Battery cell, battery device and electric device

Abstract

The invention relates to the technical field of batteries, in particular to a single battery, a battery device and a power utilization device. The negative pole piece comprises a negative current collector and a negative film layer arranged on at least one surface of the negative current collector; the negative electrode film layer comprises a binder; the negative electrode film layers sequentially comprise a first negative electrode film layer to an nth negative electrode film layer from a direction far away from the negative electrode current collector to a direction close to the negative electrode current collector, and n is a positive integer greater than or equal to 2; and the mass ratio of the binder in the (n-1) th negative electrode film layer is smaller than that in the nth negative electrode film layer. The negative pole piece disclosed by the invention is low in full-charge rebound rate, and is suitable for a single battery with high energy density and high group margin.

Description

Technical Field

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

[0002] Battery cells are widely used in many fields. In the existing technology, the negative electrode of the battery cell has a high full-charge rebound rate, which is not suitable for battery cells with high packing margin, thus affecting the energy density of the battery cell.

[0003] Therefore, it is crucial to develop a battery cell that can overcome the above-mentioned defects. Summary of the Invention

[0004] In view of the above problems, this application provides a battery cell, a battery device, and an electrical device. The negative electrode sheet described in this application has a low full-charge rebound rate and is suitable for battery cells with high energy density and high group margin.

[0005] In a first aspect, this application provides a battery cell, the battery cell including a negative electrode sheet;

[0006] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector;

[0007] The negative electrode film layer includes a binder;

[0008] From the direction away from the negative electrode current collector to the direction closer to the negative electrode current collector, the negative electrode film layer sequentially includes a first negative electrode film layer to an nth negative electrode film layer, where n is a positive integer greater than or equal to 2;

[0009] The mass percentage of the binder in the (n-1)th negative electrode film layer is less than the mass percentage of the nth negative electrode film layer.

[0010] During the compaction process of the negative electrode sheet, under the same force, the pressure borne by the nth negative electrode film layer (lower layer) is greater than that borne by the (n-1)th negative electrode film layer (upper layer), which will cause the compaction rebound of the lower negative electrode film layer to be more severe than that of the upper negative electrode film layer.

[0011] In the technical solution of this application, the mass ratio of the binder in each film layer gradually increases from the direction away from the negative electrode current collector to the direction closer to the negative electrode current collector. The nth negative electrode film layer (lower layer) has a greater bonding force than the (n-1)th negative electrode film layer (upper layer). Compared with the upper film layer with high bonding force, the lower film layer with high bonding force adopted in this application has a more significant effect on reducing the rebound of the electrode sheet. It can better reduce the compaction rebound of the electrode sheet, which is conducive to reducing the full charge rebound rate of the battery and provides the possibility of providing batteries with high mass margin and high energy density.

[0012] In some embodiments, the adhesive includes one or more of a first adhesive and a second adhesive, and may be selected as a first adhesive or a combination of a first adhesive and a second adhesive;

[0013] The first adhesive includes a polyacrylic acid compound, which may be a carbon nanotube-modified polyacrylic acid compound;

[0014] The second adhesive includes any one or a combination of at least two of styrene-butadiene rubber, styrene-acrylic rubber, or pure acrylic rubber.

[0015] In the technical solutions of the embodiments of this application, one or more of the first adhesive or the second adhesive can be selected as needed.

[0016] As an example, the binder is selected from the first binder, which is a polyacrylic acid compound containing a large number of carboxyl groups in its structure. It can interact with other components such as negative electrode active materials or conductive agents, and has strong adhesion. It can effectively reduce the full charge rebound rate of the negative electrode sheet, providing the possibility of providing batteries with high group margin and high energy density, and is especially suitable for negative electrode sheets that are prone to full charge rebound.

[0017] As an example, the binder is selected from a combination of a first binder and a second binder. The second binder has a lower cost and can partially replace the more expensive first binder. The two work together to reduce the full-charge rebound rate of the negative electrode to a certain extent, providing the possibility of providing batteries with high mass margin and high energy density. For example, it can be applied to high silicon material systems.

[0018] As an example, the polyacrylic acid compound is selected from carbon nanotube-modified polyacrylic acid compounds. Compared with unmodified polyacrylic acid compounds, carbon nanotube-modified polyacrylic acid compounds have a relatively large specific surface area, which can provide more contact points for the negative electrode active material. Therefore, it can be further combined with polyacrylic acid compounds to improve the binding ability of the negative electrode active material, suppress the rebound of the negative electrode active material, and thus reduce the full charge rebound rate of the battery, providing the possibility of providing batteries with high mass margin and high energy density. Moreover, the carbon nanotubes in the carbon nanotube-modified polyacrylic acid compounds can also improve the conductivity of the negative electrode film, reduce the film impedance, improve the dynamic performance of the battery cell, and improve its fast charging performance.

[0019] In some embodiments, the polyacrylic compound includes any one or a combination of at least two of polyacrylic acid, polymethacrylic acid, polyacrylate, or acrylic copolymers.

[0020] In the technical solution of the embodiments of this application, the polyacrylic acid compound is within the above range, the raw materials are readily available, the adhesive force is strong, and it is more conducive to reducing the full charge rebound rate of the negative electrode sheet and maintaining the structural stability of the negative electrode sheet.

[0021] In some embodiments, the total mass of the binder is greater than 0% and less than or equal to 8%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, etc., with the total mass of the negative electrode film layer being 100%, and optionally less than or equal to 5%.

[0022] In the technical solution of this application embodiment, the total mass content of the binder is within the above-mentioned range. First, it can satisfy the requirement of reducing the full charge rebound rate of the battery, providing the possibility of providing batteries with high mass margin and high energy density. Second, it has little impact on the mass content of main materials such as negative electrode active materials, reducing the problem of battery performance degradation caused by the reduction of main material content.

[0023] In some embodiments, the adhesive includes a first adhesive, extending from away from the negative electrode current collector to near the negative electrode current collector, and the negative electrode film layer sequentially includes a first negative electrode film layer and a second negative electrode film layer;

[0024] Based on the mass of the first negative electrode film layer, the mass content of the first binder is greater than 0% and less than or equal to 3%.

[0025] Based on the mass of the second negative electrode film, the mass content of the first binder is greater than 0% and less than or equal to 5%.

[0026] The first binder generally has a higher mass content in the upper negative electrode film than in the lower negative electrode film. This arrangement helps to improve the dynamic performance of the battery cell and enhance its fast charging performance. However, the lower film has a weaker adhesive force and is subjected to greater forces during cold pressing, resulting in a greater compaction and rebound of the electrode sheet.

[0027] In the technical solution of the embodiments of this application, the mass content of the first binder in the upper and lower negative electrode film layers is respectively within the range. The mass content of the first binder in the lower negative electrode film layer is greater than the mass content in the negative electrode film layer, which can effectively reduce the full charge rebound rate of the negative electrode sheet and provide the possibility of providing a battery with high mass margin and high energy density.

[0028] In some embodiments, the adhesive comprises a combination of a first adhesive and a second adhesive;

[0029] From the direction away from the negative electrode current collector to the direction closer to the negative electrode current collector, the negative electrode film layer sequentially includes a first negative electrode film layer to an nth negative electrode film layer, where n is a positive integer greater than or equal to 2;

[0030] The mass percentage of the first binder in the (n-1)th negative electrode film layer is less than the mass percentage of the nth negative electrode film layer.

[0031] In the technical solution of this application, the first binder has a high mass content in the lower negative electrode film layer, which is beneficial to reduce the full charge rebound rate of the negative electrode sheet and provides the possibility of providing a battery with high mass margin and high energy density.

[0032] In some embodiments, with the total mass of the negative electrode film layer being 100%, the total mass of the first binder is greater than 0% and less than or equal to 3.5%.

[0033] The total mass of the second adhesive is greater than 0% and less than or equal to 4.5%.

[0034] In the technical solution of this application embodiment, the total mass of the first binder and the second binder in the negative electrode film layer are respectively within the above-mentioned range, which is more conducive to reducing the full charge rebound rate of the negative electrode sheet and providing the possibility of providing a battery with high mass margin and high energy density; moreover, the overall formed negative electrode film layer has strong adhesion, reducing the possibility of film layer detachment during cycling and improving the cycle performance and safety performance of the battery.

[0035] In some embodiments, the negative electrode film layer sequentially includes a first negative electrode film layer and a second negative electrode film layer in the direction from away from the negative electrode current collector to near the negative electrode current collector;

[0036] Based on the mass of the first negative electrode film layer, the mass content of the first binder is greater than 0% and less than or equal to 1%; the mass content of the second binder is greater than 0% and less than or equal to 3%.

[0037] Based on the mass of the second negative electrode film, the mass content of the first binder is greater than 0% and less than or equal to 2%; the mass content of the second binder is greater than 0% and less than or equal to 3%.

[0038] In the technical solution of the embodiments of this application, the mass content of the first binder and the second binder in the first negative electrode film layer and the second negative electrode film layer are as described above. First, the mass content of the binder in the lower negative electrode film layer is greater than the mass content in the upper negative electrode film layer. The first binder and the second binder work together to effectively reduce the full charge rebound rate of the negative electrode sheet, providing the possibility of providing a battery with high mass margin and high energy density.

[0039] In some embodiments, the negative electrode film layer further includes a conductive agent, wherein the mass percentage of the conductive agent in the (n-1)th negative electrode film layer is greater than the mass percentage in the nth negative electrode film layer.

[0040] In the technical solution of the embodiments of this application, the mass ratio of the conductive agent in each negative electrode film layer gradually decreases, and the content of the conductive agent in the upper layer is higher, which is more conducive to improving electron transmission efficiency and can meet the requirements of fast charging performance.

[0041] In some embodiments, the total mass of the conductive agent is greater than 0% and less than or equal to 2%, based on the total mass of the negative electrode film layer being 100%.

[0042] In the technical solution of the embodiments of this application, the total mass of the above-mentioned conductive agent is within the above-mentioned range. On the basis of ensuring the basic conductivity of the negative electrode sheet, on the one hand, it has little impact on the proportion of negative electrode active material, and thus has little impact on the energy density of the battery cell; on the other hand, it can reduce the electrode impedance of the negative electrode sheet, and has little impact on the charging and discharging power of the battery cell.

[0043] In some embodiments, the negative electrode film layer sequentially includes a first negative electrode film layer and a second negative electrode film layer in the direction from away from the negative electrode current collector to near the negative electrode current collector;

[0044] Based on the mass of the first negative electrode film, the mass content of the conductive agent is greater than 0% and less than or equal to 1.2%.

[0045] Based on the mass of the second negative electrode film, the mass content of the conductive agent is greater than 0% and less than or equal to 0.8%.

[0046] In the technical solution of the embodiments of this application, the mass content of the conductive agent in the first negative electrode film layer and the second negative electrode film is within the above range, and the mass content of the conductive agent in the first negative electrode film layer is higher, which is beneficial to improving the fast charging performance of the secondary battery.

[0047] In some embodiments, the full-charge rebound rate of the negative electrode is less than 20%, and can be selected as 8%-15%.

[0048] In the technical solution of the embodiments of this application, the full charge rebound rate of the negative electrode sheet is in a low range, which provides the possibility of providing a battery with high mass margin and high energy density.

[0049] In some embodiments, the battery cell packing margin is 91%-95%.

[0050] In the technical solution of the embodiments of this application, the battery cell packing margin is at a high level, which can form a high energy density battery.

[0051] In some embodiments, the negative electrode current collector includes a polymer material substrate and a metal layer disposed on at least one surface of the polymer material substrate.

[0052] In the technical solution of the embodiments of this application, the negative electrode current collector uses a combination of a polymer material base layer and a metal layer. The polymer material base layer has better flexibility than the metal layer, which improves the toughness of the negative electrode current collector, making the mechanical stability of the secondary battery better and able to better withstand the volume changes of the secondary battery during charging and discharging, thereby improving the safety of the secondary battery.

[0053] In a second aspect, this application provides a battery device comprising a plurality of battery cells according to the first aspect.

[0054] Thirdly, this application provides an electrical device, which includes the battery cell described in the first aspect, or the battery device described in the second aspect.

[0055] 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. Detailed Implementation

[0056] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0058] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0059] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0060] 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 a 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 also expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 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 "ab" 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 "2-10" indicates that all real numbers between "2-10" have been listed in this article; "2-10" 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.

[0061] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0062] In existing technologies, the negative electrode of a battery cell has a high full-charge rebound rate, which results in a low energy density of the battery cell and affects its performance.

[0063] This application obtains a negative electrode sheet with low full-charge rebound rate by designing the change of the mass ratio of binder in different negative electrode film layers. It is suitable for battery cells with high energy density and high group margin. This application also studies and develops a battery cell, a battery device and a power consumption device.

[0064] [Battery cell]

[0065] 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.

[0066] 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., and the embodiments of this application are not limited to this.

[0067] [Electrode Assembly]

[0068] 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 negative and positive electrodes. During the charging and discharging process of a single battery cell, active ions (such as lithium ions or sodium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through.

[0069] [Negative electrode plate]

[0070] This application provides a battery cell, the battery cell including a negative electrode sheet;

[0071] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector;

[0072] The negative electrode film layer includes a binder;

[0073] From the direction away from the negative electrode current collector to the direction closer to the negative electrode current collector, the negative electrode film layer sequentially includes a first negative electrode film layer to an nth negative electrode film layer, where n is a positive integer greater than or equal to 2;

[0074] The mass percentage of the binder in the (n-1)th negative electrode film layer is less than the mass percentage of the nth negative electrode film layer.

[0075] In this application, the change in the mass percentage of the binder in each negative electrode film layer can be tested using any method known in the art. As an example, it can be determined by thermogravimetric analysis (TGA), wherein the testing tool for TGA is a thermogravimetric analyzer, the testing temperature range is 25-600℃, the heating rate is 10℃ / min, and the specific testing method is as follows:

[0076] (1) Cutting the electrode sheet: Cut the negative electrode sheet to be tested into a test sample of appropriate size (e.g., 20cm×10cm);

[0077] (2) Prepare tools: Prepare a clean blade, hold the test sample with your left hand and hold the blade with your right hand. Set the blade to 45° with the electrode. Select the middle of the test sample and scrape the powder from left to right. The length of the scraped powder is 10cm and the width is 5cm.

[0078] (3) Sample collection: Taking the same thickness of different negative electrode film layers as an example, if there are m times from the start of powder scraping to the leakage of negative electrode current collector, then the first m / n times of powder scraping are taken as the first negative electrode film layer sample, and the last m / n times of powder scraping are taken as the nth negative electrode film layer sample; it should be noted that the number of times of powder scraping is taken for different negative electrode film layers depends on their proportion of the thickness of the negative electrode film layer. For example, if the proportion of the thickness of the first negative electrode film layer in the negative electrode film layer is 1 / 3, then the first m / 3 times of powder scraping are taken as the first negative electrode film layer sample.

[0079] As an example, when the negative electrode sheet includes two negative electrode film layers of the same thickness, if there are a total of 6 times from the start of powder scraping to the leakage of the negative electrode current collector, the first 3 times of powder scraping are taken as the first negative electrode film layer sample, and the last 3 times of powder scraping are taken as the second negative electrode film layer sample. The collected samples are then stored in a sealed bottle.

[0080] (3) Thermogravimetric analysis: Weigh 50mg of the collected sample and place it in an alumina crucible and level it. Use a thermogravimetric analyzer to detect the binder content in the sample (atmosphere is nitrogen, flow rate is 20mL / min). The sample is heated from 25℃ to 600℃ at a heating rate of 10℃ / min. The percentage of mass loss of different negative electrode film layers is the mass ratio of binder in different negative electrode film layers.

[0081] During the compaction process of the negative electrode sheet, under the same force, the pressure borne by the nth negative electrode film layer (lower layer) is greater than that borne by the (n-1)th negative electrode film layer (upper layer), which will cause the compaction rebound of the lower negative electrode film layer to be more severe than that of the upper negative electrode film layer.

[0082] In the technical solution of this application embodiment, from the direction away from the negative electrode current collector to the direction closer to the negative electrode current collector, the mass ratio of the binder in each film layer gradually increases. The nth negative electrode film layer (lower layer) has a greater bonding force than the (n-1)th negative electrode film layer (upper layer). Compared with the upper film layer with high bonding force, the lower film layer with high bonding force adopted in this application has a more significant effect on reducing the rebound of the electrode sheet. It can better reduce the compaction rebound of the electrode sheet, which is conducive to reducing the full charge rebound rate of the battery and provides the possibility of providing batteries with high mass margin and high energy density.

[0083] In this application, the full-charge rebound rate is the percentage increase in electrode thickness from before assembly into a cell to after the first charge to a fully charged state (100% SOC). For example, for a negative electrode, if its thickness before assembly into a cell is L1, and its thickness when assembled into a battery cell and first charged to 100% SOC is L2, then its full-charge rebound rate is (L2-L1) / L1×100%. As an example, when lithium iron phosphate is used as the positive electrode active material, the battery cell charging steps are: first, constant current charging at 1 / 3C to 3.8V, then constant voltage charging at 3.8V until the current decreases to 0.05C; when ternary cathode material is used as the positive electrode active material, the battery cell charging steps are: first, constant current charging at 1 / 3C to 4.4V, then constant voltage charging at 4.4V until the current decreases to 0.05C.

[0084] In some embodiments, the adhesive includes one or more of a first adhesive and a second adhesive;

[0085] The first adhesive includes a polyacrylic acid compound;

[0086] The second adhesive includes any one or a combination of at least two of styrene-butadiene rubber, styrene-acrylic rubber, or pure acrylic rubber.

[0087] In the technical solutions of this application embodiment, one or more of the first adhesive or the second adhesive can be selected as needed.

[0088] In some embodiments, the binder is selected from the first binder. The polyacrylic acid compound structure contains a large number of carboxyl groups, which can interact with other components such as negative electrode active materials or conductive agents, resulting in strong adhesion. This effectively reduces the full-charge rebound rate of the negative electrode, providing the possibility of providing batteries with high charge margin and high energy density, especially suitable for negative electrode sheets prone to full-charge rebound. Furthermore, the large number of carboxyl groups in the polyacrylic acid compound structure, in applications such as lithium batteries, allows for the interaction between the carboxylate group (-COOH) and the lithium carboxylate group (-COOLi). + and Li + A reversible exchange reaction occurs, promoting Li + Transport at the electrode interface, these electrons and Li + The highly coordinated transport enhances the kinetic performance of the electrode and provides a rapid capacitor-like redox process, which is beneficial to improving the fast charging performance of the battery.

[0089] In some embodiments, the binder is selected from a combination of a first binder and a second binder. The second binder has a lower cost and can partially replace the more expensive first binder. The two binders work together to reduce the full-charge rebound rate of the negative electrode to a certain extent, providing the possibility of providing batteries with high mass margin and high energy density. This method is applicable to high-silicon material systems.

[0090] In some embodiments, the first binder is selected from carbon nanotube-modified polyacrylic acid compounds. Compared with unmodified polyacrylic acid compounds, carbon nanotube-modified polyacrylic acid compounds have a relatively large specific surface area of ​​carbon nanotubes, which can provide more contact points for the negative electrode active material. Therefore, it can be further combined with polyacrylic acid compounds to improve the binding ability of the negative electrode active material, suppress the rebound of the negative electrode active material, and thus reduce the full charge rebound rate of the battery, providing the possibility of providing batteries with high mass margin and high energy density. Moreover, the carbon nanotubes in the carbon nanotube-modified polyacrylic acid compounds can also improve the conductivity of the negative electrode film, reduce the film impedance, improve the dynamic performance of the battery cell, and improve its fast charging performance.

[0091] In this application, carbon nanotube-modified polyacrylic acid compounds refer to polyacrylic acid compounds that have been modified by doping the surface of carbon nanotubes.

[0092] The carbon nanotube-modified polyacrylic acid compound can be a commercially available product or prepared using known methods. As an example, carbon nanotubes and a polyacrylic acid compound are compounded by mixing at a temperature of 100-300°C (e.g., 200°C) and a rotation speed of 100-1000 rpm (e.g., 500 rpm) to obtain the carbon nanotube-modified polyacrylic acid compound. During the mixing process, necessary additives, such as dispersants (carboxymethyl cellulose, etc.) and solvents (ethanol, epoxy resin ethanol solution, etc.), can be selectively added as needed. A twin-screw extruder can be selected for the mixing process.

[0093] During the compounding process, the carboxyl groups in the polyacrylic acid compound react with the defects on the surface of the carbon nanotubes to form polyacrylic acid compounds that are doped and modified on the surface of the carbon nanotubes.

[0094] The mass ratio of carbon nanotubes to polyacrylic acid compounds can be 1:(2-50), where 2-50 can be 5, 10, 15, 20, 25, 30, 35, 40, 45, etc.

[0095] In some embodiments, the polyacrylic compound includes any one or a combination of at least two of polyacrylic acid, polymethacrylic acid, polyacrylate, or acrylic copolymers (e.g., copolymers of at least two of acrylic acid, methacrylic acid, or acrylates).

[0096] In the technical solution of this application embodiment, the polyacrylic acid compound is within the above-mentioned range, the raw materials are readily available, the adhesive force is strong, which is more conducive to reducing the full charge rebound rate of the negative electrode sheet and maintaining the structural stability of the negative electrode sheet.

[0097] In some embodiments, the total mass of the binder is greater than 0% and less than or equal to 8%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, etc., with the total mass of the negative electrode film layer being 100%, and optionally less than or equal to 5%.

[0098] In the technical solution of this application embodiment, the total mass content of the binder is within the above-mentioned range. First, it can satisfy the requirement of reducing the full charge rebound rate of the battery, providing the possibility of providing batteries with high mass margin and high energy density. Second, it has little impact on the mass content of main materials such as negative electrode active materials, reducing the problem of battery performance degradation caused by the reduction of main material content.

[0099] In some embodiments, the adhesive includes a first adhesive, extending from away from the negative electrode current collector to near the negative electrode current collector, and the negative electrode film layer sequentially includes a first negative electrode film layer and a second negative electrode film layer;

[0100] Based on the mass of the first negative electrode film layer, the mass content of the first binder is greater than 0% and less than or equal to 3%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, etc., and optionally less than or equal to 2%.

[0101] Based on the mass of the second negative electrode film, the mass content of the first binder is greater than 0% and less than or equal to 5%, for example, 0.5%, 1%, 2%, 3%, 4%, etc., and optionally less than or equal to 3%.

[0102] In this application, the mass percentage of the first binder is the mass percentage of the corresponding negative electrode film layer in the secondary battery. Generally, during the drying process of the negative electrode sheet and before cold pressing, the binder will float to the surface to a certain extent. Therefore, in this application, before cold pressing, the mass content of the first binder in the first negative electrode film layer is greater than 0% and less than or equal to 2.4%, optionally less than or equal to 1.6%; the mass content of the first binder in the second negative electrode film layer is greater than 0% and less than or equal to 5.6%, optionally less than or equal to 3.4%.

[0103] The first binder generally has a higher mass content in the upper negative electrode film than in the lower negative electrode film. This arrangement helps to improve the dynamic performance of the battery cell and enhance its fast charging performance. However, the lower film has a weaker adhesive force and is subjected to greater forces during cold pressing, resulting in a greater compaction and rebound of the electrode sheet.

[0104] In the technical solution of this application embodiment, the mass content of the first binder in the upper and lower negative electrode film layers are respectively within the range. The mass content of the first binder in the lower negative electrode film layer is greater than the mass content in the negative electrode film layer, which can effectively reduce the full charge rebound rate of the negative electrode sheet and provide the possibility of providing a battery with high mass margin and high energy density.

[0105] In some embodiments, the adhesive comprises a combination of a first adhesive and a second adhesive;

[0106] From the direction away from the negative electrode current collector to the direction closer to the negative electrode current collector, the negative electrode film layer sequentially includes a first negative electrode film layer to an nth negative electrode film layer, where n is a positive integer greater than or equal to 2;

[0107] The mass percentage of the first binder in the (n-1)th negative electrode film layer is less than the mass percentage of the nth negative electrode film layer.

[0108] In the technical solution of this application embodiment, the first binder has a high mass content in the lower negative electrode film layer, which is beneficial to reduce the full charge rebound rate of the negative electrode sheet and provides the possibility of providing a battery with high mass margin and high energy density.

[0109] In some embodiments, with the total mass of the negative electrode film layer being 100%, the total mass of the first binder is greater than 0% and less than or equal to 3.5%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0110] The total mass of the second adhesive is greater than 0% and less than or equal to 4.5%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc.

[0111] In the technical solution of this application embodiment, the total mass of the first binder and the second binder in the negative electrode film layer are respectively within the above-mentioned range, which is more conducive to reducing the full charge rebound rate of the negative electrode sheet and providing the possibility of providing a battery with high mass margin and high energy density; moreover, the overall formed negative electrode film layer has strong adhesion, reducing the possibility of film layer detachment during cycling and improving the cycle performance and safety performance of the battery.

[0112] In some embodiments, from the direction away from the negative electrode current collector to the direction closer to the negative electrode current collector, the negative electrode film layer sequentially includes a first negative electrode film layer and a second negative electrode film layer;

[0113] Based on the mass of the first negative electrode film layer, the mass content of the first binder is greater than 0% and less than or equal to 1%, for example, 0.2%, 0.4%, 0.6%, 0.8%, etc., and optionally less than or equal to 0.7%; the mass content of the second binder is greater than 0% and less than or equal to 3%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, etc., and optionally less than or equal to 1.2%.

[0114] Based on the mass of the second negative electrode film, the mass content of the first binder is greater than 0% and less than or equal to 2%, for example, 0.5%, 1%, 1.5%, etc., and optionally less than or equal to 0.9%; the mass content of the second binder is greater than 0% and less than or equal to 3%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, etc., and optionally less than or equal to 1.3%.

[0115] In this application, before cold pressing, the mass content of the first binder in the first negative electrode film layer is greater than 0% and less than or equal to 0.6%, optionally less than or equal to 0.5%; the mass content of the second binder is greater than 0% and less than or equal to 3.6%, optionally less than or equal to 2%.

[0116] The mass content of the first binder in the second negative electrode film layer is greater than 0% and less than or equal to 2.4%, optionally less than or equal to 1.1%; the mass content of the second binder is greater than 0% and less than or equal to 3.6%, optionally less than or equal to 2%.

[0117] In the technical solution of this application embodiment, the mass content of the first binder and the second binder in the first negative electrode film layer and the second negative electrode film layer are as described above. First, the mass content of the binder in the lower negative electrode film layer is greater than the mass content in the upper negative electrode film layer. The first binder and the second binder work together to effectively reduce the full charge rebound rate of the negative electrode sheet, providing the possibility of providing a battery with high mass margin and high energy density.

[0118] In some embodiments, the negative electrode film layer further includes a conductive agent, wherein the mass percentage of the conductive agent in the (n-1)th negative electrode film layer is greater than the mass percentage of the nth negative electrode film layer.

[0119] In the technical solution of this application embodiment, the mass ratio of conductive agent in each negative electrode film layer gradually decreases, and the content of conductive agent in the upper layer is higher, which is more conducive to improving electron transmission efficiency and can meet the requirements of fast charging performance.

[0120] In some embodiments, with the total mass of the negative electrode film layer being 100%, the total mass of the conductive agent is greater than 0% and less than or equal to 2%, for example, 0.2%, 0.5%, 1%, 1.5%, etc.

[0121] In the technical solution of this application embodiment, the total mass of the conductive agent is within the above range. On the basis of ensuring the basic conductivity of the negative electrode sheet, on the one hand, it has a small impact on the proportion of the negative electrode active material, and thus a small impact on the energy density of the battery cell; on the other hand, it can reduce the electrode impedance of the negative electrode sheet, and thus have a small impact on the charging and discharging power of the battery cell.

[0122] In some embodiments, from the direction away from the negative electrode current collector to the direction closer to the negative electrode current collector, the negative electrode film layer sequentially includes a first negative electrode film layer and a second negative electrode film layer;

[0123] Based on the mass of the first negative electrode film, the mass content of the conductive agent is greater than 0% and less than or equal to 1.2%, such as 0.2%, 0.4%, 0.6%, 0.8%, 1%, etc.

[0124] Based on the mass of the second negative electrode film, the mass content of the conductive agent is greater than 0% and less than or equal to 0.8%, such as 0.2%, 0.4%, 0.6%, etc.

[0125] In the technical solution of this application embodiment, the mass content of the conductive agent in the first negative electrode film layer and the second negative electrode film is within the above range, and the mass content of the conductive agent in the first negative electrode film layer is higher, which is beneficial to improving the fast charging performance of the secondary battery.

[0126] In some embodiments, the full-charge rebound rate of the negative electrode is less than 20%, such as 8%, 10%, 12%, 14%, 16%, 18%, etc., and can be selected as 8%-15%.

[0127] In the technical solution of the embodiments of this application, the full charge rebound rate of the negative electrode sheet is in a low range, which provides the possibility of providing a battery with high mass margin and high energy density.

[0128] In some embodiments, the battery cell packing margin is 91%-95%, such as 92%, 93%, 94%, etc.

[0129] The battery cell using this application has a low full-charge rebound rate for its negative electrode, making it suitable for battery cells with high packing margin, thus providing a basis for obtaining high-energy-density battery cells.

[0130] In some embodiments, the negative electrode current collector includes a polymer material substrate and a metal layer disposed on at least one surface of the polymer material substrate.

[0131] In the technical solution of this application embodiment, the negative electrode current collector uses a combination of a polymer material base layer and a metal layer. The polymer material base layer has better flexibility than the metal layer, which improves the toughness of the negative electrode current collector, making the secondary battery more mechanically stable and able to better withstand the volume changes of the secondary battery during charging and discharging, thereby improving the safety of the secondary battery.

[0132] In some embodiments, the conductive agent includes any one or a combination of at least two of carbon black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0133] In some embodiments, the carbon black includes any one or a combination of at least two of acetylene black, Ketjen black, or Super P.

[0134] In some embodiments, the negative electrode current collector comprises a polymeric material substrate and a metal layer. As an example, the negative electrode current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymeric material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.). The metal material is bonded to the surface of the polymeric material substrate by an adhesive.

[0135] In the technical solution of this application embodiment, the negative electrode sheet formed by the composite current collector has good toughness, which is beneficial to the improvement of the overall performance of the battery cell.

[0136] In some embodiments, the negative current collector may also 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.

[0137] In some embodiments, the negative electrode film layer further includes a negative electrode active material, which may be a negative electrode active material known in the art for use in battery cells.

[0138] As an example, the negative electrode active material includes silicon-based materials. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0139] As an example, the negative electrode active material may also include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, tin-based materials, and lithium titanate, etc. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0140] As an example, negative electrode active materials can be filled or / and deposited within the negative electrode current collector.

[0141] In some embodiments, the negative electrode current collector has ≥2 layers on one surface, and the method for preparing the negative electrode sheet includes:

[0142] (1) Dissolve the negative electrode material, such as the negative electrode active material, conductive agent, first binder, second binder and other arbitrary components in a solvent (e.g., water) to form the first to nth negative electrode slurries respectively;

[0143] (2) The nth negative electrode slurry is coated onto the negative electrode current collector to form the nth negative electrode film layer. The (n-1)th negative electrode slurry layer is coated onto the nth negative electrode film layer to form the (n-1)th negative electrode film layer. The coating is repeated according to the above operation until the second negative electrode slurry layer is coated onto the first negative electrode film layer to form the first negative electrode film layer. After drying, cold pressing and slitting, the negative electrode sheet is obtained.

[0144] The above operation can be performed on one side of the negative electrode current collector or on both sides of the negative electrode current collector.

[0145] [Positive electrode plate]

[0146] In some embodiments, the positive electrode may be a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one surface (e.g., one or two) of the positive current collector.

[0147] As an example, the positive current collector can 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 can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material base layer 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.).

[0148] In some embodiments, the positive electrode film layer comprises a positive electrode active material.

[0149] As an example, 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 may 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 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, and lithium nickel cobalt manganese oxide (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05At 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.

[0150] In some embodiments, the positive electrode can be a foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When foamed metal is used as the positive electrode, the surface of the foamed metal may or may not contain a positive electrode active material. As an example, a positive electrode active material is filled and / or deposited within the foamed metal.

[0151] [Isolation Component]

[0152] In some embodiments, the electrode assembly further includes an isolator disposed between the positive and negative electrodes.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] [Electrolytes]

[0157] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. The electrolyte can be liquid, gel, or solid.

[0158] Liquid electrolytes include electrolyte salts and solvents.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0163] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0164] 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.

[0165] 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 sulfide, silver sulfide germanium ore), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0166] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0167] [Structure of the electrode assembly]

[0168] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0169] In some embodiments, the electrode assembly is a wound structure. The positive electrode and the negative electrode are wound into a wound structure.

[0170] In some implementations, the electrode assembly is a stacked structure.

[0171] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0172] 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.

[0173] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0174] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0175] As an example, the separator can be continuously arranged between any adjacent positive or negative electrode plates by folding or rolling.

[0176] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0177] 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.

[0178] [shell]

[0179] 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.

[0180] 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 have any particular limitations.

[0181] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also have one or more.

[0182] [Electrode terminals]

[0183] 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 indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0184] [Pressure relief mechanism]

[0185] 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.

[0186] 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 creating 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.

[0187] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0188] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0189] 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.

[0190] 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.

[0191] 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.

[0192] [Battery Device]

[0193] 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.

[0194] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0195] 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.

[0196] 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.

[0197] 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.

[0198] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0199] 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.

[0200] 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.

[0201] 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.

[0202] [ Electrical appliances ]

[0203] 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.

[0204] Example 1

[0205] Negative electrode plate:

[0206] (1) Natural graphite, first binder (carbon nanotube modified polyacrylic acid, the modification method is surface doping, the mass ratio of the two is 1:10), second binder (styrene-butadiene rubber), and conductive agent (acetylene black) are dissolved in solvent (water) according to the formula shown in Table 2 to form the first negative electrode slurry.

[0207] Natural graphite, the first binder (carbon nanotube modified polyacrylic acid, modified by surface doping, with a mass ratio of 1:10), and the conductive agent (acetylene black) are dissolved in a solvent (water) according to the formulation shown in Table 2 to form the second negative electrode slurry.

[0208] (2) The second negative electrode slurry is coated on the negative electrode current collector (a polyethylene terephthalate layer with a thickness of 3.5 μm and copper layers with a thickness of 1.5 μm on both sides, the polyethylene terephthalate layer and the copper layer are bonded together with yellow glue) to form a second negative electrode film layer. Then the first negative electrode slurry is coated on the second negative electrode film layer to form a first negative electrode film layer. After drying, cold pressing and slitting, the negative electrode sheet is obtained.

[0209] Positive electrode sheet: LFP, polyvinylidene fluoride and acetylene black are dissolved in a solvent (N-methylpyrrolidone) at a mass ratio of 0.975:0.018:0.007 to form a positive electrode slurry. The positive electrode slurry is coated on a positive electrode current collector (aluminum foil), and after drying, cold pressing and slitting, a positive electrode sheet is obtained.

[0210] The separator is made of a 7μm polyethylene film as the substrate layer, and a 1μm adhesive coating (made of polyvinylidene fluoride) and a 2μm ceramic coating (made of boehmite) are sequentially disposed on the surface of the substrate layer.

[0211] Electrolyte: Lithium bis(fluorosulfonyl)imide (LiFSI) is used as the lithium salt and ethylene carbonate is used as the solvent. The two are mixed to form an electrolyte, wherein the concentration of LiFSI is 1 mol / L.

[0212] Battery cell: The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain the cell, with a casing margin of 94%. The cell is placed in the outer packaging, electrolyte is added, and after vacuum sealing, standing, formation, shaping, capacity measurement and other processes, the battery cell is obtained.

[0213] Examples 2-6 and Comparative Examples 1-2

[0214] Except for the parameters in Tables 1-3, the battery cells were prepared according to the method in Example 1.

[0215] Table 1: Types and amounts of raw materials added to the negative electrode film

[0216]

[0217]

[0218] Table 2: Mass percentage of each raw material added to the negative electrode film layer of the battery cell

[0219]

[0220] Table 3: Mass percentage of each raw material in the negative electrode film after the first charge to 100% SOC.

[0221]

[0222]

[0223] In the table, the mass percentage is based on the total mass of the negative electrode film layer being 100%. The mass percentage of the negative electrode active material, artificial graphite, is adaptively adjusted according to the mass percentage of each component until the total mass of the negative electrode film layer is 100%.

[0224] "——" represents information that is not involved.

[0225] [Performance Testing]

[0226] (1) Full charge rebound rate of negative electrode sheet: The thickness before assembly into a cell is L1, and the thickness when first charged to 100% SOC is L2. The full charge rebound rate is (L2-L1) / L1×100%. The charging steps are: first, charge at 1 / 3C constant current to 3.8V, then charge at constant voltage of 3.8V until the current drops to 0.05C, and stop charging. At this time, the state of the battery cell is 100% SOC.

[0227] Thickness test before assembly into battery cells: Take a sample of the negative electrode sheet, with a sample length of 0.5-1cm, blow away the floating powder on the surface of the negative electrode sheet, zero the micrometer, and measure 16 sets of data. Calculate the average thickness to obtain L1. After assembling the negative electrode sheet into a battery cell, charge it to 100% SOC for the first time, and obtain L2 using the aforementioned method.

[0228] (2) Cycle performance of individual battery cells: The standard cycle life of individual battery cells is tested according to GB / T 31484-2015. The specific process is as follows:

[0229] a) Initial capacity test: Under 45℃ conditions, the initial capacity of each battery cell is obtained by using a stepped charging process. The specific process is as follows:

[0230] 1) Let the individual battery cells stand for 30 minutes.

[0231] 2) Discharge to 2.0V at 1 / 3C.

[0232] 3) Let stand for 30 minutes.

[0233] 4) Charge at a constant current of 1 / 3C to 3.8V, then charge at a constant voltage of 0.05C.

[0234] 5) Let stand for 60 minutes.

[0235] 6) Discharge to 2.0V at 1 / 3C.

[0236] 7) Let stand for 10 minutes.

[0237] 8) Repeat steps 4)-7) 3 times, take the last discharge capacity as the initial capacity, and record it as C0 to complete the preprocessing;

[0238] b) Discharge treatment of individual battery cells: After pretreatment, the individual battery cells are first left to stand for 30 minutes, then charged at a constant current of 1 / 3C to 3.8V, charged at a constant voltage (3.8V) to 0.05C, left to stand for 30 minutes, and then discharged at 1C to 3% SOC.

[0239] c) 50 cycles: A battery cell discharged to 3% SOC is charged at a constant current of 0.5C to 5% SOC, then sequentially charged at the following rates: 0.5C from 5% SOC to 10% SOC, 1.5C from 10% SOC to 15% SOC, 1.48C from 15% SOC to 20% SOC, 1.45C from 20% SOC to 25% SOC, 1.44C from 25% SOC to 30% SOC, 1.5C from 30% SOC to 35% SOC, 1.43C from 35% SOC to 40% SOC, 1.29C from 40% SOC to 45% SOC, 1.17C from 45% SOC to 50% SOC, 1.06C from 50% SOC to 55% SOC, and 0.94C from 55% SOC to 60% SOC. C. Charge the battery cell at 0.83C from 60% SOC to 65% SOC, 0.72C from 65% SOC to 70% SOC, 0.61C from 70% SOC to 75% SOC, 0.5C from 75% SOC to 80% SOC, 0.33C from 80% SOC to 85% SOC, 0.33C from 85% SOC to 90% SOC, 0.33C from 90% SOC to 95% SOC, and 0.2C from 95% SOC to 100% SOC. Then discharge the battery cell at 0.5C to 3% SOC. This constitutes one cycle. Record the discharge capacity of the battery cell after the 50th cycle as C50(3% SOC - 100% SOC). Then, the capacity retention rate of the battery cell after 50 cycles is P50 = (C50 / 0.97) / C0*100%.

[0240] The test results are summarized in Tables 4 and 5.

[0241] Table 4

[0242]

[0243]

[0244] As can be seen from Examples 1-6 and Comparative Examples 1-2, the mass ratio of the binder in the first negative electrode film layer is less than that in the second negative electrode film layer, which can reduce the full charge rebound rate in the negative electrode sheet. This is suitable for batteries with high packing margin and is beneficial for obtaining high energy density battery cells.

[0245] Analysis of Examples 2 and 5 shows that the mass content of the first binder in the first negative electrode film layer is less than its mass percentage in the second negative electrode film layer, which can reduce the full-charge rebound rate of the negative electrode sheet. This demonstrates that in the technical solution where the binder includes a combination of the first and second binders, from the direction away from the negative electrode current collector to the direction closer to the negative electrode current collector, the negative electrode film layers sequentially include the first negative electrode film layer to the nth negative electrode film layer, where n is a positive integer greater than or equal to 2; the mass percentage of the first binder in the (n-1)th negative electrode film layer is less than its mass percentage in the nth negative electrode film layer, which can reduce the full-charge rebound rate of the negative electrode sheet. This is suitable for batteries with high packing margin and is beneficial for obtaining high-energy-density battery cells.

[0246] Table 5

[0247] Full charge rebound rate Capacity retention rate after 50 cycles Example 1 8％ 97.30％ Example 4 8％ 97.00％

[0248] Analysis of Examples 4 and 1 shows that, from the direction away from the negative electrode current collector to the direction closer to the negative electrode current collector, the mass ratio of the conductive agent in the (n-1)th negative electrode film layer is greater than that in the nth negative electrode film layer, which can improve the cycle capacity retention rate of the battery cell and improve the cycle performance of the battery.

[0249] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, characterized in that, The battery cell includes a negative electrode sheet; The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector; The negative electrode film layer includes a binder; From the direction away from the negative electrode current collector to the direction closer to the negative electrode current collector, the negative electrode film layer sequentially includes a first negative electrode film layer to an nth negative electrode film layer, where n is a positive integer greater than or equal to 2; The mass percentage of the binder in the (n-1)th negative electrode film layer is less than the mass percentage of the nth negative electrode film layer.

2. The battery cell according to claim 1, characterized in that, The adhesive includes one or more of a first adhesive and a second adhesive, and may be selected as a first adhesive or a combination of a first adhesive and a second adhesive; The first adhesive includes a polyacrylic acid compound, which may be a carbon nanotube-modified polyacrylic acid compound; The second adhesive includes any one or a combination of at least two of styrene-butadiene rubber, styrene-acrylic rubber, or pure acrylic rubber.

3. The battery cell according to claim 2, characterized in that, The polyacrylic compounds include any one or a combination of at least two of polyacrylic acid, polymethacrylic acid, polyacrylate, or acrylic copolymers.

4. The battery cell according to any one of claims 1-3, characterized in that, With the total mass of the negative electrode film layer being 100%, the total mass of the binder is greater than 0% and less than or equal to 8%.

5. The battery cell according to any one of claims 2-4, characterized in that, The adhesive includes a first adhesive, which extends from away from the negative electrode current collector to near the negative electrode current collector, and the negative electrode film layer sequentially includes a first negative electrode film layer and a second negative electrode film layer. Based on the mass of the first negative electrode film layer, the mass content of the first binder is greater than 0% and less than or equal to 3%. Based on the mass of the second negative electrode film, the mass content of the first binder is greater than 0% and less than or equal to 5%.

6. The battery cell according to any one of claims 2-5, characterized in that, The adhesive includes a combination of a first adhesive and a second adhesive; From the direction away from the negative electrode current collector to the direction closer to the negative electrode current collector, the negative electrode film layer sequentially includes a first negative electrode film layer to an nth negative electrode film layer, where n is a positive integer greater than or equal to 2; The mass percentage of the first binder in the (n-1)th negative electrode film layer is less than the mass percentage of the nth negative electrode film layer.

7. The battery cell according to claim 6, characterized in that, With the total mass of the negative electrode film layer being 100%, the total mass of the first binder is greater than 0% and less than or equal to 3.5%. The total mass of the second adhesive is greater than 0% and less than or equal to 4.5%.

8. The battery cell according to claim 6 or 7, characterized in that, From the direction away from the negative electrode current collector to the direction closer to the negative electrode current collector, the negative electrode film layer sequentially includes a first negative electrode film layer and a second negative electrode film layer; Based on the mass of the first negative electrode film layer, the mass content of the first binder is greater than 0% and less than or equal to 1%; the mass content of the second binder is greater than 0% and less than or equal to 3%. Based on the mass of the second negative electrode film, the mass content of the first binder is greater than 0% and less than or equal to 2%; the mass content of the second binder is greater than 0% and less than or equal to 3%.

9. The battery cell according to any one of claims 1-8, characterized in that, The negative electrode film layer also includes a conductive agent, and the mass percentage of the conductive agent in the (n-1)th negative electrode film layer is greater than the mass percentage of the nth negative electrode film layer.

10. The battery cell according to claim 9, characterized in that, With the total mass of the negative electrode film layer being 100%, the total mass of the conductive agent is greater than 0% and less than or equal to 2%.

11. The battery cell according to claim 9 or 10, characterized in that, From the direction away from the negative electrode current collector to the direction closer to the negative electrode current collector, the negative electrode film layer sequentially includes a first negative electrode film layer and a second negative electrode film layer; Based on the mass of the first negative electrode film, the mass content of the conductive agent is greater than 0% and less than or equal to 1.2%. Based on the mass of the second negative electrode film, the mass content of the conductive agent is greater than 0% and less than or equal to 0.8%.

12. The battery cell according to any one of claims 1-11, characterized in that, The full-charge rebound rate of the negative electrode sheet is less than 20%, and can be selected as 8%-15%.

13. The battery cell according to any one of claims 1-12, characterized in that, The battery cell packing margin is 91%-95%.

14. The battery cell according to any one of claims 1-13, characterized in that, The negative electrode current collector includes a polymer material base layer and a metal layer disposed on at least one surface of the polymer material base layer.

15. A battery device, characterized in that, The battery device comprises a plurality of battery cells according to any one of claims 1-14.

16. An electrical appliance, characterized in that, The electrical device includes a battery cell as described in any one of claims 1-14, or a battery device as described in claim 15.

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