A method for producing a low basis weight high density fibrous material

Abstract

The application discloses a kind of low basis weight high-density fiber material preparation methods, the fiber material includes fiber layer and hot melt powder layer;The fiber layer is filled with superfine powder;Including the following steps: (1) polyvinyl alcohol ultra-short fiber, polyester superfine ultra-short fiber, fine denier ultra-short cellulose fiber are made into mixed slurry, then wet-laid web is made;(2) the wet-laid web is consolidated into intermediate material, then the intermediate material hot water bath is made, and polyvinyl alcohol ultra-short fiber is dissolved;(3) superfine powder is made into suspension, and filled into intermediate material;(4) hot melt powder is made into suspension slurry and coated and fixed.Reduce the unit area mass of material, increase the density of material under low basis weight, utilize the thermal closing pore effect of superfine powder, ensure the safety of battery separator product.Realize the technical requirement of low basis weight, high density and high porosity, solve the problem that existing fiber material cannot meet the use requirement of battery separator.

Description

Technical Field

[0001] This invention belongs to the field of nonwoven materials technology, and particularly relates to a method for preparing low-weight, high-density fiber materials. Background Technology

[0002] In recent years, the rapid development of the new energy vehicle industry has driven the high-speed growth of the battery separator field. Currently, most power battery separator materials are non-renewable polyolefin materials. The initial investment cost for producing these materials is high, and the battery's performance and safety are also affected by the poor wettability and thermal dimensional stability of these materials. Therefore, finding a solution to address the wettability and thermal dimensional stability issues of polyolefin materials has become an important topic in this field.

[0003] Currently, battery separators prepared by wet papermaking are widely used in alkaline manganese, nickel-metal hydride, and lead-acid batteries. However, the thickness of the separator is generally above 100 micrometers, which is much higher than the thickness of less than 40 micrometers required for power lithium batteries. Therefore, the key to restricting the further application and expansion of wet papermaking and similar processes in the field of battery separators is how to reduce the thickness of the material and how to achieve better tensile strength and air permeability at a low thickness.

[0004] Chinese patent document CN108933217A discloses a method for preparing an ultra-fine polyester fiber nonwoven lithium-ion battery separator. The separator is prepared by wet nonwoven technology using ultra-fine ultra-short polyester fibers, with a thickness between 20-50 μm and an areal density between 10-35 g / m³. 2 The preparation process involves dispersing ultra-fine, short polyester fibers in water containing a fiber dispersant to form a fiber dispersion slurry. Then, using a wet nonwoven fabric manufacturing device similar to a paper machine, the nonwoven lithium-ion battery separator is produced through a series of processes including filtration, papermaking, dehydration, drying, and hot rolling. Compared with conventional polyolefin microporous membrane lithium-ion battery separators, this separator has higher temperature resistance and higher porosity, can provide greater liquid absorption and lower resistance, and can give the battery better electrical and safety performance.

[0005] However, the ultra-fine, short polyester fibers used in this material cannot provide good strength, and it does not have the function of automatically cutting off the current when the battery heats up, thus lacking sufficient safety. Summary of the Invention

[0006] To overcome the technical problems of excessive thickness and poor tensile strength of battery separator materials prepared by wet papermaking processes in the prior art, one objective of this invention is to provide a method for preparing low basis weight, high density fiber materials. By filling the fiber layer with ultrafine powder, the fiber layer is made to have multiple pores, small pore size, and uniform distribution. A hot-melt powder layer is set on one side of the fiber layer, so that the fiber material has a thermally closed-pore function, thereby increasing the safety of the battery separator.

[0007] To achieve the above objectives, the present invention employs the following technical solution: a method for preparing a low-quantity, high-density fiber material, wherein the fiber material comprises a fiber layer and a hot-melt powder layer disposed on one side of the fiber layer; the fiber layer is filled with ultrafine powder; the method for preparing the fiber material comprises the following steps:

[0008] (1) Mix polyvinyl alcohol ultra-short fibers and hydrophobic polyester ultra-fine ultra-short fibers to prepare a first slurry with a concentration of 0.5-1%;

[0009] (2) The hydrophilic fine denier ultrashort cellulose fibers are made into a fiber slurry with a concentration of 0.5-2%, and then the fiber slurry is fed into a refiner for refining to make a second slurry with a beating degree of 60°SR-85°SR.

[0010] (3) The first slurry and the second slurry are mixed and stirred to form a mixed slurry, and then the mixed slurry is pumped into the inclined wire mesh forming machine to form a wet fiber web;

[0011] (4) The wet fiber web is fed into the hydroentangling system to reinforce the front and back sides to form an intermediate material. The hydroentangling pressure is configured according to the processing sequence as low pressure, high pressure, and low pressure (40kg, 60kg, 90kg, 90kg, 70kg, 70kg).

[0012] (5) The intermediate material after hydroentanglement is dehydrated by negative pressure suction, and then the intermediate material is sent into a hot water bath at 40℃-90℃ to dissolve the polyvinyl alcohol ultra-short fiber.

[0013] (6) The intermediate material obtained in step (5) is subjected to a first-stage rolling process to achieve a first thickness of 0.15-0.25 mm;

[0014] (7) The ultrafine powder is made into a suspension, and the intermediate material after the first rolling is immersed in the suspension to fill the ultrafine powder into the intermediate material;

[0015] (8) The impregnated intermediate material is dried and then subjected to a second rolling process, with the rolling temperature controlled at 80-120°C, so that the material reaches a second thickness of 0.08-0.15 mm to form the fiber layer;

[0016] (9) The hot melt powder is made into a suspension slurry, and then the suspension slurry is coated and fixed onto one side of the fiber layer to form the hot melt powder layer;

[0017] (10) The fiber layer coated with the hot melt powder layer is subjected to a third rolling process to control the material to reach a third thickness of 0.02-0.04 mm;

[0018] (11) The fiber material is finally produced.

[0019] The length and fineness of the fibers directly affect the porosity and pore size of the fiber material. In this design, the fiber layer is composed of interconnected ultra-short fibers. This arrangement aims to achieve a smaller pore size in the fiber layer. Filling the fiber layer with ultrafine powder further enhances the uniformity of pore size distribution and reduces the overall pore size, thus meeting the technical requirements of battery separators for high porosity, small pore size, and uniform distribution.

[0020] The purpose of providing the hot-melt powder layer on one side of the fiber layer is to enable the fiber material to have a thermally closed-cell function, thereby meeting the safety requirements of the battery separator.

[0021] Furthermore, the total mass of the hot-melt powder layer accounts for 3-8% of the total mass of the fiber material; the total mass of the ultrafine powder accounts for 4-12% of the total mass of the fiber layer; the mass of the fine denier ultrashort cellulose fiber accounts for 0%-30% of the total mass of the fiber layer, and the remainder is the polyester ultrafine ultrashort fiber.

[0022] The use of the aforementioned polyester ultrafine and ultrashort fibers is based on the requirements of battery separators to achieve high tensile strength in the product. The addition of hydrophilic fine denier ultrashort cellulose fibers to the polyester ultrafine and ultrashort fibers aims to improve the wetting performance of the battery separator and enhance the electrolyte's ability to wet the material.

[0023] Furthermore, the ultrafine powder is composed of one or more combinations of alumina, silicon dioxide, zirconium oxide, titanium dioxide, and nanocellulose; the particle size of the ultrafine powder is 0.1μm-0.6μm.

[0024] Specifically, when the mass of the polyester ultrafine and ultrashort fibers is greater than 90% of the total mass of the fiber layer, the ultrafine powder includes nanocellulose.

[0025] When the proportion of the polyester ultrafine and ultrashort fibers is high (i.e., >90%), the ultrafine powder to be filled needs to be hydrophilic in order to improve wettability; filling the fiber layer with the ultrafine powder can adjust the porosity and pore size distribution of the material, wherein the nanocellulose can also enhance the wettability of the material to the electrolyte.

[0026] Furthermore, the hot-melt powder layer is made of polypropylene or polyethylene to ensure the safety of the battery separator product.

[0027] Specifically, in step (1), the mass percentage of the polyester microfiber is 50%-70%; the remainder is the polyvinyl alcohol microfiber.

[0028] The polyvinyl alcohol short fibers are mainly used to adjust the porosity of the material and reduce the mass per unit area of ​​the material.

[0029] Preferably, the polyvinyl alcohol short fibers have a length of 1-4 mm and a linear density of 0.5 dtex-2.5 dtex; the linear density or length of the polyvinyl alcohol short fibers has at least two specifications.

[0030] Preferably, the polyester ultrafine and ultrashort fibers include at least two fiber lengths; the polyester ultrafine and ultrashort fibers have a fineness of 0.05 dtex-0.5 dtex and a length of 5-10 mm.

[0031] Battery separators require pore sizes less than 0.5 μm. Compared to ordinary fibers, the polyester ultrafine and ultrashort fibers result in smaller pores and pore sizes. By controlling the fiber length ratio, materials with good uniformity and improved strength can be obtained. When the length of the polyester ultrafine and ultrashort fibers is less than 5 mm, the tensile strength of the material decreases sharply with decreasing fiber length.

[0032] Preferably, the cross-sectional shape of the polyester microfiber is one or more combinations of circles, rectangles, and triangles.

[0033] The cross-sectional shape of the fiber affects the entanglement between fibers; using fibers with different cross-sections can improve the entanglement efficiency of the fibers in the fiber layer, enabling the material to obtain better breaking strength.

[0034] Preferably, the fine denier short cellulose fiber is one or more of viscose fiber, modal fiber, and lyocell fiber; the fine denier short cellulose fiber has a fineness of 0.1 dtex-1.0 dtex and a length of 3-7 mm.

[0035] Battery separator materials have high requirements for pore size, generally requiring the pore size to be controlled below 0.5μm. Compared with ordinary fibers, ultrafine fibers can bring smaller pores and pore sizes.

[0036] Preferably, the fine denier cellulose fiber is lyocell (Tencel) fiber; after treatment, the lyocell (Tencel) fiber will have a fibrillation effect, and the fiber surface will produce fine hairs, which can bring smaller pores and pore sizes.

[0037] Preferably, the unit area mass of the fiber material is 10-30 g / m². 2 ;

[0038] Preferably, the fiber packing density of the fiber material is 0.5-1 g / cm³. 3 .

[0039] Preferably, the thickness of the fiber material is 0.02-0.04 mm; the thickness of the battery separator material directly affects the performance of the battery, and the thickness of the battery separator material should be as low as possible while ensuring the material properties.

[0040] This solution requires the battery separator material to be less than 40μm thick and its weight to be less than 30 grams; the material pore size should be smaller, meaning the fiber packing density should be higher than that of ordinary materials.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] (1) The present invention adds polyvinyl alcohol ultra-short fiber to polyester ultra-fine ultra-short fiber slurry and sets the water dissolution temperature reasonably, which not only facilitates wet web formation and fiber web reinforcement, but also reduces the unit area mass of the material because the polyvinyl alcohol ultra-short fiber is dissolved in the subsequent hot water bath, thus solving the problem that existing fiber materials cannot be applied to battery separator materials due to their high quantitative content.

[0043] (2) This invention fills the fiber layer with ultrafine powder, which reduces the pore size in the fiber layer and increases the material density at low basis weight, thus solving the problem that existing nonwoven materials cannot be used in battery separators due to their large pore size. At the same time, the thermal pore-closing effect of ultrafine powder can ensure the safety of battery separator products.

[0044] (3) The present invention applies and fixes the hot melt powder layer to one side of the fiber layer surface, further reducing the pore size of the material surface and further increasing the material density under low quantitative conditions, thereby improving the fracture strength of the material, meeting the requirements for use of battery separators, and solving the problem that existing ordinary fiber materials cannot be applied to battery separators.

[0045] (4) In the product preparation process, the intermediate material is subjected to first-stage rolling and second-stage rolling respectively, and the second-stage rolling temperature is reasonably set to gradually reduce the material thickness, increase the material density and improve the material fracture strength, so that the final product can achieve the technical requirements of low quantitative, high density and high porosity, and solve the problem that existing fiber materials cannot meet the requirements for battery separator use. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the structure of the fiber material of the present invention;

[0047] Figure 2 This is a schematic diagram of the preparation process of the fiber material of the present invention.

[0048] In the diagram: 1. Fiber layer; 2. Ultrafine powder; 3. Hot melt powder layer. Detailed Implementation

[0049] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0050] In the description of this invention, it should be noted that the directional terms such as "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", and "counterclockwise" indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this invention.

[0051] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features. Thus, the use of "first" and "second" to define a feature may explicitly or implicitly include one or more of that feature, and in the description of this invention, "a number" means two or more, unless otherwise explicitly specified.

[0052] In this invention, unless otherwise explicitly specified and limited, terms such as "set" and "install" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can also refer to a mechanical connection; they can refer to a direct connection or a connection through an intermediate medium; or they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0053] See Figures 1-2 A method for preparing a low-quantity, high-density fiber material, the fiber material comprising a fiber layer 1 and a hot-melt powder layer 3 disposed on one side of the fiber layer 1; the fiber layer 1 is filled with ultrafine powder 2; the fiber layer 1 is formed by intertwining and fixing ultrashort fibers; the ultrafine powder 2 is attached to the ultrashort fibers; the method for preparing the fiber material includes the following steps:

[0054] (1) Mix polyvinyl alcohol ultra-short fibers and hydrophobic polyester ultra-fine ultra-short fibers to prepare a first slurry with a concentration of 0.5-1%;

[0055] (2) The hydrophilic fine denier ultrashort cellulose fibers are made into a fiber slurry with a concentration of 0.5-2%, and then the fiber slurry is fed into a refiner for refining to make a second slurry with a beating degree of 60°SR-85°SR.

[0056] (3) The first slurry and the second slurry are mixed and stirred to form a mixed slurry, and then the mixed slurry is pumped into the inclined wire mesh forming machine to form a wet fiber web;

[0057] (4) The wet fiber web is fed into the hydroentangling system to reinforce the front and back sides to form an intermediate material. The hydroentangling pressure is configured according to the processing sequence as low pressure, high pressure, and low pressure (40kg, 60kg, 90kg, 90kg, 70kg, 70kg).

[0058] (5) The intermediate material after hydroentanglement is dehydrated by negative pressure suction, and then the intermediate material is sent into a hot water bath at 40℃-90℃ to dissolve the polyvinyl alcohol ultra-short fiber.

[0059] (6) The intermediate material from step (5) is subjected to a first-stage rolling process to achieve a first thickness of 0.15-0.25 mm;

[0060] (7) The ultrafine powder is made into a suspension, and the intermediate material after the first rolling is immersed in the suspension to fill the ultrafine powder into the intermediate material;

[0061] (8) The impregnated intermediate material is dried and then subjected to a second rolling process, with the rolling temperature controlled at 80-120°C, so that the material reaches a second thickness of 0.08-0.15 mm to form the fiber layer;

[0062] (9) The hot melt powder is made into a suspension slurry, and then the suspension slurry is coated and fixed onto one side of the fiber layer to form the hot melt powder layer;

[0063] (10) The fiber layer coated with the hot melt powder layer is subjected to a third rolling process to control the material to reach a third thickness of 0.02-0.04 mm;

[0064] (11) The fiber material is finally produced.

[0065] In step (1), if the concentration of the first slurry is too high, the fibers will easily entangle during the slurry transport process, resulting in uneven fabric surface; if the concentration of the first slurry is too low, it will affect production efficiency; the linear density or length of the polyvinyl alcohol short fiber is at least two specifications, for example: a mixture of 1.5dtex*1.5mm and 2dtex*2.5mm; the water solubility temperature of the polyvinyl alcohol short fiber is >70℃.

[0066] In step (1), the mass percentage of the polyester microfiber is 50%-70%; the remainder is the polyvinyl alcohol microfiber.

[0067] The purpose of adding the polyvinyl alcohol (PVA) ultrashort fibers to the raw materials is twofold: firstly, low-weight fiber webs are difficult to transfer, and adding the PVA fibers facilitates web transfer, increasing production efficiency; secondly, the surface of the polyester ultrafine and ultrashort fibers becomes very dense after hydroentangling, which is not conducive to impregnation and sizing, while the added PVA fibers leave pores after being dissolved in hot water, which facilitates the impregnation of the ultrafine powder. Using PVA fibers with a water solubility temperature >70℃ is to prevent the fibers from dissolving in water during processing.

[0068] In step (4), the hydroentangling system adopts a processing sequence of low pressure, high pressure, and low pressure, which can effectively reduce hydroentanglement marks on the material surface and improve the uniformity of the material. Hydroentangling reinforcement will cause the ultra-short fibers to interweave and bind together, and the fibers will be arranged in three dimensions to form a larger porosity.

[0069] The combination of hydroentanglement reinforcement and two rolling processes enables the material to achieve high tensile strength, meeting the requirements for battery separator applications. Simultaneously, the hydroentangled material is relatively loose and thick, with numerous and uniformly sized pores, providing sufficient space for the impregnating liquid to penetrate the material and for the ultrafine powder to adhere to each fiber. The second stage, high-temperature rolling, compresses the impregnated material, further refining the pores. Coating one side of the material with the hot-melt powder layer enables it to achieve thermal pore-closing functionality.

[0070] Thermal pore closure is a special separator technology that provides additional safety protection for lithium-ion batteries. The main parameters of this function are thermal pore closure temperature and thermal rupture temperature. The pore closure temperature is the temperature at which the micropores inside the separator close. When the battery cell is subjected to abnormal environments such as thermal abuse, overcharging, or external short circuits, the internal temperature of the cell rises rapidly. Because the separator material is a thermoplastic polymer, when the temperature approaches the polymer's melting point, the micropores inside the separator thermally close, blocking the lithium-ion transport channels and creating an open circuit inside the cell, thus protecting the battery.

[0071] The total mass of the hot-melt powder layer accounts for 3-8% of the total mass of the fiber material; the total mass of the ultrafine powder accounts for 4-12% of the total mass of the fiber layer; the mass of the fine denier ultrashort cellulose fiber accounts for 0%-30% of the total mass of the fiber layer, and the remainder is the polyester ultrafine ultrashort fiber.

[0072] If the content of the hot-melt powder layer is too low, it will affect the thermal pore-closing function; if the content is too high, it will affect the wettability of the material and increase the thickness of the material. If the content of the ultrafine powder is too low, it will be difficult to control the pore size of the material; if it is too high, it will reduce the porosity of the material and reduce the ion conduction efficiency.

[0073] The ultrafine powder is composed of one or more combinations of alumina, silicon dioxide, zirconium oxide, titanium dioxide, and nanocellulose; the particle size of the ultrafine powder is 0.1μm-0.6μm.

[0074] Generally, battery separators require the pore size in the material to be less than 0.5 μm. If the ultrafine powder particle size is too large, it is not conducive to controlling the pore size in the material. If the ultrafine powder particle size is too small, it is not conducive to its adhesion to the ultrashort fiber, and it will also reduce the ion conduction efficiency.

[0075] When the mass of the polyester ultrafine and ultrashort fibers is greater than 90% of the total mass of the fiber layer, the ultrafine powder includes nanocellulose.

[0076] The hot-melt powder layer is made of polypropylene or polyethylene; the particle size of the hot-melt powder is 0.3μm-0.8μm.

[0077] The polyvinyl alcohol short fibers have a length of 1-4 mm and a linear density of 0.5 dtex-2.5 dtex; the linear density or length of the polyvinyl alcohol short fibers has at least two specifications.

[0078] The polyester ultrafine and ultrashort fibers include at least two fiber lengths; the polyester ultrafine and ultrashort fibers have a fineness of 0.05 dtex-0.5 dtex and a length of 5-10 mm. The cross-sectional shape of the polyester ultrafine and ultrashort fibers is one or more combinations of circles, rectangles, and triangles.

[0079] The fine denier short cellulose fiber is one or more of viscose fiber, modal fiber, and lyocell fiber; the fine denier short cellulose fiber has a fineness of 0.1 dtex-1.0 dtex and a length of 3-7 mm; preferably, the fine denier cellulose fiber is lyocell (Tencel) fiber; the lyocell (Tencel) fiber will have a fibrillation effect after treatment, and the fiber surface will produce microfibers, which can bring smaller pores and pore sizes.

[0080] Example 1

[0081] A low-weight, high-density fiber material is disclosed, wherein the fiber layer is composed of PET fibers (polyethylene terephthalate fibers, specifically the polyester ultrafine and ultrashort fibers), lyocell fibers, and nanocellulose powder. The PET fibers account for 75% of the total mass of the fiber layer, with a linear density of 0.1 dtex and a length of 5 mm; the lyocell fibers account for 20% of the total mass of the fiber layer, with a linear density of 0.6 dtex and a length of 4 mm; and the nanocellulose powder accounts for 5% of the total mass of the fiber layer, with a particle size of 0.1 μm. A hot-melt powder layer, composed of polyethylene powder, is disposed on the outer surface of the fiber layer, with an average particle size of 0.5 μm. The overall weight of the material is 28 g / m³. 2 The thickness is 0.035mm.

[0082] A method for preparing a low-quantity, high-density fiber material includes the following steps:

[0083] (1) PET fiber and polyvinyl alcohol short fiber are mixed to prepare a first slurry with a concentration of 0.5%;

[0084] (2) The lyocell cellulose fiber is made into a second slurry with a slurry concentration of 0.5% and a knockout degree of 60°SR;

[0085] (3) The first slurry and the second slurry are mixed to form a mixed slurry, wherein the mass ratio of PET fiber, polyvinyl alcohol short fiber and lyocell cellulose fiber in the mixed slurry is 4:5:1; and the mixed slurry is then made into a wet fiber web.

[0086] (4) The fibers in the wet-laid fiber web are hydroentangled and reinforced to make an intermediate material;

[0087] (5) The intermediate material is placed in a hot water bath to dissolve the polyvinyl alcohol short fibers; the resulting intermediate material is then subjected to a first-stage rolling process to achieve a material thickness of 0.2 mm.

[0088] (6) Fill the intermediate material obtained in step (5) with ultrafine powder;

[0089] (7) The intermediate material filled with ultrafine powder is subjected to a second rolling process to achieve a material thickness of 0.12 mm;

[0090] (8) Apply and fix the hot-melt powder layer to one side of the intermediate material;

[0091] (9) The intermediate material coated with hot melt powder is subjected to a third rolling process to achieve a material thickness of 0.035 mm, thereby obtaining the fiber material.

[0092] Example 2

[0093] A low-quantity, high-density fiber material, differing from Example 1 only in that the length of the PET fibers in the fiber layer is 10 mm.

[0094] Example 3

[0095] A low-quantity, high-density fiber material, differing from Example 1 only in that nanocellulose powder is replaced with titanium dioxide.

[0096] Comparative Example 1

[0097] A low-quantity, high-density fiber material differs from Example 1 only in that the fiber layer does not contain ultrafine powder, and the PET fiber content in the fiber layer is 80%.

[0098] Comparative Example 2

[0099] A low-quantity, high-density fiber material differs from Example 1 only in that: the content of nanocellulose powder in the fiber layer is 15%, and the mass percentage of PET fiber in the fiber layer is 65%.

[0100] Comparative Example 3

[0101] A low-quantity, high-density fiber material, differing from Example 1 only in that the outer surface of the fiber layer does not contain a hot-melt powder layer.

[0102] Comparative Example 4

[0103] A low-quantity, high-density fiber material differs from Example 3 only in that: the fiber layer contains 95% PET fiber and does not contain hydrophilic fibers, i.e., it does not contain lyocell cellulose fibers.

[0104] Comparative Example 5

[0105] A low-quantity, high-density fiber material, differing from Example 1 only in that the length of the PET fibers in the fiber layer is 15 mm.

[0106] Comparative Example 6

[0107] A low-quantity, high-density fiber material, differing from Example 1 only in that the length of the PET fibers in the fiber layer is 3 mm.

[0108] Test case

[0109] Test objective: To determine the suitability of a test material for use in battery separators by testing its tensile strength, maximum pore size, porosity, and contact angle.

[0110] Test method:

[0111] (1) Breaking strength: Performed in accordance with ISO 9073-3 Textiles - Test methods for nonwoven fabrics - Part 3: Determination of breaking strength and elongation.

[0112] (2) Average aperture: Performed in accordance with ASTM F316-03 standard.

[0113] (3) Porosity: The porosity shall be determined in accordance with GB / T21650.2-2008 "Determination of pore size distribution and porosity of solid materials by mercury porosimetry and gas adsorption method - Part 2: Analysis of mesopores and macropores by gas adsorption method".

[0114] (4) Contact angle: in accordance with DB44 / T 1872-2016 standard.

[0115] (5) Thermal closing temperature: in accordance with INASA TM 2010-2l6099 standard.

[0116] The test results are shown in Table 1.

[0117] A comparative table of nonwoven fabric performance test data in each embodiment and comparative example

[0118]

[0119] Test Result Analysis:

[0120] 1) Comparison of data from Examples 1, 2, 5, and 6 shows that the PET fiber length in the fiber layer is in the range of 5-10 mm. Increasing the fiber length will improve the tensile strength of the material, but the uneven distribution of long fibers during the web formation process will lead to larger pore size and porosity. When the fiber length is too long, the tensile strength of the material is significantly improved, but the pore size and porosity of the material will be too large, which will not meet the requirements as a battery separator material. When the fiber length is too short, the tensile strength of the material is too low, which will make the material prone to breakage.

[0121] 2) As can be seen from the comparison between Example 1 and Example 3, after the nanocellulose powder was replaced with titanium dioxide powder, the contact angle of the material with the electrolyte increased and the wetting performance decreased.

[0122] 3) As can be seen from the comparison between Example 1 and Comparative Example 1, the ultrafine powder filled in the fiber layer can effectively improve the pore size and porosity of the material. The increase in pore size makes the material more susceptible to the influence of ion dendrite growth in the electrolyte piercing the membrane, thereby leading to safety problems such as short circuits or even explosions.

[0123] 4) As can be seen from the comparison between Example 1 and Comparative Example 2, excessive filling of the fiber layer with ultrafine powder will reduce the pore size and porosity. Too small a pore size will restrict the permeability of ions in the electrolyte, thereby increasing the internal resistance of the battery and reducing its overall performance.

[0124] 5) As can be seen from the comparison between Example 1 and Comparative Example 3, the hot melt powder layer coated on the outside of the fiber layer can play the role of thermal pore closing.

[0125] 6) As can be seen from the comparison between Example 3 and Comparative Example 4, the hydrophilic fibers and nanocellulose powder in the material can effectively reduce the contact angle between the material and the electrolyte and increase its wetting speed in the electrolyte.

[0126] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0127] The above description is only a specific embodiment of the present invention, but the technical features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for preparing a low-quantity, high-density fiber material, characterized in that: The fiber material includes a fiber layer and a hot-melt powder layer disposed on one side of the fiber layer; the fiber layer is filled with ultrafine powder, and the total mass of the ultrafine powder accounts for 4-12% of the total mass of the fiber layer; the preparation method of the fiber material includes the following steps: (1) mixing polyvinyl alcohol ultrashort fibers and polyester ultrafine ultrashort fibers to prepare a first slurry with a concentration of 0.5-1%; wherein, the mass proportion of the polyester ultrafine ultrashort fibers is 50%-70%, and the remainder is the polyvinyl alcohol ultrashort fibers; the polyester ultrafine ultrashort fibers account for 50%-70% of the mass, and the remainder is the polyvinyl alcohol ultrashort fibers; (1) The fiber fineness is 0.05dtex-0.5dtex and the length is 5-10mm; (2) The hydrophilic fine denier ultrashort cellulose fiber is made into a fiber slurry with a concentration of 0.5-2%, and then the fiber slurry is sent to a refiner for refining to make a second slurry with a beating degree of 60°SR-85°SR; (3) The first slurry and the second slurry are mixed and stirred to form a mixed slurry, and then the mixed slurry is made into a wet fiber web; (4) The wet fiber web is sent into a hydroentangling system to reinforce the front and back sides. (5) The intermediate material after hydroentangling is dehydrated by negative pressure suction, and then the intermediate material is sent into a hot water bath at 40℃-90℃ to dissolve the polyvinyl alcohol ultra-short fibers; (6) The intermediate material obtained in step (5) is subjected to first-stage rolling to achieve a first thickness of 0.15-0.25mm; (7) The ultrafine powder is made into a suspension, and then the intermediate material after first-stage rolling is sent into the suspension for immersion to fill the ultrafine powder into the intermediate material; (8) The impregnated intermediate material is then subjected to first-stage rolling to dissolve the polyvinyl alcohol ultra-short fibers; The intermediate material is dried and then rolled in a second stage, with the rolling temperature controlled at 80-120°C, so that the material reaches a second thickness of 0.08-0.15 mm to form the fiber layer; (9) the hot melt powder is made into a suspension slurry and then the suspension slurry is coated and fixed onto one side of the fiber layer to form the hot melt powder layer; (10) the fiber layer coated with the hot melt powder layer is rolled in a third stage, and the material is controlled to reach a third thickness of 0.02-0.04 mm; (11) the fiber material is finally made.

2. The preparation method according to claim 1, characterized in that: The total mass of the hot-melt powder layer accounts for 3-8% of the total mass of the fiber material; the mass of the fine denier ultra-short cellulose fiber accounts for 0%-30% of the total mass of the fiber layer.

3. The preparation method according to claim 2, characterized in that: The ultrafine powder is composed of one or more combinations of alumina, silicon dioxide, zirconium oxide, titanium dioxide, and nanocellulose; the particle size of the ultrafine powder is 0.1μm-0.6μm.

4. The preparation method according to claim 3, characterized in that: When the mass of the polyester ultrafine and ultrashort fibers is greater than 90% of the total mass of the fiber layer, the ultrafine powder includes nanocellulose.

5. The preparation method according to any one of claims 1-4, characterized in that: The hot-melt powder layer is made of polypropylene or polyethylene.

6. The preparation method according to any one of claims 1-4, characterized in that: The polyvinyl alcohol short fibers have a length of 1-4 mm and a linear density of 0.5 dtex-2.5 dtex; the linear density or length of the polyvinyl alcohol short fibers has at least two specifications.

7. The preparation method according to any one of claims 1-4, characterized in that: The polyester ultrafine and ultrashort fibers include at least two fiber lengths.

8. The preparation method according to any one of claims 1-4, characterized in that: The cross-sectional shape of the polyester microfiber is one or more combinations of circles, rectangles, and triangles.

9. The preparation method according to any one of claims 1-4, characterized in that: The fine denier ultra-short cellulose fiber is one or more of viscose fiber, modal fiber, and lyocell fiber; the fineness of the fine denier ultra-short cellulose fiber is 0.1 dtex-1.0 dtex, and the length is 3-7 mm.

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