Spiral layered gel electrolyte with high zinc ion transference number and preparation method thereof

Abstract

The invention relates to a spiral layered gel electrolyte with high zinc ion transference number, which is prepared by the following steps: firstly, carrying out ultrasonic and centrifugal treatment on 1-1.2 wt% of CNF solution, then carrying out blade coating operation on the surface of a release film, slowly drying, and repeating for multiple times to obtain a plurality of CNF films with anisotropy; the method comprises the following steps of: rotating each layer of anisotropic CNF films to a specific angle to realize staggered superposition between layers; then, a CNF film with a spiral layered structure is obtained by a hot press for 10 hours; then immersing the CNF membrane with the spiral layered structure into an aqueous solution prepared from acrylamide, polyethylene glycol diacrylate and 2-hydroxy-2-methyl-1-phenyl-1-acetone, irradiating with ultraviolet light to form PAM-CNF gel after the CNF membrane reaches an absorption equilibrium state, and finally immersing the CNF membrane into a zinc perchlorate aqueous solution to carry out solvent exchange treatment, the spiral layered zinc ion gel electrolyte is obtained. The preparation method has the beneficial effect that the problem of slow transmission of zinc ions in the gel electrolyte is solved.

Description

Technical Field

[0001] The invention belongs to aqueous gel electrolytes, and in particular relates to a structural design of zinc ion gel electrolytes. Background Art

[0002] Compared with lithium-ion batteries, zinc-ion batteries have become a promising power source for portable and wearable electronic devices due to their high energy density, low cost and inherent safety. However, unstable plating / stripping in electrolytes often leads to uncontrollable growth of dendrites. In addition, the occurrence of hydrogen evolution reaction can cause the formation of a passivation layer at the electrode-electrolyte interface, resulting in poor cycling stability, low Coulombic efficiency, and even internal short circuits, ultimately leading to battery failure. Gel electrolytes are one of the most effective strategies to solve the problems of aqueous zinc batteries due to their special structure and composition. Gel electrolytes are quasi-solid electrolytes composed of a three-dimensional hydrophilic polymer chain network and an electrolyte. With a porous structure and specific chemical composition, they can provide ion transport channels, promote uniform deposition of zinc ions and inhibit the growth of dendrites. For example, groups such as hydroxyl, carboxyl and sulfonic groups are widely present in gel electrolytes, have strong nucleophilicity for zinc ions, provide jumping points for ion transfer, improve ionic conductivity, reduce overpotential caused by concentration polarization, and alleviate the change of overpotential during cyclic charge and discharge. In addition, gel electrolytes are composed of a large number of hydrophilic polymer chains. Due to the interaction between hydrophilic chains and polar water molecules, these chains can attract water molecules and convert some of them from free water to bound water. On the one hand, the reduced activity of bound water compared with free water is beneficial to inhibit the hydrogen evolution reaction. On the other hand, the reduction in free water content can promote the desolvation and uniform deposition of ions, which will also improve ionic conductivity, inhibit the hydrogen evolution reaction and the generation of by-products, and improve the Coulomb efficiency. In addition, gel electrolytes have good mechanical strength and can generate compressive stress on dendrites, thereby inhibiting the growth of dendrites. However, ions in gel electrolytes are often transported in a disordered manner and lack effective regulation, which seriously hinders the selective transmission of ions, resulting in a low zinc ion migration number, increasing the risk of dendrite growth and side reactions, and ultimately causing the battery to fail to operate stably for a long time.

[0003] In order to overcome the above-mentioned defects in the technical field of zinc ion gel electrolyte preparation, the purpose of the present invention is to design a new gel electrolyte structure to achieve efficient zinc ion transmission in aqueous zinc ion batteries. Summary of the invention

[0004] The invention provides a spiral layered gel electrolyte with a high zinc ion migration number, which is characterized by: firstly, subjecting a 1-1.2wt% CNF solution to ultrasonic and centrifugal treatment, then placing it on the surface of a release film for scraping and slowly drying, and repeating the process for multiple times to obtain a plurality of anisotropic CNF films; rotating each layer of the anisotropic CNF films to a specific angle, preferably 36°, to achieve interlaced stacking between layers; then hot pressing for 10 hours to obtain a CNF film with a spiral layered structure; then immersing the CNF film with a spiral layered structure in an aqueous solution prepared by acrylamide, polyethylene glycol diacrylate, and 2-hydroxy-2-methyl-1-phenyl-1-propanone, irradiating it with ultraviolet light to form a PAM-CNF gel after it reaches an absorption equilibrium state, and finally immersing it in a zinc perchlorate aqueous solution for solvent exchange treatment to obtain a spiral layered zinc ion gel electrolyte.

[0005] The present invention provides a method for preparing a spiral layered gel electrolyte with a high zinc ion transference number, and the specific steps are as follows:

[0006] (1) Preparation of anisotropic cellulose fiber (CNF) film:

[0007] First, a 1-1.2 wt% CNF solution was subjected to ultrasonic dispersion (100 Hz), and then the CNF solution after ultrasonic dispersion was centrifuged to effectively eliminate bubbles generated during the dispersion process;

[0008] Secondly, take an appropriate amount of the treated CNF solution and place it on the surface of the release film laid on the doctor blade, and perform the doctor blade coating operation; during the operation, keep the same direction for uniform doctor blade coating, and repeat this step 3 to 5 times to ensure that the CNF solution forms a smooth and uniform coating on the film;

[0009] Then, the release film evenly coated with CNF solution was placed in a 30-50°C forced air oven by solvent evaporation technology; at this temperature, the solvent was gradually evaporated through a slow and uniform drying process for 5-10 hours to obtain an anisotropic CNF film (such as attached Figure 1 shown);

[0010] By repeating the above steps, several anisotropic CNF films can be obtained.

[0011] (2) Design of CNF membrane spiral layer structure:

[0012] The several anisotropic CNF membranes prepared in step (1) are stacked and rotated: each layer of the membrane is rotated to a specific angle to achieve staggered stacking between layers; then, at room temperature, a hot press is used to apply a uniform and stable pressure of 10 MPa to the stacked CNF membranes for up to 10 hours; this process not only promotes the close bonding between the membrane layers, but also further improves the physical properties of the membrane through the action of pressure, and finally a CNF membrane with high transparency and dense structure with a spiral layered structure is obtained.

[0013] Preferably, step (2) is performed under constant conditions with an ambient humidity of 70% to 90%.

[0014] (3) Preparation of PAM-CNF gel electrolyte with spiral layer structure:

[0015] Firstly, acrylamide (AM), polyethylene glycol diacrylate (PEGDA 575), and 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP) are prepared into a monomer solution of acrylamide (AM) according to a certain ratio;

[0016] Secondly, the CNF membrane with a spiral layered structure prepared in step (2) is slowly immersed in a pre-prepared and fully dissolved solution until the CNF membrane is completely absorbed and reaches an absorption equilibrium state. This step ensures that the solution can evenly and thoroughly penetrate into each spiral layer gap of the CNF membrane;

[0017] Subsequently, the membrane was placed under an ultraviolet light source for 60 minutes to induce polymerization of the substances in the membrane, thereby successfully obtaining a PAM-CNF gel with a helical layered structure.

[0018] Finally, in order to obtain a gel electrolyte, this design immersed the gel in an aqueous solution of zinc perchlorate (Zn(ClO4)2) and carried out a solvent exchange treatment to obtain a spiral layered zinc ion gel electrolyte.

[0019] Preferably, in the monomer solution of acrylamide (AM) described in step (3), the content of acrylamide is 30-70 wt %, the content of polyethylene glycol diacrylate is 0.001-0.5 mol %, and the content of 2-hydroxy-2-methyl-1-phenyl-1-propanone is 0.001-0.01 wt %.

[0020] Preferably, the concentration of the zinc perchlorate (Zn(ClO4)2) aqueous solution in step (3) is 1 to 3M.

[0021] The spiral layered gel electrolyte provided by the present invention has the beneficial effect of solving the problem of slow zinc ion transmission in the gel electrolyte. The battery with the spiral layered gel electrolyte has a zinc ion migration number as high as 0.90, which can be attributed to the spiral layered transmission channel regulating the transmission behavior of zinc ions, thereby significantly improving the zinc ion migration number. Therefore, the symmetrical zinc battery assembled using the spiral layered gel electrolyte not only has a low current density of 0.2 mA cm -2 It can show a stable polarization voltage of more than 3000h under 40mAcm -2 It can also show 500h stable cyclability at high current density. In addition, the Zn / / PANI full battery assembled using spiral layered gel electrolyte can stably cycle more than 20,000 times at room temperature. This design is expected to provide an effective way to help zinc-ion batteries operate stably for a long time, and help promote the practical application of high-performance aqueous zinc-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a microscope picture of the CNF membrane;

[0023] Figure 2 are the circular dichroism spectra of samples containing different numbers of CNF membrane layers;

[0024] Figure 3 is a photograph of the spiral layered structure gel electrolyte of the present invention;

[0025] Figure 4 is a SEM image of the spiral layered structure gel electrolyte of the present invention;

[0026] Figure 5 is the crack extension (dc / dN) diagram of the gel electrolyte with spiral layer structure under each stretching cycle as the energy release rate increases;

[0027] Figure 6 It is the CA curve after polarization and the EIS curve before polarization of the symmetric battery with spiral layered gel electrolyte;

[0028] Figure 7 Asymmetric Zn-Cu battery with helical layered gel electrolyte at 5 mA cm -2 and 1mAh cm -2 Coulomb efficiency diagram;

[0029] Figure 8 Asymmetric Zn-Cu battery with helical layered gel electrolyte at 5 mA cm -2 and 1mAh cm -2 Below, the voltage versus area capacity curve for the first cycle;

[0030] Fig. 9Symmetrical battery with helical layered gel electrolyte at 0.2 mA cm -2 and 0.2mAhcm -2 Cycle performance diagram of

[0031] Fig.10 Symmetrical battery with helical layered gel electrolyte at 40 mA cm -2 and 1mAh cm -2 Cycle performance diagram of

[0032] Fig.11 PANI / / Zn full cell with spiral layered gel electrolyte at 5Ag -1 Cycle performance diagram. DETAILED DESCRIPTION

[0033] Example 1

[0034] (1) Preparation of anisotropic CNF films:

[0035] First, take an appropriate amount of 1-1.2wt% CNF and place it on the surface of the release film on the scraper, scrape it in the same direction, and repeat scraping 3-5 times. Then, using the solvent evaporation method, put the release film evenly coated with CNF solution into a 30℃ forced air oven and slowly dry it for 10 hours to obtain an anisotropic CNF film.

[0036] (2) Preparation of spiral layered gel electrolyte:

[0037] At a certain humidity (80%), take 3 sheets of CNF membranes obtained in (1) and rotate them 36° and stack them layer by layer. Subsequently, at room temperature, a hot press (100mm / 500℃) was used to apply a pressure of 10MPa to the stacked CNF membrane for 10 hours to obtain a transparent CNF membrane (i.e., the first network). Then, the obtained CNF membrane was immersed in an aqueous solution containing a certain mass ratio of AM (66wt%), PEGDA 575 (0.001mol%) and HMPP (0.001wt%) until full absorption equilibrium was reached. Subsequently, the double network gel was obtained by polymerization under ultraviolet irradiation for 60 minutes. Finally, the double network gel was immersed in a 2M Zn(ClO4)2 aqueous solution for solvent exchange.

[0038] Example 2

[0039] (1) Preparation of anisotropic CNF films:

[0040] First, take an appropriate amount of 1-1.2wt% CNF and place it on the surface of the release film on the scraper, scrape it in the same direction, and repeat scraping 3-5 times. Then, using the solvent evaporation method, put the release film evenly coated with CNF solution into a 30℃ forced air oven and slowly dry it for 10 hours to obtain an anisotropic CNF film.

[0041] (2) Preparation of spiral layered gel electrolyte:

[0042] At a certain humidity (80%), 5 CNF membranes obtained in (1) were rotated 36° and stacked together. Subsequently, at room temperature, a heat press (100mm / 500℃) was used to apply a pressure of 10MPa to the stacked CNF membrane for 10 hours to obtain a transparent CNF membrane (i.e., the first network). Then, the obtained CNF membrane was immersed in an aqueous solution containing a certain mass ratio of AM (66wt%), PEGDA 575 (0.001mol%) and HMPP (0.001wt%) until full absorption equilibrium was reached. Subsequently, the double network gel was obtained by polymerization under ultraviolet irradiation for 60 minutes. Finally, the double network gel was immersed in a 2M Zn(ClO4)2 aqueous solution for solvent exchange.

[0043] Example 3

[0044] (1) Preparation of anisotropic CNF films:

[0045] First, take an appropriate amount of 1-1.2wt% CNF and place it on the surface of the release film on the scraper, scrape it in the same direction, and repeat scraping 3-5 times. Then, using the solvent evaporation method, put the release film evenly coated with CNF solution into a 30℃ forced air oven and slowly dry it for 10 hours to obtain an anisotropic CNF film.

[0046] (2) Preparation of spiral layered gel electrolyte:

[0047] At a certain humidity (80%), 10 CNF membranes obtained in (1) were rotated 36° and stacked together. Subsequently, at room temperature, a hot press (100mm / 500℃) was used to apply a pressure of 10MPa to the stacked CNF membrane for 10 hours to obtain a transparent CNF membrane (i.e., the first network). Then, the obtained CNF membrane was immersed in an aqueous solution containing a certain mass ratio of AM (66wt%), PEGDA575 (0.001mol%) and HMPP (0.001wt%) until full absorption equilibrium was reached. Subsequently, the double network gel was obtained by polymerization under ultraviolet irradiation for 60 minutes. Finally, the double network gel was immersed in a 2M Zn(ClO4)2 aqueous solution for solvent exchange.

[0048] The gel electrolyte prepared in Example 3 was technically characterized and tested:

[0049] (1) Characterization test of the helical structure of CNF membrane:

[0050] The helical structure of CNF films was tested using a circular dichroism spectrophotometer (Chirascan V100, Applied Photophysics).

[0051] (2) Battery assembly and electrical testing of spiral layered gel electrolyte:

[0052] The Zn / / Zn symmetric cell was measured by chronoamperometry (CA) using a CHI 760E electrochemical workstation. 2+ Number of migrations Calculation, the calculation formula is as follows:

[0053]

[0054] Where I0 and R0 are the current and resistance before polarization, I S and R S are the current and resistance after polarization, and ΔV is the applied polarization voltage (20 mV).

[0055] (3) Zinc ion battery cycle stability test

[0056] Symmetric Zn / / Zn cells were assembled in air environment, and deposition / stripping performance tests were performed on the Sunway battery test system at different current densities. Zn / / PANI cells were assembled in a similar way, and stability tests were performed on the test system at different current densities with a voltage range of 0.5V-1.5V.

[0057] The results of the circular dichroism test show that the helical structure between the cellulose membranes is successfully constructed by the technical means of the present invention. Moreover, as the number of CNF membrane layers increases, the spectrum peak moves to a smaller wavelength, indicating that the helical pitch gradually decreases (see Figure 2). Figure 2 Taking the performance of the gel electrolyte prepared by stacking 10 layers of CNF membrane as an example, its appearance is colorless and transparent (as shown in the attached Figure 3 Further observation of the microstructure of the gel electrolyte using a field emission scanning electron microscope revealed that it exhibited an obvious spiral layered structure (as shown in the attached Figure 4 The spiral layered structure gives the gel electrolyte good mechanical properties and fatigue resistance (as shown in the attached Figure 5 This can produce compressive stress on the dendrites, thereby inhibiting the growth of dendrites and reducing the risk of battery short circuit.

[0058] It is worth noting that the gel electrolyte has a high zinc ion transference number (0.9, as shown in the attached Figure 6 As shown in Figure 2, the selective transport of zinc ions was achieved. Therefore, the asymmetric Zn-Cu battery assembled using the spiral layered gel electrolyte was able to operate stably for more than 500 times while maintaining a high Coulombic efficiency (CE) of 99% (see Figure 2). Figure 7 Therefore, it is confirmed that the existence of the helical layered structure induces an optimized Zn deposition behavior, making Zn / Zn 2+ The zinc-copper battery has an initial coulombic efficiency of up to 94.7%. Figure 8 The symmetrical zinc battery has good side reaction and dendrite suppression capabilities at the initial stage. -2 Under the condition of stable polarization voltage for more than 3000h (such as the attached Fig. 9 ). Moreover, at 40 mA cm -2 Even at high current density, it can show stable cycling performance for 500h (such as Fig.10 In addition, the Zn / / PANI full battery assembled with spiral layered gel electrolyte can be stably cycled 20,000 times at room temperature (see Figure 2). Fig.11 shown).

Claims

1. A spiral layered gel electrolyte with high zinc ion transference number, Features: First, a 1-1.2wt% CNF solution is subjected to ultrasonic and centrifugal treatment, then placed on the surface of a release film for scraping and slowly drying, and repeated multiple times to obtain several anisotropic CNF films; the several anisotropic CNF films are rotated to a specific angle to achieve interlaced stacking between layers; then a hot press is used for 10 hours to obtain a CNF film with a spiral layered structure; then the CNF film with a spiral layered structure is immersed in an aqueous solution prepared by acrylamide, polyethylene glycol diacrylate, and 2-hydroxy-2-methyl-1-phenyl-1-propanone, and after it reaches an absorption equilibrium state, it is irradiated with ultraviolet light to form a PAM-CNF gel, and finally immersed in a zinc perchlorate aqueous solution for solvent exchange treatment to obtain a spiral layered zinc ion gel electrolyte.

2. A spiral layered gel electrolyte having a high zinc ion transference number as claimed in claim 1, Features: The specific angle is 36°.

3. A method for preparing a spiral layered gel electrolyte with a high zinc ion transference number, Features The preparation steps are as follows: (1) Preparation of anisotropic cellulose fiber film: First, a 1-1.2 wt% CNF solution is subjected to ultrasonic dispersion treatment, and then the CNF solution after ultrasonic dispersion is centrifuged using a centrifuge; Secondly, take an appropriate amount of the treated CNF solution and place it on the surface of the release film laid on the doctor blade, and perform the doctor blade coating operation; during the operation, keep the same direction for uniform doctor blade coating, and repeat this step 3 to 5 times to ensure that the CNF solution forms a smooth and uniform coating on the film; Then, the release film evenly coated with CNF solution is placed in a 30-50°C forced air oven using solvent evaporation technology. At this temperature, the solvent is gradually evaporated through a slow and uniform drying process for 5-10 hours to obtain an anisotropic CNF film. The above steps are repeated to obtain several anisotropic CNF films. (2) Design of CNF membrane spiral layer structure: The several anisotropic CNF membranes prepared in step (1) are stacked and rotated: each layer of the membrane is rotated to a specific angle to achieve staggered stacking between layers; then, at room temperature, a hot press is used to apply a uniform and stable pressure of 10 MPa to the stacked CNF membranes for 10 hours to obtain a CNF membrane with a spiral layered structure, high transparency and dense structure; (3) Preparation of PAM-CNF gel electrolyte with spiral layer structure: Firstly, acrylamide, polyethylene glycol diacrylate and 2-hydroxy-2-methyl-1-phenyl-1-propanone are prepared into a monomer solution of acrylamide according to a certain ratio; Secondly, the CNF membrane with a spiral layered structure prepared in step (2) is slowly immersed in a pre-prepared and fully dissolved solution until the CNF membrane is completely absorbed and reaches an absorption equilibrium state; Subsequently, the CNF membrane was placed under an ultraviolet light source for 60 minutes to induce polymerization of the substances in the membrane, thereby successfully obtaining a PAM-CNF gel with a helical layered structure. Finally, the PAM-CNF gel was immersed in a zinc perchlorate aqueous solution for solvent exchange treatment to obtain a helical layered zinc ion gel electrolyte.

4. A method for preparing a spiral layered gel electrolyte having a high zinc ion transference number as claimed in claim 3, Features: Step (2) is carried out under constant conditions of ambient humidity between 70% and 90%.

5. A method for preparing a spiral layered gel electrolyte having a high zinc ion transference number as claimed in claim 3, Features: In step (2), the specific angle is 36°.

6. A method for preparing a spiral layered gel electrolyte having a high zinc ion transference number as claimed in claim 3, Features: In the acrylamide monomer solution of step (3), the content of acrylamide is 30-70 wt %, the content of polyethylene glycol diacrylate is 0.001-0.5 mol %, and the content of 2-hydroxy-2-methyl-1-phenyl-1-propanone is 0.001-0.01 wt %.

7. A method for preparing a spiral layered gel electrolyte having a high zinc ion transference number as claimed in claim 3, Features: The concentration of the zinc perchlorate aqueous solution in step (3) is 1 to 3M.

Images