Negative electrode plate, aqueous negative electrode slurry, secondary battery and electric device

Abstract

The invention provides a negative electrode plate, water-based negative electrode slurry, a secondary battery and an electric device. The negative electrode piece 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, and the additive comprises water-soluble unsaturated organic acid salt; unsaturated groups in the water-soluble unsaturated organic acid salt comprise any one or more of an alkenyl group, an alkynyl group and # imgabs0 #. And the cycling stability of the battery cell with the negative pole piece is improved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a negative electrode sheet, an aqueous negative electrode slurry, a secondary battery, and an electrical device. Background Art

[0002] Graphite is the most widely used negative electrode material for lithium-ion batteries. It not only has the advantages of rich raw materials, low cost, low reaction potential, and good electrical conductivity, but also exhibits a small volume effect during the charge and discharge process of the battery.

[0003] During the first formation charging process of a lithium-ion battery, an SEI film will be formed on the surface of graphite to form a protective layer, but it will irreversibly consume lithium ions, resulting in a decrease in the first efficiency of the battery. Moreover, the presence of additives in the electrolyte will cause the thickening of the SEI film, resulting in an increase in the interfacial impedance and affecting the power performance of the battery; secondly, during the subsequent charge and discharge process, the negative electrode continuously expands and contracts, causing the SEI film to rupture, increasing the side reactions between the negative electrode active material and the electrolyte, and the irreversible loss of lithium ions is required to repair the SEI film again, resulting in a decrease in the battery life. Therefore, constructing an artificial SEI has become a key technology to improve the first efficiency and life of the battery. Summary of the Invention

[0004] 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.

[0005] In a first aspect of the present application, a negative electrode sheet is provided, which 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, and at least a part of the negative electrode film layer 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 an alkenyl group, an alkynyl group, and *-C≡N.

[0006] In the negative electrode sheet of the present application, the water-soluble unsaturated organic acid salt and the aqueous binder are combined. Since both are aqueous materials, they can be better fused, and the material dispersion uniformity of the negative electrode sheet is better. For example, the water-soluble unsaturated organic acid salt is better dispersed around the negative electrode active material; during the charging process, the unsaturated group of the water-soluble unsaturated organic acid salt breaks and undergoes a self-polymerization reaction to form a stable flexible SEI film on the surface of the negative electrode active material, thereby improving the cycle stability of the battery cell.

[0007] In any embodiment of the first aspect, optionally, the acid radical ions of the water-soluble unsaturated organic acid salt include any one or more of sulfonate ions, borate ions, and phosphonate ions. Since the above acid radical ions contain highly electronegative elements (S, B, P), they can preferentially occupy the active sites of the negative electrode particles and preferentially participate in film formation during the charging process (during the charging process, the negative electrode interface attracts electrons, and the double bond of the additive opens to form a polymer). Moreover, the highly electronegative elements will increase the electronegativity of the negative electrode surface, acting as an electron acceptor, weakening the binding of lithium ions to solvent molecules, facilitating the migration of lithium ions, reducing the interfacial impedance, and thus reducing the degree of impedance increase caused by film formation.

[0008] 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), and can be optionally (0.8 - 1.5):(93 - 98).

[0009] In any embodiment of the first aspect, the water-soluble unsaturated organic acid salt includes any one or more of water-soluble unsaturated organic lithium salts, water-soluble unsaturated organic sodium salts, water-soluble unsaturated organic potassium salts, water-soluble unsaturated organic magnesium salts, and water-soluble unsaturated organic calcium salts; optionally, the water-soluble unsaturated organic acid salt includes any one or more of water-soluble unsaturated sulfonates; optionally, the water-soluble unsaturated sulfonate is selected from any one or more of water-soluble unsaturated lithium sulfonates; further optionally, the water-soluble unsaturated lithium sulfonate includes any one or more of alkenyl sulfonic acid lithium salts with C1 - C6; more optionally, the water-soluble unsaturated lithium sulfonate includes any one or more of lithium vinyl sulfonate and lithium propenyl sulfonate. During charging, when the water-soluble unsaturated sulfonate forms a protective film on the surface of the negative electrode active particles, the sulfonic acid group participates in film formation, improving the stability of the film formation structure and further enhancing the service life of the battery cell.

[0010] In any embodiment of the first aspect, the negative electrode film layer further includes a polymer formed by cross-linking of the additive, and optionally at least part of the polymer coats the surface of the negative electrode active material; optionally, the polymer includes any one or more of the following structural units:

[0011]

[0012] n is any integer from 0 to 6, and optionally n is 0 or 1;

[0013] R 1 The acid radical ions of include any one or more of sulfonate ions, borate ions, and phosphonate ions, and optionally R 1 The cations in include any one or more of sodium ions, lithium ions, potassium ions, magnesium ions, and calcium ions; further optionally R 1It includes lithium sulfonate ions; optionally, in the region of the negative electrode film layer containing additives, the total weight ratio of the additives and the polymer to the weight of the negative electrode active material is (0.5 - 2):(93 - 98), and can be optionally (0.8 - 1.5):(93 - 98).

[0014] When the polymer formed after charging coats the surface of the negative electrode active material, it acts as an SEI film, providing a more direct protection to the negative electrode active material.

[0015] In any implementation manner of the first aspect, the aqueous binder includes any one or more of styrene-butadiene rubber, polyacrylic acid, and styrene-butadiene rubber.

[0016] In any implementation manner of the first aspect, the region of the negative electrode film layer including additives further includes a protective agent, and the protective agent includes any one or more of sodium dodecylbenzenesulfonate, sodium lignosulfonate, 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.

[0017] The above protective agent has a hydrophobic chain and a hydrophilic anionic group. Its hydrophilic anionic group binds to the hydrophilic additive first, avoiding the prior binding of the additive to the hydrophilic group of the aqueous binder, and effectively solving the problem of the decrease in adhesion caused by the connection between the aqueous binder and the additive. Especially when styrene-butadiene rubber is used as the aqueous binder, due to its rich hydrophilic groups on the surface, adding the above protective agent effectively prevents the binding of the hydrophilic groups on the surface of styrene-butadiene rubber to the hydrophilic groups of the additive, effectively protecting the structure of styrene-butadiene rubber and enabling it to still maintain a good adhesion effect on the negative electrode film layer and the negative electrode current collector.

[0018] In any implementation manner of the first aspect, the negative electrode film layer further includes a thickening agent, and the thickening agent includes any one or more of sodium carboxymethylcellulose, lithium carboxymethylcellulose, propylene glycol alginate, methylcellulose, sodium starch phosphate, sodium alginate, casein, sodium polyacrylate, polyoxyethylene, and polyvinylpyrrolidone; optionally, the weight ratio of the thickening agent to the negative electrode active material is (0.5 - 1.5):(93 - 98).

[0019] In any implementation manner of the first aspect, the negative electrode active material includes one or more of graphite negative electrode materials and silicon-based negative electrode materials. Optionally, the silicon-based negative electrode materials include one or more of silicon-carbon composite negative electrode materials and silicon-oxygen negative electrode materials; optionally, the graphite negative electrode materials include artificial graphite and / or natural graphite.

[0020] In any implementation manner of the first aspect, the additives are 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 with additives is the first region.

[0021] In any embodiment of the first aspect, the aqueous binder in the first region comprises polyacrylic acid.

[0022] 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 comprises styrene-butadiene rubber.

[0023] In any embodiment of the first aspect, 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 comprises natural graphite, and the third region comprises an additive.

[0024] In any embodiment of the first aspect, 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 comprises artificial graphite.

[0025] The second aspect of the present application provides an aqueous negative electrode slurry, comprising water and a negative electrode active material and an aqueous binder dispersed in the water, wherein the aqueous negative electrode slurry further comprises an additive, the additive comprises a water-soluble unsaturated organic acid salt, and the unsaturated group in the water-soluble unsaturated organic acid salt comprises any one or more of an alkenyl group, an alkynyl group, and *-C≡N. Optionally, the acid radical ion of the water-soluble unsaturated organic acid salt comprises any one or more of a sulfonate, a borate, and a phosphonate.

[0026] In the aqueous negative electrode slurry of the present application, the water-soluble unsaturated organic acid salt and the aqueous binder are combined. Since both are aqueous materials, they can be better fused, and the dispersion uniformity in the formed negative electrode sheet is better. For example, the water-soluble unsaturated organic acid salt is better dispersed around the negative electrode active material. During the charging process of the negative electrode film layer formed by using the aqueous negative electrode slurry, the unsaturated group of the water-soluble unsaturated organic acid salt breaks and undergoes a self-polymerization reaction to form a stable flexible SEI film on the surface of the negative electrode active material, thereby improving the cycle stability of the battery cell. The above acid radical ions contain highly electronegative elements (S, B, P), so they can preferentially occupy the active sites of the negative electrode particles and preferentially participate in film formation during the charging process (during the charging process, the negative electrode interface attracts electrons, and the double bond of the additive opens to form a polymer). Moreover, the highly electronegative elements will increase the electronegativity of the negative electrode surface, acting as an electron acceptor, weakening the binding between lithium ions and solvent molecules, facilitating the migration of lithium ions, reducing the interfacial impedance, and thus reducing the degree of impedance increase caused by film formation.

[0027] 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), and can be (0.8-1.5):(93-98).

[0028] In any embodiment of the second aspect, the water-soluble unsaturated organic acid salt includes any one or more of water-soluble unsaturated organic lithium salts, water-soluble unsaturated organic sodium salts, water-soluble unsaturated organic potassium salts, water-soluble unsaturated organic magnesium salts, and water-soluble unsaturated organic calcium salts; optionally, the water-soluble unsaturated organic acid salt includes any one or more of water-soluble unsaturated sulfonate salts; optionally, the water-soluble unsaturated sulfonate salt is selected from any one or more of water-soluble unsaturated lithium sulfonates; further optionally, the water-soluble unsaturated lithium sulfonate salt includes any one or more of alkenyl sulfonic acid lithium salts having 1 to 6 carbon atoms; more optionally, the water-soluble unsaturated lithium sulfonate salt includes any one or more of lithium vinyl sulfonate and lithium allyl sulfonate. When using the water-soluble unsaturated lithium sulfonate salt as an additive, the water-soluble unsaturated lithium sulfonate salt can also increase the migration rate of lithium ions, further reduce the interfacial impedance, and improve the cycle life of the battery.

[0029] 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.

[0030] In any embodiment of the second aspect, the aqueous 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; 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. It effectively solves the problem of the decrease in adhesion caused by the connection between the aqueous binder and the additive.

[0031] In any embodiment of the second aspect, the aqueous negative electrode slurry further includes a thickening agent, and the thickening agent 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, polyoxyethylene, and polyvinylpyrrolidone; optionally, the weight ratio of the thickening agent to the negative electrode active material is (0.5-1.5):(93-98).

[0032] In any embodiment of the second aspect, the negative electrode active material includes one or more of graphite negative electrode materials and silicon-based negative electrode materials; optionally, the silicon-based negative electrode materials include one or more of silicon-carbon composite negative electrode materials and silicon-oxygen negative electrode materials; optionally, the graphite negative electrode material includes artificial graphite and / or natural graphite.

[0033] The third aspect of the present application provides a secondary battery, including a negative electrode tab, wherein the negative electrode tab includes the negative electrode tab provided by any embodiment of the first aspect.

[0034] The 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

[0035] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments of the present application. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the drawings.

[0036] Figure 1 It is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0037] Figure 2 is Figure 1 The exploded view of the secondary battery according to an embodiment of the present application shown.

[0038] Figure 3 It is a schematic diagram of a battery module according to an embodiment of the present application.

[0039] Figure 4 It is a schematic diagram of a battery pack according to an embodiment of the present application.

[0040] Figure 5 is Figure 4 The exploded view of the battery pack according to an embodiment of the present application shown.

[0041] Figure 6 It is a schematic diagram of an electrical device using the secondary battery as a power source according to an embodiment of the present application.

[0042] In the drawings, the drawings are not drawn to actual scale.

[0043] Description of the Reference Numerals:

[0044] 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Secondary battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Embodiments

[0045] The following will further describe in detail the embodiments of the present application in conjunction with the drawings and embodiments. The detailed description and drawings of the following embodiments are used to exemplarily illustrate the principles of the present application, but cannot be used to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0046] Hereinafter, embodiments of the negative electrode sheet, aqueous negative electrode slurry, secondary battery, and electrical device of the present application will be specifically described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary details are omitted. For example, there are cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0047] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The range defined in this way can include or exclude the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when a certain parameter is expressed as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0048] If there is no special description, all embodiments and alternative embodiments of the present application can be combined with each other to form a new technical solution.

[0049] If there is no special description, all technical features and alternative technical features of the present application can be combined with each other to form a new technical solution.

[0050] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may also include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0051] Unless otherwise specified, the terms "comprising" and "including" mentioned in this application are open-ended. For example, the "comprising" and "including" may mean that other components not listed may also be included or comprised.

[0052] Unless otherwise specified, in this application, the term "or" is inclusive. 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) while B is true (or exists); or both A and B are true (or exist).

[0053] [Secondary battery]

[0054] A secondary battery, also known as a rechargeable battery or a storage battery, refers to a battery that can activate the active material through charging after discharging and can be used continuously.

[0055] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. During the charge and discharge process of the battery, active ions (such as lithium ions or sodium ions) intercalate and deintercalate between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows active ions to pass through. The electrolyte is between the positive electrode plate and the negative electrode plate, mainly to conduct active ions.

[0056] [Negative electrode plate]

[0057] As described in the background art, although the SEI film can be formed on the negative electrode during the first formation charging process at present, the SEI film is prone to rupture during the subsequent cyclic charge and discharge process. This problem also exists in the aqueous negative electrode plate, that is, how to ensure that the solid electrolyte interface film (SEI film) formed on the surface of graphite has good stability under the condition of an aqueous binder to improve the cycle stability of the battery has become an urgent problem to be solved. To solve this problem, this application provides a negative electrode plate, an aqueous negative electrode slurry, a secondary battery, and an electrical device.

[0058] The first embodiment of the present application provides a negative electrode plate, including a 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 includes a negative electrode active material and an aqueous binder, and at least part of the negative electrode film layer also 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 an alkene group, an alkynyl group, and *-C≡N.

[0059] In the negative electrode plate of the present application, a water-soluble unsaturated organic acid salt and an aqueous binder are combined. 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 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.

[0060] In some embodiments of the present application, optionally, the acid radical ions of the water-soluble unsaturated organic acid salt include any one or more of sulfonate ions, borate ions, and phosphonate ions. 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 during charging (charging process, the negative electrode interface attracts electrons, and the double bonds of the additive are opened to form polymers), and the high electronegativity elements increase the electronegativity of the negative electrode surface, acting 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 the interface impedance, and thus reduces the degree of impedance increase caused by film formation.

[0061] 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).

[0062] In some embodiments of the present application, the water-soluble unsaturated organic acid salt includes any one or more of water-soluble unsaturated organic lithium salt, water-soluble unsaturated organic sodium salt, water-soluble unsaturated organic potassium salt, water-soluble unsaturated organic magnesium salt, and water-soluble unsaturated organic calcium salt; optionally, the water-soluble unsaturated organic acid salt includes any one or more of water-soluble unsaturated sulfonate salts. 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 group participates in the film formation, which improves the stability of the film structure and further improves the life of the battery cell.

[0063] In some embodiments of the present application, optionally, the water-soluble unsaturated sulfonate is selected from any one or more of water-soluble unsaturated lithium sulfonates; further optionally, the water-soluble unsaturated lithium sulfonate includes any one or more of alkenyl sulfonic acid lithium salts with C1-C6; more optionally, the water-soluble unsaturated lithium sulfonate includes any one or more of lithium vinyl sulfonate and lithium propenyl sulfonate. When using the water-soluble unsaturated lithium sulfonate as an additive, the water-soluble unsaturated lithium sulfonate can also increase the migration rate of lithium ions, further reduce the interfacial impedance, and improve the cycle life of the battery.

[0064] Since the additives in the negative electrode sheet undergo a self-polymerization reaction after charging, and the unsaturated groups are broken to form polymers. In some embodiments, the negative electrode film layer further includes polymers formed by cross-linking of additives. Optionally, at least part of the polymers are coated on the surface of the negative electrode active material. When the polymers formed after charging are coated on the surface of the negative electrode active material, they act as SEI films and play a more direct protective role for the negative electrode active material.

[0065] The structural units of the polymer mainly depend on the structure of the water-soluble unsaturated organic acid salt. In some embodiments, optionally, the polymer includes any one or more of the following structural units:

[0066]

[0067] n is any integer from 0 to 6, optionally n is 0 or 1;

[0068] R 1 The acid radical ions of include any one or more of sulfonate ions, borate ions, and phosphonate ions. Optionally, the cations in R 1 include any one or more of sodium ions, lithium ions, potassium ions, magnesium ions, and calcium ions; further optionally, R 1 includes lithium sulfonate ions.

[0069] Those skilled in the art should understand that the above R 1 In addition to including the above-mentioned anion groups, it may also include alkylene groups, etc. Of course, it may also not include other groups, such as lithium vinyl sulfonate below.

[0070] 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. Moreover, the additive ultimately also plays a protective role on the negative electrode active material in the form of a polymer. In some embodiments, optionally, in the negative electrode film layer containing the additive, the weight ratio of the total weight of the additive and the polymer to the weight of the negative electrode active material is (0.5 - 2):(93 - 98), and can be optionally (0.8 - 1.5):(93 - 98). This can not only avoid the problem of the decrease in the energy density of the battery cell caused by excessive use of the additive, but also utilize the additive to achieve the protective effect on the negative electrode active material, and fully improve the cycle performance of the battery.

[0071] The aqueous binder used in this application can be selected from the aqueous binders commonly used in negative electrode plates. In some embodiments of this application, the above-mentioned aqueous binder includes any one or more of styrene-butadiene rubber, polyacrylic acid, and styrene-butadiene rubber. In particular, the carboxyl group of the hydrophilic surface group of styrene-butadiene rubber undergoes a condensation reaction with the hydroxyl group on the surface of the negative electrode current collector, thereby further enhancing the adhesion between the negative electrode film layer and the current collector.

[0072] In some embodiments of this application, the negative electrode film layer including the additive further includes a protective agent. The protective agent includes any one or more of sodium dodecylbenzenesulfonate, sodium lignosulfonate, 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.

[0073] The above-mentioned protective agent has a hydrophobic chain and a hydrophilic anionic group. Its hydrophilic anionic group first combines with the hydrophilic additive, avoiding the prior combination of the additive with the hydrophilic group of the aqueous binder, and effectively solving the problem of the decrease in adhesion caused by the connection between the aqueous binder and the additive. In particular, when styrene-butadiene rubber is used as the aqueous binder, due to its rich hydrophilic surface groups, adding the above-mentioned protective agent effectively prevents the combination of the hydrophilic groups on the surface of styrene-butadiene rubber and the hydrophilic groups of the additive, effectively protecting the structure of styrene-butadiene rubber and still retaining a good adhesion effect on the negative electrode film layer and the negative electrode current collector. In some embodiments, when the area of the negative electrode film layer has an additive and the aqueous adhesive is styrene-butadiene rubber, the aqueous negative electrode slurry in this area further includes the above-mentioned protective agent.

[0074] In some embodiments of the present application, the above-mentioned negative electrode film layer further includes a thickening agent, and the thickening agent 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, polyoxyethylene, and polyvinylpyrrolidone; optionally, the weight ratio of the thickening agent to the negative electrode active material is (0.5-1.5):(93-98). Thereby improving the stability of the slurry for forming the negative electrode film layer, and further enhancing the uniformity of the dispersion of each component in the negative electrode film layer.

[0075] In some embodiments of the present application, the above-mentioned negative electrode active material includes one or more of graphite negative electrode materials and silicon-based negative electrode materials. Optionally, the silicon-based negative electrode materials include one or more of silicon-carbon composite negative electrode materials and silicon-oxygen negative electrode materials; optionally, the graphite negative electrode materials include artificial graphite and / or natural graphite. In application, any of the above-mentioned negative electrode active materials can be selected according to the requirements for battery performance.

[0076] The negative electrode film layer of the present application can have different designs in the direction perpendicular to the negative electrode current collector. In some embodiments, 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 with the additive is the first region. Adding the additive in the first region far from the current collector, thereby making the first region with a position advantage on the surface form a SEI film more fully, giving full play to the protection efficiency of the additive, and further improving the initial efficiency and life of the battery.

[0077] In some embodiments, the water-based binder in the first region includes polyacrylic acid. The polyacrylic acid binder has many carboxyl groups, forms hydrogen bonds on the surface of the negative electrode active material, thereby endowing the negative electrode active material particles with adhesiveness to the negative electrode current collector. Therefore, the cohesion effect between its particles is good, improving the structural stability of the second film layer.

[0078] In some embodiments, 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. The water-based binder in the second region close to the current collector includes styrene-butadiene rubber, so that the negative electrode film layer can have better adhesion on the current collector.

[0079] In some embodiments, 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 an additive. The surface reaction activity uniformity of natural graphite is lower than that of artificial graphite, and the specific surface area of natural graphite is larger, with greater swelling. Therefore, the requirement for SEI film reconstruction during the cycle storage process is higher. Compared with artificial graphite, the additive has a better improvement effect on the cycle and storage performance of natural graphite, and its efficiency is better exerted. Moreover, the use of natural graphite reduces the battery cost.

[0080] 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. The kinetic performance of artificial graphite is more stable.

[0081] The coating amount or thickness relationship of the above-mentioned first region, second region, third region and fourth region can be set with reference to the conventional negative electrode film layer with a multi-layer structure, and the present application does not make special restrictions.

[0082] In some embodiments of the present application, the negative electrode film layer 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.

[0083] 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%.

[0084] In some embodiments of the present application, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0085] [Aqueous Negative Electrode Slurry]

[0086] The second embodiment of the present application provides an aqueous negative electrode slurry, which includes water and a negative electrode active material and an aqueous binder dispersed in the water. Among them, the aqueous negative electrode slurry 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 alkenyl, alkynyl, *-C≡N. Optionally, the acid radical ions of the water-soluble unsaturated organic acid salt include any one or more of sulfonate ions, borate ions, and phosphonate ions.

[0087] In the aqueous negative electrode slurry of the present application, water-soluble unsaturated organic acid salts and aqueous binders are combined, and both are aqueous materials and can be well fused, and the dispersion uniformity in the formed negative electrode pole piece is good, such as water-soluble unsaturated organic acid salts are well dispersed around the negative electrode active material. The negative electrode film layer formed by the aqueous negative electrode slurry breaks the unsaturated groups of the water-soluble unsaturated organic acid salts during charging to produce a self-polymerization reaction, and a stable flexible SEI film is formed 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, and preferentially participate in film formation during charging (charging process, the negative electrode interface attracts electrons, and the double bonds of the additives are opened to form polymers), and the high electronegativity elements will increase the electronegativity of the negative electrode surface, act 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 the interface impedance, and thus reduces the degree of impedance increase caused by film formation.

[0088] In some embodiments of the present application, the weight ratio of the above additive to the negative electrode active material is (0.5-2):(93-98), and can be (0.8-1.5):(93-98). The purpose of controlling the degree of reduction in the energy density of the battery cell caused by the use of the additive as much as possible is achieved, and the additive in the above ratio can fully play a role in improving the cycle stability of the battery cell.

[0089] In some embodiments of the present application, the water-soluble unsaturated organic acid salt includes any one or more of water-soluble unsaturated organic lithium salt, water-soluble unsaturated organic sodium salt, water-soluble unsaturated organic potassium salt, water-soluble unsaturated organic magnesium salt, and water-soluble unsaturated organic calcium salt; optionally, the water-soluble unsaturated organic acid salt includes any one or more of water-soluble unsaturated sulfonate salts. 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 group participates in the film formation, which improves the stability of the film structure and further increases the life of the battery cell.

[0090] In some embodiments of the present application, the water-soluble unsaturated sulfonate salt is optionally selected from any one or more of water-soluble unsaturated lithium sulfonates; further optionally, the water-soluble unsaturated lithium sulfonate salt includes any one or more of C1-C6 olefin lithium sulfonates; more optionally, the water-soluble unsaturated lithium sulfonate salt includes any one or more of vinyl lithium sulfonate and allyl lithium sulfonate. When the unsaturated lithium sulfonate salt is used as an additive, the unsaturated lithium sulfonate salt can also increase the migration rate of lithium ions, further reduce the interfacial impedance, and increase the cycle life of the battery.

[0091] The aqueous binder used in this application can be selected from the aqueous binders commonly used in the electrode. 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, the styrene-butadiene rubber therein undergoes a condensation reaction through the surface hydrophilic group carboxyl and the hydroxyl group on the surface of the negative electrode current collector, thereby further enhancing the adhesion between the negative electrode film layer with it and the current collector.

[0092] In some embodiments of this application, the aqueous 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 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.

[0093] The above protective agent has a hydrophobic chain and a hydrophilic anionic group, and its hydrophilic anionic group combines with the hydrophilic additive first, avoiding the prior combination of the additive with the hydrophilic group of the aqueous binder, and effectively solving the problem of the decrease in adhesion caused by the connection between the aqueous binder and the additive. In particular, when styrene-butadiene rubber is used as the aqueous binder, due to its rich surface hydrophilic groups, adding the above protective agent effectively prevents the combination of the hydrophilic groups on the surface of styrene-butadiene rubber and the hydrophilic groups of the additive, effectively protecting the structure of styrene-butadiene rubber and still retaining a good adhesion effect on the negative electrode film layer and the negative electrode current collector.

[0094] In some embodiments of this application, the above aqueous negative electrode slurry further includes a thickening agent, and the thickening agent includes any one or more of sodium carboxymethylcellulose, lithium carboxymethylcellulose, propylene glycol alginate, methylcellulose, sodium starch phosphate, sodium alginate, casein, sodium polyacrylate, polyoxyethylene, and polyvinylpyrrolidone; optionally, the weight ratio of the thickening agent to the negative electrode active material is (0.5 - 1.5):(93 - 98). Thereby improving the stability of the slurry and further enhancing the uniformity of the dispersion of each component in the negative electrode film layer.

[0095] In some embodiments of this application, the negative electrode active material includes one or more of graphite negative electrode materials, silicon-carbon composite negative electrode materials, and silicon-oxygen negative electrode materials; optionally, the graphite negative electrode material includes artificial graphite and / or natural graphite.

[0096] In some embodiments of this application, the aqueous negative electrode slurry may also optionally include 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.

[0097] 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, since excessive stirring time will cause the styrene-butadiene rubber to demulsify, the aqueous binder can be selected as the last component to be added.

[0098] In some embodiments of the present application, the negative electrode sheet of the first embodiment can be prepared by using the aqueous negative electrode slurry provided in any of the above embodiments. Optionally, the preparation process flow can refer to the following process: The above aqueous negative electrode slurry is coated on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained.

[0099] When it is necessary to form a negative electrode film layer with different multi-layer compositions, the composition of the aqueous negative electrode slurry can be changed and coated on the negative electrode current collector successively. After processes such as drying and cold pressing, the negative electrode sheet can be obtained.

[0100] [Positive electrode sheet]

[0101] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material.

[0102] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0103] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0104] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. By way of example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates having an olivine structure, lithium transition metal oxides, and modified compounds thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of the battery may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide 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 (which may also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which may also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which may also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which may also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which may also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and at least one of modified compounds thereof. Examples of the lithium-containing phosphate having an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (which may also be abbreviated 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 manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0105] In some embodiments, the positive electrode film layer may further optionally include a binder. By way of example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0106] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0107] In some embodiments, the positive electrode sheet can be prepared in the following manner: dispersing the components for preparing the positive electrode sheet described above, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet can be obtained.

[0108] [Electrolyte]

[0109] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The present application does not specifically limit the type of electrolyte, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0110] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0111] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate) borate, lithium difluoro bis(oxalate) phosphate, and lithium tetrafluorooxalate phosphate.

[0112] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0113] In some embodiments, the electrolyte solution may further optionally include additives. As an example, the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and can also include additives that can improve certain battery performance, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature or low-temperature performance of the battery, etc.

[0114] [Separator]

[0115] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0116] In some embodiments, the material of the separator membrane may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0117] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator membrane may be made into an electrode assembly by a winding process or a stacking process.

[0118] In some embodiments, the secondary battery includes secondary battery cells, or includes a battery module and a battery pack.

[0119] In some embodiments, the secondary battery may include an outer package. The outer package may be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0120] In some embodiments, the outer package of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery may also be a soft package, such as a pouch-type soft package. The material of the soft package may be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. may be listed.

[0121] The present application does not particularly limit the shape of the secondary battery cell, and it may be cylindrical, square, or any other arbitrary shape. For example, Figure 1 is a secondary battery cell 5 of a square structure as an example.

[0122] In some embodiments, referring to Figure 2 , the outer package may include a housing 51 and a top cover assembly 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator membrane may form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery cell 5 may be one or more, and those skilled in the art can select according to specific actual needs.

[0123] In some embodiments, secondary battery cells may be assembled into a battery module. The number of secondary battery cells included in the battery module may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0124] Figure 3 is a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple secondary battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Further, the multiple secondary battery cells 5 can be fixed by fasteners.

[0125] Optionally, the battery module 4 can further include a housing having an accommodation space, and the multiple secondary battery cells 5 are accommodated in the accommodation space.

[0126] In some embodiments, the above battery module can also be assembled into a battery pack. The number of battery modules included in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0127] Figure 4 and Figure 5 is a battery pack 1 as an example. Refer to Figure 4 and Figure 5 , in the battery pack 1, it can include a battery box and multiple battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery module 4. The multiple battery modules 4 can be arranged in the battery box in any manner.

[0128] In addition, the present application also provides an electric device. The electric device includes the secondary battery provided by the present application. The secondary battery can be used as the power source of the electric device or as the energy storage unit of the electric device. The electric device can 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, satellites, energy storage systems, etc., but not limited thereto.

[0129] As the electric device, the secondary battery cell, battery module or battery pack can be selected according to its usage requirements.

[0130] Figure 6 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electric device for the secondary battery, a battery pack or a battery module can be adopted.

[0131] [Embodiment]

[0132] The embodiments of the present application will be described below. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those technical or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For the reagents or instruments not indicated by the manufacturer, they are all conventional products that can be obtained through commercial purchases.

[0133] Example 1

[0134] 1) Preparation of negative electrode sheet

[0135] Mix natural graphite powder, conductive carbon super P, sodium carboxymethyl cellulose, styrene-butadiene rubber, and sodium vinyl sulfonate (as an additive) in a mass ratio of 96:0.7:1.2:1.6:0.5, then add water and stir. After uniform dispersion, coat it on the surface of the copper foil substrate, and control the single-sided coating weight at 0.1772 g / 1540.25 mm 2 , after double-sided coating is completed, dry, cold press, slit, and prepare a negative electrode sheet with a layer of negative electrode film;

[0136] 2) Preparation of positive electrode sheet

[0137] 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, coat it on the surface of the aluminum foil substrate, and control the single-sided coating weight at 0.382 g / 1540.25 mm 2 , after single-sided coating is completed, dry, cold press, slit, and prepare a positive electrode sheet;

[0138] 3) Composition of electrolyte: It contains solvent, lithium salt, and additive; Solvent: accounting for 83% of the mass percentage of the electrolyte (including ethyl methyl carbonate (EMC), ethylene carbonate (EC), dimethyl carbonate (DMC), mass ratio 2:1:1); Lithium salt: accounting for 15% of the mass percentage of the electrolyte (lithium hexafluorophosphate); Additive: accounting for 2% of the mass percentage of the electrolyte (vinylene carbonate VC).

[0139] 4) Separator: 12 μm thick PE separator (polyethylene).

[0140] 5) Preparation of battery

[0141] Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator in the middle of the anode and cathode to play a role in isolation, obtaining a bare battery cell. Place the bare battery cell in the outer package, and perform processes such as injecting the prepared electrolyte and encapsulating, injecting liquid, forming, and exhausting to obtain a lithium-ion battery.

[0142] Example 2

[0143] Others are the same as in Example 1, except that the mass ratio of graphite powder to sodium vinyl sulfonate in the negative electrode plate is 95.7:0.8, and the single-sided coating weight of the negative electrode is 0.1782 g / 1540.25 mm 2 。

[0144] Example 3

[0145] Others are the same as in Example 1, except that the mass ratio of graphite powder to sodium vinyl sulfonate in the negative electrode plate is 95.0:1.5, and the single-sided coating weight of the negative electrode is 0.0.1791 g / 1540.25 mm 2 。

[0146] Example 4

[0147] Others are the same as in Example 1, except that the mass ratio of graphite powder to sodium vinyl sulfonate in the negative electrode plate is 94.5:2, and the single-sided coating weight of the negative electrode is 0.1801 g / 1540.25 mm 2 。

[0148] Example 5

[0149] Others are the same as in Example 1, except that in the negative electrode plate, graphite powder, conductive carbon, sodium carboxymethyl cellulose, styrene-butadiene rubber, and sodium vinyl sulfonate are mixed evenly according to the mass ratio of 93.5:0.7:1.2:1.6:3.

[0150] Example 6

[0151] Others are the same as in Example 1, except that the additive in the negative electrode plate is lithium vinyl sulfonate.

[0152] Example 7

[0153] Others are the same as in Example 1, except that the additive in the negative electrode plate is lithium vinyl borate.

[0154] Example 8

[0155] Others are the same as in Example 1, except that the additive in the negative electrode plate is lithium vinyl phosphate.

[0156] Example 9

[0157] Others are the same as in Example 1, except that the additive in the negative electrode plate is sodium propargyl sulfonate.

[0158] Example 10

[0159] Others are the same as in Example 1, except that sodium dodecyl sulfonate is also added as a protective agent in the negative electrode plate, and the mass ratio of sodium dodecyl sulfonate to sodium vinyl sulfonate and graphite powder is 0.8:2:93.7.

[0160] Example 11

[0161] Other conditions are the same as those in Example 1, except that sodium dodecyl sulfonate is further added as a protective agent in the negative electrode sheet, and the mass ratio of sodium dodecyl sulfonate to sodium vinyl sulfonate and graphite powder is 1.2:2:93.3.

[0162] Example 12

[0163] Other conditions are the same as those in Example 1, except that sodium dodecyl sulfonate is further added as a protective agent in the negative electrode sheet, and the mass ratio of sodium dodecyl sulfonate to sodium vinyl sulfonate and graphite powder is 0.4:2:94.1.

[0164] Example 13

[0165] Other conditions are the same as those in Example 1, except that sodium dodecyl sulfonate is further added as a protective agent in the negative electrode sheet, and the mass ratio of sodium dodecyl sulfonate to sodium vinyl sulfonate and graphite powder is 0.6:2:93.9.

[0166] Example 14

[0167] Other conditions are the same as those in Example 1, except that sodium dodecyl sulfonate is further added as a protective agent in the negative electrode sheet, and the mass ratio of sodium dodecyl sulfonate to sodium vinyl sulfonate and graphite powder is 1:2:93.5.

[0168] Example 15

[0169] Other conditions are the same as those in Example 1, except that sodium dodecyl sulfonate is further added as a protective agent in the negative electrode sheet, and the mass ratio of sodium dodecyl sulfonate to sodium vinyl sulfonate and graphite powder is 1.26:2:93.24.

[0170] Example 16

[0171] Other conditions are the same as those in Example 10, except that sodium dodecyl benzene sulfonate is used as the protective agent.

[0172] Example 17

[0173] Other conditions are the same as those in Example 10, except that sodium dodecyl sulfate is used as the protective agent.

[0174] Example 18

[0175] Other conditions are the same as those in Example 1, except that polyacrylic acid is used to replace styrene-butadiene rubber.

[0176] Example 19

[0177] Others are the same as in Example 1, except that the negative electrode film layer of the negative electrode plate has two layers in total. The first film layer (or the second region) and the second film layer (or the first region) are arranged successively away from the negative electrode current collector. 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. 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 unit area weight ratio of the first film layer to the second film layer is 1:1, and the single-sided coating weight of each film layer is controlled at 0.1772 g / 1540.25 mm 2 。

[0178] Example 20

[0179] Others are the same as in Example 1, except that the negative electrode film layer of the negative electrode plate has two layers in total. The first film layer (or the third region) and the second film layer (or the fourth region) are arranged successively away from the negative electrode current collector. 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. 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 unit area weight ratio of the first film layer to the second film layer is 1:1, and the single-sided coating weight of each film layer is controlled at 0.1772 g / 1540.25 mm 2 。

[0180] Example 21

[0181] Others are the same as in Example 1, except that the negative electrode film layer is divided into two layers. The first film layer and the second film layer are arranged successively away from the negative electrode current collector. The binder in the first film layer is changed to polyacrylic acid, and natural graphite, conductive carbon super P, sodium carboxymethyl cellulose, polyacrylic acid, and sodium vinyl sulfonate in the graphite powder are mixed in a mass ratio of 95.5:0.7:1.2:1.6:1. Sodium vinyl sulfonate is not used in the second film layer, and artificial graphite, conductive carbon super P, sodium carboxymethyl cellulose, and styrene-butadiene rubber in the graphite powder are mixed in a mass ratio of 96.5:0.7:1.2:1.6. The unit area weight ratio of the first film layer to the second film layer is 1:1, and the single-sided coating weight is controlled at 0.1772 g / 1540.25 mm 2 。

[0182] Example 22

[0183] Others are the same as in Example 1, except that the additive in the negative electrode plate is sodium acrylate.

[0184] Comparative Example 1

[0185] Other conditions are the same as in Example 1, except that sodium vinyl sulfonate is not added to the negative electrode sheet. The artificial graphite, conductive carbon super P, sodium carboxymethyl cellulose, and styrene-butadiene rubber in the graphite powder are mixed in a mass ratio of 96.5:0.7:1.2:1.6, and other conditions are the same as in Example 1.

[0186] Comparative Example 2

[0187] Other conditions are the same as in Example 1, except that the additive in the negative electrode sheet is sodium (2-carboxyethyl) phenylphosphonate.

[0188] Test for the adhesion of the negative electrode sheet: For the cold-pressed negative electrode sheet, use a blade to cut a specimen with a width of 20 mm and a length of 100 mm; stick the special double-sided tape on a steel plate with a width of 20 mm and a length of 200 mm, the width of the tape is 20 mm and the length is 90 mm, stick the cut negative electrode sheet specimen on the double-sided tape with the test surface facing down, and then roll it three times in the same direction with a roller; insert a paper tape with the same width as the negative electrode sheet and a length of 150 mm under the negative electrode sheet and fix it with crepe tape; fix one end of the steel plate without the negative electrode sheet attached with the lower fixture. Fold the paper tape upwards and fix it with the upper fixture; turn on the tensile machine, and the upward running speed of the tensile machine is 0.05 m / min; record the tensile force value F displayed on the tensile machine when the negative electrode sheet is peeled off from the double-sided tape: Negative adhesion (N / m) = F / width of the cut negative electrode sheet.

[0189] Cyclic test: Place the battery cell in a charge-discharge device at a temperature of 45°C. According to the initial capacity C3 / hour = 1C, first leave it for 2 h to make the battery temperature at 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; leave it for 10 min, and discharge it at a constant current rate of 1C to 2.0V (recorded as the discharge capacity of the first cycle), leave it for 10 min, repeat the above charge-discharge steps, and record the ratio of the discharge capacity of each cycle to the discharge capacity of the first cycle. Test the ratio of the discharge capacity after 800 cycles to the discharge capacity of the first cycle, and record it as 45°C 0.5C / 1C cycle 800 cls.

[0190] Test for the DC resistance DCR value:

[0191] 1) Place the battery cell in a charge-discharge device at a temperature of 25°C. According to the initial capacity C3 / hour = 1C, first leave it for 2 h to keep the battery temperature at 25°C;

[0192] 2) Then charge it at a constant current rate of 0.33C to 3.8V, and then charge it at a constant voltage until the charge rate drops to 0.05C, and leave it for 10 min; record the charging capacity at this time as C4;

[0193] 3) Then discharge at a constant current rate of 0.33C for 1.5 h (adjust the battery to 50% SOC), record the voltage V1 after the discharge ends, and then let it stand for 10 min;

[0194] 4) Then discharge at a rate of 4C for 30 s, and record the voltage V2 after the discharge ends.

[0195] 5) The current I corresponding to 4C above = 4 * C3 (the unit of C3 is Ah, and the unit of current is A), and the unit of the above voltage is V;

[0196] The DCR (Ω) of the battery discharging at 4C for 30 s at 50% SOC = (V1 - V2) / I.

[0197] Storage test: Place the battery in a constant temperature furnace at 60°C. Every 15 days of storage, take it out and measure the discharge capacity retention rate in a charge and discharge device at 25°C, and record the capacity retention rate after 90 days of storage.

[0198] The test results are recorded in Table 1.

[0199] Table 1

[0200] It can be seen from the comparison between the examples and Comparative Example 1 in Table 1 that after using additives such as sodium vinyl sulfonate, the capacity retention rates of the battery after cycling and storage are both higher than those of Comparative Example 1, indicating that the additive can self-polymerize to form a protective layer on the graphite surface, thereby improving the battery life. From the comparison of Examples 1 to 4, it can be seen that the more the additive content, the higher the corresponding battery life.

[0201] However, since sodium vinyl sulfonate will damage the structure of the binder styrene-butadiene rubber, the more its content, the lower the adhesion between the negative electrode film layer and the negative electrode current collector in the negative electrode sheet. For example, in Example 5, the content of sodium vinyl sulfonate is the highest, and the adhesion of its electrode sheet is the lowest. Although the content of sodium vinyl sulfonate is also increased in Examples 10 to 15, by adding a protective agent sodium dodecyl sulfonate to protect the structure of the binder styrene-butadiene rubber, the decrease in the adhesion between the negative electrode film layer and the negative electrode current collector is effectively alleviated. 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; and due to the improvement of the electrode sheet adhesion and the stability of the expansion and contraction of the electrode sheet during the stable charge and discharge process, the capacity retention rates of the battery during cycling and storage are improved.

[0202] In Example 19, by dividing the negative electrode film layer into two layers, and setting the layer with the additive on the side far from the current collector, and adding another binder polyacrylic acid, the adhesion effect between the active layer and the current collector is also improved.

[0203] In addition, except for Examples 6 to 8, the additives used in other examples are all sodium salts. Although the formed film is stable, it does not show an enhancing effect on lithium-ion conduction. Instead, it will increase the battery impedance, increase polarization, and reduce the initial capacity of the battery. In Examples 6 to 8, the introduction of lithium salts not only forms a good SEI film, but also improves the migration rate of lithium ions, further reduces the battery impedance, and extends the battery life.

[0204] In Example 22, sodium acrylate was used as an additive, resulting in a relatively large impedance of the battery compared to that in Example 1 where sodium vinylsulfonate was used as an additive.

[0205] In Comparative Example 2, sodium (2-carboxyethyl)phenylphosphonate was used as an additive. Since it is insoluble in water and prone to agglomeration, the binder in the slurry is also unevenly distributed, reducing the adhesion of the electrode sheet and affecting the charge-discharge performance.

[0206] Although the present application has been described with reference to the preferred embodiments, various modifications can be made to it and components therein can be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A negative electrode plate, comprising 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 comprising a negative electrode active material, an aqueous binder, and at least a part of the negative electrode film layer further comprising an additive, the additive comprising a water-soluble unsaturated organic acid salt, and the unsaturated group in the water-soluble unsaturated organic acid salt comprising an alkenyl group, an alkynyl group, any one or more of 2. The negative electrode sheet according to claim 1, wherein, The acid radical ions of the water-soluble unsaturated organic acid salts include any one or more of sulfonate ions, borate ions, and phosphonate ions.

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 plate according to any one of claims 1 to 4, wherein, The water-soluble unsaturated organic acid salts include 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.

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

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

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

9. The negative electrode plate according to claim 8, wherein, The water-soluble unsaturated lithium sulfonate salts include any one or more of lithium vinyl sulfonate and lithium allyl 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, 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 including sulfonic acid lithium ions.

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 plate according to any one of claims 1 to 16, wherein, In the region of the negative electrode film layer including the additive, there is also a protective agent, and 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 plate 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 graphite negative electrode materials and silicon-based negative electrode materials.

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 with 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 aqueous 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 away 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 paste, comprising water and a negative electrode active material and an aqueous binder dispersed in the water, wherein, The aqueous negative electrode paste 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 an alkenyl group, an alkynyl group, any one or more of the following.

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 lithium alkenyl sulfonates 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 aqueous 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 aqueous negative electrode slurry further includes a protective agent, and 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.

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 includes a secondary battery, wherein, The secondary battery includes the secondary battery according to claim 40.

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