JP7814419B2 - Binder for secondary battery and manufacturing method thereof, separator, battery unit, battery and electric device - Google Patents

Description

The present application relates to the technical field of secondary batteries, and in particular to a binder for secondary batteries and a method for producing the same, as well as a separator, a battery unit, a battery, and an electric device.
[CROSS-REFERENCE TO RELATED APPLICATIONS]
This application claims priority to Chinese patent application No. 202310402475.2, filed on April 14, 2023, the entire contents of which are incorporated herein by reference.

With the rapid growth of portable electronic devices, electric vehicles, and other devices, demand for power batteries is also increasing. In this context, the electrochemical performance of batteries is also attracting increasing attention.

Currently, battery cells have a problem with large openings. This means that gaps are likely to form between the pole pieces and the separator, reducing the battery's cycling performance.

The main objective of this application is to provide a binder for secondary batteries that improves the adhesive strength between the separator and the pole pieces and improves the cycling performance of the battery.

To achieve the above objective, the present application provides a binder for secondary batteries comprising a first polymer including an acrylic acid ester copolymer and a second polymer including a water-soluble polymer.

Acrylate ester copolymers have relatively high adhesion, and using an acrylate ester copolymer results in higher adhesion between the separator and the pole pieces after cold rolling.

Water-soluble polymers are soluble in water and are not viscous when dry.

The binder comprises a first polymer containing an acrylic ester copolymer and a second polymer containing a water-soluble polymer. When the binder is applied to the separator, the water-soluble polymer acts as a support to support the first polymer, linking the first polymer to the water-soluble polymer and adhering the first polymer to the separator. Specifically, in the process of applying the binder to the separator, the binder is mixed with water to form a slurry, and the slurry is then applied to the separator. The water-soluble polymer becomes adhesive after contact with water, allowing the water-soluble polymer to adhere to the separator, and the water-soluble polymer can adhere the first polymer (including the acrylic ester copolymer) to the separator. Some of the acrylic ester copolymer and/or water-soluble polymer in the binder penetrates into the gaps in the separator and achieves adhesion to the separator. After the slurry dries, the water evaporates, causing the water-soluble polymer molecules to become entangled with each other, resulting in intermolecular interactions, thereby forming a network structure and allowing the first polymer (including the acrylic ester copolymer) to adhere to the separator. The water-soluble polymer (including the acrylic ester copolymer) acts as a support and link, adhering the first polymer particles to the separator. The slurry layer becomes an adhesive layer after drying. The adhesive layer has a side facing the separator and a side facing away from the separator. During the slurry application process, the water-soluble polymer adheres to the separator, or part of the acrylic ester copolymer and/or water-soluble polymer in the binder penetrates into the gaps in the separator, achieving adhesion to the separator, causing the adhesive layer to adhere to the separator. Because the acrylic ester copolymer and water-soluble polymer are non-viscous after drying, the adhesive layer is non-viscous on the side facing away from the separator, making it easier to roll up and unroll the separator.

When the positive and negative electrode pieces are wound and then subjected to a cold-rolling process, the binder has excellent adhesive strength, tightly bonding the positive and negative electrode pieces to the separator. Specifically, after cold-rolling, adhesive strength is provided primarily by the mechanical interlocking effect caused by the acrylic ester copolymer and water-soluble polymer in the binder penetrating into the gaps between the electrode pieces, as well as by the intermolecular interaction of the acrylic ester copolymer. Therefore, the binder of the present application improves the adhesive strength between the separator and the positive and negative electrode pieces during cold-rolling, reducing problems such as opening in battery cells and soft battery cells, thereby improving the hardness of the battery cell. At the same time, applying this binder to the separator in secondary batteries can improve the dynamic performance of the secondary battery, reduce electrochemical impedance, and enhance the rechargeability and cycling performance of the secondary battery.

Optionally, the mass ratio of the first polymer to the second polymer is 1:(0.1 to 10), preferably 1:(0.2 to 5).

By setting the mass ratio of the first polymer to the second polymer within the above range, the adhesive layer forms a continuous network structure, which helps adhere the first polymer to the separator and improve the adhesiveness of the adhesive layer at room temperature.

In other words, in the process of changing from a smaller amount to a larger amount of the second polymer, the adhesive strength of the adhesive layer tends to increase and then decrease. By controlling the mass of the first polymer and the second polymer within the above range, the adhesive strength of the binder applied to the separator is effectively improved.

Optionally, the second polymer includes one or more of polyacrylamide, polyacrylic acid, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, and polymaleic anhydride.

The second polymer contains the above-mentioned water-soluble polymer, which contains hydrophilic groups and a certain amount of hydrophobic groups. Therefore, it has a certain degree of surface activity, which reduces the surface tension of water to a certain extent and increases the solubility and dispersibility of the binder in the aqueous phase. That is, when it is made into a slurry for coating the separator, the water-soluble polymer is used to control the viscosity and rheological properties of the slurry and improve the dispersion and suspension of the binder. The second polymer also has chemical reaction functionality (e.g., carboxyl groups, hydroxyl groups, etc. that react with other groups). The polar groups in the water-soluble polymer structure can form hydrogen bonds between the first polymer and the separator and pole pieces, improving the adhesion between the separator and pole pieces.

Optionally, the volume particle size distribution Dv50 of the binder is 1 μm to 15 μm, preferably 3 μm to 12 μm.

Theoretically, the volume average particle diameter Dv50 of the binder in this application may be less than 1 μm or more than 15 μm. However, considering the application of the binder in this application to separators, setting the volume average particle diameter Dv50 of the binder within the above range alleviates the problem of the binder blocking the pores of the separator and reducing the permeability of lithium ions (for lithium ion batteries, for example, but of course other types of secondary batteries may also be used) through the separator, as well as the problem of a thick coating layer being formed when the binder is applied to the separator, which affects the energy density of the subsequently manufactured battery. Therefore, the volume particle diameter distribution Dv50 of the binder is 1 μm to 15 μm, preferably 3 μm to 12 μm.

As can be seen from Figure 1, the binder particles are secondary particles comprising primary particles of a first polymer and primary particles of a second polymer. Thus, the second polymer acts as the skeleton within the binder slurry. When the binder slurry is applied to the separator, the second polymer acts to support and connect the first polymer, adhering the first polymer to the separator. After the slurry dries to form an adhesive layer, the adhesive layer adheres to the separator. However, the side of the adhesive layer away from the separator has no adhesive strength, making it easier to wind and unwind the separator. When the separator is wound with the positive and negative electrode pieces and then subjected to a cold rolling process, the first and second polymers are deformed by force after being extruded and penetrate into the gaps between the separator and the electrode pieces, thereby achieving an adhesive effect.

Optionally, the shape of the binder includes a spherical shape.

The spherical shape helps ensure uniform dispersion and application during the slurry mixing process.

Optionally, the first polymer comprises an acrylate ester monomer, and the structure of the acrylate ester monomer is:
wherein R1 is a hydrogen atom or an alkyl group containing 1 to 12 carbon atoms, and R2 is an alkyl group containing 1 to 12 carbon atoms.

Acrylate ester monomers contain unsaturated ester groups that can enhance the polymer's anti-swelling ability, adjust the polymer's glass transition temperature as flexible monomer segments within the molecular segments, improve the binder's flexibility during use, and help it exhibit good adhesive properties.

Optionally, the acrylic acid ester monomer includes one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.

By using one or more of the above acrylic acid ester monomers, the glass transition temperature of the polymer can be adjusted and the anti-swelling ability of the polymer can be enhanced.

Optionally, the first polymer comprises an acrylonitrile-based monomer, and the structure of the acrylonitrile-based monomer is:
wherein R3 is a hydrogen atom or an alkyl group containing 1 to 6 carbon atoms.

The presence of an unsaturated cyano group in the structure of the acrylonitrile monomer helps to increase ionic conductivity and improve adhesion.

Optionally, the acrylonitrile-based monomer includes one or more of acrylonitrile and methacrylonitrile.

By using one or more of the above acrylonitrile-based monomers, the ionic conductivity of the binder can be increased.

Optionally, the first polymer comprises an acrylamide-based monomer, and the structure of the acrylamide-based monomer is:
wherein R4 is a hydrogen atom or an alkyl group containing 1 to 6 carbon atoms, and R5 is a hydrogen atom, an alkyl group containing 1 to 6 carbon atoms substituted with a hydroxy group, or an alkoxy group of 1 to 6 carbon atoms.

The third unit contains an unsaturated amide group that acts as a crosslinker and also has relatively high adhesion.

Optionally, the acrylamide-based monomer includes one or more of acrylamide, N-methylolacrylamide, and N-butoxymethacrylamide.

The use of one or more of the above acrylamide-based monomers can adjust the molecular weight of the polymer, thereby controlling the molecular weight of the binder within a certain range, which helps improve adhesion.

As can be appreciated, the constituent monomers of the first polymer can include, but are not limited to, one, two, or three of the three types of monomers listed above.

Optionally, the first polymer contains an acrylic acid ester-based monomer, an acrylonitrile-based monomer, and an acrylamide-based monomer, and the mass ratio of the acrylic acid ester-based monomer, the acrylonitrile-based monomer, and the acrylamide-based monomer ranges from 100:(1-80):(1-20), preferably 100:(20-60):(5-15).

To improve the overall performance of the first polymer, the first polymer contains an acrylic acid ester monomer, an acrylonitrile monomer, and an acrylamide monomer. When the mass ratio of the acrylic acid ester monomer, the acrylonitrile monomer, and the acrylamide monomer is in the range of 100:(1-80):(1-20), preferably 100:(20-60):(5-15), excellent adhesive properties are achieved.

The present application further provides a method for producing a binder for a secondary battery, the method including: co-mixing water, an emulsifier, an initiator, and constituent monomers of a first polymer, stirring the mixture, and heating to cause a reaction to occur, thereby obtaining a first polymer emulsion; and mixing the first polymer emulsion and the second polymer, stirring the mixture, and spray-drying the mixture to obtain a binder.

In this application, a first polymer emulsion is obtained by emulsion polymerization, and a binder is obtained by spray drying.

The binder particles are secondary particles comprising primary particles of a first polymer and primary particles of a second polymer. Thus, the second polymer acts as a skeleton to support the first polymer. When the binder is made into a slurry and applied to a separator, the second polymer adheres the first polymer to the separator. After the slurry on the separator is dried, the second polymer forms a network structure, providing support and connection for the first polymer while also adhering the first polymer particles to the separator.

An embodiment of the present application provides a separator containing the above-described secondary battery binder or a binder produced by the above-described method for producing a secondary battery binder.

An embodiment of the present application provides a battery unit including the separator described above.

An embodiment of the present application provides a battery including the above-described battery unit.

An embodiment of the present application provides the above-described battery alone or an electrical device including the above-described battery.

In order to more clearly describe the technical solutions in the embodiments of the present application or the prior art, the following will briefly describe the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings based on the structures shown in these drawings without any creative efforts.
1 is a scanning electron microscope image of a binder provided by Example 1 of the present application. FIG. 2 is a partially enlarged schematic view of the binder in Example 1 of FIG. 1 . FIG. 1 is a structural diagram of a separator provided by an embodiment of the present application. 1 is a flowchart of a method for manufacturing a binder for a secondary battery provided by an embodiment of the present application. 1 is a schematic diagram of an electrode assembly provided by an embodiment of the present application. FIG. 6 is an exploded view of an electrode assembly provided in accordance with an embodiment of the present application shown in FIG. 5. 1 is a schematic diagram of a battery module provided by an embodiment of the present application. 1 is a schematic diagram of a battery pack provided by an embodiment of the present application. FIG. 9 is an exploded view of a battery pack provided by the embodiment of the present application shown in FIG. 8. 1 is a schematic diagram of an electrical device provided by an embodiment of the present application.

Explanation of drawing symbols:
The realization of the object, functional features and advantages of the present application will be further explained in conjunction with the embodiments and with reference to the drawings.

The following clearly and completely describes the technical solutions of the embodiments of the present application in conjunction with the drawings of the embodiments of the present application. Obviously, the described embodiments are only a portion of the embodiments of the present application, and do not represent all of the embodiments. Based on the embodiments of the present application, those skilled in the art can derive all other embodiments without any creative effort, all of which fall within the scope of protection of the present application.

Hereinafter, with appropriate reference to the drawings, detailed embodiments of the present application will be described in detail, specifically disclosing the binder and its manufacturing method, as well as separators, electrode assemblies, individual batteries, batteries, and electrical devices each containing the binder. However, unnecessary detailed explanations may be omitted. For example, detailed explanations of well-known matters and repeated explanations of substantially the same structures may be omitted. This is intended to avoid unnecessary redundancy in the following explanation and to make it easier for those skilled in the art to understand. Furthermore, the drawings and the following explanation are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the scope of the claims.

Ranges disclosed herein are defined by lower and upper limits, with a given range being defined by selecting lower and upper limits that define the boundaries of that particular range. Ranges defined in this manner may or may not include the endpoint values and may be arbitrarily combined; i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are recited for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Also, if minimum range values of 1 and 2 are recited and maximum range values of 3, 4, and 5 are recited, all of the following ranges are contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. Unless otherwise specified, the numerical range "a to b" herein represents a shorthand notation for any combination of real numbers between a and b, where both a and b are real numbers. For example, a numerical range of "0 to 5" indicates that this specification lists all real numbers between "0 and 5," and "0 to 5" is merely shorthand for combinations of these values. Furthermore, describing a parameter as an integer of 2 or greater is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

Unless otherwise stated, all embodiments and alternative embodiments of this application can be combined with each other to form new technical solutions.

Unless otherwise stated, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

Unless otherwise specified, all steps herein may be performed sequentially or randomly, and are preferably performed sequentially. For example, when a method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, when a method as referred to above may further include step (c), it means that step (c) can be added to the method in any order, and for example, the method may include steps (a), (b), and (c), may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

Unless otherwise specified, the terms "comprise" and "include" used in this application can be open-ended or closed-ended. For example, the terms "comprise" and "include" can indicate that a product may further comprise or include other components not listed, or may comprise or include only the listed components.

Unless otherwise stated, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or both A and B are true (or exist).

The problem is that the battery cell has large openings. This means that gaps are likely to form between the pole pieces and the separator, reducing the battery's cycling performance.

The binder commonly used on separators is polyvinylidene fluoride. However, at present, the price of polyvinylidene fluoride is rising and market supply is tight. At the same time, a hot rolling process is required to tightly adhere the separator to the pole pieces. However, as production speeds increase, the hot rolling process is gradually being replaced by the cold rolling process. Cold rolling of battery pole pieces is intended to fix the winding core, reduce the elasticity of the battery cell, improve the pass rate of core assembly, and ensure the consistency of the thickness of battery cell products.

If the adhesion between the positive and negative electrode pieces and the separator is insufficient, problems such as battery cell opening will frequently occur, and the electrolyte will have low infiltration ability, failing to meet the coating performance requirements for the separator of the secondary battery. By tightly adhering the separator to the electrode pieces, the battery's discharge capacity can be improved, internal resistance reduced, polarization loss reduced, the battery's cycling life extended, and the utilization rate of the secondary battery improved.

As can be seen, a battery cell is formed by adhering positive and negative electrode pieces and a separator together. The battery cell has a certain hardness. That is, the adhered positive and negative electrode pieces and the separator are stuck together and supported to form a structure with a certain thickness. A structure with a certain thickness also has a certain hardness. The negative electrode swells during the charge and discharge process. If the adhesion is weak, gaps are likely to form between the positive and negative electrode pieces and the separator. This makes it difficult for the positive and negative electrode pieces and the separator to stick together and support each other, leading to loosening of the battery cell and a decrease in hardness. This reduces the dynamic performance of the battery cell, for example, reducing its power rating and cycling performance. For example, in an electric vehicle, loosening of the battery cell slows down the battery's charging speed and reduces its cycling performance, directly shortening the battery life and requiring frequent battery replacement, thereby increasing the cost to electric vehicle consumers.

Based on this, the present application provides a binder for secondary batteries comprising a first polymer including an acrylic acid ester copolymer and a second polymer including a water-soluble polymer.

A binder is a material with adhesive properties that is used to adhere different substances together.

Acrylate ester copolymer is a general term for polymers produced by copolymerization of acrylate ester monomers and other copolymerizable monomers.

The structure of acrylic ester monomers contains an acrylic ester group such as methyl acrylate, ethyl acrylate, or n-butyl acrylate.

Acrylate ester copolymers have relatively high adhesion, and using an acrylate ester copolymer results in higher adhesion between the separator and the pole pieces after cold rolling.

Water-soluble polymers are hydrophilic polymeric materials that can dissolve or swell in water to form solutions or dispersions, but are not viscous in the dry state.

The binder comprises a first polymer containing an acrylic ester copolymer and a second polymer containing a water-soluble polymer. When the binder is applied to the separator, the water-soluble polymer acts as a support to support the first polymer, linking the first polymer to the water-soluble polymer and adhering the first polymer to the separator. Specifically, in the process of applying the binder to the separator, the binder is mixed with water to form a slurry, and the slurry is then applied to the separator. The water-soluble polymer becomes adhesive after contact with water, allowing the water-soluble polymer to adhere to the separator, and the water-soluble polymer can adhere the first polymer (including the acrylic ester copolymer) to the separator. Some of the acrylic ester copolymer and/or water-soluble polymer in the binder penetrates into the gaps in the separator and achieves adhesion to the separator. After the slurry dries, the water evaporates, causing the water-soluble polymer molecules to become entangled with each other, resulting in intermolecular interactions, thereby forming a network structure and allowing the first polymer (including the acrylic ester copolymer) to adhere to the separator. The water-soluble polymer (including the acrylic ester copolymer) acts as a support and link, adhering the first polymer particles to the separator. The slurry layer becomes an adhesive layer after drying. The adhesive layer has a side facing the separator and a side facing away from the separator. During the slurry application process, the water-soluble polymer adheres to the separator, or part of the acrylic ester copolymer and/or water-soluble polymer in the binder penetrates into the gaps in the separator, achieving adhesion to the separator, causing the adhesive layer to adhere to the separator. Because the acrylic ester copolymer and water-soluble polymer are non-viscous after drying, the adhesive layer is non-viscous on the side facing away from the separator, making it easier to roll up and unroll the separator.

When the positive and negative electrode pieces are wound and then subjected to a cold-rolling process, the binder has excellent adhesive strength, tightly bonding the positive and negative electrode pieces to the separator. Specifically, after cold-rolling, adhesive strength is provided primarily by the mechanical interlocking effect caused by the acrylic ester copolymer and water-soluble polymer in the binder penetrating into the gaps between the electrode pieces, as well as by the intermolecular interaction of the acrylic ester copolymer. Therefore, the binder of the present application improves the adhesive strength between the separator and the positive and negative electrode pieces during cold-rolling, reducing problems such as opening in battery cells and soft battery cells, thereby improving the hardness of the battery cell. At the same time, applying this binder to the separator in secondary batteries can improve the dynamic performance of the secondary battery, reduce electrochemical impedance, and enhance the rechargeability and cycling performance of the secondary battery.

That is, the water-soluble polymer becomes adhesive after dissolving in water, and when the slurry is applied to the separator, the water-soluble polymer adheres to the separator. A portion of the acrylic acid ester copolymer and/or water-soluble polymer in the binder penetrates into the gaps in the separator, allowing the acrylic acid ester copolymer and water-soluble polymer in the binder to adhere to the separator. That is, as shown in Figure 3, the side 21 of the adhesive layer 20 facing the separator adheres to the separator 10.

After drying, the side 23 of the adhesive layer 20 facing away from the separator is non-adhesive, making it easier to roll up the separator. During the process of placing the pole pieces on the surface of the adhesive layer and cold rolling, some of the acrylic ester copolymer and/or water-soluble polymer in the binder further penetrates into the gaps between the separator and the pole pieces, forming intermolecular forces between the molecules on the separator and the pole pieces, effectively adhering the separator and the pole pieces together through the binder.

In one embodiment, the mass ratio of the first polymer to the second polymer is 1:(0.1-10), preferably 1:(0.2-5).

The binder is defined as comprising a first polymer and a second polymer, with the mass of the first polymer being M1, the mass of the second polymer being M2, and the mass ratio of the first polymer to the second polymer being M1:M2.

The mass ratio test method is to record the mass M1 of the first polymer and the mass M2 of the second polymer added during the binder manufacturing process, and the mass ratio of the first polymer to the second polymer is M1:M2.

By setting the mass ratio of the first polymer to the second polymer within the above range, the adhesive layer forms a continuous network structure, which adheres the first polymer to the separator and helps to improve the decrease in adhesiveness of the adhesive layer at room temperature.

In other words, in the process of changing from a smaller amount to a larger amount of the second polymer, the adhesive strength of the adhesive layer tends to increase and then decrease. By controlling the mass of the first polymer and the second polymer within the above range, the adhesive strength of the binder applied to the separator is effectively improved.

In the above 1: (0.1 to 10), the value includes the minimum and maximum values of the range, as well as each value between these minimum and maximum values. Specific examples include, but are not limited to, the point values in the examples, as well as 1:0.1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc., and range values between any two of the above point values.

In the above 1: (0.2 to 5), the value includes the minimum and maximum values of the range, as well as each value between the minimum and maximum values. Specific examples include, but are not limited to, the point values in the examples, as well as 1:0.2, 1:1, 1:2, 1:3, 1:4, 1:5, etc., and range values between any two of the above point values.

In one embodiment, the second polymer comprises one or more of polyacrylamide, polyacrylic acid, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, polymaleic anhydride, and polyethyleneimine.

The second polymer contains the water-soluble polymer described above, which contains both hydrophilic groups and a certain amount of hydrophobic groups. This allows it to have a certain degree of surface activity, reduce the surface tension of water to a certain extent, and increase the solubility and dispersibility of the binder in the aqueous phase. That is, when it is made into a slurry for use in a separator, the water-soluble polymer controls the viscosity and rheological properties of the slurry, improving the dispersion and suspension of the binder. The second polymer also has chemically reactive functionality (e.g., carboxyl groups, hydroxyl groups, etc. that react with other groups). The polar groups in the water-soluble polymer structure can form hydrogen bonds between the first polymer and the separator and pole pieces, improving the adhesion between the separator and pole pieces.

In one embodiment, the binder has a volume particle size distribution Dv50 of 1 μm to 15 μm, preferably 3 μm to 12 μm.

Dv50 refers to the particle size of the sample particles that make up 50% of the total volume, which is larger than this value, and the particle size of the other particles that make up 50% of the total volume, which is smaller than this value. Dv50 can represent the median diameter of the sample.

The volume average particle size Dv50 of a binder can be tested using methods known in the art. For example, see GB/T 19077-2016, and characterization tests can be performed using a Malvern laser particle size analyzer. For example, testing can be performed using an instrument such as Malvern's Mastersizer-3000.

Theoretically, the volume average particle diameter Dv50 of the binder in this application may be less than 1 μm or more than 15 μm. However, considering the application of the binder in this application to separators, setting the volume average particle diameter Dv50 of the binder within the above range alleviates the problem of the binder blocking the pores of the separator and reducing the permeability of lithium ions (for lithium ion batteries, for example, but of course other types of secondary batteries may also be used) through the separator, as well as the problem of a thick coating layer being formed when the binder is applied to the separator, which affects the energy density of the subsequently manufactured battery. Therefore, the volume particle diameter distribution Dv50 of the binder is 1 μm to 15 μm, preferably 3 μm to 12 μm.

In the above range of 1 μm to 15 μm, the values include the minimum and maximum values of the range, as well as each value between the minimum and maximum values. Specific examples include, but are not limited to, the point values in the examples and 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc., as well as range values between any two of the above point values.

In the above range of 3 μm to 12 μm, the values include the minimum and maximum values of the range, as well as each value between the minimum and maximum values. Specific examples include, but are not limited to, the point values in the examples and 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, etc., as well as range values between any two of the above point values.

As can be seen from Figures 1 and 2, the binder particles are secondary particles comprising primary particles of a first polymer and primary particles of a second polymer. Thus, the second polymer acts as the skeleton within the binder slurry. When the binder slurry is applied to the separator, the second polymer acts to support and connect the first polymer, adhering the first polymer to the separator. After the slurry dries to form an adhesive layer, the adhesive layer adheres to the separator. However, since the side of the adhesive layer away from the separator has no adhesive strength, the separator can be easily wound up and unwound. When the separator is wound with the positive and negative electrode pieces and then subjected to a cold rolling process, the first and second polymers are deformed by force after being extruded and penetrate into the gaps between the separator and the electrode pieces, thereby achieving an adhesive effect.

In one embodiment, the shape of the binder includes a spherical shape.

Theoretically, there is no limitation on the shape of the binder in this application, and it may be, for example, spherical or rod-shaped. Considering that a spherical shape helps to uniformly disperse and coat the slurry during the stirring process, a spherical shape is preferred.

In one embodiment, the first polymer comprises an acrylate ester monomer, and the structure of the acrylate ester monomer is:
wherein R1 is a hydrogen atom or an alkyl group containing 1 to 12 carbon atoms, and R2 is an alkyl group containing 1 to 12 carbon atoms.

Acrylate ester monomers contain unsaturated ester groups, which can enhance the polymer's anti-swelling ability, adjust the polymer's glass transition temperature as a flexible monomer segment within the molecular segment, improve the binder's flexibility during use, and help demonstrate good adhesive properties.

In one embodiment, the acrylic acid ester monomer includes one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.

In theory, the present application does not limit the type of acrylic ester monomer as long as it contains the above structure; in other words, acrylic ester monomers include the substances listed above as well as substances not listed in the present application.

By using one or more of the above acrylic acid ester monomers, the glass transition temperature of the polymer can be adjusted and the anti-swelling ability of the polymer can be enhanced.

In one embodiment, the first polymer comprises an acrylonitrile-based monomer, and the structure of the acrylonitrile-based monomer is:
wherein R3 is a hydrogen atom or an alkyl group containing 1 to 6 carbon atoms.

The presence of an unsaturated cyano group in the structure of the acrylonitrile monomer helps to increase ionic conductivity and improve adhesion.

In one embodiment, the acrylonitrile-based monomer includes one or more of acrylonitrile and methacrylonitrile.

Theoretically, the present application does not limit the type of acrylonitrile-based monomer as long as it contains the above structure; in other words, acrylonitrile-based monomers include the substances listed above as well as substances not listed in the present application.

By using one or more of the above acrylonitrile-based monomers, the ionic conductivity of the binder can be increased.

In one embodiment, the first polymer comprises an acrylamide-based monomer, and the structure of the acrylamide-based monomer is:
wherein R4 is a hydrogen atom or an alkyl group containing 1 to 6 carbon atoms, and R5 is a hydrogen atom, an alkyl group containing 1 to 6 carbon atoms substituted with a hydroxy group, or an alkoxy group of 1 to 6 carbon atoms.

The third unit contains an unsaturated amide group that acts as a crosslinker and also has relatively high adhesion.

In one embodiment, the acrylamide-based monomer includes one or more of acrylamide, N-methylolacrylamide, and N-butoxymethacrylamide.

Theoretically, the present application does not limit the type of acrylamide-based monomer as long as it contains the above structure; that is, acrylamide-based monomers include the substances listed above as well as substances not listed in the present application.

The use of one or more of the above acrylamide-based monomers can adjust the molecular weight of the polymer, thereby controlling the molecular weight of the polymer. Keeping the molecular weight of the binder within a certain range helps improve adhesion.

As can be appreciated, the constituent monomers of the first polymer can include, but are not limited to, one, two, or three of the three types of monomers described above. As can be appreciated, when the first polymer is produced using three types of monomers simultaneously, the adhesion of the first polymer is superior.

Commonly used polyvinylidene fluoride binders require a hot rolling process to achieve better adhesion. As production speeds improve and energy savings increase, the hot rolling process is gradually being replaced by a cold rolling process. Battery cells are rolled up and then cold rolled. Conventional polyvinylidene fluoride is a homopolymer with a crystallinity of around 50%, resulting in insufficient adhesion between the separator and the positive and negative electrode pieces. Conventional polyacrylic ester binders do not meet the adhesive strength requirements during cold rolling, frequently resulting in problems such as opening of battery cells and soft battery cells. At the same time, their poor electrolyte infiltration makes them unable to meet the coating performance requirements for secondary battery separators.

The binder contains an acrylic ester copolymer and a water-soluble polymer produced using the above-mentioned monomers, which gives the binder relatively high adhesion.

In one embodiment, the first polymer contains an acrylic acid ester-based monomer, an acrylonitrile-based monomer, and an acrylamide-based monomer, and the mass ratio of the acrylic acid ester-based monomer, the acrylonitrile-based monomer, and the acrylamide-based monomer is in the range of 100:(1-80):(1-20), preferably 100:(20-60):(5-15).

To improve the overall performance of the first polymer, the first polymer contains an acrylic acid ester monomer, an acrylonitrile monomer, and an acrylamide monomer. When the mass ratio of the acrylic acid ester monomer, the acrylonitrile monomer, and the acrylamide monomer is in the range of 100:(1-80):(1-20), preferably 100:(20-60):(5-15), excellent adhesive properties are achieved.

In the above 100: (1-80): (1-20) range, the values include the minimum and maximum values of the range, as well as each value between the minimum and maximum values. Specific examples include, but are not limited to, the point values in the examples, as well as 100:1:1, 100:10:1, 100:30:1, 100:50:1, 100:80:1, 100:10:5, 100:10:10, 100:10:20, 100:30:10, 100:30:20, 100:50:20, 100:80:20, etc., and range values between any two of the above point values.

In the above 100: (20-60): (5-15) range, the values include the minimum and maximum values of the range, as well as each value between the minimum and maximum values. Specific examples include, but are not limited to, the point values in the examples, as well as range values between any two of the above point values, such as 100:20:5, 100:30:10, 100:60:15, etc.

The present application also provides a method for producing a binder for a secondary battery, which includes co-mixing water, an emulsifier, an initiator, and constituent monomers of a first polymer, stirring the mixture, and heating the mixture to react with each other to obtain a first polymer emulsion;

The method includes mixing and stirring the first polymer emulsion and the second polymer, and then spray-drying the mixture to obtain a binder.

In this application, a first polymer emulsion is obtained by emulsion polymerization, and a binder is obtained by spray drying.

Regarding emulsion polymerization, emulsion polymerization is the process in which monomers are dispersed in water with an emulsifier through mechanical agitation to form an emulsion, and then an initiator is added to start the polymerization of the monomers.

Regarding emulsifiers, they are substances that can convert incompatible oil and water into an emulsion that is difficult to separate. Emulsifiers are usually surfactants that have both hydrophilic polar groups and hydrophobic (lipophilic) non-polar groups.

Regarding initiators, an initiator is a substance that can initiate the polymerization reaction of monomers. For example, a free radical initiator refers to a compound that readily decomposes into free radicals (i.e., primary free radicals) when exposed to heat, and can be used to initiate the free radical polymerization and copolymerization of olefin and diene monomers.

Water, emulsifier, initiator, and polymer constituent monomers are mixed together and stirred. After the water and emulsifier are stirred and dispersed, an emulsion is formed; that is, the emulsifier forms micelles in the aqueous phase, and the monomers are solubilized in most of the micelles. When heated, the initiator starts polymerization of the monomers inside the micelles, resulting in an emulsion.

With spray drying, the material requiring drying (a mixture of a first polymer emulsion and a second polymer) is dispersed through mechanical action into very fine, mist-like particles (increasing the surface area for water evaporation and accelerating the drying process) and then exposed to hot air, which instantly removes most of the water and dries the solids in the material into a powder.

A binder comprising the first polymer and the second polymer is obtained through a spray drying process.

An embodiment of the present application further provides a separator containing the above-described secondary battery binder or a binder manufactured by the above-described method for manufacturing a secondary battery binder. Since all of the technical solutions of all of the above-described embodiments are used in the binder, the separator has at least all of the beneficial effects provided by the technical solutions of the above-described embodiments, and detailed descriptions thereof will be omitted here.

By applying the above binder to the separator, the adhesion performance between the pole pieces and the binder can be improved, improving the opening problem that occurs in the conventional battery cell pre-cold rolling process.

An embodiment of the present application further provides a battery unit including the separator described above. Since all of the technical solutions of all of the above embodiments are used in the separator, the battery unit has at least all of the beneficial effects provided by the technical solutions of the above embodiments, and detailed descriptions thereof will be omitted here.

By applying the above separator to a single battery, the large jig circulation performance of the single battery can be improved.

An embodiment of the present application further provides a battery including the above-described battery unit. Since all of the technical solutions of all of the above-described embodiments are used in the battery unit, it has at least all of the beneficial effects provided by the technical solutions of the above-described embodiments, and detailed descriptions thereof will be omitted here.

The battery includes a battery module and a battery pack.

Embodiments of the present application further provide the above-described battery alone or an electrical device including the above-described battery. Since all of the technical solutions of all of the above-described embodiments are used in the battery alone or the battery, it has at least all of the beneficial effects provided by the technical solutions of the above-described embodiments, and detailed descriptions thereof will be omitted here.

The electrode assembly, battery unit, battery, and electrical device of the present application will be described below with appropriate reference to the drawings.

In one embodiment of the present application, an electrode assembly is provided.

Typically, an electrode assembly includes a positive electrode piece, a negative electrode piece, an electrolyte, and a separator. During the charge/discharge process of the battery, active ions are inserted and extracted back and forth between the positive electrode piece and the negative electrode piece. The electrolyte functions to conduct ions between the positive electrode piece and the negative electrode piece. The separator, located between the positive electrode piece and the negative electrode piece, primarily functions to prevent short-circuiting between the positive electrode and the negative electrode piece while allowing ions to pass through. The separator is the improved separator described in this application.

The positive electrode piece includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.

For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film layer is disposed on one or both of the two opposing surfaces of the positive electrode current collector.

In some embodiments, the positive electrode current collector may be a metal foil piece or a composite current collector. For example, aluminum foil may be used as the metal foil piece. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymeric material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

In some embodiments, when the electrode assembly is a lithium-ion battery, the positive electrode active material can be a positive electrode active material known in the art for use in lithium-ion batteries. For example, the positive electrode active material can include at least one of a lithium-containing phosphate having an olivine structure, a lithium transition metal oxide, and a modified compound thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries can also be used. These positive electrode active materials can be used alone or in combination. Here, examples of lithium transition metal oxides include lithium cobalt oxide (LiCoO ₂ , etc.), lithium nickel oxide (LiNiO ₂ , etc.), lithium manganese oxide (LiMnO ₂ , LiMn ₂ O ₄ , etc.), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also abbreviated as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (also abbreviated as NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (also abbreviated as NCM ₂₁₁ ), and LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (NCM _Examples of the lithium- _containing phosphate _{having an} olivine structure include, but are not limited to, at least one of lithium iron _phosphate ( _LiFePO4 (also _abbreviated as _{LFP )} ), lithium _iron phosphate and carbon composite, lithium manganese phosphate ( _{LiMnPO4 )} , lithium manganese phosphate and carbon composite, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composite.

In some embodiments, the positive electrode membrane layer optionally further includes a binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

In some embodiments, the positive electrode film layer optionally further comprises a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, positive electrode pieces can be manufactured by the following method: The above-mentioned components for manufacturing positive electrode pieces, such as the positive electrode active material, conductive agent, binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is then applied to a positive electrode current collector, and after processes such as drying and cold rolling, the positive electrode pieces can be obtained.

The negative electrode piece includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode film layer is disposed on one or both of the two opposing surfaces of the negative electrode current collector.

In some embodiments, the negative electrode current collector may be a metal foil piece or a composite current collector. For example, copper foil may be used as the metal foil piece. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymeric material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

In some embodiments, the negative electrode active material may be a negative electrode active material known in the art and used in batteries. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include at least one of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials in batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

In some embodiments, the negative electrode film layer optionally further includes a binder. The binder may include at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

In some embodiments, the negative electrode film layer optionally further comprises a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the negative electrode membrane layer optionally further contains other additives, such as a thickener (e.g., sodium carboxymethylcellulose (CMC-Na)).

In some embodiments, negative electrode pieces can be manufactured by the following method: The components for manufacturing the negative electrode pieces, such as the negative electrode active material, conductive agent, binder, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry, which is then applied to a negative electrode current collector, and the negative electrode pieces can be obtained after processes such as drying and cold rolling.

The electrolyte serves to conduct ions between the positive and negative electrode pieces. This application is not specifically limited to the type of electrolyte, and it can be selected as needed.

In some embodiments, the electrolyte is an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bistrifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

In some embodiments, the solvent may include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

In some embodiments, the electrolyte solution can optionally further contain additives. For example, the additives can include a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive that can improve specific battery performance, such as an additive that improves the battery's overcharge performance or an additive that improves the battery's high-temperature or low-temperature performance.

In some embodiments, the electrode assembly further includes a separator. The present application is not particularly limited by the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

In some embodiments, the separator material may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer thin film or a multi-layer composite thin film, and is not particularly limited. When the separator is a multi-layer composite thin film, the materials of the layers may be the same or different, and are not particularly limited.

In some embodiments, the positive electrode pieces, negative electrode pieces, and separators can be manufactured into an electrode assembly by a winding process or a stacking process.

In some embodiments, the electrode assembly can include an outer package. The outer package can be used to package the electrode assembly and electrolyte.

In some embodiments, the outer packaging of the electrode assembly may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the electrode assembly may be a soft bag, such as a soft bag. The soft bag may be made of plastic. Examples of plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

The present application does not particularly limit the shape of the electrode assembly, which may be cylindrical, rectangular, or any other shape. For example, Figure 5 shows an example of a secondary battery 5 with a rectangular structure.

In some embodiments, referring to FIG. 6 , the outer package may include a case 51 and a cover plate 53. Here, the case 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates surround and form a storage chamber. The case 51 has an opening communicating with the storage chamber, and the cover plate 53 may cover the opening to close the storage chamber. The positive electrode piece, the negative electrode piece, and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged within the storage chamber. The electrode assembly 52 is impregnated with an electrolyte. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art may select the number according to specific actual needs.

In some embodiments, the electrode assemblies can be assembled into a battery module. The battery module may include one or more electrode assemblies, and one skilled in the art can select the specific number depending on the application and capacity of the battery module.

Figure 7 shows an example battery module 4. Referring to Figure 7, in the battery module 4, the multiple secondary batteries 5 may be arranged in sequence along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple secondary batteries 5 can be fixed in place using a fastening member.

Optionally, the battery module 4 may further include an outer shell having a storage space in which multiple secondary batteries 5 are housed.

In some embodiments, the battery modules can be assembled into a battery pack. The battery pack can include one or more battery modules, and those skilled in the art can select the specific number depending on the application and capacity of the battery pack.

Figures 8 and 9 show an example battery pack 1. Referring to Figures 8 and 9, the battery pack 1 may include a battery box and multiple battery modules 4 installed in the battery box. The battery box includes an upper box 2 and a lower box 3, and the upper box 2 is installed to cover the lower box 3, forming an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in the battery box in any manner.

The present application also provides an electric device including at least one of the electrode assembly, battery module, or battery pack provided by the present application. The electrode assembly, battery module, or battery pack can be used as a power source for the electric device, or as an energy storage unit for the electric device. The electric device can include, but is not limited to, mobile devices (such as mobile phones and laptops), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks), trains, ships, satellites, energy storage systems, and the like.

As an electrical device, you can select an electrode assembly, battery module, or battery pack depending on your usage needs.

Figure 10 shows an example of an electric device. The electric device may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements for the electrode assembly of the electric device, a battery pack or battery module can be used.

Another example device may be a mobile phone, tablet, laptop, etc. Such devices typically require light weight and may use an electrode assembly as a power source.
Example

Examples of the present application are described below. The examples described below are illustrative and are used only to interpret the present application, and should not be understood as limiting the present application. If specific techniques or conditions are not specified in the examples, they will be carried out in accordance with the techniques or conditions described in the literature in the field or in accordance with the product specifications. If the manufacturer of the reagents or equipment used is not specified, they are all ordinary products that are commercially available.
Preparation of First Polymer Emulsion Preparation Example 1

The acrylic ester monomer methyl acrylate, the acrylonitrile monomer acrylonitrile, and the acrylamide monomer acrylamide were weighed out in a weight ratio of 100:1:10 and mixed uniformly. A 1000 mL four-neck flask equipped with a mechanical stirrer, thermometer, and condenser was charged with 200 g of the mixed monomers, 5 g of an emulsifier (sodium lauryl sulfate), 1.8 g of an initiator (ammonium persulfate), and 260 g of deionized water, and emulsified with high-speed stirring for 30 minutes. Under nitrogen gas protection, the mixture was heated to 75°C and reacted for 4 hours. The temperature was then lowered to below 40°C, the pH was adjusted to neutral with aqueous ammonia, and the mixture was filtered to obtain Preparation Example 1, a first polymer emulsion.
Production Examples 2 to 12

Based on Production Example 1, the types and mass ratios of the monomers were adjusted to obtain Production Examples 2 to 12.
Example 1
Binder manufacturing

The first polymer and the second polymer were weighed and added in a weight ratio of 1:1, and deionized water was added to adjust the solid content of the system to 20%, and the mixture was stirred to be uniformly mixed. Then, the separator binder was prepared by a spray-drying process, under the conditions of an inlet air temperature of 110°C and an outlet air temperature of 50°C.
Examples 2 to 24

Based on Example 1, the types and weight ratios of the first polymer and the second polymer were adjusted to obtain Examples 2 to 24.
Comparative Example 1

A binder was prepared based on Example 1 using only the second polymer.
Comparative Example 2

A binder was prepared based on Example 7 using only the first polymer.
Battery cell and battery manufacturing Separator manufacturing

A commercially available 7 μm thick PE microporous membrane (manufactured by Zhuoga Electronics Technology Co., Ltd.) with an average pore size of 80 nm was used as the substrate. The separator binder prepared above was mixed uniformly with deionized water by stirring to obtain a slurry (20% solids). The slurry was sprayed onto two surfaces of the substrate and dried to remove the solvent. A separator was obtained by applying the coating composition to the substrate at a coating density of 1.5 g/ ^m² .
Positive electrode piece manufacturing

Polyvinylidene fluoride (PVDF), lithium iron phosphate (LFP), carbon black (a conductive agent), and N-methylpyrrolidone (NMP) were mixed uniformly in a mass ratio of 1.2:58.38:0.42:40 through sufficient stirring to prepare a positive electrode slurry. The positive electrode slurry was uniformly applied to an aluminum foil positive electrode current collector at a loading of 200 g/ ^m2 , and then dried, cold-rolled, and divided to obtain positive electrode pieces.
Negative electrode piece manufacturing

Artificial graphite, acetylene black as a conductive agent, styrene-butadiene rubber (SBR) as a binder, and sodium carboxymethyl cellulose (CMC-Na) as a thickener were added to deionized water in a mass ratio of 96.2:1.0:1.6:1.2 and thoroughly stirred to homogeneity, producing a negative electrode slurry (solid content 63%). The negative electrode slurry was applied to a copper foil negative electrode current collector at a loading of 98 g/ ^m2 , and then dried, cold-rolled, and divided to obtain negative electrode pieces.
Electrolyte production

Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at 25°C in a volume ratio of 1:1:1 to obtain a mixed solvent, and then _LiPF6 was dissolved in the mixed solvent to obtain an electrolyte solution with a _LiPF6 concentration of 1 mol/L.
Secondary battery manufacturing

The positive electrode pieces, separator, and negative electrode pieces are stacked in order, wound up, and cold-rolled to form a battery cell (during this process, the separator adheres to the electrode pieces), and the battery cell is placed in an outer package, and the above-prepared electrolyte is added. After going through processes such as packaging, standing, chemical synthesis, and aging, a secondary battery is obtained.
Performance Tests Cold Rolled Adhesion Test:

The battery's negative electrode piece and separator were stacked and placed on a hot press. The hot press parameters were set to a temperature of 25°C, a pressure of 7 T, and a time of 30 s. Pressure was applied to produce an adhered separator/positive electrode piece sample. The separator/electrode piece sample was cut into a 150 mm x 20 mm rectangular spline. One side of the splined electrode piece was attached to a steel plate with double-sided tape, and the separator and electrode piece were separated longitudinally by 2 cm at one end of the rectangular spline to produce a test sample.

The steel plate was held horizontally and fixed with the lower clamp of a universal testing machine (Xieqiang Instrument Manufacturing (Shanghai) Co., Ltd., model number CTM2100). The peeled end of the separator was fixed with the upper clamp of the universal testing machine, and a tensile tester was connected. The test conditions were set to a pulling speed of 20 mm/min and a horizontal pull of 10 cm. After the tensile force stabilized, the tensile force value was recorded, and the adhesive strength between the separator and the pole piece was obtained from the ratio of the tensile force value to the sample width.
EIS data (electrochemical impedance spectroscopy):

Using a Shanghai Chenhua CHI660D electrochemical workstation, a sinusoidal voltage signal of frequency W1 and small amplitude was applied to the battery system, and the system generated a sinusoidal current response of frequency W2. The change in the ratio of the excitation voltage to the response current is the impedance spectrum of the electrochemical system. In the AC impedance test, the test frequency range was 10mHz to 100kHz, and the amplitude was 5mV. Through the test, information such as the real and imaginary parts of the impedance at various frequencies could be obtained.
Lithium-ion battery multiplication performance:

Using a Wuhan King Nuo Electronics CT-2001 A LAND battery testing system, the test environment was a room temperature of 25°C, a voltage range of 2.5 to 3.65V, and constant current charge-discharge cycles of 5 times were performed on test batteries assembled with the manufactured electrode materials at rates of 0.2C, 0.5C, 1C, 2C, 5C, and 0.2C. The specific cycles were 0.2C (5 cycles, the fifth capacity is designated C1), followed by 0.5C (5 cycles), 1C (5 cycles), 2C (5 cycles), 5C (5 cycles), and 0.2C (5 cycles, the fifth capacity is designated C2). The battery capacity after the first five constant current charge-discharge cycles at 0.2C is designated C1, and the battery capacity after the second five constant current charge-discharge cycles at 0.2C is designated C2. The charge-discharge cycle performance was expressed as P = (C2/C1) x 100%.

By producing a first polymer using appropriate monomers, controlling the mass ratio of the first polymer to the second polymer within an appropriate range, and then obtaining a binder through a spray drying process, the resulting binder will have relatively high adhesion, and when applied to a separator, it will help improve battery performance.

The above is merely a preferred embodiment of the present application and does not limit the scope of the patent of the present application. Equivalent structural modifications made based on the application concept of the present application and the contents of the specification and drawings of the present application, or direct or indirect applications in other related technical fields, are all within the scope of protection of the patent of the present application.

Claims (17)

A binder for a separator of a secondary battery,
a first polymer including an acrylic acid ester copolymer and a second polymer including a water-soluble polymer;
the binder particles are secondary particles including primary particles of a first polymer and primary particles of a second polymer,
The volume particle size distribution Dv50 of the binder particles is 3 μm to 15 μm.
Binder for secondary battery separators . the mass ratio of the first polymer to the second polymer is 1:(0.1 to 10);
The binder for a separator of a secondary battery according to claim 1 . the second polymer comprises one or more of polyacrylamide, polyacrylic acid, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, polymaleic anhydride, and polyethyleneimine;
The binder for a separator of a secondary battery according to claim 1 or 2. The volume particle size distribution Dv50 of the binder particles is 3 μm to 12 μm;
The binder for a separator of a secondary battery according to claim 1 or 2. The shape of the binder includes a spherical shape.
The binder for a separator of a secondary battery according to claim 1 or 2. The first polymer contains an acrylate ester-based monomer, and the structure of the acrylate ester-based monomer is
Including,
wherein R1 is a hydrogen atom or an alkyl group containing 1 to 12 carbon atoms, and R2 is an alkyl group containing 1 to 12 carbon atoms;
The binder for a separator of a secondary battery according to claim 1 or 2. The acrylic acid ester monomer includes one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.
The binder for a separator of a secondary battery according to claim 6 . The first polymer contains an acrylonitrile-based monomer, and the structure of the acrylonitrile-based monomer is

Including,
wherein R3 is a hydrogen atom or an alkyl group containing 1 to 6 carbon atoms;
The binder for a separator of a secondary battery according to claim 1 or 2. The acrylonitrile-based monomer includes one or more of acrylonitrile and methacrylonitrile.
The binder for a separator of a secondary battery according to claim 8 . The first polymer contains an acrylamide-based monomer, and the structure of the acrylamide-based monomer is

Including,
wherein R4 is a hydrogen atom or an alkyl group containing 1 to 6 carbon atoms, and R5 is a hydrogen atom, an alkyl group containing 1 to 6 carbon atoms substituted with a hydroxy group, or an alkoxy group of 1 to 6 carbon atoms.
The binder for a separator of a secondary battery according to claim 1 or 2. The acrylamide-based monomer includes one or more of acrylamide, N-methylolacrylamide, and N-butoxymethacrylamide.
The binder for a separator of a secondary battery according to claim 10. the first polymer includes an acrylic acid ester-based monomer, an acrylonitrile-based monomer, and an acrylamide-based monomer, and the mass ratio of the acrylic acid ester-based monomer, the acrylonitrile-based monomer, and the acrylamide-based monomer is in the range of 100:(1 to 80):(1 to 20);
The binder for a separator of a secondary battery according to claim 1 or 2. A method for producing the binder for a separator of a secondary battery according to claim 1,
co-mixing, stirring, and heating water, an emulsifier, an initiator, and constituent monomers of a first polymer to react them to obtain a first polymer emulsion;
and mixing and stirring the first polymer emulsion and the second polymer, and spray drying to obtain a binder.
method. A secondary battery separator comprising the binder according to claim 1.
Separator. Comprising the separator of claim 14 .
Battery alone. The battery unit according to claim 15,
battery. The battery according to claim 15 or the battery according to claim 16,
Electrical equipment.