Secondary battery, electric device, and binder

Abstract

The invention provides a secondary battery, a power utilization device and a binder, the secondary battery comprises a positive pole piece, a negative pole piece and an isolating membrane, the negative pole piece comprises a negative current collector and a negative membrane layer arranged on at least one surface of the negative current collector; the negative electrode film layer comprises a negative electrode active material and a first binder; the mass ratio of the negative electrode active material in the negative electrode film layer is 96%-98.4%; the mass ratio of the first binder in the negative electrode film layer is 0.5%-3%; the first binder includes a polymer including-COOM,-CONH2,-CN, and-COOR, where M includes an alkali metal, and R includes a substituted or unsubstituted C1-C20 alkyl group. The secondary battery in the present application has improved energy density and does not deteriorate processability.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more particularly to a secondary battery, an electrical device, and an adhesive. Background Technology

[0002] In recent years, as the application scope of secondary batteries has become increasingly wide, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, and aerospace.

[0003] Due to the significant advancements in secondary batteries, higher demands have been placed on their energy density. Summary of the Invention

[0004] This application was made in view of the above-mentioned problems, and its object is to provide a secondary battery, an electrical device, and an adhesive. The secondary battery of this application has improved energy density and does not degrade processing performance.

[0005] To achieve the above objectives, this application provides a secondary battery, comprising a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material and a first binder. The negative electrode active material accounts for 96% to 98.4% of the mass of the negative electrode film layer. The first binder accounts for 0.5% to 3% of the mass of the negative electrode film layer. The first binder includes a polymer comprising -COOM, -CONH2, -CN, and -COOR, wherein M comprises an alkali metal, and R comprises substituted or unsubstituted C1-C. 20 alkyl.

[0006] In this application, the -COOM, -CONH2, -CN, and -COOR groups in the polymer give the polymer a negative charge. The different chain segments in the polymer generate repulsive forces, causing the polymer to extend in the solution and allowing the chain segments to entangle with each other, thus improving the adhesion of the first binder and thereby improving the viscosity and stability of the negative electrode slurry. The -COOM group is hydrophilic, which is beneficial to the dispersibility of the negative electrode slurry; the -CONH2 (amide group) can regulate the polymerization reaction, which is beneficial to obtaining a polymer with suitable weight-average molecular weight, viscosity, solid content, and good stability; the -CN (nitrile group) is a strongly polar group, which is beneficial to increasing the interaction force between the first binder and other substances, thus improving the adhesion of the first binder; the alkyl side chain of the -COOR (ester group) has hydrophobic properties, forming a better affinity with the negative electrode active material and providing better encapsulation of the negative electrode active material. Furthermore, the hydrophilicity of -COOM and the hydrophobicity of -COOR are beneficial to improving the dispersibility of the negative electrode slurry. Furthermore, the alkyl side chains of -COOR (ester group) can increase the flexibility of the negative electrode slurry and reduce the stress shrinkage of the coating at high temperatures during coating, which is beneficial to improving phenomena such as coating cracking and tab wrinkling in the negative electrode film. Therefore, the first binder in this application has excellent thickening, adhesion, plasticizing, and dispersing properties. Using the first binder can reduce the total amount of binder without affecting the processing performance of the secondary battery, thereby increasing the mass ratio of the negative electrode active material in the negative electrode active film layer. That is, the secondary battery in this application has an improved energy density without deteriorating the processing performance.

[0007] In some embodiments, M includes one or more of Li, Na, and K.

[0008] In some embodiments, the first adhesive includes structural units derived from the monomer shown in Formula 1, structural units derived from the monomer shown in Formula 2, structural units derived from the monomer shown in Formula 3, and structural units derived from...

[0009] The structural unit of the single entity shown in Equation 4:

[0010]

[0011] Among them, R1 includes hydrogen or alkali metal; R2, R3, R4, R5, R6, R7, R8, R9, R 11 R 12 R 13 R 14 Each independently comprises hydrogen or substituted or unsubstituted C1-C6 alkyl groups; R 10 Including substituted or unsubstituted C1-C 20 alkyl.

[0012] In some embodiments, R1 includes hydrogen; and / or R2, R3, R4, R5, R6, R7, R8, R9, R 11 R 12 R 13 R 14 Each independently includes hydrogen; and / or, R 10 Including substituted or unsubstituted C6-C 12 alkyl.

[0013] The structural units (acrylic acid structural units) derived from the monomer shown in Formula 1 in the first binder are hydrophilic, which is beneficial for improving the dispersibility of the negative electrode slurry. In addition, the structural units of the monomer shown in Formula 1 can also provide lithium-ion transport channels. Increasing the number of these structural units in the first binder can increase the active ion transport channels, improve the transport rate of active ions, and thus improve the charging capacity of the secondary battery. Furthermore, by introducing structural units (acrylonitrile structural units) derived from the monomer shown in Formula 2 into the first binder, highly polar groups are introduced, enhancing the interaction forces between the binder and other substances, thereby strengthening the adhesion of the polymer. By introducing structural units derived from the monomer shown in Formula 3 (acrylate structural units), the hydrophobic properties of the alkyl side chains of the ester group enhance the affinity between the ester and the negative electrode active material, resulting in better encapsulation of the negative electrode active material and improved dispersibility of the negative electrode slurry. Furthermore, the longer side chain groups in the structural units of the monomer shown in Formula 3 reduce the interaction between polymer molecular chain segments, making internal rotation of single bonds easier to occur. This increases the flexibility of the prepared slurry, reduces stress shrinkage of the coating during coating, and minimizes cracking and tab wrinkling problems. Introducing structural units derived from the monomer shown in Formula 4 (acrylamide structural units) allows for regulation of the polymerization reaction, resulting in polymers with suitable weight-average molecular weight, viscosity, solid content, and good stability. Therefore, the first binder in this application exhibits excellent thickening, adhesion, plasticizing, and dispersing properties.

[0014] In some embodiments, the molar ratio of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4 in the first adhesive is (2–5):(1–4):(1–4):(0.5–3). This facilitates the acquisition of a multifunctional first adhesive with suitable thickening, adhesion, plasticizing, and dispersing properties.

[0015] In some embodiments, the molar ratio of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4 in the first binder is (3-5):(2-4):(2-4):(0.5-2). This facilitates obtaining a multifunctional first binder with more suitable thickening, adhesion, plasticizing, and dispersing properties.

[0016] In some embodiments, the molar content of the structural units of the monomer derived from Formula 3 is 10% to 40% relative to the total molar content of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4. Thus, the first binder possesses suitable hydrophobic properties and flexibility, which is beneficial for improving the dispersibility and flexibility of the negative electrode slurry, thereby improving the processing performance of the secondary battery.

[0017] In some embodiments, the molar content of the structural units of the monomer derived from Formula 1 is 20% to 50% relative to the total molar content of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4. This is advantageous for obtaining polymers with suitable hydrophilicity and viscosity, and for improving the dispersibility and adhesion of the negative electrode slurry.

[0018] In some embodiments, the molar content of the structural units of the monomer derived from formula 2 is 10% to 40% relative to the total molar content of the structural units of the monomer derived from formula 1, the monomer derived from formula 2, the monomer derived from formula 3, and the monomer derived from formula 4. This is advantageous for obtaining a polymer with suitable adhesiveness, and for improving the adhesiveness of the negative electrode slurry.

[0019] In some embodiments, the molar content of the structural units of the monomer derived from formula 4 is 5% to 30% relative to the total molar content of the structural units of the monomers derived from formula 1, formula 2, formula 3, and formula 4. This is advantageous for obtaining polymers with suitable weight-average molecular weight, viscosity, solid content, and good stability, which is beneficial for the processing performance of secondary batteries.

[0020] In some embodiments, the polymer has a weight-average molecular weight of 200,000 to 1,500,000. This is beneficial for improving the adhesion and structural stability of the polymer molecules.

[0021] In some embodiments, the negative electrode active material accounts for 97.0% to 97.9% of the mass of the negative electrode film. This ensures that the loading of the negative electrode sheet is within a suitable range, which is beneficial for balancing the energy density and processing performance of the secondary battery.

[0022] In some embodiments, the first binder accounts for 0.5% to 2% of the mass of the negative electrode film layer. This allows for a greater bonding effect with a smaller amount of binder, without affecting the processing performance of the secondary battery.

[0023] In some embodiments, the negative electrode film layer further includes a second binder; in the negative electrode film layer, the total mass ratio of the first binder and the second binder is 1% to 3%. This ensures that the viscosity of the negative electrode slurry is within a suitable range, while also allowing for a larger proportion of the negative electrode active material, which is beneficial for balancing the processing performance and energy density of the secondary battery.

[0024] In some embodiments, the second binder accounts for 0.5% to 3% of the mass of the negative electrode film. This is beneficial to the bonding performance of the negative electrode sheet.

[0025] In some embodiments, the second binder includes a styrene-butadiene rubber binder and / or a polyacrylic acid binder. Styrene-butadiene rubber binders and / or polyacrylic acid binders have advantages such as high viscosity and good stability, and when used as binders in the negative electrode film layer, they are beneficial to the processing performance of the secondary battery.

[0026] In some embodiments, the negative electrode film layer further includes a dispersant; in the negative electrode film layer, the total mass ratio of the first binder and the dispersant is 0.5% to 2%. This ensures that, on the one hand, the filtration rate of the negative electrode slurry is within a suitable range, and on the other hand, that the proportion of the negative electrode active material is relatively large, which is beneficial for balancing the processing performance and energy density of the secondary battery.

[0027] In some embodiments, the dispersant accounts for 0-2% of the mass of the negative electrode film. Therefore, during the preparation process, the dispersant effectively suspends and disperses particles such as the negative electrode active material and conductive agent, ensuring that the viscosity and filtration speed of the negative electrode slurry are within a suitable range, resulting in high stability of the negative electrode slurry and improving the processing performance of the secondary battery.

[0028] In some embodiments, the total mass percentage of the first binder, the second binder, and the dispersant in the negative electrode film layer is 1.5% to 2.5%. This is beneficial for balancing the processing performance and energy density of the secondary battery.

[0029] In some embodiments, the negative electrode film layer further includes a conductive agent; the conductive agent accounts for 0.1% to 2% of the mass of the negative electrode film layer. This is beneficial for increasing the loading of the negative electrode sheet, which in turn is beneficial for improving the energy density of the secondary battery.

[0030] In some embodiments, the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

[0031] A second aspect of this application provides an electrical device, including the secondary battery of the first aspect.

[0032] A third aspect of this application provides an adhesive comprising a polymer including -COOM, -CONH2, -CN, and -COOR, wherein M comprises an alkali metal, and R comprises substituted or unsubstituted C1-C. 20 alkyl.

[0033] In this application, the binder includes -COOM, -CONH2, -CN, and -COOR, which impart a negative charge to the polymer. This creates repulsive forces between different chain segments, causing the polymer to extend in solution and allowing the chain segments to entangle, thus improving the binder's adhesion and thickening effect. -COOM is hydrophilic, which is beneficial for improving the dispersibility of the dispersion system. -CONH2 (amide group) can regulate the polymerization reaction, resulting in a polymer with suitable weight-average molecular weight, viscosity, solid content, and good stability. -CN (nitrile group) has a strongly polar group, which can increase the interaction forces between the polymer and other substances, enhancing the binder's adhesion. The hydrophobicity of -COOR is also beneficial for improving the dispersibility of the dispersion system. Furthermore, the R in -COOR includes C1-C1 groups. 20 The presence of alkyl groups gives the polymer longer alkyl side chains, which increases the flexibility of the binder. Therefore, the binder in this application exhibits excellent adhesion, thickening, plasticizing, and dispersibility.

[0034] In some embodiments, the adhesive comprises structural units derived from the monomer shown in Formula 1, structural units derived from the monomer shown in Formula 2, structural units derived from the monomer shown in Formula 3, and structural units derived from the monomer shown in Formula 4.

[0035]

[0036] Among them, R1 includes hydrogen or alkali metal; R2, R3, R4, R5, R6, R7, R8, R9, R 11 R 12 R 13 R 14 Each independently comprises hydrogen or substituted or unsubstituted C1-C6 alkyl groups; R 10Including substituted or unsubstituted C1-C 20 alkyl.

[0037] In some embodiments, R1 includes hydrogen; and / or R2, R3, R4, R5, R6, R7, R8, R9, R 11 R 12 R 13 R 14 Each independently includes hydrogen; and / or, R 10 Including substituted or unsubstituted C6-C 12 alkyl.

[0038] In some embodiments, the molar ratio of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4 in the adhesive is (2–5):(1–4):(1–4):(0.5–3). This facilitates the acquisition of a multifunctional first adhesive with suitable adhesion, thickening, plasticizing, and dispersing properties.

[0039] In some embodiments, the molar content of the structural units of the monomer derived from formula 3 is 10% to 40% relative to the total molar content of the structural units of the monomers derived from formula 1, formula 2, formula 3, and formula 4. Thus, the adhesive possesses suitable hydrophobic properties and flexibility.

[0040] In some embodiments, the polymer has a weight-average molecular weight of 200,000 to 1,500,000. This is beneficial for improving the adhesion and structural stability of the polymer molecules. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0042] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0043] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0044] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0045] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0046] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0047] Explanation of reference numerals in the attached figures:

[0048] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0049] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, power supply device, and adhesive of this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0050] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0052] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0053] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0054] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0055] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0056] As a crucial component of secondary batteries, the performance of the negative electrode significantly impacts the overall battery performance. Currently, to improve the energy density of secondary batteries, the loading of the negative electrode is typically increased, which is usually achieved by reducing the amount of other auxiliary materials, such as binders. However, reducing the amount of binder can lead to a series of processing problems, including poor stability of the negative electrode slurry and easy detachment of the negative electrode.

[0057] Based on this, this application provides a new secondary battery, an electrical device, and an adhesive, wherein the secondary battery has improved energy density and does not deteriorate processing performance.

[0058] Secondary batteries

[0059] A first aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material and a first binder. The negative electrode active material accounts for 96% to 98.4% of the negative electrode film layer by mass. The first binder accounts for 0.5% to 3% of the negative electrode film layer by mass. The first binder includes a polymer, including -COOM, -CONH2, -CN, and -COOR, wherein M includes an alkali metal, and R includes substituted or unsubstituted C1-C. 20 alkyl.

[0060] In this application, the -COOM, -CONH2, -CN and -COOR groups in the polymer give the polymer a negative charge. Different chain segments in the polymer generate repulsive forces, which causes the polymer to extend in the solution and enable the chain segments to entangle with each other, thereby improving the adhesion of the first binder, thereby improving the viscosity of the negative electrode slurry and enhancing the stability of the slurry. The -COOM group is hydrophilic, which is beneficial to the dispersibility of the negative electrode slurry; the -CONH2 (amide group) can regulate the polymerization reaction, which is beneficial to obtaining polymers with suitable weight-average molecular weight, viscosity, solid content, and good stability; the -CN (nitrile group) is a strongly polar group, which is beneficial to increase the interaction force between the first binder and other substances, and improve the adhesion of the first binder; the alkyl side chain of the -COOR (ester group) has hydrophobic properties, which forms a better affinity with the negative electrode active material and has better encapsulation of the negative electrode active material, which is beneficial to improving the dispersibility of the negative electrode slurry. In addition, the alkyl side chain of the -COOR (ester group) can increase the flexibility of the negative electrode slurry and reduce the stress shrinkage of the coating at high temperatures during coating, which is beneficial to improving phenomena such as coating cracking and tab wrinkling of the negative electrode film. Therefore, the first binder in this application has excellent thickening, adhesion, plasticizing, and dispersing properties. Using a first binder can increase the mass ratio of the negative electrode active material in the negative electrode film layer while reducing the total amount of binder, without affecting the processing performance of the secondary battery. That is, the secondary battery in this application has an improved energy density and does not deteriorate the processing performance.

[0061] It should be noted that, due to the large load of the secondary battery in this application, the polarization during the charging and discharging process is reduced, the impedance is decreased, which is beneficial to improving the rate performance and cycle performance of the secondary battery.

[0062] In some implementations, M includes one or more of Li, Na, and K.

[0063] As C1-C 20 Alkyl groups, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl, 2-methylhexyl, heptyl, 2-methylheptyl, octyl, nonyl, decyl, undecyl, dodecyl, etc., are straight-chain or branched alkyl groups having 1 to 20 carbon atoms.

[0064] In this document, the term "substitution" means that at least one hydrogen atom of the above-mentioned group is substituted by a substituent, which can be independently selected from: hydroxyl, mercapto, amino, cyano, nitro, halogen atom (e.g., fluorine, chlorine, bromine, etc.), aryl (e.g., phenyl, naphthyl, etc.), heteroaryl (referring to an aryl group in which one or more carbon atoms are substituted by an oxygen atom, nitrogen atom, phosphorus atom or sulfur atom, such as 4-pyridyl, 2-imidazolyl, 3-pyrazolyl and isoquinolinyl), alkyl, alkoxy, alkenyl, alkynyl, etc.

[0065] The term "secondary battery" as used in this article refers to a single battery cell, battery module, or battery pack.

[0066] In some embodiments, the first adhesive includes structural units derived from the monomer shown in Formula 1, structural units derived from the monomer shown in Formula 2, structural units derived from the monomer shown in Formula 3, and structural units derived from the monomer shown in Formula 4.

[0067]

[0068] Among them, R1 includes hydrogen or alkali metal; R2, R3, R4, R5, R6, R7, R8, R9, R 11 R 12 R 13 R 14 Each independently comprises hydrogen or substituted or unsubstituted C1-C6 alkyl groups; R 10 Including substituted or unsubstituted C1-C 20 alkyl.

[0069] In some embodiments, R1 comprises an alkali metal, including lithium or sodium.

[0070] In some embodiments, R1 includes hydrogen; and / or R2, R3, R4, R5, R6, R7, R8, R9, R 11 R 12 R 13 R 14 Each independently includes hydrogen; and / or, R 10 Including C6-C 12 alkyl.

[0071] Examples of C1-C6 alkyl groups include straight-chain or branched alkyl groups having 1-6 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, and hexyl.

[0072] As C1-C 20 Alkyl groups, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, etc., are straight-chain or branched alkyl groups having 1 to 20 carbon atoms.

[0073] In this article, the term "substitution" means that at least one hydrogen atom of the above-mentioned group is replaced by a substituent, which is the same as listed above and will not be repeated here.

[0074] The inventors have discovered that the structural units (acrylic acid structural units) derived from the monomer shown in Formula 1 in the first binder are hydrophilic, which is beneficial for improving the dispersibility of the negative electrode slurry. Furthermore, the structural units of the monomer shown in Formula 1 can also provide lithium-ion transport channels. Increasing the number of these structural units in the first binder can increase the number of active ion transport channels, improve the transport rate of active ions, and thus improve the charging capacity of the secondary battery. In addition, by introducing structural units (acrylonitrile structural units) derived from the monomer shown in Formula 2 into the first binder, highly polar groups are introduced, enhancing the interaction forces between the binder and other substances, thereby strengthening the adhesion of the polymer. By introducing structural units derived from the monomer shown in Formula 3 (acrylate structural units), the hydrophobic properties of the alkyl side chains of the ester group enhance the affinity between the ester and the negative electrode active material, resulting in better encapsulation of the negative electrode active material and improved dispersibility of the negative electrode slurry. Furthermore, the longer side chain groups in the structural units of the monomer shown in Formula 3 reduce the interaction between polymer molecular chain segments, making internal rotation of single bonds easier to occur. This increases the flexibility of the prepared slurry, reduces stress shrinkage of the coating during coating, and minimizes cracking and tab wrinkling problems. Introducing structural units derived from the monomer shown in Formula 4 (acrylamide structural units) allows for regulation of the polymerization reaction, resulting in polymers with suitable weight-average molecular weight, viscosity, solid content, and good stability. Therefore, the first binder in this application exhibits excellent thickening, adhesion, plasticizing, and dispersing properties.

[0075] In some embodiments, the molar ratio of structural units derived from the monomer shown in Formula 1, structural units derived from the monomer shown in Formula 2, structural units derived from the monomer shown in Formula 3, and structural units derived from the monomer shown in Formula 4 in the first binder is (20%–50%):(10%–40%):(10%–40%):(10%–40%); alternatively, it is (30%–50%):(10%–30%):(10%–30%):(10%–20%). This facilitates obtaining a multifunctional first binder with suitable thickening, adhesion, plasticizing, and dispersing properties.

[0076] In some embodiments, the molar content of the structural units of the monomer derived from Formula 3 is 10% to 40% relative to the total molar content of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4. Thus, the first binder possesses suitable hydrophobic properties and flexibility, which is beneficial for improving the dispersibility and flexibility of the negative electrode slurry, and consequently for the processing performance of the secondary battery.

[0077] For example, the molar content of the structural units of the monomer derived from Formula 3 can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any two of these values ​​within a range. Optionally, the molar content of the structural units of the monomer derived from Formula 3 is 20% to 40%.

[0078] In this application, the monomer shown in Formula 3 can be, for example, (meth)acrylate. (Meth)acrylate includes the C1-C bonds of (meth)acrylic acid. 20 Alkyl esters. C1-C 20 Alkyl refers to a straight-chain or branched alkyl group having 1-20 carbon atoms, such as 1-15 carbon atoms, such as 1-10 carbon atoms, such as 1-5 carbon atoms. For example, the monomer shown in Formula 3 above may include one or more of the following: methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, n-octyl methacrylate, nonyl methacrylate, decyl methacrylate, undecyl methacrylate, dodecyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptyl methacrylate, octadecyl methacrylate, nonadecanyl methacrylate, eicosyl methacrylate, cyclohexyl methacrylate, neopentyl methacrylate, etc.; optionally, the monomer shown in Formula 3 above includes n-octyl acrylate.

[0079] In some embodiments, the molar content of the structural units of the monomer derived from Formula 1 is 20% to 50% relative to the total molar content of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4. This is advantageous for obtaining polymers with suitable hydrophilicity and viscosity, and for improving the dispersibility and adhesion of the negative electrode slurry.

[0080] For example, the molar content of the structural units derived from the monomer shown in Formula 1 can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any two of these values ​​within a range. Optionally, the molar content of the structural units derived from the monomer shown in Formula 1 is 30% to 50%. Examples of monomers shown in Formula 1 include acrylic acid and methacrylic acid.

[0081] In some embodiments, the molar content of the structural units of the monomer derived from Formula 2 is 10% to 40% relative to the total molar content of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4. This is advantageous for obtaining a polymer with suitable adhesiveness, and for improving the adhesiveness of the negative electrode slurry.

[0082] For example, the molar content of the structural units of the monomer derived from Formula 2 can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any two of these values ​​within a range. Optionally, the molar content of the structural units of the monomer derived from Formula 2 is 20% to 40%. Acrylonitrile, for example, can be a monomer shown in Formula 2.

[0083] In some embodiments, the molar content of the structural units of the monomer derived from Formula 4 is 5% to 30% relative to the total molar content of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4. This is advantageous for obtaining polymers with suitable weight-average molecular weight, viscosity, solid content, and good stability, which is beneficial for the processing performance of secondary batteries.

[0084] For example, the molar content of the structural units of the monomer derived from Formula 4 can be 5%, 10%, 15%, 20%, 25%, 30%, or any two of these values. Optionally, the molar content of the structural units of the monomer derived from Formula 4 can be 5% to 20%. Acrylamide, for example, can be a monomer shown in Formula 4.

[0085] In some embodiments, the weight-average molecular weight of the polymer is between 200,000 and 1,500,000; alternatively, the weight-average molecular weight of the polymer is between 500,000 and 1,000,000. Exemplarily, the weight-average molecular weight of the polymer can be a value within the range of 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,500,000, and any two of these values. A weight-average molecular weight within the above range is beneficial for improving the adhesion and structural stability of the polymer molecules.

[0086] In this application, weight-average molecular weight (MAM) has its common meaning in the art and is the average molecular weight obtained by multiplying the mass of each molecular chain in the polymer by its mole fraction in the polymer. MAM can be determined using methods known in the art, with exemplary testing methods as follows: for example, gel permeation chromatography, such as using a Waters 2695 Isocratic HPLC gel permeation chromatograph (differential refractive index detector 2141). In some embodiments, the testing method uses a 3.0% polystyrene solution sample as a reference, selecting a matched chromatographic column (oil-based: Styragel HT5DMF7.8*300mm + Styragel HT4). A 3.0% polymer gel solution is prepared using purified N-methylpyrrolidone (NMP) solvent, and the prepared solution is allowed to stand for one day for later use. During testing, tetrahydrofuran is first drawn into a syringe for rinsing, repeated several times. Then, 5 ml of the experimental solution is drawn, air is expelled from the syringe, and the needle tip is dried. Finally, the sample solution is slowly injected into the injection port. After the reading stabilizes, the data is acquired, and the weight-average molecular weight is read.

[0087] In some embodiments, the negative electrode active material comprises 97.0% to 97.9% of the negative electrode film by mass. Exemplarily, the mass percentage of the negative electrode active material is within the range of 97.0%, 97.1%, 97.2%, 97.3%, 97.4%, 97.5%, 97.6%, 97.7%, 97.8%, 97.9%, or any two of these values. This ensures that the loading of the negative electrode sheet is within a suitable range, which is beneficial for balancing the energy density and processing performance of the secondary battery.

[0088] In some embodiments, the first binder accounts for 0.5% to 2% of the mass of the negative electrode film. Exemplarily, the mass percentage of the first binder in the negative electrode film is within the range of 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, or any two of these values. This allows for a greater bonding effect with a smaller amount of binder without affecting the processing performance of the secondary battery.

[0089] In some embodiments, the negative electrode film layer further includes a second binder; in the negative electrode film layer, the total mass percentage of the first binder and the second binder is 1% to 3%; optionally, it is 1.5% to 2.5%. This ensures that the viscosity of the negative electrode slurry is within a suitable range, while also allowing for a larger proportion of the negative electrode active material, which is beneficial for balancing the processing performance and energy density of the secondary battery. For example, in the negative electrode film layer, the mass ratio of the first binder to the second binder is 1%, 1.5%, 2%, 2.5%, 3%, or a value within a range consisting of any two of these values.

[0090] In some embodiments, the second binder accounts for 0.5% to 3% of the mass of the negative electrode film. This is beneficial to the bonding performance of the negative electrode sheet. Exemplarily, the mass percentage of the second binder in the negative electrode film is a value within the range of 0.5%, 1%, 1.5%, 1.8%, 2%, 2.5%, 3%, or any two of these values.

[0091] In some embodiments, the second binder includes a styrene-butadiene rubber binder and / or a polyacrylic acid binder. Styrene-butadiene rubber binders and / or polyacrylic acid binders have advantages such as high viscosity and good stability, and when used as binders in the negative electrode film layer, they are beneficial to the processing performance of the secondary battery. In addition, polyacrylic acid binders have good film-forming properties and a strong coating effect on the active material, which can effectively suppress side reactions and improve the cycle performance of the secondary battery.

[0092] In some embodiments, the styrene-butadiene rubber adhesive is a polystyrene-butadiene copolymer.

[0093] In some embodiments, the polyacrylic adhesive includes, but is not limited to, a copolymer formed by copolymerization of acrylonitrile monomer, acrylic monomer, and acrylamide monomer (Indira's LA136D), and is neutralized with sodium hydroxide, i.e., the polyacrylic adhesive used in this application is a sodium-modified adhesive; wherein, the molar ratio of acrylonitrile monomer, acrylic monomer, and acrylamide monomer is 4:5:1.

[0094] In some embodiments, the mass percentage of styrene-butadiene rubber binder in the negative electrode film layer is 0.5% to 3%. Optionally, it is 0.5% to 2.5%. This is beneficial to the bonding performance of the negative electrode sheet. Exemplarily, the mass percentage of styrene-butadiene rubber binder in the negative electrode film layer is 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, or any two of these values.

[0095] In some embodiments, the mass percentage of the polyacrylic acid binder in the negative electrode film layer is 0.5% to 3%. Optionally, it is 0.5% to 2%. This is beneficial to the bonding performance of the negative electrode sheet. Exemplarily, the mass percentage of the polyacrylic acid binder in the negative electrode film layer is 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, or a value within the range of any two of these values.

[0096] In some embodiments, the negative electrode film layer further includes a dispersant; in the negative electrode film layer, the total mass percentage of the first binder and the dispersant is 0.5% to 2%; optionally, it is 1% to 1.5%. This ensures that, on the one hand, the filtration rate of the negative electrode slurry is within a suitable range, and on the other hand, it allows for a larger proportion of the negative electrode active material, which is beneficial for balancing the processing performance and energy density of the secondary battery. For example, in the negative electrode film layer, the mass ratio of the first binder to the dispersant is 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, or a value within a range consisting of any two of these values.

[0097] In some embodiments, the dispersant accounts for 0-2% of the mass of the negative electrode film; optionally, it is 0-1.5%. Thus, during the preparation process, the dispersant effectively suspends and disperses particles such as the negative electrode active material and conductive agent, ensuring that the viscosity and filtration speed of the negative electrode slurry are within a suitable range, resulting in high stability and improved processing performance of the secondary battery. Exemplarily, the mass percentage of the dispersant in the negative electrode film is 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.5%, 2.0%, or any two of these values.

[0098] In some embodiments, the dispersant includes one or more of sodium carboxymethyl cellulose, sodium polystyrene sulfonate, and silane coupling agents.

[0099] In some embodiments, the total mass percentage of the first binder, the second binder, and the dispersant in the negative electrode film layer is 1.5% to 2.5%. This is beneficial for balancing the processing performance and energy density of the secondary battery. Exemplarily, the total mass percentage of the first binder, the second binder, and the dispersant is a value within the range of 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, or any two of these values.

[0100] In some embodiments, the negative electrode film layer further includes a conductive agent; the mass percentage of the conductive agent in the negative electrode film layer is 0.1% to 2%; optionally, it is 0.1% to 1%. A mass percentage of the conductive agent within the above range is beneficial for increasing the loading of the negative electrode sheet, thus further improving the energy density of the secondary battery. For example, in the negative electrode film layer, the mass percentage of the conductive agent is a value within the range of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 1%, 1.5%, 2.0%, or any two of these values.

[0101] In some embodiments, the conductive agent includes conductive carbon black and / or carbon nanotubes. Exemplarily, the carbon nanotubes include single-walled carbon nanotubes or multi-walled carbon nanotubes. Because carbon nanotubes have stronger conductivity, using them as a conductive agent can further reduce the mass percentage of the conductive agent, thereby further increasing the mass percentage of the negative electrode active material in the negative electrode slurry, i.e., increasing the loading of the negative electrode sheet. This is more conducive to improving the energy density of the secondary battery.

[0102] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0103] In some embodiments, the negative electrode current collector 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.).

[0104] In some embodiments, the negative electrode active material 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 one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxides, 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.

[0105] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, first binder, second binder and dispersant, in a solvent (e.g. deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0106] Positive electrode sheet

[0107] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0108] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0109] 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.).

[0110] In some embodiments, the cathode material includes one or more of lithium iron phosphate, lithium manganese iron phosphate, and nickel-cobalt-manganese ternary materials.

[0111] In some embodiments, when the battery cell 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 / 3Mn 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 0.1O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.1 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium 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.

[0112] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., before feeding. When the positive electrode active material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0113] In some embodiments, when the battery cell is a sodium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for use in sodium-ion batteries. As an example, the positive electrode active material may include at least one of sodium-containing layered oxides, polyanionic sodium compounds, and Prussian blue sodium compounds.

[0114] As an example, sodium-containing layered oxides can be iron-manganese layered oxides. Iron-manganese layered oxides include at least one of nickel-iron-manganese layered oxides and copper-iron-manganese layered oxides.

[0115] As an optional technical approach in this application, the polyanionic sodium ion compound can be a compound containing sodium ions, transition metal ions, and 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 (YO4). n- The valence state. Polyanionic sodium compounds can also have sodium ions, transition metal ions, or tetrahedral (YO4) forms. 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.

[0116] Polyanionic sodium compounds can also be those containing sodium ions and tetrahedral (YO4) structures. n-Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n 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 ) m+ The valence state; the halogen can be at least one of F, Cl, and Br. Examples of polyanionic compounds include NaFePO4, Na3V2(PO4)3, NaM'PO4F (M' is one or more of V, Fe, Mn, and Ni), and Na3(VO4)2(PO4)3. y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0117] As an optional technical approach in this application, the polyanionic sodium ion compound can be Na… x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q d Wherein, element A represents an alkali metal element that substitutes for element Na, element M represents a metal element that substitutes for element V, element D represents a dopant element that substitutes for element P, and element Q represents a dopant element that substitutes for element F. Element D includes at least one of Si and S, and element Q includes at least one of Cl and O; 3.5≤x≤4.5, 0≤a≤0.15x, 0.8≤y≤1.1, 0≤b≤0.3y, 0≤c≤0.15, 0.8≤z≤1.1, 0≤d≤0.2z. Optionally, element A includes at least one of K and Li; element M includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0118] As an optional technical approach in this application, the polyanionic sodium ion compound can be Na… x R y (PO4)2P2O7, wherein x = 3.5–4.5, y = 2.75–3.25, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0119] As an optional technical approach in this application, the polyanionic sodium ion compound can be Na… 4+x R3-y P 4-m O 15 / C; wherein, 0 < x < 0.5, 0 < y ≤ 0.5, 0 < m ≤ 0.2, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0120] Prussian blue compounds can be a class of compounds having 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. For example, Prussian blue compounds are Na a Me b Me’ c (CN)6, wherein Me and Me’ each independently include at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, and 0 < c < 1.

[0121] In the listing of the cathode active material in this application, the molar content of O is only the theoretical value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will show fluctuations.

[0122] In some embodiments, the cathode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0123] In some embodiments, the cathode film layer may also optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0124] In some embodiments, the cathode electrode sheet can be prepared by the following method: dispersing the components for preparing the cathode electrode sheet, such as the cathode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a cathode slurry; coating the cathode slurry on the cathode current collector, and after processes such as drying and cold pressing, the cathode electrode sheet can be obtained.

[0125] Electrolyte

[0126] In some embodiments, the secondary battery cell also includes an electrolyte. During battery charging and discharging, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor of ions between the positive and negative electrode plates. This application does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0127] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0128] In some embodiments, the electrolyte salt may be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium difluorosulfonamide, sodium ditrifluoromethanesulfonamide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorooxalate borate, sodium dioxalate borate, sodium difluorodioxalate phosphate, and sodium tetrafluorooxalate phosphate.

[0129] 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.

[0130] 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.

[0131] Separating membrane

[0132] In some embodiments, the battery cell also includes a separator. The separator is disposed between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing ions to pass through. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0133] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. 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.

[0134] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0135] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0136] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0137] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0138] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0139] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0140] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0141] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0142] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0143] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0144] Electrical appliances

[0145] The second aspect of this application provides an electrical device, which includes the secondary battery provided in the first aspect of this application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0146] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0147] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0148] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0149] adhesive

[0150] A third aspect of this application provides an adhesive comprising a polymer including -COOM, -CONH2, -CN, and -COOR, wherein M comprises an alkali metal and R comprises Cl-C. 20 alkyl.

[0151] In this application, the binder includes -COOM, -CONH2, -CN, and -COOR, which impart a negative charge to the polymer. This creates repulsive forces between different chain segments, causing the polymer to extend in solution and allowing the chain segments to entangle, thus improving the binder's adhesion and thickening effect. -COOM is hydrophilic, which is beneficial for improving the dispersibility of the dispersion system. -CONH2 (amide group) can regulate the polymerization reaction, resulting in a polymer with suitable weight-average molecular weight, viscosity, solid content, and good stability. -CN (nitrile group) has a strongly polar group, which can increase the interaction forces between the polymer and other substances, enhancing the binder's adhesion. The hydrophobicity of -COOR is also beneficial for improving the dispersibility of the dispersion system. Furthermore, the R in -COOR includes substituted or unsubstituted C1-C groups. 20 The presence of alkyl groups gives the polymer longer alkyl side chains, which increases the flexibility of the binder. Therefore, the binder in this application exhibits excellent adhesion, thickening, plasticizing, and dispersibility.

[0152] In some embodiments, M includes one or more of Li, Na, and K. Therefore, when the above-mentioned binder is applied to a battery system with the corresponding metal element, the rate performance of the secondary battery can be improved.

[0153] In some embodiments, the first adhesive includes structural units derived from the monomer shown in Formula 1, structural units derived from the monomer shown in Formula 2, structural units derived from the monomer shown in Formula 3, and structural units derived from the monomer shown in Formula 4.

[0154]

[0155] Among them, R1 includes hydrogen or alkali metal; R2, R3, R4, R5, R6, R7, R8, R9, R 11 R 12 R 13 R 14 Each independently comprises hydrogen or substituted or unsubstituted C1-C6 alkyl groups; R 10 Including substituted or unsubstituted C1-C 20 alkyl.

[0156] In some embodiments, R1 includes hydrogen; and / or R2, R3, R4, R5, R6, R7, R8, R9, R 11 R 12 R 13 R 14 Each independently includes hydrogen; and / or, R 10 Including C6-C 12 alkyl.

[0157] In some embodiments, the molar ratio of structural units derived from the monomer shown in Formula 1, structural units derived from the monomer shown in Formula 2, structural units derived from the monomer shown in Formula 3, and structural units derived from the monomer shown in Formula 4 in the adhesive is (2-5):(1-4):(1-4):(0.5-3); optionally, it is (3-5):(2-4):(2-4):(0.5-2). This facilitates the acquisition of a multifunctional first adhesive with suitable adhesion, thickening, plasticizing, and dispersing properties.

[0158] In some embodiments, the molar content of the structural units of the monomer derived from Formula 3 is 10% to 40%, optionally 20% to 40%, relative to the total molar content of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4. Thus, the first adhesive possesses suitable hydrophobic properties and flexibility.

[0159] In some embodiments, the molar content of the structural units of the monomer derived from Formula 1 is 20% to 50%, optionally 30% to 50%, relative to the total molar content of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4. This is advantageous for obtaining polymers with suitable hydrophilicity and adhesiveness.

[0160] In some embodiments, the molar content of the structural units of the monomer derived from Formula 2 is 10% to 40%, optionally 20% to 40%, relative to the total molar content of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4. This is advantageous for obtaining a polymer with suitable adhesive properties.

[0161] In some embodiments, the molar content of the structural units of the monomer derived from Formula 4 is 5% to 30%, or optionally 5% to 20%, relative to the total molar content of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4. This is advantageous for obtaining polymers with suitable weight-average molecular weight, viscosity, solid content, and good stability.

[0162] In some embodiments, the weight-average molecular weight of the polymer is 200,000 to 1,500,000; alternatively, it is 500,000 to 1,000,000. This is beneficial for improving the adhesion and structural stability of the polymer molecules.

[0163] In some embodiments, the above-mentioned adhesive can be prepared by the following methods:

[0164] S1, add the initiator to the aqueous solutions of the monomers shown in Formula 1, Formula 2, Formula 3 and Formula 4, and mix them evenly to obtain a mixed solution; S2, allow the mixed solution to undergo a polymerization reaction to obtain the binder.

[0165]

[0166] Among them, R1 includes hydrogen or alkali metal; R2, R3, R4, R5, R6, R7, R8, R9, R 11 R 12 R 13 R 14 Each independently comprises hydrogen or substituted or unsubstituted C1-C6 alkyl groups; R 10 Including substituted or unsubstituted C1-C 20 alkyl.

[0167] In some embodiments, R1 includes hydrogen; and / or R2, R3, R4, R5, R6, R7, R8, R9, R 11 R 12 R 13 R 14 Each independently includes hydrogen; and / or, R 10 Including substituted or unsubstituted C6-C 12 alkyl.

[0168] In this application, by initiating the polymerization of a solution containing monomers shown in Formula 1, Formula 2, Formula 3, and Formula 4 with an initiator, a binder with excellent adhesion, dispersibility, thickening, and plasticizing properties can be prepared.

[0169] In some embodiments, in step S2, the polymerization reaction is carried out at 50°C to 80°C with stirring at 300 rpm to 1500 rpm for 4 to 12 hours; alternatively, the polymerization reaction is carried out at 60°C to 70°C with stirring at 500 rpm to 1000 rpm for 6 to 10 hours. Under these conditions, the polymerization reaction is advantageously carried out to increase the reaction rate and monomer conversion rate.

[0170] In some embodiments, in step S1, the molar ratio of the monomers shown in Formula 1, Formula 2, Formula 3 and Formula 4 is (2-5):(1-4):(1-4):(0.5-3), or optionally (3-5):(2-4):(2-4):(0.5-2). The mass ratio of the above monomers is within the above range, which is beneficial to obtaining an adhesive with the best overall performance.

[0171] In some embodiments, in step S1, the solid content of the mixed solution is 4% to 10%, and optionally, the solid content of the mixed solution is 5% to 8%. A solid content within the above range is advantageous for obtaining an adhesive with suitable viscosity, excellent processing performance, and meeting the requirements of mass production automation.

[0172] In some embodiments, in step S1, the amount of initiator is 0.05% to 0.1% of the total molar amount of the monomers shown in Formula 1, Formula 2, Formula 3, and Formula 4, and optionally, 0.05% to 0.07%. An initiator amount within the above range is beneficial for forming a polymer with a suitable weight-average molecular weight.

[0173] In some embodiments, in step S1, the initiator includes azo initiators, organic peroxide initiators, inorganic peroxides, and persulfates. Optionally, the initiator is a persulfate, and more preferably, the initiator is ammonium persulfate. Using the above initiators results in fast initiation speed, low reaction temperature, and the resulting binder has a moderate weight-average molecular weight and good stability.

[0174] Example

[0175] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0176] Example 1

[0177] Preparation of the first adhesive

[0178] S1, 0.4 mol acrylic acid, 0.3 mol acrylonitrile, 0.2 mol n-octyl acrylate and 0.1 mol acrylamide are added to the reactor, along with 1000 ml of deionized water. Then, ammonium persulfate initiator is added to obtain a mixed solution with a solid content of 6%; wherein, the amount of initiator is 0.05% of the total mass of monomers.

[0179] S2, the mixed solution obtained in step S1 is stirred at a speed of 500 rpm / min for 0.5 h, and then reacted at a constant temperature of 80℃ for 8 h to obtain a polymer. Then, deionized water is added to the obtained polymer to make the solid content of the polymer solution 5%, and lithium hydroxide is used for neutralization to adjust the pH value of the polymer solution to 8, thus obtaining the first binder.

[0180] The weight-average molecular weight of the first binder was determined using a Waters 2695 Isocratic HPLC gel permeation chromatography system. Specifically, a 3.0% polystyrene solution was used as a reference, and a matching column (oil-based: Styragel HT5DMF7.8*300mm + Styragel HT4) was selected. A 3.0% polymer solution was prepared using purified N-methylpyrrolidone (NMP) solvent and allowed to stand for one day. For testing, tetrahydrofuran was first used to flush the solution, repeated several times. Then, 5 ml of the experimental solution was drawn, air was expelled from the syringe, and the needle tip was dried. Finally, the sample solution was slowly injected into the injection port. After the reading stabilized, the data was obtained, and the weight-average molecular weight of the first binder was found to be 800,000.

[0181] Preparation of negative electrode sheet

[0182] The negative electrode active material graphite, conductive agent Super P, and first binder are dissolved in deionized water at a mass ratio of 97.5:1:1.5 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector copper foil in one step, and after drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0183] Preparation of positive electrode sheet

[0184] Lithium iron phosphate, a positive electrode active material, Super P, and PVDF binder are mixed together in a mass ratio of 97:2:1. N-methylpyrrolidone solvent is added and stirred evenly to form a positive electrode slurry. The positive electrode slurry is coated on aluminum foil for the positive electrode current collector, and then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0185] electrolyte

[0186] An organic solvent was prepared by mixing equal volumes of ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC). LiPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0187] Separating membrane

[0188] Porous polyethylene film is used as the separator.

[0189] Preparation of secondary batteries

[0190] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. This stacking process yields a bare battery cell. The bare battery cell is then placed in outer packaging, filled with the prepared electrolyte, and sealed to obtain a secondary battery.

[0191] Electrical performance testing of secondary batteries

[0192] 1) Cyclic performance

[0193] The cycle performance of the secondary battery was characterized by the number of cycles at 25°C and 80% SOH. The test procedure is as follows:

[0194] ① Charge at a constant current of 1 / 3C to 3.65V, then charge at a constant voltage of 3.65V to a current of 0.05C;

[0195] ② Let stand for 5 minutes;

[0196] ③ Discharge to 2.0V with a constant current of 1 / 3C, and record the discharge capacity D1 of the first cycle;

[0197] ④ Let stand for 5 minutes;

[0198] ⑤ Repeat steps ① to ④ n times, and record the discharge capacity to Dn;

[0199] ⑥ When Dn = D1 * 80%, record the number of cycles n, which is the number of cycles for 80% SOH.

[0200] 2) Ratio performance

[0201] The rate performance of the secondary battery was characterized by testing at 25°C within an equivalent charging window of 10% to 80% SOC. The test method is as follows:

[0202] Charge the battery at a constant current of 1 / 3C until the charging cutoff voltage is 3.65V. Then charge it at a constant voltage of 3.65V until the current is 0.05C. Let it rest for 5 minutes, and then discharge it at a constant current of 1 / 3C until the discharge cutoff voltage is 2V. Record the discharge capacity C0. Afterward, charge the secondary battery sequentially at constant currents of 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0, and 4.5C0 until the subsequent full battery charging cutoff voltage is 3.65V or 0V (whichever comes first). After each charge, discharge it at 1C0 until the full battery discharge cutoff voltage is 2V. Record the corresponding negative electrode potentials at different charging rates when charged to 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% SOC. Rate-negative electrode potential curves were plotted for different State of Charge (SOC) states. Linear fitting was then performed to obtain the charging rate corresponding to a negative electrode potential of 0V at each SOC state. This charging rate represents the charging window for the corresponding SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC. The equivalent charging window for 10%SOC to 80%SOC is the average value of the charging windows for 10%SOC, 20%SOC, 30%SOC, 40%SOC, 50%SOC, 60%SOC, 70%SOC, and 80%SOC.

[0203] A larger equivalent charging window value means that the battery can be charged and discharged at a higher rate under conditions of 25℃ and 10% to 80% SOC, and the anode is less likely to reach the 0V lithium plating potential, which means better rate performance.

[0204] Secondary battery processing performance test

[0205] After the negative electrode slurry was prepared, a portion of the negative electrode slurry was tested for solid content, viscosity, and filtration rate. The slurry was then left to stand for 48 hours and visually observed to see if sedimentation occurred. The test results are recorded in Table 2 below.

[0206] (1) The solid content of the negative electrode slurry is tested as follows: The negative electrode slurry is placed in an aluminum-plastic box with a mass of M0, and the total weight is M1. The moisture is dried in an oven, and the remaining mass is weighed as M2. The solid content of the negative electrode slurry = (M2-M0) / (M1-M0)

[0207] (2) The viscosity of the negative electrode slurry was tested in the following way: a DV-2TLV Borlefeld viscometer was used, and a 63r / 64r rotor was selected. The viscosity was tested at 25±1℃ with an SUV speed of 12r / min. The viscosity value at the 6th minute was taken as the viscosity of the negative electrode slurry.

[0208] (3) The filtration rate of the negative electrode slurry was tested in the following way: 500 mL of negative electrode slurry was taken and filtered through a 150-mesh filter to obtain 300 mL of slurry. The time required was recorded.

[0209] (4) Electrode appearance: After the negative electrode is prepared, observe whether the negative electrode is cracked and test the adhesion of the negative electrode.

[0210] The adhesion strength of the negative electrode sheet is tested as follows: At 25℃, the cold-pressed negative electrode sheet is taken as the test sheet. A sample with a width of 30mm and a length of 160mm is cut with a blade. Special double-sided tape is attached to a steel plate with a width of 20mm and a length of 150mm. The cut electrode sample is attached to the double-sided tape with the test surface facing down. Then, a pressure roller is used to roll it three times in the same direction. A paper strip with a width equal to that of the electrode sheet and a length greater than the sample length by 100mm is inserted under the electrode sheet and fixed with wrinkle glue. The power of the tensile testing machine is turned on, the indicator light illuminates, and the limit block is adjusted to... In the appropriate position, fix the end of the steel plate without the electrode attached using the lower clamp, fold the paper tape upwards and fix it using the upper clamp. Use the "up" and "down" buttons on the manual controller attached to the tensile testing machine to adjust the position of the upper clamp. Turn on the dedicated computer connected to the tensile testing machine, double-click the desktop software icon, and start the test. The tensile rate is 50 m / min, the test distance is 50 mm, and the software takes an adhesive force data point every 10 seconds. Use these data point values ​​as the vertical axis and the corresponding test distance as the horizontal axis. The vertical axis reading gradually stabilizes, and the stabilized vertical axis reading is the adhesive force.

[0211] Example 2

[0212] The negative electrode sheet was prepared in a similar manner to that in Example 1 and assembled into a secondary battery. The only difference was that when preparing the negative electrode sheet, the negative electrode active material graphite, the conductive agent Super P, the first binder, and the styrene-butadiene rubber binder SBR were dissolved in deionized water at a mass ratio of 97:1:1.5:0.5 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry was then uniformly coated onto the negative electrode current collector copper foil in one go, and the negative electrode sheet was obtained after drying, cold pressing, and slitting.

[0213] Example 3

[0214] The negative electrode sheet was prepared in a similar manner to that in Example 1 and assembled into a secondary battery. The only difference was that when preparing the negative electrode sheet, the negative electrode active material graphite, the conductive agent Super P, the first binder, and the polyacrylic acid binder LA136D were dissolved in deionized water at a mass ratio of 97:1:1.5:0.5 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry was uniformly coated onto the negative electrode current collector copper foil in one go, and the negative electrode sheet was obtained after drying, cold pressing, and slitting.

[0215] Example 4

[0216] The negative electrode sheet was prepared in a similar manner to that in Example 1 and assembled into a secondary battery. The only difference was in the preparation of the negative electrode sheet: the negative electrode active material graphite, conductive agent Super P, first binder, styrene-butadiene rubber binder SBR, polyacrylic acid binder LA136D, and dispersant CMC were dissolved in deionized water at a mass ratio of 96:1:0.5:1.5:0.5:0.5 and mixed evenly to prepare a negative electrode slurry; the negative electrode slurry was uniformly coated onto the negative electrode current collector copper foil in one go, and the negative electrode sheet was obtained after drying, cold pressing, and slitting.

[0217] Examples 5-7

[0218] The negative electrode sheet was prepared in a similar manner to that in Example 1 and assembled into a secondary battery. The only difference was that the types and mass ratios of the negative electrode active material, conductive agent, first binder, styrene-butadiene rubber binder SBR, polyacrylic acid binder LA136D and dispersant CMC in the negative electrode slurry were adjusted according to Table 2 below when preparing the negative electrode sheet.

[0219] Example 8

[0220] The negative electrode sheet was prepared in a manner similar to that in Example 1 and assembled into a secondary battery. The only difference was that in the preparation of the first binder, step S1 included: adding 0.4 mol of methacrylic acid, 0.3 mol of acrylonitrile, 0.2 mol of dodecyl acrylate, and 0.1 mol of acrylamide to the reactor, adding 1000 ml of deionized water, and then adding ammonium persulfate initiator to obtain a mixed solution with a solid content of 6%. The amount of initiator was 0.05% of the total mass of the monomers, and all other steps were the same as in Example 1.

[0221] Examples 9-13

[0222] The negative electrode sheet was prepared in a manner similar to that in Example 1 and assembled into a secondary battery, the only difference being that the first binder used in preparing the negative electrode sheet (refer to Table 1 below) was adjusted according to Table 2 below.

[0223] Comparative Example 1

[0224] The negative electrode sheet was prepared in a manner similar to that in Example 1 and assembled into a secondary battery, the only difference being that the first binder was not added when preparing the negative electrode slurry.

[0225] Comparative Example 2

[0226] The negative electrode sheet was prepared in a similar manner to that in Example 1 and assembled into a secondary battery. The only difference was that the first binder used in preparing the negative electrode sheet was a copolymer of acrylonitrile, acrylic acid, and acrylamide (Indira LA136D), and sodium hydroxide was used for neutralization. The molar ratio of the structural units of sodium acrylate monomer, acrylonitrile monomer, and acrylamide monomer in the polymer was 4:5:1.

[0227] Table 1 shows the first adhesive used in this application.

[0228] Table 1

[0229]

[0230]

[0231] In Table 1 above, lithium hydroxide was used for neutralization and the pH of the polymer solution was adjusted to 8 when preparing the first binder 1-1 to 1-7; sodium hydroxide was used for neutralization and the pH of the polymer solution was adjusted to 8 when preparing the first binder 2-1.

[0232] Table 2 shows the formulations of the first binder, conductive agent, and negative electrode slurry in Examples 1-13 and Comparative Examples 1-2, and Table 3 shows the performance test results of Examples 1-13 and Comparative Examples 1-2.

[0233] Table 2

[0234]

[0235] Table 3

[0236]

[0237]

[0238] As can be seen from Tables 2 and 3, compared to Comparative Example 1 (where the proportion of negative electrode active material is less than 96%), the negative electrode sheets of Examples 1-13 have a higher loading capacity and higher energy density. Furthermore, compared to Comparative Example 1, the negative electrode slurry of Examples 1-13 has a higher solid content, higher viscosity, and faster filtration speed. Moreover, the negative electrode sheets did not crack after coating, indicating better processing performance. Therefore, the secondary batteries in Examples 1-13 have improved energy density without deteriorating processing performance. In addition, the cycle performance of Comparative Example 1 is worse than that of Examples 1-13. This is because Comparative Example 1 uses styrene-butadiene rubber as a binder, which has poor film-forming properties and a poor coating effect on the active material, thus failing to effectively suppress side reactions.

[0239] Although Comparative Example 2 (using Indira LA136D as a binder) improved the energy density, it suffered from low solid content in the negative electrode slurry, slow filtration speed, cracking of the negative electrode sheet after coating, and weak adhesion. Therefore, the processing performance of the negative electrode sheet in Comparative Example 2 was poor. In addition, the binder used in Comparative Example 2 was a sodium-modified binder, which had worse rate performance than Examples 1-13. Furthermore, the sodium-modified binder lacked both hydrophilic and hydrophobic properties, resulting in poor dispersibility of its negative electrode slurry.

[0240] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, and a separator, wherein the negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector; The negative electrode film layer includes a negative electrode active material and a first binder; the negative electrode active material accounts for 96% to 98.4% of the mass of the negative electrode film layer; the first binder accounts for 0.5% to 3% of the mass of the negative electrode film layer. The first binder comprises a polymer including -COOM, -CONH2, -CN, and -COOR, wherein M comprises an alkali metal, and R comprises substituted or unsubstituted C1-C. 20 alkyl.

2. The secondary battery according to claim 1, characterized in that, M includes one or more of Li, Na, and K.

3. The secondary battery according to claim 1 or 2, characterized in that, The first adhesive comprises structural units derived from the monomer shown in Formula 1, structural units derived from the monomer shown in Formula 2, structural units derived from the monomer shown in Formula 3, and structural units derived from the monomer shown in Formula 4: R1 includes hydrogen or alkali metals; R2, R3, R4, R5, R6, R7, R8, R9, R 11 R 12 R 13 R 14 Each independently comprises hydrogen or substituted or unsubstituted C1-C6 alkyl groups; R 10 Including substituted or unsubstituted C1-C 20 alkyl.

4. The secondary battery according to claim 3, characterized in that, R1 includes hydrogen; and / or, R2, R3, R4, R5, R6, R7, R8, R9, R 11 R 12 R 13 R 14 Each independently includes hydrogen; and / or, R 10 Including substituted or unsubstituted C6-C 12 alkyl.

5. The secondary battery according to claim 3 or 4, characterized in that, In the first adhesive, the molar ratio of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4 is (2-5):(1-4):(1-4):(0.5-3).

6. The secondary battery according to any one of claims 3 to 5, characterized in that, In the first adhesive, the molar ratio of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4 is (3-5):(2-4):(2-4):(0.5-2).

7. The secondary battery according to any one of claims 3 to 6, characterized in that, The molar content of the structural units of the monomer derived from Formula 1, the monomer derived from Formula 2, the monomer derived from Formula 3, and the monomer derived from Formula 4 is 10% to 40% relative to the total molar content of the structural units of the monomer derived from Formula 3.

8. The secondary battery according to any one of claims 3 to 7, characterized in that, Relative to the total molar content of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4, the molar content of the structural units of the monomers derived from Formula 1 is 20% to 50%, and / or the molar content of the structural units of the monomers derived from Formula 2 is 10% to 40%; and / or the molar content of the structural units of the monomers derived from Formula 4 is 5% to 30%.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, The weight-average molecular weight of the polymer is 200,000 to 1,500,000.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, The negative electrode active material accounts for 97.0% to 97.9% of the mass of the negative electrode film.

11. The secondary battery according to any one of claims 1 to 10, characterized in that, The first binder accounts for 0.5% to 2% of the mass of the negative electrode film layer.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The negative electrode film layer also includes a second binder; In the negative electrode film layer, the total mass ratio of the first binder and the second binder is 1% to 3%.

13. The secondary battery according to claim 12, characterized in that, The second binder accounts for 0.5% to 3% of the mass of the negative electrode film layer.

14. The secondary battery according to claim 12 or 13, characterized in that, The second adhesive includes styrene-butadiene rubber adhesive and / or polyacrylic adhesive.

15. The secondary battery according to any one of claims 12 to 14, characterized in that, The negative electrode film layer also includes a dispersant; In the negative electrode film layer, the total mass percentage of the first binder and dispersant is 0.5% to 2%.

16. The secondary battery according to claim 15, characterized in that, The dispersant accounts for 0-2% of the mass of the negative electrode film.

17. The secondary battery according to claim 15 or 16, characterized in that, In the negative electrode film layer, the total mass percentage of the first binder, the second binder, and the dispersant is 1.5% to 2.5%.

18. The secondary battery according to any one of claims 1 to 17, characterized in that, The negative electrode film layer also includes a conductive agent; the conductive agent accounts for 0.1% to 2% of the mass of the negative electrode film layer.

19. The secondary battery according to any one of claims 1 to 18, characterized in that, The negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

20. An electrical device, characterized in that, The secondary battery includes any one of claims 1 to 19.

21. An adhesive, characterized in that, The polymers include -COOM, -CONH2, -CN, and -COOR, wherein M comprises an alkali metal and R comprises substituted or unsubstituted C1-C. 20 alkyl.

22. The adhesive according to claim 21, characterized in that, The adhesive comprises structural units derived from the monomer shown in Formula 1, structural units derived from the monomer shown in Formula 2, structural units derived from the monomer shown in Formula 3, and structural units derived from the monomer shown in Formula 4: R1 includes hydrogen or alkali metals; R2, R3, R4, R5, R6, R7, R8, R9, R 11 R 12 R 13 R 14 Each independently comprises hydrogen or substituted or unsubstituted C1-C6 alkyl groups; R 10 Including substituted or unsubstituted C1-C 20 alkyl.

23. The adhesive according to claim 22, characterized in that, R1 includes hydrogen; and / or R2, R3, R4, R5, R6, R7, R8, R9, R 11 R 12 R 13 R 14 Each independently includes hydrogen; and / or, R 10 Including substituted or unsubstituted C6-C 12 alkyl.

24. The adhesive according to claim 22 or 23, characterized in that, In the adhesive, the molar ratio of the structural units of the monomers derived from Formula 1, Formula 2, Formula 3, and Formula 4 is (2-5):(1-4):(1-4):(0.5-3).

25. The adhesive according to any one of claims 22 to 24, characterized in that, The molar content of the structural units of the monomer derived from Formula 1, the monomer derived from Formula 2, the monomer derived from Formula 3, and the monomer derived from Formula 4 is 10% to 40% relative to the total molar content of the structural units of the monomer derived from Formula 3.

26. The adhesive according to any one of claims 21 to 25, characterized in that, The weight-average molecular weight of the polymer is 200,000 to 1,500,000.

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