JP7848240B2 - Binders, separators, secondary batteries, and power consumption devices for secondary batteries - Google Patents

Description

Cross-reference of related applications

This application claims priority to the Chinese patent application filed on April 24, 2023, application number 202310447240.5, all of which are incorporated herein by reference.

This application relates to the field of secondary battery technology, and more particularly to binders, separators, secondary batteries, and power consumption devices for secondary batteries.

With the rapid growth of portable electronic devices and electric vehicles, the demand for power batteries is also increasing. In this context, the electrical and chemical properties of batteries are receiving increasing attention.

Currently, battery cells have an opening problem; specifically, gaps easily form between the polarity sheet and the separator, which degrades the battery's cycle characteristics.

The main objective of this invention is to provide a binder for secondary batteries that improves the adhesion between the polarity sheet and the separator, thereby improving battery performance.

To achieve the above objective, this application provides a binder for secondary batteries, wherein the binder comprises an acrylic acid ester copolymer, and the shape of the binder includes a ring shape.

Acrylic acid ester copolymers have good adhesive properties, and their use can further improve the adhesion between the separator and the polar sheet.

Annular binders have a larger bonding area. For example, when an annular binder and a polar sheet come into contact, the contact area is the annular edge of the annular binder, whereas with a spherical binder, the contact area is a point contact. Therefore, for annular and spherical binders of the same dimensions, the annular binder exhibits superior bonding performance. Furthermore, annular binders have hollow through-holes. For annular and spherical binders of the same dimensions, the annular binder has a smaller mass, thus achieving good bonding performance even when the amount of annular binder used is reduced.

Selectively, the specific surface area of the binder is in the range of 0.4 ^m² /g to ^{1.2 m²} /g, and preferably, in the range of 0.6 ^m² /g to ^{0.9 m²} /g.

Specific surface area refers to the total surface area of a unit mass of material. Based on the fact that annular binders have hollow through-holes, the specific surface area of annular binders is increased compared to spherical binders of the same dimensions. The specific surface area of the binder is in the range of 0.4 ^m² /g to ^{1.2 m²} /g, preferably in the range of 0.6 ^m² /g to ^{0.9 m²} /g. This helps to improve contact between the annular binder and the separator and polar sheet, thereby improving adhesive performance.

Selectively, the ratio of the surface area to the volume of the binder is 0.1 × ^{10⁶ m⁻¹} to 20 × ^{10⁶ m⁻¹} , and preferably, the ratio of the surface area to the volume of the binder is 0.5 × ^{10⁶ m⁻¹} to 16 × ^{10⁶ m⁻¹} .

The ratio of surface area to volume is the ratio of the total surface area to the total volume of the material. Based on the fact that annular binders have hollow through holes, the ratio of surface area to volume of an annular binder is increased compared to a spherical binder of the same dimensions. The ratio of surface area to volume of the binder is 0.1 × ^{10⁶ m⁻¹} to 20 × ^{10⁶ m⁻¹} , preferably 0.5 × ^{10⁶ m⁻¹} to 16 × ^{10⁶ m⁻¹} . This indicates that annular binders have an increased surface area compared to spherical binders, which helps to improve contact between the annular binder and the separator and polar sheet, thereby improving adhesive performance.

Selectively, the bulk density of the binder is in the range of 0.3 g/ ^cm³ to 0.8 g/ ^cm³ , and preferably, in the range of 0.4 g/ ^cm³ to 0.7 g/ ^cm³ .

Bulk density is the mass per unit volume measured immediately after filling a container with powder. Based on the fact that annular binders have hollow through-holes, after filling a container with annular binders, voids are formed in the through-holes of the annular binders. Compared to filling with spherical binders of the same dimensions, the bulk density of the annular binder decreases, with a range of 0.3 g/ ^cm³ to 0.8 g/ ^cm³ , preferably 0.4 g/ ^cm³ to 0.7 g/ ^cm³. This indicates that, under certain conditions, the adhesive performance of the binder is improved even when the mass of the annular binder is reduced.

Selectively, the shape of the binder includes annular shapes.

The annular shape is a relatively easily achievable shape based on experimental experience and the surface tension of the material.

Selectively, the range of the volume-based particle size distribution Dv50 of the binder is 1 μm to 15 μm, and preferably, the range of the volume-based particle size distribution Dv50 of the binder is 3 μm to 12 μm.

To improve the adhesion of the improved binder and reduce the gap between the separator and the polar sheet, the range of the volume-based particle size distribution Dv50 of the binder is 1 μm to 15 μm, preferably 3 μm to 12 μm.

Selectively, the constituent monomers of the acrylic acid ester copolymer include a first polymer monomer, and the structure of the first polymer monomer is
This includes, where R1 contains a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and R2 contains an alkyl group having 1 to 12 carbon atoms.

The first polymerization monomer structure contains ester groups, improving the compatibility between the acrylic ester copolymer and the electrolyte, enhancing ionic conductivity, improving the swelling resistance of the acrylic ester copolymer, and acting as a flexible monomer segment in the molecular segment, it can adjust the glass transition temperature of the acrylic ester copolymer, improving the toughness of the binder during coating and contributing to good adhesion.

Selectively, the first polymerized monomer comprises one or more of the following: 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.

Theoretically, this application does not limit the type of the first polymerized monomer, and the first polymerized monomer satisfies the requirement of including the above-described structure; that is, the first polymerized monomer includes the substances listed above and substances not listed in this application.

By using one or more of the above-mentioned first polymerization monomers, the glass transition temperature of the acrylic acid ester copolymer can be adjusted, thereby improving its swelling resistance.

Selectively, the constituent monomers of the acrylic acid ester copolymer include a second polymer monomer, and the structure of the second polymer monomer is
This includes, where R3 contains hydrogen or an alkyl group having 1 to 6 carbon atoms.

The structure of the second polymerization monomer contains carboxyl groups, which are characterized by their strong polarity. This can improve the adhesion and flexibility of the binder. For example, the carboxyl groups can form bonding forces with functional groups on the polar sheet and separator materials, thereby improving the adhesive effect.

Selectively, the second polymerized monomer contains one or more of acrylic acid, methacrylic acid, crotonic acid, and heptenoic acid.

Theoretically, this application does not limit the type of second polymerization monomer, and satisfies the requirement that the second polymerization monomer includes the above-described structure; that is, the second polymerization monomer includes the substances listed above and substances not listed in this application.

By using one or more of the above-mentioned secondary polymerization monomers, the adhesive performance of the acrylic acid ester copolymer can be improved.

Selectively, the constituent monomers of the acrylic acid ester copolymer include a third polymer monomer, and the structure of the third polymer monomer is
This includes, where R4 contains a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

The structure of the third polymerization monomer contains unsaturated cyano groups. These highly polar cyano groups contribute to improved ionic conductivity and simultaneously provide swelling resistance and high adhesion.

Selectively, the third polymerized monomer comprises one or more of acrylonitrile and methacrylonitrile.

Theoretically, this application does not limit the type of third polymerization monomer, and satisfies the requirement that the third polymerization monomer includes the above structure; that is, the third polymerization monomer includes the substances listed above and substances not listed in this application.

By using one or more of the above-mentioned third polymerization monomers, the ionic conductivity of the acrylic acid ester copolymer can be improved, thereby enhancing its adhesive properties.

Selectively, the constituent monomers of the acrylic acid ester copolymer include a fourth polymer monomer, and the structure of the fourth polymer monomer is
This includes, where R5 comprises a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R6 comprises a hydrogen atom, a hydroxyl-substituted alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms.

The structure of the fourth polymerization monomer contains an unsaturated amide group, which improves swelling and enhances adhesion.

Selectively, the fourth polymerized monomer comprises one or more of acrylamide, N-methylolacrylamide, and N-butoxymethylacrylamide.

Theoretically, this application does not limit the type of fourth polymerization monomer, and satisfies the requirement that the fourth polymerization monomer includes the above structure; that is, the fourth polymerization monomer includes the substances listed above and substances not listed in this application.

By using one or more of the above-mentioned fourth polymerization monomers, the adhesion of the acrylic acid ester copolymer can be improved.

As can be understood, when at least two of the four monomers described above are included, the adhesive effect is even better. For example, the constituent monomers of the acrylic ester copolymer include at least the first polymer monomer and the second polymer monomer, or the constituent monomers of the acrylic ester copolymer include at least the first polymer monomer and the third polymer monomer, or the constituent monomers of the acrylic ester copolymer include at least the first polymer monomer and the fourth polymer monomer. When the constituent monomers of the acrylic ester copolymer include all four monomers simultaneously, the performance of the binder is even better.

Selectively, the constituent monomers of the acrylic acid ester copolymer include a first polymer monomer, a second polymer monomer, a third polymer monomer, and a fourth polymer monomer. The mass ratio of the first polymer monomer to the second polymer monomer and the third polymer monomer to the fourth polymer monomer is 1:(0.01-0.8):(0.01-0.5):(0.01-0.3), and preferably, the mass ratio of the first polymer monomer to the second polymer monomer and the third polymer monomer to the fourth polymer monomer is 1:(0.1-0.5):(0.15-0.45):(0.1-0.22).

When the constituent monomers of an acrylic acid ester copolymer simultaneously contain the four monomers mentioned above, and the components of each monomer fall within the specified range, the overall performance is improved.

This application further provides a separator comprising a substrate and an adhesive layer provided on at least one side of the substrate, wherein the adhesive layer comprises the binder for the secondary battery.

Selectively, the surface density of the adhesive layer on the substrate is in the range of 0.7 g/ ^m² to 3 g/ ^m² , preferably 0.8 g/ ^m² to 2 g/ ^m² .

Based on the fact that the annular structure binder increases the contact area between the binder and the polar sheet and separator, that is, good adhesive performance can be achieved even when the amount of annular structure binder used is reduced. For this reason, the range value of the surface density of the adhesive layer on the substrate is 0.7 g/ ^m² to 3 g/ ^m² , and preferably the range value of the surface density of the adhesive layer on the substrate is 0.8 g/ ^m² to 2 g/ ^m² .

This application further provides a secondary battery including the aforementioned separator.

This application further provides a power consumption device including the aforementioned secondary battery.

To more clearly explain the embodiments of this application or the technical solutions in the prior art, the drawings necessary for describing the embodiments or the prior art are briefly described below. The drawings shown below represent only a few embodiments of this application, and it will be obvious to those skilled in the art that other drawings can be obtained based on the structures shown in these drawings without requiring any creative effort.

This is a scanning electron microscope image of the binder according to Example 1 of the present application. This is a scanning electron microscope image of the binder according to Example 1 of the present application. This is a flowchart of the method for manufacturing the binder according to the embodiment of the present application. This is a schematic diagram of a secondary battery according to an embodiment of the present invention. Figure 4 is an exploded view of a secondary battery according to an embodiment of the present invention. This is a schematic diagram of a battery module according to an embodiment of the present invention. This is a schematic diagram of a battery pack according to an embodiment of the present invention. Figure 7 is an exploded view of a battery pack according to an embodiment of the present invention. This is a schematic diagram of a power consumption device that uses a secondary battery as a power source according to an embodiment of the present invention. This is a schematic diagram of the binder according to Embodiment 1 of the present application.

1 Battery pack 2 Upper casing 3 Lower casing 4 Battery module 60 Ring wire 5 Secondary battery 51 Housing 52 Electrode assembly 53 Top cover assembly 61 Through hole

The realization of the objectives of this application, its functional features, and advantages will be further explained by combining examples and referring to the drawings.

The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the drawings of the embodiments. It is clear that the embodiments described are only a selection of the embodiments of this application, not all of them. All other embodiments obtained by those skilled in the art without requiring creative effort based on the embodiments of this application are all within the scope of protection of this application.

The binder of this application, its manufacturing method, and embodiments of separators, electrode assemblies, battery cells, batteries, and power consumption devices containing the binder will be described in detail below, with reference to the drawings as appropriate. However, unnecessary detailed explanations may be omitted. For example, detailed explanations of well-known matters or redundant explanations of substantially identical structures may be omitted. This is to avoid unnecessarily verbose explanations and to facilitate understanding for those skilled in the art. Furthermore, the drawings and the following explanation are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter described in the claims.

The “range” disclosed herein is defined in the form of a lower and upper limit, and a given range is defined by selecting one lower limit and one upper limit, the selected lower and upper limits defining the boundaries of a particular range. Ranges defined in this manner may or may not include the values at both ends and can be combined in any way, that is, any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60–120 and 80–110 are listed for a particular parameter, it is understood that the ranges 60–110 and 80–120 are also expected. Similarly, if the minimum range values 1 and 2 are listed, and the maximum range values 3, 4 and 5 are listed, the ranges 1–3, 1–4, 1–5, 2–3, 2–4 and 2–5 are all intended. In this application, unless otherwise specified, the numerical range “a–b” means an abbreviated expression for any combination of real numbers between a and b, where both a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are listed in this specification, and "0 to 5" is merely an abbreviated representation of combinations of these numbers. Furthermore, when a parameter is described as being an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

All embodiments and optional embodiments of this application can be combined to form new technical solutions, unless otherwise specified.

All technical features and selectable technical features of this application can be combined to form new technical solutions, unless otherwise specified.

All steps of this application may be performed sequentially or randomly, preferably sequentially, unless otherwise specified. For example, if the method includes steps (a) and (b), it indicates that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, if the method further includes step (c), it means that step (c) may be added to the method in any order, for example, that the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

Battery cells have an opening problem; specifically, gaps easily form between the polarity sheet and the separator, which degrades the battery's cycle characteristics.

For example, if the adhesive strength between the positive and negative electrode sheets and the separator is insufficient, problems such as cell openings will inevitably occur, making it impossible to meet the performance requirements for the coated separator in secondary batteries.

A cell is formed by bonding positive and negative electrode sheets to a separator. The cell has a certain hardness; that is, the bonded positive and negative electrode sheets and separator are adhered to and supported by each other, forming a structure with a certain thickness. A structure of a certain thickness has a certain hardness. However, expansion occurs in the negative electrode during the charge and discharge process. If the adhesive force is weak, a gap forms between the positive and negative electrode sheets and the separator. The positive and negative electrode sheets and separator are no longer adhered to or supported by each other, causing the cell to loosen and its hardness to decrease. At this time, the cell's power characteristics deteriorate, for example, the rate characteristics deteriorate, and simultaneously, the cycle characteristics deteriorate. For example, in an electric vehicle, if the battery cell loosens, the battery charging speed slows down, the battery's cycle characteristics deteriorate, and this directly leads to a shortened battery life. In electric vehicles, this necessitates frequent battery replacement, increasing consumer costs.

Based on this, the present application provides a binder for secondary batteries, the binder comprising an acrylic acid ester copolymer, and the shape of the binder including a ring shape.

A binder is a material with adhesive properties and is used to bond different materials together.

This is an annular binder, where through-holes are formed within the binder's structure. These through-holes penetrate two opposing surfaces of the binder, and as shown in Figures 1 and 2, it has an annular structure.

The annular binder has a ring-shaped ring, and as shown in Figure 10, a through-hole 61 is formed in the structure of the annular binder, with the ring-shaped ring 60 formed around the through-hole 61. As can be understood, when the binder is positioned on the separator along the direction toward the through-hole 61 (i.e., the opening of the through-hole 61 faces the separator), the area around the through-hole 61 is in contact with the separator, and the contact area is the ring-shaped ring. Compared to a spherical binder being placed on a separator, the spherical binder and separator make point contact, whereas the annular binder can contact the separator via the ring-shaped ring, increasing the contact area.

Regarding acrylic acid ester copolymers, they are a general term for polymers produced by copolymerizing acrylic acid ester monomers with other copolymers.

The structure of acrylic acid ester monomers contains an acrylic acid ester group; examples include methyl acrylate, ethyl acrylate, and n-butyl acrylate.

Acrylic acid ester copolymers have good adhesive properties, and their use can further improve the adhesion between the separator and the polar sheet.

Annular binders have a larger bonding area. For example, when an annular binder and a polar sheet come into contact, the contact area is the annular edge of the annular binder, whereas with a spherical binder, the contact area is a point contact. Therefore, compared to a spherical binder of the same dimensions, the annular binder has a larger contact area, resulting in superior bonding performance. Furthermore, annular binders have hollow through-holes. Compared to spherical binders of the same dimensions, annular binders have a smaller mass, thus enabling good bonding performance even when the amount of annular binder used is reduced.

By applying an annular binder to the separator, the contact area between the binder, polarity sheet, and separator can be increased, reducing the amount of binder used. This meets the requirements for cold-press adhesion between the separator and the positive and negative electrode sheets during the cold-press process, improving cell hardness and mitigating problems such as cell opening and cell softness. Simultaneously, applying this binder to the separator and applying it to secondary batteries can improve the jig-assisted cycle characteristics of the secondary battery.

The jig-assisted cycle characteristics test is a test of the cycle functionality of a cell. During the test, a jig is attached to the cell, and a constant force is applied to the jig to press the cell. When the cell is fully charged, it expands and is double-pressed by the clamping force of the jig and the force of expansion, which may cause the cell to deform. This test is used to test the cell's shape retention performance and pressure resistance performance. When using the binder of this solution, the adhesion performance is good, so the cell expansion is reduced and the cell shape is well maintained. Cells using this binder maintain good performance under the jig-assisted test conditions, which indicates that the deformation retention performance of cells obtained using the binder of this solution is excellent. Even after the cell is assembled into a battery, the cell is less likely to deform, so the space required to install the cell in the battery can be saved, and thus the volume of the battery can be reduced. If a cell is easily deformed, it can push out the surrounding structure. To mitigate this phenomenon, it's necessary to house the deformed cell in a larger space; that is, space must be secured within the battery to accommodate the deformed portion of the cell, thus occupying more space inside the battery.

At the same time, high cycle performance of the cell with its fixture indicates excellent cycle performance of the cell. For example, when a cell expands, the gap between the polarity sheet and the separator increases, lengthening the path for lithium ions (using lithium-ion batteries as an example, but of course, other types of secondary batteries may also be applicable) through the positive and negative electrodes, thus degrading cycle performance.

The binder of this invention can achieve a tighter bond between the separator and the polarity sheet, thereby improving the battery's discharge capacity, reducing internal resistance, decreasing polarization loss, extending the battery's cycle life, and improving the utilization rate of secondary batteries.

In one embodiment, the specific surface area of the binder is in the range of 0.4 ^m²/ g to ^{1.2 m²} /g, and preferably in the range of 0.6 ^m² /g to 0.9 ^m² /g.

Specific surface area refers to the total surface area of a unit mass of material, and its unit is ^m² /g.

Specific surface area test: The BET specific surface area is measured using the BET method for _N2 adsorption.

Using a NOVA 2000 specific surface area and pore size analyzer from CANTAChrome, Inc. in the United States, high-purity nitrogen gas with a purity of 99.999% or higher is used as the adsorbent. A spherical sample tube with a diameter of 20 mm is selected, 1.4000 g ± 0.2000 g of binder sample is weighed, a heating bag is placed over it, and the vacuum is evacuated to ^10⁻² Torre or higher using a vacuum pump. After the pressure stabilizes, the temperature is slowly raised to a constant temperature, the pretreatment time is controlled, and after the pretreatment is complete, the sample is cooled for 30 mins and its mass is weighed. Adsorption and desorption tests are performed on the pretreated sample for the entire process, and the isothermal adsorption and desorption curve of the sample is obtained. The data is processed using the software attached to the instrument to obtain the specific surface area parameter of the binder.

Specific surface area refers to the total surface area of a unit mass of material. Based on the fact that annular binders have hollow through holes, the specific surface area of annular binders is increased compared to spherical binders of the same dimensions. The specific surface area of the binder is in the range of 0.4 ^m² /g to ^{1.2 m²} /g, preferably in the range of 0.6 ^m² /g to ^{0.9 m²} /g. This helps to improve contact between the annular binder and the separator and polar sheet, thereby improving adhesive performance.

In the range of 0.4 ^m² /g to 1.2 ^m² /g mentioned above, the values include the minimum and maximum values within that range, and the values between the minimum and maximum values. Specific examples include the endpoint values in the examples and 0.4 ^m²/ g, 0.5 ^m² /g, 0.6 ^m² /g, 0.7 ^m² /g, 0.8 ^m² /g, ^{0.9 m²} /g, 1.0 ^m² /g, 1.1 ^m² /g, 1.2 ^m² /g, etc., as well as the range values between any two of the above endpoint values, but are not limited to these.

In the range of 0.6 ^m² /g to 0.9 ^m² /g mentioned above, the values include the minimum and maximum values within that range, as well as the values between the minimum and maximum values. Specific examples include, but are not limited to, the endpoint values in the examples and values such as 0.6 ^m² /g, ^{0.7 m²} /g, 0.8 ^m² /g, 0.9 ^m² /g, and the range values between any two of the above endpoint values.

In one embodiment, the ratio of the surface area to the volume of the binder is 0.1 × ^{10⁶ m⁻¹} to 20 × ^{10⁶ m⁻¹} , and preferably, the ratio of the surface area to the volume of the binder is 0.5 × ^{10⁶ m⁻¹} to 16 × ^{10⁶ m⁻¹} .

The ratio of surface area to volume is the ratio of the total surface area to the total volume of the material.

Regarding the test method for the ratio of surface area to volume, the surface area and volume of a certain mass of binder are measured, respectively, and then the ratio of surface area to volume is obtained by dividing the values of surface area by volume. Defining the measurement of m1 grams of binder, the surface area can be obtained using the above method for measuring specific surface area, and if the value of the specific surface area is defined as ^am² /g, then the surface area of m1 grams of binder is (m1 * a), and the unit is ^m² . The volume of m1 grams of binder is measured using the drainage method, that is, water with a volume of V1 is taken, placed in a container, and then 1 gram of binder is placed in the container to obtain a binder mixture, and if the volume of the measured mixture is V2, then the volume of m1 grams of binder is V2 - V1. The formula for calculating the ratio of surface area to volume is (m1 * a) / (V2 - V1), and the unit is m ^{- 1} .

Based on the fact that annular binders have hollow through-holes, the ratio of surface area to volume of an annular binder is increased compared to a spherical binder of the same dimensions. The ratio of surface area to volume of an annular binder is 0.1 × ^{10⁶ m⁻¹} to 20 × ^{10⁶ m⁻¹} , preferably 0.5 × ^{10⁶ m⁻¹} to 16 × ^{10⁶ m⁻¹.} This indicates that annular binders have an increased surface area compared to spherical binders, which helps to improve contact between the annular binder and the separator and polar sheet, thereby improving adhesive performance.

In the range of 0.1 × ^{10⁶ m⁻¹} to 20 × ^{10⁶ m⁻¹} , the values include the minimum and maximum values within that range, and the values between the minimum and maximum values. Specific examples include the endpoint values in the embodiment and 0.1 × ^{10⁶ m⁻¹} , 1 × ^{10⁶ m⁻¹} , 2 × ^{10⁶ m⁻¹} , 3 × ^{10⁶ m⁻¹} , 4 × 10⁶ ^m⁻¹ , 5 × ^10⁶ m⁻¹, 6 × ^{10⁶ m⁻¹} , 7 × ^{10⁶ m⁻¹} , 8 × ^{10⁶ m⁻¹} , 9 × ^{10⁶ m⁻¹} , ¹⁰ × ^{10⁶ m⁻¹} , 11 × ^{10⁶ m⁻¹} , 12 × ^{10⁶ m⁻¹} , and 13 × ^{10⁶ m⁻¹ .} This includes, but is not limited to, values such as 14 × ^{10⁶ m⁻¹} , 15 × ^{10⁶ m⁻¹} , 16 × ^{10⁶ m⁻¹} , 17 × ^{10⁶ m⁻¹} , 18 × ^{10⁶ m⁻¹} , 19 × ^{10⁶ m⁻¹} , 20 × ^{10⁶ m⁻¹} , etc., and range values between any two of the above endpoint values.

In the ranges 0.5 × ^{10⁶ m⁻¹} to 16 × ^{10⁶ m⁻¹} mentioned above, the values include the minimum and maximum values within that range, as well as the values between the minimum and maximum values. Specific examples include the endpoint values in the embodiment and 0.5 × ^{10⁶ m⁻¹} , 1 × ^{10⁶ m⁻¹} , 2 × ^{10⁶ m⁻¹} , 3 × ^{10⁶ m⁻¹} , 4 × 10⁶ ^m⁻¹ , 5 × ^10⁶ m⁻¹, 6 × ^{10⁶ m⁻¹} , 7 × ^{10⁶ m⁻¹} , 8 × ^{10⁶ m⁻¹} , 9 × ^{10⁶ m⁻¹} , 10 ^{× 10⁶ m⁻¹ ,} 11 × ^{10⁶ m⁻¹} , 12 × ^{10⁶ m⁻¹} , and 13 × ^{10⁶ m⁻¹ .} This includes, but is not limited to, values such as 14 × ^{10⁶ m⁻¹} , 15 × ^{10⁶ m⁻¹} , 16 × ^{10⁶ m⁻¹} , and range values between any two of the above endpoint values.

In one embodiment, the bulk density of the binder is in the range of 0.3 g/ ^cm³ to 0.8 g/ ^cm³ , and preferably in the range of 0.4 g/ ^cm³ to 0.7 g/ ^cm³ .

Bulk density is the mass per unit volume measured immediately after freely filling a container with powder.

The specific test steps are as follows: Using the tapping apparatus method, the sample is placed in a 100 mL graduated cylinder of the tapping apparatus, the apparatus is activated, and the graduated cylinder is vibrated using the tapping apparatus's vibrator to tap the sample. Throughout the experiment, the sample is continuously added until the sample volume stops decreasing. Finally, the mass of the sample is weighed, and the bulk density is obtained by dividing the sample mass by the sample volume.

Based on the fact that the annular binder has hollow through-holes, after filling a container with the annular binder, voids are formed in the through-holes of the annular binder. Compared to filling with a spherical binder of the same dimensions, the bulk density of the annular binder is reduced, with a range of 0.3 g/ ^cm³ to 0.8 g/ ^cm³ , preferably 0.4 g/ ^cm³ to 0.7 g/ ^cm³ . This indicates that, under certain conditions, the adhesive performance of the binder is improved even when the mass of the annular binder is reduced.

In the range of 0.3 g/ ^cm³ to 0.8 g/ ^cm³ mentioned above, the values include the minimum and maximum values within that range, as well as the values between the minimum and maximum values. Specific examples include, but are not limited to, the endpoint values in the examples and values such as 0.3 g/ ^cm³ , 0.4 g/ ^cm³ , 0.5 g/ ^cm³ , 0.6 g/ ^cm³ , 0.7 g/ ^cm³ , 0.8 g/ ^cm³ , etc., and the range values between any two of the above endpoint values.

In the range of 0.4 g/ ^cm³ to 0.7 g/ ^cm³ mentioned above, the values include the minimum and maximum values within that range, as well as the values between the minimum and maximum values. Specific examples include, but are not limited to, the endpoint values in the examples and values such as 0.4 g/ ^cm³ , 0.5 g/ ^cm³ , 0.6 g/ ^cm³ , 0.7 g/ ^cm³ , and the range values between any two of the above endpoint values.

In one embodiment, the binder's shape includes an annular shape.

The annular shape is a relatively easily achievable shape based on experimental experience and the surface tension of the material. The binder shape in this application includes annular shapes, and furthermore, the annular shape in this application may be approximately annular. For example, as shown in Figure 1, the structure of some binders is not perfectly annular; for instance, a portion is compressed to form an approximately annular structure.

In one embodiment, the range of the volume-based particle size distribution Dv50 of the binder is 1 μm to 15 μm, and preferably, the range of the volume-based particle size distribution Dv50 of the binder is 3 μm to 12 μm.

Regarding Dv50, in a sample, 50% of the particles by total volume have a particle size greater than this value, while the remaining 50% of the particles by total volume have a particle size smaller than this value. Dv50 represents the median particle size in the sample.

The volume-based particle size distribution Dv50 of the binder can be measured using methods known in this art. For example, referring to GB/T 19077-2016, characterization tests can be performed using a Malvern laser particle size analyzer, such as the Malvern Mastersizer-3000.

To improve the adhesion of the binder and reduce the gap between the separator and the polarity sheet, the range of the volume-based particle size distribution Dv50 of the binder is 1 μm to 15 μm, preferably 3 μm to 12 μm.

In the range of 1 μm to 15 μm, the values include the minimum and maximum values within that range, and the values between these minimum and maximum values. Specific examples include, but are not limited to, the endpoint values in the examples and the range values between any two endpoint values, such as 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.

In the range of 3 μm to 12 μm, the values include the minimum and maximum values within that range, and the values between these minimum and maximum values. Specific examples include, but are not limited to, the endpoint values in the examples and the range values of 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, etc., and the range values between any two of the above endpoint values.

In one embodiment, the constituent monomers of the acrylic acid ester copolymer include a first polymer monomer, and the structure of the first polymer monomer is
This includes, where R1 contains hydrogen or an alkyl group having 1 to 12 carbon atoms, and R2 contains an alkyl group having 1 to 12 carbon atoms.

The first polymerization monomer structure contains ester groups, improving the compatibility between the acrylic ester copolymer and the electrolyte, enhancing ionic conductivity, improving the swelling resistance of the acrylic ester copolymer, and acting as a flexible monomer segment in the molecular segment, it can adjust the glass transition temperature of the acrylic ester copolymer, improving the toughness of the binder during coating and contributing to good adhesion.

In one example, the first polymerized monomer contains one or more of the following: 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.

Theoretically, this application does not limit the type of the first polymerized monomer, and satisfies the requirement that the first polymerized monomer includes the above-described structure; that is, the first polymerized monomer includes the substances listed above and substances not listed in this application.

By using one or more of the above-mentioned first polymerization monomers, the glass transition temperature of the acrylic acid ester copolymer can be adjusted, thereby improving its swelling resistance.

In one embodiment, the constituent monomers of the acrylic acid ester copolymer include a second polymer monomer, and the structure of the second polymer monomer is
This includes, where R3 contains hydrogen or an alkyl group having 1 to 6 carbon atoms.

The structure of the second polymerization monomer contains carboxyl groups, which are characterized by their strong polarity. This can improve the adhesion and flexibility of the binder. For example, the carboxyl groups can form bonding forces with functional groups on the polar sheet and separator materials, thereby improving the adhesive effect.

In one example, the second polymer monomer contains one or more of acrylic acid, methacrylic acid, crotonic acid, and heptenoic acid.

Theoretically, this application does not limit the type of second polymerization monomer, and satisfies the requirement that the second polymerization monomer includes the above structure; that is, the second polymerization monomer includes the substances listed above and substances not listed in this application.

By using one or more of the above-mentioned secondary polymerization monomers, the adhesive performance of the acrylic acid ester copolymer can be improved.

In one embodiment, the constituent monomers of the acrylic acid ester copolymer include a third polymer monomer, and the structure of the third polymer monomer is
This includes, where R4 contains hydrogen or an alkyl group having 1 to 6 carbon atoms.

The structure of the third polymerization monomer contains unsaturated cyano groups. These highly polar cyano groups contribute to improved ionic conductivity and simultaneously provide swelling resistance and high adhesion.

In one example, the third polymerization monomer contains one or more of acrylonitrile and methacrylonitrile.

Theoretically, this application does not limit the type of third polymerization monomer, and satisfies the requirement that the third polymerization monomer includes the above structure; that is, the third polymerization monomer includes the substances listed above and substances not listed in this application.

By using one or more of the above-mentioned third polymerization monomers, the ionic conductivity of the acrylic acid ester copolymer can be improved, thereby enhancing its adhesive properties.

In one embodiment, the constituent monomers of the acrylic acid ester copolymer include a fourth polymer monomer, and the structure of the fourth polymer monomer is
This includes, where R5 contains hydrogen or an alkyl group having 1 to 6 carbon atoms, and R6 contains a hydrogen atom, a hydroxyl-substituted alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms.

The structure of the fourth polymerization monomer contains an unsaturated amide group, which improves swelling and enhances adhesion.

In one example, the fourth polymerized monomer comprises one or more of acrylamide, N-methylolacrylamide, and N-butoxymethylacrylamide.

Theoretically, this application does not limit the type of fourth polymerization monomer, and satisfies the requirement that the fourth polymerization monomer includes the above structure; that is, the fourth polymerization monomer includes the substances listed above and substances not listed in this application.

By using one or more of the above-mentioned fourth polymerization monomers, the adhesion of the acrylic acid ester copolymer can be improved.

As can be understood, when at least two of the four monomers described above are included, the adhesive effect is even better. For example, the constituent monomers of the acrylic ester copolymer include at least the first polymer monomer and the second polymer monomer, or the constituent monomers of the acrylic ester copolymer include at least the first polymer monomer and the third polymer monomer, or the constituent monomers of the acrylic ester copolymer include at least the first polymer monomer and the fourth polymer monomer. When the constituent monomers of the acrylic ester copolymer include all four monomers simultaneously, the performance of the binder is even better.

In one embodiment, the constituent monomers of the acrylic acid ester copolymer include a first polymer monomer, a second polymer monomer, a third polymer monomer, and a fourth polymer monomer. The mass ratio of the first polymer monomer, the second polymer monomer, and the third and fourth polymer monomers is 1:(0.01-0.8):(0.01-0.5):(0.01-0.3), and preferably, the mass ratio of the first polymer monomer, the second polymer monomer, and the third and fourth polymer monomers is 1:(0.1-0.5):(0.15-0.45):(0.1-0.22).

When the constituent monomers of an acrylic acid ester copolymer simultaneously contain the four monomers mentioned above, and the components of each monomer fall within the specified range, the overall performance is improved.

Regarding the method for measuring the mass ratio, in the manufacturing process of acrylic acid ester copolymers, the mass of each monomer introduced into the reaction process for producing the acrylic acid ester copolymer is recorded. The mass of the first polymerization monomer is denoted as m1, the mass of the second polymerization monomer as m2, the mass of the third polymerization monomer as m3, and the mass of the fourth polymerization monomer as m4. The mass ratio of the four monomers is m1:m2:m3:m4.

In the above 1: (0.01 to 0.8): (0.01 to 0.5): (0.01 to 0.3), the values include the minimum and maximum values within the range, and each value between the minimum and maximum values. Specific examples include the endpoint values in the examples and 1:0.01:0.01:0.01, 1:0.5:0.25:0.15, 1:0.8:0.5:0.3, etc., as well as the range values between any two of the above endpoint values, but are not limited to these.

In the above ranges 1: (0.1 to 0.5): (0.15 to 0.45): (0.1 to 0.22), the values include the minimum and maximum values within that range, and the values between these minimum and maximum values. Specific examples include the endpoint values in the examples and 1:0.1:0.15:0.1, 1:0.3:0.3:0.15, 1:0.5:0.45:0.22, etc., as well as the range values between any two of the above endpoint values, but are not limited to these.

In one embodiment, the present invention further provides a method for producing a binder, comprising the steps of: producing an acrylic acid ester copolymer emulsion; and spray-drying the acrylic acid ester copolymer emulsion to obtain a cyclic binder.

Spray drying uses mechanical action to disperse the material to be dried (an acrylic ester copolymer emulsion) into extremely fine mist particles. These particles are then brought into contact with hot air (which increases the surface area for water evaporation and accelerates the drying process), instantly removing most of the water and drying the solid material into a powder.

An acrylic ester copolymer emulsion is produced by emulsion polymerization, and a cyclic binder is obtained by spray drying the acrylic ester copolymer emulsion. The mechanism involves the dense deposition of the primary emulsion of the acrylic ester copolymer due to the evaporation of water, forming a cyclic binder.

In one embodiment, the steps for producing an acrylic ester copolymer emulsion include: placing water, an emulsifier, and constituent monomers of the acrylic ester copolymer in a container, stirring to emulsify, and obtaining a preliminary emulsion of the monomers; and adding an emulsifier and water to a reaction vessel, stirring to emulsify, adding the preliminary emulsion and initiator solution under heating conditions, and carrying out a heating reaction to obtain an acrylic ester copolymer emulsion.

A pre-emulsified solution is a solution obtained by pre-emulsifying monomers. Emulsification is the process of uniformly dispersing a liquid in very small droplets within another liquid that does not mix with itself. This is done by mixing water, an emulsifier, and the constituent monomers of an acrylic ester copolymer, stirring the mixture, and dispersing the monomers in the water under the action of the emulsifier.

Emulsion polymerization is a process in which monomers are dispersed in water using an emulsifier and mechanical stirring to form an emulsion, and then an initiator is added to initiate polymerization of the monomers.

Regarding emulsifiers, they are substances that convert oil and water, which do not mix well with each other, into an emulsion that is difficult to separate into layers. Emulsifiers are generally surfactants that possess both hydrophilic polar groups and hydrophobic (lipophilic) nonpolar groups.

Regarding initiators, they are substances that can initiate polymerization reactions in monomers. For example, radical initiators refer to compounds that readily decompose upon heat to form radicals (i.e., primary radicals), and can be used to initiate radical polymerization and copolymerization reactions of olefin and diene monomers.

In the step of producing an acrylic ester copolymer emulsion, a preliminary emulsification step is used, followed by a polymerization reaction step, to further homogenize the monomers. The resulting acrylic ester copolymer has more uniform particle size and more stable performance. This also promotes the formation of a cyclic binder during the spray drying process.

Polyvinylidene fluoride is widely used as the most common binder in separators, but currently, its price fluctuates significantly and its market supply is limited. Applying polyvinylidene fluoride polymer to the surface of lithium battery separators can partially solve the problem of high-temperature shrinkage of the separator. While cold pressing is performed on the wound cells, conventional polyvinylidene fluoride is a homopolymer with a crystallinity of approximately 50%, resulting in insufficient adhesion to the positive and negative electrode sheets. This consistently leads to cell opening problems and fails to meet the requirements for separator coating performance in secondary batteries.

In other words, applying polyvinylidene fluoride polymer to the surface of the battery separator can partially solve the problem of high-temperature shrinkage of the separator. While cold pressing is performed on the wound cells, ordinary polyvinylidene fluoride is a homopolymer with a crystallinity of approximately 50%, resulting in insufficient adhesion to the positive and negative electrode sheets, and the problem of cell openings consistently occurs. The formation of openings in the cells creates gaps between the polarity sheets and the separator, loosening the overall structure of the cell, reducing cell hardness, and affecting the cell's cycle characteristics.

By applying the annular binder structure of this invention to a separator and coating it, the contact area between the binder, polarity sheet, and separator can be increased, reducing the amount of binder used. This also satisfies the requirements for cold-press adhesion between the separator and the positive and negative electrode sheets during the cold-press process, improving cell hardness and avoiding problems such as cell opening and cell softness. Simultaneously, applying this binder to a separator and applying it to a secondary battery can improve the jig-assisted cycle characteristics of the secondary battery.

In one embodiment, the present invention further provides a separator comprising a substrate and an adhesive layer provided on at least one side of the substrate, wherein the adhesive layer comprises the binder for secondary batteries, or comprises a binder manufactured by the method for manufacturing the binder for secondary batteries described above.

The adhesive layer is a structure composed of a binder applied to a separator.

Before applying the binder to the separator, first, the binder paste is prepared by dissolving the binder in water. The binder paste is then applied to the separator and allowed to dry to obtain an adhesive layer.

As can be understood, after drying, the binder exhibits no adhesive force at room temperature (approximately 23 ± 2°C) without pressure. That is, in the process of not applying pressure to the separator, the side of the adhesive layer away from the separator is non-viscous, satisfying the requirements for winding and unwinding the separator. When a constant pressure is applied, the binder becomes pressure-sensitive, exhibiting excellent adhesion, satisfying the requirements for adhesion between the separator and the positive and negative polarity sheets. Simultaneously, this adhesion further forms intermolecular forces between the molecules on the separator and the polarity sheets, thereby effectively bonding the separator and polarity sheets with the binder.

Furthermore, after cold pressing, some of the hollow through-holes in the annular binder are not completely sealed, creating voids. These voids promote electrolyte wetting, improving lithium ion transmission (although lithium-ion batteries are used as an example, other types of secondary batteries may also be applicable).

The binder powder material, manufactured using a spray-drying process, achieves non-adhesion at room temperature and without pressure.

Pressure sensitivity refers to the phenomenon where, after the binder is pressed, it deforms under pressure, penetrates the gaps between the separator and electrode sheets, and creates a mechanical interlocking effect, thereby achieving adhesion.

In one embodiment, the surface density of the adhesive layer on the substrate is in the range of 0.7 g/ ^m² to 3 g/ ^m² , preferably 0.8 g/ ^m² to 2 g/ ^m² .

Surface density refers to the mass of the adhesive layer applied to one side of the separator.

The test method for surface density is as follows: A separator of a certain area is taken, its area S is determined, the weight M1 of the separator with the binder added is weighed, and the mass M2 of a separator of the same area S without the binder is weighed. The formula for calculating the surface density of the binder is (M1 - M2) / S.

Based on the fact that the annular structure binder increases the contact area between the binder and the polar sheet and separator, that is, good adhesive performance can be achieved even when the amount of annular structure binder used is reduced. For this reason, the surface density of the adhesive layer on the substrate is in the range of 0.7 g/ ^m² to ³ g/ ^m² , preferably 0.8 g/m² to 2 g/ ^m² .

In the range of 0.7 g/ ^m² to 3 g/ ^m² mentioned above, the values include the minimum and maximum values within that range, and the values between the minimum and maximum values. Specific examples include the endpoint values in the examples and values such as 0.7 g/ ^m² , 0.8 g/ ^m² , 0.9 g/ ^m² , 1 g/ ^m² , 1.5 g/ ^m² , 2 g/ ^m² , 2.5 g/ ^m² , 3 g/ ^m² , etc., as well as the range values between any two of the above endpoint values.

In the range of 0.8 g/ ^m² to 2 g/ ^m² mentioned above, the values include the minimum and maximum values within that range, and the values between the minimum and maximum values. Specific examples include the endpoint values in the examples and 0.8 g/ ^m² , 0.9 g/ ^m² , 1 g/ ^m² , 1.2 g/ ^m² , 1.5 ^{g/m² ,} 1.7 g/ ^m² , 1.9 g/m², 2 g/ ^m² , etc., as well as the range values between any two of the above endpoint values.

The embodiment of this application further provides a secondary battery including the separator.

A secondary battery includes forms such as a battery module, battery cells, and battery pack. If the secondary battery is a battery cell, the battery cell includes the separator; if the secondary battery is a battery module, the battery module includes the separator; and if the secondary battery is a battery pack, the battery pack includes the separator.

The embodiments of this application further provide a power consumption device including the above-described battery cell or the above-described battery.

Furthermore, the electrode assembly, battery cell, battery, and power consumption device of this application will be described below with reference to the drawings as appropriate.

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

Generally, an electrode assembly includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions reciprocate between the positive and negative electrode sheets, being inserted and removed. The electrolyte plays a role in conducting ions between the positive and negative electrode sheets. The separator is placed between the positive and negative electrode sheets and primarily serves to prevent short circuits between the positive and negative electrodes while simultaneously allowing ions to pass through. The separator in this application is the improved separator described above.

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

As an example, the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode film layer is provided on one or both of these opposing surfaces of the positive electrode current collector.

In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer substrate layer and a metal layer formed on at least one surface of the polymer substrate layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (for example, a 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, known positive electrode active materials for lithium-ion batteries can be used. For example, the positive electrode active material may include at least one of olivine-structured lithium-containing phosphates, lithium transition metal oxides, and modified compounds thereof. However, the present application is not limited to these materials, and other conventional materials usable as positive electrode active materials for batteries may be used. These positive electrode active materials may be used individually or in combination of two or more types. Examples of lithium transition metal oxides include lithium cobalt oxide (e.g., _LiCoO₂ ), lithium nickel oxide (e.g. _{, LiNiO₂} ), lithium manganese oxide (e.g., _LiMnO₂ , _LiMn₂O₄ ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., LiNi _1/3 Co _1/3 Mn _{1/3 O₂} (abbreviated NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _{0.3 O₂} (abbreviated NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _{0.25 O₂} (abbreviated NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O₂ _). The olivine structure lithium-containing phosphate may include, but is not limited to, at least one of the following: (abbreviated NCM ₆₂₂ ), LiNi _0.8 Co _{0.1 Mn 0.1} O ₂ (abbreviated NCM ₈₁₁ ), lithium _nickel cobalt aluminum oxide (e.g. LiNi 0.85 Co 0.15 Al _0.05 O ₂ ) and its modified compounds. The olivine structure lithium-containing phosphate may include, but is not limited to, at least one of the following: lithium ferric phosphate (e.g. LiFePO ₄ (abbreviated LFP)), a composite material of lithium ferric phosphate and carbon, lithium manganese phosphate (e.g. LiMnPO 4 ₎ , a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

In some embodiments, the positive electrode film layer may selectively further contain a binder. As an example, the binder may include at least one of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resins.

In some embodiments, the positive electrode film layer may selectively further contain a conductive agent. As an 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, a positive electrode sheet can be manufactured by the following method: Components for manufacturing the positive electrode sheet, such as a positive electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode paste. This paste is then applied to a positive electrode current collector, and the positive electrode sheet is obtained through steps such as drying and cold pressing.

The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer installed on at least one surface of the negative electrode current collector, the negative electrode film layer containing a negative electrode active material.

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

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

In some embodiments, the negative electrode active material can be a known negative electrode active material for 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, lithium titanate, etc. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy. However, this application is not limited to these materials, and other conventional materials usable as negative electrode active materials for batteries may be used. These negative electrode active materials may be used individually or in combination of two or more types.

In some embodiments, the negative electrode film layer may selectively further contain a binder. The binder may include at least one of the following: 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 may further selectively contain 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 film layer further comprises other additives, such as a selective thickener (e.g., sodium carboxymethylcellulose (CMC-Na)).

In some embodiments, a negative electrode sheet can be manufactured by the following method: Components for manufacturing the negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode paste. This paste is then applied to a negative electrode current collector, and the negative electrode sheet is obtained through steps such as drying and cold pressing.

The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. This application does not particularly limit the type of electrolyte, and it can be selected as needed.

In some embodiments, an electrolyte solution is used. The electrolyte solution comprises an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt may include at least one of the following: lithium hexafluoride phosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoride arsenate, lithium bisfluorosulfonylimide, lithium bistrifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bisoxalate borate, lithium difluorooxalate phosphate, and lithium tetrafluorooxalate phosphate.

In some embodiments, the solvent may include at least one of the following: ethylene carbonate, propylene carbonate, methyl ethyl 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 selectively further comprises additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and further, additives that can improve specific characteristics of the battery, such as additives that improve the overcharge characteristics of the battery, or additives that improve the high-temperature or low-temperature characteristics of the battery.

In some embodiments, the electrode assembly further includes a separator. This application does not particularly limit the type of separator, and any known porous structure separator having 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 film or a multilayer composite film, and is not particularly limited. If the separator is a multilayer composite film, the materials of each layer may be the same or different, and are not particularly limited.

In some embodiments, the positive electrode sheet, negative electrode sheet, and separator can be manufactured into an electrode assembly via a winding or lamination process.

In some embodiments, the electrode assembly may include an outer covering. This outer covering is used to enclose the electrode assembly and the electrolyte.

In some embodiments, the outer casing of the electrode assembly may be a rigid case, such as a hard plastic case, an aluminum case, or a steel case. Alternatively, the outer casing may be a soft pack, such as a pouch-type soft pack. The soft pack material may be plastic, and examples of such plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

This application does not particularly limit the shape of the electrode assembly; it may be cylindrical, rectangular, or any other shape. For example, Figure 4 shows a rectangular secondary battery 5 as an example.

In some embodiments, referring to Figure 5, the exterior material may include a housing 51 and a cover plate 53. The housing 51 includes a bottom plate and side plates connected to the bottom plate, forming a housing cavity enclosed by the bottom plate and side plates. The housing 51 has an opening that communicates with the housing cavity, and the cover plate 53 can cover the opening and seal the housing cavity. The positive electrode sheet, negative electrode sheet and separator can be formed by a winding process or a lamination process to form an electrode assembly 52. The electrode assembly 52 is sealed within the housing cavity. The electrolyte is impregnated into the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art can select according to specific practical requirements.

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

Figure 6 shows an example of a battery module 4. Referring to Figure 6, multiple secondary batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can be arranged in any other way. Furthermore, these multiple secondary batteries 5 can be fixed in place by fasteners.

Selectively, the battery module 4 may further include an outer case having a housing space for accommodating multiple secondary batteries 5.

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

Figures 7 and 8 show an example of a battery pack 1. Referring to Figures 7 and 8, the battery pack 1 can include a battery case and multiple battery modules 4 installed within the battery case. The battery case includes an upper housing 2 and a lower housing 3. The upper housing 2 can be placed over the lower housing 3 and forms a sealed space for housing the battery modules 4. The multiple battery modules 4 can be arranged within the battery case in any manner.

Furthermore, this application further provides a power consumption device comprising at least one of the electrode assembly, battery module, or battery pack relating to this application. The electrode assembly, battery module, or battery pack may be used as a power source for the power consumption device, or as an energy storage element for the power consumption device. The power consumption device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), trains, ships and satellites, energy storage systems, etc.

As a power consumption device, an electrode assembly, battery module, or battery pack can be selected according to the usage requirements.

Figure 9 shows an example of a power consumption device. This power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the electrode assembly of this power consumption device, a battery pack or battery module can be used.

Another example of such a device may be a mobile phone, tablet PC, or laptop computer. Such devices generally require lightweight and thin designs, and an electrode assembly can be used as the power source.

Examples The following describes examples of the present application. The examples described below are illustrative and are for illustrative purposes only, and should not be understood as limiting the present application. If specific techniques or conditions are not shown in the examples, they should be carried out in accordance with the techniques or conditions described in the literature in the art, or in accordance with the product instructions. If the manufacturer of the reagents or equipment used is not specified, they are all commercially available common products.

Example 1
Preparation of Acrylic Acid Ester Copolymer (1) Add 150 g of deionized water and 3.6 g of sodium dodecyl sulfate to each of 500 ml three-necked flasks, and stir thoroughly for 15 min to emulsify. Add 76.34 g of ethyl acrylate (first polymerization monomer), 0.76 g of acrylic acid (second polymerization monomer), 15.27 g of acrylonitrile (third polymerization monomer), and 7.63 g of N-methylolacrylamide (quaternary polymerization monomer) in a mass ratio of 1:0.01:0.2:0.1, so that the total amount of monomers is 100 g. Stir thoroughly for 60 min to obtain a preliminary emulsion of monomers, which is then removed and prepared for use.

(2) Add 100 ml of deionized water and 0.15 g of sodium dodecylbenzenesulfonate to a 500 ml four-necked flask equipped with a condenser, stirrer, peristaltic pump, and thermometer. Heat to 75°C and emulsify for 15 minutes at a rotation speed of 2000 r/min until the system is thoroughly emulsified. Then, slowly add the pre-emulsified solution and initiator solution (formed by dissolving 0.2 g of potassium persulfate in 30 g of deionized water) prepared in the previous step dropwise. After the dropwise addition is complete, raise the temperature to 90°C and allow to maintain the reaction for 1 hour. Cool to below 40°C, adjust the pH to neutral using ammonia water, then stop stirring, filter, and drain to obtain the polymer emulsion.

The volume-based particle size distribution Dv50 of the acrylic ester copolymer is 0.1 μm ± 0.01 μm (the volume-based particle size distribution Dv50 of the acrylic ester copolymer in each example is 0.1 μm ± 0.01 μm).

Binder Production The acrylic ester copolymer emulsion produced above is spray-dried to obtain a binder with a cyclic structure. The parameters for spray drying are an intake air temperature of 115°C, an exhaust air temperature of 65°C, and an air pressure of 2200 Pa.

Examples 2 to 27
Based on Example 1, the type and mass ratio of monomers to be added were changed, and the monomer composition of the acrylic ester copolymer, the volume-based particle size distribution Dv50 of the binder, and the surface density of the binder applied to the substrate were adjusted to obtain Examples 2 to 27.

Comparative Example 1
A spherical binder is obtained using an emulsion polymerization method.

(1) Add 150 g of deionized water and 3.6 g of sodium dodecyl sulfate to each of the 500 ml three-necked flasks, and stir thoroughly for 15 min to emulsify. Add 76.34 g of ethyl acrylate (first polymerization monomer), 22.9 g of acrylic acid (second polymerization monomer), 15.27 g of acrylonitrile (third polymerization monomer), and 7.63 g of N-methylolacrylamide (quaternary polymerization monomer) in a mass ratio of 1:0.3:0.2:0.1. The total amount of monomers is 100 g. Stir thoroughly for 60 min to obtain a preliminary emulsion of monomers, which is then removed and prepared for use.

(2) Add 100 ml of deionized water and 0.15 g of sodium dodecylbenzenesulfonate to a 500 ml four-necked flask equipped with a condenser, stirrer, peristaltic pump, and thermometer. Heat to 75°C and emulsify for 15 minutes at a rotation speed of 2000 r/min until the system is thoroughly emulsified. Then, slowly add the pre-emulsified solution and initiator solution (formed by dissolving 0.2 g of potassium persulfate in 30 g of deionized water) prepared in the previous step dropwise. After the dropwise addition is complete, raise the temperature to 90°C and allow to maintain the reaction for 1 hour. Cool to below 40°C, adjust the pH to neutral using ammonia water, then stop stirring, filter, and drain to obtain the first polymer emulsion.

(3) Repeat step (1) to obtain the second part of the preliminary emulsifier. Add the second part of the preliminary emulsifier and the initiator solution (form the solution by dissolving 0.2 g of potassium persulfate in 30 g of deionized water) to the first polymer emulsion obtained in step (2). After the dropwise addition is complete, raise the temperature to 90°C and allow the reaction to proceed for 1 hour. Cool to below 40°C, adjust the pH to neutral using ammonia water, then stop stirring, filter, and drain to obtain the second polymer emulsion.

Cell manufacturing and battery manufacturing (1) Separator manufacturing A commercially available PE porous film with a thickness of 7 μm and an average pore size of 80 nm (obtained from Zhuoga Electronics Technology Co., Ltd.) is used as the substrate. The separator binder manufactured by the above method is uniformly stirred and mixed in deionized water to obtain a paste (solid content 20%). The paste is applied to both sides of the substrate, dried to remove the solvent, and an adhesive layer is obtained, with a surface density of 1.35 g/ ^m² of the coating composition on the substrate, thus obtaining a separator.

(2) Manufacturing of the positive electrode sheet A positive electrode paste is manufactured by thoroughly stirring and uniformly mixing polyvinylidene fluoride (PVDF), lithium iron phosphate (LFP), the conductive agents carbon black and N-methylpyrrolidone (NMP) in a mass ratio of 1.2:58.38:0.42:40. The positive electrode paste is uniformly applied to the aluminum foil of the positive electrode current collector at a loading amount of 200 g/ ^m² , and then dried, cold pressed, and cut to obtain a positive electrode sheet.

(3) Manufacturing of the negative electrode sheet A negative electrode paste is manufactured by adding artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethylcellulose (CMC-Na) to deionized water in a mass ratio of 96.2:1.0:1.6:1.2 and stirring thoroughly to mix uniformly (solid content 63%). The negative electrode paste is applied to the copper foil of the negative electrode current collector at a load of 98 g/ ^m² , and then dried, cold pressed, and cut to obtain a negative electrode sheet.

(4) Preparation of electrolyte At 25°C, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed solvent. Then, _LiPF6 is dissolved in the above mixed solvent to obtain an electrolyte, with a concentration of _LiPF6 of 1 mol/L.

(5) Manufacturing of secondary batteries The positive electrode sheet, separator, and negative electrode sheet are laminated and wound in order, and cold press molding is performed (during which the separator and polarity sheet are bonded) to obtain a cell, the cell is placed in an outer material, the manufactured electrolyte is added, and a secondary battery is obtained through processes such as sealing, standing, chemical conversion, and aging.

Performance Test (1) Cold Press Adhesion Test Step The negative electrode sheet and separator of the battery are stacked and placed in a hot press machine. The parameters of the hot press machine are set to a temperature of 25°C, a pressure of 7t, and a time of 15s. A separator/negative electrode sheet sample is obtained by applying pressure, and the separator/negative electrode sheet sample is cut into a rectangular strip of 150 mm x 20 mm. One side of the polarity sheet of the rectangular strip is attached to a steel plate with double-sided tape, and the separator and polarity sheet are separated along the length of the rectangular strip by a length of 2 cm at one end to create a test sample.

The steel plate is held horizontally and secured with the lower clamp of a universal testing machine (Xieqiang Instruments Manufacturing (Shanghai) Co., Ltd., model number CTM2100). The peeled end of the separator is secured with the upper clamp of the universal testing machine and connected to a tensile machine. The measurement conditions are set to a tensile speed of 20 mm/min and a horizontal tension of 10 cm. After the tensile force stabilizes, the tensile force value is recorded, and the adhesive strength between the separator and the polar sheet is obtained from the ratio of the tensile force value to the sample width.

(2) Steps for measuring cell hardness Place the cell on a table with both ends level, fix the width of the central hollow part to 12 cm, and lay the cell naturally flat. Measure the distance by which the cell's center position deviates from the horizontal reference line, thereby evaluating the cell's hardness. The greater the distance the cell's center position deviates from the horizontal reference line, the lower the cell's hardness.

(3) Steps for the Cycle Characteristics Test with Fixture An external force of 10,000 N is applied to the cell using a fixture, and a cycle test is performed in this state. The test steps are as follows: At 25°C, the battery obtained in Example 1 is charged to 3.8V with a constant current of 1/3C, then charged further with a constant voltage of 3.8V until the current becomes 0.05C, left for 5 min, and then discharged at 1/3C until it becomes 2.0V. The obtained discharge capacity is taken as the initial capacity C0, and the above steps are repeated for the same battery, and the discharge capacity Cn of the battery after n cycles is recorded at the same time. The battery capacity retention rate Pn after each cycle is (Cn/C0) × 100%. The difference in cycle characteristics can be shown by the battery capacity retention rate after 500 cycles.

As can be seen from the data above, the annular binder structure increases the contact area between the binder, separator, and polar sheet, thus enabling good adhesive performance even when the amount of annular binder used is reduced.

The above are merely preferred embodiments of the present application and do not limit the scope of the patent. Any equivalent structural transformations, or direct/indirect applications to other related technical fields, performed using the content of the specification and drawings of the present application under the concept of the present application are all included within the scope of the patent protection of the present application.

Claims (16)

A binder for secondary batteries containing an acrylic acid ester copolymer, with particles having a cyclic shape, and a volume-based particle size distribution Dv50 in the range of 3 μm to 12 μm . The binder for secondary batteries according to claim 1, wherein the specific surface area is in the range of 0.4 ^m² /g to ^{1.2 m²} /g. A binder for a secondary battery according to claim 1 , wherein the ratio of surface area to volume is 0.1 × ^{10⁶ m⁻¹} to 20 × ^{10⁶ m⁻¹} . The binder for secondary batteries according to claim 1 , wherein the bulk density ranges from 0.3 g/ ^cm³ to 0.8 g/ ^cm³ . The binder for secondary batteries according to claim 1 , wherein the particle shape includes annular shapes. The binder for secondary batteries according to claim 1, wherein the constituent monomer of the acrylic acid ester copolymer comprises a first polymer monomer, and the first polymer monomer comprises 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 secondary batteries according to claim 1, wherein the constituent monomer of the acrylic acid ester copolymer includes a second polymer monomer, and the second polymer monomer includes one or more of acrylic acid, methacrylic acid, crotonic acid, and heptenoic acid. The constituent monomers of the acrylic acid ester copolymer include a third polymer monomer, and the structure of the third polymer monomer is,
The binder for secondary batteries according to claim 1 , wherein R4 comprises a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. The binder for secondary batteries according to claim 8 , wherein the third polymerized monomer comprises one or more of acrylonitrile and methacrylonitrile. The constituent monomers of the acrylic acid ester copolymer include a fourth polymer monomer, and the structure of the fourth polymer monomer is,
A binder for secondary batteries according to claim 1, wherein R5 comprises a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R6 comprises a hydrogen atom, a hydroxyl-substituted alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms. The binder for secondary batteries according to claim 10, wherein the fourth polymerized monomer comprises one or more of acrylamide, N-methylolacrylamide, and N-butoxymethylacrylamide. The binder for secondary batteries according to claim 1, wherein the constituent monomers of the acrylic acid ester copolymer include a first polymer monomer, a second polymer monomer, a third polymer monomer, and a fourth polymer monomer, and the mass ratio of the first polymer monomer, the second polymer monomer, the third polymer monomer, and the fourth polymer monomer is 1:(0.01 to 0.8):(0.01 to 0.5):(0.01 to 0.3). A separator comprising a substrate and an adhesive layer provided on at least one side of the substrate, wherein the adhesive layer contains the binder for secondary batteries described in claim 1. The separator according to claim 13 , wherein the surface density of the adhesive layer on the substrate is in the range of 0.7 g/ ^m² to 3 g/ ^m² . A secondary battery comprising the separator described in claim 13 . A power consumption device including a secondary battery as described in claim 15 .