Bacterial cellulose modified zinc metal negative electrode as well as preparation method and application thereof

Abstract

The invention discloses a bacterial cellulose modified zinc metal negative electrode as well as a preparation method and application thereof, and belongs to the field of zinc ion batteries. The bacterial cellulose modified zinc metal negative electrode comprises zinc metal and a bacterial cellulose layer coated on the surface of the zinc metal. The surface of the zinc metal is coated with the uniform bacterial cellulose coating, direct contact between the zinc metal and an electrolyte is avoided, side reactions are reduced, meanwhile,-COOH and-OH groups of the bacterial cellulose coating easily adsorb Zn < 2 + >, distribution of the Zn < 2 + > becomes uniform, uniform deposition of the Zn < 2 + > is induced, and growth of zinc dendrites is inhibited; and on the other hand, the bacterial cellulose layer has a three-dimensional porous structure, can reduce transmission obstruction of Zn < 2 + > and promote deposition and dissolution of zinc, is beneficial to improving transmission efficiency and structural stability of Zn < 2 + > in the zinc battery, and improves cycle stability and service life of the water-based zinc ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of zinc ion batteries, and particularly relates to a zinc metal negative electrode modified by bacterial cellulose, a preparation method thereof, and an application thereof. Background Art

[0002] With the increasing demand for energy, traditional fossil fuels are facing depletion. The development and research of renewable clean energy such as solar energy and wind energy have become inevitable. However, the application of these renewable energies is restricted by factors such as climate, time and space, and geographical conditions, which hinders their development. In contrast, rechargeable batteries show the advantages of good stability and convenient energy storage. Due to advantages such as long cycle life, high energy density, and high rechargeability, lithium-ion batteries dominate in electric vehicles and portable electronic devices. However, the high price of metallic lithium leads to high production costs of lithium-ion batteries, and the limited reserves of lithium in the earth's crust cannot meet the growing demand for energy storage devices. Metallic zinc (Zn) stands out among other alkali metals due to its high theoretical capacity (820 mA·h / g), low plating / stripping potential, and easy processing, becoming one of the key research directions for sustainable energy storage systems. Zinc-based batteries with zinc as the negative electrode, such as zinc-air batteries, Zn-V2O5 batteries, and Zn-MnO2 batteries, have been widely studied. More importantly, its high electrical conductivity, high power density, high stability and safety in water lay the foundation for aqueous zinc ion batteries as a key research direction in the future.

[0003] However, aqueous zinc ion batteries also have some problems. Dendrite formation and interfacial side reactions hinder their practical applications, which will seriously affect the stability and service life of the battery and easily lead to battery failures. Severe dendrite problems will pierce the separator and cause the battery to short-circuit, and even "dead zinc" (broken dendrites) will be generated. The corrosion of zinc metal will lead to a decline in battery capacity, reduce the reactive specific surface area of the zinc negative electrode, and decrease the charging efficiency. In addition, the inert corrosion products generated on the electrode surface will hinder Zn 2+ transport, reducing the reversibility of the negative electrode. To solve these existing problems, scientific researchers have proposed strategies to improve the stability of the traditional solid-liquid interface of the zinc negative electrode from different angles through the analysis of the interfacial dendrite growth mechanism. For example, some researchers have introduced a porous nano-CaCO3 coating on the zinc metal surface. Its high porosity makes it easy to be penetrated by the electrolyte, thus promoting the formation of a uniform electrolyte flux on the negative electrode surface. However, inorganic coatings are usually coated on the negative electrode surface through a binder, and the uneven contact between the nanoparticles and the binder will affect the uniformity of Zn 2+ transport, thus affecting the deposition uniformity of the zinc negative electrode. In addition, some scientists have used polymer coatings such as polyacrylonitrile and polyvinyl chloride to coat the surface of the Zn negative electrode to optimize Zn 2+Transport uniformity. As disclosed in Chinese Patent CN112490396A, a metallic zinc anode and its preparation method and an aqueous zinc-ion battery are provided. The metallic zinc anode includes a metallic zinc sheet and a modified polyacrylonitrile coating covering the surface of the metallic zinc sheet. The modified polyacrylonitrile in the modified polyacrylonitrile coating is obtained by subjecting polyacrylonitrile to a pre-oxidation treatment, and the temperature of the pre-oxidation treatment is 150 to 500 °C. In the present invention, polyacrylonitrile is subjected to a pre-oxidation treatment at 150 to 500 °C, and the surface of the obtained modified polyacrylonitrile has abundant polar bonds, such as N-H bonds. These polar bonds can guide the uniform deposition of zinc ions to inhibit dendrite growth. Based on the organic coating formed by the modified polyacrylonitrile, the zinc anode can be protected from corrosion by the electrolyte. A uniform coating is beneficial to the uniform transport of Zn 2+ However, a dense surface coating will impede the transport kinetics of Zn 2+ and increase the internal resistance of the battery, resulting in unnecessary energy loss.

[0004] Based on this, it is of great significance to develop a zinc metal anode that can not only guide the uniform deposition of Zn 2+ and inhibit dendrite growth, but also improve the transport efficiency of Zn 2+ . Summary of the Invention

[0005] Aiming at the deficiencies in the prior art, one of the purposes of the present invention is to provide a zinc metal anode modified with bacterial cellulose. By coating a uniform bacterial cellulose coating on the surface of the zinc metal, not only can the uniform transport of Zn 2+ be optimized through the uniform network structure and surface functional groups, inducing the uniform deposition of Zn 2+ , but also the transport hindrance of Zn 2+ can be reduced through the three-dimensional porous structure, promoting the deposition and dissolution of zinc, and improving the cycle stability of the zinc-ion battery.

[0006] The purpose of the present invention is achieved through the following technical solutions.

[0007] A zinc metal anode modified with bacterial cellulose, comprising a zinc metal and a bacterial cellulose layer coated on the surface of the zinc metal.

[0008] In the present invention, by coating a uniform bacterial cellulose coating on the surface of the zinc metal, while avoiding direct contact between the zinc metal and the electrolyte and reducing side reactions, the -COOH and -OH groups of the bacterial cellulose coating are easy to adsorb Zn 2+ , making the distribution of Zn 2+ become uniform, inducing the uniform deposition of Zn 2+ and inhibiting the growth of zinc dendrites; on the other hand, the bacterial cellulose layer has a three-dimensional porous structure, which can reduce the transport hindrance of Zn 2+ and promote the deposition and dissolution of zinc, which is beneficial to improving the Zn inside the zinc battery2+ Transmission efficiency and structural stability, improving the cycle stability and life of zinc-ion batteries.

[0009] The zinc metal negative electrode modified by bacterial cellulose of the present invention has the following characteristics: ① It can avoid direct contact between zinc metal and electrolyte, reducing side reactions; ② The negatively charged groups such as -COOH and -OH on the surface of the bacterial cellulose coating are easy to adsorb Zn 2+ , optimize the Zn content in aqueous electrolytes 2+ concentration distribution, inducing uniform deposition of Zn and inhibiting the growth of zinc dendrites; ③ Bacterial cellulose can self-assemble into a flexible continuous film through a three-dimensional hydrogen bond network, and an ordered three-dimensional cross-linked network structure is constructed from one-dimensional bacterial cellulose. The formed film has excellent thermal stability and mechanical strength, and has good electrolyte wettability. After the electrolyte solution successfully infiltrates into the three-dimensional pores of the bacterial cellulose film, the traditional point-to-point contact method is transformed into a large-area contact, forming a stable ion / electron three-dimensional transmission channel, which can ensure Zn 2+ The fast transmission and high thermal safety of Zn 2+ transfer efficiency and structural stability of the zinc negative electrode; ④ bacterial cellulose has excellent biocompatibility and biodegradability, and has extremely high strength and elasticity, providing a way to achieve fully degradable Zn biobatteries.

[0010] In the present invention, the thickness of the bacterial cellulose layer may be 0.01 to 0.10 mm, preferably 0.05 mm.

[0011] In the present invention, the preparation method of the bacterial cellulose modified zinc metal negative electrode comprises the following steps:

[0012] S1. Surface pretreatment of zinc metal;

[0013] S2. The bacterial cellulose gel is evenly coated on the pretreated zinc metal surface, and then dried and cured to obtain bacterial cellulose-modified zinc metal;

[0014] S3. The bacterial cellulose-modified zinc metal is aged at room temperature, and then surface polished to obtain the bacterial cellulose-modified zinc metal negative electrode.

[0015] Preferably, in step S1, the specific operation of surface pretreatment is as follows: the zinc metal surface is polished with sandpaper, and then ultrasonically cleaned with anhydrous ethanol for 3 to 5 times.

[0016] Preferably, in step S2, the concentration of the bacterial cellulose gel is ≥ 99%.

[0017] Preferably, in step S2, the coating is carried out with the following process parameters: the ambient temperature is 28-35 °C, the ambient relative humidity is 70%-90%, the coating speed is 2-4 m / min, and the pressure is 0.1-0.3 MPa.

[0018] More preferably, in step S2, the coating is carried out with the following process parameters: the ambient temperature is 28 °C, the ambient relative humidity is 80%, the coating speed is 3 m / min, and the pressure is 0.2 MPa.

[0019] By controlling the coating conditions, the thickness of the bacterial fiber coating can be adjusted, and the bacterial cellulose can be evenly distributed on the zinc metal surface; through drying and curing, normal temperature aging and surface polishing, the best modification effect can be obtained, and a thin and stable protective film can be formed.

[0020] Preferably, the drying and curing temperature is 60-90 °C, and the time is 20-36 h.

[0021] Another object of the present invention is to provide the application of the zinc metal negative electrode modified with bacterial cellulose in an aqueous zinc ion battery.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) By coating a uniform bacterial cellulose coating on the zinc metal surface, while avoiding direct contact between the zinc metal and the electrolyte and reducing side reactions, the -COOH and -OH groups of the bacterial cellulose coating are easy to adsorb Zn 2+ , making the distribution of Zn 2+ become uniform, inducing the uniform deposition of Zn 2+ , and inhibiting the growth of zinc dendrites; on the other hand, the bacterial cellulose layer has a three-dimensional porous structure, which can reduce the transport hindrance of Zn 2+ , promote the deposition and dissolution of zinc, and is beneficial to improving the Zn 2+ transport efficiency and structural stability inside the zinc battery, and improving the cycle stability and life of the aqueous zinc ion battery.

[0024] (2) Based on the NH4VO3||Zn full battery with the zinc metal negative electrode of the present invention, at a current density of 5 A / g, after 2500 stable cycles, it still maintains a specific capacity of 95 mAh / g, the capacity retention rate is 90.48%, and the Coulomb efficiency can reach 96.8%, with good capacity retention rate and Coulomb efficiency. Based on the Zn||Zn symmetric battery with the zinc metal negative electrode of the present invention, at a current density of 5 mA cm -2 , with a charge and discharge time of 12 min each and a specific capacity of 1 mAh cm -2 , there are more than 550 h of stable cycles, with good cycle stability. Description of the Drawings

[0025] Figure 1 Process flow chart for fabricating the bacterial cellulose modified zinc metal anode of the present invention;

[0026] Figure 2 Schematic diagram of button cell assembly for Zn||Zn symmetric battery and NH4VO3||Zn full battery;

[0027] Figure 3 SEM image of the bacterial cellulose modified zinc metal anode of Example 1;

[0028] Figure 4 Long cycle plot of the Zn||Zn symmetric battery based on the bacterial cellulose modified zinc metal anode of Example 1 and bare zinc sheet;

[0029] Figure 5 Cycling performance plot of the NH4VO3||Zn full battery based on the bacterial cellulose modified zinc metal anode of Example 1;

[0030] Figure 6 CV plot of the NH4VO3||Zn full battery based on the bacterial cellulose modified zinc metal anode of Example 1. Detailed implementation manners

[0031] Next, the applicant will further elaborate on the method of the present invention with specific examples, aiming to enable those skilled in the art to clearly understand the present invention. However, the following examples should not be construed as limiting the scope of protection claimed in the claims of the present invention in any way.

[0032] Example 1

[0033] As Figure 1 shown, this example provides a preparation method for a bacterial cellulose modified zinc metal anode, including the following steps:

[0034] S1. Surface pretreatment of the zinc metal, and the specific treatment method is as follows: first, polish with 80-mesh sandpaper for 2 min, and then ultrasonically clean with 99% anhydrous ethanol 3 - 5 times, 1 min each time;

[0035] S2. Wet the bottom of the zinc metal obtained in step S1 with a small amount of anhydrous ethanol, then closely attach it to a culture dish. Under the conditions of an environmental temperature of 28°C and an environmental relative humidity of 80%, coat a 99% bacterial cellulose hydrogel on the surface of the zinc metal with a thickness of 0.03 mm, the coating speed is 3 m / min, and the pressure is 0.2 MPa; then place the coated zinc metal in an electrothermal blast drying oven for drying and curing, the drying temperature is 85°C, and the drying time is 24 h;

[0036] S3. Place the dried zinc metal at room temperature of 25 °C and let it stand for aging for 2 h, then polish the surface with 240-mesh sandpaper for 2 - 3 times, 1 min each time, thus obtaining the zinc metal negative electrode modified with bacterial cellulose (denoted as BC-coated zinc sheet).

[0037] Figure 3 This is the SEM image of the zinc metal negative electrode modified with bacterial cellulose obtained in this example. It can be seen from the figure that the bacterial cellulose is evenly distributed on the surface of the zinc metal, and the bacterial cellulose film has a three-dimensional porous structure.

[0038] Example 2

[0039] As Figure 1 shown, this example provides a preparation method of a zinc metal negative electrode modified with bacterial cellulose, including the following steps:

[0040] S1. Conduct surface pretreatment on the zinc metal. The specific treatment method is as follows: First, polish with 80-mesh sandpaper for 2 min, and then ultrasonically clean with 99% absolute ethanol for 3 - 5 times, 1 min each time;

[0041] S2. Moisten the bottom of the zinc metal in step S1 with a small amount of absolute ethanol, then closely attach it to a culture dish. Under the conditions of an environmental temperature of 35 °C and an environmental relative humidity of 70%, coat the surface of the 0.03-mm-thick zinc metal with 99% bacterial cellulose hydrogel at a coating speed of 2 m / min and a pressure of 0.1 MPa; then place the coated zinc metal in an electrothermal blast drying oven for drying and curing. The drying temperature is 60 °C and the drying time is 36 h;

[0042] S3. Place the dried zinc metal at room temperature of 25 °C and let it stand for aging for 2 h, then polish the surface with 240-mesh sandpaper for 2 - 3 times, 1 min each time, thus obtaining the zinc metal negative electrode modified with bacterial cellulose.

[0043] Example 3

[0044] As Figure 1 shown, this example provides a preparation method of a zinc metal negative electrode modified with bacterial cellulose, including the following steps:

[0045] S1. Conduct surface pretreatment on the zinc metal. The specific treatment method is as follows: First, polish with 80-mesh sandpaper for 2 min, and then ultrasonically clean with 99% absolute ethanol for 3 - 5 times, 1 min each time;

[0046] S2. Moisten the bottom of the zinc metal in step S1 with a small amount of absolute ethanol, then closely attach it to the petri dish. Under the conditions of an ambient temperature of 32 °C and an ambient relative humidity of 85%, coat the 99% bacterial cellulose hydrogel on the surface of the zinc metal with a thickness of 0.03 mm at a coating speed of 4 m / min and a pressure of 0.3 MPa; then place the coated zinc metal in an electrothermal blast drying oven for drying and curing, with a drying temperature of 90 °C and a drying time of 20 h;

[0047] S3. Place the dried zinc metal at room temperature of 25 °C and let it stand for aging for 2 h, then polish the surface with 240-mesh sandpaper, polish 2 - 3 times, 1 min each time, to obtain the zinc metal negative electrode modified with bacterial cellulose.

[0048] Application Example

[0049] Prepare button cells of Zn||Zn symmetric battery and NH4VO3||Zn full battery respectively with the zinc metal negative electrode modified with bacterial cellulose in Examples 1 - 3, and conduct electrochemical performance tests.

[0050] Among them, the assembly flow chart of the Zn||Zn symmetric battery is as shown in Figure 2 the right figure. Using glass fiber as the separator and 2M ZnSO4 aqueous solution as the electrolyte, stack the negative electrode shell, BC-coated zinc sheet, separator, BC-coated zinc sheet, gasket, shrapnel, and positive electrode shell in sequence as shown in Figure 2 the right figure to assemble a button cell.

[0051] The assembly flow chart of the NH4VO3||Zn full battery is as shown in Figure 2 the left figure. The preparation method of the positive electrode sheet is as follows: Mix (NH4)2V 10 O 25 ·8H2O nanosheets, PVDF, and Super P in a mass ratio of 7:2:1, add NMP solvent and stir evenly, then coat it on carbon paper, place it in a vacuum oven and dry at 80 °C for 24 h, and cut it into circular membranes with a diameter of 12 mm after cooling to obtain the positive electrode sheet; then use the BC-coated zinc sheet as the negative electrode, glass fiber as the separator, and 2M zinc trifluoromethanesulfonate as the electrolyte, and assemble it into an NH4VO3||Zn button cell in the order shown in Figure 2 the left figure.

[0052] Use a battery test system to conduct electrochemical performance tests on the assembled batteries.

[0053] Figure 4The long-cycle comparison diagram of the Zn||Zn symmetric battery with the zinc metal anode modified by bacterial cellulose based on Example 1 and the bare zinc sheet Zn||Zn symmetric battery. It can be seen from the figure that the Zn||Zn symmetric battery with the zinc metal anode modified by bacterial cellulose based on Example 1 has a stable cycle of more than 550 h under the condition of a current density of 5 mA cm -2 and a charge-discharge time of 12 min each at a specific capacity of 1 mAh cm -2 . And from the local cycle diagram, it can be seen that compared with the ordinary bare zinc sheet Zn||Zn symmetric battery, the polarization voltage of the Zn||Zn symmetric battery with the zinc metal anode modified by bacterial cellulose based on Example 1 is basically the same, but its voltage polarization is more stable, and it always maintains a stable overpotential of 45 mV, showing stable long-cycle performance. This indicates that the zinc metal anode modified by bacterial cellulose of the present invention promotes the uniform deposition of Zn 2+ , inhibits the growth of zinc dendrites, and significantly improves the cycle stability.

[0054] Figure 5 The cycle performance diagram of the NH4VO3||Zn full battery with the zinc metal anode modified by bacterial cellulose based on Example 1. It can be seen from the figure that the NH4VO3||Zn full battery with the zinc metal anode modified by bacterial cellulose based on Example 1 still maintains a specific capacity of 95 mAh / g after 2500 stable cycles under the condition of a current density of 5 A / g, with a capacity retention rate of 90.48% and a Coulomb efficiency of up to 96.8%, showing good capacity retention rate and Coulomb efficiency. It can also be seen from the voltage-capacity curve diagram that during the initial cycle process, as the activation inside the battery and the activation of the active material insertion process occur, the capacity increases. Its specific capacity when the battery is full at 2000 cycles can still reach 100 mAh / g, showing excellent long-cycle performance and long-cycle capacity.

[0055] Figure 6 The CV diagram of the NH4VO3||Zn full battery with the zinc metal anode modified by bacterial cellulose based on Example 1. It can be seen from the figure that the two oxidation peak potentials are approximately 0.7 V and 1.0 V, corresponding to the two oxidation processes of VO3 - . The two reduction peak potentials are approximately 0.6 V and 0.9 V, and the peak spacing is roughly the same. And the ratio of the two oxidation peak currents to the reduction peak currents is close to 1, indicating that the reaction has good reversibility. At this time, the oxide of VO3 - is reduced back to VO3 - .

[0056] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A zinc metal anode modified with bacterial cellulose, characterized in that, It includes zinc metal and a bacterial cellulose layer coated on the surface of the zinc metal.

2. The zinc metal negative electrode modified with bacterial cellulose according to claim 1, wherein The thickness of the bacterial cellulose layer is 0.01 - 0.10 mm.

3. The preparation method of a zinc metal negative electrode modified with bacterial cellulose according to claim 1 or 2, characterized in that, It includes the following steps: S1. Perform surface pretreatment on the zinc metal; S2. Uniformly coat the bacterial cellulose gel on the surface of the pretreated zinc metal, and then perform drying and curing treatment to obtain the bacterial cellulose-modified zinc metal; S3. Age the bacterial cellulose-modified zinc metal at room temperature, and then perform surface polishing to obtain the bacterial cellulose-modified zinc metal negative electrode.

4. The preparation method of a zinc metal negative electrode modified with bacterial cellulose according to claim 3, characterized in that, In step S1, the specific operation of the surface pretreatment is as follows: polish the surface of the zinc metal with sandpaper, and then perform ultrasonic cleaning with absolute ethanol 3 - 5 times.

5. The preparation method of a zinc metal negative electrode modified with bacterial cellulose according to claim 3, characterized in that, In step S2, the concentration of the bacterial cellulose gel is ≥99%.

6. The preparation method of a zinc metal negative electrode modified with bacterial cellulose according to claim 3, characterized in that, In step S2, the following process parameters are adopted for the coating: the ambient temperature is 28 - 35°C, the ambient relative humidity is 70% - 90%, the coating speed is 2 - 4 m / min, and the pressure is 0.1 - 0.3 MPa.

7. The preparation method of a zinc metal negative electrode modified with bacterial cellulose according to claim 6, characterized in that, In step S2, the following process parameters are adopted for the coating: the ambient temperature is 28°C, the ambient relative humidity is 80%, the coating speed is 3 m / min, and the pressure is 0.2 MPa.

8. The preparation method of a zinc metal negative electrode modified with bacterial cellulose according to claim 3, characterized in that, The temperature for drying and curing is 60 - 90°C, and the time is 20 - 36 h.

9. Application of the bacterial cellulose-modified zinc metal negative electrode prepared by the preparation method described in claim 3 or described in claim 1 in an aqueous zinc-ion battery.

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