Battery monomer, battery device and power utilization device

Abstract

The invention relates to a battery monomer, a battery device and a power utilization device. A negative electrode material layer of the battery monomer contains a negative electrode active material and binder particles; the negative electrode material layer meets the following conditions: the negative electrode material layer is divided into a first layer region and a second layer region by taking a half position of the thickness of the negative electrode material layer as a boundary, and the second layer region is closer to the negative electrode current collector relative to the first layer region; the relation between the thermal weight loss ratio a1 of the first layer area heated from 35 DEG C to 600 DEG C and the thermal weight loss ratio a2 of the second layer area heated from 35 DEG C to 600 DEG C meets the condition that a1-a2 is larger than or equal to 0 and smaller than or equal to 0.62%. By improving the distribution uniformity of the binder particles in the negative electrode plate, the binding power between the negative electrode material layer and the negative electrode current collector is improved, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a battery cell, a battery device, and an electrical device. Background Technology

[0002] Secondary batteries, represented by lithium-ion batteries, are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. The application of secondary batteries has placed higher demands on their performance.

[0003] In the prior art, the preparation process of negative electrode sheets usually involves hot air drying. During the drying process, binder is prone to float, which affects the processing performance of negative electrode sheets as well as the electrical performance and cycle performance of the battery. Summary of the Invention

[0004] The purpose of this application is to provide a battery cell, a battery device, and an electrical device that improves the adhesion between the negative electrode material layer and the negative electrode current collector by improving the uniformity of the distribution of binder particles in the negative electrode sheet, and improves the cycle performance of the battery.

[0005] Therefore, the first aspect of this application provides a battery cell, which includes a positive electrode, a negative electrode, and a separator;

[0006] The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector; the negative electrode material layer contains a negative electrode active material and binder particles;

[0007] The negative electrode material layer meets the following conditions:

[0008] The negative electrode material layer is divided into a first layer region and a second layer region, with the boundary at half the thickness of the negative electrode material layer. The second layer region is closer to the negative electrode current collector than the first layer region.

[0009] The relationship between the thermal weight loss rate a1 of the first layer region when heated from 35℃ to 600℃ and the thermal weight loss rate a2 of the second layer region when heated from 35℃ to 600℃ satisfies: 0≤a1-a2≤0.62%.

[0010] In the embodiments of this application, the binder particles in the negative electrode material layer are relatively uniformly distributed without obvious floating phenomenon. Specifically, when the negative electrode material layer is divided into a first layer region and a second layer region for the above-mentioned thermogravimetric analysis, the result satisfies 0 ≤ a1 - a2 ≤ 0.62%. By making the binder particles uniformly distributed along the thickness direction of the negative electrode material layer, it is beneficial to improve the adhesion between the negative electrode material layer and the negative electrode current collector, thereby improving the stability of the negative electrode sheet during processing such as rolling and winding, reducing the cell impedance, and thus improving the cycle performance of the cell.

[0011] In some embodiments, the negative electrode material layer contains a crosslinking agent having at least one of the following functional groups: isocyanate, cumulative double bond, aziridine, epoxy group, and dialdehyde.

[0012] The binder and negative electrode material layer usually contain a large number of active groups such as carboxyl, hydroxyl, amino, and amide groups. When a crosslinking agent with the above functional groups is used, the crosslinking agent can produce a certain crosslinking reaction with the binder. The binder particles in the crosslinking structure are not easy to float with the moisture during the drying process, which is beneficial to improving the uniformity of the distribution of binder particles in the negative electrode sheet.

[0013] In some embodiments, the crosslinking agent includes at least one selected from the group consisting of isocyanate crosslinking agents, carbodiimide crosslinking agents, aziridine crosslinking agents, epoxysilane crosslinking agents, and glutaraldehyde crosslinking agents.

[0014] The above-mentioned crosslinking agents are all suitable for negative electrode systems and are suitable for crosslinking reactions with binder particles and other optional components in the negative electrode sheet, such as dispersants, thereby forming crosslinks between multiple materials and better reducing the floating of binder particles.

[0015] In some embodiments, the crosslinking agent accounts for 0.1% to 0.5% of the mass of the negative electrode material layer.

[0016] By ensuring that the mass ratio of the crosslinking agent is within the above range, sufficient crosslinking reaction can be generated, thereby effectively improving the floating of binder particles; and the negative electrode slurry used to form the negative electrode material layer has a suitable viscosity, which facilitates coating.

[0017] In some embodiments, the binder particles comprise modified styrene-butadiene rubber; and / or,

[0018] The modified styrene-butadiene rubber contains styrene, butadiene, and polar monomers as polymer monomers.

[0019] Styrene-butadiene rubber (SBR) contains two highly hydrophobic monomers, styrene and butadiene. Since air is also hydrophobic, SBR has a good affinity for air. This means that SBR that floats to the surface during drying rarely returns to the aqueous solvent, remaining instead on the surface. Modification with polar monomers improves the hydrophilicity of SBR, facilitating the return of the floated SBR to the aqueous phase and thus improving its uniformity within the negative electrode material layer.

[0020] In some embodiments, the polar monomer includes at least one selected from the group consisting of acrylic acid, acrylonitrile, acrylamide, hydroxyethyl acrylate, and hydroxypropyl acrylate.

[0021] The aforementioned polar monomers not only improve the hydrophilicity of SBR, but also enrich the active functional groups of the binder particles, making it easier for the binder particles to undergo cross-linking reactions with the cross-linking agent and less likely to float during the heating and drying process.

[0022] In some embodiments, the polar monomer accounts for 0.1% to 50% of the total mass of the polymeric monomers.

[0023] Modification using the above-mentioned mass percentage of polar monomers results in a reasonable proportion of polar functional groups in the binder particles, giving the binder particles good adhesion performance, hydrophilicity, and moderately improved crosslinking effect with the crosslinking agent.

[0024] In some embodiments, the particle size of the binder particles is 150–700 nm.

[0025] By using a larger particle size of 150–700 nm, the migration resistance of the binder particles is increased, and the capillary effect is also alleviated. Through these multiple effects, the floating of binder particles is suppressed, and the problem of uneven binder distribution is improved.

[0026] In some embodiments, the negative electrode current collector is a carbon-coated current collector, and the carbon layer of the carbon-coated current collector is at least disposed on the surface of the negative electrode current collector near the negative electrode material layer.

[0027] The carbon layer of the carbon-coated current collector contains active hydrogen functional groups, such as carboxyl, hydroxyl, and amino groups, which can undergo cross-linking reactions with the cross-linking agent. Thus, the cross-linking agent also improves the interaction force between the binder particles and the current collector. Before the addition of the cross-linking agent, the interaction between the binder particles and the current collector is mainly intermolecular; however, after using the carbon-coated current collector and adding the cross-linking agent, the interaction force between the binder particles and the current collector also includes chemical bonds, thereby significantly improving the adhesion between the negative electrode material layer and the negative electrode current collector.

[0028] In some embodiments, the areal density of the negative electrode sheet is 140 mg / 1540.25 mm². 2 ~200mg / 1540.25mm 2 .

[0029] The aforementioned higher areal density is beneficial for improving the energy density of the negative electrode. However, existing technologies struggle to achieve high areal densities due to the problem of binder floating; or, even if a high areal density can be achieved, uneven binder distribution can negatively impact battery performance. In the embodiments of this application, the problem of binder floating is improved. In this case, the negative electrode sheet has the aforementioned high areal density (i.e., high energy density) and also exhibits good processability, resulting in excellent battery cycle performance.

[0030] In some embodiments, the negative electrode active material comprises a silicon-carbon composite material; and the porosity of the negative electrode material layer is 25% to 50%.

[0031] Silicon-carbon composite materials typically exhibit irregular morphologies, and the addition of carbon nanotubes in the formulation often results in a low overall solid content in the negative electrode slurry. Consequently, silicon-carbon composite systems are prone to more severe binder floating and excessive electrode porosity. In the embodiments of this application, the crosslinking agent crosslinks with the binder particles and other components that may be present in the system (such as dispersants, carbon layers on the current collector surface, etc.), which helps to reduce the porosity between silicon-carbon composite materials, giving the negative electrode material layer a reasonable porosity. This improves the adhesion of the electrode and, consequently, enhances the fast-charging and cycle performance of the battery cell.

[0032] A second aspect of this application provides a battery device comprising the battery cell described in the first aspect of this application. This battery device possesses all the features and advantages of the aforementioned battery cell, which will not be repeated here.

[0033] A third aspect of this application provides an electrical device comprising the battery cell described in the first aspect or the battery device described in the second aspect. This electrical device possesses all the features and advantages of the battery cell described above, which will not be repeated here.

[0034] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0035] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. In the drawings:

[0036] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0037] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0038] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0039] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0040] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of this application is shown;

[0041] Figure 6 This is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to one embodiment of this application;

[0042] Explanation of reference numerals in the attached figures:

[0043] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Casing; 52 Electrode assembly; 53 End cap. Detailed Implementation

[0044] Exemplary embodiments of this disclosure will now be described in more detail. It should be understood that this disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0045] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; 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, it is expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0046] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0047] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0048] Unless otherwise specified, all steps of this 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 it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0049] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0050] Secondary batteries, represented by lithium-ion batteries, have been widely used. In existing technologies, the preparation process of negative electrode sheets usually involves hot air drying. During the drying process, binders are prone to floating, which affects the processing performance of the negative electrode sheet as well as the electrical performance and cycle performance of the battery.

[0051] This application improves the adhesion between the negative electrode material layer and the negative electrode current collector by improving the uniformity of the distribution of binder particles in the negative electrode material layer, and thus improves the electrical performance and cycle performance of the battery.

[0052] The solutions described in the embodiments of this application are applicable to battery cells, battery devices using battery cells, and electrical devices using at least one of the battery cells and battery devices.

[0053] battery cell

[0054] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0055] The battery cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc. In some embodiments, the battery cell is a lithium-ion battery.

[0056] [Electrode Assembly]

[0057] A single battery cell typically includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator positioned between the positive and negative electrodes. During the charging and discharging process of a single battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0058] Negative electrode sheet

[0059] In some embodiments of this application, a battery cell is provided, which includes a positive electrode, a negative electrode, and a separator;

[0060] The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector; the negative electrode material layer contains a negative electrode active material and binder particles;

[0061] The negative electrode material layer meets the following conditions:

[0062] The negative electrode material layer is divided into a first layer region and a second layer region, with the boundary at half the thickness of the negative electrode material layer. The second layer region is closer to the negative electrode current collector than the first layer region.

[0063] The relationship between the thermal weight loss rate a1 of the first layer region when heated from 35℃ to 600℃ and the thermal weight loss rate a2 of the second layer region when heated from 35℃ to 600℃ satisfies: 0≤a1-a2≤0.62%.

[0064] The floating of the binder is the primary reason for the difference in thermal weight loss rates between the upper and lower layers (i.e., the first and second layers) of the negative electrode material layer. In the embodiments of this application, the binder particles in the negative electrode material layer are relatively uniformly distributed, with no obvious floating phenomenon. Specifically, when the negative electrode material layer is divided into the first and second layers for the aforementioned thermal weight loss rate test, the condition 0 ≤ a1 - a2 ≤ 0.62% is met. By making the binder particles uniformly distributed along the thickness direction of the negative electrode material layer, it is beneficial to improve the adhesion between the negative electrode material layer and the negative electrode current collector, thereby improving the stability of the negative electrode sheet during rolling, winding, and other processing, reducing the cell impedance, and thus improving the cycle performance of the cell.

[0065] Thermogravimetric analysis (TGA) refers to the percentage of mass lost by a sample when heated from a first temperature condition to a second temperature condition, relative to the mass of the sample when it was at the first temperature condition. In some embodiments, TGA can be performed using a thermogravimetric analyzer according to GB / T 33047.1-2016. In some embodiments, specific parameters include: weighing approximately 10 mg of the sample into an alumina crucible and leveling it; parameter settings: argon atmosphere, purge gas 50 mL / min, protective gas 20 mL / min; temperature rise program: 10 °C / min, 35 °C~600 °C.

[0066] In some implementations, the difference between a1 and a2 is approximately 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.62%, etc.

[0067] In some embodiments, the negative electrode material layer contains a crosslinking agent having at least one of the following functional groups: isocyanate, cumulative double bond (referring to two pairs of double bonds on the same carbon atom), aziridine, epoxy group, and dialdehyde (referring to having two aldehyde groups simultaneously).

[0068] The binder and negative electrode material layer usually contain a large number of active groups such as carboxyl, hydroxyl, amino, and amide groups. When a crosslinking agent with the above functional groups is used, the crosslinking agent can produce a certain crosslinking reaction with the binder. The binder particles in the crosslinking structure are not easy to float with the moisture during the drying process, which is beneficial to improving the uniformity of the distribution of binder particles in the negative electrode sheet.

[0069] In some embodiments, the crosslinking agent includes at least one selected from the group consisting of isocyanate crosslinking agents, carbodiimide crosslinking agents, aziridine crosslinking agents, epoxy silane crosslinking agents, and glutaraldehyde crosslinking agents. Examples of isocyanate crosslinking agents include hexamethylene diisocyanate, isophorone diisocyanate, 4,4”-dicyclohexylmethane diisocyanate, diphenylmethane diisocyanate, and 1,5-naphthalene diisocyanate; examples of carbodiimide crosslinking agents include dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and 1-(3-dimethylaminopentyl)-3-ethylcarbodiimide hydrochloride. Salts, such as 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride; aziridinium crosslinking agents include tris(1-aziridinyl)trimethylolpropane triacrylate, tris(1-aziridinyl)ethoxylated trimethylolpropane triacrylate, tris(1-aziridinyl)pentaerythritol acrylate, trimethylolpropane tri[3-(2-methylaziridinyl)propionate], etc.; epoxy silane crosslinking agents include 3-(2,3-epoxypropoxy)propyltrimethoxysilane, etc.

[0070] The above-mentioned crosslinking agents are all suitable for negative electrode systems and are suitable for crosslinking reactions with binder particles and other optional components in the negative electrode sheet, such as dispersants, thereby forming crosslinks between multiple materials and better reducing the floating of binder particles.

[0071] In some embodiments, the crosslinking agent accounts for 0.1% to 0.5% of the mass of the negative electrode material layer; for example, it can be selected from about 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc.

[0072] By ensuring that the mass ratio of the crosslinking agent is within the above range, sufficient crosslinking reaction can be generated, thereby effectively improving the floating of binder particles; and the negative electrode slurry used to form the negative electrode material layer has a suitable viscosity, which facilitates coating.

[0073] In some embodiments, the binder particles comprise modified styrene-butadiene rubber.

[0074] In some embodiments, the polymer monomers of the modified styrene-butadiene rubber include styrene, butadiene, and polar monomers.

[0075] Styrene-butadiene rubber (SBR) contains two highly hydrophobic monomers, styrene and butadiene. Since air is also hydrophobic, SBR has a good affinity for air. This means that SBR that floats to the surface during drying rarely returns to the aqueous solvent, remaining instead on the surface. Modification with polar monomers improves the hydrophilicity of SBR, facilitating the return of the floated SBR to the aqueous phase and thus improving its uniformity within the negative electrode material layer.

[0076] In some embodiments, the polar monomer includes at least one selected from the group consisting of acrylic acid, acrylonitrile, acrylamide, hydroxyethyl acrylate, and hydroxypropyl acrylate.

[0077] The aforementioned polar monomers not only improve the hydrophilicity of SBR, but also enrich the active functional groups of the binder particles, making it easier for the binder particles to undergo cross-linking reactions with the cross-linking agent and less likely to float during the heating and drying process.

[0078] In some embodiments, the polar monomer accounts for 0.1% to 50% of the total mass of the polymeric monomers; for example, it can be selected from about 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.

[0079] Modification using the above-mentioned mass percentage of polar monomers results in a reasonable proportion of polar functional groups in the binder particles, giving the binder particles good adhesion performance, hydrophilicity, and moderately improved crosslinking effect with the crosslinking agent.

[0080] In some embodiments, the particle size of the binder particles is 150 to 700 nm; for example, it can be selected from about 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, etc.

[0081] By using a larger particle size of 150–700 nm, the migration resistance of the binder particles is increased, and the capillary effect is also alleviated. Through these multiple effects, the floating of binder particles is suppressed, and the problem of uneven binder distribution is improved.

[0082] In some embodiments, 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 material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (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.).

[0083] In some embodiments, the negative electrode current collector is a carbon-coated current collector, and the carbon layer of the carbon-coated current collector is at least disposed on the surface of the negative electrode current collector near the negative electrode material layer.

[0084] The carbon layer of the carbon-coated current collector contains active hydrogen functional groups, such as carboxyl, hydroxyl, and amino groups, which can undergo cross-linking reactions with the cross-linking agent. Thus, the cross-linking agent also improves the interaction force between the binder particles and the current collector. Before the addition of the cross-linking agent, the interaction between the binder particles and the current collector is mainly intermolecular; however, after using the carbon-coated current collector and adding the cross-linking agent, the interaction force between the binder particles and the current collector also includes chemical bonds, thereby significantly improving the adhesion between the negative electrode material layer and the negative electrode current collector.

[0085] In some embodiments, the areal density of the negative electrode sheet is 140 mg / 1540.25 mm². 2 ~200mg / 1540.25mm 2 .

[0086] The aforementioned higher areal density is beneficial for improving the energy density of the negative electrode. However, existing technologies struggle to achieve high areal densities due to the problem of binder floating; or, even if a high areal density can be achieved, uneven binder distribution can negatively impact battery performance. In the embodiments of this application, the problem of binder floating is improved. In this case, the negative electrode sheet has the aforementioned high areal density (i.e., high energy density) and also exhibits good processability, resulting in excellent battery cycle performance.

[0087] The areal density of the negative electrode sheet can be adjusted in the following ways: First, the solid content of the slurry is adjusted; with the roller gap of the coating machine fixed, the higher the solid content, the greater the areal density. Second, the roller gap of the coating machine is adjusted; the larger the roller gap, the higher the areal density. Thus, in some embodiments, a negative electrode sheet with the target areal density can be obtained mainly by adjusting the solid content of the slurry.

[0088] The areal density of the electrode can be tested using methods known in the art. For example, the following method can be used: cut a section of the coated and dried electrode and punch six 1540.25 mm² areas on a punching machine. 2 Weigh six small circular pieces using an electronic balance and calculate their surface density.

[0089] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in secondary batteries. For example, the negative electrode active material includes one or more combinations selected from the group consisting of: natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 Li-Al alloy.

[0090] In some embodiments, the negative electrode active material comprises a silicon-carbon composite material; and the porosity of the negative electrode material layer is 25% to 50%.

[0091] Silicon-carbon composite materials typically exhibit irregular morphologies, and the addition of CNTs in the formulation leads to a low overall solid content in the negative electrode slurry. This can exacerbate binder flotation and result in excessive electrode porosity. In the embodiments of this application, the crosslinking agent crosslinks with the binder particles and other components that may be present in the system (e.g., dispersants, carbon layers on the current collector surface, etc.), which helps reduce binder flotation. Large-diameter binder particles help reduce the porosity between silicon-carbon composite materials, thereby ensuring effective bonding between active materials, improving electrode adhesion, and ultimately enhancing the fast-charging and cycle performance of the battery cell.

[0092] Silicon-carbon composite materials are materials composed of carbon and silicon materials. They are commercially available and can also be prepared by methods such as chemical vapor deposition, physical vapor deposition, chemical vapor infiltration, and sol-gel methods. In some embodiments, the silicon-carbon composite materials used as negative electrode active materials have a particle size range of 5 μm to 15 μm with a Dv50.

[0093] The porosity of the negative electrode material layer can be detected by methods known in the art, for example, the following methods can be used:

[0094] Pretreatment: Using tweezers, select more than 20 round pieces with good appearance and no powder shedding from the edges and place them into the sample cup. Record the number of pieces and calculate the apparent volume;

[0095] Test: Place the sample cup containing the sample into the true density tester, seal the test system, and introduce helium gas according to the procedure. By detecting the pressure of the gas in the sample chamber and the expansion chamber, and then calculating the true volume according to Bohr's law (PV=nRT), the porosity of the sample to be tested can be obtained.

[0096] Sample cup volume: 3.5cm 3 Analyzed gas: Helium.

[0097] Porosity refers to the proportion of pore volume to the total volume in a material;

[0098] Porosity P = (V2 - V1) / V2 * 100%, apparent volume V2 = S * H ​​* A, where;

[0099] S - Area, cm² 2 ;

[0100] H - Thickness, cm;

[0101] A - Number of samples, EA;

[0102] V1 - Sample true volume, cm 3 The test results showed that...

[0103] V2 - Apparent volume of the sample, cm3.

[0104] In some embodiments, the negative electrode material may optionally include a conductive agent. For example, the conductive agent may include one or more combinations selected from the group consisting of: Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0105] In some embodiments, the negative electrode material may also optionally include other additives. For example, other additives may be thickeners (such as sodium carboxymethyl cellulose (CMC-Na)).

[0106] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned negative electrode active material, binder particles, crosslinking agent and any other components (such as conductive agent, thickener) in a solvent (e.g., deionized water) to prepare a negative electrode slurry for forming a negative electrode material layer; coating the negative electrode slurry onto the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0107] [Positive electrode plate]

[0108] In some embodiments, the positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector, the positive electrode material layer comprising a positive electrode active material.

[0109] In some embodiments, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0110] In some embodiments, the positive current collector may be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals may be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0111] In some embodiments, the positive electrode active material may include at least one of the following materials: lithium phosphate, lithium transition metal oxide, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium phosphate include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium transition metal oxides 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, and lithium nickel cobalt manganese oxide (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Modified compounds refer to substances obtained by modification methods such as doping or coating based on the above-mentioned substances.

[0112] In some embodiments, the positive electrode material layer may optionally include a binder. For example, the binder may include one or more combinations selected from the group consisting of: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0113] In some embodiments, the positive electrode material layer may optionally include a conductive agent. For example, the conductive agent may include one or more combinations selected from the group consisting of: Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0114] In some embodiments, the positive electrode sheet can be prepared by dispersing the components of the above-mentioned positive electrode material layer, such as the positive electrode active material, optional conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0115] [Isolation Component]

[0116] In some embodiments, the electrode assembly further includes a spacer disposed between the positive electrode and the negative electrode.

[0117] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0118] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. 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. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator.

[0119] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0120] [Electrolytes]

[0121] In some embodiments, the battery cell further includes an electrolyte; the electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. The electrolyte can be liquid, gel-like, or solid.

[0122] Liquid electrolytes include electrolyte salts and solvents.

[0123] 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 difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0124] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl 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. The solvent may also be an ether solvent. Ether solvents may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0125] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0126] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0127] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0128] As an example, the polymers of polymeric solid electrolytes may include polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids, cellulose, etc.

[0129] As an example, inorganic solid electrolytes can be one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ion conductor, garnet, amorphous LiPON thin film), sulfide solid electrolytes (crystalline lithium superconducting ion conductor (lithium-germanium-phosphorus-sulfur, sulfosilium-germanium), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0130] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0131] [Structure of the electrode assembly]

[0132] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0133] In some implementations, the electrode assembly is a wound structure. The positive and negative electrode sheets are wound into a wound structure.

[0134] In some implementations, the electrode assembly is a stacked structure.

[0135] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0136] As an example, multiple positive electrode sheets can be set, and negative electrode sheets are folded to form multiple stacked folded segments, with a positive electrode sheet sandwiched between adjacent folded segments.

[0137] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0138] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0139] As an example, the separator can be continuously arranged between any adjacent positive or negative electrode plates by folding or rolling.

[0140] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0141] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0142] [shell]

[0143] In some embodiments, the battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0144] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not impose any particular limitations. For example, Figure 1 This is an example of a square-shell battery cell 5.

[0145] In some implementations, refer to Figure 2 The outer casing includes an end cap 53 and a housing 51. The housing 51 has an opening, and the end cap 53 covers the opening. The housing 51 may have one or more openings. The end cap 53 may also have one or more. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within a receiving cavity formed by the housing 51 and the end cap 53. The electrolyte is immersed in the electrode assembly 52.

[0146] [Electrode terminals]

[0147] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab, or it can be indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0148] [Pressure relief mechanism]

[0149] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the battery cell.

[0150] As an example, the internal pressure or temperature of a battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is broken, thereby forming an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell.

[0151] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0152] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0153] The term "actuation" as used in this application refers to the activation or actuation of the pressure relief mechanism to a certain state, thereby releasing the internal pressure and temperature of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is activated, the high-temperature, high-pressure substances inside the battery cell are discharged as waste from the activated portion. This method allows for pressure and temperature relief of the battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0154] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for venting gas inside the battery cell.

[0155] The emissions from battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of separators, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0156] Battery device

[0157] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0158] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0159] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties. Figure 3 This is battery module 4 as an example. (See reference...) Figure 3 In the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other way.

[0160] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0161] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing. Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3, with the upper housing 2 covering the lower housing 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery pack.

[0162] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0163] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0164] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0165] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0166] Electrical appliances

[0167] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft. Figure 6 This is an example of an electrical device. The electrical device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.

[0168] Example 1

[0169] This embodiment provides a lithium-ion secondary battery, the preparation method of which is as follows:

[0170] (1) Positive electrode plate

[0171] LiNi will be used as the positive electrode active material 0.6 Mn 0.2 Co 0.2 O2 (NCM622), carbon black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are dissolved in N-methylpyrrolidone (NMP) in a weight ratio of 96:2:2. After thorough mixing, a positive electrode slurry for forming the positive electrode material layer is prepared. The positive electrode slurry is coated onto an aluminum foil that serves as the positive electrode current collector. After drying, cold pressing, and slitting, the positive electrode sheet is obtained.

[0172] (2) Negative electrode plate

[0173] Preparation of modified SBR:

[0174] Deionized water, emulsifier, styrene, and acrylic acid were mixed evenly and pre-emulsified by mechanical stirring to obtain a pre-emulsion. The pre-emulsion was homogenized using an ultrasonic cell disruptor under an ice-water bath. The homogenized fine emulsion was uniform and opaque, yielding a styrene fine emulsion. The obtained styrene fine emulsion was added to a 2L stainless steel jacketed high-pressure reactor, and potassium persulfate initiator solution was added. After purging with N2 for 15 minutes, concentrated butadiene monomer was added over 30 minutes at a stirring speed of 210 rpm to allow the butadiene to swell in the styrene droplets. The mixture was heated to 70℃ and reacted for 10 hours. Then, the mixture was slowly cooled, discharged, and filtered to obtain modified SBR hydroxystyrene-butadiene latex. The prepared modified SBR was used as a binder for the negative electrode sheet, with an average particle size of 150 nm.

[0175] Preparation of negative electrode sheet:

[0176] Graphite (Dv50 particle size: 15μm) as the negative electrode active material, carbon black as the conductive agent, the modified SBR (average particle size 150nm) as the binder, sodium carboxymethyl cellulose (CMC-Na) as the dispersant, and aziridine crosslinking agent as the crosslinking agent were dissolved in an appropriate amount of deionized water at a weight ratio of 96.25:1:1.7:1:0.1. The mixture was thoroughly stirred and mixed to obtain a negative electrode slurry for forming the negative electrode material layer. The negative electrode slurry was coated onto carbon-coated copper foil as the negative electrode current collector, and then dried, cold-pressed, and slit to obtain the negative electrode sheet with an areal density of 170mg / 1540.25mm². 2 The porosity of the negative electrode material layer is 30.4%.

[0177] (3) Separating membrane

[0178] Polyethylene (PE) porous polymer film is used as the separator.

[0179] (4) Electrolyte

[0180] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), 1 mol / L LiPF6 was dissolved in an organic solvent (ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) = 1 / 1 / 1) and stirred until homogeneous to obtain the corresponding electrolyte.

[0181] (5) Preparation of lithium-ion batteries

[0182] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound up and injected with electrolyte. Subsequently, it is hot-pressed at 100°C and 250MPa for 2 minutes to obtain a lithium-ion battery.

[0183] The relevant tests were conducted as follows:

[0184] 1. Test for the floating of binder in the negative electrode sheet

[0185] By testing the thermal weight loss rate of the upper and lower layers of the negative electrode material layer, the difference in binder content between the upper and lower layers of the negative electrode material layer can be quantitatively characterized, thereby reflecting the floating of binder particles.

[0186] 1.1 Sample Preparation: Take the negative electrode sheet and measure its thickness with a micrometer. Subtract the thickness of the substrate to obtain the thickness of the negative electrode material layer. Define the upper and lower layers of the negative electrode material layer at half the thickness, with the thickness of both layers being H. Scrape off 3 / 5H of the powder from the top of the upper layer with a knife to obtain sample 1 for testing the thermal weight loss rate of the upper powder. Scrape off 3 / 5H of the powder from the bottom of the lower layer with a knife to obtain sample 2 for testing the thermal weight loss rate of the lower powder.

[0187] 1.2 Sample preparation: Accurately weigh approximately 10 mg of sample 1 and sample 2 respectively, place them in an alumina crucible, and level them.

[0188] 1.3 Testing: A Netzsch STA449F3 thermogravimetric analyzer (Germany) was used. Parameters were set as follows: argon atmosphere, purge gas 50 mL / min, protective gas 20 mL / min; temperature rise program: 10℃ / min, 35℃~600℃. The test results were read, specifically the upper layer thermogravimetric ratio a1 and the lower layer thermogravimetric ratio a2 of the negative electrode material layer, and the value of a1-a2 was calculated.

[0189] 2. Adhesion test of negative electrode sheet

[0190] The adhesion strength of the electrode sheet was tested using a tensile testing machine. Specifically, the following steps were performed: A sample of the prepared negative electrode sheet was measured perpendicular to the machine direction (TD). A sample measuring 20mm (width) × 100mm (length) was cut. Double-sided adhesive tape, measuring 20mm (width) × 90mm (length), was applied to a steel plate. After attaching the cut electrode sample to the double-sided adhesive, it was rolled three times in the same direction using a 2kg hand roller. Then, one end of the test sample was bent 180 degrees, and the negative electrode film layer and current collector were manually peeled 25mm apart along the length direction. The test sample was then fixed in the clamps of the tensile testing machine. The tensile testing machine was held parallel to the length direction of the electrode sheet, and the machine was continuously peeled at a speed of 50mm / min to obtain the peel force curve. The peel force F0 corresponding to the stable segment of the peel force curve was taken. Therefore, the adhesion strength between the negative electrode film and the current collector in the test sample is F = F0 / width of the test sample (the unit of F is N / m).

[0191] 3. Measurement of battery DC resistance (DCR)

[0192] The battery capacity was tested at 25℃. After formation, the battery was left to stand at 25℃ for 10 minutes, then charged at 0.33C to the cutoff voltage of 4.35V. It was then charged at constant voltage until the current was ≤0.05C (defined as 100% SOC), left to stand for 10 minutes, and then discharged at 0.33C to the cutoff voltage of 2.8V. The resulting capacity is the 0.33C capacity of the battery. Next, it was charged at constant voltage at 0.05C, left to stand for 60 minutes, and then discharged at 0.33C to 50% SOC. After another 60 minutes of standing, the open-circuit voltage V1 at 50% SOC was measured. Finally, it was discharged at 1.5C for 30 seconds, and the open-circuit voltage V2 after discharge was measured. The DCR data for the 30 seconds were compiled, and the calculation formula is (V2-V1) / 1.5C.

[0193] 4. Battery cycle performance test:

[0194] The first charge and discharge cycle was performed at a constant temperature of 25°C. Constant current and constant voltage charging was carried out at a charging current of 1.0C (charging to a current of 0.05C) until the upper limit voltage reached 4.25V. After resting for 5 minutes, constant current discharge was carried out at a discharge current of 1.0C until the final voltage reached 2.8V. The discharge capacity of the first cycle was recorded. Then, continuous charge and discharge cycles were carried out according to the above method.

[0195] The capacity retention rate of the nth cycle = (discharge capacity of the nth cycle / discharge capacity of the first cycle) × 100%. The test is stopped when the cycle capacity retention rate reaches 80%, and the number of cycles at this time is obtained.

[0196] Example 2

[0197] Except that the crosslinking agent used was dicyclohexylcarbodiimide, the preparation and testing were carried out according to the same steps as in Example 1.

[0198] Example 3

[0199] Except that the crosslinking agent used was 4,4”-dicyclohexylmethane diisocyanate, the preparation and testing were carried out according to the same steps as in Example 1.

[0200] Examples 4-6

[0201] Except for the following weight ratios of negative electrode active material, conductive agent, binder, dispersant, and crosslinking agent in the negative electrode slurry, the preparation and testing were carried out according to the same steps as in Example 1.

[0202] In Example 4, the weight ratio of the above components was 96.1:1:1.7:1:0.2.

[0203] In Example 5, the weight ratio of the above components was 96.0:1:1.7:1:0.3.

[0204] In Example 6, the weight ratio of the above components was 96.8:1:1.7:1:0.5.

[0205] Example 7

[0206] Except that unmodified SBR was used as the binder, the preparation and testing were carried out in the same manner as in Example 1.

[0207] Example 8

[0208] Except for using uncoated copper foil as the negative electrode current collector, the preparation and testing were carried out according to the same steps as in Example 1.

[0209] Example 9

[0210] Except that SBR with a particle size of 700 nm was used as a binder, the preparation and testing were carried out in the same manner as in Example 1.

[0211] Example 10

[0212] Except for the following differences, the preparation and testing were carried out according to the same steps as in Example 1:

[0213] Preparation method of negative electrode sheet: Graphite (Dv50 particle size: 15μm) and silicon-carbon composite material (Dv50 particle size: 10μm) as negative electrode active materials, carbon black and single-walled carbon nanotubes as conductive agents, the above-mentioned modified SBR (average particle size 150nm) as a binder, sodium carboxymethyl cellulose (CMC-Na) as a dispersant, and aziridine crosslinking agent as a crosslinking agent are dissolved in an appropriate amount of deionized water at a weight ratio of 66.92:28.68:1:0.3:3:1:0.1. The mixture is thoroughly stirred and mixed to obtain a negative electrode slurry for forming the negative electrode material layer. The negative electrode slurry is coated onto carbon-coated copper foil as the negative electrode current collector, and then dried, cold-pressed, and slit to obtain the negative electrode sheet. The areal density of the prepared negative electrode sheet is 80mg / 1540.25mm². 2 The porosity of the negative electrode material layer is 35%.

[0214] The aforementioned silicon-carbon composite material can be prepared according to the following steps:

[0215] Step 1: Take coconut shell as a carbon material precursor and place it in a box furnace. Heat it to 600°C, introduce nitrogen gas, keep it at this temperature for 2 hours, and then cool it down before taking out the carbon substrate.

[0216] Step 2: Mix potassium hydroxide and carbon substrate at a mass ratio of 4:1, place in a box furnace, introduce nitrogen gas, heat to 800℃, keep at the temperature for 4 hours, and perform hole-forming treatment.

[0217] Step 3: Mix the carbon substrate after pore-forming treatment with 0.1 mol / L hydrochloric acid solution to remove residual potassium hydroxide from the carbon matrix, and then heat and dry at 80°C for 12 hours.

[0218] Step 4: Place the carbon substrate after pore-forming treatment in a vapor deposition rotary furnace, mix acetylene and nitrogen at a volume ratio of 2:10, heat to 950℃, and perform vapor deposition for 2 hours to control the pore size and prepare a carbon matrix with a porous structure.

[0219] Step 5: Place the carbon substrate in a vapor deposition furnace, heat it to 500°C, and introduce a mixed gas of silane and nitrogen, wherein the volume percentage of silane is 20% and the volume percentage of nitrogen is 80%, the total gas flow rate is 5L / min, and the pressure inside the furnace is controlled to be slightly higher than atmospheric pressure by 200Pa, and perform vapor deposition for 6 hours.

[0220] Step 6: Stop the introduction of silane, continue to heat to 600℃, and introduce a mixture of acetylene and nitrogen gas, wherein the volume percentage of acetylene is 20% and the volume percentage of nitrogen is 80%. Perform phase deposition for 1 hour, cool and sieve to obtain silicon-carbon composite material.

[0221] Comparative Example 1

[0222] Except that no crosslinking agent was used in the preparation of the negative electrode sheet, the preparation and testing were carried out according to the same steps as in Example 1.

[0223] Comparative Example 2

[0224] Except that no crosslinking agent was used in the preparation of the negative electrode sheet, the preparation and testing were carried out according to the same steps as in Example 7.

[0225] Comparative Example 3

[0226] Except that no crosslinking agent was used in the preparation of the negative electrode sheet, the preparation and testing were carried out according to the same steps as in Example 10.

[0227] The test results of the above embodiments and comparative examples are summarized in Table 1.

[0228] Table 1

[0229]

[0230] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A battery cell, characterized by, The positive electrode tab, the negative electrode tab, and the separator; The negative electrode tab comprises a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector; the negative electrode material layer contains a negative electrode active material and binder particles; The negative electrode material layer satisfies the following condition: The negative electrode material layer is divided into a first layer region and a second layer region by a boundary along one-half of the thickness of the negative electrode material layer, and the second layer region is closer to the negative electrode current collector than the first layer region; The relationship between the thermal weight loss rate a1 of the first layer region from 35℃ to 600℃ and the thermal weight loss rate a2 of the second layer region from 35℃ to 600℃ satisfies: 0≤a1-a2≤0.62%.

2. The battery cell of claim 1, wherein, The negative electrode material layer contains a crosslinking agent, and the crosslinking agent has at least one of the following functional groups: isocyanate, cumulative double bond, aziridine, epoxy, dialdehyde.

3. The battery cell of claim 2, wherein, The crosslinking agent comprises at least one selected from the group consisting of isocyanate crosslinking agent, carbodiimide crosslinking agent, aziridine crosslinking agent, epoxy silane crosslinking agent, glutaraldehyde crosslinking agent.

4. The battery cell according to claim 2 or 3, wherein The mass percentage of the crosslinking agent in the negative electrode material layer is 0.1%-0.5%.

5. The battery cell according to any one of claims 1 to 4, wherein The binder particles comprise modified butadiene styrene rubber; and / or, The polymerized monomers of the modified butadiene styrene rubber comprise styrene, butadiene, and polar monomers.

6. The battery cell of claim 5, wherein, The polar monomers comprise at least one selected from the group consisting of acrylic acid, acrylonitrile, acrylamide, hydroxyethyl acrylate, and hydroxypropyl acrylate.

7. The battery cell according to claim 5 or 6, wherein The mass percentage of the polar monomers in the total amount of the polymerized monomers is 0.1%-50%.

8. The battery cell according to any one of claims 1 to 7, wherein The particle size of the binder particles is 150-700nm.

9. The battery cell according to any one of claims 1 to 8, wherein The negative electrode current collector is a carbon-coated current collector, and the carbon layer of the carbon-coated current collector is arranged on at least the surface of the negative electrode current collector close to the negative electrode material layer.

10. The battery cell according to any one of claims 1 to 9, wherein The areal density of the negative electrode sheet is 140 mg / 1540.25 mm 2 ~ 200 mg / 1540.25 mm 2 .

11. The battery cell according to any one of claims 1 to 10, wherein The negative electrode active material comprises a silicon-carbon composite material; and the porosity of the negative electrode material layer is 25%-50%.

12. A battery device characterized by comprising: The battery device comprises the battery monomer of any one of claims 1-11.

13. An electrical device, comprising: The battery device comprises the battery monomer of any one of claims 1-11, or the battery device of claim 12.

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