Gradient hydrophilic-hydrophobic diaphragm for aqueous zinc ion battery, preparation method of gradient hydrophilic-hydrophobic diaphragm and aqueous zinc ion battery

Abstract

The invention provides a gradient hydrophilic-hydrophobic diaphragm for an aqueous zinc ion battery, the gradient hydrophilic-hydrophobic diaphragm 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, so that the gradient hydrophilic-hydrophobic diaphragm with alternate hydrophobicity and hydrophilicity is formed; wherein the hydrophilic diaphragm layer is prepared by adopting an electrostatic spinning process and taking a mixed solution of 4, 4 '-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA) as a hydrophilic precursor; the hydrophobic diaphragm layer is prepared by adopting an electrostatic spinning process and taking a mixed solution of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) as a hydrophobic precursor. The gradient hydrophilic-hydrophobic diaphragm disclosed by the invention can reduce a desolvation potential barrier so as to inhibit the occurrence of side reactions, inhibit disordered growth of zinc negative electrode dendrites, keep the electrochemical performance of the zinc ion battery unchanged, and improve the cycle performance of the battery.

Description

Technical Field

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

[0002] Aqueous zinc-ion batteries (AZIBs) are increasingly becoming a highly regarded low-cost energy storage solution due to their excellent safety performance, rapid charge and discharge rates, and high energy density. However, the commercialization of AZIBs still faces multiple obstacles, especially the problem of disordered growth of dendrites on the zinc anode surface. These dendrites may pierce the separator, triggering a short-circuit risk, which seriously threatens the safety of the battery. In addition, the intensification of hydrogen evolution and corrosion-related side reactions also accelerates the aging rate of the battery and shortens its cycle life. At the same time, the dissolution problem of cathode materials cannot be ignored, as it directly leads to the gradual attenuation of battery capacity. The root cause of these problems lies in the complex interactions 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 challenges.

[0003] Researchers are committed to enhancing the stability between the electrode and electrolyte interfaces and have explored and implemented various innovative strategies to significantly extend the cycle life of AZIBs. These carefully designed strategies cover cathode modification, anode modification, and fine adjustment of electrolyte composition, each aspect demonstrating a key role in improving battery performance. For example, in the exploration of cathode modification, when Sr(NO 3 ) 2 is coated on the surface of a vanadium oxide cathode, it reacts with the components in the electrolyte to form a dense CEI film. This film can tightly adhere to the surface of the cathode material, effectively isolating the direct contact between the electrode and the electrolyte. The formation of the CEI film significantly reduces the contact between the cathode material and active water, thereby reducing unnecessary side reactions between the cathode material and the electrolyte, which usually lead to corrosion of the electrode material, decomposition of the electrolyte, and degradation of battery performance. By inhibiting these side reactions, the CEI film helps to extend the service life of the battery.

[0004] In terms of anode modification, for example, a series of advanced materials such as Nano-CaCO 3 and dopamine polymers are used as protective coatings for the zinc anode. These coatings react with the components in the electrolyte to form a dense SEI film. This film can not only isolate the contact between active water and the zinc anode to inhibit the occurrence of a large number of side reactions but also guide the uniform deposition of zinc dendrites, further enhancing the stability and safety of the anode.

[0005] In addition, at the level of electrolyte regulation, a large number of attempts have also been made, using a variety of materials including carboxymethyl cellulose (CMC), silk fibroin, borate, polyacrylamide (PAM), and various gel electrolytes. By finely regulating the interaction between a single electrode and the electrolyte interface, the ion transport path can be optimized, the active water reaching the electrode surface can be reduced, thereby inhibiting the occurrence of side reactions, and the dissolution of the electrode material and the deposition of alkaline salts can be alleviated to a certain extent.

[0006] Although the growth of dendrites, anodic corrosion, and hydrogen evolution can be effectively inhibited by adjusting the negative electrode / electrolyte interface, and the side reactions such as hydrogen / oxygen evolution, alkaline salt deposition, and dissolution of the positive electrode material can be significantly reduced by adjusting the positive electrode / electrolyte interface, 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 urgently needs to be overcome.

[0007] Both the negative electrode and the positive electrode are closely related to their respective electrochemical interfaces, and the separator is in direct contact with 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 have focused on modifying glass fiber with materials such as graphene, MXene, melamine and cyanuric acid, metal-organic frameworks (MOF), and UIO-66 to form Janus separators. Although these modifications provide a uniform pore size distribution, strong mechanical strength, and high zinc ion transport efficiency, they only inhibit the disordered growth of zinc dendrites and reduce the contact of active water with the zinc anode. However, few studies have been able to improve the performance of both the negative electrode and the positive electrode in a complete battery system. In addition, glass fiber separators are usually too thick (about 200 microns) and lack sufficient mechanical strength to be practically applied in AZIBs.

[0008] To overcome the above defects, in the prior art, an electrospinning process is used to prepare a PI@PMIA nanofiber membrane with high porosity, large specific surface area, and a coarse-fine structure to improve the problems of poor mechanical properties, short service life, and uneven ion transport of the existing separator. There is also a method of mixing different fiber slurries in proportion to prepare a composite fiber separator with hydrophilic and hydrophobic properties, thereby inhibiting the disordered growth of zinc dendrites. There is also a method of simply compounding a double-layer or multi-layer dendrite-resistant separator and a hydrophilic separator using a low-melting-point reticular binder to solve the problems of dendrite formation on the zinc negative electrode and large electrolyte demand for the positive electrode in aqueous zinc-ion batteries. Although these separators have improved the electrochemical performance of zinc-ion batteries to a certain extent, due to their limited reduction of the solvation barrier, the performance improvement of zinc-ion batteries is still limited and difficult to break through the barrier.

[0009] Prior art literature:

[0010] Chinese Patent: CN115275506

[0011] Chinese Patent: CN117855747

[0012] Chinese Patent: CN119361969 Summary of the Invention

[0013] The object of the present invention is to provide a gradient hydrophilic-hydrophobic separator for aqueous zinc-ion batteries and its preparation method in view of the deficiencies of the prior art. By constructing a gradient hydrophilic / hydrophobic separator, the disordered growth and side reactions of zinc negative dendrites can be inhibited while maintaining the electrochemical performance of the zinc-ion battery unchanged and improving the cycle performance of the battery.

[0014] According to the first aspect of the object of the present invention, there is provided a gradient hydrophilic-hydrophobic separator for aqueous zinc-ion batteries, including 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 separator with alternating hydrophobic and hydrophilic properties;

[0015] Among them, the hydrophilic layer is prepared by an electrospinning process using a mixed solution of 4,4'-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA) as a hydrophilic precursor;

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

[0017] As an optional implementation manner, the thickness T of the gradient hydrophilic-hydrophobic separator ranges from 0.1 mm ≤ T < 0.3 mm.

[0018] As an optional implementation manner, the first hydrophobic layer and the second hydrophobic layer are symmetrically arranged with the hydrophilic layer as the center.

[0019] As an optional implementation manner, 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 the second aspect of the object of the present invention, there is provided a preparation method of the aforementioned gradient hydrophilic-hydrophobic separator for aqueous zinc-ion batteries, including the following steps:

[0021] Dissolve polyacrylonitrile and polyvinylidene fluoride in N,N-dimethylformamide respectively and then mix them, and stir evenly to obtain a first mixed solution;

[0022] Dissolve 4,4'-diaminodiphenyl ether and pyromellitic dianhydride in N,N-dimethylformamide in an environment filled with inert gas, and stir and react to obtain a second mixed solution;

[0023] Prepare a first hydrophobic layer by electrospinning the first mixed solution, then stack a hydrophilic layer on one side surface of the first hydrophobic layer by electrospinning the second mixed solution, and then stack a second hydrophobic layer on the hydrophilic layer by electrospinning the first mixed solution. Finally, dry the spun diaphragm to obtain the gradient hydrophilic-hydrophobic diaphragm.

[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'-diaminodiphenyl ether, pyromellitic dianhydride and N,N-dimethylformamide is (0.95 - 1):(1 - 1.05):10.

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

[0027] The concentration of the spinning solution is 10% - 12%, the injection voltage is -8 kV to -9 kV and 12 kV to 14 kV, the receiving distance is 120 mm to 150 mm, the solution propulsion speed is 0.03 mm / min to 0.05 mm / min, the head diameter is 0.86 mm to 0.95 mm, the temperature is 35 °C, and the humidity is 40%.

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

[0029] The solution concentration is 19% - 21%, the injection voltage is -8 kV to -9 kV and 12 kV to 14 kV, the receiving distance is 120 mm to 150 mm, the solution propulsion 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 °C, and the humidity is 40%.

[0030] According to the third aspect of the purpose of the present invention, a water-based zinc ion battery is provided, and the water-based zinc ion battery includes the aforementioned gradient hydrophilic-hydrophobic diaphragm for the water-based zinc ion battery.

[0031] The gradient hydrophilic-hydrophobic separator for aqueous zinc-ion batteries of the present invention uses a polyamic acid solution formed from a mixed solution of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride as the hydrophilic precursor for electrospinning, and a mixed solution of polyacrylonitrile and polyvinylidene fluoride as the hydrophobic precursor for electrospinning. First, the hydrophobic precursor is electrospun to obtain the first separator layer (the first hydrophobic layer), then the hydrophilic precursor is electrospun onto the first separator layer to prepare the second separator layer (the hydrophilic layer), and finally the hydrophobic precursor is electrospun onto the second separator layer to prepare the third separator layer (the second hydrophobic layer). The separator is placed in a vacuum oven for drying to obtain the gradient hydrophilic-hydrophobic separator;

[0032] For the separator of the present invention, the middle hydrophilic layer retains sufficient aqueous electrolyte to ensure high ionic conductivity, while 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 only selectively transport hydrophobic ions in the electrolyte, such as bis(trifluoromethanesulfonyl)imide anion (TFSI - ) and trifluoromethanesulfonate anion (OTF - ). Thereby, the desolvation barrier can be minimized. On the one hand, this can effectively reduce the nucleation overpotential of zinc deposition, enhance the interfacial charge transfer kinetics, and inhibit the disordered growth of zinc dendrites. On the other hand, it can prevent water-induced side reactions, optimize the performance of both the negative electrode and the positive electrode in the same battery system, and improve the battery performance.

[0033] The preparation method of the present invention is simple, low-cost, and does not produce pollution, showing a certain degree of environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0035] Figure 2 is the SEM image of the gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) prepared in Example 1 of the present invention; among them, a is the SEM image of the fibers of the hydrophilic layer of the gradient hydrophilic-hydrophobic separator, and b is the SEM image of the fibers 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 present invention; among them, a is the contact angle of the fibers of the hydrophilic layer of the gradient hydrophilic-hydrophobic separator, b is the contact angle of the fibers of the hydrophobic layer of the gradient hydrophilic-hydrophobic separator, and c is the contact angle of the glass fiber separator.

[0037] Figure 4It is the battery performance test chart of the zinc-ion battery in Embodiment 1 of the present invention and Comparative Example 3; wherein, a is the comparison chart of the 100-cycle performance of the zinc-ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and the glass fiber separator (GF) at a current density of 0.1 A g -1 The comparison chart of the 100-cycle performance of the zinc-ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and the glass fiber separator (GF) at a current density of 0.1 A g, b is the GCD curve chart of the zinc-ion battery using the gradient hydrophilic-hydrophobic separator at 100 cycles, and c is the GCD curve chart of the zinc-ion battery using the glass fiber separator at 100 cycles.

[0038] Figure 5 It is the battery performance test chart of the zinc-ion battery in Embodiment 1, Comparative Example 1 and Comparative Example 2 of the present invention; wherein, a is the comparison chart of the 100-cycle performance of the zinc-ion battery using gradient hydrophilic-hydrophobic separators with different thicknesses at a current density of 0.1 A g -1 The comparison chart of the 100-cycle performance of the zinc-ion battery using gradient hydrophilic-hydrophobic separators with different thicknesses at a current density of 0.1 A g, b is the GCD curve chart of the zinc-ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) at 100 cycles, c is the GCD curve chart of the zinc-ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.3 mm) at 100 cycles, and d is the GCD curve chart of the zinc-ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.1 mm) at 100 cycles.

[0039] Figure 6 It is the rate performance test chart of the zinc-ion battery in Embodiment 1 and Comparative Example 3 of the present invention; wherein, a is the comparison chart of the rate performance of the battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and the glass fiber separator, and b-c are the GCD curve charts using different electrolytes at current densities of 0.1 A g -1 , 0.2 A g -1 , 0.5 A g -1 , 1.0 A g -1 , 2.0 A g -1 , 5.0 A g -1 The GCD curve charts at current densities: b gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm); c glass fiber separator.

[0040] Figure 7 It is the ion conductivity test of the zinc-ion battery in Embodiment 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of the present invention; wherein, a is the electrochemical impedance spectra of four different separators including the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm), the gradient hydrophilic-hydrophobic separator (P-F / A 0.3 mm), the gradient hydrophilic-hydrophobic separator (P-F / A 0.1 mm) and the glass fiber separator, and b is the comparison of the ion conductivities of the zinc-ion batteries using the four different separators.

[0041] Figure 8Comparison chart of impedance curves of zinc-ion batteries of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention from 0.01 Hz to 105 Hz.

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

[0043] Figure 10 The electrochemical stabilities of the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and the glass fiber separator were evaluated on an inert stainless steel electrode using linear sweep voltammetry (LSV).

[0044] Figure 11 The electrochemical stabilities of the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and the glass fiber separator were evaluated on a Zn / / Zn symmetric battery using Tafel.

[0045] Figure 12 Raman tests of the V 2 O 5 electrode after cycling using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and the glass fiber separator. Detailed implementation manners

[0046] To better understand the technical content of the present invention, specific embodiments are given below in conjunction with the accompanying drawings for illustration.

[0047] In the present disclosure, aspects of the present invention are described with reference to the accompanying drawings, in which many illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to cover all aspects of the present invention. It should be understood that the various concepts and embodiments introduced above, as well as those concepts and embodiments described in more detail below, can be implemented in any of many ways.

[0048] Combined Figure 1 As shown, the exemplary gradient hydrophilic-hydrophobic separator for an aqueous zinc-ion battery of the present invention includes a hydrophilic layer 1, a first hydrophobic layer 2, and a second hydrophobic layer 3. 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 hydrophobic and hydrophilic properties.

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

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

[0051] As an alternative example, the thickness T of the aforementioned gradient hydrophilic-hydrophobic separator ranges from 0.1 mm ≤ T < 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 often has lower mechanical strength and is prone to damage during battery assembly or use. A damaged separator may not effectively isolate the positive and negative electrodes, resulting in internal short circuits in the battery, thereby causing safety problems. And an important function of the separator is to screen ions, only allowing specific ions to pass through. A too-thin separator may not effectively screen ions, leading to a decline in battery performance, such as capacity attenuation and poor cycle stability. At the same time, a thinner separator is more likely to be penetrated by zinc dendrites, resulting in internal short circuits in the battery and even causing safety problems such as battery explosion. And a too-thin separator may have insufficient electrolyte wettability due to insufficient surface area or structural defects, thereby affecting battery performance.

[0053] If the separator is too thick, it will increase the transmission distance of zinc ions inside the battery, thereby increasing the internal resistance of the battery. The increase in internal resistance may cause the battery to generate more heat during charging and discharging, affecting the thermal stability and safety of the battery. During the battery cycle, a large number of ions need to be quickly transmitted, and a thicker separator will hinder this process, resulting in a decrease in ionic conductivity and battery charge and discharge rates, affecting the performance and response speed of the battery. A thicker separator may not be conducive to the uniform deposition and stripping of zinc ions, thereby increasing the possibility of zinc dendrite formation, which may lead to the dendrites piercing the separator and causing battery damage.

[0054] As an alternative example, the first hydrophobic layer 2 and the second hydrophobic layer 3 are symmetrically arranged with the hydrophilic layer 1 as the center.

[0055] In a more specific example, the thicknesses of the first hydrophobic layer 2 and the second hydrophobic layer 3 are equal, so that the first hydrophobic layer 2 and the second hydrophobic layer 3 are symmetrically distributed with the hydrophilic layer 1 as the center.

[0056] As an alternative example, the thicknesses of both the first hydrophobic layer 2 and the second hydrophobic layer 3 are 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 polyamic acid (PAA) obtained by the polymerization reaction of ODA and PMDA. The diameter of the fibers is 90 nm to 120 nm, and the sizes are uniform.

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

[0060] In another exemplary embodiment of the present invention, there is also provided a method for preparing the aforementioned gradient hydrophilic-hydrophobic separator for an aqueous zinc ion battery, including the following steps:

[0061] Dissolve polyacrylonitrile and polyvinylidene fluoride into N,N-dimethylformamide respectively and then mix them, and stir evenly to obtain a first mixed solution;

[0062] Dissolve 4,4'-diaminodiphenyl ether and pyromellitic dianhydride into N,N-dimethylformamide in an environment filled with inert gas, and stir and react to obtain a second mixed solution;

[0063] Prepare a first hydrophobic layer by electrospinning the first mixed solution, then stack a hydrophilic layer on one side surface of the first hydrophobic layer by electrospinning the second mixed solution, and then stack a second hydrophobic layer on the hydrophilic layer by electrospinning the first mixed solution. Finally, dry the spun separator to obtain the gradient hydrophilic-hydrophobic separator.

[0064] In an optional example, when preparing the second mixed solution, first dissolve 4,4'-diaminodiphenyl ether into N,N-dimethylformamide to make it completely dissolved, then add pyromellitic dianhydride in batches until pyromellitic dianhydride is completely dissolved, and then stir and react to obtain a polyamic acid (PAA) solution, that is, the second mixed solution.

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

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

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

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

[0069] As an alternative example, when preparing the hydrophilic layer, the process conditions for electrospinning include:

[0070] The solution concentration is 19% - 21%, the injection voltage is -8 kV to -9 kV and 12 kV to 14 kV, the receiving distance is 120 mm to 150 mm, the solution propulsion 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 °C, and the humidity is 40%.

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

[0072] As an alternative example, the spun diaphragm is placed in a vacuum at a temperature of 50 °C to 60 °C and dried for 6 h to 8 h to obtain the gradient hydrophilic-hydrophobic diaphragm.

[0073] In other exemplary embodiments, a water-based zinc-ion battery is further provided. This water-based zinc-ion battery 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 this water-based zinc-ion battery uses vanadium pentoxide, the negative electrode material uses metallic zinc, and the electrolyte includes zinc sulfonate.

[0075] Combined Figure 1 As shown, in the water-based zinc-ion battery in the aforementioned example, Zn 2+ combines with water molecules (H 2 O), and gradually forms Zn(H 2 O) 6 2+ . The water molecules are separated from Zn(H 2 O) 6 2+ through the gradient hydrophilic-hydrophobic diaphragm, and gradually become Zn 2+ , achieving desolvation and minimizing the desolvation energy barrier.

[0076] For better understanding, the present invention will be further described below in conjunction with several specific examples, but the preparation process is not limited thereto, and the content of the present invention 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: Dissolve 1 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 evenly mixed to obtain the hydrophobic precursor.

[0080] (2) Preparation of hydrophilic precursor: Dissolve 1.914 g of 4,4'-diaminodiphenyl ether (ODA) in 20 mL of N,N-dimethylformamide (DMF) in a glove box filled with helium until the diaminodiphenyl ether (ODA) is completely dissolved (the solution is clear); then add 2.086 g of pyromellitic dianhydride (PMDA) in batches over about 1 h (add the next batch after the previous batch of pyromellitic dianhydride (PMDA) is completely dissolved) until the pyromellitic dianhydride (PMDA) is completely dissolved, and then stir the resulting solution for 12 h to react to obtain a polyamic acid (PAA) solution, and finally obtain the hydrophilic precursor.

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

[0082] Then electrospin the hydrophilic precursor on the first layer of separator under the conditions of injection voltage -9 KV / 13 KV, receiving distance 150 mm, solution propulsion speed 0.035 mm / min, needle diameter 0.86 mm - 0.95 mm, temperature 35 °C, and humidity 40% for 3 h to prepare the second layer of separator.

[0083] Finally, electrospin the hydrophobic precursor on the second layer of separator under the conditions of injection voltage -9 KV / 13 KV, receiving distance 150 mm, solution propulsion speed 0.035 mm / min, needle diameter 0.86 mm - 0.95 mm, temperature 35 °C, and humidity 40% for 5 h to prepare the third layer of separator.

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

[0085] (4) Battery assembly: Stack the negative electrode case, zinc sheet and the gradient hydrophilic-hydrophobic separator in sequence. Drop 60 μL of 2.6 mol / L zinc sulfonate electrolyte onto the gradient hydrophilic-hydrophobic separator to completely wet the gradient hydrophilic-hydrophobic separator. Then place the V 2 O 5 electrode sheet that has been pressed at 20 Mpa on the gradient hydrophilic-hydrophobic separator. Place the gasket and spring piece in order and then fasten the positive electrode case. Then use a battery assembly machine for encapsulation to obtain a zinc-ion battery.

[0086] Example 2

[0087] (1) Preparation of 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 evenly mixed to obtain the hydrophobic precursor.

[0088] (2) Preparation of hydrophilic precursor: Dissolve 1.914 g of 4,4'-diaminodiphenyl ether (ODA) in 20 mL of N,N-dimethylformamide (DMF) in a glove box filled with helium until the diaminodiphenyl ether (ODA) is completely dissolved (the solution is clear). Then add 2.086 g of pyromellitic dianhydride (PMDA) in batches over about 1 h (after each batch of pyromellitic dianhydride (PMDA) is completely dissolved, add the next batch) until the pyromellitic dianhydride (PMDA) is completely dissolved. Then stir the resulting solution for 12 h to react to obtain a polyamic acid (PAA) solution, and finally obtain the hydrophilic precursor.

[0089] (3) Preparation of gradient hydrophilic-hydrophobic separator: Electrospinning of the hydrophobic precursor was carried out under the conditions of injection voltage -9 KV / 13 KV, receiving distance 150 mm, solution propulsion 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 separator.

[0090] Then, electrospinning of the hydrophilic precursor is carried out on the first-layer separator under the conditions of a jet voltage of -9KV / 13KV, a receiving distance of 150mm, a solution propulsion speed of 0.035mm / min, a needle diameter of 0.86mm to 0.95mm, a temperature of 35°C, and a humidity of 40%. The electrospinning duration is 3h to prepare the second-layer separator.

[0091] Finally, electrospinning of the hydrophobic precursor is carried out on the second-layer separator under the conditions of a jet voltage of -9KV / 13KV, a receiving distance of 150mm, a solution propulsion speed of 0.035mm / min, a needle diameter of 0.86mm to 0.95mm, a temperature of 35°C, and a humidity of 40%. The electrospinning duration is 5h to prepare the third-layer separator.

[0092] The prepared separator is 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: Stack the negative electrode case, zinc sheet, and the gradient hydrophilic-hydrophobic separator in sequence. Drop 60μL of 2.6mol / L zinc sulfonate electrolyte onto the gradient hydrophilic / hydrophobic separator to completely wet the gradient hydrophilic / hydrophobic separator. Then place the V 2 O 5 electrode sheet that has been pressed at 20Mpa on the gradient hydrophilic / hydrophobic separator. Put in the gasket and spring piece in sequence and then fasten the positive electrode case, and then use a battery assembly machine for encapsulation to obtain a zinc-ion battery.

[0094] Example 3

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

[0096] (2) Preparation of the hydrophilic precursor: Dissolve 1.914g of 4,4'-diaminodiphenyl ether (ODA) in 20mL of N,N-dimethylformamide (DMF) in a glove box filled with helium until the diaminodiphenyl ether (ODA) is completely dissolved (the solution is clear); then add 2.086g of pyromellitic dianhydride (PMDA) in batches over about 1h (add the next batch after the previous batch of pyromellitic dianhydride (PMDA) is completely dissolved) until the pyromellitic dianhydride (PMDA) is completely dissolved, and then stir the obtained solution for 12h to react to obtain a polyamic acid (PAA) solution, and finally obtain the hydrophilic precursor.

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

[0098] Then, electrospinning of the hydrophilic precursor was carried out on the first layer of separator under the conditions of injection voltage -9 KV / 13 KV, receiving distance 150 mm, solution propulsion speed 0.035 mm / min, needle diameter 0.86 mm - 0.95 mm, temperature 35 °C, and humidity 40% for 3 h to prepare the second layer of separator.

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

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

[0101] (4) Assembly of the battery: The negative electrode shell, zinc sheet, and gradient hydrophilic / hydrophobic separator were stacked in sequence. 60 μL of 2.6 mol / L zinc sulfonate electrolyte was dropped onto the gradient hydrophilic / hydrophobic separator to completely moisten the gradient hydrophilic / hydrophobic separator. Then, the V 2 O 5 electrode sheet pressed at 20 Mpa was placed on the gradient hydrophilic / hydrophobic separator. The gasket and spring piece were placed in sequence and then the positive electrode shell was buckled. Then, a zinc-ion battery was obtained by encapsulation using a battery assembly machine.

[0102] Example 4

[0103] (1) Preparation of the 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; then 1 g of polyvinylidene fluoride (PVDF) was 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 evenly mixed to finally obtain the hydrophobic precursor.

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

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

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

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

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

[0109] (4) Assembly of battery: The negative electrode shell, zinc sheet and gradient hydrophilic / hydrophobic separator were stacked in sequence. 60 μL of 2.6 mol / L zinc sulfonate electrolyte was dropped onto the gradient hydrophilic / hydrophobic separator to completely wet the gradient hydrophilic / hydrophobic separator. Then the V 2 O 5 electrode sheet that had been pressed at 20 Mpa was placed on the gradient hydrophilic / hydrophobic separator. A gasket and a spring piece were placed in sequence and then the positive electrode shell was buckled on. Then a battery assembly machine was used for encapsulation to obtain a zinc-ion battery.

[0110] Example 5

[0111] (1) Preparation of hydrophobic precursor: Dissolve 1 g of polyacrylonitrile (PAN) in 5 mL of N,N-dimethylformamide (DMF), and stir for 4 h until 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 PVDF is completely dissolved; finally, mix the two solutions and stir for 12 h until evenly mixed to obtain the hydrophobic precursor.

[0112] (2) Preparation of hydrophilic precursor: Dissolve 1.914 g of 4,4'-diaminodiphenyl ether (ODA) in 20 mL of N,N-dimethylformamide (DMF) in a glove box filled with helium until ODA is completely dissolved (the solution is clear); then add 2.086 g of pyromellitic dianhydride (PMDA) in batches over about 1 h (add the next batch after the previous batch of PMDA is completely dissolved) until PMDA is completely dissolved, and then stir the resulting solution for 12 h to react to obtain a polyamic acid (PAA) solution, and finally obtain the hydrophilic precursor.

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

[0114] Then electrospin the hydrophilic precursor on the first layer of separator under the conditions of injection voltage -9 KV / 13 KV, receiving distance 150 mm, solution propulsion speed 0.05 mm / min, needle diameter 0.86 mm - 0.95 mm, temperature 35 °C, and humidity 40% for 3 h to prepare the second layer of separator.

[0115] Finally, electrospin the hydrophobic precursor on the second layer of separator under the conditions of injection voltage -9 KV / 13 KV, receiving distance 150 mm, solution propulsion speed 0.035 mm / min, needle diameter 0.86 mm - 0.95 mm, temperature 35 °C, and humidity 40% for 5 h to prepare the third layer of separator.

[0116] Place the prepared separator in a vacuum oven and dry it at 60 °C for 6 h to obtain a gradient hydrophilic / hydrophobic separator with a thickness of about 0.2 mm.

[0117] (4) Assembly of the battery: Stack the negative electrode case, zinc sheet, and gradient hydrophilic / hydrophobic separator in sequence. Drop 60 μL of 2.6 mol / L zinc sulfonate electrolyte onto the gradient hydrophilic / hydrophobic separator to completely moisten it. Then place the V 2 O 5 electrode sheet that has been pressed at 20 Mpa on the gradient hydrophilic / hydrophobic separator. Place the gasket and spring piece in sequence and then fasten the positive electrode case. Then use a battery assembly machine for encapsulation to obtain a zinc-ion battery.

[0118] Comparative Example 1

[0119] (1) Preparation of the hydrophobic precursor: Dissolve 1 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 evenly mixed to finally obtain the hydrophobic precursor.

[0120] (2) Preparation of the hydrophilic precursor: In a glove box filled with helium, first dissolve 1.914 g of 4,4'-diaminodiphenyl ether (ODA) in 20 mL of N,N-dimethylformamide (DMF) until the diaminodiphenyl ether (ODA) is completely dissolved (the solution is clear). Then add 2.086 g of pyromellitic dianhydride (PMDA) in batches over about 1 h (add the next batch after the previous batch of pyromellitic dianhydride (PMDA) is completely dissolved) until the pyromellitic dianhydride (PMDA) is completely dissolved. Then stir the resulting solution for 12 h to react to obtain a polyamic acid (PAA) solution, and finally obtain the hydrophilic precursor.

[0121] (3) Preparation of the gradient hydrophilic-hydrophobic separator: Electrospun the hydrophobic precursor under the conditions of injection voltage -9 KV / 13 KV, receiving distance 150 mm, solution propulsion speed 0.035 mm / min, needle diameter 0.86 mm - 0.95 mm, temperature 35 °C, and humidity 40% for 10 h to prepare the first layer of separator.

[0122] Then electrospun the hydrophilic precursor on the first layer of separator under the conditions of injection voltage -9 KV / 13 KV, receiving distance 150 mm, solution propulsion speed 0.035 mm / min, needle diameter 0.86 mm - 0.95 mm, temperature 35 °C, and humidity 40% for 6 h to prepare the second layer of separator.

[0123] Finally, the hydrophobic precursor was electrospun on the second-layer separator under the conditions of injection voltage -9 KV / 13 KV, receiving distance 150 mm, solution propulsion speed 0.035 mL / min, needle diameter 0.86 mm - 0.95 mm, temperature 35 °C, and humidity 40%, with a spinning duration of 10 h to prepare the third-layer separator.

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

[0125] (4) Battery assembly: Stack the negative electrode case, zinc sheet, and gradient hydrophilic-hydrophobic separator in sequence. Drop 60 μL of 2.6 mol / L zinc sulfonate electrolyte onto the gradient hydrophilic-hydrophobic separator to completely wet it. Then place the V 2 O 5 electrode plate that has been pressed at 20 Mpa on the gradient hydrophilic-hydrophobic separator, place the gasket and spring piece in order, then fasten the positive electrode case, and finally use a battery assembly machine for encapsulation to obtain a zinc-ion battery.

[0126] Comparative Example 2

[0127] (1) Preparation of the hydrophobic precursor: Dissolve 1 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 evenly mixed to obtain the hydrophobic precursor.

[0128] (2) Preparation of the hydrophilic precursor: Dissolve 1.914 g of 4,4'-diaminodiphenyl ether (ODA) in 20 mL of N,N-dimethylformamide (DMF) in a glove box filled with helium until the diaminodiphenyl ether (ODA) is completely dissolved (the solution is clear); then add 2.086 g of pyromellitic dianhydride (PMDA) in batches over about 1 h (add the next batch only after the previous batch of pyromellitic dianhydride (PMDA) is completely dissolved) until the pyromellitic dianhydride (PMDA) is completely dissolved, and then stir the resulting solution for 12 h to react to obtain a polyamic acid (PAA) solution, finally obtaining the hydrophilic precursor.

[0129] (3) Preparation of the gradient hydrophilic-hydrophobic separator: Electrospinning of the hydrophobic precursor was carried out under the conditions of injection voltage -9 KV / 13 KV, receiving distance 150 mm, solution propulsion speed 0.035 mm / min, needle diameter 0.86 mm to 0.95 mm, temperature 35 °C, and humidity 40% for 2.5 h to prepare the first layer of separator.

[0130] Then, electrospinning of the hydrophilic precursor was carried out on the first layer of separator under the conditions of injection voltage -9 KV / 13 KV, receiving distance 150 mm, solution propulsion speed 0.035 mm / min, needle diameter 0.86 mm to 0.95 mm, temperature 35 °C, and humidity 40% for 1.5 h to prepare the second layer of separator.

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

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

[0133] (4) Assembly of the battery: The negative electrode case, zinc sheet, and gradient hydrophilic-hydrophobic separator were stacked in sequence. 60 μL of 2.6 mol / L zinc sulfonate electrolyte was dropped onto the gradient hydrophilic-hydrophobic separator to completely wet the gradient hydrophilic-hydrophobic separator. Then, the V 2 O 5 electrode sheet that had been pressed at 20 Mpa was placed on the gradient hydrophilic-hydrophobic separator. The gasket and spring piece were placed in sequence and then the positive electrode case was buckled. Then, a zinc-ion battery was obtained by encapsulation using a battery assembly machine.

[0134] Comparative Example 3

[0135] Commercially available glass fiber (GF) (manufacturer Whatman, specification diameter 150 mm, thickness 0.28 mm, number 1820-150) was cut into a circle with a cross-sectional diameter of 16 mm as the battery separator for assembly. The negative electrode case, zinc sheet, and GF separator were stacked in sequence. 60 μL of 2.6 mol / L zinc sulfonate electrolyte was dropped onto the GF separator to completely wet the GF separator. Then, the V 2 O 5 electrode sheet that had been pressed at 20 Mpa was placed on the GF separator. The gasket and spring piece were placed in sequence and then the positive electrode case was buckled. Then, a zinc-ion battery was obtained by encapsulation using a battery assembly machine.

[0136] Comparative Example 4

[0137] The difference from Example 1 is that all three layers are hydrophilic layers. When assembling a battery the same as that in Example 1, perhaps due to the material characteristics, the voltage is close to 0V and the battery cannot be cycled.

[0138] Comparative Example 5

[0139] The difference from Example 1 is that all three layers are hydrophobic layers. When assembling a battery the same as that in Example 1, due to the characteristics of the hydrophobic separator hindering the rapid transport of ions in the battery, effective cycling cannot be carried out.

[0140] Test

[0141] [SEM test]

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

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

[0144] [Contact angle test]

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

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

[0147] [Battery performance test]

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

[0149] Figure 4 Among them, a is the cyclic performance test, the working voltage is set to 0.3 - 1.6 V, and the current density is 0.1 A g -1 , it can be seen that the cyclic stability of the zinc-ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 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 cyclic performance of the zinc-ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) is relatively stable, and the initial capacity can reach 386.22 mAh g -1 , and the capacity is 281.30 mAh g after 100 cycles -1 , and the capacity retention rate is 73.2%; although the initial capacity of the zinc-ion battery using the glass fiber separator is as high as 389.43 mAh g -1 , but the capacity shows a large attenuation around 10 cycles, and the capacity is only 148.08 mAh g after 100 cycles -1 , and the battery is damaged, and the capacity retention rate is only 38.0%.

[0151] Figure 4 Among them, b and c are the GCD curves of the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and the glass fiber separator at the 1st, 25th, 50th, 75th, and 100th cycles under the current density of 0.1 A g -1 , further proving that the zinc-ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) of the present invention can maintain a high capacity at a low current density and improve the cyclic stability of the battery.

[0152] (2) Using the Neware battery test equipment to test the battery performance of the zinc-ion batteries assembled in Example 1, Comparative Example 1, and Comparative Example 2, the results are as Figure 5 shown.

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

[0154] In the cycle of 0 to 100 circles, the zinc-ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) has relatively stable cycling performance, and the initial capacity can reach 386.22 mAh g -1 , and the capacity is 281.30 mAh g after 100 cycles -1 . The initial capacity of the zinc-ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.3mm) is 387.25 mAh g -1 , and the capacity is only 193.02 mAh g after 100 cycles -1 , and the battery is damaged, and the capacity retention rate is only 49.8%; while the initial capacity of the zinc-ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.1mm) is 396.26 mAh g -1 . Although the capacity also decays during the cycle, the decay amplitude 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 the glass fiber separator

[0155] Combined with Figure 5 b, c and d, it is proved that the zinc-ion battery using the gradient hydrophilic-hydrophobic separator of the present invention can maintain a high capacity while improving the cycling stability of the battery

[0156] (III) The rate performance of zinc-ion batteries with different separators was tested using the zinc-ion batteries assembled in Example 1 and Comparative Example 3, and the results are as Figure 6 shown

[0157] As can be seen from Figure 6 a, under the condition that the working voltage is 0.3 to 1.6 V, the capacities of the zinc-ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) at the current densities of 0.1 A g -1 , 0.2 A g -1 , 0.5 A g -1 , 1.0 A g -1 , 2.0 A g -1 , 5.0 A g -1 are 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 ; all are higher than those of the zinc-ion battery using the glass fiber separator at 0.1 A g -1 , 0.2 A g-1 , 0.5 Ag -1 , 1.0 Ag -1 , 2.0 Ag -1 , 5.0 Ag -1 The capacities at current densities of... 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] Combined with Figure 6 b and c above, it is demonstrated that the zinc-ion battery using the gradient hydrophilic-hydrophobic separator prepared by the present invention can maintain a high capacity while improving the cycle stability of the battery.

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

[0160] Figure 7 In... a is the electrochemical impedance spectrum of the symmetric battery assembled with the four different separators in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 using stainless-steel electrodes, and b is a columnar comparison chart of the ionic conductivity calculated by the formula σ = (L / RS) × 1000.

[0161] It can be seen from the figure that the conductivity of the gradient hydrophilic-hydrophobic separator (P-F / A 0.1 mm) is the highest, which is 4.00 mS cm -1 , its bulk resistance is 2.4 Ω, the conductivity of the gradient hydrophilic-hydrophobic separator (P-F / A 0.3 mm) is the lowest, which is 1.56 mS cm -1 , the bulk resistance is the highest, which is 6.4 Ω, while the conductivities of the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and the glass fiber separator are between the two, which are 3.87 mS cm -1 and 3.00 mS cm -1 , and the bulk resistances are only 3.0 Ω and 3.3 Ω, indicating that the use of the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) of the present invention has a faster ion transport rate than the glass fiber separator, making the cycle stability of the zinc-ion battery better.

[0162] (5) To further understand the cycling performance and redox kinetics of the assembled zinc-ion batteries in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, electrochemical impedance spectroscopy (EIS) was used to evaluate the charge transfer resistance.

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

[0164] This indicates that with the increase in the separator thickness of the gradient hydrophilic-hydrophobic separator, the impedance suffered by ion diffusion becomes greater; and under the comparison of the same thickness, the ion diffusion process of the gradient hydrophilic-hydrophobic separator is faster than that of the glass fiber separator, having better diffusion kinetics.

[0165] (6) After 50 cycles of the zinc-ion batteries assembled in the above Example 1 and Comparative Example 3, the zinc negative electrode was tested by SEM to observe the surface morphology of the zinc negative electrode, and the results are as Figure 9 shown.

[0166] As can be seen from Figure 9 a in, no obvious zinc dendrites appeared on the surface of the zinc negative electrode of the zinc-ion battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm), and no serious corrosion occurred either, indicating that the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) facing the zinc negative electrode protected the zinc negative electrode to a certain extent, alleviated the growth of dendrites and the corrosion of the zinc negative electrode, making it have better cycling stability.

[0167] As can be seen from Figure 9 b in, obvious disordered growth of dendrites occurred on the zinc negative electrodes of the zinc-ion batteries using the glass fiber separator, and the surface of the zinc negative electrode was severely corroded, which led to a decline in performance during the cycling process.

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

[0169] (7) The electrochemical stabilities of the gradient hydrophilic-hydrophobic separator (P-F / A 0.2 mm) and the glass fiber separator were evaluated on a zinc electrode using linear sweep voltammetry (LSV) (adopting the structure of a symmetric battery with zinc sheets as both the positive and negative electrodes).

[0170] From Figure 10It can be seen that on the anode side, zinc deposition occurs on the glass fiber separator at -0.04V. In contrast, zinc deposition using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) starts at -0.08V, which confirms that the gradient hydrophilic-hydrophobic separator can inhibit HER. The hydrophobic layer reduces the erosion of the active water on 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. Tafel curve tests were carried out on the gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) and the glass fiber separator, and the results are as Figure 11 shown (adopting the structure of a symmetric cell with zinc sheets as both the positive and negative electrodes).

[0172] As can be seen from the figure, the zinc foil using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) shows 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 corrosion current density (2.1256mA cm -2 ) of 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 invention has been significantly improved in terms of corrosion resistance, benefiting from the ability of the hydrophobic layer to block H 2 O molecules from contacting the zinc anode.

[0174] (IX) As can be seen from Figure 12 , Raman was used to test the V 2 O 5 raw material, and a V–O peak appeared at 1150cm -1 . Raman testing was carried out on the positive electrode after the battery using the glass fiber separator was cycled (fully discharged), and it was found that the V–O peak that should have appeared at 1150cm -1 disappeared because a large number of by-products were generated during the cycling of the battery, covering the surface of the positive electrode, thus masking the V–O peak.

[0175] Raman testing was carried out on the positive electrode after the battery using the gradient hydrophilic-hydrophobic separator (P-F / A 0.2mm) was cycled (fully discharged). A V–O peak still appeared at 1150cm -1 , better proving that the gradient hydrophilic-hydrophobic separator (P-F / A0.2mm) of the present invention inhibits the occurrence of side reactions by reducing the desolvation barrier, thereby improving the cycle life of the zinc-ion battery.

[0176] As can be seen from the above tests, the gradient hydrophilic-hydrophobic separator of the present invention can minimize 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 the battery performance, and enabling the zinc-ion battery to still have excellent cycle performance under extreme environments.

[0177] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Those with ordinary knowledge in the technical field to which the present invention pertains can make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to what is defined by the claims.

Claims

1. A gradient hydrophilic-hydrophobic membrane for an aqueous zinc ion battery, characterized in that: It comprises a hydrophilic layer, a first hydrophobic layer and a second hydrophobic layer, wherein the hydrophilic layer is located between the first hydrophobic layer and the second hydrophobic layer, thereby forming a gradient hydrophilic-hydrophobic membrane with alternating hydrophobic and hydrophilic layers; The hydrophilic layer is prepared by electrospinning process using a mixed solution of 4,4'-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA) as a hydrophilic precursor; 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 a hydrophobic precursor.

2. The gradient hydrophilic-hydrophobic diaphragm for aqueous zinc ion battery according to claim 1, characterized in that, The thickness T of the gradient hydrophilic-hydrophobic membrane is in the range of 0.1 mm ≤ T < 0.3 mm.

3. The gradient hydrophilic-hydrophobic diaphragm for aqueous zinc ion battery according to claim 1, characterized in that, The first hydrophobic layer and the second hydrophobic layer are symmetrically arranged with the hydrophilic layer as the center.

4. The gradient hydrophilic-hydrophobic diaphragm for aqueous zinc ion battery according to claim 1, characterized in that, 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 for preparing a gradient hydrophilic-hydrophobic membrane for an aqueous zinc ion battery according to any one of claims 1 to 4, characterized in that: The following steps are involved: Dissolving polyacrylonitrile and polyvinylidene fluoride in N,N-dimethylformamide respectively, mixing and stirring to obtain a first mixed solution; Dissolving 4,4'-diaminodiphenyl ether and pyromellitic dianhydride in N,N-dimethylformamide in an environment filled with inert gas, and stirring to react to obtain a second mixed solution; The first mixed solution is electrospinned to prepare a first hydrophobic layer, and then the second mixed solution is electrospinned to superimpose a hydrophilic layer on one side surface of the first hydrophobic layer, and then the first mixed solution is electrospinned to superimpose a second hydrophobic layer on the hydrophilic layer, and finally the spun membrane is dried to obtain the gradient hydrophilic-hydrophobic membrane.

6. The preparation method according to claim 5, characterized in that: 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'-diaminodiphenyl ether, pyromellitic anhydride and N,N-dimethylformamide is (0.95-1):(1-1.05):

10.

8. The preparation method according to claim 5, characterized in that: When preparing the first hydrophobic layer and the second hydrophobic layer, the electrospinning process conditions include: The spinning solution concentration is 10% to 12%, the jet voltage is -8KV to -9KV and 12KV to 14KV, 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°C, and the humidity is 40%.

9. The preparation method according to claim 5, characterized in that: When preparing the hydrophilic layer, the electrospinning process conditions include: Solution concentration 19% ~ 21%, spray voltage -8KV ~ -9KV and 12KV ~ 14KV, receiving distance 120mm ~ 150mm, solution advancement speed 0.035mm / min ~ 0.05mm / min, needle diameter 0.86mm ~ 0.95mm, temperature 35 ° C, humidity 40%.

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

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