Adhesive and its preparation method, negative electrode sheet, battery and electrical equipment

Abstract

The present application relates to an adhesive, a preparation method thereof, a negative electrode sheet, a battery and an electrical device. The adhesive comprises an acrylate copolymer and silicic acid. In the adhesive, the content α of silicon element ranges from 5% ≤ α ≤ 10%.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to an adhesive, a preparation method thereof, a negative electrode sheet, a battery and an electrical device using the same. Background Art

[0002] With the development of battery technology, polyacrylate adhesives, as aqueous adhesives, are widely used as adhesives for negative electrode sheets. However, polyacrylate adhesives still have problems such as insufficient suspension ability and poor slurry stability during homogenization, which makes it difficult for the adhesive to be uniformly dispersed with the active material, weakening the adhesive performance of the polyacrylate adhesive to the active material. Summary of the Invention

[0003] In view of this, the present application provides an adhesive, a preparation method thereof, a negative electrode sheet, a battery and an electrical device using the same. The adhesive has good suspension ability and good adhesive performance to the active material.

[0004] The present application provides an adhesive, which includes an acrylate copolymer and silicic acid. In the adhesive, the content α of silicon element ranges from 5% ≤ α ≤ 10%.

[0005] Further, the acrylate copolymer is a copolymer of acrylate, acrylonitrile and acrylamide.

[0006] Further, in the acrylate copolymer, the mass fraction m1 of acrylate ranges from 40% ≤ m1 ≤ 60%, the mass fraction m2 of acrylonitrile ranges from 40% ≤ m2 ≤ 60%, and the mass fraction m3 of acrylamide ranges from 0 < m3 ≤ 10%.

[0007] Further, the adhesive further includes water. The acrylate copolymer and silicic acid are dispersed in water. When the solid content of the adhesive is 3%, the viscosity μ of the adhesive ranges from 5500 mPa·s ≤ μ ≤ 9000 mPa·s, where the solid content of the adhesive is the sum of the mass fractions of the acrylate copolymer and silicic acid in the adhesive.

[0008] The present application also provides a preparation method of an adhesive for preparing the adhesive provided by the present application. The preparation method includes: providing acrylic acid, acrylonitrile, acrylamide and an initiator, and performing a polymerization reaction to form polyacrylic acid-acrylonitrile-acrylamide; and providing a silicate solution, and mixing the silicate solution with polyacrylic acid-acrylonitrile-acrylamide to obtain the adhesive, which includes an acrylate copolymer and silicic acid. In the adhesive, the content α of silicon element ranges from 5% ≤ α ≤ 10%.

[0009] Further, the silicate solution includes at least one of a saturated lithium metasilicate solution, a lithium monosilicate solution, a lithium orthosilicate solution, a saturated sodium metasilicate solution, a sodium monosilicate solution, and a sodium orthosilicate solution.

[0010] Further, providing the silicate solution and mixing the silicate solution with polyacrylic acid - acrylonitrile - acrylamide to obtain the adhesive further includes: the pH value of the adhesive at 25 °C satisfies the range: 6 ≤ pH ≤ 8.

[0011] This application provides a negative electrode sheet, which includes: a current collector layer and an active material layer. The active material layer is disposed on at least one side of the current collector layer. The active material layer includes an active material, and the active material layer further includes the adhesive provided by this application or an adhesive prepared by the preparation method of the adhesive provided by this application. The adhesive is used to bond the active material.

[0012] This application also provides a battery, which includes: the negative electrode sheet provided by this application, a separator, a positive electrode sheet, and an electrolyte. The separator is disposed on one side of the negative electrode sheet; the positive electrode sheet is disposed on the side of the separator away from the negative electrode sheet; the electrolyte is used to infiltrate at least part of the negative electrode sheet, the separator, and the positive electrode sheet.

[0013] This application also provides an electrical device, which includes: a device body and the battery provided by this application. The battery powers the device body.

[0014] In the present application, the adhesive includes an acrylate copolymer and silicic acid. The acrylate copolymer has a certain viscosity and can be used to bond active materials. The silicic acid is a neutralization product during the formation of the acrylate copolymer. Silicic acid has the ability of thickening and emulsifying and preventing the slurry from precipitating, and has strong adhesive properties, which can make the adhesive have higher suspension ability. When the adhesive is mixed with the active material to form a slurry, the silicic acid can form a colloidal solution in the slurry to improve the suspension ability of the active material in the slurry and enhance the stability of the slurry. Specifically, the colloidal particles of the silicic acid can increase the viscosity of the slurry to play a thickening role, so that the adhesive has good suspension ability. The active material can be evenly distributed in the slurry and fully mixed with the adhesive, slowing down the situation where the active material accumulates at the bottom of the slurry. And finally, when the slurry is coated on the current collector layer, the adhesive and the active material can be evenly distributed in the active material layer, and the adhesive can fully exert its adhesive properties on the active material. Furthermore, when the adhesive is applied to the active material layer, the silicic acid has a large affinity with the active material, which is convenient for the adhesive to coat the active material and further improve the adhesive properties on the active material. Further, when the content α of silicon element satisfies the range of 5% ≤ α ≤ 10%, in the adhesive, the content of silicon element is within a reasonable range. On the one hand, the content of silicon element is positively correlated with the content of silicic acid. Correspondingly, since the silicic acid is the neutralization product of acrylic acid and silicate, the silicate neutralizes a certain amount of acrylic acid and forms acrylate to avoid the aggregation of acrylic acid due to hydrogen bond action. The acrylate has a greater viscosity than acrylic acid, so that the acrylate copolymer has better adhesive properties. On the other hand, correspondingly, the content of silicic acid is within a reasonable range. The silicic acid has the ability of thickening and emulsifying and preventing the slurry from precipitating, which can make the adhesive form a colloidal solution, improve the suspension ability and stability of the adhesive, and thus is beneficial to evenly distribute the adhesive and the active material in the active material layer, and the adhesive can fully exert its adhesive properties on the active material. When the content α of silicon element is too large, correspondingly, the content of silicic acid in the adhesive increases and the content of acrylate copolymer decreases, which may weaken the adhesive properties of the adhesive, increase the risk of the active material falling off, and reduce the peeling performance of the adhesive applied to the negative electrode sheet. When the content α of silicon element is too small, on the one hand, the content of silicic acid in the solvent is too small, making it difficult for the silicic acid to play the role of increasing the viscosity of the adhesive and improving the suspension ability of the adhesive. As a result, when the adhesive is mixed with the active material, it is easy to cause the slurry to be unstable, and finally it is difficult for the adhesive and the active material to be evenly distributed in the active material layer, weakening the adhesive effect of the adhesive on the active material layer and also reducing the cycle performance of the battery when the adhesive is applied to the battery.On the other hand, if the amount of acrylic acid neutralized by the silicate is too small, there may still be a relatively large amount of acrylic acid in the acrylate copolymer. The acrylic acid may agglomerate and form spherical bodies, resulting in a decrease in the viscosity of the acrylate copolymer. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0016] Figure 1 It is a partial cross-sectional structure schematic diagram of a negative electrode sheet according to an embodiment of the present application;

[0017] Figure 2 It is a schematic flow chart of a preparation method of an adhesive according to an embodiment of the present application;

[0018] Figure 3 It is a partial cross-sectional structure schematic diagram of a battery according to an embodiment of the present application;

[0019] Figure 4 It is a schematic structural diagram of an electrical device according to an embodiment of the present application;

[0020] Figure 5 It is a circuit block diagram of an electrical device according to an embodiment of the present application.

[0021] DESCRIPTION OF THE REFERENCE NUMERALS:

[0022] 100 - Adhesive, 200 - Negative electrode sheet, 210 - Current collector layer, 220 - Active material layer, 300 - Battery, 310 - Separator, 320 - Positive electrode sheet, 330 - Electrolyte, 400 - Electrical device, 410 - Device body. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts belong to the scope of protection of the present application.

[0024] In the description, claims and the above-mentioned drawings of this application, terms such as "first" and "second" are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally further includes steps or units not listed, or optionally further includes other steps or units inherent to these processes, methods, products or devices.

[0025] Reference to "embodiment" or "embodiment mode" in this context means that a specific feature, structure or characteristic described in connection with the embodiment or embodiment mode can be included in at least one embodiment of this application. The occurrence of this phrase at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0026] With the development of battery technology, polyacrylic acid adhesives, as aqueous adhesives, are widely used as adhesives for negative electrode sheets. However, polyacrylic acid adhesives still have problems such as insufficient suspension ability and poor slurry stability during homogenization, which makes it difficult for the adhesive to be uniformly dispersed with the active material, weakening the adhesive performance of the polyacrylic acid adhesive to the active material.

[0027] It can be understood that homogenization refers to the process before the slurry is coated on the current collector layer after the polyacrylic acid adhesive and the active material are mixed. The polyacrylic acid adhesive disperses and suspends the active material through electrostatic action and steric hindrance effect to make the polyacrylic acid adhesive and the active material fully mixed evenly. If the polyacrylic acid adhesive has insufficient suspension ability during homogenization, most of the active material may aggregate at the lower layer of the slurry, and the content of the active material in the upper layer of the slurry is less. When the slurry is coated on the current collector layer, it may cause the polyacrylic acid adhesive and the active material to be unable to be mixed evenly, and some active materials may fall off from the active material layer easily because there is no adhesive around them, that is, the adhesive performance between the polyacrylic acid adhesive and the active material is poor.

[0028] It can be understood that the reasons for the insufficient suspension ability of the polyacrylic acid adhesive during homogenization include but are not limited to: firstly, the polyacrylic acid adhesive has fewer lipophilic groups and poor affinity with the active material, making it difficult to bind tightly with the active material; secondly, the viscosity of the polyacrylic acid adhesive is not high enough.

[0029] Please refer to Figure 1, the present application provides an adhesive 100, the adhesive 100 includes an acrylate copolymer and silicic acid. In the adhesive 100, the content α of silicon element ranges from 5% ≤ α ≤ 10%.

[0030] Understandably, the adhesive 100 is an aqueous adhesive 100. In the terms of the present application, an aqueous adhesive 100 refers to an adhesive 100 formed with water as a solvent or dispersant and a natural polymer or synthetic polymer as a binder. Specifically, in the present application, the adhesive 100 uses water as a solvent or dispersant and an acrylate copolymer and silicic acid as a binder.

[0031] Understandably, the adhesive 100 further includes water, and the acrylate copolymer and silicic acid are dispersed in water.

[0032] Understandably, when the adhesive 100 is applied to the negative electrode sheet 200, the negative electrode sheet 200 includes a current collector layer 210 and an active material layer 220. The active material layer 220 further includes an active material. The adhesive 100 is applied to the active material layer 220 and is used to bond the active material.

[0033] Understandably, the acrylate copolymer includes acrylate.

[0034] Understandably, in the adhesive 100, the content of the silicon element is the mass fraction of the silicon element.

[0035] Specifically, the value of the content α of the silicon element can be, but is not limited to, 5%, 5.2%, 5.3%, 5.5%, 5.6%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 9%, 9.2%, 9.5%, 9.8% and 10%, etc.

[0036] In this embodiment, the adhesive 100 includes an acrylate copolymer and silicic acid. The acrylate copolymer has a certain viscosity and can be used to bond active materials. The silicic acid is a neutralization product during the formation of the acrylate copolymer. Silicic acid has thickening and emulsifying properties and the ability to prevent slurry precipitation, and has strong adhesive properties, which can enable the adhesive 100 to have higher suspension ability. When the adhesive 100 is mixed with the active material to form a slurry, the silicic acid can form a colloidal solution in the slurry to improve the suspension ability of the active material in the slurry and enhance the stability of the slurry. Specifically, the colloidal particles of the silicic acid can increase the viscosity of the slurry to play a thickening role, so that the adhesive 100 has good suspension ability. The active material can be evenly distributed in the slurry and fully mixed with the adhesive 100, slowing down the accumulation of the active material at the bottom of the slurry. And finally, when the slurry is coated on the current collector layer 210, the adhesive 100 and the active material can be evenly distributed in the active material layer 220, and the adhesive 100 can fully exert its adhesive performance on the active material. Moreover, when the adhesive 100 is applied to the active material layer 220, the silicic acid and the active material have a large affinity, which is convenient for the adhesive 100 to coat the active material and further improve the adhesive performance on the active material. Further, when the content α of silicon element satisfies the range 5% ≤ α ≤ 10%, in the adhesive 100, the content of silicon element is within a reasonable range. On the one hand, the content of silicon element is positively correlated with the content of silicic acid. Correspondingly, since the silicic acid is the neutralization product of acrylic acid and silicate, the silicate neutralizes a certain amount of acrylic acid and forms acrylate to avoid the aggregation of acrylic acid due to hydrogen bond action. The acrylate has a greater viscosity than acrylic acid, so that the acrylate copolymer has better adhesive performance. On the other hand, correspondingly, the content of silicic acid is within a reasonable range. The silicic acid has thickening and emulsifying properties and the ability to prevent slurry precipitation, which can enable the adhesive 100 to form a colloidal solution, improve the suspension ability and stability of the adhesive 100, and thus is beneficial to evenly distribute the adhesive 100 and the active material in the active material layer 220, and the adhesive 100 can fully exert its adhesive performance on the active material. When the content α of silicon element is too large, correspondingly, the content of silicic acid in the adhesive 100 increases, and the proportion of the acrylate copolymer decreases, which may weaken the adhesive performance of the adhesive 100, increase the risk of the active material falling off, and reduce the peeling performance of the adhesive 100 applied to the negative electrode sheet 200.When the content α of silicon element is too small, on the one hand, the content of silicic acid in the solvent is too small, making it difficult for the silicic acid to play the role of increasing the viscosity of the binder 100 and enhancing the suspension ability of the binder 100. As a result, when the binder 100 is mixed with the active material, it is easy to cause the slurry to be unstable, and finally it is difficult for the binder 100 and the active material to be evenly distributed in the active material layer 220, weakening the bonding effect of the binder 100 on the active material layer 220 and also reducing the cycle performance of the battery 300 when the binder 100 is applied to the battery 300. On the other hand, if the amount of acrylic acid neutralized by the silicate is too small, there may still be a relatively large amount of acrylic acid in the acrylate copolymer. The acrylic acid may agglomerate and form spherical bodies, causing the viscosity of the acrylate copolymer to decrease.

[0037] It can be understood that silicic acid is the neutralization product in the formation process of the acrylate copolymer. Specifically, silicic acid is the neutralization product in the formation process of the acrylate. It can be understood that the raw material of the binder 100 includes acrylic acid, that is, the raw material of the acrylate copolymer includes acrylic acid. Multiple acrylic acid monomers undergo a polymerization reaction to form polyacrylic acid. However, as the chain length of polyacrylic acid increases, the structure of carboxyl groups increases continuously, and polyacrylic acid undergoes cohesion and forms hydrogen bonds, which may cause polyacrylic acid to have a spherical structure and lead to a decrease in the viscosity of polyacrylic acid. Therefore, the raw material of the binder 100 also includes silicate. By adding silicate to the binder 100, the cations in the silicate replace the hydrogen on the carboxyl group of polyacrylic acid, and the hydrogen falling off from the carboxyl group of polyacrylic acid replaces the cations on the silicate to generate polyacrylate and silicic acid.

[0038] Optionally, when the binder 100 is applied to the negative electrode sheet 200 of a sodium-ion battery, the polyacrylate is sodium polyacrylate; when the binder 100 is applied to the negative electrode sheet 200 of a lithium-ion battery, the polyacrylate is lithium polyacrylate.

[0039] Optionally, in the binder 100, the mass content of the silicic acid satisfies the range: 15% to 30%.

[0040] It can be understood that the mass content of the silicic acid is the ratio of the mass of the silicic acid to the mass of the binder 100.

[0041] Specifically, the value of the mass content of the silicic acid can be, but is not limited to, 15%, 16%, 18%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% and 30%, etc.

[0042] In the adhesive 100 provided in this embodiment, the mass content of the silicic acid satisfies the range of 15% to 30%. Then, the mass content of the silicic acid is within a reasonable range. The silicic acid is the neutralization product of acrylic acid and silicate. The silicate neutralizes a certain amount of acrylic acid and forms acrylate to prevent the aggregation of acrylic acid due to hydrogen bonding. The acrylate has a greater viscosity than acrylic acid, so that the acrylate copolymer has better adhesive properties. In addition, the silicic acid has the ability of thickening and emulsifying and preventing the precipitation of the slurry, which can make the adhesive 100 form a colloidal solution, improve the suspension ability and stability of the adhesive 100, and thus is conducive to the uniform distribution of the adhesive 100 and the active material in the active material layer 220, and the adhesive 100 can fully exert its adhesive performance on the active material.

[0043] In some embodiments, the acrylate copolymer is a copolymer of acrylate, acrylonitrile and acrylamide.

[0044] It can be understood that the acrylate copolymer is a random copolymer of polyacrylate, polyacrylonitrile and polyacrylamide. In other words, the acrylate copolymer includes polyacrylate chain segments, polyacrylonitrile chain segments and polyacrylamide chain segments.

[0045] In this embodiment, the acrylate copolymer is a copolymer of acrylate, acrylonitrile and acrylamide. Among them, the acrylate improves the dispersion performance of the acrylate copolymer in the adhesive 100; acrylonitrile makes the adhesive 100 have better affinity with the active material, so that when the adhesive 100 is mixed with the active material, the adhesive 100 can coat the outer periphery of the active material, which is conducive to improving the adhesive performance of the adhesive 100 to the active material; acrylamide enhances the fluidity of the adhesive 100, facilitating the flat distribution of the adhesive 100 in the active material layer 220. The polyacrylate chain segments, polyacrylonitrile chain segments and polyacrylamide chain segments cooperate with each other to make the acrylate copolymer have good adhesive properties.

[0046] In some embodiments, in the acrylate copolymer, the range of the mass fraction m1 of the acrylate is: 40% ≤ m1 ≤ 60%. In other words, in the copolymer of acrylate, acrylonitrile and acrylamide, the range of the mass fraction m1 of the polyacrylate chain segments is 40% ≤ m1 ≤ 60%.

[0047] Specifically, the value of the mass fraction m1 of the acrylate can be, but is not limited to, 40%, 42%, 43%, 45%, 46%, 48%, 50%, 52%, 53%, 55%, 56%, 57%, 58%, 59% and 60%, etc.

[0048] In the acrylate copolymer provided in this embodiment, when the mass fraction m1 of the acrylate satisfies the range of 40% ≤ m1 ≤ 60%, the mass fraction of the acrylate is within a reasonable range, and the acrylate has good hydrophilicity, which is beneficial to being dispersed in water, so that the acrylate copolymer can be uniformly dispersed in the adhesive 100, facilitating the uniform arrangement of the acrylate copolymer and the active material in the active material layer 220, so that the adhesive 100 can fully exert its adhesive performance on the active material. When the value of m1 is too large, the mass fraction of the acrylate is too large. Correspondingly, the mass fraction of acrylonitrile is too small. The affinity between the acrylic acid and the active material is poor, while the affinity between acrylonitrile and the active material is good. Then the affinity between the adhesive 100 and the active material is poor, which is not conducive to the adhesive 100 covering the outer periphery of the active material and effectively bonding the active material. When the value of m1 is too small, the mass fraction of the acrylate is too small, reducing the dispersion performance of the acrylate copolymer in the adhesive 100.

[0049] In some embodiments, the range of the mass fraction m2 of the acrylonitrile is: 40% ≤ m2 ≤ 60%. In other words, in the copolymer of acrylate, acrylonitrile and acrylamide, the range of the mass fraction m2 of the polyacrylonitrile segment is 40% ≤ m2 ≤ 60%.

[0050] Specifically, the value of the mass fraction m2 of the acrylonitrile can be, but is not limited to, 40%, 42%, 43%, 45%, 46%, 48%, 50%, 52%, 53%, 55%, 56%, 57%, 58%, 59% and 60%, etc.

[0051] In this embodiment, when the mass fraction m2 of the acrylonitrile satisfies the range of 40% ≤ m2 ≤ 60%, the mass fraction of the acrylonitrile is within a reasonable range. The acrylonitrile has better hydrophobicity compared with the acrylate. Correspondingly, the affinity between acrylonitrile and the active material is better, so that the adhesive 100 can cover the outer periphery of the active material and be in close contact with the active material, which is beneficial to the adhesive 100 fully exerting its adhesive performance on the active material and is beneficial to improving the viscosity of the adhesive 100.

[0052] In some embodiments, the range of the mass fraction m3 of the acrylamide is: 0 < m3 ≤ 10%. In other words, in the copolymer of acrylate, acrylonitrile and acrylamide, the range of the mass fraction m3 of the polyacrylamide segment is 0 < m3 ≤ 10%.

[0053] Specifically, the value of the mass fraction m3 of the acrylamide can be, but is not limited to, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0054] In this embodiment, when the mass fraction m3 of the acrylamide satisfies the range 0 < m3 ≤ 10%, the mass fraction of the acrylamide is within a reasonable range. The acrylamide enhances the fluidity of the adhesive 100. When the adhesive 100 is distributed on the active material layer 220, it is convenient for the adhesive 100 to level better, and finally enables the adhesive 100 to be evenly distributed on the active material layer 220.

[0055] Preferably, in the acrylate copolymer, the mass fraction of the acrylate is 40%, the mass fraction of acrylonitrile is 55%, and the mass fraction of acrylamide is 5%.

[0056] In some embodiments, the adhesive 100 further includes water. The acrylate copolymer and the silicic acid are dispersed in water. The value of the solid content β of the adhesive 100 satisfies the range: 3% ≤ β ≤ 10%. Wherein, the solid content of the adhesive 100 is the sum of the mass fraction of the acrylate copolymer and the mass fraction of the silicic acid in the adhesive 100.

[0057] It can be understood that the solid content of the adhesive 100 is the ratio of the mass of the solid components in the adhesive 100 to the mass of the adhesive 100.

[0058] It can be understood that in the adhesive 100, the acrylate copolymer and the silicic acid exist in solid form, then the solid content of the adhesive 100 is the sum of the mass fraction of the acrylate copolymer and the mass fraction of the silicic acid.

[0059] Specifically, the value of the solid content β of the adhesive 100 can be, but is not limited to, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.6%, 4.8%, 5%, 5.2%, 5.5%, 6%, 6.2%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 9.8%, 10%, etc.

[0060] In this embodiment, when the value of the solid content β of the adhesive 100 satisfies the range 3% ≤ β ≤ 10%, the solid content of the adhesive 100 is within a reasonable range. In other words, in the adhesive 100, the amounts of the acrylate copolymer and the silicic acid are both within reasonable ranges. The acrylate copolymer exhibits the adhesive property to the active material. The silicic acid, on the one hand, improves the adhesive property of the adhesive 100, and on the other hand, improves the suspension ability of the adhesive 100, so that the adhesive 100 can be uniformly mixed with the active material, and finally improves the adhesive property of the adhesive 100 to the active material. When the adhesive 100 is applied to the negative electrode plate 200 and assembled in the battery 300, the battery 300 has good cycle stability.

[0061] In some embodiments, when the solid content of the adhesive 100 is 3%, the range of the viscosity μ of the adhesive 100 is: 5500 mPa·s ≤ μ ≤ 9000 mPa·s.

[0062] Specifically, the value of the viscosity μ of the adhesive 100 can be, but is not limited to, 5500 mPa·s, 5600 mPa·s, 5800 mPa·s, 6000 mPa·s, 6200 mPa·s, 6500 mPa·s, 6800 mPa·s, 7000 mPa·s, 7200 mPa·s, 7400 mPa·s, 7500 mPa·s, 7800 mPa·s, 8000 mPa·s, 8200 mPa·s, 8500 mPa·s, 8800 mPa·s, and 9000 mPa·s, etc.

[0063] In this embodiment, when the solid content of the adhesive 100 is 3%, the viscosity μ of the adhesive 100 satisfies the range of 5500 mPa·s ≤ μ ≤ 9000 mPa·s, and the adhesive 100 has a relatively high viscosity. Compared with the existing adhesive 100, the adhesive 100 of the embodiment of the present application includes silicic acid, which has the ability of thickening and emulsifying and preventing the slurry from precipitating, and has strong adhesive performance. The silicic acid can improve the dispersion performance and suspension performance of the adhesive 100, so that when the adhesive 100 forms a slurry with the active material, the active material can be uniformly suspended in the adhesive 100, and the adhesive 100 can be uniformly mixed with the active material and exert the adhesive performance on the active material. The silicic acid and the acrylate copolymer cooperate with each other to make the adhesive 100 have a higher viscosity. When the adhesive 100 is applied to the negative electrode sheet 200 and assembled in the battery 300, the adhesive 100 has a better adhesive effect on the active material, greatly reducing the probability of the active material falling off from the active material layer 220, and avoiding increasing the internal resistance of the battery 300, so that the battery 300 has better cycle stability.

[0064] Please refer to Figure 2 , the present application provides a preparation method of an adhesive 100 for preparing the adhesive 100 provided by the present application. The preparation method includes:

[0065] S101, providing acrylic acid, acrylonitrile, acrylamide and an initiator, and performing a polymerization reaction to form polyacrylic acid-acrylonitrile-acrylamide.

[0066] It can be understood that the polymerization monomers include acrylic acid, acrylonitrile, and acrylamide. In the polymerization monomers, the mass content of acrylic acid is 40% to 60%, the mass content of acrylonitrile is 40% to 60%, and the mass content of acrylamide is less than or equal to 10%, so that in the finally formed acrylate copolymer, the mass fraction m1 of acrylate ranges from: 40% ≤ m1 ≤ 60%, the mass fraction m2 of acrylonitrile ranges from: 40% ≤ m2 ≤ 60%, and the mass fraction m3 of acrylamide ranges from: 0 < m3 ≤ 10%.

[0067] It can be understood that the polyacrylic acid-acrylonitrile-acrylamide includes polyacrylic acid, polyacrylonitrile and polyacrylamide. The polyacrylic acid is polymerized from multiple acrylic acid monomers, the polyacrylonitrile is polymerized from multiple acrylonitrile monomers, and the polyacrylamide is polymerized from multiple acrylamide monomers. The polyacrylic acid-acrylonitrile-acrylamide is a copolymer of acrylic acid, acrylonitrile and acrylamide.

[0068] Preferably, the mass ratio of the initiator, the polymerization monomer and water is 0.5:7.5:92.

[0069] Optionally, the initiator is a solution with a mass fraction of 20% of ammonium persulfate.

[0070] It can be understood that in the initiator, the mass fraction of ammonium persulfate is 20%.

[0071] S102. Provide a silicate solution, and mix the silicate solution with polyacrylic acid - acrylonitrile - acrylamide to obtain the adhesive 100. The adhesive 100 includes an acrylate copolymer and silicic acid. In the adhesive 100, the content α of silicon element ranges from 5% ≤ α ≤ 10%.

[0072] In this embodiment, the polymerization monomers acrylic acid, acrylonitrile, and acrylamide undergo a polymerization reaction under the action of an initiator to form the polyacrylic acid - acrylonitrile - acrylamide. The polyacrylic acid - acrylonitrile - acrylamide is a copolymer of acrylic acid, acrylonitrile, and acrylamide. However, as the chain length of polyacrylic acid increases, the structure of carboxyl groups continuously increases, and polyacrylic acid undergoes cohesion and forms hydrogen bonds, which may cause polyacrylic acid to assume a spherical structure and result in a decrease in the viscosity of polyacrylic acid. Further, by mixing the provided silicate solution with polyacrylic acid - acrylonitrile - acrylamide and neutralizing the polyacrylic acid - acrylonitrile - acrylamide, the cations in the silicate solution replace the hydrogen on the carboxyl group of polyacrylic acid, and the hydrogen falling off from the carboxyl group of polyacrylic acid replaces the cations on the silicate, so that polyacrylic acid becomes polyacrylate, and the silicate becomes silicic acid, and finally the adhesive 100 is formed. The adhesive 100 includes an acrylate copolymer and silicic acid. Among them, the polyacrylate has a higher viscosity than the polyacrylic acid, which is beneficial to improving the adhesion performance of the adhesive 100. Secondly, the silicic acid can form a colloidal solution in an aqueous solution to improve the suspension performance of the adhesive 100 for the active material and further improve the slurry stability. In addition, the silicic acid also has good affinity with the active material, which is beneficial to the close contact between the adhesive 100 and the active material. Finally, when the generated adhesive 100 is applied to the negative electrode sheet 200, the adhesive 100 and the active material can be evenly distributed in the active material layer 220, and the adhesive 100 has good adhesion performance to the active material. When the negative electrode sheet 200 is applied to the battery 300, the probability of the active material falling off from the active material layer 220 can be reduced, so that the battery 300 has good cycle stability.

[0073] Optionally, the providing of acrylic acid, acrylonitrile, acrylamide, and an initiator, and carrying out a polymerization reaction to form polyacrylic acid - acrylonitrile - acrylamide includes:

[0074] S1011, Add partial acrylic acid, partial acrylonitrile and partial acrylamide into water at the first temperature T1. After introducing nitrogen for 2 h, add an initiator, start the reaction and raise the temperature to the second temperature T2, then start dropping the remaining acrylic acid, remaining acrylonitrile and remaining acrylamide. After reacting for 22 h, poly(acrylic acid-acrylonitrile-acrylamide) is obtained, and the relationship 18 °C ≤ T2 - T1 ≤ 30 °C is satisfied.

[0075] Optionally, the first temperature T1 satisfies the range 45 °C ≤ T1 ≤ 55 °C, and the second temperature T2 satisfies the range 65 °C ≤ T2 ≤ 75 °C.

[0076] Preferably, the first temperature is 50 °C and the second temperature is 70 °C.

[0077] S1012, Wash the poly(acrylic acid-acrylonitrile-acrylamide) 2 to 3 times.

[0078] Wash the poly(acrylic acid-acrylonitrile-acrylamide) 2 to 3 times to remove unreacted monomers and small molecule impurities.

[0079] In the above preparation process, the polymerization monomers can be fully mixed to enable the polymerization reaction to proceed fully, and finally make the components of the poly(acrylic acid-acrylonitrile-acrylamide) and the final acrylate copolymer meet a reasonable range.

[0080] Optionally, in some embodiments, the step of providing a silicate solution and mixing the silicate solution with poly(acrylic acid-acrylonitrile-acrylamide) to obtain the adhesive 100 further includes: the pH value of the adhesive 100 at 25 °C satisfies the range 6 ≤ pH ≤ 8.

[0081] Specifically, the pH value of the adhesive 100 at 25 °C can be, but is not limited to, 6, 6.2, 6.4, 6.7, 6.8, 7, 7.1, 7.2, 7.5, 7.6, 7.7, 7.8, 7.9 and 8, etc.

[0082] It can be understood that the silicate solution can ionize OH - in water to make the pH of the adhesive 100 satisfy the range 6 ≤ pH ≤ 8.

[0083] In this embodiment, when the pH of the adhesive 100 at 25 °C satisfies the range 6 ≤ pH ≤ 8, so that the silicate solution is relatively sufficient or slightly excessive, the silicate solution can react fully with polyacrylic acid in polyacrylic acid-acrylonitrile-acrylamide, and the cations in the silicate solution can replace the hydrogen on the polyacrylic acid, generating polyacrylate and silicic acid. The polyacrylate has a higher viscosity than polyacrylic acid, and the silicic acid can enhance the suspension ability of the adhesive 100, so that the active material can be uniformly dispersed in the adhesive 100, and the adhesive 100 can be mixed evenly with the active material, which is beneficial to the adhesive 100 to fully exert its adhesive performance.

[0084] Optionally, in some other embodiments, the step of providing a silicate solution and mixing the silicate solution with polyacrylic acid-acrylonitrile-acrylamide to obtain the adhesive 100 further includes:

[0085] The silicate solution further includes one of lithium ions or sodium ions. The polyacrylic acid-acrylonitrile-acrylamide includes polyacrylic acid. In the silicate solution, the amount of substance of the lithium ions or sodium ions is n1, and in the polyacrylic acid-acrylonitrile-acrylamide, the amount of substance of the carboxyl groups in the polyacrylic acid is n2. Then, the relational expression 0.8 ≤ n1 / n2 ≤ 1.2 is satisfied.

[0086] It can be understood that when the adhesive 100 is applied to the negative electrode plate 200 and assembled in a sodium ion battery, the silicate solvent includes sodium ions; when the adhesive 100 is applied to the negative electrode plate 200 and assembled in a lithium ion battery, the silicate solvent includes lithium ions.

[0087] Specifically, the value of n1 / n2 can be, but is not limited to, 0.8, 0.82, 0.84, 0.85, 0.86, 0.88, 0.9, 0.92, 0.95, 0.96, 0.98, 1, 1.02, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, and 1.2, etc.

[0088] In this embodiment, when n1 and n2 satisfy the range of 0.8 ≤ n1 / n2 ≤ 1.2, during the neutralization of the polyacrylic acid-acrylonitrile-acrylamide, the amount of substance of lithium ions or sodium ions in the silicate solution is within a reasonable range, so that lithium ions or sodium ions can replace the hydrogen on the carboxyl group of the polyacrylic acid, and the hydrogen falling off from the carboxyl group of the polyacrylic acid replaces the lithium ions or sodium ions on the silicate to generate polyacrylate and silicic acid. On the one hand, it can ensure that the polyacrylic acid in the polyacrylic acid-acrylonitrile-acrylamide is fully neutralized to form polyacrylate, so as to prevent the existence of excess polyacrylic acid in the binder 100 and avoid the cohesion of the polyacrylic acid from weakening the bonding performance of the binder 100. On the other hand, since silicic acid is the neutralization product of the polyacrylic acid and the silicate solution, the content of the generated silicic acid is also within a reasonable range. The silicic acid has the ability of thickening and emulsifying and preventing the precipitation of the slurry, which can improve the suspension ability of the binder 100, so that during the homogenization process, the acrylate copolymer can be uniformly mixed with the active material, improving the stability of the slurry, and finally enabling the binder 100 and the active material to be uniformly dispersed in the active material layer 220, and the binder 100 can fully exert its bonding performance on the active material, and the negative electrode sheet 200 has a large peeling force.

[0089] In some embodiments, the silicate solution includes at least one of a lithium metasilicate saturated solution, a lithium monosilicate solution, a lithium orthosilicate solution, a sodium metasilicate saturated solution, a sodium monosilicate solution, and a sodium orthosilicate solution.

[0090] It can be understood that when the binder 100 is applied to the negative electrode sheet 200 and assembled in a sodium ion battery, the silicate solvent includes at least one of a sodium metasilicate (Na2SiO3 or Na2O·SiO2) saturated solution, a sodium monosilicate (Na8SiO6 or 4Na2O·SiO2) solution, and a sodium orthosilicate (Na4SiO4 or 2Na2O·SiO2) solution.

[0091] It can be understood that when the binder 100 is applied to the negative electrode sheet 200 and assembled in a lithium ion battery, the silicate solvent includes at least one of a lithium metasilicate (Li2SiO3 or Li2O·SiO2) saturated solution, a lithium monosilicate (Li8SiO6 or 4Li2O·SiO2) solution, and a lithium orthosilicate (Li4SiO4 or 2Li2O·SiO2) solution.

[0092] In this embodiment, during the neutralization of the sediment, saturated lithium metasilicate solution, lithium monosilicate solution, and lithium orthosilicate solution can provide lithium ions and replace the hydrogen on the carboxyl group of polyacrylic acid, so that polyacrylic acid forms lithium polyacrylate, improving the adhesion performance of the adhesive 100. Similarly, saturated sodium metasilicate solution, sodium monosilicate solution, and sodium orthosilicate solution can provide sodium ions and replace the hydrogen on the carboxyl group of polyacrylic acid, so that polyacrylic acid forms sodium polyacrylate, also improving the adhesion performance of the adhesive 100. In addition, the above silicate solutions all contain silicate ions, and silicic acid, a by-product, can be formed during the neutralization of the sediment, improving the suspension ability of the adhesive 100 and further enhancing the stability of the slurry when the adhesive 100 is mixed with the active material. Therefore, it is beneficial for the adhesive 100 to fully exert its role in bonding the active material, and to improve the peel strength of the negative electrode sheet 200 when the adhesive 100 is applied to the negative electrode sheet 200.

[0093] Please refer to Figure 1 , this application also provides a negative electrode sheet 200, which includes a current collector layer 210 and an active material layer 220. The active material layer 220 is disposed on at least one side of the current collector layer 210. The active material layer 220 includes an active material, and the active material layer 220 further includes the adhesive 100 provided by this application or the adhesive 100 prepared by the preparation method of the adhesive 100 provided by this application. The adhesive 100 is used to bond the active material.

[0094] It can be understood that in some embodiments, the number of the active material layers 220 is one layer, and the active material layer 220 is disposed on one side of the current collector layer 210; in other embodiments, the number of the active material layers 220 is two layers, and the two active material layers 220 are respectively disposed on opposite sides of the current collector layer 210.

[0095] Optionally, the active material can be, but is not limited to, graphite, hard carbon, etc.

[0096] In this embodiment, the active material layer 220 includes an active material, and the binder 100 provided by the present application or the binder 100 prepared by the preparation method of the binder 100 provided by the present application. During the preparation process of the negative electrode tab 200, the binder 100 and the active material form a slurry. The binder 100 includes an acrylate copolymer and silicic acid. The silicic acid has the ability of thickening and emulsifying and preventing the slurry from precipitating, and can form a colloidal solution in the slurry, improving the suspension ability of the binder 100 and uniformly dispersing the active material in the slurry, avoiding the deposition of the active material to the bottom of the slurry and resulting in insufficient amount of the active material in the upper layer of the slurry. When the slurry is coated on the current collector layer 210, the binder 100 and the active material are uniformly mixed, so that after rolling and drying, the binder 100 and the active material can be uniformly dispersed in the active material layer 220. The binder 100 has a strong adhesive force to the active material, also making the adhesive force between the active material layer 220 and the current collector layer 210 strong, and finally making the negative electrode tab 200 have a large peel force. When the negative electrode tab 200 is applied to the battery 300, during the charge and discharge process of the battery 300, the active material is not easily detached from the active material layer 220, which can slow down the increase of the internal resistance of the battery 300, so that the battery 300 has good cycle stability.

[0097] Optionally, the active material layer 220 further includes a styrene-butadiene rubber binder, and the styrene-butadiene rubber binder cooperates with the binder 100 to effectively bond the active material.

[0098] Please refer to Figure 3 , the present application provides a battery 300, which includes: the negative electrode tab 200 provided by the present application, a separator 310, a positive electrode tab 320, and an electrolyte 330. The separator 310 is disposed on one side of the negative electrode tab 200; the positive electrode tab 320 is disposed on the side of the separator 310 away from the negative electrode tab 200; the electrolyte 330 is used to infiltrate at least part of the negative electrode tab 200, the separator 310, and the positive electrode tab 320.

[0099] It can be understood that the negative electrode tab 200, the separator 310, and the positive electrode tab 320 are arranged in sequence.

[0100] Optionally, in some embodiments, the battery 300 is a lithium-ion battery; in other embodiments, the battery 300 is a sodium-ion battery.

[0101] In this embodiment, the electrolyte 330 is used to infiltrate at least part of the negative electrode plate 200, at least part of the separator 310, and at least part of the positive electrode plate 320, so that the active ions in the electrolyte 330 can be transmitted between the negative electrode plate 200 and the positive electrode plate 320 to realize the charge and discharge process of the battery 300. Among them, the negative electrode plate 200 includes the adhesive 100 provided in this application or the adhesive 100 prepared by the preparation method of the adhesive 100. The adhesive 100 includes an acrylate copolymer and silicic acid. The acrylate copolymer and the silicic acid cooperate with each other so that when the adhesive 100 is mixed with the active material, the adhesive 100 can be fully and evenly mixed with the active material and has a relatively large viscosity, and the negative electrode plate 200 has a relatively large peeling force. During the charge and discharge process of the battery 300, the active material is not easily detached from the active material layer 220, which can slow down the increase in the internal resistance of the battery 300, so that the battery 300 has better cycle stability.

[0102] The technical solution of this application will be further introduced in multiple embodiments as follows:

[0103] Examples 1 to 8, Comparative Examples 1 to 3:

[0104] 1. Preparation of the adhesive 100:

[0105] An initiator (ammonium persulfate solution), polymerization monomers, and water are provided. The polymerization monomers include 50% by mass of acrylic acid, 45% by mass of acrylonitrile, and 5% by mass of acrylamide. At 50 °C, 25% by mass of acrylic acid, 22.5% by mass of acrylonitrile, and 2.5% by mass of acrylamide are added to water. After introducing nitrogen for 2 h, the initiator is added. After the reaction starts and the temperature rises to 70 °C, the remaining polymerization monomers are added dropwise. After reacting for 22 h, polyacrylic acid-acrylonitrile-acrylamide is obtained, and polyacrylic acid-acrylonitrile-acrylamide is washed. Further, a silicate solution is added dropwise to neutralize polyacrylic acid-acrylonitrile-acrylamide to obtain the adhesive 100 of Examples 1 to 8 and Comparative Examples 1 to 3. The adhesive 100 includes an acrylate copolymer and silicic acid. In the adhesive 100, the content α of silicon element ranges from 5% ≤ α ≤ 10%.

[0106] Among them, the types of silicate solutions, the viscosity μ value of the adhesive 100 when the solid content is 3%, and the pH value of the adhesive 100 at 25 °C are shown in Table 1.

[0107] Among them, the viscosity μ of the adhesive 100 when the solid content is 3% is obtained by a rotational viscometer. The specific test method is as follows: ① First, install a rotor of No. 63 on the rotational viscometer, and at the same time adjust the instrument to be horizontal and calibrate the zero position; ② Process the sample to be tested into a state suitable for testing, pour it into the sample pool, and ensure that the liquid level reaches the specified position and there are no bubbles; ③ Set the rotation speed to 6 rpm, the measurement time to 3 minutes, keep the sample at a temperature of 45 °C, start the instrument for measurement, and record the viscosity data after stabilization, so as to obtain the viscosity μ of the adhesive 100.

[0108] Among them, the pH of the adhesive 100 at 25 °C is measured by a pH meter (model: Mettler FE28). The specific test method is as follows: Take the sample to be tested, and the amount of the sample to be tested is greater than 200 g, and place it in a thermostatic bath to ensure that the temperature is constant at 25 °C. Use the Leici calibration solutions 4.00, 6.86, and 9.18 to perform three-point calibration on the pH meter to ensure the accuracy of the measurement. Immerse the calibrated pH meter electrode into the sample to be tested, and record the reading after the signal is stable. Conduct 5-6 groups of parallel tests, and take the average value as the pH of the adhesive 100.

[0109] 2. Preparation of the negative electrode plate 200:

[0110] The active material (graphite), conductive agent (conductive carbon black), adhesive 100, and solvent water are prepared into a negative electrode slurry according to the kneading process. The active material layer 220 is coated on the base-coated current collector layer 210 (copper foil) by a coater, and the moisture is removed by high-temperature baking. The obtained electrode plate is rolled to obtain the negative electrode plates 200 of Examples 1 to 8 and Comparative Examples 1 to 3. The compaction density of the negative electrode plate 200 is 1.5 g / cm 3 .

[0111] Among them, the adhesive 100 of Example 1 is applied to the negative electrode plate 200 of Example 1, the adhesive 100 of Example 2 is applied to the negative electrode plate 200 of Example 2, the adhesive 100 of Comparative Example 1 is applied to the negative electrode plate 200 of Comparative Example 1, and so on.

[0112] Among the negative electrode plates 200 of Examples 1 to 8 and Comparative Examples 1 to 3, the value α of the silicon element content in the adhesive 100 is shown in Table 1.

[0113] Specifically, the content α of silicon element in the adhesive 100 is obtained by ICP element detection method as follows: Use a pole piece cutter (CP) to cut the negative pole piece 200 into a size suitable for observation, usually about 1 cm × 1 cm. Place the processed sample on the SEM (scanning electron microscope) sample stage, ensure that the sample is stable and the cutting surface is facing up. Observe the sample under the SEM to find the area where the adhesive 100 is located; Before performing EDS (energy dispersive X-ray spectrometer) analysis, calibrate the EDS system using a standard sample (such as a pure silicon standard sample or a standard sample containing a known silicon content), then focus the electron beam on the selected adhesive 100 area and start collecting X-ray spectra. Record the energy and intensity of the characteristic X-rays, and use the EDS software to calculate the percentage content of silicon element.

[0114] 3. Preparation of the battery 300:

[0115] Provide a positive pole piece 320, a separator 310 and an electrolyte 330, where the positive pole piece 320, the separator 310 and the electrolyte 330 are of conventional formulations in the art and are not limited herein.

[0116] Stack the above positive pole piece 320, separator 310, and negative pole piece 200 in sequence, so that the separator 310 is between the positive pole piece 320 and the negative pole piece 200 to play an isolation role, and then wind them into a bare electrode assembly; After welding the tab, place the bare battery 300 in the outer packaging case, inject the above electrolyte 330 after drying, and after vacuum packaging, standing, forming, shaping, etc., finally prepare the implementation batteries 1 to 8 and the comparative batteries 1 to 3.

[0117] Among them, the negative pole piece 200 of Example 1 is assembled into the implementation battery 1, the negative pole piece 200 of Example 2 is assembled into the implementation battery 2, the negative pole piece 200 of Comparative Example 1 is assembled into the comparative battery 1, and so on.

[0118] The following Table 1 is a table of relevant parameters of the adhesive 100 of Examples 1 to 8 and Comparative Examples 1 to 3.

[0119]

[0120] Among them, in the preparation process of the adhesive 100 of Comparative Example 1, the solution for neutralizing the polyacrylic acid-acrylonitrile-acrylamide is a Li2CO3 solution, so that the adhesive 100 of Comparative Example 1 does not include silicic acid.

[0121] Understandably, the pH value of the adhesive 100 depends on the content of each component in the acrylate copolymer. When the content of each component in the acrylate copolymer is determined, the pH value of the adhesive 100 remains unchanged. For example, in Examples 1 to 3, the mass fraction m1 of acrylate, the mass fraction m2 of acrylonitrile, and the mass fraction m3 of acrylamide in the acrylate copolymer are equal one by one, making the pH values of the adhesives 100 in Examples 1 to 3 equal.

[0122] Performance test of the negative electrode sheet 200:

[0123] The tensile machine was used to test the peel strength of the negative electrode sheets 200 of Examples 1 to 8 and Comparative Examples 1 to 3. The test method was as follows: Step 1, lay the negative electrode sheet 200 flat, and use a ruler and a utility knife to prepare the negative electrode sheet 200 into strips with a specification of 200 mm × 25 mm. Usually, 3 to 5 test strips need to be prepared for a group of samples; Step 2, stick one side of the double-sided tape to the middle of the steel plate, and roll it back and forth with a roller 3 times to firmly bond it to the test steel plate; Step 3, align one end of the test strip with the steel plate, with the double-sided tape slightly wider on both sides, and fit it parallel and centered to the other side of the double-sided tape. Roll it with a roller 3 times in one direction to make it fit flat. Manually peel the test strip 5 mm to 10 mm from the bottom, and use the tensile machine to perform peeling with a 90° clamp to obtain the peel force of the test strip.

[0124] Among them, the peel force of the test strip can characterize the peel force of the negative electrode sheet 200. More specifically, it can characterize the peel force between the active material layer 220 and the current collector layer 210 in the negative electrode sheet 200. The greater the peel force of the negative electrode sheet 200, the better the bonding performance of the adhesive 100. Correspondingly, the adhesive 100 has better bonding performance for the active material.

[0125] The peel strength refers to the peel force required per unit width of the bonding surface of the adhesive 100 in the direction perpendicular to the bonding surface. In other words, the peel strength is the ratio of the peel force to the width of the bonding surface of the adhesive 100. In this application, the peel strength of the negative electrode sheet 200 is the ratio of the peel force of the test strip to the width (25 mm). Thus, the peel strength values of the negative electrode sheets 200 of Examples 1 to 8 and Comparative Examples 1 to 3 are obtained.

[0126] Among them, the peel strength values of the negative electrode sheets 200 of Examples 1 to 8 and Comparative Examples 1 to 3 are shown in Table 2.

[0127] Performance test of the battery 300:

[0128] The above-mentioned implementation batteries 1 to 8 and comparative batteries 1 to 3 were subjected to a constant-power charge-discharge cycle test on a charge-discharge instrument. The test temperature was 25°C, and the charge-discharge rate was 0.5C (the magnitude of the charge-discharge current is usually represented by the charge-discharge rate. The calculation formula for the charge-discharge current is: charge-discharge power = voltage platform of battery 300 (3.2V) × rated capacity of battery 300). The charge-discharge voltage window was 2.5V to 3.65V (i.e., the charge cut-off voltage of battery 300 was 3.65V, and the discharge cut-off voltage of battery 300 was 2.5V; generally, when the charge cut-off voltage ≥ 4V, the charge cut-off voltage of battery 300 is relatively high). The capacity retention rate after 1000 cycles was calculated. The calculation formula was: capacity retention rate after the Nth cycle = (discharge capacity after the Nth cycle / discharge capacity of the first cycle) × 100%.

[0129] Among them, usually, one complete charge and discharge is called one charge-discharge cycle, that is, battery 300 is first charged from 2.5V to 3.65V, and then discharged from 3.65V to 2.5V, thus forming one charge-discharge cycle. Cycling N times means repeating the above process N times.

[0130] Among them, the values of the capacity retention rates of implementation batteries 1 to 8 and comparative batteries 1 to 3 after 1000 cycles are shown in Table 2.

[0131] The following Table 2 shows the performance parameters of the negative electrode plates 200 of Examples 1 to 8 and Comparative Examples 1 to 3, as well as the performance parameters of implementation batteries 1 to 8 and comparative batteries 1 to 3.

[0132]

[0133] Among them, the capacity retention rate of Example 1 after 1000 cycles represents the capacity retention rate of implementation battery 1 after 1000 cycles, the capacity retention rate of Example 2 after 1000 cycles represents the capacity retention rate of implementation battery 2 after 1000 cycles, the capacity retention rate of Comparative Example 1 after 1000 cycles represents the capacity retention rate of comparative battery 1 after 1000 cycles, and so on.

[0134] Please refer to Table 1 and Table 2. From the data of Examples 1 to 3 and Comparative Example 1, it can be seen that during the preparation of the adhesive 100 in Examples 1 to 3, a silicate solution was used to neutralize the polyacrylic acid-acrylonitrile-acrylamide formed by the polymerization monomers, so that the adhesive 100 includes the acrylate copolymer and silicic acid, and the addition amount of the silicate solution is within a reasonable range. The content α of silicon element in the adhesive 100 satisfies a reasonable range. During the preparation of the adhesive 100 in Comparative Example 1, Li2CO3 solution was directly used to neutralize the polyacrylic acid-acrylonitrile-acrylamide, so that the adhesive 100 in Comparative Example 1 only includes the acrylate copolymer and does not include silicic acid. This makes the pH value of the adhesive 100 in Examples 1 to 3 greater than that of the adhesive 100 in Comparative Example 1. When the solid content of Examples 1 to 3 is 3%, the viscosity μ of the adhesive 100 is within a reasonable range and greater than the viscosity μ of the adhesive 100 with a solid content of 3% in Comparative Example 1. Moreover, the peel strength of the negative electrode plate 200 in Examples 1 to 3 is greater than that of the negative electrode plate 200 in Comparative Example 1. The capacity retention rate of Battery 1 to Battery 3 after 1000 cycles is higher than that of Comparative Battery 1 after 1000 cycles. The reason is as follows: In Examples 1 to 3, the silicate solution provided is used to neutralize the polyacrylic acid-acrylonitrile-acrylamide. The cations in the silicate solution replace the hydrogen on the carboxyl group of the polyacrylic acid, and the hydrogen falling off from the carboxyl group of the polyacrylic acid replaces the cation on the silicate, so that the polyacrylic acid becomes polyacrylate and the silicate becomes silicic acid, and finally the adhesive 100 is formed. Among them, the polyacrylate has a higher viscosity than the polyacrylic acid, which is beneficial to improving the adhesion performance of the adhesive 100. Secondly, the silicic acid can form a colloidal solution in the aqueous solution to improve the suspension performance of the adhesive 100. When the adhesive 100 is mixed with the active material to form a slurry, the active material can be uniformly dispersed in the adhesive 100, further improving the slurry stability. In addition, the silicic acid also has a good affinity with the active material, which is beneficial to the close contact between the adhesive 100 and the active material. Finally, when the generated adhesive 100 is applied to the negative electrode plate 200, the adhesive 100 and the active material can be uniformly distributed in the active material layer 220. The adhesive 100 has good adhesion performance to the active material, so the adhesive 100 in Examples 1 to 3 has a greater peeling force, effectively reducing the probability of the active material falling off from the active material layer 220, and finally making Battery 1 to Battery 3 have good cycle stability. Furthermore, under the same other conditions, using Li2SiO3 solution to neutralize the polyacrylic acid-acrylonitrile-acrylamide has the best effect, making the peeling force of the negative electrode plate 200 in Example 1 the largest.In Comparative Example 1, only Li2CO3 solution was used to neutralize polyacrylic acid-acrylonitrile-acrylamide. However, the reaction between Li2CO3 solution and polyacrylic acid could not produce by-product silicic acid. In the slurry formed by the binder 100 and the active material, the suspension ability of the binder 100 was still too poor, and the content of the active material in the upper layer of the slurry was small. When the slurry was coated on the current collector layer 210, the binder 100 and the active material were not evenly mixed, so that part of the binder 100 could not effectively bond the active material, increasing the probability of the active material peeling off from the active material layer 220. As a result, the peeling force of the negative electrode sheet 200 in Comparative Example 1 was too small, and the cycle stability of the comparative battery 1 was poor.

[0135] Further, please refer to Example 1, Example 4, Example 5 and Comparative Example 2. During the preparation of the adhesive 100 in Example 1, Example 4, Example 5 and Comparative Example 2, Li2SiO3 solution was used to neutralize polyacrylic acid-acrylonitrile-acrylamide. By adjusting the value of n1 / n2, the content α of silicon element in the corresponding generated adhesive 100 can be made different, and finally affect the viscosity of the adhesive 100, the peel strength of the negative electrode sheet 200 and the cycle stability of the battery 300. Specifically, under the same other conditions, the content α of silicon element in the adhesive 100 and the viscosity μ value of the adhesive 100 when the solid content is 3% in Example 1, Example 4 and Example 5 are all within a reasonable range, while the content α of silicon element in the adhesive 100 and the viscosity μ value of the adhesive 100 when the solid content is 3% in Comparative Example 1 are both too small, which makes the peel strength of the negative electrode sheet 200 in Example 1, Example 4 and Example 5 greater than that of the negative electrode sheet 200 in Comparative Example 2, and the capacity retention rate of the implemented battery 1, the implemented battery 4 and the implemented battery 5 after 1000 cycles is greater than that of the comparative battery 1 after 1000 cycles. In addition, when the content α of silicon element in the adhesive 100 satisfies a reasonable range, as the value of α gradually increases, the viscosity μ value of the adhesive 100 when the solid content is 3% gradually increases, the pH value of the adhesive 100 gradually increases, and correspondingly, the peel strength of the negative electrode sheet 200 gradually increases, and the capacity retention rate of the battery 300 after 1000 cycles gradually increases. The reason is as follows: when the content α of silicon element satisfies the range of 5% ≤ α ≤ 10%, in the adhesive 100, the content of silicon element is within a reasonable range. On the one hand, the content of silicon element is positively correlated with the content of silicic acid. Correspondingly, silicic acid is the neutralization product of acrylic acid and silicate, so the silicate neutralizes a certain amount of acrylic acid and forms acrylate to avoid the aggregation of acrylic acid due to hydrogen bond action. Acrylate has a greater viscosity than acrylic acid, so that the acrylate copolymer has better adhesion performance. On the other hand, correspondingly, the content of silicic acid is within a reasonable range. The silicic acid has the ability of thickening and emulsifying and preventing the slurry from precipitating, which can make the adhesive 100 form a colloidal solution, improve the suspension ability and stability of the adhesive 100, so as to facilitate the uniform distribution of the adhesive 100 and the active material in the active material layer 220. The adhesive 100 can fully exert its adhesion performance to the active material, so that the negative electrode sheet 200 has a greater peel strength, and its corresponding battery 300 has better cycle stability. Correspondingly, the greater the value of the content α of silicon element, the more silicic acid is generated, the stronger the suspension ability of the adhesive 100, the more beneficial it is to increase the viscosity of the adhesive 100, and improve the peel strength of its corresponding negative electrode sheet 200 and the cycle stability of its corresponding battery 300.

[0136] In addition, please refer to Example 5 and Comparative Example 3. The content α of silicon element in the adhesive 100 in Comparative Example 3 is twice that of the adhesive 100 in Example 5. However, when the solid content of Comparative Example 3 is 3%, the viscosity μ of the adhesive 100 is compared with the viscosity μ of the adhesive 100 when the solid content of Example 5 is 3%. This shows that when α increases to a certain extent, it is difficult to further increase the viscosity of the adhesive 100. In addition, the pH value of the adhesive 100 in Comparative Example 3 is much higher than that in Example 5. The peel strength of the negative electrode sheet 200 in Example 5 is much greater than that of the negative electrode sheet 200 in Comparative Example 3, and the capacity retention rate of the implemented battery 5 after 1000 cycles is much greater than that of the comparative battery 3 after 1000 cycles. This is because when the content α of silicon element in the adhesive 100 is excessive, the content of silicic acid in the adhesive 100 increases, and the increase in the content of silicic acid cannot improve the bonding performance of the adhesive 100, resulting in a decrease in the peel strength of the corresponding negative electrode sheet 200 and a reduction in the cycle stability of the corresponding battery 300.

[0137] Furthermore, please refer to Example 1, Example 6 to Example 8. Under the same other conditions, by adjusting the mass fraction m1 of acrylic acid, the mass fraction m2 of acrylonitrile, and the mass fraction m3 of acrylamide in the acrylate copolymer, the viscosity μ of the adhesive 100 when the solid content is 3% can be adjusted. Specifically, as the mass fraction m2 of acrylonitrile increases, the viscosity of the adhesive 100 gradually increases. Correspondingly, the peel force of the corresponding negative electrode sheet 200 gradually increases, and the capacity retention rate of the corresponding battery 300 after 1000 cycles gradually increases.

[0138] Please refer to Figure 4 and Figure 5 , this application provides an electrical device 400, which includes: a device body 410 and the battery 300 provided by this application, and the battery 300 supplies power to the device body 410.

[0139] It can be understood that the battery 300 is electrically connected to the device body 410.

[0140] In this embodiment, the negative electrode plate 200 of the battery 300 includes the binder 100 provided by the present application or the binder 100 prepared by the preparation method of the binder 100 provided by the present application. The binder 100 includes an acrylate copolymer and silicic acid. The acrylate copolymer and the silicic acid cooperate with each other so that when the binder 100 is mixed with the active material, the binder 100 can be fully and evenly mixed with the active material and has a relatively large viscosity, and the negative electrode plate 200 has a relatively large peel force. During the charge and discharge process of the battery 300, the active material is not easily detached from the active material layer 220, which can slow down the increase in the internal resistance of the battery 300, thereby enabling the battery 300 to have better cycle stability. When the battery 300 powers the device body 410, the battery 300 can provide stable electric energy for the device body 410, which is beneficial to improving the user experience.

[0141] Optionally, the electrical device 400 in the embodiments of the present application may be, but is not limited to, portable electronic devices such as mobile phones, tablet computers, laptop computers, desktop computers, smart bracelets, smart watches, e-readers, game consoles, etc. It may also be transportation means such as cars, trucks, sedans, freight trucks, bullet trains, high-speed rails, and electric scooters. In addition, it may also be various household appliances, etc. The present application Figure 4 The electrical device 400 in the embodiment of the present application is an energy storage battery cabinet.

[0142] It can be understood that the electrical device 400 described in this embodiment is only one form of the electrical device 400 to which the battery 300 is applied, and should not be construed as a limitation on the electrical device 400 provided by the present application, nor should it be construed as a limitation on the electrical device 400 provided by each embodiment of the present application.

[0143] In the present application, the mention of "embodiment" and "embodiment" means that the specific features, structures, or characteristics described in connection with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described in the present application can be combined with other embodiments. In addition, it should also be understood that the features, structures, or characteristics described in each embodiment of the present application can be combined arbitrarily without contradiction to form another embodiment that does not depart from the spirit and scope of the technical solution of the present application.

[0144] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the above preferred embodiments, those of ordinary skill in the art should understand that modifications or equivalent replacements can be made to the technical solutions of the present application without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. An adhesive, characterized in that, The adhesive includes an acrylate copolymer and silicic acid. In the adhesive, the content α of silicon element ranges from 5% ≤ α ≤ 10%; the mass content of the silicic acid satisfies the range: 15% to 30%; the acrylate copolymer is a copolymer of acrylate, acrylonitrile and acrylamide; in the acrylate copolymer, the mass fraction m1 of the acrylate ranges from 40% ≤ m1 ≤ 60%, the mass fraction m2 of the acrylonitrile ranges from 40% ≤ m2 ≤ 60%, and the mass fraction m3 of the acrylamide ranges from 0 < m3 ≤ 10%; wherein, the silicic acid is obtained by the reaction of polyacrylic acid-acrylonitrile-acrylamide and silicate.

2. The adhesive according to claim 1, characterized in that, The adhesive further includes water, and the acrylate copolymer and silicic acid are dispersed in water. When the solid content of the adhesive is 3%, the viscosity μ of the adhesive ranges from 5500 mPa·s ≤ μ ≤ 9000 mPa·s, wherein the solid content of the adhesive is the sum of the mass fractions of the acrylate copolymer and the silicic acid in the adhesive.

3. A method for preparing an adhesive, which is used to prepare the adhesive according to claim 1 or 2, characterized in that, The preparation method includes: Providing acrylic acid, acrylonitrile, acrylamide and an initiator, and carrying out a polymerization reaction to form polyacrylic acid-acrylonitrile-acrylamide; and Providing a silicate solution, and mixing the silicate solution with polyacrylic acid-acrylonitrile-acrylamide to obtain the adhesive, the adhesive includes an acrylate copolymer and silicic acid, and in the adhesive, the content α of silicon element ranges from 5% ≤ α ≤ 10%.

4. The preparation method of the adhesive according to claim 3, wherein The silicate solution includes at least one of a saturated solution of lithium metasilicate, a solution of lithium monosilicate, a solution of lithium orthosilicate, a saturated solution of sodium metasilicate, a solution of sodium monosilicate, and a solution of sodium orthosilicate.

5. The preparation method of the adhesive according to claim 3, wherein, The step of providing a silicate solution and mixing the silicate solution with polyacrylic acid-acrylonitrile-acrylamide to obtain the adhesive further includes: the pH value of the adhesive at 25°C satisfies the range: 6 ≤ pH ≤ 8.

6. A negative electrode plate, characterized in that, The negative electrode sheet includes: A current collector layer; and An active material layer, the active material layer is disposed on at least one side of the current collector layer, the active material layer includes an active material, and the active material layer further includes the adhesive according to claim 1 or 2 or the adhesive prepared by the preparation method of the adhesive according to claims 3 to 5, and the adhesive is used to bond the active material.

7. A battery, characterized in that, The battery includes: The negative electrode sheet according to claim 6; A separator, the separator is disposed on one side of the negative electrode sheet; A positive electrode sheet, the positive electrode sheet is disposed on the side of the separator away from the negative electrode sheet; and An electrolyte, the electrolyte is used to infiltrate at least part of the negative electrode sheet, the separator and the positive electrode sheet.

8. An electrical equipment, characterized in that, The electrical device includes: A device body; and The battery according to claim 7, and the battery supplies power to the device body.

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