Negative electrode sheet, water-based negative electrode slurry, secondary battery and electric device

Abstract

The present application provides a negative electrode sheet, a water-based negative electrode slurry, a secondary battery and an electric device. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector. The negative electrode film layer comprises a negative electrode active material and a water-based binder. At least part of the negative electrode film layer further comprises an additive. The additive comprises a water-soluble unsaturated organic acid salt, and an unsaturated group in the water-soluble unsaturated organic acid salt comprises any one or more of alkenyl, alkynyl and formula (I). The cycling stability of a cell comprising the negative electrode sheet is improved.

Description

Negative electrode sheet, aqueous negative electrode slurry, secondary battery and electrical device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Chinese patent application No. 202410094562.0 filed on January 23, 2024, entitled “Negative electrode sheet, aqueous negative electrode slurry, secondary battery and electrical device,” the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a negative electrode sheet, an aqueous negative electrode slurry, a secondary battery, and an electrical device. Background Art

[0003] Graphite is the most widely used negative electrode material in lithium-ion batteries. It not only has the advantages of abundant raw materials, low cost, low reaction potential, and good conductivity, but also exhibits a small volume effect during the battery charging and discharging process.

[0004] During the initial formation and charging process of a lithium-ion battery, an SEI film forms as a protective layer on the graphite surface. However, this requires irreversible consumption of lithium ions, resulting in a reduction in the battery's initial efficiency. Furthermore, the presence of additives in the electrolyte can cause the SEI film to thicken, increasing interfacial impedance and affecting battery power performance. Furthermore, during the subsequent charge and discharge processes, the negative electrode continuously expands and contracts, causing the SEI film to rupture, increasing side reactions between the negative electrode active material and the electrolyte. Furthermore, repairing the SEI film requires further irreversible loss of lithium ions, resulting in a reduction in battery life. Therefore, constructing an artificial SEI has become a key technology for improving battery initial efficiency and lifespan. Summary of the Invention

[0005] The present application relates to a negative electrode sheet, an aqueous negative electrode slurry, a secondary battery and an electrical device to improve the cycle stability of the battery.

[0006] The first aspect of the present application provides a negative electrode plate, comprising a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material and an aqueous binder, and at least part of the negative electrode film layer further comprises an additive, wherein the additive comprises a water-soluble unsaturated organic acid salt, and the unsaturated groups in the water-soluble unsaturated organic acid salt comprise alkenyl, alkynyl, * ——Any one or more of C≡N.

[0007] The negative electrode plate of the present application comprises a combination of a water-soluble unsaturated organic acid salt and an aqueous binder. Since both are aqueous materials, they can be well integrated, and the material dispersion uniformity of the negative electrode plate is good. For example, the water-soluble unsaturated organic acid salt is well dispersed around the negative electrode active material. During the charging process, the unsaturated groups of the water-soluble unsaturated organic acid salt break and undergo a self-polymerization reaction, forming a stable and flexible SEI film on the surface of the negative electrode active material, thereby improving the cycle stability of the battery cell.

[0008] In any embodiment of the first aspect, optionally, the acid radical ion of water-soluble unsaturated organic acid salt includes any one or more of sulfonate ion, borate ion, and phosphonate ion. Above-mentioned acid radical ion contains high electronegativity element (S, B, P), therefore can preferentially occupy the active site of negative electrode particle, preferentially participate in film forming (charging process, negative electrode interface attracts electrons, and the double bond of additive opens to form polymer) during charging, and high electronegativity element can increase the electronegativity of negative electrode surface, serves as the effect of electron acceptor, makes the combination of lithium ion and solvent molecule weaken, is conducive to lithium ion migration, reduces interfacial impedance, thus reduces the degree of impedance increase caused by film forming.

[0009] In any embodiment of the first aspect, in the region of the negative electrode film layer containing the additive, the weight ratio of the additive to the negative electrode active material is (0.5-2):(93-98), optionally (0.8-1.5):(93-98).

[0010] In any embodiment of the first aspect, the water-soluble unsaturated organic acid salt includes any one or more of a water-soluble unsaturated organic lithium salt, a water-soluble unsaturated organic sodium salt, a water-soluble unsaturated organic potassium salt, a water-soluble unsaturated organic magnesium salt, and a water-soluble unsaturated organic calcium salt; optionally, the water-soluble unsaturated organic acid salt includes any one or more of a water-soluble unsaturated sulfonate salt; optionally, the water-soluble unsaturated sulfonate salt is selected from any one or more of a water-soluble unsaturated lithium sulfonate; further optionally, the water-soluble unsaturated lithium sulfonate salt includes any one or more of a C1-C6 alkenyl lithium sulfonate; more optionally, the water-soluble unsaturated lithium sulfonate salt includes any one or more of vinyl lithium sulfonate and allyl lithium sulfonate. During charging, when the water-soluble unsaturated sulfonate salt forms a protective film on the surface of the negative electrode active particles, the sulfonic acid groups participate in the film formation, thereby improving the stability of the film structure and further extending the life of the battery cell.

[0011] In any embodiment of the first aspect, the negative electrode film layer further comprises a polymer formed by cross-linking the additive, and optionally at least a portion of the polymer is coated on the surface of the negative electrode active material; optionally, the polymer comprises any one or more of the following structural units:

[0012]

[0013] n is any integer from 0 to 6, optionally n is 0 or 1;

[0014] R 1 The acid ions include any one or more of sulfonate ions, borate ions, and phosphonate ions, and optionally R 1 The cations in the formula include any one or more of sodium ions, lithium ions, potassium ions, magnesium ions, and calcium ions; further optionally, R 1 Including lithium sulfonate ions; optionally, in the area of ​​the negative electrode film layer containing the additive, the weight ratio of the total weight of the additive and the polymer to the negative electrode active material is (0.5-2):(93-98), optionally (0.8-1.5):(93-98).

[0015] When the polymer formed after charging is coated on the surface of the negative electrode active material as a SEI film, it plays a more direct protective role for the negative electrode active material.

[0016] In any embodiment of the first aspect, the aqueous binder includes any one or more of styrene-butadiene rubber, polyacrylic acid, and styrene-butadiene rubber.

[0017] In any embodiment of the first aspect, the region of the negative electrode film layer including the additive also includes a protective agent, and the protective agent includes any one or more of sodium dodecylbenzenesulfonate, sodium ligninsulfonate, sodium alkyl glycerol ether sulfonate, sodium dodecylsulfonate, and sodium dodecyl sulfate; optionally, the weight ratio of the protective agent to the additive is (0.2-0.6):1, and can be optionally (0.3-0.5):1.

[0018] The protective agent has a hydrophobic chain and a hydrophilic anionic group. Its hydrophilic anionic group preferentially bonds with the hydrophilic additive, preventing the additive from pre-bonding with the hydrophilic groups of the aqueous binder. This effectively addresses the problem of decreased adhesion of the aqueous binder due to bonding with the additive. In particular, when styrene-butadiene rubber (SBR) is used as the aqueous binder, due to its abundant surface hydrophilic groups, the addition of the protective agent effectively prevents the SBR surface hydrophilic groups from bonding with the hydrophilic groups of the additive, effectively protecting the SBR structure and maintaining a good bonding effect with the negative electrode film and negative electrode current collector.

[0019] In any embodiment of the first aspect, the negative electrode film layer further includes a thickener, and the thickener includes any one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, propylene glycol alginate, methyl cellulose, sodium starch phosphate, sodium alginate, casein, sodium polyacrylate, polyethylene oxide and polyvinyl pyrrolidone; optionally, the weight ratio of the thickener to the negative electrode active material is (0.5-1.5): (93-98).

[0020] In any embodiment of the first aspect, the negative electrode active material includes one or more of a graphite negative electrode material and a silicon-based negative electrode material. Optionally, the silicon-based negative electrode material includes one or more of a silicon-carbon composite negative electrode material and a silicon-oxygen negative electrode material; optionally, the graphite negative electrode material includes artificial graphite and / or natural graphite.

[0021] In any embodiment of the first aspect, the additive is dispersed in a region of the negative electrode film layer away from the negative electrode current collector, and the region of the negative electrode film layer having the additive is the first region.

[0022] In any embodiment of the first aspect, the aqueous binder in the first region comprises polyacrylic acid.

[0023] In any embodiment of the first aspect, the negative electrode film layer region between the first region and the negative electrode current collector is the second region, and the aqueous binder in the second region includes styrene-butadiene rubber.

[0024] In any embodiment of the first aspect, a region of the negative electrode film layer close to the negative electrode current collector is the third region, the negative electrode active material in the third region includes natural graphite, and the third region includes an additive.

[0025] In any embodiment of the first aspect, a region of the negative electrode film layer away from the negative electrode current collector is the fourth region, and the negative electrode active material in the fourth region includes artificial graphite.

[0026] The second aspect of the present application provides an aqueous negative electrode slurry, comprising water, a negative electrode active material dispersed in water, and an aqueous binder, wherein the aqueous negative electrode slurry further comprises an additive, the additive comprising a water-soluble unsaturated organic acid salt, the unsaturated group in the water-soluble unsaturated organic acid salt comprising an alkenyl group, an alkynyl group, * —C≡N, and optionally, the acid radical ions of the water-soluble unsaturated organic acid salt include any one or more of sulfonate, borate, and phosphonate.

[0027] In the aqueous negative electrode slurry of the present application, water-soluble unsaturated organic acid salt and aqueous binder are combined, and the two are preferably fused because they are aqueous materials, and dispersion uniformity is better in the formed negative electrode pole piece, such as water-soluble unsaturated organic acid salt is preferably dispersed around the negative electrode active material. The negative electrode film layer formed using the aqueous negative electrode slurry breaks the unsaturated group of the water-soluble unsaturated organic acid salt during charging and undergoes self-polymerization reaction, forming a stable flexible SEI film on the surface of the negative electrode active material, thereby improving the cycle stability of the battery core. The above-mentioned acid radical ions contain high electronegativity elements (S, B, P), so they can preferentially occupy the active sites of the negative electrode particles, preferentially participate in film formation (charging process, the negative electrode interface attracts electrons, and the double bond of the additive opens to form a polymer) during charging, and high electronegativity elements can increase the electronegativity of the negative electrode surface, serve as the effect of electron acceptors, so that the combination of lithium ions and solvent molecules is weakened, which is conducive to lithium ion migration, reduces interfacial impedance, thereby reducing the degree of impedance increase caused by film formation.

[0028] In any embodiment of the second aspect, the weight ratio of the additive to the negative electrode active material is (0.5-2):(93-98), optionally (0.8-1.5):(93-98).

[0029] In any embodiment of the second aspect, the water-soluble unsaturated organic acid salt includes any one or more of a water-soluble unsaturated organic lithium salt, a water-soluble unsaturated organic sodium salt, a water-soluble unsaturated organic potassium salt, a water-soluble unsaturated organic magnesium salt, and a water-soluble unsaturated organic calcium salt; optionally, the water-soluble unsaturated organic acid salt includes any one or more of a water-soluble unsaturated sulfonate salt; optionally, the water-soluble unsaturated sulfonate salt is selected from any one or more of a water-soluble unsaturated lithium sulfonate; further optionally, the water-soluble unsaturated lithium sulfonate salt includes any one or more of a C1-C6 olefin lithium sulfonate; more optionally, the water-soluble unsaturated lithium sulfonate salt includes any one or more of vinyl lithium sulfonate and allyl lithium sulfonate. When a water-soluble unsaturated lithium sulfonate salt is used as an additive, the water-soluble unsaturated lithium sulfonate salt can also increase the migration rate of lithium ions, further reduce interfacial impedance, and improve the cycle life of the battery.

[0030] In any embodiment of the second aspect, the aqueous binder includes any one or more of styrene-butadiene rubber, polyacrylic acid, and styrene-butadiene rubber.

[0031] In any embodiment of the second aspect, the aqueous negative electrode slurry further includes a protective agent, which includes any one or more of sodium dodecylbenzene sulfonate, sodium lignin sulfonate, sodium alkyl glycerol ether sulfonate, sodium dodecyl sulfonate, and sodium dodecyl sulfate. Optionally, the weight ratio of the protective agent to the additive is (0.2-0.6):1, optionally (0.3-0.5):1. This effectively solves the problem of decreased adhesion of the aqueous binder due to contact with the additive.

[0032] In any embodiment of the second aspect, the aqueous negative electrode slurry further includes a thickener, and the thickener includes any one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, propylene glycol alginate, methyl cellulose, sodium starch phosphate, sodium alginate, casein, sodium polyacrylate, polyethylene oxide and polyvinyl pyrrolidone; optionally, the weight ratio of the thickener to the negative electrode active material is (0.5-1.5): (93-98).

[0033] In any embodiment of the second aspect, the negative electrode active material includes one or more of a graphite negative electrode material and a silicon-based negative electrode material; optionally, the silicon-based negative electrode material includes one or more of a silicon-carbon composite negative electrode material and a silicon-oxygen negative electrode material; optionally, the graphite negative electrode material includes artificial graphite and / or natural graphite.

[0034] A third aspect of the present application provides a secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises the negative electrode plate provided by any embodiment of the first aspect.

[0035] A fourth aspect of the present application provides an electrical device including a secondary battery, wherein the secondary battery includes the secondary battery provided by any embodiment of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0037] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0038] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .

[0039] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0040] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0041] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0042] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0043] In the drawings, the drawings are not drawn to scale.

[0044] Description of reference numerals:

[0045] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0046] The following detailed description of the embodiments of the present application is provided in conjunction with the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present application, but are not intended to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0047] Below, the embodiments of the negative electrode sheet, aqueous negative electrode slurry, secondary battery and electric device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0048] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0049] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0050] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0051] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0052] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or comprised.

[0053] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0054] [Secondary battery]

[0055] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged to activate the active materials after discharge and continue to be used.

[0056] Typically, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the battery's charge and discharge process, active ions (such as lithium ions or sodium ions) are embedded and released back and forth between the positive and negative electrode sheets. The separator is set between the positive and negative electrode sheets, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The electrolyte is between the positive and negative electrode sheets, mainly to conduct active ions.

[0057] [Negative electrode]

[0058] As described in the background technology, although the initial formation charge process can form an SEI film on the negative electrode, the SEI film is easily broken during the later cycle charge and discharge. This problem also exists in aqueous negative electrode sheets. That is, how to ensure that the solid electrolyte interface film (SEI film) formed on the graphite surface has good stability under the conditions of aqueous binders to improve the cycle stability of the battery has become an urgent problem to be solved. To solve this problem, the present application provides a negative electrode sheet, an aqueous negative electrode slurry, a secondary battery, and an electrical device.

[0059] The first embodiment of the present application provides a negative electrode plate, comprising a current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material and an aqueous binder, and at least part of the negative electrode film layer further comprises an additive, wherein the additive comprises a water-soluble unsaturated organic acid salt, and the unsaturated groups in the water-soluble unsaturated organic acid salt comprise alkenyl, alkynyl, * —Any one or more of C≡N.

[0060] The negative electrode plate of the present application comprises a combination of a water-soluble unsaturated organic acid salt and an aqueous binder. Since both are aqueous materials, they can be well integrated, and the material dispersion uniformity of the negative electrode plate is good. For example, the water-soluble unsaturated organic acid salt is well dispersed around the negative electrode active material. During the charging process, the unsaturated groups of the water-soluble unsaturated organic acid salt break and undergo a self-polymerization reaction, forming a stable and flexible SEI film on the surface of the negative electrode active material, thereby improving the cycle stability of the battery cell.

[0061] In some embodiments of the present application, optionally, the acid radical ion of the water-soluble unsaturated organic acid salt includes any one or more of sulfonate ion, borate ion, and phosphonate ion. The above-mentioned acid radical ion contains high electronegativity elements (S, B, P), and therefore can preferentially occupy the active site of the negative electrode particles, preferentially participate in film formation (charging process, the negative electrode interface attracts electrons, and the double bond of the additive is opened to form a polymer) during charging, and the high electronegativity element can increase the electronegativity of the negative electrode surface, serve as the effect of the electron acceptor, so that the combination of lithium ions and solvent molecules is weakened, which is conducive to lithium ion migration, reduces interfacial impedance, and thus reduces the degree of impedance increase caused by film formation.

[0062] The above-mentioned additives do not exert capacity activity. In order to control the degree of reduction in the energy density of the battery cell caused by the use of the additives as much as possible, and enable the additives to fully play a role in improving the cycle stability of the battery cell, in some embodiments, in the area of ​​the negative electrode film layer containing the additives, the weight ratio of the additives to the negative electrode active material is (0.5-2):(93-98), and can be optionally (0.8-1.5):(93-98).

[0063] In some embodiments of the present application, the water-soluble unsaturated organic acid salt includes any one or more of a water-soluble unsaturated organic lithium salt, a water-soluble unsaturated organic sodium salt, a water-soluble unsaturated organic potassium salt, a water-soluble unsaturated organic magnesium salt, and a water-soluble unsaturated organic calcium salt; alternatively, the water-soluble unsaturated organic acid salt includes any one or more of a water-soluble unsaturated sulfonate salt. During charging, when the water-soluble unsaturated sulfonate salt forms a protective film on the surface of the negative electrode active particles, the sulfonic acid groups participate in the film formation, improving the stability of the film structure and further extending the battery cell life.

[0064] In some embodiments of the present application, the water-soluble unsaturated sulfonate salt is optionally selected from any one or more water-soluble unsaturated lithium sulfonates; further optionally, the water-soluble unsaturated lithium sulfonate salt includes any one or more C1-C6 olefin lithium sulfonates; and more optionally, the water-soluble unsaturated lithium sulfonate salt includes any one or more of vinyl lithium sulfonate and allyl lithium sulfonate. When the water-soluble unsaturated lithium sulfonate salt is used as an additive, it can also increase the migration rate of lithium ions, further reduce interfacial impedance, and improve the cycle life of the battery.

[0065] Because the unsaturated groups in the additives in the negative electrode plate break after charging, a self-polymerization reaction forms a polymer. In some embodiments, the negative electrode film layer also includes a polymer formed by cross-linking the additives, and at least a portion of the polymer optionally coats the surface of the negative electrode active material. When the polymer formed after charging coats the surface of the negative electrode active material, it acts as an SEI film, providing more direct protection for the negative electrode active material.

[0066] The structural units of the polymer mainly depend on the structure of the water-soluble unsaturated organic acid salt. In some embodiments, the polymer optionally includes any one or more of the following structural units:

[0067]

[0068] n is any integer from 0 to 6, optionally n is 0 or 1;

[0069] R 1 The acid radical ions include any one or more of sulfonate ions, borate ions, and phosphonate ions, and optionally R 1 The cations in the formula include any one or more of sodium ions, lithium ions, potassium ions, magnesium ions, and calcium ions; further optionally, R 1 Including lithium sulfonate ions.

[0070] Those skilled in the art should understand that the above R 1 In addition to the above-mentioned anionic groups, the compound may also include alkylene groups, etc., and may not include other groups, such as lithium vinyl sulfonate mentioned below.

[0071] Regardless of the degree of polymerization of the additive, the total weight of the additive and the polymer is substantially equivalent to the weight of the additive before polymerization. Furthermore, the additive ultimately protects the negative electrode active material in the form of a polymer. In some embodiments, optionally, in the negative electrode film layer comprising the additive, the weight ratio of the total weight of the additive and the polymer to the negative electrode active material is (0.5-2):(93-98), optionally (0.8-1.5):(93-98). This can avoid the problem of decreased energy density of the battery cell due to excessive use of additives, and can utilize the additive to protect the negative electrode active material, thereby substantially improving the cycle performance of the battery.

[0072] The aqueous binder used in this application can be selected from aqueous binders commonly used in negative electrode sheets. In some embodiments of this application, the aqueous binder includes any one or more of styrene-butadiene rubber (SBR), polyacrylic acid, and styrene-butadiene rubber (SBS). In particular, the SBR surface hydrophilic carboxyl groups undergo a condensation reaction with the hydroxyl groups on the surface of the negative electrode current collector, thereby further enhancing the adhesion between the negative electrode film and the current collector.

[0073] In some embodiments of the present application, the above-mentioned negative electrode film layer including additives also includes a protective agent, and the protective agent includes any one or more of sodium dodecylbenzenesulfonate, sodium ligninsulfonate, sodium alkyl glycerol ether sulfonate, sodium dodecylsulfonate, and sodium dodecyl sulfate; optionally, the weight ratio of the protective agent to the additive is (0.2-0.6):1, and can be optionally (0.3-0.5):1.

[0074] The protective agent has a hydrophobic chain and a hydrophilic anionic group. Its hydrophilic anionic group first binds to the hydrophilic additive, preventing the additive from first binding to the hydrophilic group of the aqueous binder, effectively solving the problem of decreased adhesion of the aqueous binder due to contact with the additive. In particular, when styrene-butadiene rubber is used as the aqueous binder, due to its abundant surface hydrophilic groups, the addition of the protective agent effectively prevents the hydrophilic groups on the surface of the styrene-butadiene rubber from binding to the hydrophilic groups of the additive, effectively protecting the structure of the styrene-butadiene rubber, so that it still retains a good bonding effect on the negative electrode film layer and the negative electrode current collector. In some embodiments, when the region of the negative electrode film layer has an additive and the aqueous adhesive is styrene-butadiene rubber, the aqueous negative electrode slurry in this region also includes the protective agent.

[0075] In some embodiments of the present application, the negative electrode film layer further includes a thickener, which includes any one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, propylene glycol alginate, methyl cellulose, sodium starch phosphate, sodium alginate, casein, sodium polyacrylate, polyethylene oxide, and polyvinyl pyrrolidone; optionally, the weight ratio of the thickener to the negative electrode active material is (0.5-1.5): (93-98). This improves the stability of the slurry forming the negative electrode film layer and further enhances the uniformity of the dispersion of the components in the negative electrode film layer.

[0076] In some embodiments of the present application, the negative electrode active material includes one or more of a graphite negative electrode material and a silicon-based negative electrode material. Optionally, the silicon-based negative electrode material includes one or more of a silicon-carbon composite negative electrode material and a silicon-oxygen negative electrode material. Optionally, the graphite negative electrode material includes artificial graphite and / or natural graphite. Any of the above negative electrode active materials can be selected based on the battery performance requirements.

[0077] The negative electrode film layer of the present application can have different designs along a direction perpendicular to the negative electrode current collector. In some embodiments, the additive is dispersed in a region of the negative electrode film layer away from the negative electrode current collector, and the region of the negative electrode film layer containing the additive is the first region. Adding the additive to the first region away from the current collector allows the additive to more fully form the SEI film in the first region with a favorable surface position, thereby fully utilizing the protective efficiency of the additive and further improving the initial efficiency and life of the battery.

[0078] In some embodiments, the aqueous binder in the first region includes polyacrylic acid. The polyacrylic acid binder has numerous carboxyl groups that form hydrogen bonds on the surface of the negative electrode active material, thereby imparting adhesion between the negative electrode active material particles and the negative electrode current collector. This improves the cohesive force between the particles and enhances the structural stability of the second film layer.

[0079] In some embodiments, the negative electrode film layer region between the first region and the negative electrode current collector is the second region, and the aqueous binder in the second region includes styrene-butadiene rubber. The aqueous binder in the second region near the current collector includes styrene-butadiene rubber, thereby enabling the negative electrode film layer to have better adhesion to the current collector.

[0080] In some embodiments, the region of the negative electrode film layer adjacent to the negative electrode current collector is the third region, the negative electrode active material in the third region includes natural graphite, and the third region includes an additive. Natural graphite has a lower surface reactivity uniformity than artificial graphite, and natural graphite has a larger specific surface area and greater expansion, thus requiring a higher SEI film reconstruction during cycling and storage. Compared to artificial graphite, additives have a greater effect on improving the cycling and storage performance of natural graphite, resulting in better efficiency, and utilizing natural graphite reduces battery costs.

[0081] In some embodiments, the region of the negative electrode film layer away from the negative electrode current collector is the fourth region, and the negative electrode active material in the fourth region includes artificial graphite. Artificial graphite has more stable kinetic properties.

[0082] The coating amount or thickness relationship of the first region, the second region, the third region and the fourth region may refer to the conventional negative electrode film layer with a multi-layer structure, and is not particularly limited in this application.

[0083] In some embodiments of the present application, the negative electrode film further includes a conductive agent. As an example, the conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0084] In some embodiments of the present application, the mass content of the negative electrode active material in the negative electrode film layer can be selected as 93%-98%, the mass content of the conductive agent can be selected as 0.5%-1.5%, the mass content of the thickener can be selected as 0.5%-1.5%, the mass content of the binder can be selected as 0.5%-2%, and the mass content of the additive can be selected as 0.5%-2%.

[0085] In some embodiments of the present application, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0086] [Aqueous negative electrode slurry]

[0087] The second embodiment of the present application provides an aqueous negative electrode slurry, comprising water, a negative electrode active material dispersed in water, and an aqueous binder, wherein the aqueous negative electrode slurry further comprises an additive, the additive comprising a water-soluble unsaturated organic acid salt, the unsaturated group in the water-soluble unsaturated organic acid salt comprising an alkenyl group, an alkynyl group, * —C≡N, optionally, the acid ions of the water-soluble unsaturated organic acid salt include any one or more of sulfonate ions, borate ions, and phosphonate ions.

[0088] In the aqueous negative electrode slurry of the present application, water-soluble unsaturated organic acid salt and aqueous binder are combined, and the two are preferably fused because they are aqueous materials, and dispersion uniformity is better in the formed negative electrode pole piece, such as water-soluble unsaturated organic acid salt is preferably dispersed around the negative electrode active material. The negative electrode film layer formed using the aqueous negative electrode slurry breaks the unsaturated group of the water-soluble unsaturated organic acid salt during charging and undergoes self-polymerization reaction, forming a stable flexible SEI film on the surface of the negative electrode active material, thereby improving the cycle stability of the battery core. The above-mentioned acid radical ions contain high electronegativity elements (S, B, P), so they can preferentially occupy the active sites of the negative electrode particles, preferentially participate in film formation (charging process, the negative electrode interface attracts electrons, and the double bond of the additive opens to form a polymer) during charging, and high electronegativity elements can increase the electronegativity of the negative electrode surface, serve as the effect of electron acceptors, so that the combination of lithium ions and solvent molecules is weakened, which is conducive to lithium ion migration, reduces interfacial impedance, thereby reducing the degree of impedance increase caused by film formation.

[0089] In some embodiments of the present application, the weight ratio of the above-mentioned additive to the negative electrode active material is (0.5-2):(93-98), and can be optionally (0.8-1.5):(93-98). This achieves the purpose of minimizing the reduction in the energy density of the battery cell caused by the use of the additive, and the additive in the above ratio can fully play a role in improving the cycling stability of the battery cell.

[0090] In some embodiments of the present application, the water-soluble unsaturated organic acid salt includes any one or more of a water-soluble unsaturated organic lithium salt, a water-soluble unsaturated organic sodium salt, a water-soluble unsaturated organic potassium salt, a water-soluble unsaturated organic magnesium salt, and a water-soluble unsaturated organic calcium salt; alternatively, the water-soluble unsaturated organic acid salt includes any one or more of a water-soluble unsaturated sulfonate salt. During charging, when the water-soluble unsaturated sulfonate salt forms a protective film on the surface of the negative electrode active particles, the sulfonic acid groups participate in the film formation, improving the stability of the film structure and further extending the battery cell life.

[0091] In some embodiments of the present application, the water-soluble unsaturated sulfonate salt is optionally selected from any one or more water-soluble unsaturated lithium sulfonates; further optionally, the water-soluble unsaturated lithium sulfonate salt includes any one or more C1-C6 olefin lithium sulfonates; and more optionally, the water-soluble unsaturated lithium sulfonate salt includes any one or more of vinyl lithium sulfonate and allyl lithium sulfonate. When an unsaturated lithium sulfonate salt is used as an additive, it can also increase the migration rate of lithium ions, further reduce interfacial impedance, and improve the cycle life of the battery.

[0092] The aqueous binder used in this application can be selected from commonly used aqueous binders for electrode sheets. In some embodiments of this application, the aqueous binder includes any one or more of styrene-butadiene rubber, polyacrylic acid, and styrene-butadiene rubber. In particular, styrene-butadiene rubber, through its surface hydrophilic carboxyl groups, undergoes a condensation reaction with the hydroxyl groups on the surface of the negative electrode current collector, thereby further enhancing the adhesion between the negative electrode film layer and the current collector.

[0093] In some embodiments of the present application, the aqueous negative electrode slurry further includes a protective agent, which includes any one or more of sodium dodecylbenzene sulfonate, sodium lignin sulfonate, sodium alkyl glycerol ether sulfonate, sodium dodecyl sulfonate, and sodium dodecyl sulfate; optionally, the weight ratio of the protective agent to the additive is (0.2-0.6):1, optionally (0.3-0.5):1.

[0094] The protective agent has a hydrophobic chain and a hydrophilic anionic group. Its hydrophilic anionic group preferentially bonds with the hydrophilic additive, preventing the additive from pre-bonding with the hydrophilic groups of the aqueous binder. This effectively addresses the problem of decreased adhesion of the aqueous binder due to bonding with the additive. In particular, when styrene-butadiene rubber (SBR) is used as the aqueous binder, due to its abundant surface hydrophilic groups, the addition of the protective agent effectively prevents the SBR surface hydrophilic groups from bonding with the hydrophilic groups of the additive, effectively protecting the SBR structure and maintaining a good bonding effect with the negative electrode film and negative electrode current collector.

[0095] In some embodiments of the present application, the aqueous negative electrode slurry further includes a thickener, which includes any one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, propylene glycol alginate, methyl cellulose, sodium starch phosphate, sodium alginate, casein, sodium polyacrylate, polyethylene oxide, and polyvinyl pyrrolidone; optionally, the weight ratio of the thickener to the negative electrode active material is (0.5-1.5): (93-98). This improves the stability of the slurry and further enhances the uniformity of the dispersion of the components in the negative electrode film layer.

[0096] In some embodiments of the present application, the negative electrode active material includes one or more of a graphite negative electrode material, a silicon-carbon composite negative electrode material, and a silicon-oxygen negative electrode material; optionally, the graphite negative electrode material includes artificial graphite and / or natural graphite.

[0097] In some embodiments of the present application, the aqueous negative electrode slurry may further include a conductive agent. For example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] In some embodiments of the present application, the components of the aqueous negative electrode slurry are mixed and stirred to obtain the aqueous negative electrode slurry. In some embodiments, when styrene-butadiene rubber is used as the aqueous binder, the aqueous binder can be added as the last component because the stirring time is too long and the styrene-butadiene rubber may break.

[0099] In some embodiments of the present application, the aqueous negative electrode slurry provided in any of the above embodiments can be used to prepare the negative electrode sheet of the above-mentioned first embodiment. The optional preparation process flow can refer to the following process: the above-mentioned aqueous negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0100] When it is necessary to form multiple layers of negative electrode film with different compositions, the composition of the aqueous negative electrode slurry can be changed and coated on the negative electrode current collector in turn. After drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0101] [Positive electrode]

[0102] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0103] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0104] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0105] In some embodiments, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0106] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0107] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0108] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0109] [Electrolytes]

[0110] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0111] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0112] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0113] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0114] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0115] [Isolation film]

[0116] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0117] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0118] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0119] In some embodiments, the secondary battery includes a secondary battery cell, or includes a battery module and a battery pack.

[0120] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0121] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0122] The present application has no particular limitation on the shape of the secondary battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery cell 5 with a square structure as an example.

[0123] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a top cover assembly 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0124] In some embodiments, secondary battery cells may be assembled into a battery module. The battery module may contain one or more secondary battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0125] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple secondary battery cells 5 may be secured together using fasteners.

[0126] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of secondary battery cells 5 are accommodated in the accommodation space.

[0127] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0128] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0129] In addition, the present application also provides an electrical device, which includes the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0130] As the electrical device, a secondary battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0131] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0132] [Example]

[0133] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0134] Example 1

[0135] 1) Preparation of negative electrode sheet

[0136] The graphite powder natural graphite, conductive carbon super P, sodium carboxymethyl cellulose, styrene-butadiene rubber, and sodium vinyl sulfonate (as an additive) were mixed in a mass ratio of 96:0.7:1.2:1.6:0.5, and then water was added and stirred. After uniform dispersion, the mixture was coated on the surface of the copper foil substrate. The single-sided coating weight was controlled at 0.1772 g / 1540.25 mm 2 After the double-sided coating is completed, drying, cold pressing, slitting, and preparing a negative electrode sheet with a negative electrode film layer;

[0137] 2) Preparation of positive electrode sheet

[0138] Mix lithium iron phosphate powder, conductive agent super P, and polyvinylidene fluoride in a mass ratio of 97.2:1:1.8, then add N-methylpyrrolidone and stir. After uniform dispersion, apply it on the surface of the aluminum foil substrate. The single-sided coating weight is controlled at 0.382g / 1540.25mm 2 After the single-side coating is completed, drying, cold pressing, slitting and preparation are carried out to obtain the positive electrode sheet;

[0139] 3) Electrolyte composition: includes solvent, lithium salt, and additives; solvent: 83% by weight of the electrolyte (including ethyl methyl carbonate (EMC), ethylene carbonate (EC), and dimethyl carbonate (DMC), with a mass ratio of 2:1:1); lithium salt: 15% by weight of the electrolyte (lithium hexafluorophosphate); additive: 2% by weight of the electrolyte (vinylene carbonate VC).

[0140] 4) Separator: 12 μm thick PE separator (polyethylene).

[0141] 5) Battery Preparation

[0142] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the cathode and anode to provide isolation, to obtain a bare cell. The bare cell is then placed in an outer package, injected with the prepared electrolyte, and subjected to the following steps: encapsulation, electrolyte injection, formation, and venting, to obtain a lithium-ion battery.

[0143] Example 2

[0144] The other parts are the same as those in Example 1, except that the mass ratio of graphite powder to sodium vinyl sulfonate in the negative electrode is 95.7:0.8, and the negative electrode single-side coating weight is 0.1782 g / 1540.25 mm 2 .

[0145] Example 3

[0146] The other parts are the same as those in Example 1, except that the mass ratio of graphite powder to sodium vinyl sulfonate in the negative electrode is 95.0:1.5, and the negative electrode single-side coating weight is 0.0.1791g / 1540.25mm 2 .

[0147] Example 4

[0148] The other parts are the same as those in Example 1, except that the mass ratio of graphite powder to sodium vinyl sulfonate in the negative electrode is 94.5:2, and the negative electrode single-side coating weight is 0.1801 g / 1540.25 mm 2 .

[0149] Example 5

[0150] The rest is the same as Example 1, except that the graphite powder, conductive carbon, sodium carboxymethyl cellulose, styrene-butadiene rubber, and sodium vinyl sulfonate in the negative electrode are mixed in a mass ratio of 93.5:0.7:1.2:1.6:3.

[0151] Example 6

[0152] Other aspects are the same as those of Example 1, with the only difference being that the additive in the negative electrode plate is lithium vinyl sulfonate.

[0153] Example 7

[0154] Other aspects are the same as those of Example 1, with the only difference being that the additive in the negative electrode plate is lithium vinyl borate.

[0155] Example 8

[0156] Other aspects are the same as those of Example 1, with the only difference being that the additive in the negative electrode plate is lithium vinyl phosphate.

[0157] Example 9

[0158] Other aspects are the same as in Example 1, except that the additive in the negative electrode plate is sodium propargyl sulfonate.

[0159] Example 10

[0160] The rest is the same as Example 1, except that sodium dodecyl sulfonate is further added to the negative electrode plate as a protective agent, and the mass ratio of sodium dodecyl sulfonate to sodium vinyl sulfonate and graphite powder is 0.8:2:93.7.

[0161] Example 11

[0162] The rest is the same as Example 1, except that sodium dodecyl sulfonate is further added to the negative electrode plate as a protective agent, and the mass ratio of sodium dodecyl sulfonate to sodium vinyl sulfonate and graphite powder is 1.2:2:93.3.

[0163] Example 12

[0164] The rest is the same as Example 1, except that sodium dodecyl sulfonate is further added to the negative electrode plate as a protective agent, and the mass ratio of sodium dodecyl sulfonate to sodium vinyl sulfonate and graphite powder is 0.4:2:94.1.

[0165] Example 13

[0166] The rest is the same as Example 1, except that sodium dodecyl sulfonate is further added to the negative electrode plate as a protective agent, and the mass ratio of sodium dodecyl sulfonate to sodium vinyl sulfonate and graphite powder is 0.6:2:93.9.

[0167] Example 14

[0168] The rest is the same as Example 1, except that sodium dodecyl sulfonate is further added to the negative electrode plate as a protective agent, and the mass ratio of sodium dodecyl sulfonate to sodium vinyl sulfonate and graphite powder is 1:2:93.5.

[0169] Example 15

[0170] The rest is the same as Example 1, except that sodium dodecyl sulfonate is further added to the negative electrode plate as a protective agent, and the mass ratio of sodium dodecyl sulfonate to sodium vinyl sulfonate and graphite powder is 1.26:2:93.24.

[0171] Example 16

[0172] The other steps are the same as those in Example 10, except that sodium dodecylbenzenesulfonate is used as the protective agent.

[0173] Example 17

[0174] The other steps are the same as those in Example 10, except that sodium lauryl sulfate is used as the protective agent.

[0175] Example 18

[0176] The other steps are the same as those in Example 1, except that polyacrylic acid is used instead of styrene-butadiene rubber.

[0177] Example 19

[0178] The other parts are the same as those in Example 1, with the only difference being that the negative electrode film layer of the negative electrode plate has two layers, the first film layer (or the second region) and the second film layer (or the first region) are sequentially arranged away from the negative electrode current collector, wherein sodium vinyl sulfonate is not used in the first film layer, and natural graphite, conductive carbon super P, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed in a mass ratio of 96.5:0.7:1.2:1.6, and the binder in the second film layer is polyacrylic acid, and artificial graphite, conductive carbon super P, sodium carboxymethyl cellulose, polyacrylic acid, and sodium vinyl sulfonate are mixed in a mass ratio of 95.5:0.7:1.2:1.6:1. The weight ratio per unit area of ​​the first film layer and the second film layer is 1:1, and the single-sided coating weight of each film layer is controlled at 0.1772g / 1540.25mm 2 .

[0179] Example 20

[0180] The rest is the same as in Example 1, except that the negative electrode film layer of the negative electrode sheet has two layers. The first film layer (or the third region) and the second film layer (or the fourth region) are sequentially arranged away from the negative electrode current collector. The natural graphite, conductive carbon super P, sodium carboxymethyl cellulose, styrene-butadiene rubber, and sodium vinyl sulfonate in the first film layer are mixed in a mass ratio of 95.5:0.7:1.2:1.6:1, and the artificial graphite, conductive carbon super P, sodium carboxymethyl cellulose, and polyacrylic acid in the second film layer are mixed in a mass ratio of 96.5:0.7:1.2:1.6. The weight ratio per unit area of ​​the first film layer and the second film layer is 1:1, and the coating weight of each film layer on one side is controlled at 0.1772g / 1540.25mm 2 .

[0181] Example 21

[0182] The other aspects are the same as those of Example 1, except that the negative electrode film layer is divided into two layers, the first film layer and the second film layer are sequentially arranged away from the negative electrode current collector, the binder in the first film layer is changed to polyacrylic acid, and the graphite powder natural graphite, conductive carbon super P, sodium carboxymethyl cellulose, polyacrylic acid, and sodium vinyl sulfonate are in a mass ratio of 95.5:0.7:1.2:1.6:1; there is no sodium vinyl sulfonate in the second film layer, and the graphite powder artificial graphite, conductive carbon super P, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed in a mass ratio of 96.5:0.7:1.2:1.6; the weight ratio per unit area of ​​the first film layer and the second film layer is 1:1, and the single-sided coating weight is controlled at 0.1772 g / 1540.25 mm 2 .

[0183] Example 22

[0184] Other aspects are the same as those of Example 1, with the only difference being that the additive in the negative electrode plate is sodium acrylate.

[0185] Comparative Example 1

[0186] The rest is the same as in Example 1, except that sodium vinyl sulfonate is not added to the negative electrode plate, and the graphite powder (artificial graphite), conductive carbon super P, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed in a mass ratio of 96.5:0.7:1.2:1.6. The rest is the same as in Example 1.

[0187] Comparative Example 2

[0188] Other aspects are the same as those of Example 1, except that the additive in the negative electrode plate is sodium (2-carboxyethyl)phenylphosphonate.

[0189] Negative electrode sheet adhesion test: Use a blade to cut a 20mm wide by 100mm long sample from the cold-pressed negative electrode sheet. Apply special double-sided tape (20mm wide by 90mm long) to a 20mm wide by 200mm long steel plate. Place the cut negative electrode sheet sample on the double-sided tape with the test side facing down, then roll it three times in the same direction with a roller. Insert a 150mm long paper tape, the same width as the negative electrode sheet, underneath the negative electrode sheet and secure it with crepe tape. Secure the end of the steel sheet not attached to the negative electrode sheet with the lower clamp. Fold the paper tape upward and secure it with the upper clamp. Start the tensile testing machine at an upward speed of 0.05m / min. Record the tensile force (F) displayed on the tensile testing machine when the negative electrode sheet is peeled from the double-sided tape: Negative electrode adhesion (N / m) = F / Negative electrode sheet cut width.

[0190] Cycle test: Place the battery cell in a charge and discharge device at a temperature of 45°C. Based on the initial capacity C3 / hour = 1C, first let it sit for 2 hours to allow the battery temperature to reach 45°C. Then charge it at a constant current rate of 0.5C to 3.8V, and then charge it at a constant voltage until the charge rate drops to 0.05C; then let it sit for 10 minutes, and discharge it at a constant current rate of 1C to 2.0V (recorded as the first cycle discharge capacity). Let it sit for 10 minutes, and repeat the above charge and discharge steps. Each charge and discharge is recorded as a cycle. Record the ratio of each cycle discharge capacity to the first cycle discharge capacity. Test the ratio of the discharge capacity after 800 cycles to the first cycle discharge capacity, and record it as 45°C 0.5C / 1C cycle 800cls.

[0191] DC resistance DCR value test:

[0192] 1) Place the battery cell in a charging and discharging device at a temperature of 25°C. Based on the initial capacity C3 / hour = 1C, leave it for 2 hours to keep the battery temperature at 25°C.

[0193] 2) Then charge at a constant current rate of 0.33C to 3.8V, then charge at a constant voltage until the charge rate drops to 0.05C, and let it rest for 10 minutes; record the charge capacity at this time as C4;

[0194] 3) Discharge the battery at a constant current rate of 0.33C for 1.5 hours (the battery is adjusted to 50% SOC), record the voltage V1 after the discharge is completed, and then leave it for 10 minutes;

[0195] 4) Discharge at a rate of 4C for 30 seconds and record the voltage V2 after the discharge is completed.

[0196] 5) The current corresponding to the above 4C is I = 4*C3 (the unit of C3 is Ah, and the unit of current is A). The unit of the above voltage is V;

[0197] The battery is at 50% SOC and discharged at 4C for 30s. DCR (Ω) = (V1-V2) / I.

[0198] Storage test: The battery was placed in a constant temperature oven at 60°C for 15 days. After storage, the battery was taken out and discharged in a 25°C charge and discharge device to calculate the capacity retention rate. The capacity retention rate was recorded after 90 days of storage.

[0199] The test results are recorded in Table 1.

[0200] Table 1

[0201] Comparisons of the Examples and Comparative Example 1 in Table 1 show that the use of additives such as sodium vinyl sulfonate resulted in higher capacity retention rates after cycling and storage than in Comparative Example 1, indicating that the additives can self-polymerize on the graphite surface to form a protective layer, thereby improving battery life. Comparisons of Examples 1 to 4 show that a higher additive content correlates with a longer battery life.

[0202] However, because sodium vinyl sulfonate can destroy the structure of the styrene-butadiene rubber binder, the higher its content, the lower the bonding strength between the negative electrode film layer and the negative electrode current collector in the corresponding negative electrode plate. For example, in Example 5, which has the highest sodium vinyl sulfonate content, its plate bonding strength is the lowest. Although Examples 10 to 15 also increase the content of sodium vinyl sulfonate, they effectively alleviate the reduction in bonding strength between the negative electrode film layer and the negative electrode current collector by adding the protective agent sodium dodecyl sulfonate to protect the structure of the styrene-butadiene rubber binder. The protective agent is non-conductive, but it contains highly electronegative groups, so its addition only slightly increases the DCR value of the battery cell. Moreover, due to the improved bonding strength of the plate, the stability of the plate expansion and contraction during charge and discharge is stabilized, thereby improving the capacity retention rate of the battery cycle and storage.

[0203] In Example 19, the bonding effect between the active layer and the current collector is also improved by dividing the negative electrode film layer into two layers, placing the layer with the additive on the side away from the current collector, and adding another binder polyacrylic acid.

[0204] In addition, except for Examples 6 to 8, the additives used in other Examples are all sodium salts. Although their film formation is stable, they do not show an enhanced effect on lithium ion conductivity. Instead, they increase battery impedance, increase polarization, and reduce the initial capacity of the battery. Examples 6 to 8 introduce lithium salts, which not only form a good SEI film, but also increase the migration rate of lithium ions, further reduce the battery impedance, and improve the battery life.

[0205] Example 22 uses sodium acrylate as an additive, so that the impedance of the battery is larger than that of Example 1 when sodium vinyl sulfonate is used as an additive.

[0206] Comparative Example 2 uses sodium (2-carboxyethyl)phenylphosphonate as an additive. Since it is insoluble in water and easily agglomerates, the binder in the slurry is unevenly distributed, which reduces the bonding force of the electrode and affects the charge and discharge performance.

[0207] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material and an aqueous binder. At least part of the negative electrode film layer further includes an additive, and the additive includes a water-soluble unsaturated organic acid salt. The unsaturated group in the water-soluble unsaturated organic acid salt includes any one or more of an alkenyl group, an alkynyl group, and *-C≡N.

2. The negative electrode sheet according to claim 1, wherein The acid radical ions of the water-soluble unsaturated organic acid salt include any one or more of a sulfonate ion, a borate ion, and a phosphonate ion.

3. The negative electrode sheet according to claim 1 or 2, wherein In the region of the negative electrode film layer containing the additive, the weight ratio of the additive to the negative electrode active material is (0.5 - 2):(93 - 98).

4. The negative electrode sheet according to claim 3, wherein, In the region containing the additive, the weight ratio of the additive to the negative electrode active material is (0.8 - 1.5):(93 - 98).

5. The negative electrode sheet according to any one of claims 1 to 4, wherein The water-soluble unsaturated organic acid salt includes any one or more of a water-soluble unsaturated lithium salt, a water-soluble unsaturated sodium salt, a water-soluble unsaturated potassium salt, a water-soluble unsaturated magnesium salt, and a water-soluble unsaturated calcium salt.

6. The negative electrode sheet according to claim 5, wherein, The water-soluble unsaturated organic acid salt includes any one or more of water-soluble unsaturated sulfonates.

7. The negative electrode sheet according to claim 6, wherein, The water-soluble unsaturated sulfonate includes any one or more of unsaturated lithium sulfonates.

8. The negative electrode sheet according to claim 7, wherein, The water-soluble unsaturated lithium sulfonate includes any one or more of C1 - C6 alkenyl sulfonic acid lithium salts.

9. The negative electrode plate according to claim 8, wherein, The water-soluble unsaturated lithium sulfonate includes any one or more of lithium vinyl sulfonate and lithium propenyl sulfonate.

10. The negative electrode sheet according to any one of claims 1 to 9, wherein, The negative electrode film layer further includes a polymer formed by cross-linking of the additive. The polymer includes any one or more of the following structural units: n is any integer from 0 to 6, and optionally n is 0 or 1. R 1 The acid radical ions of include any one or more of sulfonate ions, borate ions, and phosphonate ions.

11. The negative electrode sheet according to claim 10, wherein, R 1 The cations in it include any one or more of sodium ions, lithium ions, potassium ions, magnesium ions, and calcium ions.

12. The negative electrode sheet according to claim 11, wherein, R 1 comprises a sulfonic acid lithium ion.

13. The negative electrode sheet according to any one of claims 10 to 12, wherein In the region of the negative electrode film layer containing the additive, the weight ratio of the total weight of the additive and the polymer to the negative electrode active material is (0.5 - 2):(93 - 98).

14. The negative electrode sheet according to claim 13, wherein, In the region of the negative electrode film layer containing the additive, the weight ratio of the total mass of the additive and the polymer to the negative electrode active material is (0.8 - 1.5):(93 - 98).

15. The negative electrode sheet according to any one of claims 10 to 14, wherein At least part of the polymer coats the surface of the negative electrode active material.

16. The negative electrode sheet according to any one of claims 1 to 15, wherein, The aqueous binder includes any one or more of styrene-butadiene rubber, polyacrylic acid, and styrene-butadiene rubber.

17. The negative electrode sheet according to any one of claims 1 to 16, wherein, In the region of the negative electrode film layer including the additive, a protective agent is further included. The protective agent includes any one or more of sodium dodecylbenzenesulfonate, sodium lignosulfonate, sodium alkyl glycerol ether sulfonate, sodium dodecyl sulfonate, and sodium dodecyl sulfate.

18. The negative electrode sheet according to claim 17, wherein, The weight ratio of the protective agent to the additive is (0.2 - 0.6):

1.

19. The negative electrode sheet according to claim 18, wherein, The weight ratio of the protective agent to the additive is (0.3 - 0.5):

1.

20. The negative electrode sheet according to any one of claims 1 to 19, wherein, The negative electrode active material includes one or more of a graphite negative electrode material and a silicon-based negative electrode material.

21. The negative electrode sheet according to any one of claims 1 to 20, wherein, The additive is dispersed in the region of the negative electrode film layer far from the negative electrode current collector, and the region of the negative electrode film layer having the additive is the first region.

22. The negative electrode sheet according to claim 21, wherein, The aqueous binder in the first region includes polyacrylic acid.

23. The negative electrode sheet according to claim 21 or 22, wherein, The region of the negative electrode film layer between the first region and the negative electrode current collector is the second region, and the water-based binder in the second region includes styrene-butadiene rubber.

24. The negative electrode sheet according to any one of claims 1 to 20, wherein, The region of the negative electrode film layer close to the negative electrode current collector is the third region, the negative electrode active material in the third region includes natural graphite, and the third region includes the additive.

25. The negative electrode sheet according to claim 24, wherein, The region of the negative electrode film layer far from the negative electrode current collector is the fourth region, and the negative electrode active material in the fourth region includes artificial graphite.

26. An aqueous negative electrode slurry, comprising water and a negative electrode active material and an aqueous binder dispersed in the water, wherein, The water-based negative electrode slurry further includes an additive, the additive includes a water-soluble unsaturated organic acid salt, and the unsaturated group in the water-soluble unsaturated organic acid salt includes any one or more of alkenyl, alkynyl, and *-C≡N.

27. The aqueous negative electrode paste according to claim 26, wherein The acid radical ions of the water-soluble unsaturated organic acid salt include any one or more of sulfonate, borate, and phosphonate.

28. The aqueous negative electrode paste according to claim 27, wherein, The weight ratio of the additive to the negative electrode active material is (0.5 - 2):(93 - 98).

29. The aqueous negative electrode paste according to claim 28, wherein, The weight ratio of the additive to the negative electrode active material is (0.8 - 1.5):(93 - 98).

30. The aqueous negative electrode paste according to any one of claims 26 to 29, wherein, The water-soluble unsaturated organic acid salt includes any one or more of water-soluble unsaturated lithium salts, water-soluble unsaturated sodium salts, water-soluble unsaturated potassium salts, water-soluble unsaturated magnesium salts, and water-soluble unsaturated calcium salts.

31. The aqueous negative electrode paste according to claim 30, wherein, The water-soluble unsaturated organic acid salt includes any one or more of water-soluble unsaturated sulfonates.

32. The aqueous negative electrode paste according to claim 31, wherein, The water-soluble unsaturated sulfonate includes any one or more of water-soluble unsaturated lithium sulfonates.

33. The aqueous negative electrode paste according to claim 32, wherein, The water-soluble unsaturated lithium sulfonate includes any one or more of alkenyl sulfonate lithium with C1 - C6.

34. The aqueous negative electrode paste according to claim 33, wherein, The water-soluble unsaturated lithium sulfonate includes any one or more of lithium vinyl sulfonate and lithium propenyl sulfonate.

35. The aqueous negative electrode paste according to any one of claims 26 to 34, wherein, The water-based binder includes any one or more of styrene-butadiene rubber, polyacrylic acid, and styrene-butadiene rubber.

36. The aqueous negative electrode paste according to any one of claims 26 to 35, wherein, The water-based negative electrode slurry further includes a protective agent, and the protective agent includes any one or more of sodium dodecylbenzenesulfonate, sodium lignosulfonate, alkyl glycerol ether sulfonate, sodium dodecyl sulfonate, and sodium dodecyl sulfate.

37. The aqueous negative electrode paste according to claim 36, wherein, The weight ratio of the protective agent to the additive is (0.2 - 0.6):

1.

38. The aqueous negative electrode paste according to claim 37, wherein, The weight ratio of the protective agent to the additive is (0.3 - 0.5):

1.

39. The aqueous negative electrode paste according to any one of claims 26 to 38, wherein, The negative electrode active material includes natural graphite.

40. A secondary battery includes a negative electrode tab, wherein, The negative electrode sheet includes the negative electrode sheet according to any one of claims 1 to 25.

41. An electric device, comprising a secondary battery, wherein, The secondary battery includes the secondary battery according to claim 40.

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