A functional composition, a battery separator comprising the same, and a preparation method thereof

Abstract

The present invention provides a functional composition, a battery separator comprising the same, and a preparation method. In terms of mass percentage, the functional composition comprises 60-80% of an insulating resin and 5-15% of an ion-conducting resin; the insulating resin comprises an imide polymer; the molecular chain of the imide polymer contains an aliphatic structural unit and a functional group; the ion-conducting resin comprises at least one of polyamic acid salt, polyimide-amide acid salt or polyacrylonitrile-acrylate. In the present invention, the functional composition is compounded with insulating resin and ion-conducting resin of specific contents and types, so that the separator comprising the functional composition has excellent breakdown strength, good ion transportability and good adhesion to the electrode tab, can improve the structural stability of the separator, reduce the risk of battery short circuit, and improve the use safety of the battery separator.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a functional composition, a battery separator containing the functional composition, and a preparation method thereof. Background Art

[0002] Lithium-ion battery separators mainly play an important role in isolating the positive and negative electrodes, preventing battery short circuits, and providing lithium ion transmission channels to ensure the normal operation of the battery. Therefore, lithium-ion battery separators play a vital role in the internal resistance, capacity, cycle life and safety of the battery.

[0003] At present, with the rapid development of the new energy industry, consumer electronic devices have become smaller and smaller, and the space for accommodating batteries has been greatly compressed. At the same time, the demand for the range of electric vehicles has increased significantly, and the energy density of batteries has become increasingly higher. Therefore, the thinning of battery separators has become the mainstream direction of today's technological development. However, as the separator becomes thinner, the insulation performance of the separator decreases significantly, and it is very easy to be broken down under the working voltage, so that the positive and negative electrodes are in direct contact and short-circuited, which in turn causes the battery to catch fire and explode, posing a great threat to the safety of terminal equipment.

[0004] CN107611322A discloses a high-strength lithium battery separator and its production process, wherein a halogenated ketone compound and a dihydroxy compound are placed in a solvent to synthesize polyetheretherketone under the action of carbonate, and the polyetheretherketone nanofiber membrane obtained by melt extrusion is stretched at high temperature to form a high-strength lithium battery separator. The high-strength lithium battery separator has the advantages of small pore size, large specific surface area, high tear strength, high puncture strength, high electrical breakdown strength, and good chemical stability. However, the breakdown strength, ion transmission performance and air permeability of the separator need to be further improved.

[0005] CN103000851A discloses a polysulfone nanofiber diaphragm for lithium batteries and a preparation method thereof. The polysulfone nanofiber diaphragm for lithium batteries is made by dissolving one or multiple polysulfones in any proportion in a polar organic solvent and then electrospinning; it has tear resistance, heat shrinkage resistance, high temperature resistance, good uniformity, and high porosity. However, the breakdown strength, ion transmission performance, and air permeability of the diaphragm need to be further improved.

[0006] Therefore, how to improve the breakdown strength of lightweight and thin membranes, ensure the safety of batteries in normal use scenarios, and improve the ion transmission performance and air permeability of the membrane has become a key technical problem that needs to be urgently solved in the field of lithium battery membranes. Summary of the invention

[0007] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a functional composition, a battery separator containing the same, and a preparation method. The functional composition is compounded with insulating resin and ion-conducting resin in specific contents and types, so that the separator including the functional composition has excellent breakdown strength, good ion transportability, and good adhesion to the electrode plate, can improve the structural stability of the separator, reduce the risk of battery short circuit, and improve the safety of use of the battery separator.

[0008] To achieve this purpose, the present invention adopts the following technical solutions:

[0009] In the first aspect, the present invention provides a functional composition. In terms of mass percentage, the functional composition includes 60-80% of insulating resin and 5-15% of ion-conducting resin; the insulating resin includes imide polymers; the molecular chain of the imide polymer contains an aliphatic structural unit and a functional group; the ion-conducting resin includes at least one of polyamic acid salt, polyimide-amide acid salt, or polyacrylonitrile-acrylate.

[0010] In the present invention, an imide polymer with an aliphatic structural unit and a functional group in its molecular chain is selected. On the one hand, the dielectric constant of the aliphatic structural unit is small, which can endow the imide polymer with excellent insulating properties, thus effectively improving the breakdown strength of the battery separator; on the other hand, the aliphatic structural unit has good flexibility, which can reduce the glass transition temperature of the insulating resin and improve the permeability of the functional layer, thereby enhancing the adhesion between the functional layer and the porous substrate film; the introduction of the functional group can increase the cohesive force of the functional layer and further improve the adhesion between the separator functional layer and the separator; by compounding a specific type of ion-conducting resin with the insulating resin, while effectively improving the lithium ion transport performance of the functional layer, the compatibility with the insulating resin containing imide polymer is improved, avoiding the phase separation phenomenon caused by component repulsion, effectively improving the stability and coating consistency of the separator functional layer coating slurry, thereby reducing the coating defects of the separator functional layer and reducing the possibility of being voltage-breakdown due to the coating defects of the functional layer during the battery operation, and improving the breakdown strength of the separator.

[0011] Preferably, in terms of mass percentage, the functional composition includes 60-80% of insulating resin, for example, it can be 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, etc.

[0012] Preferably, by mass percentage, the functional composition comprises 5-15% of an ion-conductive resin, such as 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, etc.

[0013] Preferably, the functional groups include at least one of an amide group, an ether group, an ester group, a urethane group, a urea group, a carbonate group, a siloxane group or an epoxy group.

[0014] Preferably, the imide polymers include at least one of polyamide-imide, polyether-imide, polyester-imide, polyurethane-imide, polyurea-imide, polycarbonate-amide, polyurethane-amide-imide, polysiloxane-imide or polysiloxane-epoxy-imide.

[0015] Preferably, the mass percentage of the aliphatic structural units in the molecular chain of the imide polymers is ≥30%, such as 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc.

[0016] Preferably, the aliphatic structural units include chain-type divalent aliphatic hydrocarbon structural units.

[0017] In the present invention, for the imide polymers, as long as they can obtain the technical characteristics and structural characteristics of the imide polymers described in the present invention, there are no particular restrictions on their obtaining routes and obtaining methods. They can be purchased from commercially available products or obtained by design synthesis. When the imide polymers are obtained by design synthesis, their synthesis methods and synthesis routes are not particularly limited. For example, a diamine or diamine prepolymer with an aliphatic or semi-aliphatic structure containing one or more groups of an amide group, an ether group, an ester group, a urethane group, a urea group, a carbonate group, a siloxane group or an epoxy group in the main chain can be first synthesized by a disclosed method, and then subjected to a condensation polymerization reaction with a dianhydride and an acyl chloride-dianhydride. Specifically, as an example that can be listed but not limited, molten polymerization reaction can be carried out between hexamethylenediamine in excess molar ratio and dodecanedioic acid to generate a polyamide prepolymer terminated with diamine, and then condensation polymerization is carried out with pyromellitic dianhydride, followed by dehydration reaction to generate polyamide-imide; for another example, condensation polymerization can be carried out between polyetheramine D400, hexamethylenediamine and biphenyltetracarboxylic dianhydride, followed by dehydration reaction to generate polyether-imide; for another example, reaction can be carried out between hexamethylene diisocyanate in excess molar ratio and polyether diol N210 to generate a polyurethane prepolymer terminated with diisocyanate group, and then condensation polymerization is carried out with 3,3',4,4'-benzophenone tetracarboxylic dianhydride to generate polyurethane-imide.

[0018] Preferably, the polyamic acid salt includes at least one of a lithium polyamic acid salt, a sodium polyamic acid salt, or a potassium polyamic acid salt.

[0019] Preferably, the polyimide-amide acid salt includes at least one of a lithium polyimide-amide acid salt, a sodium polyimide-amide acid salt, or a potassium polyimide-amide acid salt.

[0020] Preferably, the polyacrylonitrile-acrylate includes at least one of a lithium polyacrylonitrile-acrylate, a sodium polyacrylonitrile-acrylate, or a potassium polyacrylonitrile-acrylate.

[0021] Preferably, based on mass percentage, the functional composition further includes 5-15% of an adhesive resin, which can be, for example, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, etc.

[0022] Preferably, the adhesive resin includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-propylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, vinylidene fluoride-trifluorochloroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, polyacrylonitrile, polyacrylamide, polymethyl methacrylate, or polyethyl methacrylate.

[0023] Preferably, based on mass percentage, the functional composition further includes 5-15% of an inorganic filler, which can be, for example, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, etc.

[0024] Preferably, the inorganic filler includes at least one of aluminum oxide, silicon dioxide, titanium dioxide, zirconium dioxide, tin dioxide, zinc oxide, calcium oxide, magnesium oxide, magnesium nitride, boehmite, or barium sulfate.

[0025] Preferably, the particle size of the inorganic filler is 0.02-2 μm, which can be, for example, 0.04 μm, 0.06 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, etc.

[0026] In the present invention, the addition of the inorganic filler helps to protect the surface of the separator, improve the surface hardness, reduce the risk of defects in the separator caused by mechanical external force and subsequent voltage breakdown; meanwhile, it improves the resistance of the separator to thermal shock.

[0027] In the present invention, if the particle size of the inorganic filler is too large, it will lead to an excessive thickness of the functional layer, an extended lithium ion transmission path, and an increase in the internal resistance of the battery.

[0028] In a second aspect, the present invention provides a battery separator, which comprises a porous base film and a functional layer; the functional layer covers at least one surface of the porous base film, is distributed inside the porous base film and / or penetrates through two surfaces of the porous base film; and the material of the functional layer comprises the functional composition as described in the first aspect.

[0029] Preferably, the functional layer is a reticular porous structure.

[0030] Preferably, the thickness of the functional layer is ≤ 3 μm, and for example, it can be 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, etc.

[0031] In the present invention, the thickness refers to the thickness of a single-layer functional layer. Increasing the thickness of the functional layer can increase the breakdown strength of the battery separator, but it will simultaneously extend the lithium ion transmission path and reduce the lithium ion passing speed, thereby increasing the internal resistance of the battery cell and affecting the performance of the battery cell. When the functional layer is within a specific thickness range, it can not only maintain excellent insulation performance of the separator but also meet the performance requirements of the battery cell.

[0032] Preferably, the material of the porous base film comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyacrylonitrile, polyimide, polyamide, polyester, polyether ether ketone, polyurethane, polyurea, polysulfone, polyphenylene sulfide, polystyrene, polyvinyl acetate, polyethylene terephthalate, polymethyl methacrylate or cellulose acetate.

[0033] Preferably, the thickness of the porous base film is 5 - 10 μm, and for example, it can be 6 μm, 7 μm, 8 μm, 9 μm, etc.

[0034] Preferably, the breakdown strength of the battery separator is greater than 180 kV / mm, and for example, it can be 185 kV / mm, 190 kV / mm, 200 kV / mm, 205 kV / mm, 210 kV / mm, 215 kV / mm, 220 kV / mm, 225 kV / mm, 230 kV / mm, 240 kV / mm, 250 kV / mm, 260 kV / mm, 270 kV / mm, 280 kV / mm, 290 kV / mm, 300 kV / mm, etc.

[0035] In a third aspect, the present invention provides a preparation method of the battery separator as described in the second aspect, and the preparation method comprises:

[0036] (1) Mix the functional composition with a solvent to obtain a slurry;

[0037] (2) Coat the slurry obtained in step (1) onto at least one surface of the porous base film to obtain a coated film; cure the coated film to obtain the battery separator.

[0038] Preferably, the solvent in step (1) includes a mixed solution of an organic solvent and water.

[0039] Preferably, the organic solvent includes, but is not limited to, N-methylpyrrolidone.

[0040] Preferably, the mixing in step (1) includes pre-mixing an insulating resin, an ion-conducting resin and an optional adhesive resin, and then adding an optional inorganic filler for mixing to obtain the slurry.

[0041] Preferably, the rotation speed of the pre-mixing is 500 - 1000 rpm, for example, it can be 600 rpm, 700 rpm, 800 rpm, 900 rpm, etc.

[0042] Preferably, the rotation speed of the mixing is 1500 - 2500 rpm, for example, it can be 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm, 2000 rpm, 2100 rpm, 2200 rpm, 2300 rpm, 2400 rpm, etc.

[0043] Preferably, the coating method in step (2) includes at least one of dip coating, spray coating, spin coating, roll coating or blade coating.

[0044] Preferably, the curing method in step (2) includes at least one of non-solvent induced phase separation curing, thermal curing or ultraviolet curing.

[0045] Preferably, the non-solvent induced phase separation curing method includes soaking the coated film in a first-stage coagulation bath and a second-stage coagulation bath in sequence, and drying to obtain the battery separator.

[0046] Preferably, the first-stage coagulation bath includes a mixed solution of an organic solvent and water with a volume ratio of (70 - 80):(20 - 30); for example, it can be 70:30, 72:28, 75:25, 78:22, 80:20, etc.

[0047] Preferably, the soaking time in the first-stage coagulation bath is 50 - 70 s, for example, it can be 55 s, 60 s, 65 s, etc.

[0048] Preferably, the second-stage coagulation bath comprises a mixed solution of an organic solvent and water with a volume ratio of (15-25):(75-85); for example, it can be 15:85, 18:82, 20:80, 22:78, 25:75, etc.

[0049] Preferably, the soaking time in the second-stage coagulation bath is 20-40 s, for example, it can be 25 s, 30 s, 35 s, etc.

[0050] In the present invention, the organic solvent in the coagulation bath includes but is not limited to N-methylpyrrolidone and / or dimethylacetamide.

[0051] In the present invention, the drying temperature is 50-70 °C, for example, it can be 55 °C, 60 °C, 65 °C, etc.

[0052] The numerical ranges described in the present invention not only include the above-listed point values, but also include any point values between the above numerical ranges not listed. Due to space limitations and for the sake of simplicity, the specific point values included in the described ranges are not exhaustively listed in the present invention.

[0053] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0054] The functional composition provided by the present invention, through the compounding of insulating resin and ion-conducting resin with specific contents and types, enables the separator including the functional composition to have excellent breakdown strength, good ion transportability, and good adhesion to the electrode pole piece, can improve the structural stability of the separator, reduce the risk of battery short circuit, and improve the safety of use of the battery separator. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a scanning electron microscope picture of the battery separator provided in Example 1 of the present invention.

[0056] Figure 2 It is a scanning electron microscope picture of the battery separator provided in Example 2 of the present invention.

[0057] Figure 3 It is a scanning electron microscope picture of the battery separator provided in Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0058] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0059] In the present invention, the materials used are as follows:

[0060] Polyimide-amide acid lithium salt: Fill a round-bottom flask with nitrogen to completely displace the air inside. Under stirring at room temperature, dissolve 6.49 g of 4,4'-diaminodiphenyl ether and 3.95 g of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane in 150 g of N-methylpyrrolidone, and then gradually add 9.56 g of pyromellitic dianhydride. Stir and react at room temperature for 10 h. Then slowly add 15 g of a 10% LiOH aqueous solution thereto, stir and react for 4 h. Place the obtained glue solution in a vacuum oven at 100 °C for drying to obtain polyimide-amide acid lithium salt.

[0061] Polyimide-amide acid sodium salt: The preparation method is the same as that of polyimide-amide acid lithium salt, except that LiOH is replaced with an equal mass of NaOH aqueous solution (mass concentration 10%).

[0062] Polyacrylonitrile-acrylic acid lithium salt: Fill a round-bottom flask with nitrogen to completely displace the air inside. Disperse 7.37 g of acrylonitrile, 0.12 g of nonylphenol polyoxyethylene ether, and 0.09 g of potassium persulfate evenly in 20 g of deionized water by stirring. Raise the temperature to 63 °C, and then dropwise add an aqueous solution of lithium acrylate (50 wt%) containing 2.49 g. Keep the temperature and react for 4 h. After vacuum drying to remove water, polyacrylonitrile-acrylic acid lithium salt is obtained.

[0063] Preparation Example 1

[0064] Polyamide-imide

[0065] The preparation method includes: Add 116 g of hexamethylenediamine, 153 g of dodecanedioic acid, and 90 g of deionized water to a pressure-resistant reaction kettle. While introducing nitrogen, heat up to 80 °C with stirring to form a polyamide prepolymer terminated with diamine. Then add 109 g of pyromellitic dianhydride, seal the reaction kettle, heat up to 220 °C with stirring, and at the same time, discharge water vapor through the exhaust valve to keep the pressure inside the kettle constant. React in this way for 2 h. Then raise the temperature to 260 °C, maintain the kettle temperature and react for 2 h, and discharge water vapor through the exhaust valve during this period. After uniformly reducing the pressure inside the kettle to atmospheric pressure, use a vacuum system to reduce the kettle pressure to -0.06 MPa and continue to react for 1 h. Stop vacuum pumping, fill nitrogen to 0.5 MPa, open the discharge valve to discharge the material, and after cooling and pulverizing, polyamide-imide is obtained.

[0066] Preparation Example 2

[0067] Polyether-imide

[0068] The preparation method includes: adding 100 g of polyetheramine D400, 87 g of hexamethylenediamine, and 218 g of biphenyltetracarboxylic dianhydride into a pressure-resistant reaction kettle. After introducing nitrogen, the reaction kettle is sealed. While stirring, the temperature is raised to 205 °C. Meanwhile, water vapor is discharged through the exhaust valve to keep the pressure in the kettle constant. The reaction is carried out for 2 h in this way. Then the temperature is raised to 230 °C, and the reaction is maintained at this temperature for 2 h. During this period, water vapor is discharged through the exhaust valve. After the pressure in the kettle is uniformly reduced to atmospheric pressure, the pressure in the kettle is reduced to -0.06 MPa through a vacuum system and the reaction continues for 1 h. The vacuum pumping is stopped, nitrogen is filled to 0.5 MPa, the discharge valve is opened to discharge the material, and after cooling and pulverizing, polyether-imide is obtained.

[0069] Preparation Example 3

[0070] Polyurethane-imide

[0071] The preparation method includes: adding 300 g of polyether diol N210 into an atmospheric-pressure reaction kettle equipped with a stirrer. Nitrogen is introduced and stirring is started. A mixed solution containing 168 g of hexamethylene diisocyanate and 468 g of N-methylpyrrolidone is gradually added dropwise. The temperature is kept at 55 °C and the reaction is carried out for 2 h to form a polyurethane prepolymer solution capped with a biisocyanate group. Then 225 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride is added into the reaction kettle, and the temperature is raised to 140 °C for polycondensation reaction for 4 h. After the reaction is completed, the solvent is removed by drying to obtain polyurethane-imide.

[0072] Example 1

[0073] This example provides a functional composition, including 72 g of polyamide-imide (Preparation Example 1), 13 g of polyimide-amide acid lithium salt, 10 g of polyvinylidene fluoride (PVDF, Solvay, USA), and 5 g of boehmite.

[0074] This example provides a battery separator with a thickness of 10 μm. The battery separator includes a porous polyethylene film (thickness 7 μm) and a functional layer (the material is the above functional composition).

[0075] This example provides a preparation method of a battery separator, which specifically includes the following steps:

[0076] (1) According to the formula amount, add the polyamide-imide, polyimide-amide acid lithium salt, and polyvinylidene fluoride into a mixed solution of 560 g of N-methylpyrrolidone (NMP) and 8 g of ultrapure water. After stirring and dissolving at a stirring speed of 600 rpm, add boehmite and carry out stirring and dispersion at a dispersion speed of 2000 rpm to obtain a coating slurry;

[0077] (2) The coating slurry obtained in step (1) is uniformly coated on both surfaces of a porous polyethylene-based membrane by a microgravure coater to obtain a coated membrane; the coated membrane is subjected to non-solvent induced phase separation curing in a coagulation bath, soaked in a first-stage coagulation bath (NMP: water volume ratio = 75:25) for 60 s, soaked in a second-stage coagulation bath (NMP: water volume ratio = 20:80) for 30 s, and then washed with deionized water to remove the residual solvent in the separator coating. After drying in an oven at 60 °C, the battery separator is obtained.

[0078] The morphology of the battery separator obtained in Example 1 was characterized by scanning electron microscopy (Zeiss SEM GeminiSEM field emission scanning electron microscope), and the results are as Figure 1 shown, and it can be seen that the functional layer on the surface of the separator is a porous structure.

[0079] Example 2

[0080] This example provides a functional composition, including 60 g of polyether-imide (Preparation Example 2), 15 g of polyimide-amino acid lithium salt, 10 g of polyvinylidene fluoride (PVDF, Solvay, USA), and 15 g of boehmite.

[0081] This example provides a battery separator with a thickness of 10 μm. The battery separator includes a porous polyethylene-based membrane (thickness 7 μm) and a functional layer (the material is the above-mentioned functional composition).

[0082] This example provides a method for preparing a battery separator, which specifically includes the following steps:

[0083] (1) According to the formula amount, the polyether-imide, polyimide-amino acid lithium salt, and polyvinylidene fluoride are added to a mixed solution of 490 g of N-methylpyrrolidone (NMP) and 6 g of ultrapure water, stirred and dissolved at a stirring speed of 600 rpm, and then boehmite is added and stirred and dispersed at a dispersion speed of 2000 rpm to obtain a coating slurry;

[0084] (2) The coating slurry obtained in step (1) is uniformly coated on both surfaces of a porous polyethylene-based membrane by a microgravure coater to obtain a coated membrane; the coated membrane is subjected to non-solvent induced phase separation curing in a coagulation bath, soaked in a first-stage coagulation bath (NMP: water volume ratio = 75:25) for 60 s, soaked in a second-stage coagulation bath (NMP: water volume ratio = 20:80) for 30 s, and then washed with deionized water to remove the residual solvent in the separator coating. After drying in an oven at 60 °C, the battery separator is obtained.

[0085] The morphology of the battery separator obtained in Example 2 was characterized using a scanning electron microscope (Zeiss SEM GeminiSEM field emission scanning electron microscope), and the results are as follows: Figure 2 As shown, it can be seen that the functional layer on the separator surface is a porous structure.

[0086] Example 3

[0087] This example provides a functional composition, including 80 g of polyurethane-imide (Preparation Example 3), 5 g of polyimide-sodium amide, 6 g of polyvinylidene fluoride (PVDF, Solvay, USA), and 9 g of boehmite.

[0088] This example provides a battery separator with a thickness of 11 μm. The battery separator includes a porous polypropylene base film (thickness 7 μm) and a functional layer (the material is the above functional composition).

[0089] This example provides a method for preparing a battery separator, and the specific steps are the same as those in Example 2.

[0090] The morphology of the battery separator obtained in Example 3 was characterized using a scanning electron microscope (Zeiss SEM GeminiSEM field emission scanning electron microscope), and the results are as follows: Figure 3 As shown, it can be seen that the functional layer on the separator surface is a porous structure.

[0091] Example 4

[0092] This example provides a functional composition, including 80 g of polyurethane-imide (Preparation Example 3), 5 g of polyacrylonitrile-lithium acrylate, 5 g of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, Arkema, France), and 10 g of boehmite.

[0093] This example provides a battery separator with a thickness of 10 μm. The battery separator includes a porous polypropylene base film (thickness 7 μm) and a functional layer (the material is the above functional composition).

[0094] This example provides a method for preparing a battery separator, and the specific steps are the same as those in Example 2.

[0095] Example 5

[0096] This example provides a functional composition, including 72 g of polyamide-imide (Preparation Example 1), 13 g of polyimide-amide lithium salt, 10 g of polyvinylidene fluoride (PVDF, Solvay, USA), and 5 g of aluminum oxide.

[0097] This example provides a battery separator with a thickness of 15 μm. The battery separator includes a porous polypropylene base film (thickness 9 μm) and a functional layer (the material is the above functional composition).

[0098] This embodiment provides a method for preparing a battery separator, which specifically includes the following steps:

[0099] (1) According to the formulation amounts, add the polyamide-imide, polyimide-amide acid lithium salt, and polyvinylidene fluoride into a mixed solution of 560 g of N-methylpyrrolidone (NMP) and 8 g of ultrapure water. After stirring and dissolving at a stirring speed of 800 rpm, add aluminum oxide and perform stirring and dispersion at a dispersion speed of 2200 rpm to obtain a coating slurry.

[0100] (2) Uniformly coat the coating slurry obtained in step (1) on both surfaces of a porous polyethylene film through a microgravure coater to obtain a coated film; subject the coated film to non-solvent induced phase separation curing in a coagulation bath. Immerse it in the first-stage coagulation bath (volume ratio of dimethylacetamide: water = 80:20) for 60 s, immerse it in the second-stage coagulation bath (volume ratio of dimethylacetamide: water = 25:75) for 30 s, and then wash it with deionized water to remove the residual solvent in the separator coating. After drying in an oven at 60 °C, obtain the battery separator.

[0101] Example 6

[0102] This embodiment provides a functional composition and a battery separator containing the functional composition. The difference from Example 1 is only that in the method for preparing the battery separator, first mix boehmite and polyvinylidene fluoride with a mixed solution of N-methylpyrrolidone and ultrapure water, coat it on both surfaces of the porous polyethylene film, and after drying at 60 °C, obtain an inorganic filler layer; subsequently, mix polyamide-imide and polyimide-amide acid lithium salt with a mixed solution of N-methylpyrrolidone and ultrapure water, coat it on the surface of the inorganic filler layer, and perform step (2). Other raw materials, dosages, and step parameters are the same as those in Example 1.

[0103] Comparative Example 1

[0104] This comparative example provides a functional composition. The difference from Example 1 is only that the polyamide-imide is replaced with an equal mass of wholly aromatic polyether-imide (Sabic, CRS5001), and other components and dosages are the same as those in Example 1.

[0105] This comparative example provides a battery separator. The difference from Example 1 is only that the material of the functional layer is the functional composition provided in Comparative Example 1, and other materials, structures, and preparation methods are the same as those in Example 1.

[0106] Comparative Example 2

[0107] This comparative example provides a functional composition, which is only different from Example 1 in that the polyamide-imide is replaced with an equal mass of semi-aromatic polyimide (BASF, Germany, Matrimid 5218, with the mass fraction of aliphatic structural units being 15%), and the other components and their dosages are the same as those in Example 1.

[0108] This comparative example provides a battery separator, which is only different from Example 1 in that the material of the functional layer is the functional composition provided in Comparative Example 2, and the other materials, structures and preparation methods are the same as those in Example 1.

[0109] Comparative Example 3

[0110] This comparative example provides a functional composition, which is only different from Example 1 in that the polyimide-amide acid lithium salt is replaced with an equal mass of lithium polymethacrylate, and the other components and their dosages are the same as those in Example 1.

[0111] This comparative example provides a battery separator, which is only different from Example 1 in that the material of the functional layer is the functional composition provided in Comparative Example 3, and the other materials, structures and preparation methods are the same as those in Example 1.

[0112] Comparative Example 4

[0113] This comparative example provides a functional composition, comprising 40 g of polyamide-imide, 20 g of polyimide-amide acid lithium salt, 20 g of polyvinylidene fluoride and 20 g of boehmite.

[0114] This comparative example provides a battery separator, which is only different from Example 1 in that the material of the functional layer is the functional composition provided in Comparative Example 4, and in step (1) of the preparation method, the solvent is a mixed solution of 550 g of N-methylpyrrolidone and 8 g of ultrapure water, and the other materials, structures and preparation methods are the same as those in Example 1.

[0115] Comparative Example 5

[0116] This comparative example provides a functional composition, comprising 90 g of polyamide-imide, 3 g of polyimide-amide acid lithium salt, 4 g of polyvinylidene fluoride and 3 g of boehmite.

[0117] This comparative example provides a battery separator, which is only different from Example 1 in that the material of the functional layer is the functional composition provided in Comparative Example 5, and in step (1) of the preparation method, the solvent is a mixed solution of 530 g of N-methylpyrrolidone and 7 g of ultrapure water, and the thickness of the separator is 9 μm, and the other materials, structures and preparation methods are the same as those in Example 1.

[0118] Comparative Example 6

[0119] This comparative example provides a functional composition, which is different from Example 1 only in that the polyimide-amino acid lithium salt is replaced with an equal mass of polyamic acid, and other components and dosages are the same as those in Example 1.

[0120] This comparative example provides a battery separator, which is different from Example 1 only in that the material of the functional layer is the functional composition provided in Comparative Example 6, and other materials, structures and preparation methods are the same as those in Example 1.

[0121] Comparative Example 7

[0122] This comparative example provides a functional composition, which is different from Example 1 only in that the total amount of polyamide-imide and polyimide-amino acid lithium salt remains unchanged, and their mass percentages in the functional composition are 55% and 30% respectively, and other components and dosages are the same as those in Example 1.

[0123] This comparative example provides a battery separator, which is different from Example 1 only in that the material of the functional layer is the functional composition provided in Comparative Example 7, and other materials, structures and preparation methods are the same as those in Example 1.

[0124] Comparative Example 8

[0125] This comparative example provides a functional composition, which is different from Example 1 only in that the total amount of polyamide-imide and polyimide-amino acid lithium salt remains unchanged, and their mass percentages in the functional composition are 83% and 2% respectively, and other components and dosages are the same as those in Example 1.

[0126] This comparative example provides a battery separator, which is different from Example 1 only in that the material of the functional layer is the functional composition provided in Comparative Example 8, and other materials, structures and preparation methods are the same as those in Example 1.

[0127] Performance Test

[0128] The battery separators provided in Examples 1 to 6 and Comparative Examples 1 to 8 are tested as follows:

[0129] (1) Thickness: The thicknesses of 10 points on the battery separator are measured with a micrometer, and the average value is taken.

[0130] (2) Air permeability: According to GB / T 458-2008 Gurley method, the time required for 100 mL of air to pass through the separator with an area of 6.45 cm 2 is measured, and the average value of 3 test results is taken as the air permeability value of the separator.

[0131] (3) Breakdown strength: Referring to the diaphragm breakdown voltage test method of Patent CN104090217A, the breakdown voltage of the diaphragm was tested using a Changzhou Yangzi YD9810A programmable withstand voltage tester, and then the breakdown strength of the diaphragm was calculated through the formula (breakdown strength = breakdown voltage / diaphragm thickness).

[0132] (4) Ionic conductivity: Inside an argon-filled glove box, the diaphragm was assembled into a CR2016 coin cell, and the electrolyte (EC:EMC:DEC = 1:1:1, containing 1.0 mol / L LiPF6) was injected. The intrinsic resistance value of the diaphragm was measured using AC impedance testing in an electrochemical workstation, and then the ionic conductivity of the diaphragm was calculated through the formula (ionic conductivity = diaphragm thickness / (diaphragm intrinsic resistance × effective diaphragm area)).

[0133] The specific test results are shown in Table 1 as follows:

[0134] Table 1

[0135]

[0136]

[0137] As can be seen from Table 1, for the functional composition provided by the present invention, through the compounding of insulating resins and ion-conducting resins with specific contents and types, the diaphragm including the functional composition has excellent breakdown strength, good ion transportability, and good adhesion to the electrode plate, which can improve the structural stability of the diaphragm, reduce the risk of battery short circuit, and improve the safety of use of the battery diaphragm. From Examples 1 to 5, it can be seen that the breakdown strength of the diaphragm is 207 - 269 kV / mm, the air permeability is 142 - 225 s / 100 mL, and the ionic conductivity is 2.8 - 3.7 mS·cm -1 .

[0138] As can be seen from Examples 1, Comparative Example 1, and Comparative Example 2, when there are no aliphatic structural units, the content of aliphatic structural units is small, and there are no functional groups in the imide polymer, the dielectric constant is relatively large and the flexibility is poor, resulting in a significant reduction in the breakdown strength.

[0139] As can be seen from Examples 1 and Comparative Example 3, when using an ion-conducting resin with poor affinity for the imide polymer, a phase separation phenomenon occurs due to repulsion between components, thereby significantly reducing the breakdown strength of the battery diaphragm.

[0140] As can be seen from Examples 1 and Comparative Example 4, the insufficient amount of imide polymer leads to a significant reduction in the breakdown strength.

[0141] As can be seen from Example 1 and Comparative Example 5, when the ion-conducting resin used in the functional layer is insufficient, although the battery separator has a high breakdown strength, its ionic conductivity is significantly reduced, resulting in a relatively large internal resistance of the battery cell and affecting the performance of the battery cell.

[0142] As can be seen from Example 1 and Comparative Examples 6 to 8, when the ion-conducting resin is not a polymer salt, or the insulating resin and the ion-conducting resin are not in a specific mass ratio, the breakdown strength, air permeability and ionic conductivity of the separator are reduced.

[0143] In summary, the functional composition provided by the present invention is prepared by compounding an insulating resin and an ion-conducting resin with specific contents and types, and simultaneously combining a binder and an inorganic filler with specific contents, so that the separator including the functional composition has excellent breakdown strength, good ion transportability and good adhesion to the electrode plate, can improve the structural stability of the separator, reduce the risk of battery short circuit, and improve the safety of using the battery separator.

[0144] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A functional composition for a battery separator, characterized in that, By mass percentage, the functional composition comprises 60-80% insulating resin and 5-15% ion-conductive resin; The insulating resin comprises an imide polymer; The molecular chain of the imide polymer contains an aliphatic structural unit and a functional group; The ion-conductive resin comprises at least one of polyamide acid salt, polyimide-amide acid salt or polyacrylonitrile-acrylate; The mass percentage of the aliphatic structural unit in the molecular chain of the imide polymer is ≥30%; The functional group comprises at least one of an amide group, an ether group, an ester group, a urethane group, a urea group, a carbonate group, a siloxane group or an epoxy group.

2. The functional composition according to claim 1, wherein The imide polymer comprises at least one of polyamide-imide, polyether-imide, polyester-imide, polyurethane-imide, polyurea-imide, polycarbonate-amide, polyurethane-amide-imide, polysiloxane-imide or polysiloxane-epoxy-imide.

3. The functional composition according to claim 1, characterized in that, The polyamide acid salt comprises at least one of lithium polyamide acid salt, sodium polyamide acid salt or potassium polyamide acid salt.

4. The functional composition according to claim 1, wherein The polyimide-amide acid salt comprises at least one of lithium polyimide-amide acid salt, sodium polyimide-amide acid salt or potassium polyimide-amide acid salt.

5. The functional composition according to claim 1, characterized in that, The polyacrylonitrile-acrylate comprises at least one of lithium polyacrylonitrile-acrylate, sodium polyacrylonitrile-acrylate or potassium polyacrylonitrile-acrylate.

6. The functional composition according to any one of claims 1 to 5, characterized in that, By mass percentage, the functional composition further comprises 5-15% adhesive resin.

7. The functional composition according to claim 6, wherein The adhesive resin comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-propylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, polyacrylonitrile, polyacrylamide, polymethyl methacrylate or polyethyl methacrylate.

8. The functional composition according to any one of claims 1 to 5, characterized in that, By mass percentage, the functional composition further comprises 5-15% inorganic filler.

9. The functional composition according to claim 8, wherein The inorganic filler comprises at least one of aluminum oxide, silicon dioxide, titanium dioxide, zirconium dioxide, tin dioxide, zinc oxide, calcium oxide, magnesium oxide, magnesium nitride, boehmite or barium sulfate.

10. The functional composition according to claim 8, characterized in that, The particle size of the inorganic filler is 0.02-2 μm.

11. A battery separator, characterized in that, The battery separator comprises a porous base film and a functional layer; The functional layer covers at least one surface of the porous base film, is distributed inside the porous base film and / or penetrates through two surfaces of the porous base film; The material of the functional layer comprises the functional composition according to any one of claims 1-10.

12. The battery separator according to claim 11, wherein, The functional layer is a reticular porous structure.

13. The battery separator according to claim 11, wherein, The thickness of the functional layer is ≤3 μm.

14. The battery separator according to any one of claims 11 to 13, characterized in that, The material of the porous base film comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyacrylonitrile, polyimide, polyamide, polyester, polyether ether ketone, polyurethane, polyurea, polysulfone, polyphenylene sulfide, polystyrene, polyvinyl acetate, polyethylene terephthalate, polymethyl methacrylate or cellulose acetate.

15. The battery separator according to any one of claims 11 to 13, characterized in that, The thickness of the porous base film is 5-10 μm.

16. The battery separator according to any one of claims 11 to 13, characterized in that, The breakdown strength of the battery separator is greater than 180 kV / mm.

17. A method for preparing a battery separator according to any one of claims 11 to 16, characterized in that, The preparation method includes: (1) Mix the functional composition with a solvent to obtain a slurry; (2) Coat the slurry obtained in step (1) on at least one surface of the porous base film to obtain a coated film; cure the coated film to obtain the battery separator.

18. The preparation method according to claim 17, characterized in that, The solvent in step (1) includes a mixed solution of an organic solvent and water.

19. The preparation method according to claim 17, characterized in that, The mixing in step (1) includes pre-mixing an insulating resin, an ion-conducting resin, and an optional adhesive resin, and then adding an optional inorganic filler for mixing to obtain the slurry.

20. The preparation method according to claim 19, characterized in that, The rotation speed of the pre-mixing is 500 - 1000 rpm.

21. The preparation method according to claim 19, wherein, The rotation speed of the mixing is 1500 - 2500 rpm.

22. The preparation method according to claim 17, wherein, The coating method in step (2) includes at least one of dip coating, spray coating, spin coating, roll coating, or knife coating.

23. The preparation method according to claim 17, characterized in that, The curing method in step (2) includes at least one of non-solvent induced phase separation curing, thermal curing, or ultraviolet curing.

24. The preparation method according to claim 23, characterized in that, The method of non-solvent induced phase separation curing includes immersing the coated film in a first-stage coagulation bath and a second-stage coagulation bath in sequence, and drying to obtain the battery separator.

25. The preparation method according to claim 24, characterized in that, The first-stage coagulation bath includes a mixed solution of an organic solvent and water with a volume ratio of (70 - 80):(20 - 30).

26. The preparation method according to claim 24, wherein, The immersion time in the first-stage coagulation bath is 50 - 70 s.

27. The preparation method according to claim 24, wherein The second-stage coagulation bath includes a mixed solution of an organic solvent and water with a volume ratio of (15 - 25):(75 - 85).

28. The preparation method according to claim 24, wherein The immersion time in the second-stage coagulation bath is 20 - 40 s.

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