A battery separator and method of making the same

Abstract

The application discloses a battery diaphragm and a preparation method thereof, and belongs to the technical field of diaphragms. The preparation method of the battery diaphragm comprises the following steps: an extraction step: extracting a base material to obtain a porous film; a coating step: coating ceramic slurry on the porous film to form a coated film; and a drying and shaping step: drying and shaping the coated film to obtain the battery diaphragm. In the coating step, the water content of the porous film is 1% to 5%, and the solid content of the ceramic slurry is 45% to 80%. According to the above method, the preparation process of the battery diaphragm can be simplified, the preparation efficiency can be improved, the adhesion of the battery diaphragm can be improved, and the thermal shrinkage rate can be reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of diaphragm, in particular to a battery diaphragm and a preparation method thereof. BACKGROUND

[0002] At present, the basic process of wet coating diaphragm of lithium battery is that a wet base film with a certain thickness is produced by a wet production line, then subsequent pulping and coating processes are carried out, and finally the finished diaphragm with different widths is cut. Specifically, the wet base film production process includes feeding, extrusion casting, two-way stretching, extraction, drying and setting, winding, and cutting. The coating diaphragm production process includes pulping, unwinding, preheating, coating, drying, winding, cutting, and packaging and delivery.

[0003] However, the current preparation process of wet coating diaphragm is long and complex, the preparation efficiency of wet coating diaphragm is low, and the prepared coating diaphragm has low adhesion and high thermal shrinkage. SUMMARY

[0004] Based on the above-mentioned deficiencies, the present application provides a battery diaphragm and a preparation method thereof to improve the preparation efficiency and quality of the diaphragm.

[0005] The present application is implemented as follows:

[0006] In a first aspect, examples of the present application provide a preparation method of a battery diaphragm, comprising:

[0007] An extraction step of extracting the base material to obtain a porous film;

[0008] A coating step of coating ceramic slurry on the porous film to form a coated film;

[0009] A drying and setting step of drying and setting the coated film to obtain the battery diaphragm;

[0010] In the coating step, the water content of the porous film is 1% to 5%, and the solid content of the ceramic slurry is 45% to 80%.

[0011] In the above implementation process, the base material is extracted to form a porous film, then ceramic slurry is coated on the extracted porous film, the water content of the porous film is 1% to 5%, and the solid content of the ceramic slurry is 45% to 80%, and then the coated film after coating is dried and set, so that the drying of the porous film and the coating layer can be realized in one drying and setting process, compared with the traditional ceramic slurry coating on the surface of the diaphragm after drying and setting, the number of drying and setting can be reduced, and the preparation efficiency of the battery diaphragm is improved.

[0012] And, the water content of the porous membrane after extraction is 1% to 5%, and the solid content of the ceramic slurry is 45% to 80%, so that after drying and shaping, the adhesion between the ceramic coating and the porous membrane in the battery separator can be improved, and the thermal shrinkage of the battery separator can be reduced.

[0013] In combination with the first aspect, in an optional implementation, the water content of the porous membrane is 2% to 3%, and the solid content of the ceramic slurry is 50% to 60%.

[0014] In the above implementation process, when the water content of the porous membrane obtained after extraction is 2% to 3%, the ceramic slurry with a solid content of 50% to 60% is coated on the porous membrane, so that the adhesion of the battery separator can be further improved, and the thermal shrinkage of the battery separator can be reduced.

[0015] In combination with the first aspect, in an optional implementation, the method for adjusting the water content of the porous membrane includes: in the extraction step, the temperature of the extraction roller is 25 to 60°C, the temperature of the extraction heating plate is 50 to 100°C, the ambient temperature is 20 to 40°C, and the exhaust power is 20 to 30 Hz.

[0016] In the above implementation process, when the substrate is extracted, the temperature of the extraction roller is adjusted to 25 to 60°C, the temperature of the extraction heating plate is adjusted to 50 to 100°C, the ambient temperature is adjusted to 20 to 40°C, and the exhaust power is adjusted to 20 to 30 Hz, so that the porous membrane with a water content of 1% to 5% can be obtained. Subsequently, the ceramic slurry with a solid content of 45% to 80% is coated on the porous membrane with a water content of 1% to 5%, so that the adhesion of the battery separator can be improved, and the thermal shrinkage of the battery separator can be reduced.

[0017] In combination with the first aspect, in an optional implementation, the method for coating the ceramic slurry on the porous membrane includes:

[0018] The ceramic slurry is coated on the porous membrane by using a gravure roller or a slot die at a coating speed of 60 to 120 m / min.

[0019] Optionally, the ceramic slurry with a solid content of 50% to 60% is coated on the porous membrane by using a slot die method.

[0020] In the above implementation process, the ceramic slurry is coated on the porous membrane by using a gravure roller or a slot die at a coating speed of 60 to 120 m / min, so that the coating quality can be improved. The ceramic slurry with a solid content of 50% to 60% is coated on the porous membrane by using a slot die method, so that the coating quality can be improved, the adhesion of the battery separator can be improved, and the thermal shrinkage of the battery separator can be reduced.

[0021] In combination with the first aspect, in an optional implementation, the porous thickness is 3-30 μm, and the ceramic coating on the porous membrane has a thickness of 1-5 μm.

[0022] In combination with the first aspect, in an optional implementation, the ceramic slurry comprises ceramic powder, solvent and adhesive.

[0023] In combination with the first aspect, in an optional implementation, in the drying and setting step, the coated membrane is sequentially passed through a preheating section and a setting section in an oven, the preheating section has a temperature of 80-140 ℃, and the setting section has a temperature of 90-150 ℃.

[0024] In the above implementation process, when the coated membrane coated with the ceramic slurry is dried and set, the coated membrane is first preheated in a preheating section with a temperature of 80-140 ℃, and then set in a setting section with a temperature of 90-150 ℃, so that the adhesion of the battery separator can be improved, and the thermal shrinkage rate of the battery separator can be reduced.

[0025] In combination with the first aspect, in an optional implementation, the preparation method further comprises a pretreatment step before the extraction step, and the pretreatment step comprises: melt-extruding raw materials for forming a base material to a casting roll to form a casting sheet; and performing bidirectional stretching on the casting sheet to obtain the base material.

[0026] Optionally, the preparation method further comprises a post-treatment step after the drying and setting step, and the post-treatment step comprises: sequentially winding and slitting the battery separator obtained in the drying and setting step.

[0027] In the above implementation process, the raw materials for forming the base material are melt-extruded to form a casting sheet, and then the casting sheet is bidirectionally stretched, so that the base material with a certain thickness and width can be obtained, thereby facilitating subsequent extraction, coating, drying and setting, winding and slitting of the base material to obtain a battery separator with a suitable size.

[0028] In combination with the first aspect, in an optional implementation, the raw materials comprise polyolefin and pore-forming agent; the cooling temperature of the casting roll is 19-30 ℃, the speed is 4-11 m / min, and the residence time is 10-15 min; the bidirectional stretching comprises longitudinal stretching and transverse stretching, the longitudinal stretching ratio is 6-12 times, and the transverse stretching ratio is 5-10 times.

[0029] In the second aspect, examples of the present application provide a battery separator prepared by the preparation method according to the first aspect.

[0030] The battery separator prepared by the preparation method according to the first aspect has high adhesion and low thermal shrinkage rate, and when applied to a battery, the cycle performance and safety of the battery can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows.

[0032] Figure 1 A schematic diagram of a battery separator provided for the examples of the present application;

[0033] Figure 2 A schematic diagram of a preparation process of a battery separator provided for the comparative technology;

[0034] Figure 3 A schematic diagram of a preparation process of a battery separator provided for the examples of the present application.

[0035] Figure legend: 100 - battery separator; 101 - porous membrane; 102 - ceramic coating. DETAILED DESCRIPTION

[0036] The embodiments of the present application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. If the specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0037] In lithium batteries, the main function of the separator is to keep the positive and negative electrodes apart to prevent short circuiting, while allowing the rapid transfer of ions, and it is a relatively important component in lithium ion batteries. The performance of the separator will directly affect the characteristics of the battery, such as the capacity, internal resistance, rate, cycle and self-discharge of the battery.

[0038] Currently, the material of lithium ion battery separator is usually polyolefin material, which has poor heat resistance. When the battery temperature continues to rise, the separator will shrink and even melt, and the positive and negative electrodes will directly contact and cause internal short circuit, resulting in rapid rise of battery temperature, reaching the thermal decomposition temperature of positive and negative electrode materials, and further causing the battery to smoke, catch fire or even explode.

[0039] In order to improve the thermal stability of the separator, please refer to Figure 1 , the current method is to coat a ceramic coating 102 composed of ceramic and adhesive on the polyolefin porous membrane 101. Since the ceramic coating 102 has good thermal stability and mechanical properties, it greatly improves the safety performance of the battery.

[0040] Generally, please refer to Figure 2 , the preparation process of the battery separator 100 with ceramic coating 102 includes:

[0041] S1, wet base film production process;

[0042] S2, coating diaphragm production process.

[0043] Wherein, please continue to refer to Figure 2 S1, wet base film production process, comprising:

[0044] S11, feeding; S12, extruding cast piece; S13, bidirectional stretching; S14, extraction; S15, drying and shaping; S16, winding; S17, slitting.

[0045] Wherein, please continue to refer to Figure 2 S2, coating diaphragm production process, comprising:

[0046] S21, pulping; S22, unwinding; S23, preheating; S24, coating; S25, drying; S26, winding; S27, slitting; S28, packaging and delivery.

[0047] At present, in the preparation process of the battery diaphragm 100, the porous film 101 is first prepared by the wet base film production process, and then the ceramic coating 102 is prepared on the porous film 101 by the coating diaphragm production process. The preparation process of the battery diaphragm 100 is complex, the preparation efficiency is low, and the prepared battery diaphragm 100 has low adhesion and high thermal shrinkage.

[0048] Therefore, the preparation process of the battery diaphragm 100 is further improved, so that the preparation efficiency and quality of the battery diaphragm can be improved to some extent. In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application.

[0049] Please refer to Figure 3 The preparation method of the battery diaphragm provided by the embodiments of the present application comprises:

[0050] S31, feeding;

[0051] S32, extruding cast piece;

[0052] S33, bidirectional stretching;

[0053] S34, extraction;

[0054] S351, pulping;

[0055] S35, online coating;

[0056] S36, drying and shaping;

[0057] S37, winding;

[0058] S38, slitting;

[0059] S39, package delivery.

[0060] In the preparation method provided in the examples of the present application, the substrate is extracted to form a porous membrane 101, then the ceramic slurry is coated on the porous membrane 101 after extraction, and the water content of the porous membrane 101 is 1% to 5%, and the solid content of the ceramic slurry is 45% to 80%, then the coated film after coating is dried and shaped, and the battery separator 100 can be obtained. The slurry coating is performed on the porous membrane 101 after extraction, and the coated film is dried and shaped after the slurry coating, so that the drying and shaping of the porous membrane 101 and the ceramic coating 102 can be realized in one drying and shaping process. Compared with the ceramic slurry coating on the surface of the separator obtained after traditional drying and shaping, the number of drying and shaping can be reduced, and the porous membrane 101 does not need to be preheated before the ceramic slurry is coated, so that the preparation efficiency of the battery separator can be improved.

[0061] The water content of the porous membrane 101 after extraction is controlled to be 1% to 5%, and the solid content of the ceramic slurry is controlled to be 45% to 80%, so that the adhesion between the ceramic coating 102 and the porous membrane 101 in the battery separator 100 can be improved after subsequent drying and shaping, and the thermal shrinkage rate of the battery separator 100 can be reduced.

[0062] In step S31, the raw material for forming the substrate is pretreated according to the formula, and is transported to the extruder for mixing and melting. The solid material is plasticized and melted into a homogeneous melt and continuously extruded.

[0063] The present application does not limit the composition of the raw material. In some possible embodiments, the raw material can include polyolefin powder and pore-forming agent.

[0064] Illustratively, the material of the polyolefin powder can be selected from polyethylene.

[0065] Illustratively, the weight average molecular weight of the polyethylene can be 0.5×10 6 ~1.5×10 6 .

[0066] Illustratively, the pore-forming agent can be selected from paraffin.

[0067] Further, the present application does not limit the specific ratio of polyolefin powder and pore-forming agent in the raw material. In some possible embodiments, the mass ratio of polyolefin powder to pore-forming agent in the raw material can be 1:1 to 10.

[0068] Illustratively, the mass ratio of polyolefin powder to pore-forming agent in the raw material can be one of 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, or a range between any two of them.

[0069] Further, in some possible embodiments, the extruder can be selected from a twin-screw extruder.

[0070] In some possible embodiments, the rotation speed of the twin screw can be controlled at 50-200 rpm, the melt pump pressure can be controlled at 10-50 bar, the residence time can be 10-20 min, and the extrusion amount can be 50-600 kg / min.

[0071] In step S32, the extruder extrudes the raw material in a molten state from a die head to a casting roll, and cools to obtain a film-shaped base material containing the pore-forming agent.

[0072] Further, the present application does not limit the specific parameters of the casting sheet forming, and in some possible embodiments, the cooling temperature of the casting roll after the die head can be 19-30°C, the speed can be 4-11 m / min, and the residence time can be 10-15 min.

[0073] Illustratively, the cooling temperature of the casting roll can be one of 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, or 30°C, or a range between any two of them.

[0074] Illustratively, the speed of the chill roll can be one of 4 m / min, 5 m / min, 6 m / min, 7 m / min, 8 m / min, 9 m / min, 10 m / min, or 11 m / min, or a range between any two of them.

[0075] Illustratively, the residence time can be one of 10 min, 11 min, 12 min, 13 min, 14 min, or 15 min, or a range between any two of them.

[0076] In step S33, the present application does not limit the specific stretching ratio of bidirectional stretching of the casting sheet obtained in step S32, and in some possible embodiments, the casting sheet can be stretched longitudinally and transversely, the longitudinal stretching ratio can be 6-12 times, and the transverse stretching ratio can be 5-10 times.

[0077] Illustratively, the longitudinal stretching ratio can be one of 6 times, 7 times, 8 times, 9 times, 10 times, 11 times, or 12 times, or a range between any two of them.

[0078] Illustratively, the transverse stretching ratio can be one of 5 times, 6 times, 7 times, 8 times, 9 times, or 10 times, or a range between any two of them.

[0079] In step S34, the base material containing the pore-forming agent is transported into an extraction tank, and the pore-forming agent is replaced out by using an extractant to form a porous structure on the base material, and a porous membrane 101 is obtained.

[0080] The present application does not limit the type of extractant. In one possible embodiment, the extractant can be selected from dichloromethane.

[0081] The water content of the porous membrane 101 can be tested by the weighing method.

[0082] The testing method of the water content of the porous membrane 101 includes:

[0083] Take a certain area of the porous membrane 101 from the extraction tank that has not yet passed into the rear drying box, and weigh the wet membrane weight m1 with an electronic balance with a precision of 0.0001 g. Dry the water on the surface of the porous membrane 101 with paper, and weigh again to obtain the dry membrane weight m2. The water content calculation formula is as follows:

[0084]

[0085] In some possible embodiments, the water content of the porous membrane 101 after extraction can be one of 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, or a range between any two of them.

[0086] Further, the present application does not limit the specific extraction parameters. In order to facilitate the adjustment of the water content of the porous membrane 101, in some possible embodiments, the present application provides an example of a method for regulating the water content of the porous membrane 101, including: in the extraction step, adjusting the temperature of the extraction roller to 25-60°C, adjusting the temperature of the extraction heating plate to 50-100°C, the ambient temperature to 20-40°C, and the exhaust power to 23-30 Hz.

[0087] For example, the temperature of the extraction roller can be one of 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C, or a range between any two of them.

[0088] For example, the temperature of the extraction heating plate can be one of 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C, or a range between any two of them.

[0089] For example, the ambient temperature can be one of 20°C, 25°C, 30°C, 35°C, or 40°C, or a range between any two of them.

[0090] For example, the exhaust power can be set to one of 23 Hz, 24 Hz, 25 Hz, 26 Hz, 27 Hz, 28 Hz, 29 Hz, or 30 Hz, or a range between any two of them.

[0091] Further, the water content of the porous membrane 101 after extraction can be controlled to 2%-3%.

[0092] In step S35, the ceramic slurry is coated on the porous membrane 101, and the water content of the porous membrane 101 is 1% to 5%, and the solid content of the ceramic slurry is 45% to 80%.

[0093] In some possible embodiments, the solid content of the ceramic slurry can be 45% to 80%.

[0094] For example, the solid content of the ceramic slurry can be one of 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%, or a range between any two of them.

[0095] Further, in some possible embodiments, the solid content of the ceramic slurry can be 50% to 60%.

[0096] The present application does not limit the components of the ceramic slurry, and in some possible embodiments, the ceramic slurry can include ceramic powder, solvent, and adhesive.

[0097] For example, the ceramic powder can be selected from one of alumina, zirconia, silica, magnesium oxide, calcium oxide, or boehmite, or a range between any two of them.

[0098] For example, the particle size of the ceramic powder can be 0.3-2 μm.

[0099] For example, the adhesive can be selected from at least one of polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), and polyvinylidene fluoride (PVDF).

[0100] For example, the solvent can be selected from water, ethanol, glycerol, or other polar organic solvents, or acetone, NMP, or other non-polar organic solvents.

[0101] Further, additives such as dispersants, wetting agents, or surfactants, etc. can also be added to the ceramic slurry.

[0102] Further, the present application does not limit the specific coating process, and in some possible embodiments, a gravure roll or a slot die coating head can be used to coat the ceramic slurry on the porous membrane at a coating speed of 60-120 m / min.

[0103] For example, the coating speed can be one of 60 m / min, 70 m / min, 80 m / min, 90 m / min, 100 m / min, 110 m / min, or 120 m / min, or a range between any two of them.

[0104] Further, when the solid content of the ceramic slurry is 50% to 60%, a slot die coating head is used for coating.

[0105] In step S36, the coated film obtained in step S35 is dried and shaped.

[0106] In some possible embodiments, the coated film is sequentially passed through a preheating section and a setting section in the oven, the temperature of the preheating section is 80-140℃, and the temperature of the setting section is 90-150℃.

[0107] Preheating the coated film in the preheating section at 80-140℃ and setting the coated film in the setting section at 90-150℃ can reduce the water content of the battery separator 100 and improve the adhesion of the battery separator 100.

[0108] For example, the temperature of the preheating section can be one of 80℃, 90℃, 100℃, 110℃, 120℃, 130℃ or 140℃, or a range between any two of them.

[0109] For example, the temperature of the heat setting section can be one of 90℃, 100℃, 110℃, 120℃, 130℃, 140℃ or 150℃, or a range between any two of them.

[0110] In steps S37 and S38, the battery separator 100 is wound and slitted to obtain a battery separator 100 of a set size. In step S39, the battery separator 100 is packed for easy delivery.

[0111] Further, the examples of the present application provide a battery separator 100 prepared according to the above preparation method.

[0112] The battery separator 100 provided by the examples of the present application comprises a porous film 101 and a ceramic coating 102 coated on the porous film 101.

[0113] In some possible embodiments, the thickness of the porous film 101 can be 3-30μm, the thickness of the ceramic coating 102 can be 1-5μm, and the thickness of the battery separator 100 can be 4-35μm.

[0114] In the battery separator 100 provided by the examples of the present application, the porous film 101 and the ceramic coating 102 have high adhesion, and the battery separator 100 has low thermal shrinkage, which can improve the safety and stability of the battery when applied to the battery.

[0115] The battery separator 100 of the present application is further described in detail below in conjunction with embodiments.

[0116] Embodiment 1

[0117] Embodiment 1 provides a battery separator 100, and the preparation method is as follows:

[0118] (1) Feeding step: the raw materials include 20% polyethylene powder and 80% paraffin oil by mass percentage; the raw materials are input into an extruder for melt extrusion;

[0119] (2) Extrusion casting step: the cooling temperature of the casting roll after the die head is 20℃, the speed is 6m / min, and the residence time is 10min;

[0120] (3) Two-way stretching step: the longitudinal stretching ratio is 6 times, and the transverse stretching ratio is 5 times;

[0121] (4) Extraction step: the substrate is input into an extraction tank for extraction to remove part of the paraffin oil in the substrate and form pores to obtain a porous membrane 101; in the extraction process, the extraction hot plate temperature is 60℃, the roll temperature is 35℃, the environmental temperature is 26℃, the exhaust power is 25Hz, and the water content of the porous membrane 101 after extraction is controlled to be 2%;

[0122] (5) Coating step: ceramic slurry is coated on the porous membrane 101 by using a slot coating head to fully mix the ceramic slurry and the water on the surface of the porous membrane 101, the coating speed is 80m / min, the coating thickness is 3μm, and a coated membrane is obtained; the solid content of the ceramic slurry is 50%, and the components of the ceramic slurry include, by weight percentage: 48% of alumina powder, 46.4% of water, 4.3% of adhesive, and 1.3% of other additives.

[0123] (6) Drying and shaping step: the coated membrane is transported to an oven for drying and shaping. The oven process temperature is set to be step-controlled, the preheating section temperature is 80℃, and the shaping section temperature is 100℃, to obtain a battery separator 100 with a porous membrane 101 thickness of 9μm and a ceramic coating 102 thickness of 3μm.

[0124] Example 2

[0125] Example 2 provides a battery separator 100, and the difference between Example 2 and Example 1 is that:

[0126] In step (4), the extraction hot plate temperature is 60℃, the roll temperature is 34℃, the environmental temperature is 25℃, the exhaust power is 25Hz, and the water content of the porous membrane 101 after extraction is controlled to be 2.3%;

[0127] In step (5), the coating speed is 78m / min, the solid content of the ceramic slurry is 55%, and the components of the ceramic slurry include, by weight percentage: 52% of alumina powder, 40.5% of water, 5.5% of adhesive, and 2.0% of other additives;

[0128] In step (6), the preheating section temperature is 79℃, and the shaping section temperature is 98℃.

[0129] Example 3

[0130] Example 3 provides a battery separator 100, and the difference between Example 3 and Example 1 is that:

[0131] In step (4), the extraction hot plate temperature is 58℃, the roller temperature is 34℃, the ambient temperature is 25℃, the exhaust power is 23Hz, and the water content of the porous membrane 101 after extraction is controlled to be 2.8%.

[0132] In step (5), the coating speed is 75m / min, the solid content of the ceramic slurry is 60%, and the components of the ceramic slurry include, by weight percentage: 57% of alumina powder, 34.7% of water, 6% of adhesive, and 2.3% of other additives.

[0133] In step (6), the preheating section temperature is 78℃, and the setting section temperature is 98℃.

[0134] Comparative Example 1

[0135] Comparative Example 1 provides a battery separator 100, which is prepared as follows:

[0136] (1) Feeding step: the raw materials include, by mass percentage: 20% of polyethylene powder and 80% of paraffin oil; the raw materials are input into an extruder for melt extrusion;

[0137] (2) Extrusion casting step: the cooling temperature of the casting roller after the die head is 20℃, the speed is 6m / min, and the residence time is 10min;

[0138] (3) Two-way stretching step: the longitudinal stretching ratio is 6 times, and the transverse stretching ratio is 5 times;

[0139] (4) Extraction step: the substrate is input into an extraction tank for extraction to remove part of the paraffin oil in the substrate and form pores, to obtain a porous membrane 101; in the extraction process, the extraction hot plate temperature is 60℃, the roller temperature is 35℃, and the ambient temperature is 25℃;

[0140] (5) Drying and setting step: the porous membrane 101 is transported to an oven for drying and setting. The oven process temperature is 100℃, and the porous membrane 101 with a thickness of 9μm is obtained after winding.

[0141] (6) Unwinding and preheating: the porous membrane 101 is unwound and preheated; the preheating temperature is 70℃.

[0142] (7) Coating step: the ceramic slurry is coated on the porous membrane 101 using a gravure roll, the coating speed is 120m / min, the coating thickness is 3μm, and a coated membrane is obtained; the solid content of the ceramic slurry is 35%, and the components of the ceramic slurry include, by weight percentage: 32% of alumina powder, 63.3% of water, 3.2% of adhesive, and 1.5% of other additives.

[0143] (8) Drying and setting step: the coated film is transported to an oven for drying and setting. The oven process temperature is set to step control, the preheating section temperature is 60℃, and the setting section temperature is 65℃, to obtain a battery separator 100 with a porous membrane 101 thickness of 9μm and a ceramic coating 102 thickness of 3μm.

[0144] Comparative Example 2

[0145] Comparative Example 2 provides a battery separator 100, which is different from Example 1 in that:

[0146] In step (4), in the extraction process, the extraction hot plate temperature is 62℃, the roller temperature is 30℃, and the ambient temperature is 27℃, and the water content of the porous membrane 101 after extraction is controlled to be 1%.

[0147] In step (5), the solid content of the ceramic slurry is 35%, and the components of the ceramic slurry include, by weight percentage: 32% alumina powder, 63.3% water, 3.2% adhesive, and 1.5% other additives.

[0148] Comparative Example 3

[0149] Comparative Example 3 provides a battery separator 100, which is different from Example 1 in that:

[0150] In step (4), in the extraction process, the extraction hot plate temperature is 50℃, the roller temperature is 30℃, and the ambient temperature is 20℃, and the water content of the porous membrane 101 after extraction is controlled to be greater than 5%.

[0151] In step (5), the solid content of the ceramic slurry is 65%, and the components of the ceramic slurry include, by weight percentage: 62% alumina powder, 29.3% water, 6.4% adhesive, and 2.5% other additives.

[0152] Test Example

[0153] The battery separators 100 provided in Examples 1-3 and Comparative Examples 1-3 are subjected to heat shrinkage rate testing, peel strength testing, and moisture content testing, and the test results are shown in Table 1.

[0154] The heat shrinkage rate testing method includes:

[0155] Five samples with a size of 160mm×130mm are uniformly cut in the TD direction of the film roll, and a 100mm×100mm area is drawn with a ruler to measure the original length L1.

[0156] The oven is preheated to the set temperature and stabilized for more than 2 hours. The sample film with the drawn lines is clamped between two A4 papers and placed in the oven. After the specified time, it is taken out and cooled to room temperature. The longitudinal and transverse marker lengths L2 are measured, and the heat shrinkage calculation formula is as follows:

[0157]

[0158] In the formula:

[0159] S - thermal shrinkage, %;

[0160] L1 - length before heating, mm;

[0161] L2 - length after heating, mm.

[0162] The arithmetic mean of 5 samples was taken.

[0163] The peeling force test method includes:

[0164] Using an electronic tensile testing machine, the film roll was cut into a standard sample of 150 mm long x 15 mm wide, and a 30 mm double-sided adhesive tape was cut and adhered to the glass slide. The ceramic side of the sample was adhered to the tape, and the end of the sample was torn open about 1 cm. The upper end of the clamp was clamped to the glass slide, and the lower end was clamped to the end of the sample that had been torn open. The peeling speed was selected, the start button was pressed, and the effective peeling length of the adhesive surface was 100 mm to ensure that the peeling test was conducted. The peeling curve was recorded.

[0165] Five samples were taken in the longitudinal and transverse directions, respectively, and the arithmetic mean was taken after testing to obtain the peeling force data of the sample.

[0166] The moisture content test method includes:

[0167] The Karl Fischer moisture test method was used to test the moisture content of the diaphragm product. The specific steps are as follows:

[0168] The sample was weighed and placed in a dry container, and Karl Fischer reagent was added to completely cover the sample.

[0169] The sample and Karl Fischer reagent were thoroughly mixed to allow the reaction to proceed.

[0170] During the reaction, iodine in the Karl Fischer reagent reacts with water in the sample, consuming a certain amount of iodine.

[0171] By measuring the change in iodine concentration before and after the reaction, the moisture content of the sample can be calculated. This method is suitable for measuring trace amounts of moisture.

[0172] Five samples were taken, tested, and the arithmetic mean was taken to obtain the moisture data of the sample.

[0173] Table 1

[0174]

[0175] Results analysis:

[0176] As can be seen from Table 1, in Comparative Examples 1-3 and Comparative Examples 2-3, in Comparative Example 2, the solid content of the ceramic slurry is 35%, which is lower than 45%, and the battery separator 100 obtained has a larger thermal shrinkage and a smaller peeling force; in Comparative Example 3, the water content of the porous membrane exceeds 5%, and the battery separator 100 obtained has a smaller peeling force, which indicates that, according to the preparation method provided in the embodiments of the present application, the ceramic slurry is coated on the porous membrane 101 after extraction to form a coated membrane, and then the coated membrane is dried and shaped, and the water content of the porous membrane 101 is 1%-5% and the solid content of the ceramic slurry is 45-80%, which can improve the adhesion of the battery separator 100 while reducing the thermal shrinkage.

[0177] As can be seen from Comparative Examples 1-3 and Comparative Example 1, it is indicated that, according to the preparation method provided in the embodiments of the present application, the ceramic slurry is coated on the porous membrane 101 after extraction to form a coated membrane, and then the coated membrane is dried and shaped, which not only can simplify the preparation process and improve the preparation efficiency, but also can improve the adhesion of the battery separator 100 while reducing the thermal shrinkage.

[0178] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Those skilled in the art can make various modifications and changes to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of preparing a battery separator, characterized by, The preparation method comprises the following steps: an extraction step of extracting the substrate to obtain a porous membrane; a coating step of coating a ceramic slurry on the porous membrane to form a coated membrane; a drying and setting step of drying and setting the coated membrane to obtain the battery separator; wherein, in the coating step, the water content of the porous membrane is 1-5%, and the solid content of the ceramic slurry is 45-80%; the method for regulating the water content of the porous membrane comprises: in the extraction step, the temperature of the extraction roller is 25-60 ℃, the temperature of the extraction hot plate is 50-100 ℃, the ambient temperature is 20-40 ℃, and the exhaust power is 23-30 Hz; the preparation method comprises: after the extraction of the porous membrane, the slurry is coated on the porous membrane, and then the coated membrane is dried and set to realize the drying of the porous membrane and the coating layer in one drying and setting process.

2. The production method according to claim 1, characterized by, The water content of the porous membrane is 2-3%, and the solid content of the ceramic slurry is 50-60%.

3. The production method according to claim 2, characterized by, The method for coating the ceramic slurry on the porous membrane comprises: The ceramic slurry is coated on the porous membrane by using a gravure roller or a slot die at a coating speed of 60-120 m / min.

4. The production method according to claim 3, characterized by, The ceramic slurry with a solid content of 50-60% is coated on the porous membrane by using a slot die.

5. The production method according to claim 1, characterized by, The thickness of the porous membrane is 3-30 μm, and the thickness of the ceramic slurry coated on the porous membrane is 1-5 μm.

6. The method of claim 1, wherein, The ceramic slurry comprises ceramic powder, a solvent and an adhesive.

7. The production method according to claim 1, characterized by, In the drying and setting step, the coated membrane sequentially passes through a preheating section and a setting section in an oven, the temperature of the preheating section is 80-140 ℃, and the temperature of the setting section is 90-150 ℃.

8. The method of claim 1, wherein, The preparation method further comprises a pretreatment step before the extraction step, and the pretreatment step comprises: melting and extruding raw materials for forming the substrate to a casting roller to form a casting sheet; and obtaining the substrate by stretching the casting sheet in two directions.

9. The production method according to claim 8, characterized by, The preparation method further comprises a post-treatment step after the drying and setting step, and the post-treatment step comprises: sequentially winding and slitting the battery separator obtained in the drying and setting step.

10. The preparation method according to claim 8, characterized in that The raw materials comprise polyolefin and pore-forming agent; The cooling temperature of the casting roller is 19-30 ℃, the speed is 4-11 m / min, and the residence time is 10-15 min; The two-way stretching comprises longitudinal stretching and transverse stretching, the stretching ratio of the longitudinal stretching is 6-12 times, and the stretching ratio of the transverse stretching is 5-10 times.

11. A battery separator characterized by, The battery separator is prepared by the preparation method according to any one of claims 1-10.

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