Nanocellulose-based sodium-ion battery diaphragm as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of sodium-ion batteries, and discloses a nanocellulose-based sodium-ion battery diaphragm and a preparation method thereof. The preparation method of the nano-cellulose-based sodium-ion battery diaphragm comprises the following steps: uniformly dispersing halloysite particles in a nano-cellulose suspension to obtain a mixed solution, carrying out vacuum filtration on the mixed solution to obtain a nano-cellulose-based wet film, soaking the nano-cellulose-based wet film in an organic solvent for solvent replacement, and carrying out drying treatment to obtain the nano-cellulose-based sodium-ion battery diaphragm. The nanocellulose-based sodium-ion battery diaphragm is obtained. The invention also discloses an application of the nanocellulose-based sodium-ion battery diaphragm in preparation of a sodium-ion battery. The prepared nanocellulose-based sodium-ion battery diaphragm is high in porosity, capable of promoting rapid transportation of ions and good in thermal stability and mechanical performance, and the preparation method is simple, safe and environmentally friendly. The sodium-ion battery assembled by the nano-cellulose-based sodium-ion battery diaphragm prepared by the invention has excellent cycle performance and rate capability.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a nanocellulose-based sodium ion battery separator and a preparation method and application thereof. Background Art

[0002] As an important component of sodium-ion batteries, the diaphragm plays an important role in isolating the positive and negative electrodes of the battery and providing ion channels. Existing commercial polyolefin diaphragms, such as polyethylene and polypropylene diaphragms, have poor wettability to sodium-ion battery electrolytes and relatively insufficient thermal stability, and are not very suitable for the application scenarios of sodium-ion batteries. Although glass fiber diaphragms exhibit excellent electrolyte wettability and thermal stability, however, defects in mechanical properties limit their application potential in high-performance sodium-ion batteries, especially in the field of flexible batteries. Therefore, it is particularly important to design and develop a new diaphragm that can match the sodium-ion battery system.

[0003] Cellulose is the most abundant biomass material in nature. It has the advantages of high strength, biodegradability and renewability, and is widely used in the field of battery separators. Nanocellulose is a nanoscale product separated from cellulose. Its surface contains functional groups such as hydroxyl and carboxyl groups. However, there are strong hydrogen bonds between and within nanocellulose molecules, which has a negative impact on the porosity of the prepared nanocellulose-based sodium ion battery separator and easily leads to a decrease in ion transmission efficiency. Therefore, it is necessary to modify the cellulose-based separator to meet the needs of the development of sodium ion battery separators. Summary of the invention

[0004] In view of the problems and shortcomings in the prior art, the purpose of the present invention is to provide a nanocellulose-based sodium ion battery separator and a preparation method and application thereof.

[0005] Based on the above purpose, the present invention adopts the following technical solution:

[0006] The first aspect of the present invention provides a method for preparing a nanocellulose-based sodium ion battery separator, which specifically comprises the following steps:

[0007] 1) adding halloysite particles to the nanocellulose suspension, stirring and ultrasonically dispersing to obtain a mixed solution;

[0008] 2) vacuum filtering the mixed solution obtained in step 1) to obtain a nanocellulose-based wet membrane;

[0009] 3) The nanocellulose-based wet film obtained in step 2) is immersed in an organic solvent for solvent replacement and drying to obtain a nanocellulose-based sodium ion battery separator.

[0010] Preferably, in step 1), the mass ratio of the halloysite particles to the nanocellulose is (0.18-1.5):1.

[0011] Preferably, the mass fraction of the nanocellulose suspension in step 1) is 1% to 2%; more preferably, the mass fraction of the nanocellulose suspension is 1.53%.

[0012] Preferably, the organic solvent in step 3) is any one or more of methanol, ethanol or tert-butanol.

[0013] Preferably, the replacement time in step 3) is 8 to 24 hours.

[0014] Preferably, the replacement time in step 3) is 12 hours.

[0015] Preferably, the drying process in step 3) is freeze drying process or paper sheet forming machine drying process.

[0016] Preferably, the outer diameter of the halloysite particles in step 1) is 30-200 nm, and the length is 100 nm-30 um.

[0017] The second aspect of the present invention provides a nanocellulose-based sodium ion battery separator prepared by the method described in the first aspect.

[0018] The third aspect of the present invention provides the use of the nanocellulose-based sodium ion battery separator described in the second aspect in a sodium ion battery.

[0019] The fourth aspect of the present invention provides a sodium ion battery, wherein the sodium ion battery uses sodium vanadium phosphate as a positive electrode and is assembled with the nanocellulose-based sodium ion battery separator described in the second aspect above.

[0020] Preferably, the nanocellulose-based sodium ion battery separator has a diameter of 16 mm and is produced by punching.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The surface of nanocellulose is rich in hydroxyl groups and is a highly polar one-dimensional nanomaterial. After drying and dehydration, the strong hydrogen bonding between the hydroxyl groups on the fiber surface causes the nanocellulose to assemble and aggregate into micrometer-level. If it is to be dispersed into a nanofiber state again, it often needs to be treated by high-pressure shearing or high-intensity ultrasound. The present invention directly uses a nanocellulose suspension to prepare a nanocellulose-based sodium ion battery separator, and a nanocellulose suspension with a concentration of 1% to 2% has a high viscosity, which facilitates the dispersion of halloysite and reduces the deposition of halloysite.

[0023] (2) The nanocellulose-based sodium ion battery separator prepared by the present invention contains halloysite particles. The halloysite particles are unique micro-nano-sized hollow tubular structures with abundant specific surface area, which can increase the porosity of the separator. Moreover, the hydroxyl functional groups on the surface of the halloysite particles can enhance their affinity with polar electrolytes, thereby improving the wettability between the nanocellulose-based sodium ion battery separator and the electrolyte, and promoting rapid ion transport. At the same time, the nanocellulose-based sodium ion battery separator also has good thermal stability and mechanical properties.

[0024] (3) The sodium ion battery assembled from the nanocellulose-based sodium ion battery separator prepared by the present invention has excellent cycle performance and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The nanocellulose-based sodium ion battery separator obtained in Example 4;

[0026] Figure 2 This is a scanning electron microscope image of the nanocellulose-based sodium ion battery separator obtained in Example 4;

[0027] Figure 3 The cycle performance results of the button-type sodium ion half-cell assembled with the nanocellulose-based sodium ion battery separator obtained in Example 4, the button-type sodium ion half-cell assembled with the nanocellulose-based sodium ion battery separator obtained in Comparative Example 1, and the button-type sodium ion half-cell assembled with the commercial GF / A glass fiber separator at 1C are shown;

[0028] Figure 4 The figure shows the rate performance results of the button-type sodium-ion half-cell assembled with the nanocellulose-based sodium-ion battery separator obtained in Example 4, the button-type sodium-ion half-cell assembled with the nanocellulose-based sodium-ion battery separator obtained in Comparative Example 1, and the button-type sodium-ion half-cell assembled with the commercial GF / A glass fiber separator. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail by way of embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] Example 1

[0031] This embodiment provides a nanocellulose-based sodium ion battery separator and a preparation method thereof, wherein the steps are as follows:

[0032] (1) adding 36 mg of halloysite particles to 1.57 g of nanocellulose suspension (mass fraction 1.53%), adding an appropriate amount of deionized water thereto, and then stirring and ultrasonically treating the mixture to obtain a uniform mixed solution;

[0033] (2) vacuum filtering the obtained mixed solution to obtain a nanocellulose sodium ion battery-based wet membrane;

[0034] (3) Then, the nanocellulose-based wet film was immersed in tert-butyl alcohol for 12 hours to replace the moisture in the wet film; the replaced wet film was subjected to low-temperature freeze-drying (vacuum degree 0.02 mbar, cold trap temperature -55°C) to obtain a nanocellulose-based sodium ion battery separator.

[0035] Example 2

[0036] This embodiment provides a nanocellulose-based sodium ion battery separator and a preparation method thereof, wherein the preparation method is:

[0037] (1) adding 24 mg of halloysite particles to 3.66 g of nanocellulose suspension (mass fraction 1.53%), adding an appropriate amount of deionized water thereto, and then stirring and ultrasonically treating the mixture to obtain a uniform mixed solution;

[0038] (2) vacuum filtering the obtained mixed solution to obtain a nanocellulose-based sodium ion battery wet membrane;

[0039] (3) Then, the nanocellulose-based wet film is immersed in anhydrous ethanol for 12 hours to replace the moisture in the wet film; the replaced wet film is dried by a paper sheet forming machine (vacuum pressing force ~0.1Mpa, drying temperature 95°C) to obtain a nanocellulose-based sodium ion battery separator.

[0040] Example 3

[0041] This embodiment provides a nanocellulose-based sodium ion battery separator and a preparation method thereof, wherein the preparation method is:

[0042] (1) adding 45 mg of halloysite particles to 3.59 g of nanocellulose suspension (mass fraction 1.53%), adding an appropriate amount of deionized water thereto, and then stirring and ultrasonically treating the mixture to obtain a uniform mixed solution;

[0043] (2) vacuum filtering the obtained mixed solution to obtain a nanocellulose-based sodium ion battery wet membrane;

[0044] (3) Then, the nanocellulose-based wet film was immersed in methanol for 12 hours to replace the moisture in the wet film; the replaced wet film was dried by a paper sheet forming machine (vacuum pressing force ~0.1Mpa, drying temperature 95°C) to obtain a nanocellulose-based sodium ion battery separator.

[0045] Example 4

[0046] This embodiment provides a nanocellulose sodium ion battery-based diaphragm and a preparation method thereof, wherein the preparation method is:

[0047] (1) adding 36 mg of halloysite particles to 2.88 g of nanocellulose suspension (mass fraction 1.53%), adding an appropriate amount of deionized water thereto, and then stirring and ultrasonically treating the mixture to obtain a uniform mixed solution;

[0048] (2) vacuum filtering the obtained mixed solution to obtain a nanocellulose-based sodium ion battery wet membrane;

[0049] (3) Then, the nanocellulose-based wet film is immersed in anhydrous ethanol for 12 hours to replace the moisture in the wet film; the replaced wet film is dried by a paper sheet forming machine (vacuum pressing force ~0.1Mpa, drying temperature 95°C) to obtain a nanocellulose-based sodium ion battery separator.

[0050] The nanocellulose-based sodium ion battery separator Figure 1 .

[0051] The microscopic morphology of the nanocellulose-based sodium ion battery separator obtained in Example 4 was observed using a scanning electron microscope. Figure 2 .

[0052] Depend on Figure 2 It can be seen that the halloysite nanotube structures are scattered in the cellulose network of the nanocellulose-based sodium ion battery separator obtained in Example 4, which disrupts the original regular network structure of cellulose, thereby increasing the porosity of the separator and promoting the ion transport process.

[0053] Comparative Example 1

[0054] This comparative example provides a nanocellulose-based sodium ion battery separator and a preparation method thereof, wherein the preparation method is:

[0055] (1) Adding an appropriate amount of deionized water to 5.23 g of nanocellulose suspension (mass fraction 1.53%), stirring and ultrasonically treating to obtain a uniform mixed solution;

[0056] (2) vacuum filtering the obtained mixed solution to obtain a nanocellulose-based sodium ion battery wet membrane;

[0057] (3) Then, the nanocellulose-based wet film is immersed in anhydrous ethanol for 12 hours to replace the moisture in the wet film; the replaced wet film is dried by a paper sheet forming machine (vacuum pressing force ~0.1Mpa, drying temperature 95°C) to obtain a nanocellulose-based sodium ion battery separator.

[0058] Example 5 Assembly and performance verification of button-type sodium ion half-cell

[0059] The button-type sodium ion half-cell is composed of sodium vanadium phosphate as the positive electrode, sodium sheet as the negative electrode, and a separator. The battery specification is 2032.

[0060] The separators are respectively the nanocellulose-based sodium ion battery separator obtained in Example 4, the nanocellulose-based sodium ion battery separator obtained in Comparative Example 1, and a separator with a diameter of 16 mm cut from a commercial GF / A glass fiber separator purchased from Whatman.

[0061] The cycling performance and rate performance of the three button-type sodium ion half-cells were tested by detecting the discharge capacity of the three batteries at 1C (the theoretical specific capacity of sodium vanadium phosphate is 117.6 mAh / g) and the discharge capacity at different rates. The results are shown in Figure 3 and Figure 4 .

[0062] Cycle performance results such as Figure 3 As shown, it can be seen that the button-type sodium ion half-cell assembled with the nanocellulose-based sodium ion battery separator obtained in Example 4 has a maximum cycle number of 680 times, and the discharge specific capacity drops from the initial 105.7mAh / g to 101mAh / g, with only slight attenuation. The button-type sodium ion half-cell assembled with the nanocellulose-based sodium ion battery separator obtained in Comparative Example 1 could not continue the cycle test after 100 cycles. The button-type sodium ion half-cell assembled with the commercial GF / A glass fiber separator had a discharge specific capacity drop from the initial 102.6mAh / g to 88.2mAh / g after 550 cycles, after which the cycle experiment could not continue. The results show that the button-type sodium ion half-cell assembled with the nanocellulose-based sodium ion battery separator obtained in Example 4 exhibits excellent cycle performance.

[0063] The rate performance results are as follows Figure 4 As shown, it can be seen that under the condition of high rate 5C, the button-type sodium ion half-cell assembled by the nanocellulose-based sodium ion battery diaphragm obtained in Example 4 has a discharge specific capacity of 93.1 mAh / g; the button-type sodium ion half-cell assembled by the nanocellulose-based sodium ion battery diaphragm obtained in Comparative Example 1 has a discharge specific capacity of 18.6 mAh / g; the button-type sodium ion half-cell assembled by the commercial GF / A glass fiber diaphragm has a discharge specific capacity of 86.4 mAh / g.

[0064] The results show that the button-type sodium ion half-cell assembled with the nanocellulose-based sodium ion battery membrane obtained in Example 4 exhibits better rate performance, which fully demonstrates that the hydroxyl functional groups on the surface of the halloysite particles can enhance its affinity with the polar electrolyte, thereby improving the wettability between the nanocellulose-based sodium ion battery membrane and the electrolyte and promoting rapid ion transport.

[0065] The above is an explanation of the embodiments of the present invention. By describing the disclosed embodiments, professionals in the field can implement or use the present invention, but it is not used to limit the present invention. It is impossible to fully reflect the various contents involved in the present invention in the above embodiments. Any equivalent changes or modifications made by any professional familiar with this technology without departing from the spirit or scope of the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a nanocellulose-based sodium ion battery separator, characterized in that: The specific steps include: 1) adding halloysite particles to the nanocellulose suspension, stirring and ultrasonically dispersing to obtain a mixed solution; 2) vacuum filtering the mixed solution obtained in step 1) to obtain a nanocellulose-based wet membrane; 3) The nanocellulose-based wet film obtained in step 2) is immersed in an organic solvent for solvent replacement and drying to obtain a nanocellulose-based sodium ion battery separator.

2. The preparation method according to claim 1, characterized in that: The mass ratio of halloysite to nanocellulose in step 1) is (0.18-1.5):

1.

3. The preparation method according to claim 1, characterized in that: The mass fraction of the nanocellulose suspension in step 1) is 1% to 2%.

4. The preparation method according to claim 1, characterized in that: The organic solvent in step 3) is any one or more of methanol, ethanol or tert-butanol.

5. The preparation method according to claim 1, characterized in that: The replacement time in step 3) is 8 to 24 hours.

6. The preparation method according to claim 1, characterized in that: The drying process in step 3) is freeze drying or paper sheet forming machine drying.

7. The preparation method according to claim 1, characterized in that: The outer diameter of the halloysite particles in step 1) is 30-200 nm, and the length is 100 nm-30 um.

8. A nanocellulose-based sodium ion battery separator prepared by the method of any one of claims 1 to 7.

9. Use of the nanocellulose-based sodium ion battery separator according to claim 8 in sodium ion batteries.

10. A sodium ion battery, characterized in that: The sodium ion battery uses sodium vanadium phosphate as the positive electrode and is assembled with the nanocellulose-based sodium ion battery separator according to claim 8.

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