Hydrogel with in-situ interface regulation and control function and preparation method thereof

Abstract

The invention discloses hydrogel with an in-situ interface regulation and control function, and a preparation method of the hydrogel comprises the following steps: dissolving carboxymethyl cellulose and sodium lignin sulfonate in water, and then adding a phosphoric acid aqueous solution; pouring the obtained dispersion liquid into a mold above a copper block cooled by liquid nitrogen; freezing and drying the product and then applying pressure; and finally, washing the product with water and immersing the product into a zinc perchlorate aqueous solution. Through a directional freezing technology and component optimization, the hydrogel product has significantly improved ionic conductivity and zinc ion transference number. In addition, the hydrogel can form a zinc phosphate protective layer with high ionic conductivity and excellent zinc affinity on the surface of a zinc electrode in situ, and the problems of zinc dendrites and side reactions are effectively solved. The zinc / / zinc symmetric battery using the hydrogel stably operates for at least 1500h under the conditions of 4mA / cm < 2 > and 2mAh / cm < 2 >, and the zinc / / manganese dioxide battery keeps 88.5% of the initial capacity after 1000 times of circulation.

Description

Technical Field

[0001] The present invention relates to the field of new materials and new energy technologies, and in particular to a hydrogel with in-situ interface regulation function and a preparation method thereof. Background Art

[0002] With the transformation of the global energy structure, the demand for efficient, safe and low-cost energy storage technology is becoming increasingly urgent. Although traditional lithium-ion batteries have high energy density and mature commercial applications, their high cost, limited resources, poor safety and other issues have limited their further promotion in the field of large-scale energy storage. Therefore, the development of new energy storage technologies has become the focus of current research. As an emerging energy storage technology, zinc-ion batteries have attracted widespread attention due to their advantages such as low cost, high safety, environmental friendliness and high power density. However, the practical application of zinc-ion batteries still faces the following challenges: (1) During the charging process, dendrites are easily formed on the surface of the zinc electrode, resulting in shortened battery life or even short circuit problems; (2) The zinc electrode is prone to hydrogen evolution reaction and corrosion in aqueous electrolytes, which significantly reduces the cycle stability of the battery; (3) The OH produced by the hydrogen evolution reaction - Anions can cause a sharp increase in the pH value of the electrolyte in local areas of the negative electrode surface, resulting in the formation of inert byproducts (such as hydrated basic zinc sulfate), which will not only passivate the zinc electrode, but also make the electric field distribution on the zinc electrode surface more uneven, thereby aggravating the dendrite problem.

[0003] Hydrogel electrolytes have been shown to be able to inhibit zinc dendrites and side reactions. On the one hand, hydrogel electrolytes are generally able to adhere well to the surface of the zinc electrode, and the polymer skeleton of some hydrogel electrolytes, such as carboxymethyl cellulose, has the function of regulating the zinc ion transfer flux, thereby inhibiting the two-dimensional diffusion of zinc ions on the surface of the zinc electrode and reducing the formation of zinc dendrites. On the other hand, because the hydrogel electrolyte contains limited active water, it can limit the hydrogen evolution reaction and corrosion, while avoiding the formation of inert byproducts. Although hydrogel electrolytes have shown significant advantages in zinc-ion batteries, the existing system still has deficiencies in interface regulation and zinc ion transfer kinetics. Specifically, the current hydrogel electrolytes are difficult to effectively solve the problems of dendrites and side reactions of the zinc negative electrode while taking into account the requirements of high specific capacity and excellent rate performance of the battery, which seriously restricts the practical application and development of zinc-ion batteries. Summary of the Invention

[0004] Purpose of the invention: To address the deficiencies of the prior art, a hydrogel is provided that can simultaneously promote zinc ion transport and in situ regulate the zinc electrode / electrolyte interface, and a method for preparing the hydrogel is provided.

[0005] Technical solution: A hydrogel with in-situ interface regulation function, including carboxymethyl cellulose, zinc perchlorate, phosphoric acid and sodium lignin sulfonate, has directional channels perpendicular to its surface and can in-situ regulate its interface with the zinc metal electrode.

[0006] A method for preparing a hydrogel with in-situ interface regulation function comprises the following steps:

[0007] (1) Add carboxymethyl cellulose and sodium lignin sulfonate into deionized water and continue stirring until they are completely dissolved;

[0008] (2) adding a 68% by mass phosphoric acid aqueous solution to the solution obtained in step (1) under stirring, and performing ultrasonic treatment to remove bubbles;

[0009] (3) The dispersion obtained in step (2) is poured into a mold placed above a copper block, and the copper block is immersed in liquid nitrogen (see schematic diagram Figure 1 );

[0010] (4) freeze-drying the product obtained in step (3) and applying a pressure of 6 MPa in a direction perpendicular to the surface thereof;

[0011] (5) The film obtained in step (4) was rinsed with deionized water and immersed in a 3M zinc perchlorate aqueous solution for 48 hours to obtain a hydrogel product.

[0012] Furthermore, in step (1), the mass ratio of the carboxymethyl cellulose to the deionized water is 0.25-0.5:9.3, and the mass ratio of the sodium lignin sulfonate to the deionized water is 0.1-0.2:9.3.

[0013] Furthermore, the ratio of the 68% by mass phosphoric acid aqueous solution in step (2) to the deionized water in step (1) is 0.5-0.75 mL:9.3 g.

[0014] Beneficial Effects: The present invention realizes a hydrogel with in-situ interface control function for zinc ion batteries through directional freezing technology and component optimization. It has a high ionic conductivity of 32.3mS / cm and a zinc ion transference number of 0.45. It can also form zinc phosphate with high ionic conductivity and excellent zinc affinity on the surface of the zinc electrode in situ, effectively solving the problems of zinc dendrites and side reactions. The hydrogel of the present invention makes the Zn / / Zn symmetrical battery at 4mA / cm 2 and 2mAh / cm 2 The battery can operate stably for at least 1500 hours under normal conditions, and the zinc / / manganese dioxide battery can still maintain a high capacity at high rates and achieve a capacity retention rate of up to 88.5% after 1000 cycles, which is conducive to promoting the development and progress of zinc-ion batteries.

[0015] Compared with the existing technology, the obtained product has the following advantages: (1) In the assembled battery, it can promote the in situ generation of a zinc phosphate protective layer with high zinc ion conductivity and outstanding zinc affinity on the surface of the zinc electrode, preventing direct contact between zinc metal and water molecules while ensuring efficient zinc ion transmission and uniform deposition; (2) Sodium lignin sulfonate is distributed in the hydrogel electrolyte, and its hydrophobic main chain tends to adsorb on the protrusions and tips on the surface of the zinc electrode, further preventing direct contact between zinc metal and water, while the sulfonic acid group and phenolic hydroxyl hydrophilic group of sodium lignin sulfonate can regulate the zinc ion flux, promote the desolvation process of hydrated zinc ions, and reduce the zinc deposition nucleation overpotential; (3) The anisotropic structure, zinc phosphate protective layer and sodium lignin sulfonate play a synergistic role, significantly improving the interfacial stability and electrochemical performance of zinc ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the directional freezing process in the patent of this invention;

[0017] Figure 2 This is a SEM image of the surface of the freeze-dried hydrogel obtained in Example 1;

[0018] Figure 3 This is an SEM image of the cross section of the freeze-dried hydrogel obtained in Example 1;

[0019] Figure 4 The cycling performance of the Zn / / Zn symmetric battery assembled using the hydrogel obtained in Example 1;

[0020] Figure 5 : This is the XRD pattern of the zinc electrode after cycling of the Zn / / Zn symmetric battery assembled using the hydrogel obtained in Example 1;

[0021] Figure 6 The rate performance of the Zn / / MnO2 battery assembled using the hydrogel obtained in Example 1;

[0022] Figure 7 The cycling performance of the Zn / / MnO2 battery assembled using the hydrogel obtained in Example 1;

[0023] Figure 8 This is the XRD pattern of the zinc electrode after cycling of the Zn / / Zn symmetric battery assembled with the glass fiber separator and liquid electrolyte in Comparative Example 1. DETAILED DESCRIPTION

[0024] In order to further understand the content of the present invention, the present invention is described in detail with reference to the accompanying drawings and embodiments.

[0025] Example 1

[0026] 0.5 g of carboxymethyl cellulose and 0.2 g of sodium lignin sulfonate were added to 9.3 g of deionized water and stirred continuously until completely dissolved. 0.75 mL of 68% phosphoric acid aqueous solution was added to the carboxymethyl cellulose solution while stirring, and the bubbles were removed by ultrasonic treatment. The above dispersion was poured into a mold placed above a copper block, which was immersed in liquid nitrogen (see the schematic diagram). Figure 1 ); subsequently, the above product was freeze-dried and a pressure of 6 MPa was applied in a direction perpendicular to its surface; finally, the obtained film was rinsed with deionized water and immersed in a 3M zinc perchlorate aqueous solution for 48 h to obtain a hydrogel product.

[0027] Figure 2 This is a SEM image of the surface of the freeze-dried hydrogel obtained in this example. It can be seen that the hydrogel contains a large number of pore structures. Figure 3 This is an SEM image of a cross-section of the freeze-dried hydrogel obtained in this example. It shows that the hydrogel has pores running perpendicular to the surface. These results indicate that the hydrogel obtained in this example has a directional pore structure, which facilitates the transport of electrolyte ions between the positive and negative electrodes.

[0028] The hydrogel prepared in this example was assembled with two stainless steel sheets into a stainless steel / stainless steel battery. Electrochemical impedance spectroscopy (ECI) measurements were performed, and the ionic conductivity of the hydrogel obtained in this example was calculated to be 32.3 mS / cm (in the direction perpendicular to the electrodes and the hydrogel surface). Further testing yielded a zinc ion transference number of 0.45. These results demonstrate that the hydrogel can facilitate the transport of zinc ions between the positive and negative electrodes.

[0029] The hydrogel prepared in this example was assembled with two pieces of zinc foil to form a Zn / / Zn symmetric battery. 2 Current density and 2mAh / cm 2 Constant current charge and discharge test was carried out under area capacity. Figure 4 The charge and discharge curve of the battery during long-term cycling shows that the battery can operate stably for at least 1500 hours. This result shows that the hydrogel obtained in this example can significantly improve the reversibility of zinc stripping / deposition. After cycling the Zn / / Zn symmetric battery for a period of time, the zinc electrode (zinc deposition state) was removed from the battery, washed and dried, and then XRD analysis was performed. The results are shown in Figure 5 The diffraction peak of Zn3(PO4)2·4H2O can be observed on the surface of the zinc electrode, indicating that a zinc phosphate interface layer is generated in situ on the zinc electrode. This interface layer has high zinc ion conductivity and outstanding zinc affinity. It can prevent direct contact between zinc metal and water molecules while ensuring efficient zinc ion transport and uniform deposition, thereby promoting zinc ion migration, inhibiting zinc dendrites and preventing side reactions. Figure 5It can also be found that the zinc foil surface after electrochemical cycling does not appear the XRD diffraction peak of the inert by-product with low ionic conductivity.

[0030] The manganese dioxide positive material, conductive carbon black conductive agent, and polyvinylidene fluoride (dissolved in N-methylpyrrolidone) were coated on a titanium foil at a mass ratio of 7:2:1, dried at 80°C for 12 h, and then cut into a circular piece with a diameter of 12 mm as a working electrode. The above working electrode was used to assemble a zinc / / manganese dioxide battery together with a zinc foil negative electrode and the hydrogel obtained in the present example as an electrolyte. Figure 6 The rate performance of the zinc / / manganese dioxide battery assembled using the present example was tested. The discharge specific capacity of the battery at the last cycle was 214.9, 201.6, 171.9, 129.2, 104.5, and 70.5 mAh / g at a current density of 0.1, 0.2, 0.5, 1, 2, and 3 A / g, respectively. Moreover, when the current was restored to 0.1 A / g, the capacity could be restored. Figure 7 The cycle performance of the zinc / / manganese dioxide battery assembled using the hydrogel obtained in the present example was tested. The discharge specific capacity of the battery after 1000 cycles at a current density of 1 A / g was 123.4 mAh / g, corresponding to a capacity retention rate of 88.5% (relative to the first cycle).

[0031] Comparative Example 1

[0032] A glass fiber separator (wetted with a 3M zinc perchlorate aqueous solution) was used to replace the hydrogel in Example 1 to assemble a battery, which was tested under the same conditions.

[0033] The ion conductivity and zinc ion transference number measured in the present comparative example were 24.0 mS / cm and 0.31, respectively, both of which were significantly lower than the related values of the hydrogel obtained in Example 1.

[0034] The Zn / / Zn symmetric battery in the present comparative example was tested by galvanostatic charge-discharge at a current density of 2 mA / cm 2 and a capacity area of 2 mAh / cm 2 The cycle life was only 300 h, which was much lower than that of the battery in Example 1.

[0035] Figure 8 The XRD pattern of the zinc foil in the Zn / / Zn symmetric battery in the present comparative example after a period of cycling did not show the diffraction peak of zinc phosphate, but showed the diffraction peak of the inert by-product Zn4ClO4(OH)7 with low ionic conductivity, indicating that a serious side reaction occurred.

[0036] The specific discharge capacities of the zinc / manganese dioxide battery in this comparative example at current densities of 0.1, 0.2, 0.5, 1, 2, and 3 A / g were 181.8, 143.5, 114.8, 94.9, 75.8, and 60.0 mAh / g, respectively (at the last cycle at each current density), all significantly lower than those of the battery in Example 1. The specific discharge capacity of the zinc / manganese dioxide battery in this comparative example after 1000 cycles at a current density of 1 A / g was 52.2 mAh / g, corresponding to a capacity retention rate of 48.8% (relative to the first cycle), which was significantly lower than that of the battery in Example 1.

Claims

1. A hydrogel with in situ interface regulation function, characterized in that: It includes carboxymethyl cellulose, zinc perchlorate, phosphoric acid and sodium lignin sulfonate, has directional channels perpendicular to its surface, and can in situ regulate its interface with the zinc metal electrode.

2. A method for preparing the hydrogel with in situ interface regulation function according to claim 1, characterized in that: The following steps are involved: (1) Add carboxymethyl cellulose and sodium lignin sulfonate into deionized water and continue stirring until they are completely dissolved; (2) adding a 68% by mass phosphoric acid aqueous solution to the solution obtained in step (1) under stirring, and performing ultrasonic treatment to remove bubbles; (3) pouring the dispersion obtained in step (2) into a mold placed above a copper block, and the copper block is immersed in liquid nitrogen (see Figure 1 for a schematic diagram); (4) freeze-drying the product obtained in step (3) and applying a pressure of 6 MPa in a direction perpendicular to the surface thereof; (5) The film obtained in step (4) was rinsed with deionized water and immersed in a 3M zinc perchlorate aqueous solution for 48 hours to obtain a hydrogel product.

3. The method for preparing a hydrogel with in situ interface regulation function according to claim 2, characterized in that: In step (1), the mass ratio of carboxymethyl cellulose to deionized water is 0.25-0.5:9.3, and the mass ratio of sodium lignin sulfonate to deionized water is 0.1-0.2:9.

3.

4. The method for preparing a hydrogel with in situ interface regulation function according to claim 2, characterized in that: The ratio of the 68% by mass phosphoric acid aqueous solution in step (2) to the deionized water in step (1) is 0.5-0.75 mL:9.3 g.

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