional example, when the hydrophilic layer is prepared, the process conditions of electrospinning include:

[0070] The concentration of the solution is 19% to 21%, the jet voltage is -8KV to -9KV and 12KV to 14KV, the receiving distance is 120mm to 150mm, the solution advancing speed is 0.035mm / min to 0.05mm / min, the head diameter is 0.86mm to 0.95mm, the temperature is 35℃, and the humidity is 40%.

[0071] As an optional example, the inert gas filled environment is a glove box filled with helium.

[0072] As an optional example, the completed spinning diaphragm is dried in a vacuum at a temperature of 50℃ to 60℃ for 6h to 8h to obtain the gradient hydrophilic-hydrophobic diaphragm.

[0073] In other exemplary embodiments, a water-based zinc ion battery is also provided, which uses the aforementioned gradient hydrophilic-hydrophobic diaphragm for water-based zinc ion batteries as the battery diaphragm, and the hydrophobic layers on both sides of the diaphragm are respectively close to the positive electrode and the negative electrode.

[0074] In one example, the positive electrode material of the water-based zinc ion battery uses vanadium pentoxide, the negative electrode material uses metallic zinc, and the electrolyte includes zinc sulfonate.

[0075] In combination Figure 1 As shown, in the water-based zinc ion battery in the aforementioned example, Zn 2+ binds with water molecules (H2O) to gradually form Zn(H2O)6 2+ , water molecules are separated from Zn(H2O)6 2+ through the gradient hydrophilic-hydrophobic diaphragm, and gradually become Zn 2+ , achieving desolvation and minimizing the desolvation barrier.

[0076] For better understanding, the present application is further described below in combination with several specific examples, but the preparation process is not limited thereto, and the content of the present application is not limited thereto.

[0077] Unless otherwise specified, the materials in the examples are prepared according to existing methods or directly purchased from the market.

[0078] Example 1

[0079] (1) Preparation of hydrophobic precursor: 1 g of polyacrylonitrile (PAN) was dissolved in 5 mL of N,N-dimethylformamide (DMF) and stirred for 4 h until the polyacrylonitrile (PAN) was completely dissolved; 1 g of polyvinylidene fluoride (PVDF) was then dissolved in 5 mL of N,N-dimethylformamide (DMF) and stirred for 6 h until the polyvinylidene fluoride (PVDF) was completely dissolved; finally, the two solutions were mixed and stirred for 12 h until uniform, and the hydrophobic precursor was finally obtained.

[0080] (2) Preparation of hydrophilic precursor: 1.914 g of 4,4'-diaminodiphenyl ether (ODA) was first dissolved in 20 mL of N,N-dimethylformamide (DMF) in a helium-filled glove box until the diamino diphenyl ether (ODA) was completely dissolved (the solution was clear); then 2.086 g of pyromellitic dianhydride (PMDA) was added in batches (each batch of pyromellitic dianhydride (PMDA) was completely dissolved before the next batch was added) for about 1 h until the pyromellitic dianhydride (PMDA) was completely dissolved, and the resulting solution was stirred for 12 h to obtain a polyamic acid (PAA) solution, and the hydrophilic precursor was finally obtained.

[0081] (3) Preparation of gradient hydrophilic-hydrophobic membrane: the hydrophobic precursor was electrospun under the conditions of jet voltage -9KV / 13KV, receiving distance 150 mm, solution advancing speed 0.035 mm / min, needle diameter 0.86 mm-0.95 mm, temperature 35°C, humidity 40%, and the spinning time was 5 h to prepare the first layer of membrane.

[0082] The hydrophilic precursor was then electrospun on the first layer of membrane under the conditions of jet voltage -9KV / 13KV, receiving distance 150 mm, solution advancing speed 0.035 mm / min, needle diameter 0.86 mm-0.95 mm, temperature 35°C, humidity 40%, and the spinning time was 3 h to prepare the second layer of membrane.

[0083] Finally, the hydrophobic precursor was electrospun on the second layer of membrane under the conditions of jet voltage -9KV / 13KV, receiving distance 150 mm, solution advancing speed 0.035 mm / min, needle diameter 0.86 mm-0.95 mm, temperature 35°C, humidity 40%, and the spinning time was 5 h to prepare the third layer of membrane.

[0084] The prepared membrane was placed in a vacuum oven and dried at 60°C for 6 h to obtain a gradient hydrophilic-hydrophobic membrane with a thickness of about 0.2 mm (P-F / A 0.2 mm).

[0085] (4) Assembly of the battery: stack the negative shell, zinc sheet and gradient hydrophilic-hydrophobic separator in order, drop 60 μL of 2.6 mol / L zinc sulfonate electrolyte onto the gradient hydrophilic-hydrophobic separator to make the gradient hydrophilic-hydrophobic separator completely wet, place the V2O5 electrode sheet pressed at 20 MPa on the gradient hydrophilic-hydrophobic separator, place the gasket and spring in order, and then buckle the positive shell, and then use the battery assembly machine to package to obtain a zinc ion battery.

[0086] Example 2

[0087] (1) Preparation of the hydrophobic precursor: dissolve 2 g of polyacrylonitrile (PAN) in 5 mL of N,N-dimethylformamide (DMF) and stir for 4 h until the polyacrylonitrile (PAN) is completely dissolved; then dissolve 1 g of polyvinylidene fluoride (PVDF) in 5 mL of N,N-dimethylformamide (DMF) and stir for 6 h until the polyvinylidene fluoride (PVDF) is completely dissolved; finally, mix the two solutions and stir for 12 h until uniform, to obtain the hydrophobic precursor.

[0088] (2) Preparation of the hydrophilic precursor: in a glove box filled with helium, dissolve 1.914 g of 4,4'-diaminodiphenyl ether (ODA) in 20 mL of N,N-dimethylformamide (DMF) until the diamino diphenyl ether (ODA) is completely dissolved (the solution is clear); then add 2.086 g of pyromellitic dianhydride (PMDA) in batches (add the next batch after the pyromellitic dianhydride (PMDA) in each batch is completely dissolved), until the pyromellitic dianhydride (PMDA) is completely dissolved, and then stir the obtained solution for 12 h to obtain a polyamic acid (PAA) solution, and finally obtain the hydrophilic precursor.

[0089] (3) Preparation of the gradient hydrophilic-hydrophobic separator: electrospin the hydrophobic precursor under the conditions of spraying voltage -9KV / 13KV, receiving distance 150 mm, solution advancing speed 0.035 mm / min, needle diameter 0.86 mm-0.95 mm, temperature 35°C, and humidity 40%, for a spinning time of 5 h, to prepare the first layer of the separator.

[0090] Then electrospin the hydrophilic precursor on the first layer of the separator under the conditions of spraying voltage -9KV / 13KV, receiving distance 150 mm, solution advancing speed 0.035 mm / min, needle diameter 0.86 mm-0.95 mm, temperature 35°C, and humidity 40%, for a spinning time of 3 h, to prepare the second layer of the separator.

[0091] Finally, the hydrophobic precursor was electrospun on the second layer of the separator under the conditions of a spraying voltage of -9KV / 13KV, a receiving distance of 150mm, a solution advancing speed of 0.035mm / min, a needle diameter of 0.86mm-0.95mm, a temperature of 35°C, and a humidity of 40%, for a spinning duration of 5h, to prepare a third layer of the separator.

[0092] The prepared separator was placed in a vacuum oven and dried at 60°C for 6h, to obtain a gradient hydrophilic-hydrophobic separator with a thickness of about 0.2mm.

[0093] (4) Assembly of the battery: the negative electrode shell, zinc sheet, and gradient hydrophilic-hydrophobic separator were sequentially stacked in order, 60μL of a 2.6mol / L zinc sulfonate electrolyte was added to the gradient hydrophilic-hydrophobic separator to make the gradient hydrophilic-hydrophobic separator completely wet, a V2O5 electrode sheet pressed at 20Mpa was placed on the gradient hydrophilic-hydrophobic separator, a gasket and a spring were sequentially placed, and a positive electrode shell was buckled, and the battery was packaged using a battery assembly machine to obtain a zinc ion battery.

[0094] Example 3

[0095] (1) Preparation of the hydrophobic precursor: 1g of polyacrylonitrile (PAN) was dissolved in 5mL of N,N-dimethylformamide (DMF) and stirred for 4h until the polyacrylonitrile (PAN) was completely dissolved; 2g of polyvinylidene fluoride (PVDF) was dissolved in 5mL of N,N-dimethylformamide (DMF) and stirred for 6h until the polyvinylidene fluoride (PVDF) was completely dissolved; finally, the two solutions were mixed and stirred for 12h until uniform, to obtain the hydrophobic precursor.

[0096] (2) Preparation of the hydrophilic precursor: in a glove box filled with helium, 1.914g of 4,4'-diamino diphenyl ether (ODA) was first dissolved in 20mL of N,N-dimethylformamide (DMF) until the diamino diphenyl ether (ODA) was completely dissolved (the solution was clear); then, 2.086g of pyromellitic dianhydride (PMDA) was added in batches (each batch of pyromellitic dianhydride (PMDA) was completely dissolved before the next batch was added) for about 1h until the pyromellitic dianhydride (PMDA) was completely dissolved, and the obtained solution was stirred for 12h to obtain a polyamic acid (PAA) solution, and finally the hydrophilic precursor was obtained.

[0097] (3) Preparation of the gradient hydrophilic-hydrophobic separator: the hydrophobic precursor was electrospun under the conditions of a spraying voltage of -9KV / 13KV, a receiving distance of 150mm, a solution advancing speed of 0.035mm / min, a needle diameter of 0.86mm-0.95mm, a temperature of 35°C, and a humidity of 40%, for a spinning duration of 5h, to prepare a first layer of the separator.

[0098] The hydrophilic precursor was electrospun on the first layer of the separator under the conditions of a spraying voltage of -9KV / 13KV, a receiving distance of 150mm, a solution advancing speed of 0.035mm / min, a needle diameter of 0.86mm-0.95mm, a temperature of 35°C, and a humidity of 40%, for a spinning time of 3h, to prepare a second layer of the separator.

[0099] Finally, the hydrophobic precursor was electrospun on the second layer of the separator under the conditions of a spraying voltage of -9KV / 13KV, a receiving distance of 150mm, a solution advancing speed of 0.035mm / min, a needle diameter of 0.86mm-0.95mm, a temperature of 35°C, and a humidity of 40%, for a spinning time of 5h, to prepare a third layer of the separator.

[0100] The prepared separator was dried in a vacuum oven at 60°C for 6h, to obtain a gradient hydrophilic-hydrophobic separator with a thickness of about 0.2mm.

[0101] (4) Assembly of the battery: the negative electrode shell, zinc sheet, and gradient hydrophilic-hydrophobic separator were sequentially stacked in order, 60μL of 2.6mol / L zinc sulfonate electrolyte was added to the gradient hydrophilic-hydrophobic separator to make the gradient hydrophilic-hydrophobic separator completely wet, the V2O5 electrode sheet pressed at 20Mpa was placed on the gradient hydrophilic-hydrophobic separator, the gasket and spring were sequentially placed, the positive electrode shell was buckled, and the battery was packaged using a battery assembly machine to obtain a zinc ion battery.

[0102] Example 4

[0103] (1) Preparation of the hydrophobic precursor: 1g of polyacrylonitrile (PAN) was dissolved in 5mL of N,N-dimethylformamide (DMF) and stirred for 4h until the polyacrylonitrile (PAN) was completely dissolved; 1g of polyvinylidene fluoride (PVDF) was dissolved in 5mL of N,N-dimethylformamide (DMF) and stirred for 6h until the polyvinylidene fluoride (PVDF) was completely dissolved; finally, the two solutions were mixed and stirred for 12h until uniform, to obtain the hydrophobic precursor.

[0104] (2) Preparation of the hydrophilic precursor: 1.914g of 4,4'-diaminodiphenyl ether (ODA) was first dissolved in 20mL of N,N-dimethylformamide (DMF) in a helium-filled glove box until the diamino diphenyl ether (ODA) was completely dissolved (the solution was clear); then, 2.086g of pyromellitic dianhydride (PMDA) was added in batches (each batch of pyromellitic dianhydride (PMDA) was completely dissolved before the next batch was added) for about 1h, until the pyromellitic dianhydride (PMDA) was completely dissolved; the obtained solution was stirred for 12h to obtain a polyamic acid (PAA) solution, and finally the hydrophilic precursor was obtained.

[0105] (3) Preparation of gradient hydrophilic-hydrophobic separator: the hydrophobic precursor was electrospun under the conditions of spray voltage -9KV / 13KV, receiving distance 150mm, solution advancing speed 0.05mm / min, needle diameter 0.86mm-0.95mm, temperature 35°C, humidity 40%, and the spinning time was 5h to prepare the first layer of separator.

[0106] Then the hydrophilic precursor was electrospun on the first layer of separator under the conditions of spray voltage -9KV / 13KV, receiving distance 150mm, solution advancing speed 0.035mL / min, needle diameter 0.86mm-0.95mm, temperature 35°C, humidity 40%, and the spinning time was 3h to prepare the second layer of separator.

[0107] Finally, the hydrophobic precursor was electrospun on the second layer of separator under the conditions of spray voltage -9KV / 13KV, receiving distance 150mm, solution advancing speed 0.05mm / min, needle diameter 0.86mm-0.95mm, temperature 35°C, humidity 40%, and the spinning time was 5h to prepare the third layer of separator.

[0108] The prepared separator was placed in a vacuum oven and dried at 60°C for 6h to obtain a gradient hydrophilic-hydrophobic separator with a thickness of about 0.2mm.

[0109] (4) Assembly of battery: the negative shell, zinc sheet and gradient hydrophilic-hydrophobic separator were sequentially stacked in order, 60μL of 2.6mol / L zinc sulfonate electrolyte was added to the gradient hydrophilic-hydrophobic separator to make the gradient hydrophilic-hydrophobic separator completely wet, and the V2O5 electrode sheet pressed at 20Mpa was placed on the gradient hydrophilic-hydrophobic separator, and then the gasket and spring were placed in order and the positive shell was buckled, and then the battery assembly machine was used for packaging to obtain a zinc ion battery.

[0110] Example 5

[0111] (1) Preparation of hydrophobic precursor: 1g of polyacrylonitrile (PAN) was dissolved in 5mL of N,N-dimethylformamide (DMF) and stirred for 4h until the polyacrylonitrile (PAN) was completely dissolved; then 1g of polyvinylidene fluoride (PVDF) was dissolved in 5mL of N,N-dimethylformamide (DMF) and stirred for 6h until the polyvinylidene fluoride (PVDF) was completely dissolved; finally, the two solutions were mixed and stirred for 12h until uniform, and the hydrophobic precursor was finally obtained.

[0112] (2) Preparation of the hydrophilic precursor: 1.914 g of 4,4'-diaminodiphenyl ether (ODA) was first dissolved in 20 mL of N,N-dimethylformamide (DMF) in a glove box filled with helium until the diamino diphenyl ether (ODA) was completely dissolved (the solution was clear); then 2.086 g of pyromellitic dianhydride (PMDA) was added in batches (each batch of pyromellitic dianhydride (PMDA) was completely dissolved before the next batch was added) for about 1 h until the pyromellitic dianhydride (PMDA) was completely dissolved, and the resulting solution was stirred for 12 h to obtain a polyamic acid (PAA) solution. Finally, the hydrophilic precursor was obtained.

[0113] (3) Preparation of the gradient hydrophilic-hydrophobic diaphragm: the hydrophobic precursor was electrospun under the conditions of spray voltage -9KV / 13KV, receiving distance 150 mm, solution advancing speed 0.035 mm / min, needle diameter 0.86 mm-0.95 mm, temperature 35°C, humidity 40%, and the spinning time was 5 h to prepare the first layer diaphragm.

[0114] Then the hydrophilic precursor was electrospun on the first layer diaphragm under the conditions of spray voltage -9KV / 13KV, receiving distance 150 mm, solution advancing speed 0.05 mm / min, needle diameter 0.86 mm-0.95 mm, temperature 35°C, humidity 40%, and the spinning time was 3 h to prepare the second layer diaphragm.

[0115] Finally, the hydrophobic precursor was electrospun on the second layer diaphragm under the conditions of spray voltage -9KV / 13KV, receiving distance 150 mm, solution advancing speed 0.035 mm / min, needle diameter 0.86 mm-0.95 mm, temperature 35°C, humidity 40%, and the spinning time was 5 h to prepare the third layer diaphragm.

[0116] The prepared diaphragm was placed in a vacuum oven and dried at 60°C for 6 h to obtain a gradient hydrophilic / hydrophobic diaphragm with a thickness of about 0.2 mm.

[0117] (4) Assembly of the battery: the negative shell, zinc sheet, and gradient hydrophilic / hydrophobic diaphragm were sequentially stacked in order, 60 μL of 2.6 mol / L zinc sulfonate electrolyte was added to the gradient hydrophilic / hydrophobic diaphragm to make the gradient hydrophilic / hydrophobic diaphragm completely wet, and the V2O5 electrode sheet pressed at 20 Mpa was placed on the gradient hydrophilic / hydrophobic diaphragm, followed by the gasket and spring, and then the positive shell was buckled, and the battery was packaged using a battery assembly machine to obtain a zinc ion battery.

[0118] Comparative Example 1

[0119] (1) Preparation of hydrophobic precursor: 1 g of polyacrylonitrile (PAN) was dissolved in 5 mL of N,N-dimethylformamide (DMF) and stirred for 4 h until the polyacrylonitrile (PAN) was completely dissolved; 1 g of polyvinylidene fluoride (PVDF) was then dissolved in 5 mL of N,N-dimethylformamide (DMF) and stirred for 6 h until the polyvinylidene fluoride (PVDF) was completely dissolved; finally, the two solutions were mixed and stirred for 12 h until uniform, and the hydrophobic precursor was finally obtained.

[0120] (2) Preparation of hydrophilic precursor: 1.914 g of 4,4'-diaminodiphenyl ether (ODA) was first dissolved in 20 mL of N,N-dimethylformamide (DMF) in a helium-filled glove box until the dianinodiphenyl ether (ODA) was completely dissolved (the solution was clear); then 2.086 g of pyromellitic dianhydride (PMDA) was added in batches (each batch of pyromellitic dianhydride (PMDA) was completely dissolved before the next batch was added) for about 1 h until the pyromellitic dianhydride (PMDA) was completely dissolved, and the resulting solution was stirred for 12 h to obtain a polyamic acid (PAA) solution, and the hydrophilic precursor was finally obtained.

[0121] (3) Preparation of gradient hydrophilic-hydrophobic membrane: the hydrophobic precursor was electrospun under the conditions of jet voltage -9KV / 13KV, receiving distance 150 mm, solution advancing speed 0.035 mm / min, needle diameter 0.86 mm-0.95 mm, temperature 35°C, and humidity 40%, and the first layer of membrane was prepared by electrospinning for 10 h.

[0122] The hydrophilic precursor was then electrospun on the first layer of membrane under the conditions of jet voltage -9KV / 13KV, receiving distance 150 mm, solution advancing speed 0.035 mm / min, needle diameter 0.86 mm-0.95 mm, temperature 35°C, and humidity 40%, and the second layer of membrane was prepared by electrospinning for 6 h.

[0123] Finally, the hydrophobic precursor was electrospun on the second layer of membrane under the conditions of jet voltage -9KV / 13KV, receiving distance 150 mm, solution advancing speed 0.035 mL / min, needle diameter 0.86 mm-0.95 mm, temperature 35°C, and humidity 40%, and the third layer of membrane was prepared by electrospinning for 10 h.

[0124] The prepared membrane was placed in a vacuum oven and dried at 60°C for 6 h to obtain a gradient hydrophilic-hydrophobic membrane (P-F / A 0.3 mm) with a thickness of 0.3 mm.

[0125] (4) The assembly of the battery: the negative shell, zinc sheet and gradient hydrophilic-hydrophobic separator are stacked in sequence, 60 μL of 2.6 mol / L zinc sulfonate electrolyte is added to the gradient hydrophilic-hydrophobic separator to make the gradient hydrophilic-hydrophobic separator completely wet, the V2O5 electrode sheet pressed at 20 MPa is placed on the gradient hydrophilic-hydrophobic separator, the gasket and spring are placed in sequence, the positive shell is buckled, and the battery assembly machine is used for packaging to obtain a zinc ion battery.

[0126] Comparative Example 2

[0127] (1) Preparation of the hydrophobic precursor: 1 g of polyacrylonitrile (PAN) is dissolved in 5 mL of N,N-dimethylformamide (DMF) and stirred for 4 h until the polyacrylonitrile (PAN) is completely dissolved; 1 g of polyvinylidene fluoride (PVDF) is dissolved in 5 mL of N,N-dimethylformamide (DMF) and stirred for 6 h until the polyvinylidene fluoride (PVDF) is completely dissolved; finally, the two solutions are mixed and stirred for 12 h until uniform, and the hydrophobic precursor is finally obtained.

[0128] (2) Preparation of the hydrophilic precursor: 1.914 g of 4,4'-diamino diphenyl ether (ODA) is first dissolved in 20 mL of N,N-dimethylformamide (DMF) in a helium-filled glove box until the diamino diphenyl ether (ODA) is completely dissolved (the solution is clear); then 2.086 g of pyromellitic dianhydride (PMDA) is added in batches (each batch of pyromellitic dianhydride (PMDA) is completely dissolved before the next batch is added), until the pyromellitic dianhydride (PMDA) is completely dissolved, and the resulting solution is stirred for 12 h to obtain a polyamic acid (PAA) solution, and the hydrophilic precursor is finally obtained.

[0129] (3) Preparation of the gradient hydrophilic-hydrophobic separator: the hydrophobic precursor is electrospun under the conditions of spraying voltage -9KV / 13KV, receiving distance 150 mm, solution advancing speed 0.035 mm / min, needle diameter 0.86 mm-0.95 mm, temperature 35°C, and humidity 40%, and the first layer of the separator is prepared by electrospinning for 2.5 h.

[0130] The hydrophilic precursor is electrospun on the first layer of the separator under the conditions of spraying voltage -9KV / 13KV, receiving distance 150 mm, solution advancing speed 0.035 mm / min, needle diameter 0.86 mm-0.95 mm, temperature 35°C, and humidity 40%, and the second layer of the separator is prepared by electrospinning for 1.5 h.

[0131] Finally, the hydrophobic precursor was electrospun on the second layer of the separator under the conditions of a jet voltage of -9KV / 13KV, a receiving distance of 150mm, a solution advancing speed of 0.035mm / min, a needle diameter of 0.86mm-0.95mm, a temperature of 35°C, and a humidity of 40%, for a spinning time of 2.5h, to prepare a third layer of the separator.

[0132] The prepared separator was placed in a vacuum oven and dried at 60°C for 6h to obtain a gradient hydrophilic-hydrophobic separator (P-F / A 0.1mm) with a thickness of 0.1mm.

[0133] (4) Assembly of the battery: the negative electrode shell, zinc sheet, and gradient hydrophilic-hydrophobic separator were sequentially stacked in order, 60μL of a 2.6mol / L zinc sulfonate electrolyte was added to the gradient hydrophilic-hydrophobic separator to completely wet the gradient hydrophilic-hydrophobic separator, a V2O5 electrode sheet that had been pressed at 20Mpa was placed on the gradient hydrophilic-hydrophobic separator, a gasket and a spring were sequentially placed, a positive electrode shell was buckled, and a battery assembly machine was used to package the zinc ion battery.

[0134] Comparative Example 3

[0135] Commercial glass fibers (GF) (manufacturer Whatman, specifications diameter 150mm, thickness 0.28mm, number 1820-150) were cut into circles with a cross-sectional diameter of 16mm for assembly as a battery separator, the negative electrode shell, zinc sheet, and GF separator were sequentially stacked in order, 60μL of a 2.6mol / L zinc sulfonate electrolyte was added to the GF separator to completely wet the GF separator, a V2O5 electrode sheet that had been pressed at 20Mpa was placed on the GF separator, a gasket and a spring were sequentially placed, a positive electrode shell was buckled, and a battery assembly machine was used to package the zinc ion battery.

[0136] Comparative Example 4

[0137] The difference from Example 1 is that all three layers are hydrophilic layers, and the battery is assembled as in Example 1. The voltage is close to 0V, and the battery cannot be cycled, possibly due to the material properties.

[0138] Comparative Example 5

[0139] The difference from Example 1 is that all three layers are hydrophobic layers, and the battery is assembled as in Example 1. The hydrophobic separator hinders the rapid transmission of ions in the battery, and the battery cannot be effectively cycled.

[0140] Test

[0141] [SEM test]

[0142] The hydrophobic layer spun fiber and the hydrophilic layer spun fiber prepared in Example 1 were subjected to SEM test, and the results are shown in Figure 2 .

[0143] Figure 2 a in FIG. 1 is a fiber composed of polyamide acid (PAA) obtained by polymerization reaction of 4,4'-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA), from which it can be seen that the fiber diameter is uniform, about 100 nm; Figure 2 b in FIG. 1 is a fiber composed of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF), from which it can be seen that the fiber diameter is uniform, about 100 nm.

[0144] [Contact angle test]

[0145] The hydrophobic layer spun fiber, the hydrophilic layer spun fiber and the glass fiber prepared in Example 1 were subjected to contact angle test, and the results are shown in Figure 3 .

[0146] Figure 3 a in FIG. 2 is the contact angle of the hydrophilic layer in Example 1, from which it can be found that the contact angle is close to 1°, indicating that it has excellent hydrophilic property; Figure 3 b in FIG. 2 is the contact angle of the hydrophobic layer in Example 1, from which it can be found that the contact angle is close to 110°, indicating that it has excellent hydrophobic property; Figure 3 c in FIG. 2 is the contact angle of the glass fiber, which has a contact angle close to 5°, indicating that it has excellent hydrophilic property.

[0147] [Battery performance test]

[0148] (I) The zinc ion battery assembled in Example 1 and Comparative Example 3 was subjected to battery performance test using a new battery test device, and the results are shown in Figure 4 .

[0149] Figure 4 a in FIG. 3 is the cycle performance test, the working voltage is set to 0.3-1.6 V, and the current density is 0.1 Ag -1 , it can be seen that the cycle stability of the zinc ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A0.2 mm) in Example 1 is higher than that of the zinc ion battery using the glass fiber separator (Comparative Example 3).

[0150] In the cycle of 0-100 cycles, the zinc ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A0.2 mm) has relatively stable cycle performance, and the initial capacity can reach 386.22 mAh g -1 , and the capacity is 281.30 mAh g -1, the capacity retention rate was 73.2%; the zinc ion battery using the glass fiber diaphragm had an initial capacity as high as 389.43 mAh g -1 , but the capacity had a large amplitude attenuation after 10 cycles, and the capacity was only 148.08 mAh g -1 after 100 cycles, and the battery was damaged, and the capacity retention rate was only 38.0%.

[0151] Figure 4 In b, c, the gradient hydrophilic-hydrophobic diaphragm (P-F / A 0.2 mm) and the glass fiber diaphragm had a working voltage of 0.3-1.6 V and a current density of 0.1 A g -1 The GCD curves of the first cycle, the 25th cycle, the 50th cycle, the 75th cycle and the 100th cycle at a current density of 0.1 A g -1 further prove that the zinc ion battery using the gradient hydrophilic-hydrophobic diaphragm (P-F / A 0.2 mm) of the application can maintain high capacity and improve the cycle stability of the battery at low current density.

[0152] (II) The zinc ion batteries assembled in Example 1, Comparative Example 1 and Comparative Example 2 were tested for battery performance using a new wei battery test device, and the results are shown in Table 2. Figure 5

[0153] Figure 5 In a, the cycle performance test, the working voltage was set to 0.3-1.6 V, and the current density was 0.1 A g -1 It can be seen that the cycle stability of the zinc ion battery using the gradient hydrophilic-hydrophobic diaphragm (P-F / A 0.2 mm) in Example 1 is higher than that of the zinc ion batteries using the gradient hydrophilic-hydrophobic diaphragm (P-F / A 0.3 mm) (Comparative Example 1) and the gradient hydrophilic-hydrophobic diaphragm (P-F / A 0.1 mm) (Comparative Example 2).

[0154] In the 0-100 cycle, the zinc ion battery using the gradient hydrophilic-hydrophobic diaphragm (P-F / A 0.2 mm) had a stable cycle, an initial capacity of 386.22 mAh g -1 , and a capacity of 281.30 mAh g -1 after 100 cycles, and the capacity retention rate was 73.2%; the zinc ion battery using the gradient hydrophilic-hydrophobic diaphragm (P-F / A 0.3 mm) had an initial capacity of 387.25 mAh g -1 , and the capacity was only 193.02 mAh g -1 after 100 cycles, and the battery was damaged, and the capacity retention rate was only 49.8%; and the zinc ion battery using the gradient hydrophilic-hydrophobic diaphragm (P-F / A 0.1 mm) had an initial capacity of 396.26 mAh g -1Although the capacity also attenuates in the cycle process, the attenuation range is not large, and the capacity is still 233.60 mAh g after 100 cycles -1 , and the capacity retention rate reaches 60.1%, which is much higher than that of the zinc ion battery using a glass fiber separator.

[0155] In combination with Figure 5 b, c and d, it is proved that the zinc ion battery using the gradient hydrophilic-hydrophobic separator of the application can maintain high capacity while improving the cycle stability of the battery.

[0156] (III) The rate performance test of the zinc ion battery using different separators was carried out on the zinc ion battery assembled in Example 1 and Comparative Example 3, and the results are shown in Figure 6 .

[0157] As can be seen from Figure 6 , under the condition of working voltage of 0.3-1.6V, the capacity of the zinc ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) at the current density of 0.1A g -1 , 0.2A g -1 , 0.5Ag -1 , 1.0Ag -1 , 2.0Ag -1 , 5.0Ag -1 is 399.79 mAh g -1 , 381.85 mAh g -1 , 350.24 mAh g -1 , 331.86 mAh g -1 , 311.08 mAh g -1 , 255.55 mAh g -1 , respectively, all of which are higher than the capacity of the zinc ion battery using a glass fiber separator at the current density of 0.1Ag -1 , 0.2Ag -1 , 0.5Ag -1 , 1.0Ag -1 , 2.0Ag -1 , 5.0Ag -1 , which are 388.08 mAh g -1 , 324.50 mAh g -1 , 264.80 mAh g -1 , 228.90 mAh g -1 , 208.95 mAh g -1 , 184.72 mAh g -1 .

[0158] In combination with Figure 6b and c, it is proved that the zinc ion battery using the gradient hydrophilic-hydrophobic separator prepared by the application can maintain high capacity while improving the cycle stability of the battery.

[0159] (Four) The ionic conductivities of the stainless steel symmetric batteries (stainless steel gaskets are used for the positive and negative electrodes) assembled using the four different separators in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 are tested, and the results are shown in Figure 7

[0160] Figure 7 a are the electrochemical impedance spectra of the symmetric batteries tested using the stainless steel electrodes of the four different separators in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3, b is a columnar comparison chart of the ionic conductivities calculated by the formula σ = (L / RS) x 1000.

[0161] As can be seen from the figure, the conductivity of the gradient hydrophilic-hydrophobic separator (P-F / A 0.1 mm) is the highest, being 4.00 mS cm -1 , and the bulk resistance is 2.4 Ω, the conductivity of the gradient hydrophilic-hydrophobic separator (P-F / A 0.3 mm) is the lowest, being 1.56 mS cm -1 , and the bulk resistance is the highest, being 6.4 Ω, while the conductivity of the battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and the glass fiber separator is between the two, being 3.87 mS cm -1 and 3.00 mS cm -1 , and the bulk resistance is only 3.0 Ω and 3.3 Ω, which shows that the ion transmission rate of the battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) of the application is faster than that of the battery using the glass fiber separator, and the cycle stability of the zinc ion battery is better.

[0162] (Five) In order to further understand the cycle performance and redox kinetics of the zinc ion batteries assembled in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3, the electrochemical impedance spectroscopy (EIS) is used to evaluate the charge transfer resistance.

[0163] As shown in Figure 8 , the zinc ion batteries using the four different separators produce semicircular arcs in the high frequency region, and the radius of the arc reflects the charge transfer resistance (Rct), the impedance of the battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.1 mm) is the lowest (253 Ω), the impedance of the battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.1 mm) is 448 Ω, the impedance of the battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.3 mm) is 623 Ω, and the impedance of the battery using the glass fiber separator is 489 Ω.

[0164] ​This shows that the gradient hydrophilic-hydrophobic separator has greater impedance to ion diffusion as the thickness of the separator increases; and in comparison under the same thickness, the gradient hydrophilic-hydrophobic separator accelerates the ion diffusion process and has better diffusion kinetics than the glass fiber separator.

[0165] (VI) The zinc negative electrode of the zinc ion battery assembled in the above Example 1 and Comparative Example 3 was subjected to SEM testing after 50 cycles, and the surface morphology of the zinc negative electrode was observed, and the results are shown in Figure 9 .

[0166] From Figure 9 a, it can be seen that the zinc negative electrode of the zinc ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) does not have obvious zinc dendrites, and there is also no serious corrosion, which indicates that the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) on the side facing the zinc negative electrode protects the zinc negative electrode to some extent, alleviates the growth of dendrites and the corrosion of the zinc negative electrode, and makes it have good cycle stability.

[0167] From Figure 9 b, it can be seen that the zinc negative electrode of the zinc ion battery using the glass fiber separator has obvious dendrite disorder growth, and the surface of the zinc negative electrode is seriously corroded, which makes its performance decrease during the cycle.

[0168] The above shows that the zinc ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) of the present application can inhibit the generation of by-products on the surface of the zinc negative electrode.

[0169] (VII) The electrochemical stability of the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and the glass fiber separator was evaluated on the zinc electrode using linear sweep voltammetry (LSV) (using the structure of a symmetrical battery with zinc sheets as both the positive electrode and the negative electrode).

[0170] From Figure 10 , it can be seen that on the anode side, the glass fiber separator deposits zinc at -0.04 V, while the zinc using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) starts to deposit at -0.08 V, which confirms that the gradient hydrophilic-hydrophobic separator can inhibit HER, and the hydrophobic layer reduces the erosion of active water to the zinc anode, thereby inhibiting the occurrence of side reactions.

[0171] (VIII) The Tafel curve reflects the corrosion reaction between the zinc anode and the electrolyte, and the TAFEL curve test was performed on the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and the glass fiber separator, and the results are shown in Figure 11 , using the structure of a symmetrical battery with zinc sheets as both the positive electrode and the negative electrode.

[0172] As can be seen from the figure, the zinc foil using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) exhibits a more positive corrosion potential (-0.002V) and a lower corrosion current density (0.1382mA cm -2 ), far superior to the corrosion potential (-0.012V) and the corrosion current density (2.1256mA cm -2 ) of the battery using the glass fiber separator.

[0173] This indicates that the zinc anode in contact with the gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) of the present application has been significantly improved in corrosion resistance, thanks to the hydrophobic layer which can block H2O molecules from contacting the zinc anode.

[0174] (Nine) As can be seen from Figure 12 , the V2O5 raw material was tested using Raman, and a V–O peak appeared at 1150cm -1 ; the positive electrode after the battery using the glass fiber separator was cycled (full discharge) was tested using Raman, and it was found that the V–O peak that should have appeared at 1150cm -1 disappeared, because a large amount of by-products were generated during the cycling of the battery, covering the surface of the positive electrode, thereby masking the V–O peak.

[0175] In contrast, the positive electrode after the battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) was cycled (full discharge) was tested using Raman, and a V–O peak still appeared at 1150cm -1 , which better proves that the gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) of the present application inhibits the occurrence of side reactions by reducing the desolvation barrier, thereby improving the cycle life of the zinc ion battery.

[0176] From the above tests, it can be seen that the gradient hydrophilic-hydrophobic separator of the present application can maximize the reduction of the desolvation barrier, thereby effectively reducing the nucleation overpotential of zinc deposition, enhancing the interfacial charge transfer kinetics, inhibiting the disordered growth of zinc dendrites, preventing water-induced side reactions, improving battery performance, and the zinc ion battery still has excellent cycle performance in extreme environments.

[0177] Although the present application has been disclosed with reference to the preferred embodiments above, it is not intended to limit the present application. Those skilled in the art without departing from the spirit and scope of the present application can make various modifications and improvements. Therefore, the scope of protection of the present application shall be subject to the scope defined by the claims.

Claims

1. A gradient hydrophilic-hydrophobic separator for aqueous zinc-ion batteries, characterized in that, The gradient hydrophilic-hydrophobic membrane comprises a hydrophilic layer, a first hydrophobic layer and a second hydrophobic layer, and the hydrophilic layer is located between the first hydrophobic layer and the second hydrophobic layer, thereby forming a gradient hydrophilic-hydrophobic membrane with alternating hydrophilic and hydrophobic layers; The hydrophilic layer is prepared by using a mixed solution of 4,4'-diamino diphenyl ether (ODA) and pyromellitic dianhydride (PMDA) as a precursor of polyamide acid solution through electrospinning process. The first hydrophobic layer and the second hydrophobic layer are prepared by using a mixed solution of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) as a precursor of hydrophobic solution through electrospinning process.

2. The gradient hydrophilic-hydrophobic separator for aqueous zinc-ion batteries according to claim 1, characterized in that, The thickness T of the gradient hydrophilic-hydrophobic membrane ranges from 0.1 mm to 0.3 mm.

3. The gradient hydrophilic-hydrophobic separator for aqueous zinc-ion batteries of claim 1, wherein, The first hydrophobic layer and the second hydrophobic layer are symmetrically arranged around the hydrophilic layer.

4. The gradient hydrophilic-hydrophobic separator for aqueous zinc ion batteries of claim 1, wherein, The thickness ratio of the first hydrophobic layer, the hydrophilic layer and the second hydrophobic layer is (0.4-0.5):(1-1.1):(0.4-0.5).

5. A method of preparing a gradient hydrophilic-hydrophobic separator for aqueous zinc-ion batteries according to any one of claims 1-4, characterized in that, The method comprises the following steps: Polyacrylonitrile and polyvinylidene fluoride are dissolved in N,N-dimethylformamide respectively and then mixed to obtain a first mixed solution; 4,4'-diamino diphenyl ether and pyromellitic dianhydride are dissolved in N,N-dimethylformamide in an inert gas-filled environment to obtain a second mixed solution; The first mixed solution is electrospun to prepare the first hydrophobic layer, the second mixed solution is electrospun to stack the hydrophilic layer on one side of the first hydrophobic layer, then the first mixed solution is electrospun to stack the second hydrophobic layer on the hydrophilic layer, and finally the prepared membrane is dried to obtain the gradient hydrophilic-hydrophobic membrane.

6. The production method according to claim 5, wherein The mass ratio of polyacrylonitrile, polyvinylidene fluoride and N,N-dimethylformamide is (0.95-1.05):(1-1.05):

10.

7. The preparation method according to claim 5, characterized in that, The mass ratio of 4,4'-diamino diphenyl ether, pyromellitic dianhydride and N,N-dimethylformamide is (0.95-1):(1-1.05):

10.

8. The preparation method according to claim 5, characterized in that, The process conditions of electrospinning for preparing the first hydrophobic layer and the second hydrophobic layer include: The ratio of solute mass to solvent mass of the spinning solution is 20%-30%, the jet voltage is -8 KV to -9 KV and 12 KV to 14 KV, the receiving distance is 120 mm to 150 mm, the solution advancing speed is 0.03 mm / min to 0.05 mm / min, the needle diameter is 0.86 mm to 0.95 mm, the temperature is 35℃, and the humidity is 40%.

9. The preparation method according to claim 5, characterized in that, The process conditions of electrospinning for preparing the hydrophilic layer include: The ratio of solute mass to solvent mass of the spinning solution is 19%-21%, the jet voltage is -8 KV to -9 KV and 12 KV to 14 KV, the receiving distance is 120 mm to 150 mm, the solution advancing speed is 0.035 mm / min to 0.05 mm / min, the needle diameter is 0.86 mm to 0.95 mm, the temperature is 35℃, and the humidity is 40%.

10. An aqueous zinc-ion battery, characterized in that, The aqueous zinc ion battery comprises the gradient hydrophilic-hydrophobic membrane for the aqueous zinc ion battery according to any one of claims 1-4.

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