阅读说明：本技术 二次电池、电池隔膜以及制备电池隔膜涂层的浆料 (Secondary battery, battery diaphragm and slurry for preparing battery diaphragm coating ) 是由 邱长泉 鲁秀玲 苏晓明 金颖 杨小峰 何王涛 孙同睿 程跃 于 2021-06-30 设计创作，主要内容包括：本申请涉及电池材料领域,具体而言,涉及一种二次电池、电池隔膜以及制备电池隔膜涂层的浆料。电池隔膜的涂层含有粘合剂,粘合剂包括重均分子量为20万～60万的水溶性高分子聚合物,水溶性高分子聚合物含有第一结构单元和第二结构单元。由第一结构单元、第二结构单元构成的水溶性高分子聚合物刚性较强,加热后收缩率较小；其用于电池隔膜的涂层后,可以改善电池隔膜卷边；此外,该电池隔膜的耐热性能得到了有效改善,电池隔膜的热收缩率较小。该电池隔膜一面覆盖涂层或者两面覆盖涂层均具有较佳的耐热性能。(The application relates to the field of battery materials, in particular to a secondary battery, a battery diaphragm and slurry for preparing a battery diaphragm coating. The coating layer of the battery separator contains a binder including a water-soluble high molecular polymer having a weight-average molecular weight of 20 to 60 ten thousand, the water-soluble high molecular polymer containing a first structural unit and a second structural unit. The water-soluble high molecular polymer composed of the first structural unit and the second structural unit has stronger rigidity and smaller shrinkage rate after heating; after the coating is used for coating the battery diaphragm, the curling of the battery diaphragm can be improved; in addition, the heat resistance of the battery diaphragm is effectively improved, and the heat shrinkage rate of the battery diaphragm is small. One surface of the battery diaphragm is covered with the coating or two surfaces of the battery diaphragm are covered with the coatings, and the battery diaphragm has better heat resistance.)

1. A battery separator comprising a base film and a coating layer covering a surface of the base film;

the coating contains a binder, the binder comprises a water-soluble high molecular polymer with the weight-average molecular weight of 20-60 ten thousand, and the water-soluble high molecular polymer contains a first structural unit and a second structural unit;

wherein the first monomer forming the first structural unit is a monomer with a polar group and a carbon-carbon double bond functional group, and the glass transition temperature of the homopolymer of the first monomer is not less than 90 ℃;

the second monomer forming the second structural unit is a monomer having a polar group and at least two carbon-carbon double bond functional groups.

2. The battery separator of claim 1, wherein the first monomer comprises at least one of acrylic acid, methacrylic acid, acrylamide, acrylonitrile, methyl methacrylate, methacrylamide, and styrene.

3. The battery separator according to claim 1,

the polar group in the second monomer is an ester group or an amide;

optionally, the second monomer comprises N, N-methylenebisacrylamide and/or propylene methacrylate.

4. The battery separator according to any one of claims 1 to 3, wherein, in the water-soluble high-molecular polymer: the ratio of the number of the first structural units to the number of the second structural units is (85-95): (5-15).

5. The battery separator of any of claims 1-3, wherein the coating covers only one surface of the base film.

6. The battery separator according to any of claims 1-3, wherein the coating has a thickness of 2 μm to 4 μm.

7. The battery separator of any of claims 1-3, wherein the coating further comprises ceramic particles and a dispersant; the weight ratio of the ceramic particles, the adhesive and the dispersant is (90-96): (3-7): (1-3);

optionally, the ceramic particles comprise at least one of alumina, silica, titania, magnesia, zirconia, and boehmite;

optionally, the ceramic particles have a median particle diameter of 0.1 to 1 μm and a specific surface area of 2m²/g～50m²Between/g;

optionally, the dispersant comprises at least one of ammonium polyacrylate, sodium polyacrylate, and sodium hexametaphosphate.

8. The battery separator according to claim 1, wherein the material of the base film comprises polyethylene and/or polypropylene;

optionally, the porosity of the base film is 35% to 60%;

optionally, the base film has a thickness of 5 μm to 25 μm.

9. A secondary battery comprising a positive electrode tab, a negative electrode tab, and the battery separator of any one of claims 1-8 positioned between the positive electrode tab and the negative electrode tab.

10. The slurry for preparing the battery diaphragm coating is characterized by comprising ceramic particles, a binder, a dispersant and a solvent;

the adhesive comprises a water-soluble high molecular polymer containing a first structural unit and a second structural unit;

wherein the first monomer forming the first structural unit is a monomer with a polar group and a carbon-carbon double bond functional group, and the glass transition temperature of the homopolymer of the first monomer is not less than 90 ℃;

the second monomer forming the second structural unit is a monomer having a polar group and at least two carbon-carbon double bond functional groups.

Technical Field

The application relates to the field of battery materials, in particular to a secondary battery, a battery diaphragm and slurry for preparing a battery diaphragm coating.

Background

A separator is one of important components of a secondary battery (e.g., a lithium battery) and is an important component of battery safety. The raw material of the lithium ion battery diaphragm is polyolefin, and in order to solve the problem of serious shrinkage deformation of the polyolefin diaphragm, a single-sided or double-sided inorganic ceramic coating film is usually formed on the surface of the polyolefin. This can improve the polyolefin separator shrinkage deformation to some extent. However, the heat resistance of the separator is an important factor to be considered in the improvement process.

Disclosure of Invention

An object of embodiments of the present application is to provide a secondary battery, a battery separator, and a slurry for preparing a battery separator coating layer, which aim to improve the heat resistance of the battery separator.

A battery separator includes a base film and a coating layer covering a surface of the base film;

the coating contains a binder, the binder comprises a water-soluble high molecular polymer with the weight-average molecular weight of 20-60 ten thousand, and the water-soluble high molecular polymer contains a first structural unit and a second structural unit;

wherein the first monomer forming the first structural unit is a monomer with a polar group and a carbon-carbon double bond functional group, and the glass transition temperature of the homopolymer of the first monomer is not less than 90 ℃;

the second monomer forming the second structural unit is a monomer having a polar group and at least two carbon-carbon double bond functional groups.

The water-soluble high molecular polymer molecular chain composed of the first structural unit and the second structural unit has stronger rigidity and smaller shrinkage rate after heating and curing; after the coating is used for coating the battery diaphragm, the curling of the battery diaphragm can be improved; in addition, the heat resistance of the battery diaphragm is effectively improved, and the heat shrinkage rate of the battery diaphragm is small. One surface of the battery diaphragm is covered with the coating or two surfaces of the battery diaphragm are covered with the coatings, and the battery diaphragm has better heat resistance.

In some embodiments of the present application, the first monomer comprises at least one of acrylic acid, methacrylic acid, acrylamide, acrylonitrile, methyl methacrylate, methacrylamide, and styrene.

In some embodiments of the present application, the second monomer comprises N, N-methylenebisacrylamide and/or propylene methacrylate.

In some embodiments of the present application, in the water-soluble high molecular polymer: the ratio of the number of the first structural units to the number of the second structural units is (85-95): (5-15).

In some embodiments of the present application, the coating covers only one surface of the base film;

optionally, the coating has a thickness of 2 μm to 4 μm.

In some embodiments of the present application, the coating further comprises ceramic particles and a dispersant; the weight ratio of the ceramic particles, the adhesive and the dispersant is (90-96): (3-7): (1-3);

optionally, the ceramic particles comprise at least one of alumina, silica, titania, magnesia, zirconia, and boehmite;

optionally, the ceramic particles have a median particle diameter of 0.1 to 1 μm and a specific surface area of 2m²/g～50m²Between/g;

optionally, the dispersant comprises at least one of ammonium polyacrylate, sodium polyacrylate, and sodium hexametaphosphate.

In some embodiments of the present application, the material of the base film comprises polyethylene and/or polypropylene;

optionally, the porosity of the base film is 35% to 60%;

optionally, the base film has a thickness of 5 μm to 25 μm.

The application also provides a secondary battery, which comprises a positive pole piece, a negative pole piece and a battery diaphragm positioned between the positive pole piece and the negative pole piece.

The secondary battery provided by the application has the advantages of the battery diaphragm, and is good in heat resistance and good in electrical property.

The application also provides slurry for preparing the battery diaphragm coating, wherein the slurry for preparing the battery diaphragm coating comprises ceramic particles, a binder, a dispersant and a solvent;

the adhesive comprises a water-soluble high molecular polymer containing a first structural unit and a second structural unit;

wherein the first monomer forming the first structural unit is a monomer with a polar group and a carbon-carbon double bond functional group, and the glass transition temperature of the homopolymer of the first monomer is not less than 90 ℃;

the second monomer forming the second structural unit is a monomer having a polar group and at least two carbon-carbon double bond functional groups.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The application number CN202011456668.9 provides a ceramic coating isolation membrane of a lithium ion battery, which comprises a porous base membrane and a coating layer coated on at least one side of the porous base membrane, wherein the coating layer comprises a binding agent and ceramic particles; the adhesive comprises polymer spherical emulsion particles which are formed by copolymerization of a first monomer unit and a second monomer unit and have a core-shell structure.

The polymer spherical emulsion particles with the core-shell structure can improve the problem that a ceramic layer is easy to collapse in the drying process, so that the phenomena of edge warping and curling of a ceramic coating isolating membrane are optimized, but the heat shrinkage resistance of the isolating membrane is poor at high temperature such as 150 ℃.

Therefore, the present application is directed to improving the heat resistance of the separator.

The following are secondary batteries, battery separators, and slurries for preparing battery separator coatings according to examples of the present application.

A battery separator includes a base film and a coating layer covering a surface of the base film;

the coating contains a binder, the binder comprises a water-soluble high molecular polymer with the weight-average molecular weight of 20-60 ten thousand, and the water-soluble high molecular polymer contains a first structural unit and a second structural unit;

wherein the first monomer forming the first structural unit is a monomer with a polar group and a carbon-carbon double bond functional group, and the glass transition temperature of the homopolymer of the first monomer is not less than 90 ℃;

the second monomer forming the second structural unit is a monomer having a polar group and at least two carbon-carbon double bond functional groups.

The inventor finds out in the research process that: the reason why the coating is easy to curl is that the water-soluble binder used in the coating is a long-chain high molecular polymer, and the molecular chain is changed into a contracted coil shape in an extending state in the drying process of the coating, so that the stress state of the coating surface and the stress state of the non-coating surface of the single-surface coating film are different, and the single-surface coating film is curled.

Among them, the molecular chain flexibility or rigidity of the water-soluble binder is closely related to the degree of curling of the coating film. The softer the molecular chain of the binder, the more severe the curling degree of the coating film; on the other hand, the more rigid the binder molecular chain, the less the molecular chain shrinks and curls, and therefore the degree of curling deformation of the coating film is small. The molecular chain flexibility of the water-soluble adhesive is related to the glass transition temperature (Tg) and the crosslinking structure of the water-soluble adhesive. The glass transition temperature of a polymer copolymer is related to the glass transition temperature of its monomeric homopolymer.

In the application, a proper high molecular polymer is selected as the adhesive, and the rigidity of a polymer molecular chain and the glass transition temperature are controlled, so that the aim of improving or eliminating the curling of the diaphragm coating is fulfilled.

The battery separator includes a base film and a coating layer covering a surface of the base film, and in this application, the coating layer may cover one surface of the base film, or the coating layer may cover both opposite surfaces of the base film.

In this embodiment, the coating includes ceramic particles, a dispersant, and a binder. In some embodiments of the present application, the weight ratio of the ceramic particles, the binder, and the dispersant is (90-96): (3-7): (1-3); for example, the mass ratio of ceramic particles, binder, and dispersant is 90:3:1, 90:4:3, 90:5:2, 90:7:2, 92:3:3, 92:4:1, 92:7:3, 96: 5:1, 96:3:1, 96: 7:1, 96:3:1, and so forth.

For example, the ceramic particles include at least one of alumina, silica, titania, magnesia, zirconia, and boehmite.

Illustratively, the water-soluble high molecular polymer has a weight average molecular weight of 20 to 60 ten thousand; for example, the weight average molecular weight of the water-soluble high molecular polymer may be 20 ten thousand, 22 ten thousand, 24 ten thousand, 26 ten thousand, 27 ten thousand, 29 ten thousand, 30 ten thousand, 31 ten thousand, 35 ten thousand, 36 ten thousand, 39 ten thousand, 41 ten thousand, 44 ten thousand, 47 ten thousand, 53 ten thousand, 57 ten thousand, 60 ten thousand, or the like.

In some embodiments of the present application, the ceramic particles have a median particle diameter of 0.1 μm to 1 μm and a specific surface area of 2m²/g～50m²Between/g; for example, the median particle diameter of the ceramic particles may be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, or the like. For example, the specific surface area of the ceramic particles is 2m²/g、5m²/g、8m²/g、11m²/g、13m²/g、17m²/g、19m²/g、21m²/g、24m²/g、26m²/g、29m²/g、34m²/g、38m²/g、41m²/g、45m²/g、47m²/g、50m²G,/etc.

For example, the dispersant includes at least one of ammonium polyacrylate, sodium polyacrylate, and sodium hexametaphosphate.

In other embodiments of the present application, the coating may also include other materials, such as solvents that are not completely volatilized, and the like.

The adhesive comprises a water-soluble high-molecular polymer containing a first structural unit and a second structural unit.

Illustratively, the first monomer includes at least one of acrylic acid, methacrylic acid, acrylamide, acrylonitrile, methyl methacrylate, methacrylamide, and styrene.

In other embodiments of the present application, the first monomer may be other monomers having one polar group and one carbon-carbon double bond functional group, and the glass transition temperature of the homopolymer of the first monomer is greater than or equal to 90 ℃, for example, the glass transition temperature of the homopolymer of the first monomer is 90 ℃, 93 ℃, 96 ℃, 100 ℃, 106 ℃, 130 ℃, 150 ℃, and the like.

The polar group in the second monomer is an ester group or an amide. Illustratively, the second monomer includes N, N-methylenebisacrylamide and/or propylene methacrylate. In other embodiments of the present application, the second monomer may be a monomer having at least two functional groups.

As an example, among the water-soluble high molecular polymers: the ratio of the number of the first structural unit to the number of the second structural unit is (85-95): (5-15). For example, the ratio of the number of units of the first structural unit and the second structural unit may be 85: 15. 86:14, 87:13, 88:12, 89:11, 90:10, 91:10, 92:8, 93:7, 94:6, 95: 5, etc.

The weight average molecular weight is 20-60 ten thousand, the rigidity of the molecular chain of the adhesive is stronger, the molecular chain is not easy to shrink and curl, the diaphragm is not easy to shrink after being heated, and the heat resistance is better.

As mentioned above, the coating layer may cover one surface of the base film, or may cover both surfaces of the base film; in the present application, for the embodiment in which the coating layer covers one surface of the base film, the heat resistance of the coating layer is also better, and the shrinkage amount of the coating layer is smaller, so that the difference in the stress on both surfaces of the base film can be reduced, thereby preventing shrinkage.

In some embodiments of the present application, the coating has a thickness of 2 μm to 4 μm, for example the coating may have a thickness of 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm.

In the present embodiment, the material of the base film includes polyethylene and/or polypropylene, and the application does not limit the polyethylene, and for example, the material may be linear polyethylene, branched polyethylene; alternatively, the polyethylene can be high density polyethylene with the density of 0.941-0.960 g/cc or low density polyethylene with the density of 0.915-0.940 g/cc. Copolymers of polyethylene and polypropylene are also possible.

In other embodiments of the present application, the material of the base film may be other high molecular materials. Such as polytetrafluoroethylene, polystyrene, and the like.

In some embodiments of the present application, the porosity of the substrate film is between 35% and 65%, for example, the porosity of the base film is 35%, 36%, 40%, 42%, 46%, 47%, 49%, 52%, 55%, 58%, 60%, 63%, 65%, and so forth.

The thickness of the base film is 5-25 μm. For example, the thickness of the base film may be 5 μm, 6 μm, 7 μm, 9 μm, 11 μm, 13 μm, 18 μm, 21 μm, 23 μm, 25 μm, or the like.

It should be noted that in other embodiments of the present application, the void ratio of the base film and the thickness of the base film may be set according to the performance requirements of the battery separator, and the embodiments of the present application do not limit the void ratio and the thickness of the base film.

It is further noted that in other embodiments of the present application, the material of the coating other than the binder may be selected according to its properties, for example, the dispersant and the ceramic particles may be selected from other materials. Accordingly, the coating may contain other components in addition to the dispersant and the ceramic particles.

The battery diaphragm that this application embodiment provided has following advantage at least:

the water-soluble high molecular polymer composed of the first structural unit and the second structural unit has stronger rigidity and smaller shrinkage rate after heating; after the coating is used for coating the battery diaphragm, the curling of the battery diaphragm can be improved; in addition, the heat resistance of the battery diaphragm is effectively improved, and the heat shrinkage rate of the battery diaphragm is small. One surface of the battery diaphragm is covered with the coating or two surfaces of the battery diaphragm are covered with the coatings, and the battery diaphragm has better heat resistance.

The application also provides a secondary battery, which comprises a positive pole piece, a negative pole piece and a battery diaphragm. The battery diaphragm is positioned between the positive pole piece and the negative pole piece and can separate the positive pole piece and the negative pole piece.

For example, in some embodiments, the battery separator is attached to the positive and negative electrode plates by hot pressing.

Residing in the above-mentioned advantage of battery diaphragm, the secondary cell that this application provided's heat resistance is better, has also improved secondary cell's electrical property.

The application also provides slurry for preparing the battery diaphragm coating, which comprises ceramic particles, a binder, a dispersant and a solvent.

The binder includes a water-soluble high molecular polymer, and the molecular formula, structure, and the like of the water-soluble high molecular polymer are described above.

Further, in some embodiments, the properties and parameters of the ceramic particles, the dispersant, and the like are described above and will not be described herein.

In some embodiments of the present application, the solvent for preparing the slurry for coating the battery separator is water, and in other embodiments, other solvents, such as organic solvents like ethanol, may be used.

The slurry for preparing the battery diaphragm coating is coated on the base film, and the coating can be formed on the surface of the base film after the slurry is cured. The coating obtained by the slurry has better heat resistance.

The features and properties of the present application are described in further detail below with reference to examples.

Example 1

The application provides a battery diaphragm, which is mainly prepared by the following steps:

preparing a water-soluble high-molecular polymer:

adding a certain amount of n-butanol and ethanol into a four-neck flask provided with a stirrer, a thermometer and a reflux condenser, heating to 140 ℃, and then mixing methacrylic acid, acrylamide and methacrylate acrylate monomers according to a molar mass ratio of 80: 10: and (3) dropwise adding the mixture of 10 and the initiator within 4 hours, preserving the heat for 2 hours, supplementing the initiator, preserving the heat for 2 hours, neutralizing the pH value to 4-6, adding water, filtering and discharging to obtain the water-soluble high-molecular polymer adhesive.

Preparing slurry of a battery diaphragm coating:

adding dispersant (ammonium polyacrylate) into water, and mixing to obtain dispersant solution; adding ceramic particles (alumina) into a dispersant solution, performing ball milling dispersion to obtain slurry, adding a water-soluble high molecular polymer as a binder, and mixing to obtain coating slurry; wherein, the weight portion of the ceramic particles is 90 portions and the weight portion of the adhesive is 5 portions based on 100 portions of the total weight of the ceramic particles, the adhesive and the dispersant.

Coating the coating slurry on one side surface of the polyethylene base material by a gravure coating method, and drying.

Example 2 to example 4

Examples 2 to 4 provide a battery separator, respectively, and a method for preparing the battery separator is described in example 1, which mainly differs from the method for preparing the water-soluble high molecular polymer in that the first monomer and the second monomer are different, and specifically, refer to table 1.

Comparative examples 1 to 4

Comparative examples 1 to 4 provide a battery separator, respectively, the method of preparing the battery separator being described in example 1, mainly different from the method of preparing the water-soluble high molecular polymer in the first monomer and the second monomer, which are described in table 1.

The method of preparing the emulsion type high molecular polymer in comparative example 2 is different from that of example 1, and in comparative example 2, the method of preparing the emulsion type high molecular polymer is as follows:

adding a certain amount of deionized water, an emulsifier and 5 wt% of a first monomer and a second monomer (the sum of the first monomer and the second monomer is 5 wt%) mixed monomer into a four-neck flask provided with a stirrer, a thermometer and a reflux condenser, stirring for 30 minutes, heating to 80 ℃, then dropwise adding the rest 95% of the first monomer and second monomer mixture within 3 hours, and then cooling to 50 ℃; adding ammonia water to adjust the pH value to 7-8, filtering and discharging to obtain the emulsion type high molecular polymer adhesive.

TABLE 1

In Table 1, the abbreviations AA, MAa, AM, AN, MMA, MAM, MBA, AMA, and MA refer to acrylic acid, methacrylic acid, acrylamide, acrylonitrile, methyl methacrylate, methacrylamide, N-methylenebisacrylamide, allyl methacrylate, and methyl acrylate, respectively. The values in Table 1 represent the molar ratio of the monomers in the total monomers of the examples or comparative examples.

Test examples

The performance of the separators provided in examples 1 to 4 and comparative examples 1 to 4 was tested.

The specific test method is introduced as follows:

the thickness is measured by a Mark film thickness gauge (Millimar C1208, German Mark Co.), according to GB/T6672-2001.

The heat shrinkage test, test method is described in GB/T12027-2004, including: the original length L0 of the sample along the machine advancing direction and the original length T0 of the sample perpendicular to the machine advancing direction are respectively measured at room temperature, the sample is heated in a constant-temperature constant-humidity controllable oven according to a specified time at a test temperature and then cooled to the original test condition, the length L1 of the sample along the machine advancing direction and the length T1 of the sample perpendicular to the machine advancing direction at the moment are measured, and the calculation formula is as follows:

MD％＝(L1-L0)/L0×100％

TD％＝(T1-T0)/T0×100％

and (3) testing the crimpness: a coating sample to be measured with the width and the length of 1m is taken and placed on a test table top engraved with a straight line (a line for short) of 1m and a straight line (b line for short) perpendicular to the straight line in the middle, and two ends of the sample are aligned with two ends of the a line. A straight steel ruler was placed perpendicular to line b and the distance in mm from the edge of the sample near line a to the table top was measured. When reading, the decimal point is followed by an estimated value. The larger the distance, the higher the degree of curling of the coating film, and the smaller the distance, the smaller the degree of curling of the coating film. The test results are shown in table 2.

TABLE 2

As can be seen from tables 1 and 2, the separators provided in examples 1 to 4 of the present application have a relatively good heat shrinkage ratio, which indicates that the heat resistance is good. In addition, the curling of the separator is also effectively improved.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.