Adhesive, negative electrode containing the adhesive, secondary battery and battery pack

Abstract

This application provides an adhesive, a negative electrode sheet containing the adhesive, a secondary battery, and a battery pack, wherein the adhesive comprises a copolymer formed by polymerizing acrylic acid, acrylonitrile, and acrylamide; the adhesive also contains lithium and copper elements, wherein the molar ratio of lithium to copper is 1 to 5:1.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and more particularly to a binder, a negative electrode sheet containing the binder, a secondary battery, and a battery pack. Background Technology

[0002] Secondary batteries (such as lithium-ion batteries) have advantages such as high energy density, low self-discharge, and light weight, and are therefore widely used in energy storage devices and other fields.

[0003] As a key structural component of secondary batteries, the negative electrode plays a crucial role in their performance. With increasing demands for secondary battery performance, particularly in wind power and solar power energy storage applications, improving the peel strength and flexibility of the negative electrode to further enhance the cycle performance of the secondary battery has become a pressing issue. Summary of the Invention

[0004] To address the aforementioned technical problems, this application discloses an adhesive, a negative electrode sheet containing the adhesive, a secondary battery, and a battery pack, in order to improve the cycle performance of the secondary battery.

[0005] In a first aspect, this application provides an adhesive comprising a copolymer formed by polymerizing acrylic acid, acrylonitrile, and acrylamide;

[0006] The adhesive also contains lithium and copper, wherein the molar ratio of lithium to copper is 1 to 5:1.

[0007] In some embodiments of this application, the molar ratio of lithium to copper is 2 to 3:1.

[0008] In some embodiments of this application, based on the total mass of the copolymer, the mass percentage of acrylic acid is 40% to 60%, the mass percentage of acrylonitrile is 30% to 50%, and the mass percentage of acrylamide is 2% to 10%.

[0009] In some embodiments of this application, the adhesive is a lithium copper acrylate polymer.

[0010] Secondly, this application provides a method for preparing an adhesive as described in the first aspect, comprising the following steps:

[0011] The reaction product is obtained by polymerizing acrylic acid, acrylonitrile and acrylamide;

[0012] The first solution is added to the reaction product, and the binder is obtained after neutralization.

[0013] Alternatively, acrylic acid, acrylonitrile, and acrylamide can be mixed with the first solution and polymerized to obtain the adhesive.

[0014] The first solution includes a first solvent and a second solvent. The first solvent includes a lithium-containing alkali and / or salt, and the second solvent includes a copper-containing alkali and / or salt. The molar ratio of lithium to copper in the first solution is 1 to 5:1.

[0015] In some embodiments of this application, the molar ratio of lithium to copper in the first solution is 2 to 3:1.

[0016] In some embodiments of this application, the first solvent includes at least one of lithium hydroxide and lithium carbonate, and the second solvent includes at least one of copper hydroxide and copper carbonate.

[0017] Thirdly, this application provides a negative electrode sheet, including a negative current collector, at least one side of which has a negative active material layer, the negative active material layer including a negative active material and a binder, the negative active material including a carbon material, wherein the binder is the binder described in the first aspect, or the binder is prepared by the method of preparing the binder described in the second aspect.

[0018] In some embodiments of this application, the carbon material includes at least one of artificial graphite, natural graphite, and hard carbon.

[0019] In some embodiments of this application, the peel strength of the negative electrode sheet is not less than 8 N / m, and the flexibility value is not higher than 425 mN.

[0020] Fourthly, this application provides a secondary battery, including the negative electrode sheet described in the third aspect.

[0021] Fifthly, this application provides a battery pack including a housing and at least one secondary battery as described in the fourth aspect, the secondary battery being housed within the housing.

[0022] In a sixth aspect, this application provides an electrical device including the secondary battery described in the fourth aspect or the battery pack described in the fifth aspect.

[0023] Compared with the prior art, this application has at least the following beneficial effects:

[0024] This application provides an adhesive, a negative electrode sheet containing the adhesive, a secondary battery, and a battery pack. The adhesive comprises a copolymer formed by polymerizing acrylic acid, acrylonitrile, and acrylamide. The adhesive also contains lithium and copper elements, with a lithium to copper molar ratio of 1 to 5:1. The adhesive of this application includes lithium and copper elements, and by adjusting the lithium to copper molar ratio within the range of this application, a lithium copper acrylate polymer can be formed. In this lithium copper acrylate polymer, one lithium ion can bond with one carboxyl group in the copolymer to form a one-dimensional structure, and one copper ion can bond with two carboxyl groups in the copolymer to form a three-dimensional cross-linked structure. Through the combined action of the one-dimensional and three-dimensional cross-linked structures, the negative electrode active material can be effectively dispersed and bonded, thereby improving the peel strength and flexibility of the negative electrode sheet, and thus improving the cycle performance of the secondary battery. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the "linear-spherical-dot" composite structure according to one embodiment of this application;

[0027] Figure 2 This is a schematic diagram of the structure of a residential energy storage system according to one embodiment of this application;

[0028] Figure 3 This is a schematic diagram of the energy storage system according to one embodiment of this application.

[0029] Explanation of reference numerals in the attached drawings: 1-Energy storage device, 2-Electric power conversion device, 3-First user load, 4-Second user load, 10-Negative electrode active material particles, 11-Three-dimensional cross-linked structure, 12-One-dimensional structure, 400-Energy storage system, 410-High voltage cable, 420-First electric power conversion device, 430-Second electric power conversion device. Detailed Implementation

[0030] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0032] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0033] Furthermore, the terms "installation," "setup," "equipped with," "connection," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0034] Furthermore, the terms "first," "second," etc., are primarily used to distinguish different devices, elements, or components (which may be the same or different in specific type and construction), and are not intended to indicate or imply the relative importance or quantity of the indicated devices, elements, or components. Unless otherwise stated, "a plurality of" means two or more.

[0035] It should be noted that this application uses lithium-ion batteries as an example of secondary batteries to explain the application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0036] This application provides an adhesive comprising a copolymer formed by polymerizing acrylic acid, acrylonitrile, and acrylamide, and further comprising lithium and copper elements, wherein the molar ratio of lithium to copper is 1 to 5:1; in another optional embodiment, the molar ratio of lithium to copper is 2 to 3:1. For example, the molar ratio of lithium to copper is 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, or 5:1.

[0037] The binder of this application includes lithium and copper elements. By adjusting the molar ratio of lithium to copper elements within the above-mentioned range, in this binder, one lithium ion can bond with one carboxyl group in the copolymer to form a one-dimensional structure, and one copper ion can bond with two carboxyl groups in the copolymer to form a three-dimensional cross-linked structure, thereby making it easier to form a "linear-spherical-dot" composite structure with carbon-based negative electrode active materials.

[0038] refer to Figure 1 , Figure 1 This is a schematic diagram of a "linear-spherical-dot" composite structure according to one embodiment of this application. The composite structure has three parts: the first part is dot-shaped negative electrode active material particles 10, such as graphite particles; the second part is a three-dimensional cross-linked structure 11 formed by copper ions and carboxyl groups in the copolymer, which is spherical; and the third part is a one-dimensional structure 12 formed by lithium ions and carboxyl groups in the copolymer, which is linear. The three-dimensional cross-linked structure of the second part more easily combines with carbon-based negative electrode active materials, thereby improving the interfacial adhesion performance of the negative electrode active material; the one-dimensional structure of the third part can provide steric hindrance, thereby improving the dispersibility of the negative electrode slurry. Under the action of this "linear-spherical-dot" composite structure, the negative electrode active material can be effectively dispersed and bonded, thereby improving the peel strength and flexibility of the negative electrode sheet, and thus improving the cycle performance of the lithium-ion battery.

[0039] In some embodiments of this application, based on the total mass of the copolymer, the mass percentage of acrylic acid is 40% to 60%, the mass percentage of acrylonitrile is 30% to 50%, and the mass percentage of acrylamide is 2% to 10%. For example, the mass percentage of acrylic acid is 40%, 45%, 50%, 55%, or 60%; the mass percentage of acrylonitrile is 30%, 35%, 40%, 45%, or 50%; and the mass percentage of acrylamide is 2%, 4%, 5%, 7%, 9%, or 10%. By controlling the content of each monomer in the copolymer within the above ranges, the monomers can be fully polymerized to form the copolymer, which is beneficial for obtaining an adhesive with high bonding performance.

[0040] In some embodiments of this application, the binder is a lithium copper acrylate polymer containing lithium and copper ions, which makes it easier to form a "linear-spherical-dot" composite structure with the carbon-based negative electrode active material, thereby improving the peel strength and flexibility of the negative electrode sheet.

[0041] This application does not impose any particular limitation on the molecular weight of the copolymer, as long as it achieves the purpose of this application. For example, the weight-average molecular weight of the copolymer is 100,000 to 1,200,000.

[0042] This application also provides a method for preparing the adhesive according to any of the above embodiments, comprising the following steps:

[0043] The reaction product is obtained by polymerizing acrylic acid, acrylonitrile and acrylamide;

[0044] The first solution was added to the reaction product, and after neutralization, the binder was obtained.

[0045] Alternatively, acrylic acid, acrylonitrile, and acrylamide are mixed with the first solution and polymerized to obtain the binder;

[0046] The first solution comprises a first solvent and a second solvent. The first solvent includes a lithium-containing alkali and / or salt, and the second solvent includes a copper-containing alkali and / or salt. The molar ratio of lithium to copper in the first solution is 1 to 5:1. In another optional embodiment, the molar ratio of lithium to copper in the first solution is 2 to 3:1. For example, the molar ratio of lithium to copper in the first solution is 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, or 5:1.

[0047] This application controls the molar ratio of lithium to copper in the first solution to be within the above-mentioned range. Since the lithium and copper elements in the binder are introduced during the addition of the first solution, the molar ratio of lithium to copper in the binder can be kept within the range of this application, which is beneficial to the formation of the "linear-spherical-dot" composite structure.

[0048] This application allows the first solution to be added to the reaction product for neutralization after the polymerization reaction; alternatively, the first solution can be added simultaneously with each monomer during the polymerization reaction stage, as long as the binder of this application can be obtained. This application allows the neutralization reaction to be stopped once the pH value of the mixture reaches the target pH value, which can be any value between 6.8 and 7.2, preferably pH = 7.0.

[0049] This application does not impose any particular restrictions on the amount of the first solution added, as long as the pH value of the neutralized mixture reaches the target pH value. Correspondingly, since the lithium and copper elements in the binder are introduced during the addition of the first solution, this application does not impose any particular restrictions on the lithium and / or lithium content in the binder, as long as the molar ratio of lithium to copper is within the range of this application.

[0050] This application does not impose any particular restrictions on the polymerization reaction process, as long as a copolymer can be obtained. For example, the monomers can be added to the reactor simultaneously at once for reaction, or the monomers can be added to the reactor in batches for reaction.

[0051] In one example, the preparation process of the adhesive includes:

[0052] Step A: Weigh acrylic acid, acrylonitrile, and acrylamide according to the calculated mass ratio, and use them as reaction raw materials;

[0053] Step B: At 45℃~55℃, add deionized water to the reactor, then add half of the weighed reaction raw materials to the reactor, and purge with nitrogen for 1h~3h. Next, add ammonium persulfate (15%~25% by mass) as an initiator to the reactor, and then gradually heat the reactor to 70℃~75℃. Add the other half of the reaction raw materials to the reactor and stir continuously. After reacting for 20h~24h, a precipitate is obtained. The mass ratio of deionized water, reaction raw materials, and initiator is 90~92∶7~8∶0.5.

[0054] Step C: Wash the obtained precipitate with deionized water 2 to 5 times to remove unreacted monomers and small molecule impurities to obtain copolymer;

[0055] Step D: Slowly add the first solution to the obtained copolymer while stirring continuously to dissolve the copolymer and form a mixture. Stop neutralization when the pH value of the mixture reaches the target pH value to obtain a liquid binder.

[0056] In one example, the preparation process of the adhesive includes:

[0057] Step A': Weigh acrylic acid, acrylonitrile, and acrylamide according to the calculated mass ratio, and use them as reaction raw materials;

[0058] Step B': At 45℃~55℃, add deionized water to the reactor, then add half of the weighed reaction raw materials to the reactor. Slowly add the first solution to the reactor until the pH of the liquid in the reactor reaches the target pH value, then stop neutralization. Next, add ammonium persulfate with a mass concentration of 15%~25% as an initiator to the reactor. Gradually raise the temperature of the reactor to 70℃~75℃, then add the other half of the reaction raw materials to the reactor, stirring continuously. After reacting for 20h~24h, a precipitate is obtained. The mass ratio of deionized water, reaction raw materials, and initiator is 90~92∶7~8∶0.5.

[0059] Step C': Wash the obtained precipitate with deionized water 2 to 5 times to remove unreacted monomers and small molecule impurities to obtain a liquid binder.

[0060] In some embodiments of this application, the first solvent includes at least one of lithium hydroxide and lithium carbonate, with lithium hydroxide being preferred due to its better solubility; the second solvent includes at least one of copper hydroxide and copper carbonate, with copper hydroxide being preferred due to its better solubility, which is beneficial for the full progress of the neutralization reaction.

[0061] This application provides a method for preparing a binder, which features readily available raw materials and a simple preparation process. When the binder prepared by this method is applied to the negative electrode sheet, it can effectively disperse and bind the negative electrode active material, thereby improving the peel strength and flexibility of the negative electrode sheet, and ultimately improving the cycle performance of the lithium-ion battery.

[0062] This application also provides a negative electrode sheet, including a negative electrode current collector, at least one side of which has a negative electrode active material layer, the negative electrode active material layer including a negative electrode active material and a binder, the negative electrode active material including a carbon material, wherein the binder is the binder of any of the above embodiments, or the binder is prepared by the method of preparing the binder of any of the above embodiments.

[0063] The negative electrode sheet of this application includes a negative electrode active material, which includes carbon material. The carbon material is more likely to form a "linear-spherical-dot" composite structure with the binder of this application, thereby effectively dispersing and bonding the negative electrode active material, improving the peel strength and flexibility of the negative electrode sheet, and thus improving the cycle performance of the lithium-ion battery.

[0064] In some embodiments of this application, the carbon material includes at least one of artificial graphite, natural graphite, and hard carbon, which is beneficial for forming a "linear-spherical-dot-like" composite structure with the binder of this application.

[0065] In some embodiments of this application, the peel strength of the negative electrode sheet is not less than 8 N / m, and the flexibility value is not higher than 425 mN, exhibiting excellent peel strength and flexibility. For example, the peel strength of the negative electrode sheet is 8 N / m to 15 N / m; in another embodiment, the peel strength of the negative electrode sheet is 11 N / m to 15 N / m. The flexibility value of the negative electrode sheet is 100 mN to 425 mN; in another embodiment, the flexibility value of the negative electrode sheet is 110 mN to 150 mN.

[0066] The negative electrode active material layer of this application can be disposed on one or both surfaces of the negative electrode current collector in the thickness direction. In this application, the negative electrode active material layer is disposed on the surface of the negative electrode current collector; that is, the negative electrode active material layer can be disposed on a portion of one surface of the negative electrode current collector, or it can be disposed on the entire surface of one surface of the negative electrode current collector. This application does not have any particular limitation on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, copper foil, copper alloy foil, nickel foil, or composite current collectors. In this application, there is no particular limitation on the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application; for example, a thickness of 4 μm to 12 μm. The single-sided thickness of the negative electrode active material layer in this application can be 70 μm to 200 μm.

[0067] This application also provides a secondary battery, including the negative electrode sheet described in any of the above embodiments.

[0068] The secondary battery of this application may also include a positive electrode, a separator, and an electrolyte, wherein the separator is located between the positive electrode and the negative electrode and serves as a separator.

[0069] This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet typically includes a positive current collector and a positive active material layer. The positive active material layer can be disposed on one surface or on two surfaces in the thickness direction of the positive current collector. In this application, the positive active material layer is disposed on the surface of the positive current collector, that is, the positive active material layer can be disposed on a portion of a surface of the positive current collector or on the entire surface of a surface of the positive current collector. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application, it can be, for example, including but not limited to aluminum foil, aluminum alloy foil, or composite current collectors. In this application, there is no particular limitation on the thickness of the positive current collector, as long as it achieves the purpose of this application, for example, a thickness of 8μm to 13μm. The single-sided thickness of the positive active material layer in this application can be 100μm to 200μm.

[0070] In this application, the positive electrode active material layer includes a positive electrode active material. This application does not have any particular restrictions on the positive electrode active material, as long as it can achieve the purpose of this application. For example, it may include at least one of lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, and lithium manganese iron phosphate.

[0071] In this application, the positive electrode active material layer may also include a positive electrode binder. This application does not have any particular limitation on the positive electrode binder, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of fluorinated resin, polypropylene resin, fiber-type binder, rubber-type binder or polyimide-type binder.

[0072] This application does not impose any particular limitation on the diaphragm; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected.

[0073] The secondary battery of this application also includes a casing. This application does not impose any particular restrictions on the casing, and those skilled in the art can choose one according to actual needs, as long as it can achieve the purpose of this application. For example, the casing may include an aluminum-plastic film.

[0074] This application does not impose any particular limitation on the preparation method of the secondary battery. Any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the preparation method of the secondary battery includes, but is not limited to, the following steps: stacking the positive electrode, separator and negative electrode in sequence, and winding and folding them as needed to obtain a bare cell with a wound structure; placing the bare cell in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the secondary battery.

[0075] This application also provides a battery pack, including a housing and at least one secondary battery as described in any of the above embodiments, the secondary battery being housed within the housing. The battery pack with this secondary battery exhibits excellent performance, which is beneficial for its use. Housed within the housing, the battery is secured and protected, thus extending the battery pack's lifespan. It is understood that the battery pack may contain one or more secondary batteries, and when the battery pack contains multiple secondary batteries, these batteries can be connected in at least one manner, such as parallel or series connection.

[0076] This application also provides an electrical device including a secondary battery or battery pack as described in any of the above embodiments, which is beneficial for improving the product competitiveness and performance of the electrical device. In an optional embodiment, the electrical device includes an electrical device body, and the secondary battery or battery pack is used to supply power to the electrical device body. In an optional embodiment, the electrical device body includes a positive terminal and a negative terminal, the positive terminal of the secondary battery or battery pack is used to electrically connect to the positive terminal of the electrical device body, and the negative terminal of the secondary battery or battery pack is used to electrically connect to the negative terminal of the electrical device body, so as to supply power to the electrical device.

[0077] The electrical equipment covered by this application may include, but is not limited to: containers, household energy storage systems, electric vehicles, electric cars, ships, spacecraft, electric toys, and power tools, etc. Among them, spacecraft include, for example, airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include, for example, stationary or mobile electric toys, specifically, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include, for example, metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, specifically, electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers.

[0078] Please see Figure 2 , Figure 2 This is a schematic diagram of the structure of a residential energy storage system according to one embodiment of this application, and this application... Figure 2 The implementation plan is illustrated using the residential energy storage scenario in user-side energy storage as an example. The energy storage device in this application is not limited to the residential energy storage scenario.

[0079] This application provides a residential energy storage system, which includes a power conversion device 2 (photovoltaic panel), a first user load 3 (streetlight), a second user load 4 (e.g., household appliances such as air conditioners), and an energy storage device 1. The energy storage device 1 is a small energy storage box that can be wall-mounted to an outdoor wall. Specifically, the photovoltaic panel can convert solar energy into electrical energy during periods of low electricity prices, and the energy storage device 1 is used to store this electrical energy and supply it to streetlights and household appliances during periods of high electricity prices, or to provide power during power outages / power failures.

[0080] Please see Figure 3 , Figure 3 This is a schematic diagram of the structure of an energy storage system 400 according to one embodiment of this application, and this application Figure 3 The implementation plan is illustrated using the shared energy storage scenario on the power generation / distribution side as an example. The energy storage device 1 in this application is not limited to the power generation / distribution side energy storage scenario.

[0081] This application provides an energy storage system 400, which includes a high-voltage cable 410, a first power conversion device 420, a second power conversion device 430, and the energy storage device 1 provided in this application. During power generation, the first power conversion device 420 and the second power conversion device 430 convert other forms of energy into electrical energy, which is then connected to the high-voltage cable 410 and supplied to the power consumption side of the distribution network. When the power load is low and the first power conversion device 420 and the second power conversion device 430 generate excess power, the excess power is stored in the energy storage device 1, reducing wind and solar curtailment rates and improving the absorption of new energy power generation. When the power load is high, the power grid issues an instruction to transmit the power stored in the energy storage device 1, along with the high-voltage cable 410, in a grid-connected mode to supply power to the power consumption side. This provides various services such as peak shaving, frequency regulation, and backup for the power grid operation, fully leveraging the peak shaving function of the power grid, promoting peak shaving and valley filling, and alleviating the power supply pressure on the power grid.

[0082] Optionally, the first power conversion device 420 and the second power conversion device 430 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electrical energy.

[0083] The number of energy storage devices 1 can be multiple, and these devices can be connected in series or in parallel. The multiple energy storage devices 1 are supported and electrically connected by an isolation plate (not shown). In this embodiment, "multiple" refers to two or more. An energy storage box can also be provided outside the energy storage device 1 to house it.

[0084] Optionally, the energy storage device 1 may include, but is not limited to, a single battery cell, a battery module, a battery pack, or a battery system. The actual application form of the energy storage device 1 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 1. This application embodiment only uses a multi-cell battery as an example for illustration. When the energy storage device 1 is a single battery cell, the energy storage device 1 may be at least one of cylindrical batteries, prismatic batteries, etc.

[0085] Example

[0086] The following examples, embodiments, and comparative examples illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0087] Example 1

[0088] <Preparation of Adhesive>

[0089] Acrylic acid, acrylonitrile, and acrylamide were weighed in a mass ratio of 50:45:5 to obtain the reaction raw materials. Deionized water was added to a reactor at 50°C, followed by half of the weighed reaction raw materials. Nitrogen gas was purged for 2 hours, and then 20% ammonium persulfate was added as an initiator. The reactor was then gradually heated to 70°C, and the other half of the reaction raw materials were added while continuously stirring. After reacting for 22 hours, a precipitate was obtained. The precipitate was washed three times with deionized water to remove unreacted monomers and small molecule impurities, yielding a copolymer. A first solution was slowly added to the obtained copolymer while continuously stirring to dissolve the copolymer and form a mixture. The addition of the first solution was stopped when the pH of the mixture reached 7.0, terminating the neutralization reaction and yielding the binder. The mass ratio of deionized water, reaction raw materials, and initiator is 92:7.5:0.5. The first solution is a mixture of lithium hydroxide and copper hydroxide, wherein the molar concentration of lithium hydroxide in the first solution is 0.2 mol / L and the molar concentration of copper hydroxide in the first solution is 0.1 mol / L. Therefore, the molar ratio of lithium to copper in the first solution is 2:1, and the molar ratio of lithium to copper in the binder obtained after neutralization is also 2:1.

[0090] <Preparation of Negative Electrode Sheets>

[0091] Artificial graphite (anode active material), sodium carboxymethyl cellulose (CMC) thickener, conductive carbon black (Super-P), and a prepared binder were mixed in a mass ratio of 96:2:1:1. Deionized water was added to prepare a negative electrode slurry with a solid content of 50 wt%, and the mixture was stirred evenly. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil current collector. After drying, cold pressing, slitting, and cutting, the negative electrode sheet was obtained. The single-sided thickness of the negative electrode active material layer was 70 μm.

[0092] <Preparation of the positive electrode>

[0093] Lithium iron phosphate (LiFePO4), conductive carbon black (Super-P), and PVDF binder were mixed at a mass ratio of 94:3:3. Then, N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry with a solid content of 60 wt%, which was stirred evenly. The positive electrode slurry was then uniformly coated onto one surface of a 10 μm thick aluminum foil used as a positive electrode current collector. After drying, cold pressing, slitting, and cutting, the positive electrode sheet was obtained. The single-sided thickness of the positive electrode active material layer was 100 μm.

[0094] <Preparation of Electrolyte>

[0095] In an argon-atmosphere glove box with a moisture content ≤1ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 1:1:1. Lithium salt LiPF6 was then added and dissolved in the solvent. After thorough mixing, an electrolyte was obtained. The molar concentration of LiPF6 in the electrolyte was 1 mol / L.

[0096] <Preparation of the diaphragm>

[0097] A porous polyethylene (PE) film with a thickness of 16 μm was used as the separator.

[0098] <Preparation of Lithium-ion Batteries>

[0099] The positive electrode, separator, and negative electrode prepared above are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting cells are then wound to obtain a bare battery cell. The bare battery cell is placed in an aluminum-plastic film packaging bag, vacuum dried, and then injected with electrolyte. After vacuum sealing, settling, and formation processes, a lithium-ion battery is obtained.

[0100] Example 2

[0101] Except for adjusting the molar ratio of lithium hydroxide to copper hydroxide in the first solution to 2.3:1 in the <Preparation of Adhesive> section, and changing the molar ratio of lithium to copper in the adhesive as shown in Table 1, the rest is the same as in Example 1.

[0102] Example 3

[0103] Except for adjusting the molar ratio of lithium hydroxide to copper hydroxide in the first solution to 2.5:1 in the <Preparation of Adhesive> section, and changing the molar ratio of lithium to copper in the adhesive as shown in Table 1, the rest is the same as in Example 1.

[0104] Example 4

[0105] Except for adjusting the molar ratio of lithium hydroxide to copper hydroxide in the first solution to 2.7:1 in the <Preparation of Adhesive> section, and changing the molar ratio of lithium to copper in the adhesive as shown in Table 1, the rest is the same as in Example 1.

[0106] Example 5

[0107] Except for adjusting the molar ratio of lithium hydroxide to copper hydroxide in the first solution to 3:1 in the <Preparation of Adhesive> section, and changing the molar ratio of lithium to copper in the adhesive as shown in Table 1, the rest is the same as in Example 1.

[0108] Example 6

[0109] Except for adjusting the molar ratio of lithium hydroxide to copper hydroxide in the first solution to 1:1 in the <Preparation of Adhesive> section, and changing the molar ratio of lithium to copper in the adhesive as shown in Table 1, the rest is the same as in Example 1.

[0110] Example 7

[0111] Except for adjusting the molar ratio of lithium hydroxide to copper hydroxide in the first solution to 5:1 in the <Preparation of Adhesive> section, and changing the molar ratio of lithium to copper in the adhesive as shown in Table 1, the rest is the same as in Example 1.

[0112] Example 8

[0113] Except for adjusting the mass ratio of acrylic acid, acrylonitrile, and acrylamide to 40:50:10 in the <Preparation of Adhesive> section, the rest is the same as in Example 1.

[0114] Example 9

[0115] Except for adjusting the mass ratio of acrylic acid, acrylonitrile, and acrylamide to 60:32:8 in the <Preparation of Adhesive> section, the rest is the same as in Example 1.

[0116] Example 10

[0117] Except for adjusting the mass ratio of acrylic acid, acrylonitrile, and acrylamide to 50:48:2 in the <Preparation of Adhesive> section, the rest is the same as in Example 1.

[0118] Example 11

[0119] Except for replacing artificial graphite with hard carbon in the <Preparation of Negative Electrode Sheet>, the rest is the same as in Example 1.

[0120] Comparative Example 1

[0121] Except for adjusting the molar ratio of lithium hydroxide to copper hydroxide in the first solution to 1:0 in the <Preparation of Adhesive> section, i.e., the first solution does not contain copper hydroxide, and the molar ratio of lithium to copper in the adhesive changes accordingly as shown in Table 1, the rest is the same as in Example 1.

[0122] Comparative Example 2

[0123] Except for adjusting the molar ratio of lithium hydroxide to copper hydroxide in the first solution to 0:1 in the <Preparation of Adhesive> section, i.e., the first solution does not contain lithium hydroxide, and the molar ratio of lithium to copper in the adhesive changes accordingly as shown in Table 1, the rest is the same as in Example 1.

[0124] Test methods and equipment:

[0125] Inductively coupled plasma (ICP) elemental spectroscopy detection:

[0126] The binders prepared in each embodiment and comparative example were injected into an ICP analyzer, and the content of each element in the binder was analyzed by the ICP analyzer. The lithium and copper content results obtained by the ICP analyzer are the lithium and copper content in the binder.

[0127] Peel strength test:

[0128] One side of the negative electrode sheet of the sample is adhered to a steel plate with double-sided tape. The steel plate is mounted on a fixed fixture at the bottom of the high-speed rail tensile testing machine. After confirming that the bottom layer of the sample is firmly bonded to the steel plate, approximately 1 cm is torn along the interface between the negative electrode sheet and the double-sided tape at one end of the sample's length. This torn corner of the negative electrode sheet is then clamped onto a movable fixture at the top of the high-speed rail tensile testing machine. The sample preparation is now complete. Testing: Tension angle 90°, tension speed 20 mm / min, until the interface between the negative electrode sheet and the double-sided tape is completely separated. After separation, the negative electrode material layer is adhered to the surface of the double-sided tape, and the other side of the separated interface is at least partially exposed of the negative electrode current collector. Record the average load force (N) during the tensile process, divide it by the sample width to obtain the peel strength between the negative electrode active material layer and the negative electrode current collector, and then take the average value.

[0129] Flexibility test:

[0130] ① Cut the negative electrode sheet into a sample 60cm long and 40cm wide using a cutting knife. ② Place the sample into the fixture of the flexibility tester (model PY-H613). ③ Make the negative electrode sheet at a 90° angle with the test head, and press the test head vertically into the negative electrode sheet to a depth of 8±0.5mm. Record the maximum pressure value displayed by the sensor of the test head, which is the flexibility value, in mN.

[0131] Cyclic performance test:

[0132] The test temperature was 25℃. The lithium-ion battery was charged at a constant current of 1% (C) to 3.65V, then charged at a constant voltage to the cutoff current of 0.05C. After resting for 30 minutes, it was discharged at a constant power of 1C to 2.5V. This was recorded as one charge-discharge cycle, and the capacity obtained in this step was taken as the initial discharge capacity C0. The same conditions were applied for 1000 cycles, and the discharge capacity of the 1000th cycle was recorded. Cycle capacity retention rate = (Discharge capacity of the 1000th cycle / Initial discharge capacity C0) × 100%.

[0133] Table 1. Preparation parameters and test results for each embodiment and comparative example.

[0134]

[0135] As can be seen from Examples 1 to 7 and Comparative Examples 1 to 2, when the binder contains only lithium and no copper (e.g., Comparative Example 1), although the flexibility of the negative electrode sheet is relatively good, the peel strength is low, resulting in a low capacity retention rate of the lithium-ion battery. When the binder contains only copper and no lithium (e.g., Comparative Example 2), the peel strength of the negative electrode sheet is low, and the flexibility is also poor, resulting in a low capacity retention rate of the lithium-ion battery. This may be because the glass transition temperature of copper salt is high, making the binder hard and brittle, which is not conducive to slurry coating. However, the negative electrode sheet of this application has higher peel strength and exhibits good flexibility, thus improving the capacity retention rate of the lithium-ion battery. It is evident that this application improves the peel strength and flexibility of the negative electrode sheet, thereby improving the cycle performance of the lithium-ion battery.

[0136] As can be seen from Examples 1 to 5, by adjusting the molar ratio of lithium to copper in the binder to 2 to 3:1, the negative electrode sheet exhibits higher peel strength and excellent flexibility, and the capacity retention rate of the lithium-ion battery is further improved.

[0137] The composition of the copolymer also usually affects the performance of the binder. As can be seen from Examples 1 and 8 to 10, by adjusting the composition of the copolymer within the scope of this application, it is beneficial to obtain a negative electrode sheet with high peel strength and good flexibility, which is beneficial to improving the capacity retention rate of lithium-ion batteries.

[0138] As can be seen from Examples 1 and 11, by controlling the type of negative electrode active material within the scope of this application, it is beneficial to obtain a negative electrode sheet with high peel strength and good flexibility, which is beneficial to improving the capacity retention rate of lithium-ion batteries.

[0139] The adhesive, the negative electrode sheet containing the adhesive, the secondary battery, and the battery pack of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the technical solutions and core inventive points of the embodiments of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. An adhesive, characterized in that, The adhesive comprises a copolymer formed by polymerizing acrylic acid, acrylonitrile, and acrylamide; The adhesive also contains lithium and copper elements, wherein the molar ratio of lithium to copper is 1 to 5:1, and the adhesive is a lithium copper acrylate polymer.

2. The adhesive according to claim 1, characterized in that, The molar ratio of lithium to copper is 2 to 3:

1.

3. The adhesive according to claim 1, characterized in that, Based on the total mass of the copolymer, the acrylic acid content is 40% to 60% by mass, the acrylonitrile content is 30% to 50% by mass, and the acrylamide content is 2% to 10% by mass.

4. A negative electrode sheet, characterized in that, The present invention includes a negative electrode current collector, wherein at least one side of the negative electrode current collector has a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material and a binder, and the negative electrode active material includes a carbon material. The adhesive is the adhesive according to any one of claims 1 to 3.

5. The negative electrode sheet according to claim 4, characterized in that, The carbon material includes at least one of artificial graphite, natural graphite, and hard carbon.

6. The negative electrode sheet according to claim 4, characterized in that, The peel strength of the negative electrode sheet is not less than 8 N / m, and the flexibility value is not higher than 425 mN.

7. A secondary battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 4 to 6.

8. A battery pack, characterized in that, It includes a housing and at least one secondary battery as described in claim 7, the secondary battery being housed within the housing.

9. An electrical appliance, characterized in that, It includes the secondary battery as described in claim 7 or the battery pack as described in claim 8.

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