Composite conductive binder and preparation method thereof, negative pole piece, secondary battery and electric device

Abstract

The invention relates to a composite conductive binder and a preparation method thereof, a negative pole piece, a secondary battery and an electric device. The composite conductive binder comprises a flexible binder and a polymer-grafted carbon nanotube, and the polymer comprises a structural unit derived from a first monomer represented by a free formula (I) and a structural unit derived from a second monomer represented by a free formula (II), the flexible adhesive comprises a structural unit derived from a third monomer as shown in a free formula (I) and a structural unit derived from a fourth monomer as shown in a free formula (II), R1, R2, R3, R4, R5, R6, R7 and R8 are independently selected from H and substituted or unsubstituted C1-6 alkyl groups, a substituent group of the substituted C1-6 alkyl groups is selected from at least one of amino, hydroxyl and halogen, and a substituent group of the substituted C1-6 alkyl groups is selected from at least one of amino, hydroxyl and halogen. The third monomer is the same as or different from the first monomer, and the fourth monomer is the same as or different from the second monomer. # imgabs0 #

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and particularly to a composite conductive binder, a preparation method thereof, a negative electrode sheet, a secondary battery, and an electrical device. Background Art

[0002] In recent years, with the increasingly wide application range of lithium-ion batteries, lithium-ion batteries are widely used in energy storage power systems such as hydraulic, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the great development of lithium-ion batteries, higher requirements are also put forward for their energy density, cycle performance, safety performance, etc. Silicon-based negative electrode materials have attracted much attention because they can improve the energy density of lithium-ion batteries.

[0003] However, with the addition of silicon materials, the silicon materials expand in volume, the particles are pulverized, and phenomena such as powder falling and film peeling occur during the battery cycle, resulting in a low battery cycle life. In addition, silicon materials have poor conductivity and large polarization. In order to maintain the conductive network, carbon nanotubes are usually added as a conductive agent to the negative electrode slurry composition. However, carbon nanotubes are prone to agglomeration or sedimentation in the negative electrode slurry composition. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a composite conductive binder that has improved stability, can achieve long-term storage, and at the same time can reduce the brittleness of the electrode sheet, increase the toughness of the electrode sheet, and make the electrode sheet less likely to have phenomena such as powder falling and film peeling. The present application also provides a preparation method of the composite conductive binder, a negative electrode sheet, a secondary battery, and an electrical device.

[0005] To achieve the above object, a first aspect of the present application provides a composite conductive binder, including a flexible binder and polymer-grafted carbon nanotubes, wherein the polymer includes structural units derived from a first monomer represented by formula (I) and structural units derived from a second monomer represented by formula (II), and the flexible binder includes structural units derived from a third monomer represented by formula (I) and structural units derived from a fourth monomer represented by formula (II):

[0006]

[0007] Wherein, R 1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、R 8 each independently selected from H, substituted or unsubstituted C1-6 Alkyl, substituted C 1-6 The substituent of the alkyl is selected from at least one of amino, hydroxyl, and halogen, and

[0008] wherein, the third monomer is the same as or different from the first monomer, and the fourth monomer is the same as or different from the second monomer.

[0009] The composite conductive binder in the embodiments of the present application has improved stability, can be stably stored for more than 6 months without agglomeration or sedimentation, and at the same time can reduce the brittleness of the electrode sheet, increase the toughness of the electrode sheet, make the electrode sheet not prone to powder falling and film peeling, thereby enhancing the cycle performance of the battery.

[0010] In some embodiments, R 1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、R 8 are each independently selected from H or unsubstituted C 1-6 alkyl; optionally, R 1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、R 8 are each independently selected from H or unsubstituted C 1-4 alkyl. Thus, the composite conductive binder in the embodiments of the present application has further improved stability.

[0011] In some embodiments, the flexible binder further includes a structural unit derived from a fifth monomer shown in formula (III) and a structural unit derived from a sixth monomer shown in formula (IV):

[0012]

[0013] wherein, R 9 、R 10 、R 11 、R 12 、R 13 、R 14 are each independently selected from H, substituted or unsubstituted C 1-6 alkyl, substituted C 1-6 alkyl, the substituent of which is selected from at least one of amino, hydroxyl, and halogen; n is an integer selected from 2 to 6.

[0014] Through the above flexible binder, the composite conductive binder in the embodiments of the present application has strong adhesion. Moreover, this flexible binder helps to reduce the brittleness of the electrode sheet, increase the toughness of the electrode sheet, and prevent the electrode sheet from easily falling off powder or peeling off the film.

[0015] In some embodiments, R 9 、R 10 、R 11 、R 12 、R 13 、R 14 are each independently selected from H or unsubstituted C 1-6 alkyl; optionally, R 9 、R 10 、R 11 、R 12 、R 13 、R 14 are each independently selected from H or unsubstituted C 1-4 alkyl; and / or

[0016] n is an integer selected from 2 to 4.

[0017] By selecting the above groups, it is beneficial to make the composite conductive binder in the embodiments of the present application have further enhanced adhesion.

[0018] In some embodiments, the weight ratio W1 of the flexible binder to the polymer-grafted carbon nanotubes is 2 to 100, optionally 5 to 50. By controlling the weight ratio of the flexible binder and the polymer-grafted carbon nanotubes within this range, the flexibility of the electrode sheet can be effectively improved, the release of the negative electrode material from the mold can be reduced, and at the same time, the anti-settling property of the composite conductive binder can be improved.

[0019] In some embodiments, in the polymer-grafted carbon nanotubes, the mass fraction of the structural unit derived from the first monomer is 20% to 80%, optionally 30% to 70%; the mass fraction of the structural unit derived from the second monomer is 5% to 40%, optionally 10% to 30%; the mass fraction of the carbon nanotubes is 10% to 60%, optionally 20% to 50%. By controlling the weight ratio between the structural units in the polymer-grafted carbon nanotubes within the above range, it is beneficial to further improve the stability of the composite conductive binder.

[0020] In some embodiments, in the flexible binder, the mass fraction of the structural unit derived from the third monomer is 20% to 70%, optionally 30% to 60%; the mass fraction of the structural unit derived from the fourth monomer is 0.1% to 20%, optionally 5% to 15%; the mass fraction of the structural unit derived from the fifth monomer is 10% to 40%, optionally 20% to 30%; and the mass fraction of the structural unit derived from the sixth monomer is 10% to 50%, optionally 15% to 40%. By controlling the weight ratio between the structural units of the flexible binder within the above range, it is beneficial to further enhance the bonding performance of the composite conductive binder, and at the same time, it is beneficial to further reduce the brittleness of the electrode sheet and increase the toughness of the electrode sheet.

[0021] In some embodiments, the glass transition temperature of the flexible binder is 40°C to 90°C. By controlling the glass transition temperature of the flexible binder within the above range, it is beneficial to reduce the brittleness of the electrode sheet and increase the toughness of the electrode sheet.

[0022] In some embodiments, the weight-average molecular weight of the flexible binder is 500,000 to 2,500,000, optionally 600,000 to 1,000,000; and / or

[0023] The weight-average molecular weight of the polymer grafted with carbon nanotubes is 2000 to 30000, optionally 3000 to 20000.

[0024] By controlling the weight-average molecular weight of the flexible binder and / or the polymer grafted with carbon nanotubes within the above range, it is at least beneficial to adjust the viscosity of the composite conductive binder.

[0025] In some embodiments, the composite conductive binder further comprises a pH regulator and / or a dispersion medium;

[0026] Relative to the total weight of the composite conductive binder, the content of the flexible binder is 3 wt% to 8 wt%, optionally 3 wt% to 7 wt%; and / or

[0027] Relative to the total weight of the composite conductive binder, the content of the carbon nanotubes grafted with the polymer is 0.05 wt% to 1 wt%, optionally 0.08 wt% to 0.67 wt%, optionally 0.14 wt% to 0.55 wt%.

[0028] In some embodiments, at 25°C, the viscosity of an aqueous solution of the flexible binder with a solid content of 15 to 25% is 15000 to 31000 mPa·s; and / or

[0029] At 25°C, the viscosity of an aqueous solution of the carbon nanotubes grafted with the polymer with a solid content of 0.7 to 1.5% is 8000 to 35000 mPa·s; and / or

[0030] At 25 °C, the viscosity of the aqueous solution of the composite conductive binder with a solid content of 1.5% to 10% is 8000 to 35000 mPa·s.

[0031] By making the composite conductive binder have a higher viscosity, it is at least beneficial for the negative electrode active material to be better suspended in the negative electrode paste.

[0032] In some embodiments, the carbon nanotubes include at least one of single-walled carbon nanotubes, oligomeric-walled carbon nanotubes, or multi-walled carbon nanotubes. Thus, the composite conductive binder has conductivity.

[0033] In some embodiments, the length of the carbon nanotubes is 0.5 um to 30 um. Controlling the length of the carbon nanotubes within the above range is at least beneficial for the suspension of the carbon nanotubes in the composite conductive binder and the negative electrode paste.

[0034] The second aspect of the present application provides a method for preparing the composite conductive binder of the first aspect of the present application, and the preparation method includes:

[0035] Adding a first monomer and a second monomer to a dispersion liquid containing carbon nanotubes to obtain a first reaction mixture, and in the presence of a first initiator, making the first reaction mixture react. After the reaction ends, diluting the obtained reaction product with a first diluent to obtain a pre-dispersion liquid including polymer-grafted carbon nanotubes;

[0036] Mixing a third monomer and a fourth monomer with a solvent to obtain a second reaction mixture, and in the presence of a second initiator, making the second reaction mixture react. After the reaction ends, diluting the obtained reaction product with a second diluent to obtain a flexible binder; and

[0037] Mixing the prepared pre-dispersion liquid including polymer-grafted carbon nanotubes and the flexible binder to obtain the composite conductive binder.

[0038] In the embodiments of the present application, by grafting a first monomer and a second monomer onto carbon nanotubes to obtain polymer-grafted carbon nanotubes, and mixing the polymer-grafted carbon nanotubes and a flexible binder containing a third monomer and a fourth monomer to obtain a composite conductive binder. The composite conductive binder obtained thereby has improved stability, can be stably stored for more than 6 months without agglomeration or sedimentation, and at the same time can reduce the brittleness of the electrode sheet, increase the toughness of the electrode sheet, make the electrode sheet not prone to powder falling and film peeling, and further enhance the cycle performance of the battery.

[0039] In some embodiments, in the step of preparing the flexible binder, it includes:

[0040] Mix the third monomer, the fourth monomer, the fifth monomer, and the sixth monomer with a solvent to obtain a second reaction mixture; wherein the fifth monomer is represented by formula (III) and the sixth monomer is represented by formula (IV):

[0041]

[0042] wherein, R 9 、R 10 、R 11 、R 12 、R 13 、R 14 are each independently selected from H, substituted or unsubstituted C 1-6 alkyl, and the substituents of the substituted C 1-6 alkyl are selected from at least one of amino, hydroxyl, and halogen; n is an integer selected from 2 to 6.

[0043] In an embodiment of the present application, a flexible binder is prepared using the third monomer represented by formula (I), the third monomer represented by formula (II), the fifth monomer represented by formula (III), and the sixth monomer represented by formula (IV), thereby enabling the composite conductive binder to have a strong adhesive force, while helping to reduce the brittleness of the electrode sheet, increase the toughness of the electrode sheet, and prevent the electrode sheet from easily falling off powder and peeling off the film.

[0044] The third aspect of the present application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector; the negative electrode film layer includes a negative electrode active material and a composite conductive binder, and the composite conductive binder is the composite conductive binder of the first aspect of the present application or the composite conductive binder prepared by the preparation method of the second aspect of the present application. The brittleness of the negative electrode sheet is reduced, the toughness is increased, and it is not easy to fall off powder and peel off the film.

[0045] In some embodiments, the negative electrode active material includes at least one of elemental silicon, silicon oxide, silicon-carbon composite, and silicon alloy. Using the negative electrode active material is beneficial to improving the energy density of the lithium-ion battery.

[0046] In some embodiments, the negative electrode sheet further includes an undercoat layer provided between the negative electrode current collector and the negative electrode film layer. By further including the undercoat layer, the adhesive force between the active material and the current collector can be increased, and further, the electrode sheet is not easy to fall off powder and peel off the film during charge and discharge.

[0047] The fourth aspect of the present application provides a secondary battery, and the secondary battery includes the negative electrode sheet of the third aspect of the present application. During the cycling process of the battery, the electrode sheet is not easy to fall off powder and peel off the film, which is beneficial to enhancing the cycling performance of the battery, and at the same time, the battery has a reduced impedance.

[0048] The fifth aspect of the present application provides an electrical device, which includes the secondary battery of the fourth aspect of the present application. The electrical device has a more durable battery.

[0049] The present application provides a composite conductive binder, which includes a flexible binder and polymer-grafted carbon nanotubes. The polymer includes structural units derived from a first monomer represented by formula (I) and structural units derived from a second monomer represented by formula (II). In formula (I) and formula (II), R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 are each independently selected from H, substituted or unsubstituted C 1-6 alkyl, and the substituents of the substituted C 1-6 alkyl are selected from at least one of amino, hydroxyl, and halogen. By including polymer-grafted carbon nanotubes, the carbon nanotubes have good dispersibility in the composite conductive binder, so that the composite conductive binder has improved stability and can be stably stored for more than 6 months without agglomeration or sedimentation. Furthermore, the carbon nanotubes have good dispersibility in the negative electrode slurry, and the viscosity rebound of the negative electrode slurry is small. By including a flexible binder containing a third monomer and a fourth monomer, the bonding force of the composite conductive binder is enhanced, the brittleness of the electrode sheet can be reduced, the toughness of the electrode sheet can be increased, and the phenomena of powder falling off and film peeling of the electrode sheet are not likely to occur.

[0050] The present application also provides a preparation method of the composite conductive binder. In this method, a pre-dispersion liquid of polymer-grafted carbon nanotubes and a flexible binder are mixed to prepare the composite conductive binder. The polymer-grafted carbon nanotubes enable the carbon nanotubes to have good dispersibility in the negative electrode slurry, and the viscosity rebound of the negative electrode slurry is small. The flexible binder in this method can reduce the brittleness of the electrode sheet, increase the toughness of the electrode sheet, and make the electrode sheet less likely to have the phenomena of powder falling off and film peeling. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0052] Figure 2 is Figure 1 a decomposition diagram of the battery cell according to an embodiment of the present application shown in

[0053] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0054] Figure 4It is a schematic diagram of a battery pack according to an embodiment of the present application.

[0055] Figure 5 is Figure 4 an exploded view of the battery pack according to an embodiment of the present application shown.

[0056] Figure 6 It is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0057] Explanation of reference numerals:

[0058] 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly Detailed implementation manners

[0059] Hereinafter, embodiments of the composite conductive binder, its preparation method, negative electrode sheet, secondary battery, and electrical device of the present application specifically disclosed will be described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter claimed in the present application.

[0060] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The range defined in this way can include or not include the end values and can be combined arbitrarily, 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, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0061] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0062] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0063] Unless otherwise specified, all steps of the present application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may also include steps (a), (c) and (b), or may also include steps (c), (a) and (b), etc.

[0064] As described above, silicon-based anode materials have attracted much attention because they can improve the energy density of lithium-ion batteries. However, with the addition of silicon materials, the silicon materials expand in volume, the particles are pulverized, and powder falling and demoulding occur during the battery cycling process, resulting in a low battery cycle life. In addition, silicon materials have poor conductivity and large polarization. In order to maintain the conductive network, carbon nanotubes are usually added as a conductive agent in the binder composition or the anode slurry composition. Among them, the conductive agent carbon nanotubes are mixed in the composition in a physical blending manner, and are prone to agglomeration or sedimentation, resulting in poor stability of the binder composition or the anode slurry composition including the conductive agent carbon nanotubes, being not suitable for storage, and needing to be used immediately after preparation.

[0065] Based on this, the present application proposes a composite conductive binder, a preparation method thereof, a negative electrode sheet, a battery and an electrical device. The following will describe the present application and optional embodiments in more detail.

[0066] [Composite Conductive Binder]

[0067] The present application proposes a composite conductive binder. The composite conductive binder includes a flexible binder and polymer-grafted carbon nanotubes, wherein the polymer includes structural units derived from a first monomer represented by formula (I) and structural units derived from a second monomer represented by formula (II), and the flexible binder includes structural units derived from a third monomer represented by formula (I) and structural units derived from a fourth monomer represented by formula (II):

[0068]

[0069] Wherein, R 1 、R 2 、R3 , R 4 , R 5 , R 6 , R 7 , R 8 Each independently selected from H, substituted or unsubstituted C 1-6 alkyl, substituted C 1-6 The substituent of the alkyl may be selected from at least one of amino, hydroxyl, and halogen.

[0070] The third monomer is the same as or different from the first monomer, and the fourth monomer is the same as or different from the second monomer.

[0071] As used herein, the term "flexible binder" refers to a polyacrylic acid (PAA) binder having a glass transition temperature of 40 to 90 °C. The flexible binder has a relatively large chain flexibility and can be softened by means of the chain movement of the flexible binder, expanding the free volume of the chain movement.

[0072] "Polymer-grafted carbon nanotubes" refers to carbon nanotubes covalently grafted with a polymer.

[0073] "C 1-6 alkyl" refers to a straight-chain or branched-chain aliphatic hydrocarbon group having 1 to 6 carbon atoms. Optional C 1-6 alkyl includes straight-chain or branched-chain C 1-5 alkyl having 1 to 5 carbon atoms. Optional C 1-6 alkyl includes straight-chain or branched-chain C 1-4 alkyl having 1 to 4 carbon atoms. Optional C 1-6 alkyl includes straight-chain or branched-chain C 1-3 alkyl having 1 to 3 carbon atoms. Optional C 1-6 alkyl includes C 1-2 alkyl having 1 to 2 carbon atoms. Optional C 1-6 alkyl includes C 1 alkyl having 1 carbon atom. C 1-6 Examples of C

[0074] "Unsubstituted" means that the group mentioned has no substituent group.

[0075] "Substituted" means that the group mentioned has a substituent group. Examples of the substituent group may include, but are not limited to, hydroxyl (OH), halogen (F, Cl, Br, I), amino (NH 2 ), cyano (CN), nitro (NO 2 ), C 1-6Alkylamino, phenyl (Ph). When a group is substituted, it may have more than one substituent group, for example, having 1, 2 or 3 substituent groups. For example, the substituted group may have 1 or 2 substituent groups.

[0076] The composite conductive binder of the present application includes polymer-grafted carbon nanotubes. The polymer includes structural units derived from a first monomer represented by formula (I) and structural units derived from a second monomer represented by formula (II). The polymer can increase the steric hindrance of the carbon nanotubes, enabling better dispersion of the carbon nanotubes and reducing the aggregation of the carbon nanotubes. Thereby, the stability of the composite conductive binder is improved, and it can be stably stored for more than 6 months without agglomeration or sedimentation. At the same time, the composite conductive binder has good conductivity and can be used as a conductive agent. Applying the above composite conductive binder to the negative electrode slurry can improve the anti-agglomeration performance and anti-gel performance of the negative electrode slurry, thereby improving its processing performance. The composite conductive binder of the present application further includes a flexible binder containing structural units of a third monomer represented by formula (I) and structural units of a fourth monomer represented by formula (II). The flexible binder can reduce the brittleness of the electrode sheet, increase the toughness of the electrode sheet, and prevent the electrode sheet from easily showing phenomena such as powder falling off and film peeling.

[0077] In some embodiments, R 1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、R 8 are each independently selected from H or unsubstituted C 1-6 alkyl. Optionally, R 1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、R 8 are each independently selected from H or unsubstituted C 1-4 alkyl. Optionally, R 1 、R 2 、R 3 、R 4 、R 5 、R 6 、R 7 、R 8 are all H. The composite conductive binder according to these embodiments helps to further enhance the stability of the composite conductive binder.

[0078] In some embodiments, the flexible binder further includes structural units derived from a fifth monomer shown in Formula (III) and structural units derived from a sixth monomer shown in Formula (IV):

[0079]

[0080] R 9 、R 10 、R 11 、R 12 、R 13 、R 14 are each independently selected from H, substituted or unsubstituted C 1-6 alkyl. The substituents of the substituted C 1-6 alkyl can be selected from at least one of amino, hydroxyl, and halogen. n is an integer selected from 2 to 6.

[0081] Among them, the structural units derived from the third monomer included in the flexible binder may be the same as or different from the structural units derived from the first monomer included in the above polymer. The structural units derived from the fourth monomer included in the flexible binder may be the same as or different from the structural units derived from the second monomer included in the above polymer.

[0082] The above flexible binder is a polyacrylic acid polymer, and simultaneously has CN, COOH, hydroxyl, ester group, and amide group, and has further enhanced adhesion. Moreover, this flexible binder helps to further reduce the brittleness of the electrode sheet, increase the toughness of the electrode sheet, and make the electrode sheet less likely to have the phenomena of powder falling off and film peeling.

[0083] In some embodiments, R 9 、R 10 、R 11 、R 12 、R 13 、R 14 are each independently selected from H or unsubstituted C 1-6 alkyl. Optionally, R 9 、R 10 、R 11 、R 12 、R 13 、R 14 are each independently selected from H or unsubstituted C 1-4 alkyl. Optionally, R 9 、R 10 、R 11 、R 12 、R 13 、R 14All are H. In some embodiments, n is an integer selected from 2 to 4. Optionally, n is 2, 3, or 4. Here, selecting the above groups helps to further enhance the adhesion of the composite conductive binder.

[0084] In some embodiments, the weight ratio W1 of the flexible binder to the polymer-grafted carbon nanotubes can be 1 to 200, optionally 2 to 100, and optionally 5 to 50. Optionally, the weight ratio of the flexible binder to the polymer-grafted carbon nanotubes can be 1, 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or 200, but not limited thereto. Controlling the weight ratio of the flexible binder and the polymer-grafted carbon nanotubes within this range can effectively improve the flexibility of the electrode sheet, reduce the release of the negative electrode material, and at the same time improve the anti-settling property of the composite conductive binder.

[0085] In some embodiments, in the polymer-grafted carbon nanotubes, the mass fraction of the structural unit derived from the first monomer is 20% to 80%, optionally 30% to 70%. For example, it can be 20%, 30%, 40%, 50%, 60%, 70%, or 80%; the mass fraction of the structural unit derived from the second monomer is 5% to 40%, optionally 10% to 30%. For example, it can be 5%, 10%, 20%, 30%, or 40%; the mass fraction of the carbon nanotubes is 10% to 60%, optionally 20% to 50%. For example, it can be 10%, 20%, 30%, 40%, 50%, or 60%.

[0086] Controlling the weight ratio between the structural units in the polymer-grafted carbon nanotubes within the above range is beneficial to improving the stability of the composite conductive binder. At the same time, the content of polar groups such as carboxyl and amide groups is maintained within a suitable range, reducing the possibility of aggregation due to strong polarity.

[0087] In some embodiments, in the flexible binder, the mass fraction of the structural unit derived from the third monomer is 20% to 70%, optionally 30% to 60%. For example, it can be 20%, 30%, 40%, 50%, 60%, or 70%; the mass fraction of the structural unit derived from the fourth monomer is 0.1% to 20%, optionally 5% to 15%. For example, it can be 0.1%, 5%, 10%, 15%, or 20%; the mass fraction of the structural unit derived from the fifth monomer is 10% to 40%, optionally 20% to 30%. For example, it can be 10%, 15%, 25%, 35%, or 40%; and the mass fraction of the structural unit derived from the sixth monomer is 10% to 50%, optionally 15% to 40%. For example, it can be 10%, 15%, 25%, 35%, 45%, or 50%.

[0088] Controlling the weight ratio between the structural units of the flexible binder within the above range is beneficial to enhancing the bonding performance of the composite conductive binder, and at the same time is beneficial to reducing the brittleness of the electrode sheet and increasing the toughness of the electrode sheet.

[0089] In some embodiments, the glass transition temperature of the flexible binder is 40°C to 90°C, optionally 45°C to 70°C, optionally 45°C to 60°C. For example, it can be 40°C, 50°C, 55°C, 65°C, 75°C, 85°C or 90°C, but not limited thereto.

[0090] In some embodiments, the weight average molecular weight of the flexible binder can be 500,000 to 2,500,000, optionally 600,000 to 1,000,000. For example, it can be 500,000, 600,000, 650,000, 700,000, 750,000, 800,000, 850,000, 900,000, 950,000, 1,000,000, 1,100,000, 1,200,000, 1,300,000, 1,400,000, 1,500,000, 1,600,000, 1,700,000, 1,800,000, 1,900,000, 2,000,000, 2,100,000, 2,200,000, 2,300,000, 2,400,000 or 2,500,000, but not limited thereto.

[0091] Controlling the glass transition temperature and / or the weight average molecular weight of the flexible binder within the above range is beneficial to adjusting the viscosity of the composite conductive binder and enhancing its bonding performance, and at the same time is beneficial to reducing the brittleness of the electrode sheet and increasing the toughness of the electrode sheet.

[0092] In some embodiments, the weight average molecular weight of the polymer grafted with carbon nanotubes can be 1000 to 50000, optionally 2000 to 30000, optionally 3000 to 20000. For example, it can be 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 15000, 25000, 35000, 45000 or 50000, but not limited thereto. Controlling the weight average molecular weight of the polymer grafted with carbon nanotubes within the above range enables the composite conductive binder to have high stability while making the negative electrode slurry have good anti-gel performance, and at the same time is beneficial to adjusting the viscosity of the composite conductive binder.

[0093] In some embodiments, the composite conductive binder further comprises a pH regulator and / or a dispersion medium. With respect to the total weight of the composite conductive binder, the content of the flexible binder may be 3 wt% to 8 wt%, optionally 3 wt% to 7 wt%. For example, it may be 3 wt%, 3.5 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt% or 8 wt%, but is not limited thereto. Controlling the content of the flexible binder within the above range is beneficial to exert the advantages of the flexible binder in reducing the brittleness of the electrode sheet and increasing the toughness of the electrode sheet. In some embodiments, with respect to the total weight of the composite conductive binder, the content of the polymer-grafted carbon nanotubes may be 0.05 wt% to 1 wt%, optionally 0.08 wt% to 0.67 wt%. For example, it may be 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt% or 1 wt%, but is not limited thereto. Controlling the content of the polymer-grafted carbon nanotubes within the above range is beneficial to exert its advantages in improving the stability of the composite conductive binder and enhancing the anti-gel performance of the slurry.

[0094] In some embodiments, the pH regulator may be at least one of LiOH, NaOH, and KOH. The pH regulator can adjust the composite conductive binder to be neutral, improve its stability, and reduce the battery impedance when the composite conductive binder is applied to the electrode sheet.

[0095] In some embodiments, the dispersion medium may be an aqueous solvent. Optionally, the dispersion medium may include or be deionized water.

[0096] In some embodiments, at 25 °C, the viscosity of an aqueous solution of a flexible binder with a solids content of 15% to 25% can be 15,000 to 31,000 mPa·s, optionally 22,000 to 30,000 mPa·s. For example, it can be 15,000 mPa·s, 17,000 mPa·s, 18,000 mPa·s, 20,000 mPa·s, 21,000 mPa·s, 23,000 mPa·s, 24,000 mPa·s, 25,000 mPa·s, 26,000 mPa·s, 27,000 mPa·s, 28,000 mPa·s, 29,000 mPa·s, 30,000 mPa·s or 31,000 mPa·s, but not limited thereto. In some embodiments, at 25 °C, the viscosity of an aqueous solution of polymer-grafted carbon nanotubes with a solids content of 0.7% to 1.5% can be 8,000 to 35,000 mPa·s, optionally 10,000 to 27,000 mPa·s. For example, it can be 8,000 mPa·s, 10,000 mPa·s, 12,000 mPa·s, 14,000 mPa·s, 16,000 mPa·s, 18,000 mPa·s, 20,000 mPa·s, 22,000 mPa·s, 24,000 mPa·s, 26,000 mPa·s, 28,000 mPa·s, 30,000 mPa·s or 31,000 mPa·s, but not limited thereto. In some embodiments, at 25 °C, the viscosity of an aqueous solution of a composite conductive binder with a solids content of 1.5% to 10% can be 8,000 to 35,000 mPa·s, optionally 10,000 to 28,000 mPa·s. For example, it can be 8,000 mPa·s, 10,000 mPa·s, 12,000 mPa·s, 14,000 mPa·s, 16,000 mPa·s, 18,000 mPa·s, 20,000 mPa·s, 22,000 mPa·s, 24,000 mPa·s, 26,000 mPa·s, 28,000 mPa·s, 30,000 mPa·s, 32,000 mPa·s, 34,000 mPa·s, 34,500 mPa·s or 35,000 mPa·s, but not limited thereto. When the composite conductive binder with high viscosity is used for the silicon negative electrode, it can have a good suspension effect on the negative electrode active material. During the preparation of the negative electrode slurry, only a small amount of dispersant such as sodium carboxymethylcellulose is needed to disperse the negative electrode active material, and there is no need for a large amount of dispersant such as sodium carboxymethylcellulose to maintain the suspension of the negative electrode slurry, which can further increase the content of the negative electrode active material in the negative electrode slurry and improve the viscosity stability of the negative electrode slurry at the same time.

[0097] In some embodiments, the carbon nanotubes include at least one of single-walled carbon nanotubes, oligomeric-walled carbon nanotubes, and multi-walled carbon nanotubes. Further, the length of the carbon nanotubes can be 0.5 um to 30 um, optionally 0.5 um to 20 um, optionally 0.5 um to 10 um, optionally 3 um to 8 um, optionally 4 um to 6 um, but not limited thereto. For example, it can be 3.5 um to 7.5 um, 4 um to 7 um, 4.5 um to 6.5 um, 5 um to 6 um, etc. The carbon nanotubes have high electrical conductivity and a relatively high conductivity rate, and can construct an efficient conductive network in the silicon-based anode electrode sheet. Using the conductive binder containing carbon nanotubes in the silicon anode can, on the one hand, effectively reduce the impedance of the silicon anode, reduce polarization, improve the electron transport ability, reduce the amount of conductive agent used, and thus increase the usage amount of the anode active material; on the other hand, the conductive binder containing carbon nanotubes is wound around the surface of the anode active material, which can effectively construct a conductive network and inhibit the particle swelling of the active material, reducing the thickness rebound of the active material layer. Controlling the length of the carbon nanotubes within the above range is at least beneficial to the suspension of the carbon nanotubes in the composite conductive binder and the anode slurry.

[0098] [Preparation Method of Composite Conductive Binder]

[0099] The present application also provides a preparation method of the above composite conductive binder. The preparation method includes:

[0100] Adding a first monomer represented by formula (I) and a second monomer represented by formula (II) to a dispersion liquid containing carbon nanotubes to obtain a first reaction mixture, and in the presence of a first initiator, reacting the first reaction mixture. After the reaction is completed, diluting the obtained reaction product with a first diluent to obtain a pre-dispersion liquid including polymer-grafted carbon nanotubes;

[0101] Mixing a third monomer represented by formula (I) and a fourth monomer represented by formula (II) with a solvent to obtain a second reaction mixture, and in the presence of a second initiator, reacting the second reaction mixture. After the reaction is completed, diluting the obtained reaction product with a second diluent to obtain a flexible binder; and

[0102] Mixing the prepared pre-dispersion liquid including polymer-grafted carbon nanotubes and the provided flexible binder to obtain a composite conductive binder.

[0103] In some embodiments, the step of preparing the flexible binder includes: mixing a third monomer represented by formula (I), a fourth monomer represented by formula (II), a fifth monomer represented by formula (III), and a sixth monomer represented by formula (IV) with a solvent to obtain a second reaction mixture.

[0104] In some embodiments, relative to the total added mass of the first monomer, the second monomer, and the carbon nanotubes, the mass fraction of the added first monomer can be 20% to 80%, optionally 30% to 70%; the mass fraction of the added second monomer can be 5% to 40%, optionally 10% to 30%; the mass fraction of the added carbon nanotubes can be 10% to 60%, optionally 20% to 50%.

[0105] In some embodiments, relative to the total added mass of the third monomer, the fourth monomer, the fifth monomer, and the sixth monomer, the mass fraction of the added third monomer can be 20% to 70%, optionally 30% to 60%; the mass fraction of the added fourth monomer can be 0.1% to 20%, optionally 5% to 15%; the mass fraction of the added fifth monomer can be 10% to 40%, optionally 20% to 30%; the mass fraction of the added sixth monomer can be 10% to 50%, optionally 15% to 40%.

[0106] In some embodiments, the reaction temperature of the first reaction mixture can be selected according to specific actual requirements. Exemplarily, the reaction temperature of the first reaction mixture can be 50°C to 80°C; for example, it can be 55°C to 75°C, 60°C to 70°C, or 65°C to 70°C, etc. The reaction time of the first reaction mixture can be selected according to specific actual requirements. Exemplarily, the reaction time of the first reaction mixture can be 0.5 h to 10 h; for example, it can be 0.5 h to 9 h, 0.5 h to 8 h, 0.5 h to 7 h, 0.5 h to 6 h, 0.5 h to 5 h, 0.5 h to 4 h, 0.5 h to 3 h, 0.5 h to 2 h, or 0.5 h to 1 h, etc.

[0107] In some embodiments, the reaction temperature of the second reaction mixture can be selected according to specific actual requirements. Exemplarily, the reaction temperature of the second reaction mixture can be 50°C to 110°C; for example, it can be 55°C to 100°C, 60°C to 90°C, or 70°C to 80°C, etc. The reaction time of the second reaction mixture can be selected according to specific actual requirements. Exemplarily, the reaction time of the second reaction mixture can be 5 h to 20 h; for example, it can be 5.5 h to 18 h, 6 h to 16 h, 7 to 14 h, or 8 h to 12 h, etc.

[0108] In some embodiments, the first initiator and the second initiator can be the same or different. The first initiator and the second initiator can be selected from the initiators commonly used in the art. The initiator can include but is not limited to persulfates, such as ammonium persulfate, potassium persulfate, and sodium persulfate.

[0109] In some embodiments, the solvent can be selected from the solvents commonly used in the art. The solvent can include but is not limited to aqueous solvents, such as deionized water.

[0110] In some embodiments, the first diluent and the second diluent may be the same or different. The first diluent and the second diluent may be selected from diluents commonly used in the art. The diluent may include, but is not limited to, aqueous solvents, such as deionized water.

[0111] In some embodiments, those skilled in the art can select the preparation method of the carbon nanotube-containing dispersion according to specific actual needs. For example, the carbon nanotubes can be ball-milled to the required length and then added to a solution containing a dispersant to obtain the carbon nanotube-containing dispersion. The dispersant can be a dispersant commonly used in the art, such as sodium carboxymethyl cellulose, polyvinyl alcohol cellulose, etc., but is not limited thereto.

[0112] [Negative electrode plate]

[0113] This application also provides a negative electrode plate. The negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer is formed by a negative electrode active material and a composite conductive binder, and the composite conductive binder is the composite conductive binder described above or the composite conductive binder prepared by the preparation method described above.

[0114] As an example, the negative electrode current collector has two surfaces opposite to 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.

[0115] In some embodiments, the negative electrode plate further includes a primer layer disposed between the negative electrode current collector and the negative electrode film layer. The primer layer can be a primer layer for batteries well-known in the art, and is usually formed by a primer slurry including a conductive agent, a binder, a dispersant, and deionized water. The conductive agent, binder, and dispersant therein can be the conductive agent, binder, and dispersant for batteries well-known in the art. By further including the primer layer, the adhesion between the active material and the current collector can be increased, and the phenomenon of powder falling off and film peeling is not likely to occur during the charge and discharge process of the electrode plate.

[0116] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as 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.).

[0117] In some embodiments, the negative electrode active material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys. The negative electrode active material may further include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, tin-based materials, and lithium titanate, etc. The tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0118] In some embodiments, the negative electrode film layer may optionally further include other binders. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0119] In some embodiments, the negative electrode film layer may optionally further include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0120] In some embodiments, the negative electrode film layer may optionally further include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0121] In some embodiments, the negative electrode plate can be prepared in the following manner: dispersing the components for preparing the negative electrode plate, such as the negative electrode active material, the conductive agent, the composite conductive binder of the present application, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0122] In addition, the secondary battery and the electrical device of the present application will be described below with appropriate reference to the drawings.

[0123] In one embodiment of the present application, a secondary battery is provided.

[0124] The term "secondary battery" mentioned herein refers to a battery cell, a battery module, or a battery pack. The following will be described separately.

[0125] Generally, a secondary battery cell includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0126] [Positive electrode tab]

[0127] The positive electrode tab includes a positive current collector and a positive electrode film layer provided on at least one surface of the positive current collector, and the positive electrode film layer includes a positive electrode active material.

[0128] As an example, the positive current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive current collector.

[0129] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. 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 (such as aluminum, aluminum 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.).

[0130] 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-containing phosphates with olivine structure, lithium transition metal oxides, sodium transition metal oxides, polyanionic compounds, Prussian blue compounds, and their respective modified compounds. However, the present 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. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (which can also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which can also be abbreviated as NCM 523 ), LiNi 0.5Co 0.25 Mn 0.25 O 2 (It can also be abbreviated as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O 2 (It can also be abbreviated as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (It can also be abbreviated as NCM 811 )、lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ) and at least one of its modified compounds, etc. Examples of olivine-structured lithium-containing phosphates may include but are not limited to lithium iron phosphate (such as LiFePO 4 (It can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0131] As an alternative technical solution of the present application, in the sodium transition metal oxide, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na x MO 2 , where M is one or several of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≤ 1.

[0132] As an alternative technical solution of the present application, the polyanion-type compound can be a class of compounds having sodium ions, transition metal ions, and tetrahedral (YO 4 ) n- anion 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 the valence state of (YO 4 ) n- .

[0133] The polyanion-type compound can also be a compound having sodium ions, transition metal ions, tetrahedral (YO 4 ) n-A class of compounds containing anionic units and halogen 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 the valence state of (YO 4 ) n- ; the halogen can be at least one of F, Cl, and Br.

[0134] The polyanionic compound can also be a class of compounds having sodium ions, tetrahedral (YO 4 ) n- anionic units, polyhedral units (ZO y ) m+ and optionally halogen anions. Y can be at least one of P, S, and Si, and n represents the valence state of (YO 4 ) n- ; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents the valence state of (ZO y ) m+ ; the halogen can be at least one of F, Cl, and Br.

[0135] Examples of polyanionic compounds are NaFePO 4 , Na 3 V 2 (PO 4 ) 3 , NaM’PO 4 F (M’ is one or more of V, Fe, Mn, and Ni) and Na 3 (VO y ) 2 (PO 4 ) 2 F 3-2y (0 ≤ y ≤ 1), among others.

[0136] 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. Examples of Prussian blue compounds are Na a Me b Me’ c (CN) 6 , where Me and Me’ are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0137] In some embodiments, the positive electrode film layer may further 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.

[0138] In some embodiments, the positive electrode film layer may further 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.

[0139] In some embodiments, the positive electrode sheet can be prepared by the following method: dispersing the components for preparing the positive electrode sheet described above, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N - methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet can be obtained.

[0140] [Electrolyte]

[0141] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. There is no specific limitation on the type of electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel - like, or all - solid - state.

[0142] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0143] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro - bis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0144] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4 - butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0145] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives capable of improving certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0146] [Separator]

[0147] In some embodiments, the battery cell further includes a separator. The present application does not particularly limit the type of the separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0148] In some embodiments, the material of the separator may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0149] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be made into an electrode assembly by a winding process or a stacking process.

[0150] In some embodiments, the battery cell may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0151] In some embodiments, the outer package of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic may include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0152] The present application does not particularly limit the shape of the battery cell, and it may be cylindrical, square, or any other arbitrary shape. For example, Figure 1 is a battery cell 5 with a square structure as an example.

[0153] In some embodiments, referring to Figure 2 , the outer package may include a housing 51 and a top cover assembly 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator may form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte infiltrates in the electrode assembly 52. The number of the electrode assemblies 52 included in the battery cell 5 may be one or more, and those skilled in the art can select according to specific actual requirements.

[0154] In some embodiments, battery cells can be assembled into a battery module. The number of battery cells included in the battery module can be one or more, and those skilled in the art can select the specific number according to the application and capacity of the battery module.

[0155] Figure 3 This is the battery module 4 as an example. Refer to Figure 3 , in the battery module 4, multiple battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the multiple battery cells 5 can be fixed by fasteners.

[0156] Optionally, the battery module 4 can further include a housing having an accommodation space, and the multiple battery cells 5 are accommodated in the accommodation space.

[0157] In some embodiments, the above battery module can be further assembled into a battery pack. The number of battery modules included in the battery pack can be one or more, and those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0158] Figure 4 and Figure 5 This is the battery pack 1 as an example. Refer to Figure 4 and Figure 5 , in the battery pack 1, it can include a battery box and multiple battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in the battery box in any way.

[0159] In addition, the present application also provides an electrical device, and the electrical device includes the secondary battery provided by the present application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but not limited thereto.

[0160] As the electrical device, battery cells, battery modules or battery packs can be selected according to its usage requirements.

[0161] Figure 6 This is an example of an electrical device. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or a battery module can be used.

[0162] Another exemplary device can be a mobile phone, a tablet computer, a laptop computer, etc. This device generally requires being thin and light, and a single battery cell can be used as the power source.

[0163] Embodiment

[0164] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those techniques or conditions not specified in the embodiments, they shall be carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. For reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchase.

[0165] [Preparation of Composite Conductive Binder]

[0166] Embodiment 1

[0167] (1) Preparation of Single-Walled Carbon Nanotube (SWCNT) Pre-Dispersion

[0168] 40 g of SWCNT was processed to a length of 5 - 10 μm by a ball mill, added to 400 g of carboxymethyl cellulose solution, heated to 65°C, and then 0.48 g of ammonium persulfate and monomers (50 g of acrylic acid, 10 g of acrylamide) were dropped into the solution within 3 h, and kept at a constant temperature for 1 h to obtain a viscous product. After cooling to room temperature, it was washed with water, centrifuged to remove impurities, and then diluted with deionized water to obtain an SWCNT pre-dispersion with a solid content of 1.0%.

[0169] (2) Preparation of Flexible Binder

[0170] 30 g of acrylic acid, 5 g of acrylamide, 25 g of acrylonitrile, and 40 g of 2-hydroxyethyl acrylate monomers were added to a three-necked flask equipped with a reflux condenser and a stirrer, 63 ml of deionized water was added, and then 0.8 g of ammonium persulfate was added. At a temperature of 80°C and a rotation speed of 500 rp, the reaction was carried out at a constant temperature for 8 - 12 h, and an acrylic acid - acrylamide - acrylonitrile - 2-hydroxyethyl acrylate copolymer was obtained after the reaction. It was diluted with deionized water to a flexible binder with a solid content of 20 wt%.

[0171] (3) Preparation of Composite Conductive Binder

[0172] 33 g of the SWCNT pre-dispersion obtained in step (1) and 49 g of deionized water were mixed at 80°C for 1 h, and then 18 g of the flexible binder obtained in step (2) was added to the system. After stirring at a constant temperature for 8 - 12 h, a LiOH solution with a concentration of 30% was added to adjust the pH = 7 - 8, and a black viscous solution with a solid content of 4% was obtained.

[0173] Embodiments 2 to 24

[0174] Examples 2 to 24 have substantially the same preparation method as Example 1, with specific parameters adjusted. See Tables 1 to 4 for details.

[0175] Comparative Examples 1 to 3

[0176] The composite conductive binder of Comparative Example 1 includes carbon nanotubes grafted with the polymer numbered 1-1 in Table 1 and a commercially available polyacrylic acid binder (Sichuan Yindi Le Technology Co., Ltd., LA136D, solid content 6%).

[0177] The composite conductive binder of Comparative Example 2 includes a commercially available single-walled carbon nanotube slurry (OCSiAl Company of Russia, product 02HO17, solid content 1%) and a commercially available polyacrylic acid binder (solid content 6%).

[0178] The composite conductive binder of Comparative Example 3 includes a commercially available single-walled carbon nanotube slurry (OCSiAl Company of Russia, product 02HO17, solid content 1%) and the flexible binder numbered 2-7 in Table 2.

[0179] [Preparation of the bottom-coated current collector]

[0180] The conductive agent conductive carbon black SP, binder styrene-butadiene rubber SBR, dispersant sodium carboxymethyl cellulose CMC-Na and deionized water were mixed at a ratio of 1.5 kg: 0.13 kg: 0.13 kg: 8.24 kg, stirred at 1800 r / min and 25 °C for 2 h to be uniformly mixed. The above slurry was filtered through a 200-mesh filter to obtain a bottom-coated slurry with a solid content of 15% - 30% and a viscosity of 100 mPa·s - 1000 mPa·s. The bottom-coated slurry was gravure-coated on the copper foil current collector substrate and dried to obtain a bottom-coated layer with a thickness of 2 μm.

[0181] [Preparation of the negative electrode slurry]

[0182] The active material graphite, SiO, carbon black, composite conductive binder, thickener sodium carboxymethyl cellulose (CMC) and deionized water were mixed at weights of 1.37 kg, 0.15 kg, 7.8 g, 0.57 kg, 9.36 g, 0.88 kg, stirred at 1800 r / min and 25 °C for 3 h to be uniformly mixed to obtain the negative electrode slurry.

[0183] [Preparation of the negative electrode plate]

[0184] The negative electrode slurry was uniformly coated on the negative electrode current collector copper foil coated with the bottom-coated slurry once or multiple times, and after drying, cold pressing and slitting, the negative electrode plate was obtained.

[0185] [Preparation of the positive electrode plate]

[0186] Mix lithium nickel cobalt manganese LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM 622 ) material, conductive agent carbon black, PVDF, and N-methylpyrrolidone (NMP) in a weight ratio of 96.9:2:1:21 and stir to mix evenly to obtain the positive electrode paste; then evenly coat the positive electrode paste on the positive electrode current collector, and then dry, cold press, and slit to obtain the positive electrode plate.

[0187] [Preparation of electrolyte]

[0188] Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1, and then dissolve LiPF 6 uniformly in the above solution to obtain the electrolyte. In this electrolyte, the concentration of LiPF 6 is 1 mol / L.

[0189] [Separator]

[0190] Select a 12-μm-thick polyethylene porous membrane as the separator.

[0191] [Preparation of battery]

[0192] Stack the positive electrode plate, separator, and negative electrode plate in sequence, with the separator between the positive and negative electrode plates to play a role in isolation, then wind to obtain the bare battery cell, weld the tab to the bare battery cell, and place the bare battery cell into an aluminum shell, and bake at 80 °C to remove water, then immediately inject the electrolyte and seal to obtain a non-charged battery. The non-charged battery is then successively subjected to processes such as standing, thermal and cold pressing, formation, shaping, and capacity testing to obtain the battery product.

[0193] [Measurement of weight-average molecular weight]

[0194] Use a Waters 2695 Isocratic HPLC gel permeation chromatograph (differential refractive index detector 2141). Use a polystyrene solution sample with a mass fraction of 3.0% as a reference, and select a matching chromatographic column (for oily: Styragel HT5DMF7.8×300mm + Styragel HT4). Prepare a 3.0% conductive binder composition solution with purified N-methylpyrrolidone (NMP) solvent, and let the prepared solution stand for one day for standby. During testing, first suck tetrahydrofuran with a syringe for flushing, and repeat several times. Then suck 5 ml of the experimental solution, remove the air in the syringe, and dry the tip of the needle. Finally, slowly inject the sample solution into the injection port. After the reading is stable, obtain the data and read the weight-average molecular weight.

[0195] [Viscosity test]

[0196] Use a rotating viscometer to measure the viscosity of the primer slurry. Select a suitable rotor, fix the viscometer rotor, place the liquid to be tested under the viscometer rotor, and the slurry just submerges the scale line of the rotor. Instrument model: Shanghai Fangrui NDJ-5S, rotor: 63# (2000-10000mPa.s), 64# (10000-50000mPa.s), speed: 12 rpm, test temperature: 25℃, test time is 5 minutes, and read the data after the display is stable.

[0197] [Glass transition temperature test]

[0198] The glass transition temperature was tested using a TA company's differential scanning calorimeter (Q1000). 6-9g of polymer sample was dried into a film, and then heated from 0℃ to 200℃ at a heating rate of 10℃ / min, and kept at 200℃ for 3h. The obtained differential scanning calorimetry curve was analyzed, and the temperature at which the glass transition occurred during the second heating period was taken as the glass transition temperature of the polymer, in ℃.

[0199] [Observation of the state of the composite conductive adhesive composition after 180 days of storage]

[0200] Test the solid content of the surface and bottom layer of the composite conductive adhesive composition. If the difference between the solid content of the upper layer and the solid content of the lower layer exceeds 10%, it is judged as "sedimentation". If the difference between the solid content of the upper layer and the solid content of the lower layer is 5% to 10%, it is judged as "slight" sedimentation.

[0201] At the same time, observe whether there are agglomerated particles in the composite conductive adhesive composition.

[0202] If the solid content of the upper layer and the lower layer is less than 5%, and no agglomerated particles appear, record it as "OK".

[0203] [24h gel state test of negative electrode slurry]

[0204] Use a steel ruler to lift the negative electrode slurry in the beaker and judge whether there is gel according to its flow state. If there is no gel, record it as "OK". If there is gel, record it as "mild", "mild", "moderate" or "severe" according to the degree of gel.

[0205] “Minor”: small agglomerates appear in the negative electrode slurry, but the fluidity is OK;

[0206] “Mild”: The negative electrode slurry has small agglomerates and occasional interruptions;

[0207] “Moderate”: Large agglomerates appear in the negative electrode slurry, and current is interrupted;

[0208] “Serious”: The negative electrode slurry appears jelly-like and has no fluidity;

[0209] "OK": The negative electrode paste flows naturally without interruption, flows smoothly on the surface of the steel ruler, and has no lumps.

[0210] [Adhesion Test of the Electrode Plate]

[0211] Referring to the national standard GB-T2790-1995 "Test Method for 180° Peel Strength of Adhesives", the adhesion test procedures for the examples and comparative examples of this application are as follows: Use a blade to cut a sample with a width of 30 mm and a length of 100 - 160 mm. Stick a special double-sided tape on the steel plate, with the tape width of 20 mm and the length of 90 - 150 mm. Stick the negative electrode film surface of the previously cut electrode plate sample on the double-sided tape, and then roll it three times in the same direction with a 2 kg roller. Fix a paper tape with the same width as the electrode plate and a length of 250 mm on the current collector of the electrode plate, and fix it with crepe glue. Turn on the power of the Sansi tensile machine (sensitivity is 1 N), the indicator light is on, adjust the limit block to the appropriate position, and fix one end of the steel plate without the electrode plate with the lower fixture. Fold the paper tape upwards and fix it with the upper fixture, and adjust the position of the upper fixture using the "up" and "down" buttons on the manual controller attached to the tensile machine. Then conduct the test and read the value, with the tensile speed of 50 mm / min. Divide the force when the electrode plate is in force balance by the width of the tape as the adhesion of the negative electrode coating per unit length to characterize the adhesion strength between the negative electrode coating and the current collector.

[0212] [Warpage Height Test]

[0213] Coat the negative electrode paste on the negative electrode current collector, bake it at 100 °C for 1 min to remove most of the water; then cut it into 10 negative electrode plates with a size of 4 cm × 4 cm; then place the cut negative electrode plates on a heating plate at 120 °C and keep it for 1 min, and measure the height of the 4 corners of each negative electrode plate that are warped with a scale, denoted as h1, h2, h3, and h4 respectively. Calculate the average value of h1, h2, h3, and h4 corresponding to each negative electrode plate, denoted as H. Take the average value of the average values H corresponding to the 10 negative electrode plates as the warpage height of the negative electrode plate.

[0214] [Negative Electrode Plate Thickness Rebound Rate Test]

[0215] At 25 °C, charge the secondary batteries corresponding to the examples and comparative examples at a rate of 0.5C to 4.4V and then charge at a constant voltage until the current is lower than 0.05C, and then discharge at a rate of 1C to 2.8V; after cycling the secondary batteries 100 times, charge at a constant current of 1C to a voltage of 4.25V, and then charge at a constant voltage of 4.25V until the current is less than or equal to 0.05C, and then let it stand for 5 min. At this time, the battery is in a fully charged state, and then disassemble the cycled battery in a drying room to obtain the negative electrode plates after full charge cycling.

[0216] Measure the thickness L1 of the negative electrode plate with a micrometer. After cold pressing, the thickness of the negative electrode plate measured is L0. Calculate the rebound rate of the negative active material layer based on the formula (L1 - L0) / L1 * 100.

[0217] [Full charge interface state test]

[0218] After carefully disassembling the fully charged battery, observe whether there is any film peeling or other phenomena at the corners of the negative electrode plate. If there is no film peeling phenomenon, it is judged as "no", and the film peeling situation is recorded as first-level film peeling, second-level film peeling, and third-level film peeling.

[0219] "First-level demolding" means that only the inner ring corner has film peeling;

[0220] "Second-level demolding" means that the inner, middle, and outer ring corners have film peeling;

[0221] "Third-level demolding" means that there are bubbles, peeling, and film peeling at the corners and their vicinity.

[0222] [500-cycle capacity retention rate test]

[0223] Charge the lithium-ion battery at a constant current of 0.33C to 4.3V in a constant temperature environment of 25°C, then charge it at a constant voltage of 4.3V until the current drops to 0.05C, and then discharge it at a constant current of 0.33C to 3.0V to obtain the first-cycle discharge specific capacity (C 0 ). Repeat the charge and discharge process until the 500th cycle to obtain the discharge specific capacity after 500 cycles, denoted as C n .

[0224] Capacity retention rate = Discharge specific capacity after 500 cycles (C n ) / First-cycle discharge specific capacity (C 0 ).

[0225] Table 1: Composition of polymer-grafted carbon nanotubes

[0226]

[0227] Table 2: Composition of flexible binder

[0228]

[0229] Table 3: Composition of the composite conductive binder for Examples 1 - 24 and Comparative Examples 1 - 3

[0230]

[0231]

[0232] Table 4: Performance test results of the composite conductive binder for Examples 1 - 24 and Comparative Examples 1 - 3

[0233]

[0234]

[0235]

[0236] According to the above results, Examples 1 to 24 of the present invention are generally excellent in terms of fluidity after 180 days of storage, gel state at 24 h, bonding strength, warpage height, pole piece thickness rebound rate, full charge interface state, and cycle performance.

[0237] The difference between Example 12 and Comparative Example 1 is that Example 12 includes the flexible binder of the present invention, while Comparative Example 1 includes a commercially available polyacrylic acid binder. The difference between Example 12 and Comparative Example 2 is that Example 12 includes the flexible binder of the present invention and polymer-grafted carbon nanotubes, while Comparative Example 2 includes a commercially available carbon nanotube slurry and a commercially available polyacrylic acid binder. The difference between Example 12 and Comparative Example 3 is that Example 12 includes the polymer-grafted carbon nanotubes of the present invention, while Comparative Example 3 includes a commercially available carbon nanotube slurry. According to the test results, when any one of the flexible binder and polymer-grafted carbon nanotubes of the present invention is replaced with a commercially available product, the resulting binder deteriorates in at least one aspect of fluidity after 180 days of storage, gel state at 24 h, bonding strength, warpage height, pole piece thickness rebound rate, full charge interface state, and cycle performance.

[0238] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same structure in essence as the technical idea and achieving the same effect within the technical solution scope of the present application are all included in the technical scope of the present application. In addition, within the scope not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art to the embodiments and other forms constructed by combining some constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A composite conductive adhesive, characterized in that: A carbon nanotube grafted with a flexible binder and a polymer, wherein the polymer comprises a structural unit derived from a first monomer represented by formula (I) and a structural unit derived from a second monomer represented by formula (II), and the flexible binder comprises a structural unit derived from a third monomer represented by formula (I) and a structural unit derived from a fourth monomer represented by formula (II): Wherein, R1, R2, R3, R4, R5, R6, R7, R8 are each independently selected from H, substituted or unsubstituted C 1-6 Alkyl, substituted C 1-6 The substituent of the alkyl group is selected from at least one of amino, hydroxyl and halogen; and The third monomer is the same as or different from the first monomer, and the fourth monomer is the same as or different from the second monomer.

2. The composite conductive adhesive according to claim 1, characterized in that: R1, R2, R3, R4, R5, R6, R7, and R8 are each independently selected from H or unsubstituted C 1-6 alkyl; optionally, R1, R2, R3, R4, R5, R6, R7, R8 are each independently selected from H or unsubstituted C 1-4 alkyl.

3. The composite conductive adhesive according to claim 1 or 2, characterized in that: The flexible adhesive further comprises a structural unit derived from a fifth monomer represented by formula (III) and a structural unit derived from a sixth monomer represented by formula (IV): Among them, R9, R 10 , R 11 , R 12 , R 13 , R 14 are each independently selected from H, substituted or unsubstituted C 1-6 Alkyl, substituted C 1-6 The substituent of the alkyl group is selected from at least one of amino, hydroxyl and halogen; n is an integer selected from 2 to 6.

4. The composite conductive adhesive according to claim 3, characterized in that: R9, R 10 , R 11 , R 12 , R 13 , R 14 are each independently selected from H or unsubstituted C 1-6 Alkyl; optionally, R9, R 10 , R 11 , R 12 , R 13 , R 14 are each independently selected from H or unsubstituted C 1-4 Alkyl; and / or n is an integer selected from 2-4.

5. The composite conductive adhesive according to any one of claims 1 to 4, characterized in that: The weight ratio W1 of the flexible binder to the polymer-grafted carbon nanotubes is 2-100, and optionally 5-50.

6. The composite conductive adhesive according to any one of claims 1 to 5, characterized in that: In the polymer-grafted carbon nanotubes, the mass fraction of the structural units derived from the first monomer is 20% to 80%, optionally 30% to 70%; the mass fraction of the structural units derived from the second monomer is 5% to 40%, optionally 10% to 30%; the mass fraction of the carbon nanotubes is 10% to 60%, optionally 20% to 50%.

7. The composite conductive adhesive according to any one of claims 3 to 6, characterized in that: In the flexible adhesive, the mass fraction of the structural unit derived from the third monomer is 20% to 70%, optionally 30% to 60%; The mass fraction of the structural unit derived from the fourth monomer is 0.1% to 20%, optionally 5% to 15%; the mass fraction of the structural unit derived from the fifth monomer is 10% to 40%, optionally 20% to 30%; and the mass fraction of the structural unit derived from the sixth monomer is 10% to 50%, optionally 15% to 40%.

8. The composite conductive adhesive according to any one of claims 1 to 7, characterized in that: The glass transition temperature of the flexible adhesive is 40°C to 90°C.

9. The composite conductive adhesive according to any one of claims 1 to 8, characterized in that: The weight average molecular weight of the flexible binder is 500,000 to 2.5 million, optionally 600,000 to 1 million; and / or The weight average molecular weight of the polymer grafted with the carbon nanotubes is 2,000 to 30,000, and optionally 3,000 to 20,000.

10. The composite conductive adhesive according to any one of claims 1 to 9, characterized in that: The composite conductive adhesive further includes a pH regulator and / or a dispersion medium; Relative to the total weight of the composite conductive adhesive, the content of the flexible adhesive is 3wt% to 8wt%, optionally 3wt% to 7wt%; and / or Relative to the total weight of the composite conductive adhesive, the content of the polymer-grafted carbon nanotubes is 0.05 wt% to 1 wt%, and optionally 0.08 wt% to 0.67 wt%.

11. The composite conductive adhesive according to any one of claims 1 to 10, characterized in that: At 25°C, the viscosity of an aqueous solution of the flexible binder having a solid content of 15% to 25% is 15,000 to 31,000 mPa·s; and / or At 25° C., the viscosity of an aqueous solution of polymer-grafted carbon nanotubes having a solid content of 0.7% to 1.5% is 8000 to 35000 mPa·s; and / or At 25° C., the viscosity of an aqueous solution of the composite conductive adhesive with a solid content of 1.5% to 10% is 8000 to 35000 mPa·s.

12. The composite conductive adhesive according to any one of claims 1 to 11, characterized in that: The carbon nanotubes include at least one of single-walled carbon nanotubes, few-walled carbon nanotubes or multi-walled carbon nanotubes.

13. The composite conductive adhesive according to any one of claims 1 to 12, characterized in that: The length of the carbon nanotube is 0.5um to 30um.

14. The method for preparing a composite conductive adhesive according to claim 1, characterized in that: The preparation method comprises: Adding a first monomer and a second monomer to a dispersion containing carbon nanotubes to obtain a first reaction mixture, reacting the first reaction mixture in the presence of a first initiator, and after the reaction is completed, diluting the obtained reaction product with a first diluent to obtain a pre-dispersion containing polymer-grafted carbon nanotubes; Mixing the third monomer and the fourth monomer with a solvent to obtain a second reaction mixture, reacting the second reaction mixture in the presence of a second initiator, and after the reaction is completed, diluting the obtained reaction product with a second diluent to obtain a flexible adhesive; and The prepared pre-dispersion liquid including the polymer-grafted carbon nanotubes and the flexible adhesive are mixed to obtain the composite conductive adhesive.

15. The method for preparing the composite conductive adhesive according to claim 14, characterized in that: The step of preparing the flexible adhesive comprises: The third monomer, the fourth monomer, the fifth monomer and the sixth monomer are mixed with a solvent to obtain a second reaction mixture; wherein the fifth monomer is represented by formula (III) and the sixth monomer is represented by formula (IV): Among them, R9, R 10 , R 11 , R 12 , R 13 , R 14 are each independently selected from H, substituted or unsubstituted C 1-6 Alkyl, substituted C 1-6 The substituent of the alkyl group is selected from at least one of amino, hydroxyl and halogen; n is an integer selected from 2 to 6.

16. A negative electrode plate, characterized in that: It includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector; the negative electrode film layer includes a negative electrode active material and a composite conductive adhesive, and the composite conductive adhesive is the composite conductive adhesive described in any one of claims 1 to 13 or a composite conductive adhesive prepared by the preparation method described in claim 14 or 15.

17. The negative electrode sheet according to claim 16, characterized in that: The negative electrode active material includes at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon composites and silicon alloys.

18. The negative electrode sheet according to claim 16 or 17, characterized in that: The negative electrode plate further includes a primer layer disposed between the negative electrode current collector and the negative electrode film layer.

19. A secondary battery, characterized in that: The secondary battery comprises the negative electrode sheet according to any one of claims 16 to 18.

20. An electrical device, characterized in that: The electric device comprises the secondary battery according to claim 19.

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