High-strength titanium dioxide / nanocellulose composite zinc ion battery diaphragm and preparation method thereof

Abstract

The invention relates to a titanium dioxide / nanocellulose composite zinc ion battery diaphragm and a preparation method thereof, and belongs to the field of zinc ion batteries. According to the method, a nanocellulose suspension is utilized to prepare a nanocellulose diaphragm, and then a simple dispensing method is adopted to prepare the titanium dioxide / nanocellulose composite zinc ion battery diaphragm. Compared with a glass fiber diaphragm, the preparation method has the advantages that the raw materials are green and environment-friendly, the preparation process is simple and convenient, the prepared diaphragm has good mechanical strength, ionic conductivity, cycle performance and rate capability, and the performance of the zinc ion battery can be remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of zinc ion batteries, and specifically relates to a high-strength titanium dioxide / nanocellulose composite zinc ion battery separator and a preparation method thereof. Background Art

[0002] At present, the most commonly used diaphragm material in zinc-ion batteries is glass fiber. Although the glass fiber diaphragm has the advantages of rich pores, good hydrophilicity, and excellent ionic conductivity, its internal structure is relatively loose, resulting in poor mechanical properties of the diaphragm. In addition, the large thickness of the glass fiber diaphragm will seriously reduce the volume energy density of the battery, while extending the ion transmission distance and increasing the internal resistance of the battery. In addition, the poor uniformity of the pore structure of the glass fiber diaphragm will lead to uneven deposition of zinc ions, resulting in serious dendrite problems, which will affect the coulombic efficiency and long-term stable operation of the zinc ion battery. The dendrite growth problem of the zinc negative electrode is essentially caused by the mismatch of electrochemical polarization and deposition kinetics caused by the zinc ion concentration gradient at the interface. The local electric field distortion caused by the tip effect will drive the zinc ions to preferentially deposit on the protruding parts, forming a self-accelerating growth dendrite structure. To address this problem, from the perspective of the diaphragm, the current main strategy is to modify the diaphragm functionally and optimize the interfacial compatibility between the diaphragm and the electrolyte and electrode through coating technology, so as to achieve the regulation of zinc ion deposition behavior. Nanocellulose is a nano-scale fiber material extracted from natural cellulose, which has a large specific surface area, good thermal stability and excellent electrolyte wettability. Therefore, nanocellulose can be used to prepare high-performance zinc-ion battery separators. However, the membranes prepared from nanocellulose have poor mechanical strength and cannot meet the high safety requirements of zinc-ion batteries. Therefore, it is necessary to improve the mechanical strength of nanocellulose separators to meet the application needs of zinc-ion batteries.

[0003] In the existing technology, the Chinese patent "A cellulose diaphragm suitable for zinc-ion batteries and its application" with application number 112615106 discloses a method for improving the mechanical strength of the diaphragm by modifying cellulose. Compared with the filter paper diaphragm without modification and enhancement, its tensile strength is greatly improved, but the cycle performance of the assembled symmetrical battery is still poor. The Chinese patent "Aramid nanofiber / nanocellulose composite zinc-ion battery diaphragm and its preparation method, zinc-ion battery" with application number 202311747173 discloses a method for preparing an aramid nanofiber / nanocellulose composite zinc-ion battery diaphragm. The electrochemical properties of the composite diaphragm are improved, but the process is complicated and the cost is high, which is not conducive to production and application. Nano-titanium dioxide has the advantages of large specific surface area, high dielectric constant and good hydrophilicity. As a diaphragm modification material, it can improve the dimensional stability, electrolyte wettability and thermal stability of the diaphragm. Therefore, nano-titanium dioxide has been widely used in the field of battery diaphragms. Although titanium dioxide as a coating modification material can produce a polarization effect to uniform the internal electric field of the battery, the interface compatibility between inorganic nanoparticles and the matrix material is insufficient, which can easily cause the coating to fall off, thereby reducing the cycle stability. Cao et al. reported a method for preparing a ZrO2 / nanocellulose composite membrane [Modulating Zn deposition via ceramic-cellulose separator with interfacial polarization effect for durable zincanode. Nano Energy 89,106322 (2021)]. Although the introduction of ZrO2 nanoparticles greatly improved the ionic conductivity of the ZrO2 / nanocellulose composite membrane, the mechanical properties of the composite membrane were poor. Therefore, it is necessary to find a simple method to enhance the bonding force between the modified material and nanocellulose, so as to improve the mechanical strength of the nanocellulose membrane and optimize the interfacial stability of the membrane. Summary of the invention

[0004] To this end, it is necessary to provide a high-strength titanium dioxide / nanocellulose composite zinc ion battery separator and a preparation method thereof to improve the performance of the zinc ion battery separator.

[0005] To achieve the above object, the present invention provides a high-strength titanium dioxide / nanocellulose composite zinc ion battery separator and a preparation method thereof, comprising the following steps: (1) Mixing and dispersion: The nanocellulose suspension is diluted with water, and a uniform nanocellulose / water suspension is obtained after magnetic stirring and ultrasonic dispersion. (2) Wet film forming: the nanocellulose / water suspension obtained in step (1) is filtered to obtain a nanocellulose wet film; (3) Wet film drying: drying the nanocellulose wet film obtained in step (2) to obtain a nanocellulose film; (4) Preparation of modified liquid: titanium dioxide, polyvinylidene fluoride and N-methylpyrrolidone are mixed, and after magnetic stirring and ultrasonic dispersion, a uniform titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified liquid is obtained; (5) Single-sided drop coating of the modified liquid: the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified liquid obtained in step (4) is drop coated onto the surface of the nanocellulose diaphragm obtained in step (3) according to different mass ratios to obtain a single-sided modified wet film; (6) Drying the single-sided modified wet film: drying the wet film obtained in step (5) to obtain a single-sided modified composite diaphragm; (7) Double-sided drip coating of the modified liquid: drip coating the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified liquid obtained in step (4) onto the other surface of the single-sided modified composite diaphragm obtained in step (6) to obtain a double-sided modified wet film; (8) Drying the double-sided modified wet film: The wet film obtained in step (7) is dried to obtain a titanium dioxide / nanocellulose composite membrane.

[0006] Furthermore, in step (5), the mass ratio of titanium dioxide to nanocellulose is 5% to 20%.

[0007] Furthermore, the mechanical strength of the titanium dioxide / nanocellulose composite membrane prepared by the preparation method is 25MPa to 33MPa, the elongation at break of the membrane is 11% to 12.8%, and the ionic conductivity of the membrane is 2.1 mS / cm to 4.1mS / cm.

[0008] Different from the prior art, the present invention utilizes titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified liquid as a coating modified material and adopts a simple drip coating method. The mechanical strength of the obtained titanium dioxide / nanocellulose composite zinc ion battery separator is significantly better than that of the glass fiber separator, thereby improving the safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a line graph of the mechanical strength of zinc ion battery separators of specific embodiments 1-4 and comparative example 1.

[0010] Figure 2 It is a bar graph of the ionic conductivity of zinc ion battery separators of specific embodiments 1-4 and comparative example 1.

[0011] Figure 3 It is a line graph of the rate performance of the zinc ion battery separator in specific embodiment 1.

[0012] Figure 4 It is a line graph of the rate performance of the zinc ion battery separator of specific embodiment 2.

[0013] Figure 5 It is a line graph of the rate performance of the zinc ion battery separator of specific embodiment 3.

[0014] Figure 6 It is a line graph of the rate performance of the zinc ion battery separator of specific embodiment 4.

[0015] Figure 7 It is a line graph of the rate performance of the zinc ion battery separator of comparative example 1. DETAILED DESCRIPTION

[0016] In order to explain in detail the technical content, features, achieved objectives and effects of the technical solution, the following is a detailed description in conjunction with specific embodiments. Example 1

[0017] A method for preparing a high-strength titanium dioxide / nanocellulose composite zinc ion battery separator, the specific preparation method comprising the following steps: (1) Weigh 15 g of nanocellulose suspension with a solid content of 2% and add it to a beaker. Then weigh 180 mL of deionized water and add it to the beaker. Stir magnetically for 24 h. Place the stirred nanocellulose suspension in an ultrasonic cleaner for ultrasonic dispersion for 2 h until all the nanofibers are evenly dispersed. (2) Place a filter membrane with a pore size of 0.45 μm and a diameter of 8 cm into a sand core filter, draw 30 mL of the nanocellulose suspension obtained in the above step (1) with a syringe, and filter to obtain a nanocellulose wet membrane; (3) The wet film obtained in step (2) was placed in a vacuum drying oven at 80 °C for 12 h to obtain a nanocellulose film, and the dried nanocellulose film was cut into discs with a diameter of 17 mm; (4) Weigh 0.02 g of titanium dioxide particles with a particle size of 60 nm and 0.002 g of polyvinylidene fluoride into 5 mL of N-methylpyrrolidone, stir magnetically for 12 h, and place the stirred modified solution in an ultrasonic cleaner for ultrasonic dispersion for 1 h until the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified solution is evenly dispersed; (5) Using a pipette, take 25 μL of the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified solution obtained in step (4) and drop it on the surface of the nanocellulose film with a diameter of 17 mm obtained in step (3), thereby obtaining a single-sided modified titanium dioxide / nanocellulose wet film; (6) placing the wet film obtained in the above step (5) in a vacuum drying oven at 60 °C for 12 h to obtain a single-sided modified titanium dioxide / nanofiber film; (7) Using a pipette, take 25 μL of the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified solution obtained in step (4) and drop it on the other surface of the single-sided modified titanium dioxide / nanofiber film obtained in step (6) to obtain a wet film; (8) The wet film obtained in the above step (7) was placed in a vacuum drying oven and dried at 60 °C for 12 h to obtain a titanium dioxide / nanocellulose composite membrane. Example 2

[0018] A method for preparing a high-strength titanium dioxide nanocellulose composite zinc ion battery separator, the specific preparation method comprising the following steps: (1) Weigh 15 g of nanocellulose suspension with a solid content of 2% and add it to a beaker. Then weigh 180 mL of deionized water and add it to the beaker. Stir magnetically for 24 h. Place the stirred nanocellulose suspension in an ultrasonic cleaner for ultrasonic dispersion for 2 h until all the nanofibers are evenly dispersed. (2) Place a nylon filter membrane with a pore size of 0.45 μm and a diameter of 8 cm into a sand core filter, draw 30 mL of the nanocellulose suspension obtained in step (1) with a syringe, and filter to obtain a nanocellulose wet membrane; (3) placing the wet film obtained in the above step (2) in a vacuum drying oven at 80 °C for 12 h to obtain a nanocellulose film, and cutting the nanocellulose film into discs with a diameter of 17 mm; (4) Weigh 0.039 g of titanium dioxide particles with a particle size of 60 nm and add 0.004 g of polyvinylidene fluoride to 5 ml of N-methylpyrrolidone. Stir magnetically for 12 h. Place the stirred modified solution in an ultrasonic cleaner and ultrasonically disperse for 1 h until the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified solution is evenly dispersed. (5) Using a pipette, take 25 μL of the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified solution obtained in step (4) and drop it on the surface of the nanocellulose film with a diameter of 17 mm obtained in step (3), thereby obtaining a single-sided modified titanium dioxide / nanocellulose wet film; (6) placing the wet film obtained in the above step (5) in a vacuum drying oven at 60 °C for 12 h to obtain a single-sided modified titanium dioxide / nanocellulose film; (7) Using a pipette, take 25 μL of the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified solution obtained in step (4) and drop it on the other surface of the single-sided modified titanium dioxide / nanocellulose film obtained in step (6) to obtain a wet film; (8) The wet film obtained in the above step (7) was placed in a vacuum drying oven and dried at 60 °C for 12 h to obtain a titanium dioxide / nanocellulose composite membrane. Example 3

[0019] A method for preparing a high-strength titanium dioxide nanocellulose composite zinc ion battery separator, the specific preparation method comprising the following steps: (1) Weigh 15 g of nanocellulose suspension with a solid content of 2% and add it to a beaker. Then weigh 180 mL of deionized water and add it to the beaker. Stir magnetically for 24 h. Place the stirred nanocellulose suspension in an ultrasonic cleaner for ultrasonic dispersion for 2 h until all the nanofibers are evenly dispersed. (2) Place a nylon filter membrane with a pore size of 0.45 μm and a diameter of 8 cm into a sand core filter, draw 30 mL of the nanocellulose suspension obtained in step (1) with a syringe, and filter to obtain a nanocellulose wet membrane; (3) placing the wet film obtained in the above step (2) in a vacuum drying oven at 80 °C for 12 h to obtain a nanocellulose film, and cutting the nanocellulose film into discs with a diameter of 17 mm; (4) Weigh 0.059 g of titanium dioxide particles with a particle size of 60 nm and add 0.007 g of polyvinylidene fluoride to 5 mL of N-methylpyrrolidone. Stir magnetically for 12 h. Place the stirred modified solution in an ultrasonic cleaner and ultrasonically disperse it for 1 h until the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified solution is evenly dispersed. (5) Using a pipette, take 25 μL of the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified solution obtained in step (4) and drop it on the surface of the nanocellulose film with a diameter of 17 mm obtained in step (3), thereby obtaining a single-sided modified titanium dioxide / nanocellulose wet film; (6) placing the wet film obtained in the above step (5) in a vacuum drying oven at 60 °C for 12 h to obtain a single-sided modified titanium dioxide / nanocellulose film; (7) Using a pipette, take 25 μL of the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified solution obtained in step (4) and drop it on the other surface of the single-sided modified titanium dioxide / nanocellulose film obtained in step (6) to obtain a wet film; (8) The wet film obtained in the above step (7) was placed in a vacuum drying oven and dried at 60 °C for 12 h to obtain a titanium dioxide / nanocellulose composite membrane. Example 4

[0020] A method for preparing a high-strength titanium dioxide nanocellulose composite zinc ion battery separator, the specific preparation method comprising the following steps: (1) Weigh 15 g of nanocellulose suspension with a solid content of 2% and add it to a beaker. Then weigh 180 mL of deionized water and add it to the beaker. Stir magnetically for 24 h. Place the stirred nanocellulose suspension in an ultrasonic cleaner for ultrasonic dispersion for 2 h until all the nanofibers are evenly dispersed. (2) Place a nylon filter membrane with a pore size of 0.45 μm and a diameter of 8 cm into a sand core filter, draw 30 mL of the nanocellulose suspension obtained in step (1) with a syringe, and filter to obtain a nanocellulose wet membrane; (3) placing the wet film obtained in the above step (2) in a vacuum drying oven at 80 °C for 12 h to obtain a nanocellulose film, and cutting the nanocellulose film into discs with a diameter of 17 mm; (4) Weigh 0.078 g of titanium dioxide particles with a particle size of 60 nm and add 0.09 g of polyvinylidene fluoride to 5 ml of N-methylpyrrolidone. Stir magnetically for 12 h. Place the stirred modified solution in an ultrasonic cleaner and ultrasonically disperse for 1 h until the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified solution is evenly dispersed. (5) Using a pipette, take 25 μL of the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified solution obtained in step (4) and drop it on the surface of the nanocellulose film with a diameter of 17 mm obtained in step (3), thereby obtaining a single-sided modified titanium dioxide / nanocellulose wet film; (6) placing the wet film obtained in the above step (5) in a vacuum drying oven at 60 °C for 12 h to obtain a single-sided modified titanium dioxide / nanocellulose film; (7) Using a pipette, take 25 μL of the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified solution obtained in step (4) and drop it on the other surface of the single-sided modified titanium dioxide / nanocellulose film obtained in step (6) to obtain a wet film; (8) The wet film obtained in the above step (7) was placed in a vacuum drying oven and dried at 60 °C for 12 h to obtain a titanium dioxide / nanocellulose composite separator. Comparative Example 1

[0021] The GF / D glass fiber diaphragm produced by Whatman was directly selected for performance comparison and testing.

[0022] The tensile strength test was performed on the zinc ion battery separators of Examples 1-4 and Comparative Example 1: A universal tensile testing machine was used to measure the tensile strength of the diaphragm. The diaphragm was cut into rectangular strips with a length of 20 mm and a width of 10 mm. The tensile rate was set at 5 mm / min. The experimental results are shown in Figure 1 And as shown in Table 1.

[0023] The ionic conductivity test was performed on the zinc ion battery separators of Examples 1-4 and Comparative Example 1: The steel sheet / diaphragm / steel sheet battery was assembled and the bulk resistance of the diaphragm was tested by an electrochemical workstation. The frequency was set to 0.01 Hz-0.1 MHz and the scan rate was 10 mV / s. The ionic conductivity of the diaphragm was calculated by the following formula: σ = L / AR Where L (cm) is the thickness of the diaphragm, A (cm 2 ) is the area of ​​the stainless steel electrode sheet, R (Ω) is the diaphragm resistance, and the experimental results are as follows Figure 2 And as shown in Table 1.

[0024] The rate performance test was performed on the zinc ion battery separator assembled symmetrical battery of Examples 1-4 and Comparative Example 1: The zinc / separator / zinc symmetric battery was assembled and the rate performance was tested using the Blue Battery Test System. The zinc / separator / zinc symmetric battery was tested at 0.2 mA cm -2 , 0.5 mA cm -2 , 1 mA cm -2 , 2 mA cm -2 and 5 mA cm -2 The test was carried out at a current density of 10 cycles per current density. The experimental results are shown in Figure 4 ~ 7 shown.

[0025] The physical properties of the zinc battery separator of the present invention are shown in Table 1 below:

[0026] Depend on Figure 1 ~ Figure 7 It can be concluded from Table 1 that the tensile strength and rate performance of the embodiment are better than those of the comparative example, and the ionic conductivity of embodiments 1 to 3 is greater than that of the comparative example.

[0027] In summary, the following conclusions can be drawn: the tensile strength and elongation at break of the titanium dioxide / nanocellulose composite zinc-ion battery separator obtained with titanium dioxide / polyvinylidene fluoride as coating modification material are significantly better than those of the glass fiber separator. The increase in tensile strength can effectively improve the rate performance of the titanium dioxide / nanocellulose composite zinc-ion battery separator, thereby improving the safety of the battery.

[0028] The above descriptions are merely embodiments of the present invention, and are not intended to limit the patent protection scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention's specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a high-strength titanium dioxide / nanocellulose composite zinc ion battery separator, characterized in that: The following steps are involved: (1) Mixing and dispersion: The nanocellulose suspension is diluted with water, and a uniform nanocellulose / water suspension is obtained after magnetic stirring and ultrasonic dispersion. (2) Wet film forming: the nanocellulose / water suspension obtained in step (1) is filtered to obtain a nanocellulose wet film; (3) Wet film drying: drying the nanocellulose wet film obtained in step (2) to obtain a nanocellulose film; (4) Preparation of modified liquid: titanium dioxide, polyvinylidene fluoride and N-methylpyrrolidone are mixed, and after magnetic stirring and ultrasonic dispersion, a uniform titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified liquid is obtained; (5) Single-sided drop coating of the modified liquid: the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified liquid obtained in step (4) is drop coated onto the surface of the nanocellulose diaphragm obtained in step (3) according to different mass ratios to obtain a single-sided modified wet film; (6) Drying the single-sided modified wet film: drying the wet film obtained in step (5) to obtain a single-sided modified composite diaphragm; (7) Double-sided drip coating of the modified liquid: drip coating the titanium dioxide / polyvinylidene fluoride / N-methylpyrrolidone modified liquid obtained in step (4) onto the other surface of the single-sided modified composite diaphragm obtained in step (6) to obtain a double-sided modified wet film; (8) Drying the double-sided modified wet film: The wet film obtained in step (7) is dried to obtain a titanium dioxide / nanocellulose composite membrane.

2. The preparation method according to claim 1, characterized in that: The mass ratio of titanium dioxide to nanocellulose in step (5) is 5% to 20%.

3. The preparation method according to claim 1, characterized in that: The diaphragm prepared by this method has a mechanical strength of 25 MPa ~ 33 MPa, an elongation at break of 11% ~ 12.8%, and an ionic conductivity of 2.1 mS / cm ~ 4.1 mS / cm.

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