Aramid nanofiber / nanocellulose composite zinc-ion battery separator and its preparation method, zinc-ion battery

Abstract

This invention proposes an aramid nanofiber / nanocellulose composite zinc-ion battery separator and its preparation method, as well as a zinc-ion battery, belonging to the field of electrochemical energy storage technology. The preparation method includes the following steps: 1) mixing aramid nanofiber slurry, unsulfonated nanocellulose slurry, and sulfonated nanocellulose slurry, ultrasonically dispersing, and then vacuum filtering to obtain an aramid nanofiber / nanocellulose filter cake; 2) freezing the above aramid nanofiber / nanocellulose filter cake with liquid nitrogen and then drying it to obtain the aramid nanofiber / nanocellulose composite zinc-ion battery separator. The obtained zinc-ion battery separator is mainly used for preparing zinc-ion batteries. This method is simple to operate, low in cost, and the resulting zinc-ion battery has a long cycle life and excellent battery performance.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, and particularly relates to aramid nanofiber / nanocellulose composite zinc-ion battery separator and its preparation method, and zinc-ion battery. Background Technology

[0002] Zinc-ion batteries possess advantages such as high theoretical energy density, environmental friendliness, high safety, and low cost, demonstrating great potential in large-scale energy storage systems. However, zinc dendrite formation during operation is one of the causes of short circuits, and hydrogen evolution reactions and byproducts during cycling also lead to a decrease in battery capacity. Currently widely used glass fiber separators cannot effectively suppress dendrite growth, and they suffer from poor mechanical properties, uneven ion flux, and high production costs, failing to meet the needs of practical production and daily life. To address these issues, numerous researchers have optimized battery separators, but the processes are complex and costly; therefore, the fabrication of high-performance battery separators remains a significant challenge.

[0003] Aramid fiber, also known as polyphenylene phthalate, is one of the world's three major high-performance specialty fibers. Due to its high strength, high modulus, high temperature resistance, and good dimensional stability, it is widely used in various fields. Nanomaterials, due to their unique nano-effects and distinctive surface and interface properties, often exhibit physical or chemical properties not seen in conventional macroscopic materials during application. Therefore, they have found wide application in cutting-edge scientific research and industrial fields.

[0004] In recent years, aramid nanofibers (ANFs) have been widely used in supercapacitors, battery separator materials, and high-temperature resistant filter materials. They exhibit the characteristics of high modulus, high temperature resistance, and good dimensional stability of conventional-sized aramid fibers, and also have advantages such as large specific surface area, high aspect ratio, and small size. Their polar molecular structure is also considered to be beneficial for ion adsorption.

[0005] Cellulose, a large polysaccharide composed of glucose, is the most abundant and inexpensive natural polymer material, holding a leading position in the application of biomass separation materials. Cellulose possesses a large specific surface area and electrolyte affinity, facilitating electrolyte absorption and ion migration and desolvation, resulting in low interfacial resistance and high ion mobility. Furthermore, cellulose exhibits excellent thermal stability and dimensional stability at high temperatures, effectively preventing short circuits caused by direct contact between positive and negative electrodes due to separator damage under abnormal battery heating and high-temperature conditions, thus significantly improving battery safety. Due to these superior properties, cellulose has been widely applied in the research of high-performance battery separators.

[0006] Currently used zinc-ion battery separators are mainly made of glass fiber, which is expensive, prone to dendrite formation causing short circuits and other problems that damage the battery and lead to failure. Furthermore, its thickness is several times greater than that of commercial lithium-ion battery separators (approximately 25µm), resulting in increased ion transport distance and internal resistance, leading to poor cycle performance. Therefore, developing a zinc-ion battery separator with superior electrochemical performance and effective prevention of zinc dendrite formation is urgently needed. Summary of the Invention

[0007] This invention provides an aramid nanofiber / nanocellulose composite zinc-ion battery separator and its preparation method, as well as a zinc-ion battery, which can effectively improve the performance and lifespan of zinc-ion batteries.

[0008] This invention proposes a method for preparing a zinc-ion battery separator, comprising the following steps:

[0009] 1) Mix aramid nanofiber slurry, unsulfonated nanocellulose slurry, and sulfonated nanocellulose slurry, disperse by ultrasonication, and then filter by vacuum to obtain aramid nanofiber / nanocellulose filter cake.

[0010] 2) After freezing the above aramid nanofiber / nanocellulose filter cake with liquid nitrogen, it is dried to obtain an aramid nanofiber / nanocellulose composite zinc-ion battery separator.

[0011] Further, in step 1), the ratio of the oven-dry mass of each fiber after dehydration in the aramid nanofiber slurry, the unsulfonated nanocellulose slurry, and the sulfonated nanocellulose slurry is 1-2:1-9:1-5.

[0012] Preferably, the oven-dry mass ratio of aramid nanofiber slurry, unsulfonated nanocellulose, and sulfonated nanocellulose slurry is 1:2 to 6:1 to 4.

[0013] Furthermore, in step 1), the vacuum filtration time is 2 to 60 minutes; the vacuum filtration pressure is -0.08 to -0.3 MPa.

[0014] Preferably, the sizing agent obtained by mixing aramid nanofiber sizing agent, unsulfonated nanocellulose sizing agent, and sulfonated nanocellulose sizing agent has a total oven-dry fiber content of 10–150 g / m³ after dehydration. 2 Vacuum filtration is performed.

[0015] Further, in step 1), the aramid nanofiber slurry is prepared by the following steps:

[0016] Aramid fibers and water are mixed and pulped. The resulting pulped fibers are diluted with water and subjected to high-pressure homogenization to obtain aramid nanofiber slurry.

[0017] Preferably, the aramid fiber is a para-aramid short-cut fiber; the length of the aramid fiber is 1-6 mm.

[0018] Further, in step 1), the unsulfonated nanocellulose slurry is prepared by the following steps: mixing unsulfonated cellulose with water, performing a pulping process, diluting the resulting pulped fiber with water, and then performing a high-pressure homogenization process to obtain the unsulfonated nanocellulose slurry.

[0019] Further, in step 1), the sulfonated nanocellulose is prepared by the following steps: drying and dehydrating the unsulfonated nanocellulose slurry, adding sulfuric acid solution, stirring, adjusting the pH to neutral, washing and drying to obtain acid-treated nanocellulose;

[0020] The acid-treated nanocellulose was added to N,N-dimethylformamide and reacted. Then, sulfur trioxide-pyridine complex was added, stirred, and the pH was adjusted to neutral. After washing and drying, sulfonated nanocellulose was obtained.

[0021] Preferably, the dry weight ratio of unsulfonated nanocellulose to sulfuric acid solution is 1-2 g: 5-20 ml;

[0022] More preferably, the ratio of acid-treated nanocellulose, N,N-dimethylformamide, and sulfur trioxide-pyridine complex is 1-2 g: 10-30 ml: 1.71-12 g.

[0023] Further, in step 1), the sulfonated nanocellulose slurry is prepared by the following steps: mixing sulfonated nanocellulose with water, performing a pulping process, diluting with water, and then performing a high-pressure homogenization process to obtain the sulfonated nanocellulose slurry.

[0024] Furthermore, in step 2), the liquid nitrogen freezing adopts copper plate thermal conductivity unidirectional freezing technology, the freezing temperature is -130 to -200℃, and the freezing time is 2 to 10 minutes;

[0025] Preferably, in step 2), the drying is vacuum freeze drying; the temperature of the vacuum freeze drying is -40 to -60°C, and the vacuum freeze drying time is 24 to 48 hours.

[0026] The present invention also proposes zinc-ion battery separators prepared by any of the above-described preparation methods.

[0027] The present invention also proposes a zinc-ion battery, wherein the zinc-ion battery includes any of the zinc-ion battery separators described above.

[0028] This invention has the following advantages:

[0029] This invention proposes a method for preparing an aramid nanofiber / nanocellulose composite zinc-ion battery separator. By adjusting the mixing ratio of aramid nanofiber slurry, unsulfonated nanocellulose slurry, and sulfonated nanocellulose slurry, the hydrophilicity / hydrophobicity of the aramid nanofiber / nanocellulose composite zinc-ion battery separator is controlled, thereby improving battery cycle performance. Adjusting the vacuum filtration conditions controls the total content of oven-dried fibers to a suitable range, avoiding poor separator performance due to excessively thin or thick separators. The obtained aramid nanofiber / nanocellulose filter cake is then frozen in liquid nitrogen under specific conditions to ensure uniform pore size. Subsequent vacuum drying prevents reduced ion mobility and zinc dendrite growth caused by decreased porosity, ultimately yielding the aramid nanofiber / nanocellulose composite zinc-ion battery separator. This method is simple to operate, low in cost, and produces zinc-ion batteries with long cycle life and excellent performance. Attached Figure Description

[0030] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0031] Figure 1 This is a scanning electron microscope (SEM) image of the aramid nanofiber / nanocellulose composite zinc-ion battery separator prepared in Example 1 of the present invention.

[0032] Figure 2 The image shows the physical sample and thickness of the aramid nanofiber / nanocellulose composite zinc-ion battery separator prepared in Example 1 of this invention.

[0033] Figure 3 The contact angle diagram is shown for the aramid nanofiber / nanocellulose composite zinc-ion battery separator prepared in Example 1 of this invention. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0035] On one hand, embodiments of the present invention propose a method for preparing an aramid nanofiber / nanocellulose composite zinc-ion battery separator, comprising the following steps:

[0036] 1) Mix aramid nanofiber slurry, unsulfonated nanocellulose slurry, and sulfonated nanocellulose slurry, disperse by ultrasonication, and then filter by vacuum to obtain aramid nanofiber / nanocellulose filter cake.

[0037] 2) After freezing the above aramid nanofiber / nanocellulose filter cake with liquid nitrogen, it is dried to obtain an aramid nanofiber / nanocellulose composite zinc-ion battery separator.

[0038] In this embodiment of the invention, the combined action of aramid nanofibers, sulfonated cellulose nanofibers, unsulfonated cellulose nanofibers, polar hydrophobic aramid nanofibers, and hydrophilic cellulose nanofibers rich in hydroxyl and sulfonic acid groups, with varying affinity for aqueous zinc ion electrolytes, is beneficial for optimizing the zinc ion solubilization shell. This reduces hydrogen evolution reaction and byproduct formation, and also facilitates zinc ion deposition onto a plane. Planar deposition reduces zinc dendrite formation, thereby extending battery life. Simultaneously, by adjusting the raw material ratio in the zinc ion battery separator, the hydrophobicity of the aramid nanofiber / cellulose nanofiber composite zinc ion battery separator is adjusted, thereby improving battery cycle performance. Furthermore, polar groups such as sulfonic acid groups promote uniform zinc ion deposition, thus extending battery life, and the application of sulfonated cellulose nanofibers effectively improves battery performance and reduces battery polarization. Furthermore, the obtained aramid nanofiber / nanocellulose filter cake is frozen with liquid nitrogen, avoiding the disordered growth of ice crystals caused by conventional freezing methods. Disordered ice crystal growth easily leads to uneven pore size and distribution. Vacuum freeze-drying effectively preserves the membrane's porosity, avoiding the porosity reduction caused by room temperature and heating drying. Reduced porosity easily leads to decreased ion mobility, resulting in zinc dendrite growth. This method is simple to operate, low in cost, and environmentally friendly, effectively solving the problems of high cost, complex processes, poor battery performance, and short lifespan associated with other types of battery separators used in zinc-ion batteries.

[0039] In one embodiment of the present invention, in step 1), the oven-dry mass ratio of each fiber in the aramid nanofiber slurry, the unsulfonated nanocellulose slurry, and the sulfonated nanocellulose slurry after dehydration is 1–2:1–9:1–5. Preferably, in step 1), the oven-dry mass ratio of the aramid nanofiber slurry, the unsulfonated nanocellulose slurry, and the sulfonated nanocellulose slurry is 1:2–6:1–4. It should be noted that the oven-dry mass mentioned in the present invention refers to the mass obtained after the slurry is dried and dehydrated.

[0040] In this invention, aramid nanofibers, unsulfonated nanocellulose, and sulfonated nanocellulose are combined to improve the problem of excessive hydrophilicity causing difficulty in zinc ion desolvation and dendrite formation in the separator, and excessive hydrophobicity causing the hydrated solvated shell of zinc ions to easily reach the negative electrode surface, forming by-products and hydrogen gas, leading to battery failure. By cleverly utilizing the hydrophilicity and hydrophobicity of each material and adjusting the mass ratio, the aramid nanofiber / nanocellulose composite zinc-ion battery separator achieves the optimal range of hydrophilic and hydrophobic properties. During battery operation, it effectively accelerates zinc ion desolvation and deposition, separates the positive and negative electrodes, delays short circuits caused by dendrite growth, and reduces the formation of by-products and hydrogen evolution reactions, thus giving the battery excellent performance. When hydrophilicity increases beyond this range, zinc dendrite growth is rapid during battery operation; when hydrophobicity increases beyond this range, hydrogen evolution reaction is accelerated, by-products are formed, and the battery's range is less than 300 cycles, resulting in poor performance.

[0041] In one embodiment of the present invention, in step 1), the vacuum filtration time is 2 to 60 minutes; preferably, the vacuum filtration time is 2 minutes.

[0042] In one embodiment of the present invention, in step 1), the pressure of vacuum filtration is -0.08 to -0.3 MPa.

[0043] In one embodiment of the present invention, in step 1), the slurry obtained by mixing aramid nanofiber slurry, unsulfonated nanocellulose slurry, and sulfonated nanocellulose slurry is such that the total oven-dry fiber content of each fiber after dehydration is 10-150 g / m³. 2 Vacuum filtration is performed. In this embodiment of the invention, when the total content of oven-dry fibers is less than 10 g / m³... 2 When the total dry fiber content exceeds 150g / m³, the battery cannot complete the charge-discharge cycle and does not meet the usage requirements. 2 As the battery thickness increases, the ion transport distance increases, causing uneven ion deposition and the formation of dendrites. This can lead to a short circuit in the battery within a very short time, rendering it unusable.

[0044] In one embodiment of the present invention, in step 1), the aramid nanofiber slurry is prepared by the following steps:

[0045] Aramid fibers and water are mixed and pulped. The resulting pulped fibers are diluted with water and subjected to high-pressure homogenization to obtain aramid nanofiber slurry.

[0046] Preferably, the mass ratio of aramid fiber to water is 1:9; the mass ratio of fiber to water in the pulping treatment is 1:19.

[0047] In a preferred embodiment of the present invention, the aramid fiber is a para-aramid short-cut fiber; the length of the aramid fiber is 1-6 mm.

[0048] Preferably, during the pulping process, the total number of revolutions in the pulping process is 20,000 to 100,000 r.

[0049] Preferably, the pressure of the high-pressure homogenization process is 50-120 MPa, and the number of high-pressure homogenization processes is 20-100.

[0050] Preferably, in the obtained aramid nanofiber slurry, the average diameter of the aramid nanofibers is 50-300 nm, and the aspect ratio of the aramid nanofibers is 100-600.

[0051] In this embodiment of the invention, aramid nanofibers can be uniformly dispersed in water to form a uniform aramid nanofiber slurry, and can be uniformly blended with nanocellulose slurry, thus improving the previous problem that aramid nanofibers are not easy to be uniformly blended with other fibers in water.

[0052] In one embodiment of the present invention, in step 1), the unsulfonated nanocellulose slurry is prepared by the following steps:

[0053] Unsulfonated cellulose is mixed with water and then pulped. The resulting pulped fiber is diluted with water and subjected to high-pressure homogenization to obtain unsulfonated nanocellulose slurry.

[0054] Preferably, the mass ratio of unsulfonated cellulose to water is 1:9; the mass ratio of pulping fiber to water is 1:9.

[0055] Preferably, during the pulping process, the total number of revolutions in the pulping process is 5000 to 10000 r.

[0056] Preferably, the pressure of the high-pressure homogenization process is 50-70 MPa, and the number of high-pressure homogenization processes is 10-20.

[0057] The unsulfonated nanocellulose slurry obtained by this invention has an average diameter of 50-1000 nm and a length of 100-1000 μm.

[0058] It should be noted that the unsulfonated nanocellulose and the sulfonated nanocellulose used in the embodiments of the present invention have a molecular weight of approximately 80,000 to 130,000.

[0059] In one embodiment of the present invention, in step 1), the sulfonated nanocellulose is prepared by the following steps:

[0060] The unsulfonated nanocellulose slurry was dried and dehydrated, then sulfuric acid solution was added, stirred, and the pH was adjusted to neutral. After washing and drying, acid-treated nanocellulose was obtained.

[0061] The acid-treated nanocellulose was added to N,N-dimethylformamide and reacted. Then, sulfur trioxide-pyridine complex was added, stirred, and the pH was adjusted to neutral. After washing and drying, sulfonated nanocellulose was obtained.

[0062] In this embodiment of the invention, polar groups such as sulfonic acid groups are beneficial to the uniform sedimentation of zinc ions, thereby extending the battery's lifespan. Furthermore, the application of sulfonated nanocellulose can effectively improve battery performance and reduce battery polarization.

[0063] Preferably, the sulfuric acid solution has a mass fraction of 30-50%, and the dry mass ratio of the unsulfonated nanocellulose to the sulfuric acid solution is 1-2 g: 5-20 ml.

[0064] Preferably, sodium hydroxide is used to adjust the pH to neutral.

[0065] Preferably, the ratio of acid-treated nanocellulose, N,N-dimethylformamide, and sulfur trioxide-pyridine complex is 1-2 g: 10-30 ml: 1.71-12 g; more preferably, the ratio of acid-treated nanocellulose, N,N-dimethylformamide, and sulfur trioxide-pyridine complex is 1.63 g: 25 ml: 1.71-12 g.

[0066] The degree of sulfonic acid substitution on the sulfonated nanocellulose obtained in the embodiments of the present invention is 0.6-2 mmol / g.

[0067] In one embodiment of the present invention, in step 1), the sulfonated nanocellulose slurry is prepared by the following steps:

[0068] Sulfonated nanocellulose is mixed with water and then pulped. The resulting pulped fiber is diluted with water and subjected to high-pressure homogenization to obtain sulfonated nanocellulose slurry.

[0069] Preferably, the mass ratio of sulfonated cellulose to water is 1:9; the mass ratio of pulping fiber to water is 1:9.

[0070] Preferably, during the pulping process, the total number of revolutions in the pulping process is 5000 to 10000 r.

[0071] Preferably, the pressure of the high-pressure homogenization process is 50-70 MPa, and the number of high-pressure homogenization processes is 10-20.

[0072] Preferably, the sulfonated nanocellulose slurry has an average diameter of 50-1000 nm and a length of 100-1000 μm.

[0073] In one embodiment of the present invention, in step 2), the liquid nitrogen freezing adopts copper plate thermal conductivity unidirectional freezing technology, the freezing temperature is -130 to -200°C, and the freezing time is 2 to 10 minutes.

[0074] In this embodiment of the invention, the liquid nitrogen freezing used is a copper plate thermally conductive unidirectional freezing technology, which can effectively preserve the uniform pore size and distribution of the diaphragm before freezing, avoiding the disordered growth of ice crystals caused by conventional freezing methods. The disordered growth of ice crystals can easily cause uneven pore size and uneven distribution.

[0075] In one embodiment of the present invention, in step 2), the drying is vacuum freeze drying; the temperature of the vacuum freeze drying is -40 to -60°C, and the vacuum freeze drying time is 24 to 48 hours.

[0076] In this embodiment of the invention, the vacuum freeze-drying method can effectively preserve the porosity of the membrane, avoiding the porosity reduction problem caused by room temperature and heating drying. The reduction in porosity can easily lead to a decrease in ion mobility, thereby causing zinc dendrite growth.

[0077] On the other hand, embodiments of the present invention also propose an aramid nanofiber / nanocellulose composite zinc-ion battery separator prepared using any of the above preparation methods.

[0078] In another aspect, embodiments of the present invention also propose a zinc-ion battery, wherein the zinc-ion battery comprises any of the aforementioned aramid nanofiber / nanocellulose composite zinc-ion battery separators. The zinc-ion symmetric battery based on the aramid nanofiber / nanocellulose composite zinc-ion battery separator of the present invention exhibits a low electrochemical impedance value (100–300 Ω), a high corrosion resistance voltage (-0.0225–-0.015 V), and a short three-dimensional uniform zinc deposition transition time. Simultaneously, the symmetric battery cycle time exceeds 3500 hours, the total cell cycle count exceeds 1000 cycles, and the battery capacity retention rate is greater than 80%, demonstrating excellent electrochemical performance.

[0079] The present invention will now be described in detail with reference to the accompanying drawings.

[0080] Example 1 A method for preparing an aramid nanofiber / nanocellulose composite zinc-ion battery separator includes:

[0081] a) Preparation of aramid nanofiber / nanocellulose filter cake

[0082] a1) Preparation of aramid nanofiber slurry

[0083] Aramid fibers (3 mm in length) and water were mixed at a mass ratio of 1:9 and then ground in a refiner at a total speed of 50,000 rpm. The mixture was then diluted with water at a mass ratio of 1:19 and subjected to high-pressure homogenization. The homogenizer was set to a discharge pressure of 120 MPa and the homogenization cycle was 50 times to obtain an aramid nanofiber slurry. The diameter of the aramid nanofibers in the obtained aramid nanofiber slurry ranged from 50 to 300 nm, and the aspect ratio was 100-600.

[0084] a2) Preparation of unsulfonated nanocellulose slurry

[0085] Unsulfonated cellulose and water were mixed at a ratio of 1:9 and then subjected to a pulping process with a total of 7000 revolutions. Subsequently, water was added at a fiber-to-water mass ratio of 1:9 and the mixture was subjected to high-pressure homogenization at a pressure of 55 MPa for 20 cycles to obtain an unsulfonated nanocellulose slurry. The diameter of the unsulfonated nanocellulose was found to be in the range of 50–1000 nm, and the length of the nanocellulose was found to be in the range of 100–1000 μm.

[0086] a3) Preparation of sulfonated nanocellulose and sulfonated nanocellulose slurry

[0087] 1.63 g of unsulfonated nanocellulose slurry was weighed and dried. After dehydration, 16.3 ml of 40% sulfuric acid solution was added and stirred for 5 h. The solution was then adjusted to neutral with sodium hydroxide, washed, and dried again. 25 ml of N,N-dimethylformamide was added and stirred at 40 °C for 0.5 h. 1.71 g of sulfur trioxide-pyridine complex was added and stirred for 4 h. Subsequently, the solution was adjusted to neutral with sodium hydroxide, washed three times with anhydrous ethanol, and then vacuum dried to obtain sulfonated nanocellulose. The diameter of the sulfonated nanocellulose ranged from 50 to 1000 nm, and the length ranged from 100 to 1000 μm.

[0088] Sulfonated nanocellulose was mixed with water at a mass ratio of 1:9 and then subjected to a pulping process. The total number of pulping revolutions was 7000 revolutions. After the pulping process, the fiber and water were diluted with water at a mass ratio of 1:9 and subjected to high-pressure homogenization at a pressure of 55 MPa for 20 cycles to obtain sulfonated nanocellulose slurry.

[0089] a4) Preparation of aramid nanofiber / nanocellulose filter cake

[0090] According to the absolute dry mass ratio of aramid nanofiber slurry, unsulfonated nanocellulose slurry, and sulfonated nanocellulose slurry being 1:2:2, mix the aramid nanofiber slurry obtained in step a1), the unsulfonated nanocellulose slurry obtained in step a2), and the sulfonated nanocellulose slurry obtained in step a2). After ultrasonic dispersion, for the slurry obtained by mixing the aramid nanofiber slurry, unsulfonated nanocellulose slurry, and sulfonated nanocellulose slurry, according to the total absolute dry fiber content after dehydration of each fiber being 80 g / m 2 Perform vacuum filtration for 2 minutes at a vacuum filtration pressure of -0.08 MPa to obtain an aramid nanofiber / nanocellulose filter cake;

[0091] b) Freeze the aramid nanofiber / nanocellulose filter cake with liquid nitrogen (using the copper plate heat conduction unidirectional freezing technique, the freezing temperature is -196°C, and the freezing time is 3 minutes), and then place it in a freeze dryer for vacuum freeze drying (the temperature is -55°C, and the time is 24 hours) to obtain an aramid nanofiber / nanocellulose composite zinc ion battery separator.[[ID=⑥]] [[ID=⑦]]

[0092] [[ID=⑧]]The scanning electron microscope image of the obtained aramid nanofiber / nanocellulose composite zinc ion battery separator is as[[ID=⑨]] Figure 1 [[ID=⑩]]shown, and the physical object and thickness diagram are as[[ID=⑪]] Figure 2 [[ID=⑫]]shown. The thickness is 0.341 μm. From[[ID=⑬]] Figure 1 [[ID=⑭]]and[[ID=⑮]] Figure 2 [[ID=⑯]]it can be seen that the surface of the separator obtained in this invention is smoother and the thickness is lower. The smooth surface is conducive to reducing dendrite growth, and the reduction in thickness is conducive to reducing the battery volume and increasing the energy density.[[ID=⑰]] [[ID=⑱]]

[0093] [[ID=⑲]] Example 2 [[ID=⑳]] [[ID=㉑]]

[0094] [[ID=㉒]]Same as Example 1, the difference is that: in step a4), mix according to the absolute dry mass ratio of aramid nanofiber:nanocellulose:sulfonated nanocellulose being 1:3:1. [[ID=㉓]] [[ID=㉔]]

[0095] [[ID=㉕]] Example 3 [[ID=㉖]] [[ID=㉗]]

[0096] [[ID=㉘]]Same as Example 1, the difference is that: in step a4), mix according to the absolute dry mass ratio of aramid nanofiber:nanocellulose:sulfonated nanocellulose being 1:3:2.[[ID=㉙]] [[ID=㉚]]

[0097] [[ID=㉛]] Comparative Example 1 [[ID=㉜]] [[ID=㉝]]

[0098] [[ID=㉞]]Same as Example 1, the difference is that: in step a1), the aramid fiber is not treated.[[ID=㉟]] [[ID=㊱]]

[0099] [[ID=㊲]] Comparative Example 2 [[ID=㊳]]A method for preparing a zinc ion battery separator without adding nanocellulose specifically includes:[[ID=㊴]] [[ID=㊵]]

[0100] Aramid fibers (3 mm in length) were mixed with water and placed in a refiner for refining. The total refining speed was 50,000 rpm. Then, water was added to dilute the slurry and high-pressure homogenization was performed. The slurry was placed in a high-pressure homogenizer with an output pressure of 120 MPa and a cycle of 50 times to obtain aramid nanofiber slurry.

[0101] After determining the moisture content of the aramid nanofiber slurry, the oven-dry fiber content was set at 80 g / m³. 2 Vacuum filtration was performed for 3 minutes, followed by freezing with liquid nitrogen for 3 minutes. The mixture was then placed in a freeze dryer for vacuum freeze drying for 24 hours to obtain an aramid nanofiber zinc-ion battery separator.

[0102] Comparative Example 3

[0103] Same as Example 1, except that in step a4), the aramid nanofiber / nanocellulose mixed slurry is prepared with a total oven-dry fiber content of 240 g / m³ after dehydration of each fiber. 2 Perform vacuum filtration.

[0104] Comparative Example 4

[0105] Same as Example 1, except that in step b), the vacuum freeze-drying time is 2 hours.

[0106] Comparative Example 5

[0107] Same as Example 1, except that step a4) is to blend aramid nanofiber slurry, unsulfonated nanocellulose slurry, and sulfonated nanocellulose slurry in an oven-dry mass ratio of 3:1:1.

[0108] Comparative Example 6

[0109] Same as Example 1, except that: sulfonated nanocellulose was not added to the diaphragm in step a4), resulting in an aramid nanofiber / nanocellulose mixed slurry.

[0110] Experimental Example 1 Battery separator performance test

[0111] The battery separators obtained in the examples and comparative examples were subjected to contact angle tests, symmetrical battery cycle performance tests, impedance performance tests, and full battery cycle performance tests, as detailed below:

[0112] 1) Contact angle test

[0113] A drop of 2M zinc sulfate solution was added to the surface of the obtained battery separator, and the contact angle of the droplet was observed using a contact angle meter. The results are shown in Table 1.

[0114] 2) Symmetrical battery cycle performance test and impedance performance test

[0115] The obtained battery separator was cut into 32mm diameter discs. 50µL of 2M zinc sulfate electrolyte was added to each disc. These discs were then assembled with the battery casing, two zinc plates as positive and negative electrodes, a stainless steel gasket, and a stainless steel spring to form a zinc-ion symmetric battery. Subsequently, a 1mA / cm test was performed using a battery testing system. 2 Current density and 1mAh / cm 2 The cycle performance of the symmetric cell with unit areal capacity was characterized by impedance characterization in an electrochemical workstation, and the results are shown in Table 2.

[0116] 3) Full battery cycle performance test

[0117] The obtained battery separator was cut into 32mm diameter discs. 50µL of 2M zinc sulfate electrolyte was added to each disc. These discs were then assembled with the battery casing, a zinc sheet (as the negative electrode), carbon cloth containing 1mg of vanadium pentoxide (as the positive electrode), a stainless steel gasket, and a stainless steel spring to form a zinc-ion full cell. The full cell cycle performance was then characterized using a battery testing system, and the results are shown in Table 3.

[0118] The contact angle of the battery separator obtained in Example 1 is as follows: Figure 3 As shown, a contact angle of 40–70° is beneficial for improving battery performance.

[0119] As shown in Tables 1-3, the zinc-ion symmetric battery assembled with the battery separator obtained in Example 1 can achieve a speed of 1 mA / cm². 2 Current density and 1mAh / cm 2 With a unit area capacity, it can stably cycle for more than 3,500 hours and the full battery can stably cycle for more than 2,000 times, demonstrating excellent performance.

[0120] In Comparative Example 1, the aramid fibers were not nano-sized. The large size of the fibers caused uneven ion distribution and made it easy to form dendrites. As a result, the symmetrical battery assembled with the resulting separator had poor cycle performance and short circuit occurred after 170 hours.

[0121] In Comparative Example 2, without the addition of nanocellulose, the hydrophobicity of the membrane increased, resulting in severe hydrogen evolution. The symmetrical battery assembled with the obtained membrane short-circuited after 100 hours of cycling.

[0122] In Comparative Example 3, the high content of oven-dry fibers affected the battery performance. The ion transport path increased, and zinc ions moved along a single path to form dendrites. The symmetrical battery assembled with this separator short-circuited after 5 hours of cycling.

[0123] In Comparative Example 4, the reduced freeze-drying time resulted in incomplete removal of moisture from the membrane, making it impossible to prepare the membrane.

[0124] In Comparative Example 5, aramid nanofibers, unsulfonated nanocellulose, and sulfonated nanocellulose were blended at an oven-dry mass ratio of 3:1:1. The increased hydrophobicity of the separator led to severe hydrogen evolution, and the zinc-ion symmetric battery assembled using this separator short-circuited after 200 hours of cycling.

[0125] In Comparative Example 6, due to the absence of sulfonated nanocellulose, hydrogen gas was released and byproducts were generated. The zinc-ion symmetric battery assembled using this membrane short-circuited after 125 hours of cycling.

[0126] Table 1

[0127] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Contact angle (°) 63.3 59.7 58.5 59.3 75.2 64.8 none 73.5 73..2

[0128] Table 2

[0129] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Cycle time (h) 3500 1500 1600 170 100 5 none 200 125 Impedance (Ω) 250 270 200 243 450 1500 none 600 750

[0130] Table 3

[0131] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Number of cycles 2000 2000 2000 200 150 120 none 30 70

[0132] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an aramid nanofiber / nanocellulose composite zinc-ion battery separator, characterized in that, Includes the following steps: 1) Mix aramid nanofiber slurry, unsulfonated nanocellulose slurry, and sulfonated nanocellulose slurry, disperse by ultrasonication, and then filter by vacuum to obtain aramid nanofiber / nanocellulose filter cake. In the aramid nanofiber slurry, the diameter of the aramid nanofibers ranges from 50 to 300 nm, and the aspect ratio of the aramid nanofibers is 100-600. The oven-dry mass ratio of each fiber after dehydration in the aramid nanofiber slurry, the unsulfonated nanocellulose slurry, and the sulfonated nanocellulose slurry is 1-2:1-9:1-5. The slurry obtained by mixing the aramid nanofiber slurry, the unsulfonated nanocellulose slurry, and the sulfonated nanocellulose slurry has an oven-dry fiber content of 10-150 g / m³. 2 Perform vacuum filtration; 2) After freezing the above aramid nanofiber / nanocellulose filter cake with liquid nitrogen, it was then freeze-dried under vacuum to obtain an aramid nanofiber / nanocellulose composite zinc-ion battery separator.

2. The preparation method according to claim 1, characterized in that, In step 1), the ratio of the oven-dry mass of each fiber after dehydration in the aramid nanofiber slurry, the unsulfonated nanocellulose slurry, and the sulfonated nanocellulose slurry is 1:2~6:1~4.

3. The preparation method according to claim 1, characterized in that, In step 1), the vacuum filtration time is 2~60 min; the vacuum filtration pressure is -0.08~-0.3MPa.

4. The preparation method according to claim 1, characterized in that, In step 1), the aramid nanofiber slurry is prepared by the following steps: Aramid fibers and water are mixed and pulped. The resulting pulped fibers are diluted with water and subjected to high-pressure homogenization to obtain aramid nanofiber slurry.

5. The preparation method according to claim 1, characterized in that, In step 1), the unsulfonated nanocellulose slurry is prepared by the following steps: mixing unsulfonated cellulose with water, performing a pulping process, diluting the resulting pulped fiber with water, and then performing a high-pressure homogenization process to obtain the unsulfonated nanocellulose slurry.

6. The preparation method according to claim 1, characterized in that, In step 1), the sulfonated nanocellulose is prepared by the following steps: drying and dehydrating unsulfonated nanocellulose slurry, adding sulfuric acid solution, stirring, adjusting the pH to neutral, washing and drying to obtain acid-treated nanocellulose; The acid-treated nanocellulose was added to N,N-dimethylformamide and reacted. Then, sulfur trioxide-pyridine complex was added, stirred, and the pH was adjusted to neutral. After washing and drying, sulfonated nanocellulose was obtained.

7. The preparation method according to claim 6, characterized in that, In step 1), the dry weight ratio of unsulfonated nanocellulose to sulfuric acid solution is 1~2g:5~20ml; The ratio of acid-treated nanocellulose, N,N-dimethylformamide, and sulfur trioxide-pyridine complex is 1~2 g: 10~30 ml: 1.71~12 g.

8. The preparation method according to claim 1, characterized in that, In step 1), the sulfonated nanocellulose slurry is prepared by the following steps: mixing sulfonated nanocellulose with water, grinding the mixture, diluting it with water, and then homogenizing it under high pressure to obtain the sulfonated nanocellulose slurry.

9. The preparation method according to claim 1, characterized in that, In step 2), the liquid nitrogen freezing adopts copper plate thermal conductivity unidirectional freezing technology, the freezing temperature is -130~-200℃, and the freezing time is 2~10min.

10. The preparation method according to claim 1, characterized in that, In step 2), the temperature of the vacuum freeze-drying is -40 to -60°C, and the vacuum freeze-drying time is 24 to 48 hours.

11. The zinc-ion battery separator prepared by the preparation method according to any one of claims 1 to 10.

12. A zinc-ion battery, the zinc-ion battery comprising the zinc-ion battery separator of claim 11.

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