WO2024011422A1

WO2024011422A1 - Toughening agent, preparation method therefor, binder, secondary battery, battery module, battery pack, and electric device

Info

Publication number: WO2024011422A1
Application number: PCT/CN2022/105278
Authority: WO
Inventors: 曾琦; 孙成栋; 郑义; 艾少华; 张玉玺; 周鑫; 陈煜�
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-07-12
Filing date: 2022-07-12
Publication date: 2024-01-18
Also published as: CN118044004A

Abstract

The present application provides a toughening agent, a preparation method therefor, a binder, a secondary battery, a battery module, a battery pack, and an electric device. The toughening agent comprises: a core and a shell. The core is a cross-linked polymer comprising a structural unit derived from a monomer as represented by formula (I), the shell is a non-crosslinked polymer comprising structural units respectively derived from monomers as represented by formula (II) and formula (III), and the shell at least partially covers the surface of the core, wherein R₁ is selected from hydrogen or C₃-C₁₂ alkyl, R₂ is selected from C₃-C₁₂ alkyl, R₃ is selected from a benzene ring or methyl, R₄ is selected from methyl or ethyl, and R₅ is selected from hydrogen or substituted or unsubstituted C₁-C₅ alkyl. By adding the toughening agent of the present application to an electrode sheet, the flexibility of the electrode sheet can be improved, the elongation at break of the electrode sheet is increased, and the probability of brittle fracture of the electrode sheet is reduced, thereby improving the safety performance of the battery.

Description

Toughening agent, preparation method thereof, binder, secondary battery, battery module, battery pack and electrical device

Technical field

The present application relates to the technical field of secondary batteries, and in particular to a toughening agent, its preparation method, a binder, a secondary battery, a battery module, a battery pack and an electrical device.

Background technique

In recent years, secondary batteries have been widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

As a component of secondary battery materials, although the amount of binder is small, it plays a vital role in the mechanical properties and processability of the pole piece, especially the thick-coated pole piece. Existing technology often uses polyvinylidene fluoride (PVDF) as a binder. However, the crystallinity of PVDF homopolymer can reach 65% to 78%. Highly crystalline binders are prone to brittleness during battery use. It is a major safety hazard. Therefore, existing adhesives are in urgent need of improvement.

Contents of the invention

This application was made in view of the above problems, and its purpose is to provide a toughening agent and a binder containing the toughening agent to improve the flexibility of the pole piece and thereby improve the safety performance of the battery.

The first aspect of the present application provides a toughening agent, which includes: a core part, which is a cross-linked polymer containing structural units derived from the monomer shown in Formula I; and a shell part, which The shell part is a non-crosslinked polymer containing structural units derived from monomers represented by formula II and formula III, and the shell part at least partially covers the surface of the core part,

Wherein, R ₁ is selected from hydrogen or C ₃ -C ₁₂ alkyl group, R ₂ is selected from C ₃ -C ₁₂ alkyl group, R ₃ is selected from benzene ring or methyl group, R ₄ is selected from methyl group or ethyl group, R ₅ is selected from hydrogen or substituted or unsubstituted C ₁ -C ₅ alkyl.

The addition of the toughening agent to the pole piece can improve the flexibility of the pole piece, increase the elongation at break of the pole piece, and reduce the probability of brittle fracture of the pole piece, thereby improving the safety performance of the battery.

In any embodiment, the average particle size D50 of the core portion is 80 to 100 nm, and the average particle size D50 of the toughening agent is 120 to 150 nm. Toughening agents within this particle size range can further improve the flexibility of the pole piece, increase the elongation at break of the pole piece, and reduce the probability of brittle fracture of the pole piece, thereby improving the safety performance of the battery.

In any embodiment, the mass content of the core part is 60%-80%, and the mass content of the shell part is 20%-40%, based on the total mass of the toughening agent. The toughening agent within this content range can not only improve the flexibility of the pole piece, increase the elongation at break of the pole piece, reduce the probability of brittle fracture of the pole piece, thereby improving the safety performance of the battery, but also ensure that the pole piece has sufficient Adhesion to ensure battery performance and service life.

In any embodiment, the mass content of the monomer represented by Formula III is 1% to 5%, based on the total mass of the toughener. The toughening agent within this content range can ensure that the pole piece has effective adhesion, thereby ensuring that the battery has excellent electrical properties and cycle performance while improving safety performance.

In any embodiment, the glass transition temperature of the core is not higher than -20°C and the glass transition temperature of the shell is not lower than 50°C.

The core part of the glass transition temperature forms a soft segment, and the shell part of the glass transition temperature forms a hard segment. The hard segment covering the soft segment to form a core-shell structure can improve the processability of the toughener and reduce the The agglomeration of soft segments in the toughened substrate further improves the toughening performance of the toughening agent.

In any embodiment, the monomer represented by Formula I is selected from one or more of butyl acrylate, isooctyl acrylate, and lauric acid methacrylate.

In any embodiment, the monomer represented by Formula II is selected from one or more of methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and propyl acrylate.

In any embodiment, the monomer represented by Formula III is selected from one or more types of acrylic acid and methacrylic acid.

A second aspect of the application also provides a binder, the binder includes polyvinylidene fluoride and a toughening agent, the toughening agent includes a core part and a shell part, the core part is derived from formula I A cross-linked polymer of structural units of the monomers shown, the shell part is a non-cross-linked polymer containing structural units derived from the monomers shown in Formula II and Formula III, and the shell part at least partially covers the the surface of the core,

The binder makes the pole piece more flexible and has a longer elongation at break, thus improving the safety performance of the battery.

In any embodiment, the mass content of the toughening agent is 5% to 50%, optionally 15% to 25%, based on the total mass of the binder. Binders within this mass content range can further balance the flexibility and bonding strength of the pole pieces, thereby improving the comprehensive performance of the battery including safety performance, electrical performance, and cycle performance.

In any embodiment, the mass content of the core part is 60%-80%, and the mass content of the shell part is 20%-40%, based on the total mass of the toughening agent. Binders within this mass content range can further balance the flexibility and bonding strength of the pole pieces, thereby improving the comprehensive performance of the battery including safety performance, electrical performance, and cycle performance.

In any embodiment, the mass content of the monomer represented by Formula III is 1% to 5%, based on the total mass of the toughener. The mass content of the monomer represented by Formula III within a suitable range can enable the toughener to have good adhesive force.

The third aspect of this application provides a method for preparing a toughening agent. The preparation method includes:

Cross-linking and polymerizing the monomer represented by Formula I under polymerizable conditions to prepare a cross-linked polymer to form a core;

After mixing the cross-linked polymer, the monomer represented by formula II and the monomer represented by formula III, non-cross-linked polymerization is performed, and the monomer represented by formula II and the monomer represented by III form at least part of the package. a shell covering the surface of the core,

The toughening agent prepared by this preparation method can improve the flexibility of the pole piece, increase the fracture elongation of the pole piece, and reduce the probability of brittle fracture of the pole piece, thereby improving the safety performance of the battery.

A fourth aspect of the present application provides a secondary battery, including a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte. The positive electrode sheet includes the toughening agent of the first aspect of the present application or the second aspect of the present application. of adhesive.

A fifth aspect of the present application provides a battery module including the secondary battery of the fourth aspect of the present application.

A sixth aspect of the present application provides a battery pack, including the battery module of the fifth aspect of the present application.

A seventh aspect of the present application provides an electrical device, including at least one selected from the secondary battery of the fourth aspect of the present application, the battery module of the fifth aspect of the present application, or the battery pack of the sixth aspect of the present application. kind.

Description of drawings

Figure 1 is a schematic structural diagram of a toughening agent according to an embodiment of the application.

FIG. 2 is a schematic diagram of a secondary battery according to an embodiment of the present application.

FIG. 3 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 2 .

Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application.

Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application.

FIG. 6 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 5 .

FIG. 7 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.

Figure 8 is the adhesion testing device of this application.

Figure 9 is the pole piece elongation at break testing device of this application.

Explanation of reference symbols:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 top cover assembly; 6 pole piece; 61 current collector; 62 coating; 63 additional Toughening agent; 631 core part; 632 shell part; 7 double-sided tape; 8 steel plate; 91 upper clamp; 92 lower clamp.

Detailed ways

Hereinafter, embodiments that specifically disclose the binder, preparation method, electrode, battery and electrical device of the present application will be described in detail with reference to the accompanying drawings as appropriate. However, unnecessary detailed explanations may be omitted. For example, detailed descriptions of well-known matters may be omitted, or descriptions of substantially the same structure may be repeated. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

"Ranges" disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the

minimum range values

1 and 2 are listed, and if the

maximum range values

3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5. In this application, unless stated otherwise, the numerical range "a-b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

If there is no special description, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

If there is no special instructions, all steps of the present application can be performed sequentially or randomly, and are preferably performed sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, mentioning that the method can also include step (c) means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.

If there is no special explanation, the words "include" and "include" mentioned in this application represent open expressions, which may also be closed expressions. For example, "comprising" and "comprising" may mean that other components not listed may also be included or included, or only the listed components may be included or included.

In this application, the term "or" is inclusive unless otherwise stated. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, condition "A or B" is satisfied by any of the following conditions: 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).

Polyvinylidene fluoride (PVDF) is currently the most widely used binder for secondary ion batteries. However, PVDF binder has shortcomings such as large modulus and high crystallinity, which results in insufficient flexibility of the battery pole pieces. During molding and use Brittle fracture is prone to occur during the process, which may lead to battery safety issues.

Based on this, this application proposes a toughening agent and a binder containing the toughening agent to improve the flexibility of the pole piece and thereby improve the safety performance of the battery.

[Binder]

Based on this, this application proposes a toughening agent, which includes: a core part, which is a cross-linked polymer containing structural units derived from the monomer shown in formula I, and a shell part, so The shell part is a non-crosslinked polymer containing structural units derived from monomers represented by formula II and formula III, and the shell part at least partially covers the surface of the core part,

In this article, the term "cross-linked polymer" refers to a polymer in which long chains in the molecular structure are connected by atoms or short chains to form a three-dimensional network structure. Due to the strong binding force of chemical bonds in cross-linked polymers, cross-linked polymers cannot be dissolved in any solvent or melted by heating. Cross-linked polymers can be obtained by polymerizing monomers with multiple functionalities, or they can be cross-linked by linear polymers under the action of cross-linking agents.

In this article, the term "non-crosslinked polymer" refers to polymers that have not undergone cross-linking reactions, mainly including linear polymers and branched polymers. Different from cross-linked polymers, its molecular arrangement is loose and the intermolecular force is weak. It can be melted by heating and can be dissolved in appropriate solvents.

As used herein, the term "C ₃ -C ₁₂ alkyl" refers to a straight or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, without unsaturation present in the group, having from three to twelve A carbon atom and is attached to the rest of the molecule by a single bond. Examples of C ₃ -C ₁₂ alkyl groups include, but are not limited to: n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl , neopentyl, n-hexyl, n-heptyl, n-octyl, n-decyl, dodecyl. The term "C ₁ -C ₅ alkyl" should be interpreted accordingly.

As used herein, the term "substituted" means substituted by a substituent, each of which is independently selected from the group consisting of: hydroxyl, mercapto, amino, cyano, nitro, aldehyde, and halogen atoms.

Figure 1 is a schematic structural diagram of a toughening agent in an embodiment of the present application. The toughening agent 63 includes a core part 631 and a shell part 632. The shell part 632 covers the surface of the core part 631. The core part 631 is a cross-linked polymer containing structural units derived from the monomer shown in Formula I. The monomer shown in Formula I has a low glass transition temperature and is easy to form soft segments with large free volume. Soft segments with large free volume are easily formed. The chain segments can absorb external energy through chain segment movement to achieve energy-absorbing and toughening effects; at the same time, the cross-linked network structure of the cross-linked polymer makes the core structure more stable and can maintain structural stability in solvents and toughened matrix. It has a lasting toughening effect. The shell portion 632 is a non-cross-linked polymer containing structural units derived from the monomers represented by formulas II and formula III. The high glass transition temperatures of the monomers represented by formulas II and formula III are easy to form hard segments. The hard segments The soft segment coated on the core forms a toughening agent with a core-shell structure. The coating of the hard segments of the shell part 632 can not only improve the processability of the core part 631, but also play a strengthening and toughening role. That is, the shell part 632 covers the core part 631 and rivets it into the toughened matrix. The stress concentration caused by the portion 632 induces craze dispersion energy in the toughened matrix, thereby further improving the toughening performance of the toughening agent. At the same time, the shell 632 forms a non-cross-linked network to facilitate swelling or dissolution in the solvent to improve the compatibility of the toughening agent 632 with the solvent and the toughened matrix, thereby improving the dispersion of the toughening agent in the toughened matrix. properties, enhancing the toughening effect. Furthermore, the monomer represented by formula III in the shell part 632 contains a carboxyl functional group, and its strong polarity can generate a large intermolecular force, so that the toughening agent has excellent bonding properties.

In some embodiments, the core is a cross-linked polymer of butyl acrylate, a cross-linked polymer of isooctyl acrylate, a cross-linked polymer of dodecyl methacrylate, or a mixture thereof.

In some embodiments, the shell is methyl acrylate - a non-cross-linked polymer of acrylic acid, ethyl acrylate - a non-cross-linked polymer of acrylic acid, methyl methacrylate - a non-cross-linked polymer of acrylic acid, methacrylic acid Ethyl acrylate - non-cross-linked polymer of acrylic acid, propyl acrylate - non-cross-linked polymer of acrylic acid, methyl acrylate - non-cross-linked polymer of methacrylic acid, ethyl acrylate - non-cross-linked polymer of methacrylic acid , Methyl methacrylate-non-cross-linked polymer of methacrylic acid, ethyl methacrylate-non-cross-linked polymer of methacrylic acid, propyl acrylate-non-cross-linked polymer of methacrylic acid.

In some embodiments, the average particle size D50 of the core is 80 to 100 nm, and the average particle size D50 of the toughening agent is 120 to 150 nm.

D50 refers to the particle size corresponding to when the cumulative particle size distribution percentage of the sample reaches 50%. Methods and instruments known in the art can be used for determination. For example, you can refer to the GB/T 19077-2016 particle size distribution laser diffraction method and use a laser particle size analyzer to measure it.

The addition of cross-linking agent can provide more core growth points and/or shell grafting points, which is conducive to the polymerization of the core and shell. Therefore, the higher the cross-linking agent content, the smaller the core and toughening agent particles. The larger the diameter. If the particle size of the core and the toughening agent is too small, it means that the polymerization degree of the core and the toughening agent is low and it cannot play a significant toughening effect; if the particle size of the core and the toughening agent is too large, the functional groups of the shell will As the relative content decreases, the bonding force of the toughening agent decreases. At the same time, due to the excessive particle size, the dispersibility of the toughening agent in the solvent and the toughened matrix decreases, and the toughening effect is weakened. Toughening agents within this particle size range can further improve the flexibility of the pole piece, increase the elongation at break of the pole piece, and reduce the probability of brittle fracture of the pole piece, thereby improving the safety performance of the battery.

In some embodiments, the mass content of the core part is 60%-80%, and the mass content of the shell part is 20%-40%, based on the total mass of the toughening agent. In some embodiments, the mass content of the core part can be selected from 65% to 80%, 70% to 80%, or 75% to 80%, based on the total mass of the toughening agent.

If the mass content of the core part in the toughener is too high, the bonding force of the toughened matrix will be greatly reduced; if the mass content of the shell part is too high, the toughening performance of the toughener will be greatly reduced. .

The toughening agent within this content range can not only improve the flexibility of the pole piece, increase the elongation at break of the pole piece, reduce the probability of brittle fracture of the pole piece, thereby improving the safety performance of the battery, but also ensure that the pole piece has sufficient Adhesion to ensure battery performance and service life.

In some embodiments, the mass content of the monomer represented by Formula III is 1% to 5%, based on the total mass of the toughener. In some embodiments, the mass content of the monomer represented by Formula III is 2% to 5%, 3% to 5%, or 4% to 5%, based on the total mass of the toughener.

If the mass content of the monomer shown in Formula III is too high, the toughening agent cannot be dissolved in the solvent, especially the oily solvent, which reduces the effective addition content of the toughening agent, making the toughening agent unable to play an effective toughening effect. Too little quantity and quality of the monomer shown in Formula III will lead to a significant decrease in the adhesion of the toughened matrix.

The toughening agent within this content range can ensure that the pole piece has effective adhesion, thereby ensuring that the battery has excellent electrical properties and cycle performance while improving safety performance.

In some embodiments, the cross-linked polymer of the core is in a highly elastic state at room temperature, and the non-cross-linked polymer of the shell is in a glassy state at room temperature.

In some embodiments, the glass transition temperature of the cross-linked polymer of the core is not higher than -20°C, and the glass transition temperature of the non-cross-linked polymer of the shell is not lower than 50°C. The glass transition temperature of the cross-linked polymer in the core is not higher than -20°C, that is, the cross-linked polymer in the core is in a highly elastic state at room temperature. In the highly elastic state of the polymer, the chain segments keep moving but the entire molecular chain does not move. At this time, the polymer can undergo severe deformation under relatively small force, and the deformation can be completely restored after the external force is removed, which has a significant energy-absorbing and toughening effect. The glass transition temperature of the non-cross-linked polymer in the shell is not lower than 50°C, that is, the non-cross-linked polymer in the shell is in a glassy state at room temperature. The riveting effect of the glassy polymer in the toughened matrix can trigger the shear yielding and silvering of the matrix, and the toughening performance of the toughening agent can be further improved by strengthening the toughening effect. Coating rubbery polymers with glassy polymers can also shape the toughening agent into easily processable powders or particles, improve the processability of the toughening agent, and reduce the loss of highly elastic polymers in the toughened substrate. agglomeration, thereby further improving the toughening properties.

In some embodiments, the monomer represented by Formula I is selected from one or more of butyl acrylate, isooctyl acrylate, and dodecyl methacrylate.

In some embodiments, the monomer represented by Formula II is selected from one or more of methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and propyl acrylate.

In some embodiments, the monomer represented by Formula III is selected from one or more of acrylic acid and methacrylic acid.

Another embodiment of the present application provides a binder. The binder includes polyvinylidene fluoride and a toughening agent. The toughening agent includes a core part and a shell part. The core part is derived from the formula A cross-linked polymer of structural units of the monomer represented by I, the shell portion is a non-cross-linked polymer containing structural units derived from the monomer represented by formula II and formula III, and the shell portion at least partially covers the The surface of the core,

As used herein, the term "binder" refers to a chemical compound, polymer, mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.

As used herein, the term "polyvinylidene fluoride" refers to a polymer of vinylidene fluoride.

In some embodiments, the dispersion medium of the adhesive is an oily solvent. Examples of the oily solvent include but are not limited to dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dicarbonate Methyl ester, ethyl cellulose, polycarbonate.

In some embodiments, adhesives are used to hold electrode materials and/or conductive agents in place and adhere them to conductive metal components to form electrodes.

In some embodiments, the binder serves as a positive electrode binder and is used to bind the positive electrode active material and/or the conductive agent to form the positive electrode.

In some embodiments, the binder serves as a negative electrode binder and is used to bind the negative electrode active material and/or the conductive agent to form the negative electrode.

Using a mixture of polyvinylidene fluoride and a toughening agent as a binder can improve the flexibility of the binder while reducing the crystallinity of polyvinylidene fluoride. The energy-absorbing toughening of the core part of the toughening agent and the strengthening and toughening of the shell part can synergistically improve the toughness of the pole piece. The binder makes the pole piece more flexible and has a longer elongation at break, thus improving the safety performance of the battery.

In some embodiments, the mass content of the toughening agent is 5% to 50%, optionally 15% to 25%, based on the total mass of the binder. In some embodiments, the mass content of the toughening agent is 17% to 25%.

When the content of the toughening agent is too low, the effect of toughening the binder and reducing the crystallinity of polyvinylidene fluoride cannot be achieved; when the content of the toughening agent is too high, the bonding force of the binder will decrease significantly. , resulting in a low bonding force between the active material layer in the pole piece and the current collector, and an increased risk of demoulding of the active material layer during long cycles, making the battery a greater safety hazard.

Binders within this mass content range can further balance the flexibility and bonding force of the pole pieces, thereby improving the comprehensive performance of the battery including safety performance, electrical performance, and cycle performance.

In some embodiments, the mass content of the core part is 60%-80%, and the mass content of the shell part is 20%-40%. In some embodiments, the mass content of the core part can be selected from 65% to 80%, 70% to 80%, or 75% to 80%, based on the total mass of the toughening agent.

The binder within this content range can not only improve the flexibility of the pole piece, increase the elongation at break of the pole piece, reduce the probability of brittle fracture of the pole piece, thereby improving the safety performance of the battery, but also ensure that the pole piece has sufficient Adhesion to ensure battery performance and service life.

In some embodiments, the mass content of the monomer represented by Formula III is 1% to 5%, based on the total mass of the polymer. In some embodiments, the mass content of the monomer represented by Formula III is 2% to 5%, 3% to 5%, or 4% to 5%, based on the total mass of the toughener.

The binder within this content range can ensure that the pole piece has effective bonding force, thereby ensuring that the battery has excellent electrical performance and cycle performance while improving safety performance.

In one embodiment of the present application, a method for preparing a toughening agent is provided. The preparation method includes:

In some embodiments, the monomer represented by Formula I is cross-linked and polymerized with a cross-linking agent to prepare a cross-linked polymer.

In some embodiments, the monomer represented by formula II and the monomer represented by formula III are polymerized to form the shell part and are grafted with the cross-linked polymer of the core part, thereby improving the stability of the core-shell structure of the toughener. sex.

[Positive pole piece]

The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. The positive electrode film layer includes a binder, and the binder includes a toughening agent or any embodiment in any embodiment of the present application. The toughener prepared by the toughener preparation method in the method, or the binder is the binder in any embodiment of the present application.

As an example, the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the cathode active material may be a cathode active material known in the art for batteries. As an example, the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO ₂ ), lithium nickel oxides (such as LiNiO ₂ ), lithium manganese oxides (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (can also be abbreviated to NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (can also be abbreviated to NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (can also be abbreviated to NCM ₆₂₂ ), LiNi At least one of _0.8 Co _0.1 Mn _0.1 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and its modified compounds. The olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode film layer optionally further includes 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, the positive electrode sheet can be prepared by: dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, toughening agent, binder and any other components in In a solvent (such as N-methylpyrrolidone), a positive electrode slurry is formed; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode piece can be obtained.

[Negative pole piece]

In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

As an example, the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

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

[electrolytes]

The electrolyte plays a role in conducting ions between the positive and negative electrodes. There is no specific restriction on the type of electrolyte in this application, and it can be selected according to needs. For example, the electrolyte can be liquid, gel, or completely solid.

In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes electrolyte salts and solvents.

In some embodiments, the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.

In some embodiments, the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

In some embodiments, the electrolyte optionally further includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[Isolation film]

In some embodiments, the secondary battery further includes a separator film. There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.

[Secondary battery]

In one embodiment of the present application, a secondary battery is provided, including a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. The positive electrode sheet includes the toughening agent in any embodiment or the toughening agent in any embodiment. Binder.

Typically, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator. During the charging and discharging process of the secondary battery, active ions are inserted and detached back and forth between the positive electrode piece and the negative electrode piece. The electrolyte plays a role in conducting ions between the positive and negative electrodes. The isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows ions to pass through.

In some embodiments, the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer packaging. The outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

This application has no particular limitation on the shape of the battery, which can be cylindrical, square or any other shape. For example, FIG. 2 shows a square-structured secondary battery 5 as an example.

In some embodiments, referring to FIG. 3 , the outer package may include a housing 51 and a cover 53 . The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity. The positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into the electrode assembly 52 . The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[Battery module]

In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.

Figure 4 is a battery module 4 as an example. Referring to FIG. 4 , in the battery module 4 , a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 . Of course, it can also be arranged in any other way. Furthermore, the plurality of secondary batteries 5 can be fixed by fasteners.

Optionally, the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.

[battery pack]

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

Figures 5 and 6 show the battery pack 1 as an example. Referring to FIGS. 5 and 6 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box 2 and a lower box 3 . The upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 . Multiple battery modules 4 can be arranged in the battery box in any manner.

[Electrical device]

In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack may be used as a power source for the electrical device, or may be used as an energy storage unit for the electrical device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric golf carts). , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

As the power-consuming device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

Fig. 7 is an electrical device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the electrical device, a battery pack or battery module can be used.

As another example, the device may be a mobile phone, a tablet, a laptop, etc. The device is usually required to be thin and light, and a secondary battery can be used as a power source.

Example

Hereinafter, examples of the present application will be described. The embodiments described below are illustrative and are only used to explain the present application and are not to be construed as limitations of the present application. If specific techniques or conditions are not specified in the examples, the techniques or conditions described in literature in the field or product instructions will be followed. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

Example 1

1) Preparation of toughening agent

Taking the unit mass as 1 part, mix 70 parts of butyl acrylate monomer, 1.5 parts of alkylphenol allyl polyether sulfate emulsifier, 0.1 part of ethylene glycol dimethacrylate (cross-linking agent), and 100 parts. Add ionized water into the pre-emulsification kettle and stir at 200r/min for 30 minutes to prepare the core pre-emulsion. Add 2 parts of acrylic acid monomer (AA), 28 parts of methyl methacrylate monomer (MMA), 0.6 parts of emulsifier, and 40 parts of deionized water into the pre-emulsification kettle, and stir at 200 r/min for 30 minutes to prepare the shell pre-emulsifier. emulsion. Add 0.5 parts of sodium persulfate and 0.5 parts of sodium bicarbonate to 40 parts of deionized water and dissolve them to form an initiator solution.

Add 1 part of alkylphenol allyl polyether sulfate emulsifier, 100 parts of deionized water, 5wt% nuclear pre-emulsion and 5wt% initiator solution to the reaction kettle. When the temperature in the reaction kettle reaches 75°C, blue color will appear. When the color fluorescence phenomenon occurs, add the remaining core pre-emulsion and 45wt% initiator solution dropwise at a constant speed for 120 minutes. After the dropwise addition, continue to keep the temperature for 60 minutes. Under the action of the ethylene glycol dimethacrylate cross-linking agent, The monomers in the core emulsion form cross-linked polymers that serve as the core;

Then continue to add shell pre-emulsion and 50wt% initiator solution to the reaction system. After the dropwise addition, continue to keep it warm for 60 minutes to form a non-cross-linked polymer in the shell. Cool, use sodium sulfate to break the emulsion, filter the material, and dry it.

2) Preparation of positive electrode pieces

Stir and mix the toughening agent, polyvinylidene fluoride (PVDF), lithium iron phosphate (LFP), conductive agent carbon black, and N-methylpyrrolidone (NMP) in a weight ratio of 0.3:0.9:58.38:0.42:40. , to obtain the positive electrode slurry; then the positive electrode slurry is evenly coated on the positive electrode current collector, and then dried, cold pressed, and cut to obtain the positive electrode piece.

3) Preparation of negative electrode piece

Dissolve the active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC) in the solvent deionized water in a weight ratio of 96.2:0.8:0.8:1.2 , mix evenly and prepare negative electrode slurry; apply the negative electrode slurry one or more times evenly on the negative electrode current collector copper foil, and then dry, cold press, and cut to obtain negative electrode sheets.

4) Isolation film

Use polypropylene film as the isolation film.

5) Preparation of electrolyte

In an argon atmosphere glove box (H ₂ O <0.1ppm, O ₂ <0.1ppm), mix the organic solvent ethylene carbonate (EC)/ethyl methyl carbonate (EMC) evenly according to the volume ratio of 3/7, and add LiPF Dissolve _{the 6} lithium salt in the organic solvent, stir evenly, and prepare a 1M LiPF ₆ EC/EMC solution to obtain an electrolyte.

6) Preparation of battery

Stack the positive electrode piece, isolation film, and negative electrode piece in order in Example 1 so that the isolation film plays an isolation role between the positive and negative electrode pieces, then wind it to obtain a bare battery core, and weld the tabs to the bare battery core. , put the bare battery core into an aluminum case, bake it at 80°C to remove water, then inject electrolyte and seal it to obtain an uncharged battery. The uncharged battery then undergoes processes such as standing, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product of Example 1.

The batteries of Examples 2 to 19 and the batteries of Comparative Examples 1 to 4 are similar to the battery preparation method of Example 1, but the raw materials and proportions of the toughener preparation and the proportion of the binder in the positive electrode sheet are adjusted. Specifically, The parameters are shown in Table 1, and the preparation method of the comparative example is as follows:

Comparative example 1

1) Preparation of toughening agent

Add 70 parts of butyl acrylate monomer, 1.5 parts of alkylphenol allyl polyether sulfate emulsifier, 0.1 part of ethylene glycol dimethacrylate and 100 parts of deionized water into the pre-emulsification kettle, at 200r/min Stir for 30 minutes to prepare core pre-emulsion. Add 30 parts of methyl methacrylate monomer (MMA), 0.6 parts of emulsifier, and 40 parts of deionized water into the pre-emulsification kettle, and stir at 200 r/min for 30 minutes to prepare a shell pre-emulsion. Add 0.5 parts of sodium persulfate and 0.5 parts of sodium bicarbonate to 40 parts of deionized water and dissolve them to form an initiator solution.

Add 1 part of alkylphenol allyl polyether sulfate emulsifier, 100 parts of deionized water, 5% nuclear pre-emulsion and 5% initiator solution to the reaction kettle. When the temperature in the reaction kettle reaches 75°C, a blue color will appear. When the color fluorescence phenomenon occurs, add the remaining core pre-emulsion and 45% initiator solution dropwise at a constant speed for 120 minutes. After the dropwise addition, continue to keep the temperature for 60 minutes to form a core cross-linked polymer, and then continue to add the shell pre-emulsion and 50% initiator solution. % initiator solution, after the dropwise addition, continue to keep it warm for 60 minutes to form a polymer, cool it, use sodium sulfate to break the emulsification, filter out the material, and dry it.

Comparative example 2

In Comparative Example 2, no toughening agent is added, and the weight ratio of polyvinylidene fluoride (PVDF), lithium iron phosphate (LFP), conductive agent carbon black, and N-methylpyrrolidone (NMP) is 1.2:58.38:0.42: 40 Stir and mix evenly to obtain the positive electrode slurry; then apply the positive electrode slurry evenly on the positive electrode current collector, and then dry, cold press, and cut to obtain the positive electrode pieces.

Comparative example 3

In the binder of Comparative Example 3, no core-shell structure toughening agent was added, but butyl acrylate cross-linked polymer was added. The preparation method is as follows:

Add 70 parts of butyl acrylate monomer, 1.5 parts of alkylphenol allyl polyether sulfate emulsifier, 0.1 part of ethylene glycol dimethacrylate and 100 parts of deionized water into the pre-emulsification kettle, at 200r/min Stir for 30 minutes to prepare a pre-emulsion.

Add 1 part alkylphenol allyl polyether sulfate emulsifier, 100 parts deionized water, 5% pre-emulsion and 5% initiator solution to the reaction kettle. When the temperature in the reaction kettle reaches 75°C, blue color will appear. When the fluorescence phenomenon occurs, add the remaining pre-emulsion and 45% initiator solution dropwise at a constant speed for 120 minutes. After the dropwise addition, continue to keep it warm for 60 minutes to form a polymer, cool it, use sodium sulfate to break the emulsion, filter the material, and dry it. .

Comparative example 4

The binder of Comparative Example 4 does not add a core-shell structure toughening agent, but adds butyl acrylate-methyl methacrylate-acrylic acid polymer. The preparation method is as follows:

Mix 70 parts of butyl acrylate monomer, 2 parts of acrylic acid monomer (AA), 28 parts of methyl methacrylate monomer (MMA), 2 parts of alkylphenol allyl polyether sulfate emulsifier, and 100 parts of deionized Add water to the pre-emulsification kettle and stir at 200r/min for 30 minutes to prepare the core pre-emulsion. Add 0.5 parts of sodium persulfate and 0.5 parts of sodium bicarbonate to 40 parts of deionized water and dissolve them to form an initiator solution.

Add 1 part alkylphenol allyl polyether sulfate emulsifier, 100 parts deionized water, 5% pre-emulsion and 5% initiator solution to the reaction kettle. When the temperature in the reaction kettle reaches 75°C, blue color will appear. When the fluorescence phenomenon occurs, add the remaining pre-emulsion and 45% initiator solution dropwise at a constant speed for 120 minutes. After the dropwise addition, continue to keep the temperature for 60 minutes to form a butyl acrylate-methyl methacrylate-acrylic acid polymer. Cool and use. Sodium sulfate is demulsified, filtered and discharged, and dried.

The relevant parameters of the cathode materials of the above-mentioned Examples 1 to 19 and Comparative Examples 1 to 4 are shown in Table 1 below.

In addition, the polymers, pole pieces and batteries obtained in the above-mentioned Examples 1 to 19 and Comparative Examples 1 to 4 were subjected to performance tests. The test method is as follows:

1. Average particle size D50 test

The particle size of the core cross-linked polymer and core-shell toughener was analyzed using a laser particle sizer.

2. Adhesion test

Cut the positive electrode piece into a test sample with a size of 20*100mm and set it aside. The test method is shown in Figure 8. Double-sided tape 7 is pasted on one side of the pole piece 6, and pressed with a pressure roller to completely fit it with the pole piece; the other side of the double-sided tape 7 is pasted on the surface of the steel plate 8, and one end of the current collector 61 is bent in the opposite direction. The bending angle is 180°, as shown by the arrow in Figure 8; a high-speed rail tensile machine is used for testing. One end of the steel plate 8 is fixed to the lower clamp of the tensile machine, and the bent end of the current collector 61 is fixed to the upper clamp. Adjust the angle of the current collector to ensure that it is up and down. The end is in a vertical position, and then the sample is stretched at a speed of 50mm/min until the current collector 61 is completely peeled off from the coating 62 on the surface of the current collector 61. The displacement and force during the process are recorded, and the force when the force is balanced is taken as The bonding force of pole piece 6.

3. Pole piece breaking elongation test

Cut the positive electrode piece into a test sample with a size of 15*100mm and set it aside. The test method is shown in Figure 9. Fix both ends of the sample to the upper clamp 91 and the lower clamp 92 of the high-speed rail tensioner respectively, and then stretch the sample at a speed of 5 mm/min until the sample breaks. Record the displacement and force during the process; use the By dividing the displacement by the length of the specimen, the elongation at break of the pole piece can be obtained.

4. Flexibility test of pole pieces

Cut the positive electrode piece into a test sample with a size of 15* ^2.5cm2 and set aside. Bend the pole piece in half and fix it. Use a 2kg rolling roller to roll it once. Check whether there is light leakage through the metal at the folded part of the pole piece. If there is no light leakage through the metal, fold the pole piece in half again and fix it. Use a 2kg rolling roller to roll it once and check whether there is light leakage through the metal at the folded part of the pole piece. Repeat the above steps until there is light leakage through the metal at the folded part of the pole piece. Record the number of times the pole piece has been rolled.

Embodiments 1 to 19 provide a toughening agent, which includes: a core part and a shell part. The core part is a cross-linked polymer containing structural units derived from butyl acrylate, and the shell part is a cross-linked polymer containing structural units derived from methyl methacrylate. It is a non-crosslinked polymer of structural units of ester and acrylic acid, and the shell part at least partially covers the surface of the core part.

From the comparison between Examples 1 to 19 and Comparative Example 2 in which the binder only contains polyvinylidene fluoride, it can be seen that the addition of the toughening agent to the pole piece can improve the flexibility of the pole piece and increase the breaking elongation of the pole piece. The length rate reduces the probability of brittle fracture of the pole piece, thereby improving the safety performance of the battery.

From the comparison between Example 1 and Comparative Examples 3 and 4 in which the toughening agent in the binder has a non-core-shell structure, it can be seen that the toughening agent in the core-shell structure can further improve the flexibility of the pole piece and increase the fracture of the pole piece. The elongation rate reduces the probability of brittle fracture of the pole piece, thereby improving the safety performance of the battery.

From the comparison between Examples 1, 2, and 3 and Examples 4 and 5, it can be seen that when the particle size of the core part of the toughening agent is 80 to 100 nm, and the particle size of the toughening agent is 120 to 150 nm, it can further improve the pole piece. The flexibility increases the elongation at break of the pole piece and reduces the probability of brittle fracture of the pole piece, thus improving the safety performance of the battery.

From the comparison of Examples 1, 6, 7 and Examples 8 and 9, it can be seen that the mass content of the core is 60% to 80%, and the mass content of the shell is 20% to 40%, based on the total mass of the toughening agent. , the toughening agent can not only improve the flexibility of the pole piece, increase the elongation at break of the pole piece, reduce the probability of brittle fracture of the pole piece, but also ensure that the diaphragm layer in the pole piece and the current collector have a certain bonding force , thereby obtaining a battery with excellent comprehensive performance including electrical performance, cycle performance and safety performance.

It can be seen from the comparison between Examples 1, 10, 12, Examples 11, 13 and Comparative Example 1 that the mass content of acrylic acid is 1% to 5%. Based on the total mass of the toughening agent, the toughening agent can improve the pole piece. The toughness ensures the adhesion between the diaphragm layer in the pole piece and the current collector, thereby obtaining a battery with excellent comprehensive performance including electrical performance, cycle performance and safety performance.

Embodiments 1 to 19 provide a binder, which includes polyvinylidene fluoride and a toughening agent. The toughening agent includes a core part and a shell part. The core part is derived from butyl acrylate. A cross-linked polymer of structural units, the shell part is a non-cross-linked polymer containing structural units derived from methyl methacrylate and acrylic acid, and the shell part at least partially covers the surface of the core part.

From the comparison between Examples 1 to 19 and Comparative Example 2 in which the binder only contains polyvinylidene fluoride, it can be seen that the binder makes the pole piece have better flexibility and longer elongation at break, resulting in The battery has better safety performance.

It can be seen from Examples 1 and 14 to 18 that when the mass content of the toughening agent is 5% to 50% based on the total mass of the binder, the binder enables the pole piece to have both excellent flexibility and adhesive force. , thus making the battery have excellent safety performance and electrical performance. When the mass content of the toughening agent is 15% to 25% based on the total mass of the binder, the binder can further balance the flexibility and bonding force of the pole piece, thereby further optimizing the overall performance of the battery.

It should be noted that the present application is not limited to the above-described embodiment. The above-mentioned embodiments are only examples. Within the scope of the technical solution of the present application, embodiments that have substantially the same structure as the technical idea and exert the same functions and effects are included in the technical scope of the present application. In addition, within the scope that does not deviate from the gist of the present application, various modifications to the embodiments that can be thought of by those skilled in the art, and other forms constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application. .

Claims

A toughening agent, characterized by containing:

A core part, which is a cross-linked polymer containing structural units derived from the monomer represented by Formula I; and

A shell part, which is a non-crosslinked polymer containing structural units derived from monomers represented by formula II and formula III, and the shell part at least partially covers the surface of the core part,

Wherein, R 1 is selected from hydrogen or C 3 -C 12 alkyl group, R 2 is selected from C 3 -C 12 alkyl group, R 3 is selected from benzene ring or methyl group, R 4 is selected from methyl group or ethyl group, R 5 is selected from hydrogen or substituted or unsubstituted C 1 -C 5 alkyl.
The toughening agent according to claim 1, wherein the average particle diameter D50 of the core portion is 80 to 100 nm, and the average particle diameter D50 of the toughening agent is 120 to 150 nm.
The toughening agent according to claim 1, characterized in that the mass content of the core part is 60% to 80%, the mass content of the shell part is 20% to 40%, based on the toughening agent Total mass meter.
The toughening agent according to any one of claims 1 to 3, characterized in that the mass content of the monomer represented by Formula III is 1% to 5%, based on the total mass of the toughening agent.
The toughening agent according to any one of claims 1 to 5, characterized in that the monomer shown in Formula I is selected from the group consisting of butyl acrylate, isooctyl acrylate, and dodecyl methacrylate. one or more.
The toughening agent according to any one of claims 1 to 5, characterized in that the monomer represented by formula II is selected from the group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate. , one or more propyl acrylates.
The toughening agent according to any one of claims 1 to 5, characterized in that the monomer represented by Formula III is selected from one or more of acrylic acid and methacrylic acid.
A binder, characterized in that it contains polyvinylidene fluoride and a toughening agent, the toughening agent includes a core part and a shell part, the core part contains a structural unit derived from the monomer represented by Formula I A cross-linked polymer, the shell part is a non-cross-linked polymer containing structural units derived from the monomers shown in Formula II and Formula III, and the shell part at least partially covers the surface of the core part,

Wherein, R 1 is selected from hydrogen or C 3 -C 12 alkyl group, R 2 is selected from C 3 -C 12 alkyl group, R 3 is selected from benzene ring or methyl group, R 4 is selected from methyl group or ethyl group, R 5 is selected from hydrogen or substituted or unsubstituted C 1 -C 5 alkyl.
The adhesive according to claim 8, characterized in that the mass content of the toughening agent is 5% to 50%, optionally 15% to 25%, based on the total mass of the adhesive.
The adhesive according to claim 8 or 9, characterized in that the mass content of the core part is 60% to 80%, and the mass content of the shell part is 20% to 40%. Based on the toughening The total mass of the agent.
The adhesive according to any one of claims 8 to 10, characterized in that the mass content of the monomer represented by Formula III is 1% to 5%, based on the total mass of the toughening agent.
A method for preparing a toughening agent, which includes:

Cross-linking and polymerizing the monomer represented by Formula I under polymerizable conditions to prepare a cross-linked polymer to form a core;

After mixing the cross-linked polymer, the monomer represented by formula II and the monomer represented by formula III, non-cross-linked polymerization is performed, and the monomer represented by formula II and the monomer represented by formula III form at least part of a shell covering the surface of the core,

Wherein, R 1 is selected from hydrogen or C 3 -C 12 alkyl group, R 2 is selected from C 3 -C 12 alkyl group, R 3 is selected from benzene ring or methyl group, R 4 is selected from methyl group or ethyl group, R 5 is selected from hydrogen or substituted or unsubstituted C 1 -C 5 alkyl.
A secondary battery, characterized in that it includes a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, the positive electrode sheet includes the toughening agent according to any one of claims 1 to 7 or claim 8 The adhesive described in any one of ~11.
A battery module comprising the secondary battery according to claim 13.
A battery pack, characterized by comprising the battery module according to claim 14.
An electric device, characterized in that it includes at least one selected from the group consisting of the secondary battery according to claim 13, the battery module according to claim 14, or the battery pack according to claim 15.