Secondary battery, electric device, and polyacrylic acid binder

Abstract

A secondary battery, an electric device, and a polyacrylic acid binder, relating to the technical field of secondary batteries. By using a polyacrylic acid binder containing a flexible group as a binder, linear coating of a negative electrode active material in a negative electrode active material layer can be implemented, effectively increasing the adhesion between particles of the negative electrode active material, thereby achieving the effect of alleviating expansion of a negative electrode sheet. In addition, the flexible group enables the polyacrylic acid binder to have better flexibility, thereby allowing a slurry in a preparation process of the negative electrode active material layer to have better flexibility, reducing the brittleness of the prepared negative electrode active material layer, and further reducing the severity of shedding of the negative electrode active material layer.

Description

A secondary battery, electrical equipment, and polyacrylic adhesive. Cross-referencing

[0001] This application claims priority to Chinese Patent Application No. 2024114330602, filed on October 14, 2024, entitled "A Secondary Battery, Electrical Equipment, and Polyacrylic Acid Adhesive", the contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of secondary battery technology, and more specifically, to a secondary battery, electrical equipment, and a polyacrylic adhesive. Background Technology

[0003] During battery use, the negative electrode plate may expand, mainly due to internal electrochemical reactions and the aging of binder materials. This expansion can affect the battery's health, safety, and lifespan. Summary of the Invention

[0004] In view of the above problems, this application provides a secondary battery, electrical equipment, and polyacrylic acid binder that can improve the expansion of the negative electrode sheet while reducing the brittleness of the negative electrode active material layer.

[0005] In a first aspect, this application provides a secondary battery, the secondary battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative active material layer attached to at least one side of the negative current collector; the negative active material layer comprising a polyacrylic binder, the polyacrylic binder comprising flexible groups, the flexible groups comprising at least one of ester groups or ether groups.

[0006] In the technical solution of this application embodiment, by using a polyacrylic acid binder containing flexible groups, the negative electrode active material in the negative electrode active material layer can be wound to achieve "linear" coating, which plays a good binding role for the negative electrode active material and effectively increases the adhesion between the negative electrode active material particles, thereby improving the expansion effect of the negative electrode sheet. At the same time, ester groups, ether groups, etc. have CO bonds and fewer atoms around the oxygen atom, resulting in less steric hindrance for internal rotation, thus making the molecular chain more flexible. This gives these groups a certain degree of flexibility, which enables the polyacrylic acid binder to have good flexibility, thereby enabling the slurry in the preparation process of the negative electrode active material layer to have good flexibility, reducing the brittleness of the prepared negative electrode active material layer, and thus reducing the severity of powder shedding from the negative electrode active material layer.

[0007] In some embodiments, the polyacrylic adhesive comprises structural units derived from the monomer shown in Formula 1.

[0008] Formula 1:

[0009] Among them, R 01 Including any one or more of H, halogens, substituted or unsubstituted C1-C6 saturated alkyl groups, and substituted or unsubstituted C2-C6 alkenyl groups, R 02 It includes flexible groups, which include any one or more of C2-C6 ester groups or C2-C6 ether groups.

[0010] In the above implementation process, by using monomers containing flexible groups as reactive monomers to form structural units of polyacrylic acid binders, the polyacrylic acid binders can reduce the brittleness of the entire negative electrode active material layer, thereby reducing the severity of powder shedding from the negative electrode active material layer.

[0011] In some embodiments, the monomer shown in Formula 1 includes at least one of hydroxyethyl acrylate, hydroxybutyl vinyl ether, methyl acrylate, ethyl acrylate, butyl acrylate, or ethyl butenoate.

[0012] In the above implementation process, monomers containing flexible groups, such as hydroxyethyl acrylate, hydroxybutyl vinyl ether, methyl acrylate, ethyl acrylate, butyl acrylate, or ethyl butyrate, are used as reactive monomers to form the structural unit of polyacrylic acid binder. This polyacrylic acid binder can reduce the brittleness of the entire negative electrode active material layer, thereby reducing the severity of powder shedding from the negative electrode active material layer.

[0013] In some embodiments, the structural units derived from the monomers shown in Formula 1 account for 10%-20% by mass in the polyacrylic adhesive.

[0014] In the above implementation process, by controlling the structural unit derived from the monomer shown in Formula 1 to account for 10% to 20% of the total mass of the polyacrylic adhesive, the polyacrylic adhesive can have better flexibility and reduce the probability of powder shedding from the negative electrode sheet.

[0015] In some embodiments, the polyacrylic adhesive has a weight-average molecular weight of 2 million to 2.5 million.

[0016] In the above implementation process, the higher the weight average molecular weight of the polyacrylic adhesive, the better the bonding performance of the polyacrylic adhesive. The lower the weight average molecular weight of the polyacrylic adhesive, the better its dispersibility. By controlling the weight average molecular weight of the polyacrylic adhesive to be 2 million to 2.5 million, good dispersion can be achieved without the addition of additional additives, while also achieving a good bonding effect.

[0017] In some embodiments, the polyacrylic adhesive comprises structural units derived from the monomer shown in Formula 2.

[0018] Formula 2:

[0019] Among them, R 03 Including any one or more of H, halogens, substituted or unsubstituted C1-C6 saturated alkyl groups, and substituted or unsubstituted C2-C6 alkenyl groups; R 04 It includes polar groups, which include any one or more of the following: amino, hydroxyl, carboxyl, carboxyl, cyano, amide, phenol, sulfonic acid, or sulfonate groups.

[0020] In the above implementation process, groups such as amine, hydroxyl, carboxyl, carboxyl salt, cyano, amide, phenol, or sulfonic acid groups have strong polarity and can form strong hydrogen bonds with the surface of the active material, which can better promote the dispersion of the negative electrode active material and thus better suppress the volume expansion of the negative electrode active material layer.

[0021] In some embodiments, the monomer shown in Formula 2 includes at least one of acrylic acid, butenoic acid, lithium acrylate sulfonate, allyl alcohol, acrylamide, isobutyleneamide, acrylonitrile, or isobutylene nitrile.

[0022] In the above implementation process, monomers containing polar groups, such as acrylic acid, butenoic acid, lithium acrylate sulfonate, allyl alcohol, acrylamide, isobutylene amide, acrylonitrile, or isobutylene nitrile, are used as reactive monomers to form the structural unit of polyacrylic acid binder. This allows the polyacrylic acid binder to form strong hydrogen bonds with the surface of the active material, which can better promote the dispersion of the negative electrode active material and thus better suppress the volume expansion of the negative electrode active material layer.

[0023] In some embodiments, the structural units derived from the monomer shown in Formula 2 account for 80%-90% by mass in the polyacrylic adhesive.

[0024] In the above implementation process, by controlling the structural units of the monomers derived from Formula 2 to account for 80% to 90% of the total mass of the polyacrylic adhesive, the polyacrylic adhesive can have better adhesion and the negative electrode sheet can have lower expansion.

[0025] In some embodiments, the polyacrylic adhesive comprises the structural formula shown in Formula I:

[0026] Formula I:

[0027] Wherein, R1, R2 and R3 are each independently selected from polar groups, and the polar groups include any one or more of the following: amino group, hydroxyl group, carboxyl group, carboxyl group, cyano group, amide group, phenolic group, sulfonic acid group or sulfonate group;

[0028] R4 is selected from flexible groups, including at least one of C2-C6 ester groups or C2-C6 ether groups;

[0029] R5, R6, R7 and R8 are each independently selected from one or more of H, halogens, substituted or unsubstituted C1 to C6 saturated alkyl groups or substituted or unsubstituted C2 to C6 alkenyl groups;

[0030] a, b, c, and d are each independently selected from positive integers.

[0031] In some embodiments, R5, R6, R7 and R8 are each independently selected from H.

[0032] In some embodiments, R1 is selected from at least one of a carboxylate group or a sulfonate group; and / or

[0033] R2 is selected from cyano groups; and / or

[0034] R3 is selected from an amide group; and / or

[0035] The carboxyl group includes lithium carboxyl groups; and / or

[0036] The sulfonate group includes lithium sulfonate.

[0037] In the above implementation process, by controlling the selection of each group from different functional groups, more functions can be given to the binder. Among them, the introduction of groups such as carboxyl groups or sulfonate groups can be beneficial to lithium-ion conduction, thereby improving the rate performance of the battery; the introduction of groups such as cyano groups can have a synergistic effect with the electrolyte of the battery, thereby improving the wetting of the electrode; the introduction of groups such as amide groups can increase the strength of the slurry, thereby making it suitable for the electrode preparation process of first forming an active material layer film and then combining it with the current collector.

[0038] In some embodiments, in the polyacrylic adhesive, the mass ratio of the structural unit to which R1, R2, R3, and R4 belong is (3-7):(1-2):(1-2):(1-2).

[0039] In the above implementation process, by controlling the mass ratio of structural units R1, R2, R3 and R4 in the polyacrylic binder to (3-7):(1-2):(1-2), it is possible to improve the expansion of the negative electrode sheet of the secondary battery and reduce the brittleness of the negative electrode active material layer.

[0040] In some embodiments, the polyacrylic binder accounts for 1% to 2% of the mass of the negative electrode active material layer.

[0041] In the above implementation process, the greater the amount of polyacrylic acid binder, the better the bonding effect on the negative electrode active material, which in turn helps to reduce the probability of expansion of the negative electrode active material layer. The smaller the amount of polyacrylic acid binder, the better the energy density of the secondary battery and the wetting of the negative electrode sheet. By controlling the mass ratio of polyacrylic acid binder in the active material layer to 1% to 2%, the energy density and anti-expansion performance of the secondary battery as well as the negative electrode wetting speed of the electrode sheet can be balanced.

[0042] In some embodiments, the negative electrode active material layer further includes polytetrafluoroethylene.

[0043] In the above implementation process, adding polytetrafluoroethylene to the negative electrode active material layer is more conducive to confining the negative electrode active material, thereby improving the expansion of the negative electrode sheet.

[0044] In some embodiments, the polytetrafluoroethylene accounts for 0.1% to 0.5% of the mass of the negative electrode active material layer.

[0045] In the above implementation process, by controlling the mass ratio of polytetrafluoroethylene in the negative electrode active material layer to 0.1% to 0.5%, the negative electrode active material can achieve better confinement.

[0046] In some embodiments, when the secondary battery is fully charged, the expansion rate of the negative electrode does not exceed 21.4%.

[0047] In the above implementation process, by controlling the expansion rate of the negative electrode sheet to not exceed 21.4% under full charge, it is beneficial to the battery's service life.

[0048] Secondly, this application provides an electrical device that includes the secondary battery provided in the first aspect.

[0049] Thirdly, this application provides a polyacrylic adhesive comprising a flexible group, wherein the flexible group comprises at least one of an ester group or an ether group.

[0050] In the technical solution of this application embodiment, the polyacrylic acid binder containing flexible groups is applied to a secondary battery. This binder can wrap the negative electrode active material in the negative electrode active material layer, achieving "linear" coating and providing good confinement. This effectively increases the adhesion between the negative electrode active material particles, thereby improving the expansion of the negative electrode sheet. Simultaneously, the ester and ether groups have CO bonds and fewer atoms around the oxygen atom, resulting in less steric hindrance for internal rotation. This makes the molecular chain more flexible, giving these groups a certain degree of flexibility. The flexible groups can reduce the brittleness of the entire negative electrode active material layer, thereby reducing the severity of powder shedding from the negative electrode active material layer.

[0051] In some embodiments, the polyacrylic adhesive comprises structural units derived from the monomer shown in Formula 1.

[0052] Formula 1:

[0053] Among them, R 01 Including any one or more of H, halogens, substituted or unsubstituted C1-C6 saturated alkyl groups, and substituted or unsubstituted C2-C6 alkenyl groups, R 02 It includes flexible groups, which include any one or more of C2-C6 ester groups or C2-C6 ether groups.

[0054] In the above implementation process, by using monomers containing flexible groups as reactive monomers to form structural units of polyacrylic acid binders, the polyacrylic acid binders can reduce the brittleness of the entire negative electrode active material layer, thereby reducing the severity of powder shedding from the negative electrode active material layer.

[0055] In some embodiments, the monomer shown in Formula 1 includes at least one of hydroxyethyl acrylate, hydroxybutyl vinyl ether, methyl acrylate, ethyl acrylate, butyl acrylate, or ethyl butenoate.

[0056] In the above implementation process, monomers containing flexible groups, such as hydroxyethyl acrylate, hydroxybutyl vinyl ether, methyl acrylate, ethyl acrylate, butyl acrylate, or ethyl butyrate, are used as reactive monomers to form the structural unit of polyacrylic acid binder. This polyacrylic acid binder can reduce the brittleness of the entire negative electrode active material layer, thereby reducing the severity of powder shedding from the negative electrode active material layer.

[0057] In some embodiments, the structural units derived from the monomers shown in Formula 1 account for 10%-20% by mass in the polyacrylic adhesive.

[0058] In the above implementation process, by controlling the structural unit derived from the monomer shown in Formula 1 to account for 10% to 20% of the total mass of the polyacrylic adhesive, the polyacrylic adhesive can have better flexibility and reduce the probability of powder shedding from the negative electrode sheet.

[0059] In some embodiments, the polyacrylic adhesive has a weight-average molecular weight of 2 million to 2.5 million.

[0060] In the above implementation process, the higher the weight average molecular weight of the polyacrylic adhesive, the better the bonding performance of the polyacrylic adhesive. The lower the weight average molecular weight of the polyacrylic adhesive, the better its dispersibility. By controlling the weight average molecular weight of the polyacrylic adhesive to be 2 million to 2.5 million, good dispersion can be achieved without the addition of additional additives, while also achieving a good bonding effect.

[0061] In some embodiments, the polyacrylic adhesive comprises structural units derived from the monomer shown in Formula 2.

[0062] Formula 2:

[0063] Among them, R 03 Including any one or more of H, halogens, substituted or unsubstituted C1-C6 saturated alkyl groups, and substituted or unsubstituted C2-C6 alkenyl groups; R 04 It includes polar groups, which include any one or more of the following: amino, hydroxyl, carboxyl, carboxyl, cyano, amide, phenol, sulfonic acid, or sulfonate groups.

[0064] In the above implementation process, groups such as amine, hydroxyl, carboxyl, carboxyl salt, cyano, amide, phenol, or sulfonic acid groups have strong polarity and can form strong hydrogen bonds with the surface of the active material, which can better promote the dispersion of the negative electrode active material and thus better suppress the volume expansion of the negative electrode active material layer.

[0065] In some embodiments, the monomer shown in Formula 2 includes at least one of acrylic acid, butenoic acid, lithium acrylate sulfonate, allyl alcohol, acrylamide, isobutyleneamide, acrylonitrile, or isobutylene nitrile.

[0066] In the above implementation process, monomers containing polar groups, such as acrylic acid, butenoic acid, lithium acrylate sulfonate, allyl alcohol, acrylamide, isobutylene amide, acrylonitrile, or isobutylene nitrile, are used as reactive monomers to form the structural unit of polyacrylic acid binder. This allows the polyacrylic acid binder to form strong hydrogen bonds with the surface of the active material, which can better promote the dispersion of the negative electrode active material and thus better suppress the volume expansion of the negative electrode active material layer.

[0067] In some embodiments, the structural units derived from the monomer shown in Formula 2 account for 80%-90% by mass in the polyacrylic adhesive.

[0068] In the above implementation process, by controlling the structural units of the monomers derived from Formula 2 to account for 80% to 90% of the total mass of the polyacrylic adhesive, the polyacrylic adhesive can have better adhesion and the negative electrode sheet can have lower expansion.

[0069] In some embodiments, the polyacrylic adhesive comprises the structural formula shown in Formula I:

[0070] Formula I:

[0071] Wherein, R1, R2 and R3 are each independently selected from polar groups, and the polar groups include any one or more of the following: amino group, hydroxyl group, carboxyl group, carboxyl group, cyano group, amide group, phenolic group, sulfonic acid group or sulfonate group;

[0072] R4 is selected from flexible groups, including at least one of C2-C6 ester groups or C2-C6 ether groups;

[0073] R5, R6, R7 and R8 are each independently selected from one or more of H, halogens, substituted or unsubstituted C1-C6 saturated alkyl groups and substituted or unsubstituted C2-C6 alkenyl groups;

[0074] a, b, c, and d are each independently selected from positive integers.

[0075] In some embodiments, R5, R6, R7 and R8 are each independently selected from H.

[0076] In some embodiments, R1 is selected from at least one of a carboxylate group or a sulfonate group; and / or

[0077] R2 is selected from cyano groups; and / or

[0078] R3 is selected from an amide group; and / or

[0079] The carboxyl group includes lithium carboxyl groups; and / or

[0080] The sulfonate group includes lithium sulfonate.

[0081] In the above implementation process, by controlling the selection of each group from different functional groups, more functions can be given to the binder. Among them, the introduction of groups such as carboxyl groups or sulfonate groups can be beneficial to lithium-ion conduction, thereby improving the rate performance of the battery; the introduction of groups such as cyano groups can have a synergistic effect with the electrolyte of the battery, thereby improving the wetting of the electrode; the introduction of groups such as amide groups can increase the strength of the slurry, thereby making it suitable for the electrode preparation process of first forming an active material layer film and then combining it with the current collector.

[0082] In some embodiments, in the polyacrylic adhesive, the mass ratio of the structural unit to which R1, R2, R3, and R4 belong is (3-7):(1-2):(1-2):(1-2).

[0083] In the above implementation process, by controlling the mass ratio of structural units R1, R2, R3 and R4 in the polyacrylic binder to (3-7):(1-2):(1-2), it is possible to improve the expansion of the negative electrode sheet of the secondary battery and reduce the brittleness of the negative electrode active material layer. Attached Figure Description

[0084] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0085] Figure 1 is a structural schematic diagram of a vehicle provided in some embodiments of this application;

[0086] Figure 2 is an exploded structural diagram of a secondary battery provided in some embodiments of this application;

[0087] Figure 3 is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0088] Figure 4 is an exploded view of a single battery cell provided in some embodiments of this application;

[0089] Figure 5 is a schematic diagram of the first structure of the negative electrode sheet provided in some embodiments of this application;

[0090] Figure 6 is a schematic diagram of the second structure of the negative electrode sheet provided in some embodiments of this application;

[0091] Figure 7 shows the infrared detection results of the adhesive provided in some embodiments of this application;

[0092] Figure 8 is a flowchart of a method for preparing an electrode sheet according to some embodiments of this application.

[0093] The reference numerals in the detailed embodiments are as follows:

[0094] 1000 - Vehicle; 100 - Secondary battery; 200 - Motor; 300 - Controller; 10 - Housing; 11 - Accommodation space; 12 - First part; 13 - Second part; 20 - Battery cell; 21 - Shell; 211 - Opening; 22 - End cap assembly; 221 - End cap; 222 - Electrode terminal; 23 - Electrode assembly; 231 - Negative electrode sheet; 2311 - Negative current collector; 2312 - Negative active material layer; 24 - Current collector component; 25 - Insulation protection component. Detailed Implementation

[0095] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0096] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0097] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0098] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0099] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0100] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0101] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0102] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0103] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0104] Power batteries can be either lithium-ion or sodium-ion rechargeable batteries, which are widely used in portable electronic devices, electric vehicles, and other fields. During battery use, the electrodes may expand, mainly due to internal electrochemical reactions and the aging of the binder materials. This expansion can affect the battery's health, safety, and lifespan.

[0105] Currently, common binders used in batteries include CMC and SBR. To improve the problem of electrode expansion, the amount or polarity of the binder can be increased. However, increasing the amount or polarity of the binder can lead to excessive electrode swelling or worsening of electrode brittleness, resulting in electrode powder and material shedding. Furthermore, current binders such as CMC and SBR coat the active material in a "point-to-point" manner, so even after increasing the amount or polarity of the binder, the improvement in electrode expansion remains limited.

[0106] Based on the above considerations, in order to improve the expansion of the negative electrode sheet while reducing the brittleness of the negative electrode active material layer, this application proposes a secondary battery. The secondary battery includes a negative electrode sheet, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer attached to at least one side of the negative electrode current collector; the negative electrode active material layer includes a polyacrylic acid binder, the polyacrylic acid binder includes flexible groups, and the flexible groups include at least one of ester groups or ether groups.

[0107] In such secondary batteries, the use of polyacrylic acid binders containing flexible groups allows for the winding of active materials within the active material layer, achieving a "linear" coating. This provides effective confinement of the active materials, significantly increasing the adhesion between active material particles and thus mitigating electrode expansion. Simultaneously, ester and ether groups, with their CO bonds and fewer atoms surrounding the oxygen atom, exhibit less steric hindrance to internal rotation, resulting in more flexible molecular chains. This flexibility enhances the flexibility of the polyacrylic acid binder, which in turn improves the flexibility of the slurry used in the preparation of the negative electrode active material layer. This reduces the brittleness of the prepared negative electrode active material layer and consequently minimizes powder shedding.

[0108] This secondary battery can be used, but is not limited to, in electrical equipment such as vehicles, ships, or aircraft. The power system of such electrical equipment can be constructed using the secondary battery disclosed in this application.

[0109] This application provides an electrical device that uses a battery as a power source. The electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0110] For ease of explanation, the following embodiments will use a vehicle as an example of an electrical device according to an embodiment of this application.

[0111] Please refer to Figure 1, which is a structural schematic diagram of a vehicle provided in some embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. A secondary battery 100 is installed inside the vehicle 1000, and the secondary battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The secondary battery 100 can be used to power the vehicle 1000; for example, the secondary battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 300 and a motor 200. The controller 300 is used to control the secondary battery 100 to supply power to the motor 200, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0112] In some embodiments of this application, the secondary battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0113] In this application, the secondary battery 100 can refer to a single battery cell 20, or it can refer to a single physical module comprising multiple battery cells 20 to provide higher voltage and capacity, which can be in the form of a battery pack, battery module, etc. The secondary battery 100 may include a housing 10 for encapsulating multiple battery cells 20, and the housing 10 can prevent liquids or other foreign objects from affecting the charging or discharging of the battery cells 20.

[0114] Figure 2 is an exploded structural diagram of a secondary battery 100 provided in some embodiments of this application. Referring to Figure 2, the secondary battery 100 includes a housing 10 and battery cells 20, with the battery cells 20 housed within the housing 10.

[0115] The housing 10 provides a receiving space 11 for the battery cell 20. In some embodiments, the housing 10 may include a first portion 12 and a second portion 13, which overlap each other to define the receiving space 11 for accommodating the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 may be sealed by a sealant (not shown), such as a sealing ring, sealant, etc.

[0116] The first part 12 and the second part 13 can be of various shapes, such as cuboids, cylinders, etc. The first part 12 can be a hollow structure with one side open to form a cavity for accommodating the battery cell 20, and the second part 13 can also be a hollow structure with one side open to form a cavity for accommodating the battery cell 20. The opening side of the second part 13 covers the opening side of the first part 12, thus forming a box 10 with a accommodating space 11. Of course, as shown in Figure 2, the first part 12 can also be a hollow structure with one side open, and the second part 13 can be a plate-like structure. The second part 13 covers the opening side of the first part 12, thus forming a box 10 with a accommodating space 11.

[0117] In the secondary battery 100, there can be one or more battery cells 20. If there are multiple battery cells 20, they can be connected in series, in parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells 20 are connected in both series and parallel. Multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed configuration, and then the whole assembly of multiple battery cells 20 is housed in the housing 10. Alternatively, multiple battery cells 20 can first be connected in series, in parallel, or in a mixed configuration to form a battery module, and then multiple battery modules can be connected in series, in parallel, or in a mixed configuration to form a whole, which is then housed in the housing 10. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes. Figure 2 illustrates an example of a square battery cell 20.

[0118] In some embodiments, the secondary battery 100 may further include a busbar (not shown), through which multiple battery cells 20 can be electrically connected to each other to achieve series, parallel, or mixed connection of multiple battery cells 20.

[0119] Figure 3 is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of this application, and Figure 4 is an exploded view of a battery cell 20 provided in some embodiments of this application. Referring to Figures 3 and 4, the battery cell 20 may include a housing 21, an end cap assembly 22, and an electrode assembly 23. The housing 21 has an opening 211, the electrode assembly 23 is accommodated within the housing 21, and the end cap assembly 22 is used to seal the opening 211.

[0120] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 is a cuboid structure, the housing 21 can also be a cuboid structure. Figures 3 and 4 exemplarily show the case where the housing 21 and the electrode assembly 23 are square.

[0121] The outer shell 21 can also be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc. This application embodiment does not impose any special restrictions on this.

[0122] The end cap assembly 22 includes an end cap 221 and electrode terminals 222. The end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a sealed mounting space (not shown) for accommodating the electrode assembly 23. The mounting space also accommodates an electrolyte, such as an electrolyte solution. As a component that outputs electrical energy to the electrode assembly 23, the end cap assembly 22 has electrode terminals 222 for electrical connection to the electrode assembly 23, specifically, the electrode terminals 222 are electrically connected to the tabs of the electrode assembly 23. For example, the electrode terminals 222 and the tabs are connected via a current collector 24 to achieve the electrical connection between the electrode terminals 222 and the tabs.

[0123] It should be noted that the opening 211 of the outer casing 21 can be one or two. If the outer casing 21 has one opening 211, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22. The two electrode terminals 222 are used to electrically connect to the positive electrode tab and the negative electrode tab of the electrode assembly 23, respectively. If the outer casing 21 has two openings 211, for example, the two openings 211 are located on opposite sides of the outer casing 21, the end cap assembly 22 can also be two, and the two end cap assemblies 22 respectively cover the two openings 211 of the outer casing 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal, used to electrically connect to the positive electrode tab of the electrode assembly 23; the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal, used to electrically connect to the negative electrode plate 231 of the electrode assembly 23.

[0124] In some embodiments, as shown in FIG4, the battery cell 20 may further include an insulating protective member 25 fixed to the outer periphery of the electrode assembly 23. The insulating protective member 25 is used to insulate and isolate the electrode assembly 23 from the housing 21. Exemplarily, the insulating protective member 25 is an adhesive tape bonded to the outer periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 surrounds the outer periphery of multiple electrode assemblies 23, forming multiple electrode assemblies 23 into an integral structure to maintain the structural stability of the electrode assembly 23.

[0125] The electrode assembly 23 includes a positive electrode plate, a negative electrode plate 231, and a separator. The electrode assembly 23 can be a wound electrode assembly or a stacked electrode assembly, and the embodiments of this application are not limited thereto.

[0126] The positive electrode sheet includes a positive current collector and a positive active material layer. The positive active material layer is coated on the surface of the positive current collector. The positive current collector without the positive active material layer protrudes from the positive current collector with the positive active material layer. The positive current collector without the positive active material layer serves as the positive electrode tab.

[0127] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0128] In some embodiments, when the secondary battery 100 is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811At least one of lithium nickel cobalt aluminum oxides and their modified compounds. Examples of lithium-containing phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0129] In some embodiments, when the secondary battery 100 is a sodium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for sodium-ion batteries. As examples, at least one of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds may be used. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0130] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x M02, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 <x≤1。

[0131] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (Y04). n- The price state.

[0132] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0133] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) n+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (Y04).n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) n+ The valence state; the halogen can be at least one of F, Cl and Br.

[0134] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3, NaM'PO4F (where M' is one or more of V, Fe, Mn, and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0135] Prussian blue compounds can be a class of compounds containing sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Examples of Prussian blue compounds include Na. a Me b Me' c (CN)6 where Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 <a≤2,0<b<1,0<c<1。

[0136] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0137] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0138] 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, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0139] The negative electrode sheet 231 includes a negative electrode current collector 2311 and a negative electrode active material layer 2312. The negative electrode active material layer 2312 is coated on the surface of the negative electrode current collector 2311. The negative electrode current collector 2311 without the negative electrode active material layer 2312 is protruding from the negative electrode current collector 2311 with the negative electrode active material layer 2312 coated. The negative electrode current collector 2311 without the negative electrode active material layer 2312 is used as a negative electrode tab.

[0140] In some embodiments, the negative electrode current collector 2311 may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0141] In some embodiments, the negative electrode active material layer 2312 includes a negative electrode active material, which may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0142] In some embodiments, the negative electrode active material layer 2312 may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0143] In some embodiments, the negative electrode active material layer 2312 may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0144] In some implementations, in order to ensure that a large current can pass through without melting, there are multiple positive electrode tabs stacked together, and multiple negative electrode tabs stacked together.

[0145] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0146] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polytetrafluoroethylene. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0147] The electrolyte acts as a conductor of ions between the positive and negative electrode plates 231. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0148] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0149] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0150] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl 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.

[0151] In some embodiments, the electrolyte may optionally include 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 battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0152] This application provides a secondary battery, wherein the battery cell 20 includes a negative electrode sheet 231, the negative electrode sheet 231 includes a negative current collector 2311 and a negative active material layer 2312 attached to at least one side of the negative current collector 2311; the negative active material layer 2312 includes a polyacrylic acid binder, the polyacrylic acid binder includes flexible groups, the flexible groups include at least one of ester groups or ether groups.

[0153] Referring to Figure 5, in one embodiment, a negative electrode active material layer 2312 is disposed on one surface of the negative electrode current collector 2311; referring to Figure 6, in another embodiment, a negative electrode active material layer 2312 is disposed on both surfaces of the negative electrode current collector 2311.

[0154] Flexible groups refer to groups that are flexible, such as ester groups (R1-COOR2) and ether groups (R1-O-R2).

[0155] The groups in the binder can be detected by infrared spectroscopy (IR) and nuclear magnetic resonance (NMR) 1H and 1C spectroscopy. For example, the specific process of NMR 1H and 1C spectroscopy is as follows: use deuterated solvents such as CCl4 and deuterated chloroform to dissolve the sample and measure H1-NMR and C13-NMR.

[0156] This secondary battery 100 employs a polyacrylic acid binder containing flexible groups, which allows for the winding of the negative electrode active material in the negative electrode active material layer, achieving a "linear" coating. This provides effective binding of the negative electrode active material, significantly increasing the adhesion between the particles and thus mitigating the expansion of the negative electrode sheet. Simultaneously, the ester and ether groups, with their CO bonds and fewer atoms surrounding the oxygen atom, result in less steric hindrance for internal rotation, making the molecular chains more flexible. This flexibility contributes to the flexibility of the polyacrylic acid binder, which in turn enhances the flexibility of the slurry used in the preparation of the negative electrode active material layer. This reduces the brittleness of the prepared negative electrode active material layer and consequently minimizes powder shedding.

[0157] In the technical solution of this application embodiment, the polyacrylic adhesive includes structural units derived from the monomer shown in Formula 1.

[0158] Formula 1:

[0159] Among them, R 01 Including any one or more of H, halogens, substituted or unsubstituted C1-C6 saturated alkyl groups, and substituted or unsubstituted C2-C6 alkenyl groups, R 02 It includes flexible groups, which include any one or more of C2-C6 ester groups or C2-C6 ether groups.

[0160] Those skilled in the art will understand that the structural unit derived from the monomer shown in Formula 1 can be

[0161] By using monomers containing flexible groups as reactive monomers, structural units of polyacrylic acid binders are formed, which can reduce the brittleness of the entire negative electrode active material layer, thereby reducing the severity of powder shedding from the negative electrode active material layer.

[0162] Furthermore, the monomer shown in Formula 1 includes at least one of hydroxyethyl acrylate, hydroxybutyl vinyl ether, methyl acrylate, ethyl acrylate, butyl acrylate, or ethyl butyrate. By using monomers containing flexible groups, such as hydroxyethyl acrylate, hydroxybutyl vinyl ether, methyl acrylate, ethyl acrylate, butyl acrylate, or ethyl butyrate, as reactive monomers, the structural unit of the polyacrylic acid binder is formed. This polyacrylic acid binder can reduce the brittleness of the entire negative electrode active material layer, thereby reducing the severity of powder shedding from the negative electrode active material layer.

[0163] In the technical solution of this application embodiment, the structural unit of the monomer derived from Formula 1 accounts for 10%-20% of the mass of the polyacrylic adhesive. By controlling the structural unit of the monomer derived from Formula 1 to account for 10%-20% of the mass of the entire polyacrylic adhesive, the polyacrylic adhesive can have better flexibility and reduce the probability of powder shedding from the negative electrode sheet.

[0164] For example, the mass percentage of the structural unit derived from the monomer shown in Formula 1 in the polyacrylic adhesive can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%, or any value within the range of 10% to 20%.

[0165] In the technical solution of this application embodiment, the weight-average molecular weight of the polyacrylic adhesive is 2 million to 2.5 million.

[0166] Weight-average molecular weight (MAM) is the statistical average molecular weight of a polymer by mass, that is, the molecular weight averaged per unit weight. Methods for determining MAM include light scattering and gel permeation chromatography.

[0167] The higher the weight-average molecular weight of polyacrylic adhesives, the better their bonding performance. Conversely, the lower the weight-average molecular weight, the better their dispersibility. By controlling the weight-average molecular weight of polyacrylic adhesives to be between 2 million and 2.5 million, good dispersion can be achieved without the addition of additional additives, while also maintaining a good bonding effect.

[0168] For example, the weight-average molecular weight of polyacrylic adhesives can be 2 million, 2.05 million, 2.1 million, 2.15 million, 2.2 million, 2.25 million, 2.3 million, 2.35 million, 2.4 million, 2.45 million, or 2.5 million, etc., or any value in the range of 2 million to 2.5 million.

[0169] In the technical solution of this application embodiment, the polyacrylic adhesive includes structural units derived from the monomer shown in Formula 2.

[0170] Formula 2:

[0171] Among them, R 03 Including any one or more of H, halogens, substituted or unsubstituted C1-C6 saturated alkyl groups, and substituted or unsubstituted C2-C6 alkenyl groups; R 04 The active material includes polar groups, which include any one or more of the following: amino, hydroxyl, carboxyl, carboxylate, cyano, amide, phenolic, sulfonic acid, or sulfonate groups. These groups, such as amino, hydroxyl, carboxyl, carboxylate, cyano, amide, phenolic, or sulfonic acid groups, possess strong polarity and can form strong hydrogen bonds with the surface of the active material, thus better promoting the dispersion of the negative electrode active material and better suppressing the volume expansion of the negative electrode active material layer.

[0172] Those skilled in the art will understand that the polarity of a polar group is generally positively correlated with its dipole moment, and the greater the polarity of the polar group, the stronger the hydrogen bonding force it forms with the surface of the negative electrode active material. In other embodiments, the polar group can be a polar group with a dipole moment of not less than 0.5D. This can better promote the dispersion of the negative electrode active material, thereby better suppressing the volume expansion of the negative electrode active material layer.

[0173] Those skilled in the art will understand that the structural unit derived from the monomer shown in Formula 2 can be

[0174] Furthermore, the monomers shown in Formula 2 include at least one of acrylic acid, butenoic acid, lithium acrylate sulfonate, allyl alcohol, acrylamide, isobutyleneamide, acrylonitrile, or isobutylene nitrile. By using monomers containing polar groups, such as acrylic acid, butenoic acid, lithium acrylate sulfonate, allyl alcohol, acrylamide, isobutyleneamide, acrylonitrile, or isobutylene nitrile, as reactive monomers, the structural unit of the polyacrylic acid binder is formed. This allows the polyacrylic acid binder to form strong hydrogen bonds with the surface of the active material, which can better promote the dispersion of the negative electrode active material and thus better suppress the volume expansion of the negative electrode active material layer.

[0175] In the technical solution of this application embodiment, the structural unit of the monomer derived from Formula 2 accounts for 80%-90% of the mass of the polyacrylic adhesive. By controlling the structural unit of the monomer derived from Formula 2 to account for 80%-90% of the mass of the entire polyacrylic adhesive, the polyacrylic adhesive can have better adhesion and the negative electrode sheet can have lower expansion.

[0176] For example, the mass percentage of the structural unit derived from the monomer shown in Formula 2 in the polyacrylic adhesive can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, or 90%, or any value within the range of 80% to 90%.

[0177] In the technical solution of this application embodiment, the polyacrylic adhesive includes the structural formula shown in Formula I:

[0178] Formula I:

[0179] Wherein, R1, R2 and R3 are each independently selected from polar groups, and the polar groups include any one or more of the following: amino group, hydroxyl group, carboxyl group, carboxyl group, cyano group, amide group, phenolic group, sulfonic acid group or sulfonate group;

[0180] R4 is selected from flexible groups, including at least one of C2-C6 ester groups or C2-C6 ether groups;

[0181] R5, R6, R7 and R8 are each independently selected from one or more of H, halogens, substituted or unsubstituted C1 to C6 saturated alkyl groups or substituted or unsubstituted C2 to C6 alkenyl groups;

[0182] a, b, c, and d are each independently selected from positive integers.

[0183] In the technical solutions of this application embodiment, R5, R6, R7 and R8 are each independently selected from H.

[0184] Those skilled in the art will understand that when R5, R6, R7, and R8 are each independently selected from H, the polyacrylic adhesive includes the structural formula shown in Formula II:

[0185] Formula II:

[0186] Wherein, R1, R2 and R3 are each independently selected from polar groups, and the polar groups include any one or more of the following: amino group, hydroxyl group, carboxyl group, carboxyl group, cyano group, amide group, phenolic group, sulfonic acid group or sulfonate group;

[0187] R4 is selected from flexible groups, including at least one of C2-C6 ester groups or C2-C6 ether groups;

[0188] a, b, c, and d are each independently selected from positive integers.

[0189] In the technical solution of this application embodiment, R1 is selected from at least one of a carboxyl group or a sulfonate group; R2 is selected from a cyano group; R3 is selected from an amide group; wherein, the carboxyl group can be selected from lithium carboxyl; the sulfonate group can be selected from lithium sulfonate. By controlling the selection of each group from different functional groups, more functions are given to the binder. The introduction of carboxyl groups or sulfonate groups can facilitate lithium-ion conduction, thereby improving the rate performance of the battery; the introduction of cyano groups can have a synergistic effect with the electrolyte of the battery, thereby facilitating the wetting of the electrode; the introduction of amide groups can increase the strength of the slurry, thus making it suitable for electrode preparation processes in which an active material layer film is first formed and then composited with a current collector. Using lithium carboxyl as a carboxyl group to introduce binder enables the binder to act as an artificial SEI film, improving the cycle performance of the battery.

[0190] The following is a detailed explanation using two specific examples of the preparation of polyacrylic acid adhesives: 1. Add the free radical initiator and the monomers to be polymerized in a certain mass ratio (acrylic acid: acrylate: acrylonitrile: acrylamide = 50:10:20:20), heat to 80℃ and then keep it at that temperature for 30 hours for polymerization. Then add LiOH for neutralization, filter, cool and defoam to obtain adhesive 1.

[0191] 2. The free radical initiator and monomers to be polymerized were added in a certain mass ratio (acrylic acid: acrylate: acrylonitrile: acrylamide = 50:20:10:20), heated to 80℃ and then held at that temperature for 30 hours for polymerization. LiOH was then added for neutralization, filtered, and cooled to defoam, yielding binder 2. The obtained product was subjected to infrared spectroscopy; the results are shown in Figure 7.

[0192] It should be noted that polyacrylic acid binders of different molecular weights can be prepared by adjusting the mixing ratio of raw materials, controlling the temperature range, and time. Furthermore, different R1, R2, R3, and R4 groups on the binder can be obtained by substituting the raw materials, or by substituting them after the binder is prepared. The monomers to be polymerized can be: hydroxyethyl acrylate, hydroxybutyl vinyl ether, methyl acrylate, ethyl acrylate, butyl acrylate, ethyl butyrate, acrylic acid, butyric acid, lithium acrylate sulfonate, allyl alcohol, acrylamide, isobutyleneamide, acrylonitrile, or isobutylene nitrile, etc.

[0193] In the technical solution of this application embodiment, the mass ratio of structural units R1, R2, R3, and R4 in the polyacrylic binder is (3-7):(1-2):(1-2):(1-2). By controlling the mass ratio of structural units R1, R2, R3, and R4 in the polyacrylic binder to (3-7):(1-2):(1-2), the expansion of the negative electrode sheet in the secondary battery can be improved while reducing the brittleness of the negative electrode active material layer. In the technical solution of this application embodiment, the mass percentage of the polyacrylic binder in the negative electrode active material layer is 1%-2%.

[0194] The greater the amount of polyacrylic binder used, the better the bonding effect on the negative electrode active material, which in turn helps to reduce the probability of expansion of the negative electrode active material layer. The smaller the amount of polyacrylic binder used, the better the energy density of the secondary battery 100 and the wetting of the negative electrode sheet. By controlling the mass ratio of polyacrylic binder in the negative electrode active material layer to 1% to 2%, the energy density, anti-expansion performance and wetting speed of the negative electrode sheet of the secondary battery 100 can be balanced.

[0195] For example, the mass percentage of polyacrylic acid binder in the negative electrode active material layer can be 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%, or any value within the range of 1% to 2%.

[0196] In the technical solution of this application embodiment, the negative electrode active material layer also includes polytetrafluoroethylene (PTFE). PTFE acts as a reinforcing agent; by adding PTFE to the negative electrode active material layer, it is more effective in confining the negative electrode active material, thereby improving the expansion of the negative electrode sheet.

[0197] In the technical solution of this application embodiment, the mass percentage of polytetrafluoroethylene in the negative electrode active material layer is 0.1% to 0.5%. By controlling the mass percentage of polytetrafluoroethylene in the negative electrode active material layer to be 0.1% to 0.5%, the negative electrode active material can achieve better confinement.

[0198] For example, the mass percentage of polytetrafluoroethylene in the negative electrode active material layer can be 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%, or any value within the range of 0.1% to 0.5%.

[0199] In the technical solution of this application embodiment, the expansion rate of the negative electrode active material layer of the secondary battery does not exceed 21.4% when fully charged. By controlling the expansion rate of the negative electrode sheet to not exceed 21.4% when fully charged, it is beneficial to the service life of the battery.

[0200] This application also provides a polyacrylic adhesive, which includes flexible groups, including at least one of ester groups or ether groups.

[0201] Flexible groups refer to groups that are flexible, such as ester groups (R1-COOR2) and ether groups (R1-O-R2).

[0202] The groups in the binder can be detected by infrared spectroscopy (IR) and nuclear magnetic resonance (NMR) 1H and 1C spectroscopy. For example, the specific process of NMR 1H and 1C spectroscopy is as follows: use deuterated solvents such as CCl4 and deuterated chloroform to dissolve the sample and measure H1-NMR and C13-NMR.

[0203] Applying this polyacrylic acid binder containing flexible groups to secondary batteries enables the winding of the negative electrode active material in the negative electrode active material layer, achieving "linear" coating and providing good binding effect. This effectively increases the adhesion between the negative electrode active material particles, thereby improving the expansion of the negative electrode sheet. Simultaneously, the ester and ether groups, with their CO bonds and fewer atoms surrounding the oxygen atom, result in less steric hindrance for internal rotation, making the molecular chains more flexible. This flexibility reduces the brittleness of the entire negative electrode active material layer, thus mitigating the severity of powder shedding.

[0204] In the technical solution of this application embodiment, the polyacrylic adhesive includes structural units derived from the monomer shown in Formula 1, Formula 1: Among them, R 01 Including any one or more of H, halogens, substituted or unsubstituted C1-C6 saturated alkyl groups, and substituted or unsubstituted C2-C6 alkenyl groups, R 02 The material includes flexible groups, which include any one or more of C2-C6 ester groups or C2-C6 ether groups. By using monomers containing flexible groups as reactive monomers, structural units of polyacrylic acid binders are formed, enabling these binders to reduce the brittleness of the entire negative electrode active material layer, thereby reducing the severity of powder shedding from the negative electrode active material layer.

[0205] Those skilled in the art will understand that the structural unit derived from the monomer shown in Formula 1 can be

[0206] Furthermore, the monomer shown in Formula 1 includes at least one of hydroxyethyl acrylate, hydroxybutyl vinyl ether, methyl acrylate, ethyl acrylate, butyl acrylate, or ethyl butyrate. By using monomers containing flexible groups, such as hydroxyethyl acrylate, hydroxybutyl vinyl ether, methyl acrylate, ethyl acrylate, butyl acrylate, or ethyl butyrate, as reactive monomers, the structural unit of the polyacrylic acid binder is formed. This polyacrylic acid binder can reduce the brittleness of the entire negative electrode active material layer, thereby reducing the severity of powder shedding from the negative electrode active material layer.

[0207] In the technical solution of this application embodiment, the structural unit of the monomer derived from Formula 1 accounts for 10%-20% of the mass of the polyacrylic adhesive. By controlling the structural unit of the monomer derived from Formula 1 to account for 10%-20% of the mass of the entire polyacrylic adhesive, the polyacrylic adhesive can have better flexibility and reduce the probability of powder shedding from the negative electrode sheet.

[0208] In the technical solution of this application embodiment, the weight-average molecular weight of the polyacrylic adhesive is 2 million to 2.5 million. Weight-average molecular weight is the statistical average molecular weight of the polymer by mass, that is, the molecular weight obtained on average per unit weight. Methods for determining weight-average molecular weight include light scattering and gel permeation chromatography. A higher weight-average molecular weight of the polyacrylic adhesive is more beneficial to its bonding performance, while a lower weight-average molecular weight is more beneficial to its dispersibility. By controlling the weight-average molecular weight of the polyacrylic adhesive to be between 2 million and 2.5 million, good dispersion can be achieved without adding additional additives, while also achieving a good bonding effect.

[0209] In the technical solution of this application embodiment, the polyacrylic adhesive includes structural units derived from the monomer shown in Formula 2, Formula 2: Among them, R 03 Including any one or more of H, halogens, substituted or unsubstituted C1-C6 saturated alkyl groups, and substituted or unsubstituted C2-C6 alkenyl groups; R 04 The active material includes polar groups, which include any one or more of the following: amino, hydroxyl, carboxyl, carboxylate, cyano, amide, phenolic, sulfonic acid, or sulfonate groups. These groups, such as amino, hydroxyl, carboxyl, carboxylate, cyano, amide, phenolic, or sulfonic acid groups, possess strong polarity and can form strong hydrogen bonds with the surface of the active material, thus better promoting the dispersion of the negative electrode active material and better suppressing the volume expansion of the negative electrode active material layer.

[0210] Those skilled in the art will understand that the structural unit derived from the monomer shown in Formula 2 can be

[0211] Furthermore, the monomers shown in Formula 2 include at least one of acrylic acid, butenoic acid, lithium acrylate sulfonate, allyl alcohol, acrylamide, isobutyleneamide, acrylonitrile, or isobutylene nitrile. By using monomers containing polar groups, such as acrylic acid, butenoic acid, lithium acrylate sulfonate, allyl alcohol, acrylamide, isobutyleneamide, acrylonitrile, or isobutylene nitrile, as reactive monomers, the structural unit of the polyacrylic acid binder is formed. This allows the polyacrylic acid binder to form strong hydrogen bonds with the surface of the active material, which can better promote the dispersion of the negative electrode active material and thus better suppress the volume expansion of the negative electrode active material layer.

[0212] In the technical solution of this application embodiment, the structural unit of the monomer derived from Formula 2 accounts for 80%-90% of the mass of the polyacrylic adhesive. By controlling the structural unit of the monomer derived from Formula 2 to account for 80%-90% of the mass of the entire polyacrylic adhesive, the polyacrylic adhesive can have better adhesion and the negative electrode sheet can have lower expansion.

[0213] In the technical solution of this application embodiment, the polyacrylic adhesive includes the structural formula shown in Formula I: Formula I: Wherein, R1, R2, and R3 are each independently selected from polar groups, including any one or more of amino, hydroxyl, carboxyl, carboxylate, cyano, amide, phenol, sulfonic acid, or sulfonate groups; R4 is selected from flexible groups, including at least one of C2-C6 ester or C2-C6 ether groups; R5, R6, R7, and R8 are each independently selected from any one or more of H, halogen, substituted or unsubstituted C1-C6 saturated alkyl or substituted or unsubstituted C2-C6 alkenyl groups; a, b, c, and d are each independently selected from positive integers.

[0214] Furthermore, R5, R6, R7 and R8 are each independently selected from H.

[0215] Those skilled in the art will understand that when R5, R6, R7, and R8 are each independently selected from H, the polyacrylic adhesive includes the structure shown in Formula II: Formula II: Wherein, R1, R2 and R3 are each independently selected from polar groups, including any one or more of amino, hydroxyl, carboxyl, carboxylate, cyano, amide, phenol, sulfonic acid or sulfonate groups; R4 is selected from flexible groups, including at least one of C2-C6 ester or C2-C6 ether groups; a, b, c and d are each independently selected from positive integers.

[0216] Furthermore, R1 is selected from at least one of a carboxyl group or a sulfonate group; R2 is selected from a cyano group; R3 is selected from an amide group; the carboxyl group includes lithium carboxyl; the sulfonate group includes lithium sulfonate. By controlling the selection of each group from different functional groups, more functions can be imparted to the binder. Among them, the introduction of groups such as carboxyl groups and sulfonate groups can facilitate lithium-ion conduction, thereby improving the rate performance of the battery; the introduction of groups such as cyano groups can have a synergistic effect with the electrolyte of the battery, thereby facilitating the wetting of the electrode; the introduction of groups such as amide groups can increase the strength of the slurry, thus making it suitable for electrode preparation processes in which an active material layer film is first formed and then composited with a current collector.

[0217] In the technical solution of this application embodiment, the mass ratio of structural units R1, R2, R3, and R4 in the polyacrylic binder is (3-7):(1-2):(1-2):(1-2). By controlling the mass ratio of structural units R1, R2, R3, and R4 in the polyacrylic binder to (3-7):(1-2):(1-2), the expansion of the negative electrode sheet in the secondary battery can be improved while reducing the brittleness of the negative electrode active material layer.

[0218] Having introduced the polyacrylic acid binder and its application to the corresponding battery electrode structure, the preparation method of the electrode will now be described in detail.

[0219] The preparation method of the electrode includes the following steps: preparing active materials, conductive agents, binders and reinforcing agents (polytetrafluoroethylene) into agglomerated materials, extruding and hot-pressing the obtained agglomerated materials to form a thick film, rolling the obtained thick film to thin it and then compounding it with a current collector, and drying it to obtain the electrode. The binder includes polyacrylic acid binders, and the binder contains flexible groups, including at least one of ester groups or ether groups.

[0220] This method utilizes a polyacrylic acid binder containing flexible groups to achieve linear coating of the active material in the active material layer, effectively increasing the adhesion between active material particles and thus improving electrode expansion. Simultaneously, the flexible groups reduce the brittleness of the entire active material layer, thereby decreasing the probability of powder shedding from the active material layer.

[0221] Figure 8 is a flowchart of a method for preparing an electrode according to some embodiments of this application. Referring to Figure 8, an embodiment of this application provides a method for preparing an electrode, the method including:

[0222] S110, Preparation of adhesive solution: Dispersing the adhesive in a solvent to form an adhesive solution.

[0223] The solvent can be one or more of deionized water, dimethyl glutarate, and N-methylpyrrolidone.

[0224] S120, Preparation of Agglomerated Material: The active material, conductive agent, reinforcing agent (polytetrafluoroethylene) and adhesive are kneaded together to form a granular material.

[0225] The solid content of the lumpy material is 70%–95%. Kneading can be performed using an internal mixer, kneader, or twin-screw extruder. The screw element of the twin-screw extruder can be a combination of one or more of the following: threaded parts, meshing blocks, and toothed discs, to fully balance shearing, mixing, and conveying capacity.

[0226] S130, Preparation of thick film: The obtained agglomerated material is extruded or hot-pressed to obtain a thick film.

[0227] Thick film preparation equipment can include twin-screw extruders, hydraulic extruders, plunger extruders, hot presses, and open mills. The screw element of a twin-screw extruder can be composed of one or more of threaded components, meshing blocks, and toothed discs, to fully balance shearing, mixing, and conveying capabilities.

[0228] S140, Preparation of electrode sheet: The obtained thick film sheet is thinned by rolling and then combined with the current collector, and then dried to obtain the electrode sheet.

[0229] The above preparation process requires only a small amount of solvent. Therefore, the extruded film can greatly promote particle slippage during the rolling thinning process. The solvent acts like a "lubricant," making the film less prone to over-rolling, resulting in a more flexible film with better processing performance. The electrode is also easier to compact, facilitating the fabrication of thicker electrodes and achieving high-energy-density batteries. The amount of solvent added to the formulation is far lower than that used in industry wet coating processes, significantly reducing drying energy consumption and environmental pollution. Of course, wet coating processes can also be used to prepare the electrode in other embodiments.

[0230] After preparing the electrode sheet (which can be a positive electrode sheet and / or a negative electrode sheet 231), the first separator, the positive electrode sheet, the second separator, and the negative electrode sheet 231 are stacked in sequence, wound to form a wound flat structure, and then hot-pressed to obtain a wound electrode assembly 23; or, after preparing the electrode sheet (which can be a positive electrode sheet and / or a negative electrode sheet 231), the positive electrode sheet, the separator, the negative electrode sheet 231, and the separator are stacked in sequence to form a stacked electrode assembly 23.

[0231] The electrode assembly 23 can be used to prepare a battery cell 20, which can be used to prepare a secondary battery 100 and provide electrical energy to electrical devices.

[0232] The following examples will describe one or more embodiments in more detail. Of course, these examples do not limit the scope of the one or more embodiments.

[0233] Examples and Comparative Examples

[0234] Example 1

[0235] Preparation of the positive electrode sheet

[0236] Lithium iron phosphate (LiFePO4), conductive carbon black, and PVDF (PVDF) binder were mixed in a specific mass ratio and then N-methylpyrrolidone (NMP) solvent was added. The slurry had a solid content of 65%. This mixture was then coated onto both sides of an aluminum foil, and after cold pressing and cutting, the positive electrode sheet was obtained. The weight percentages of the positive active material layer were 97.7%, the conductive agent 0.5%, and the binder 1.8%.

[0237] Preparation of adhesives

[0238] A certain mass ratio of monomers to be polymerized (acrylic acid:acrylonitrile:acrylamide:hydroxyethyl acrylate in a mass ratio of 50%:20%:20%:10%) and free radical initiator ammonium persulfate were mixed and fed into the reactor. The polymerization reaction was carried out at a reaction temperature of 65±2℃. Then, LiOH was added to neutralize the mixture until the pH reached 7.2. The mixture was then filtered, cooled, and defoamed to obtain the binder.

[0239] In Example 1, the amount of initiator was 0.15 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time was 8 h.

[0240] Preparation of the negative electrode sheet

[0241] The negative electrode active material, artificial graphite, the binder prepared above, the conductive agent, carbon black (Super P), and the reinforcing agent, PTFE, are thoroughly mixed in an appropriate amount of deionized water to form a uniform negative electrode slurry. This slurry is then uniformly coated onto the surface of a copper foil current collector. After drying and cold pressing, the negative electrode sheet is obtained. The combined weight of the negative electrode active material and binder is 99.1% of the negative electrode active material layer, the conductive agent is 0.6% of the negative electrode active material layer, and the PTFE is 0.3% of the negative electrode active material layer.

[0242] Preparation of Electrolyte

[0243] Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, thoroughly dried LiPF6 was dissolved in this organic solvent to obtain an electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0244]

Isolation Film

[0245] A porous polyethylene membrane with a thickness of 13μm was used as the separator.

[0246] [Preparation of Secondary Batteries]

[0247] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0248] Example 2

[0249] The difference between Example 2 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: hydroxyethyl acrylate = 50%: 20%: 20%: 10%, the amount of initiator is 0.12 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 15 h. The rest are similar to Example 1.

[0250] Example 3

[0251] The difference between Example 3 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: hydroxyethyl acrylate = 50%: 20%: 20%: 10%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 20 h. The rest are similar to Example 1.

[0252] Example 4

[0253] The difference between Example 4 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: hydroxybutyl vinyl ether = 50%: 20%: 20%: 10%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 20 h. The rest are similar to Example 1.

[0254] Example 5

[0255] The difference between Example 5 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: hydroxyethyl acrylate = 50%: 20%: 10%: 20%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 20 h. The rest are similar to Example 1.

[0256] Example 6

[0257] The difference between Example 6 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: hydroxyethyl acrylate = 50%: 10%: 20%: 20%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 20 h. The rest are similar to Example 1.

[0258] Example 7

[0259] The difference between Example 7 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: lithium sulfonate acrylate: hydroxyethyl acrylate = 50%: 20%: 10%: 10%: 10%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 20 h. The rest is similar to Example 1.

[0260] Example 8

[0261] The difference between Example 8 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: lithium sulfonate acrylate: hydroxyethyl acrylate = 45%: 20%: 10%: 15%: 10%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 20 h. The rest is similar to Example 1.

[0262] Example 9

[0263] The difference between Example 9 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: lithium acrylate sulfonate: hydroxyethyl acrylate = 35%: 20%: 10%: 25%: 10%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 20 h. The rest is similar to Example 1.

[0264] Example 10

[0265] The difference between Example 10 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: allyl alcohol: hydroxyethyl acrylate = 50%: 20%: 10%: 10%: 10%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 20 h. The rest is similar to Example 1.

[0266] Example 11

[0267] The difference between Example 11 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: allyl alcohol: hydroxyethyl acrylate = 45%: 20%: 10%: 15%: 10%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 20 h. The rest is similar to Example 1.

[0268] Example 12

[0269] The difference between Example 12 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: allyl alcohol: hydroxyethyl acrylate = 35%: 20%: 10%: 25%: 10%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 20 h. The rest is similar to Example 1.

[0270] Example 13

[0271] The difference between Example 13 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: hydroxyethyl acrylate = 60%: 20%: 10%: 10%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 20 h. The rest are similar to Example 1.

[0272] Example 14

[0273] The difference between Example 14 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: hydroxyethyl acrylate = 60%: 10%: 20%: 10%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 20 h. The rest are similar to Example 1.

[0274] Example 15

[0275] The difference between Example 15 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: hydroxyethyl acrylate = 60%: 10%: 10%: 20%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 20 h. The rest are similar to Example 1.

[0276] Example 16

[0277] The difference between Example 16 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide: hydroxyethyl acrylate = 70%: 10%: 10%: 10%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 20 h. The rest are similar to Example 1.

[0278] Example 17

[0279] The difference between Example 17 and Example 1 is that the mass percentage of the binder in the negative electrode active material layer is 1.00%, while the rest is the same as in Example 1.

[0280] Example 18

[0281] The difference between Example 18 and Example 1 is that the mass percentage of the binder in the negative electrode active material layer is 2.00%, while the rest is the same as in Example 1.

[0282] Comparative Example 1

[0283] The difference between Comparative Example 1 and Example 1 is that in the preparation of the binder, the mass ratio of the monomers to be polymerized is: acrylic acid: acrylonitrile: acrylamide = 60%: 20%: 20%, the amount of initiator is 0.10 wt% of the total mass of the monomers to be polymerized, and the polymerization reaction time is 15 h. The rest are similar to Example 1.

[0284] Comparative Example 2

[0285] The difference between Comparative Example 2 and Example 1 is that the binder used is CMC and SBR, wherein the mass percentage of CMC in the negative electrode active material layer is 0.7% and the mass percentage of SBR in the negative electrode active material layer is 1.3%.

[0286] The main parameter controls for each embodiment and comparative example are shown in the table below:

[0287] In the table, " / " indicates that the substance was not added.

[0288] The electrodes and secondary batteries provided in each embodiment and comparative example were tested, including:

[0289] Adhesion test: Take the negative electrode sheet to be tested and cut it into a strip 400mm long * 30mm wide using a custom die. Then take a flat, thin steel plate, approximately 200-300mm long and 40-60mm wide. Apply a strip of double-sided tape (longer than the sample test length, 20mm wide) to the center of the steel plate and smooth it firmly to ensure it adheres tightly to the center. Peel off the double-sided tape and attach the electrode sheet to the tape strip. Then insert the steel plate with the attached electrode sheet into the lower clamp of the tensile testing machine and fix it vertically. Insert the electrode sheet without tape into the upper clamp and fix it, so that the electrode sheet attached to the tape forms a 180° angle with the electrode sheet fixed in the upper clamp. After fixing the test sample, calibrate and zero the sample, set the test width, electrode peeling length of 50mm, peeling speed of 100mm / min, and then start the test. After the test is completed, the load and fixture displacement data during the peeling process can be obtained. The adhesive force can be calculated as: adhesive force = load / double-sided tape width. Plotting the adhesive force against the displacement will give the peeling force curve. The adhesive force corresponding to the flat point of the curve is the adhesive force of the electrode.

[0290] Cohesion Test: Take the negative electrode sheet to be tested and cut a sample with a width of 30mm and a length of 130mm using a blade. Apply NITTO.NO5000NS double-sided adhesive to a steel plate, with a width of 20mm and a length of 130mm. Place the cut negative electrode sheet sample onto the double-sided adhesive, ensuring the side of the negative current collector aluminum foil facing away from the negative electrode active layer faces the double-sided adhesive and is bonded to it. Smoothly adhere a 20mm wide and 270mm long piece of low-tack green tape (MD-XTG-620-2335L) to the surface of the negative electrode active layer in the negative electrode sheet sample and secure the opposite ends of the paper bag with wrinkle adhesive. Then, roll the negative electrode sheet sample three times in the same direction using a 3kg roller to obtain the test sample. Then, the sample to be tested is placed between the upper and lower clamps of the testing machine (Instron 3343), so that the direction pointing to the negative electrode sample (i.e., the thickness direction of the negative electrode active layer) is parallel to the horizontal direction. The end of the steel plate not attached to the negative electrode sample is fixed with the lower clamp. The low-viscosity green tape is folded upward and fixed with the upper clamp. The upper clamp of the testing machine applies a peeling force at a peeling speed of 10 mm / min. When the upper clamp moves 50 mm, the peeling force F (in N) is recorded. The cohesive force of the negative electrode active layer is f2, f2 = F / L, where the unit of f2 is N / m and L is the width of the low-viscosity green tape.

[0291] Expansion rate test of negative electrode sheet under full charge: The secondary battery was disassembled under low relative humidity conditions to obtain the negative electrode sheet. The thickness of the negative electrode sheet after cold pressing and after full charge (at 25℃, constant current charging at a rate of 0.5C to 3.65V) was measured respectively. The expansion rate of the negative electrode sheet under full charge was calculated by normalizing the thickness of the negative electrode sheet after cold pressing as the standard. The expansion rate of the negative electrode sheet under full charge = (thickness of the negative electrode sheet after full charge - thickness of the negative electrode sheet after cold pressing) / thickness of the negative electrode sheet after cold pressing.

[0292] Powder shedding test method: After disassembling the secondary battery, bend the negative electrode sheet obtained at 180° and visually inspect whether black powder falls off. If so, it is determined to be powder shedding.

[0293] The test results are shown in the table below:

[0294] In the table, " / " indicates that the value was not tested or there are no special cases.

[0295] As can be seen from the table above, the negative electrode sheet prepared using the binder provided in the embodiments of this application has good anti-expansion performance. By comparing Examples 1 to 18 and Comparative Examples 1 to 2, it can be seen that the binder provided in the embodiments of this application can improve the expansion rate of the negative electrode sheet under full charge state while reducing the brittleness of the negative electrode active material layer.

[0296] Comparison of data from Examples 1 to 3 shows that as the weight-average molecular weight of the binder gradually increases, the adhesion and cohesion of the electrode active material layer generally increase, while the expansion rate of the negative electrode under full charge generally decreases. Controlling the weight-average molecular weight of the binder to 200w to 250w enables the electrode active material layer to have good adhesion and cohesion, as well as a good expansion rate of the negative electrode under full charge. At the same time, the electrode has a high pass rate and significantly reduces the powder shedding of the active material layer.

[0297] A comparison of the data from Examples 3 and 4 shows that the binder containing flexible groups such as ester and ether groups has better adhesion, cohesion, and expansion rate of the negative electrode sheet under full charge.

[0298] Comparison of data from Examples 3 and 5 to 6 shows that as the proportion of flexible monomer groups gradually increases, the adhesion and cohesion of the active material layer of the electrode gradually decrease, while the expansion rate of the negative electrode under full charge generally increases. Controlling the proportion of flexible monomer groups to 10% to 20% can keep the expansion rate of the negative electrode under full charge below 20% and significantly reduce the powder shedding of the active material layer.

[0299] A comparison of the data from Examples 3 and 7 to 16 shows that the higher the proportion of monomers containing carboxylic acid groups and / or sulfonate groups in the polar monomers, the greater the overall expansion rate of the negative electrode sheet under full charge. Controlling the proportion of monomers containing carboxylic acid groups and / or sulfonate groups to below 60% can ensure that the expansion rate of the negative electrode sheet under full charge is below 21.4%.

[0300] By comparing the data from Examples 3 and 17 to 18, it can be seen that as the mass percentage of the binder in the negative electrode active material layer increases, the expansion rate of the negative electrode sheet under full charge generally shows a gradual decreasing trend. When the mass percentage of the binder in the negative electrode active material layer is above 1%, the expansion rate of the negative electrode sheet under full charge can be kept below 20%.

[0301] The above are merely specific embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A secondary battery characterized by comprising: The secondary battery includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative active material layer attached to at least one side of the negative current collector; the negative active material layer includes a polyacrylic binder, the polyacrylic binder includes flexible groups, the flexible groups include at least one of ester groups or ether groups.

2. The secondary battery according to claim 1, characterized by The polyacrylic adhesive comprises structural units derived from the monomer shown in Formula 1. Formula 1: wherein R 01 including any one or more of H, halogen, substituted or unsubstituted C1-C6 saturated alkyl, and substituted or unsubstituted C2-C6 alkenyl, R 02 including a flexible group comprising any one or more of a C2-C6 ester group or a C2-C6 ether group.

3. The secondary battery according to claim 2, characterized by The monomer shown in Formula 1 includes at least one of hydroxyethyl acrylate, hydroxybutyl vinyl ether, methyl acrylate, ethyl acrylate, butyl acrylate, or ethyl butenoate.

4. The secondary battery according to any one of claims 2 to 3, characterized by, In the polyacrylic adhesive, the structural units derived from the monomer shown in Formula 1 account for 10%-20% by mass.

5. The secondary battery according to any one of claims 1 to 4, characterized by The weight-average molecular weight of the polyacrylic adhesive is 2 million to 2.5 million.

6. The secondary battery according to any one of claims 1 to 5, characterized by The polyacrylic adhesive comprises structural units derived from the monomer shown in Formula 2. Formula 2: wherein R 03 including any one or more of H, halogen, substituted or unsubstituted C1-C6 saturated alkyl, and substituted or unsubstituted C2-C6 alkenyl; R 04 including a polar group comprising any one or more of an amine group, a hydroxyl group, a carboxyl group, a carboxylate salt, a cyano group, an amide group, a phenol group, a sulfonic acid group, or a sulfonate salt group.

7. The secondary battery according to claim 6, characterized by The monomers shown in Formula 2 include at least one of acrylic acid, butenoic acid, lithium acrylate sulfonate, allyl alcohol, acrylamide, isobutyleneamide, acrylonitrile, or isobutylene nitrile.

8. The secondary battery according to any one of claims 6 to 7, characterized by, In the polyacrylic adhesive, the structural units derived from the monomer shown in Formula 2 account for 80%-90% by mass.

9. The secondary battery according to any one of claims 1 to 8, characterized by, The polyacrylic adhesive includes the structural formula shown in Formula I: Formula I: Wherein, R1, R2 and R3 are each independently selected from polar groups, and the polar groups include any one or more of the following: amino group, hydroxyl group, carboxyl group, carboxyl group, cyano group, amide group, phenolic group, sulfonic acid group or sulfonate group; R4 is selected from flexible groups, including at least one of C2-C6 ester groups or C2-C6 ether groups; R5, R6, R7 and R8 are each independently selected from one or more of H, halogens, substituted or unsubstituted C1-C6 saturated alkyl groups and substituted or unsubstituted C2-C6 alkenyl groups; a, b, c, and d are each independently selected from positive integers.

10. The secondary battery according to claim 9, characterized by R5, R6, R7, and R8 are each independently selected from H.

11. The secondary battery according to claim 9, characterized by R1 is selected from at least one of a carboxylate group or a sulfonate group; and / or R2 is selected from cyano groups; and / or R3 is selected from amide groups; and / or The carboxyl group includes lithium carboxyl groups; and / or The sulfonate group includes lithium sulfonate.

12. The secondary battery of claim 11, wherein In the polyacrylic adhesive, the mass ratio of the structural unit to which R1, R2, R3, and R4 belong is (3-7):(1-2):(1-2):(1-2).

13. The secondary battery according to any one of claims 1 to 12, characterized by The polyacrylic binder accounts for 1% to 2% of the mass of the negative electrode active material layer.

14. The secondary battery according to any one of claims 1 to 13, characterized by, The negative electrode active material layer also includes polytetrafluoroethylene.

15. The secondary battery according to claim 14, characterized by The polytetrafluoroethylene (PTFE) accounts for 0.1% to 0.5% of the mass of the negative electrode active material layer.

16. The secondary battery according to any one of claims 1 to 15, characterized by When the secondary battery is fully charged, the expansion rate of the negative electrode does not exceed 21.4%.

17. An electrical device, characterized by The electrical equipment includes the secondary battery as described in any one of claims 1 to 16.

18. A polyacrylic binder, characterized by The polyacrylic adhesive includes flexible groups, which include at least one of ester or ether groups.

19. The polyacrylic binder according to claim 18, characterized in that The polyacrylic adhesive comprises structural units derived from the monomer shown in Formula 1. Formula 1: wherein R 01 including any one or more of H, halogen, substituted or unsubstituted C1-C6 saturated alkyl, and substituted or unsubstituted C2-C6 alkenyl, R 02 including a flexible group comprising any one or more of a C2-C6 ester group and a C2-C6 ether group.

20. The polyacrylic binder according to claim 18 or 19, characterized in that The polyacrylic adhesive comprises structural units derived from the monomer shown in Formula 2. Formula 2: wherein R 03 including any one or more of H, halogen, substituted or unsubstituted C1-C6 saturated alkyl, and substituted or unsubstituted C2-C6 alkenyl; R 04 including a polar group comprising any one or more of an amine group, a hydroxyl group, a carboxyl group, a carboxylate salt, a cyano group, an amide group, a phenol group, a sulfonic acid group, or a sulfonate salt group.

21. The polyacrylic adhesive according to any one of claims 19-20, characterized in that, In the polyacrylic adhesive, the structural units derived from the monomer shown in Formula 1 constitute 10%-20% by mass; and / or, In the polyacrylic adhesive, the structural units derived from the monomer shown in Formula 2 constitute 80%-90% by mass; and / or, The weight-average molecular weight of the polyacrylic adhesive is 2 million to 2.5 million.

22. The polyacrylic adhesive according to any one of claims 18-21, characterized in that, The polyacrylic adhesive includes the structural formula shown in Formula I: Formula I: Wherein, R1, R2 and R3 are each independently selected from polar groups, and the polar groups include any one or more of the following: amino group, hydroxyl group, carboxyl group, carboxyl group, cyano group, amide group, phenolic group, sulfonic acid group or sulfonate group; R4 is selected from flexible groups, including at least one of C2-C6 ester groups or C2-C6 ether groups; R5, R6, R7 and R8 are each independently selected from one or more of H, halogens, substituted or unsubstituted C1-C6 saturated alkyl groups and substituted or unsubstituted C2-C6 alkenyl groups; a, b, c, and d are each independently selected from positive integers.

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