Battery cell and preparation method therefor, battery, and electrical apparatus

Abstract

A battery cell and a preparation method therefor, a battery, and an electrical apparatus. The battery cell comprises a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer provided on the surface of at least one side of the negative electrode current collector. The negative electrode film layer comprises a first negative electrode active layer and a second negative electrode active layer. The second negative electrode active layer is located between the negative electrode current collector and the first negative electrode active layer. The first negative electrode active layer comprises a first negative electrode active material, and the second negative electrode active layer comprises a second negative electrode active material. The volume particle size distribution Dv501 of the first negative electrode active material satisfies: Dv501 ≤ 2 μm. The volume particle size distribution Dv991 of the first negative electrode active material satisfies: Dv991 ≤ 5 μm. The volume particle size distribution Dv502 of the second negative electrode active material satisfies: Dv502 ≥ Dv991. The thickness d1 of the first negative electrode active layer and the thickness d2 of the second negative electrode active layer satisfy: d1:d2 = (0.023 to 0.25):1. The technical solution of the present application can improve battery performance in low-temperature environments.

Description

Battery cells and their preparation methods, batteries, and electrical devices Technical Field

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

[0002] In recent years, with the increasingly wide range of applications, batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0003] The development of battery technology requires consideration of various design factors, such as energy density, cycle life, storage performance, charge / discharge rate, and reliability. However, when batteries are used in low-temperature environments, their charging rate, charging efficiency, and lifespan all decrease. Therefore, improving battery performance in low-temperature environments is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell and its preparation method, battery, and power device to improve the performance of the battery in low-temperature environments.

[0005] In a first aspect, a battery cell is provided, comprising: a negative electrode sheet, the negative electrode sheet including 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 including a first negative electrode active layer and a second negative electrode active layer, the second negative electrode active layer being located between the negative current collector and the first negative electrode active layer, the first negative electrode active layer including a first negative electrode active material, the second negative electrode active layer including a second negative electrode active material, wherein the volumetric particle size distribution of the first negative electrode active material is Dv50. 1 Satisfying: Dv50 1 ≤2μm, the volumetric particle size distribution Dv99 of the first negative electrode active material 1 Satisfying: Dv99 1 ≤5μm; the volumetric particle size distribution Dv50 of the second negative electrode active material 2 Satisfying: Dv50 2 ≥Dv99 1 The thickness d1 of the first negative electrode active layer and the thickness d2 of the second negative electrode active layer satisfy the following condition: d1:d2=(0.023~0.25):1.

[0006] In this embodiment, the volumetric particle size distribution of the first negative electrode active material is Dv50. 1 ≤2μm, Dv99 1With a thickness ≤5μm, the ion transport path of the first negative electrode active material, which is far from the current collector, is shortened, thus improving the kinetic performance of this layer. This expands the surface pulse rate window of the pulse cell, contributing to improved high-rate pulse self-heating. Simultaneously, the Dv50 of the second negative electrode active material... 2 ≥Dv99 1 This reduces the specific surface area of ​​the second negative electrode active material and decreases surface reaction sites, which reduces irreversible lithium consumption during film formation, thereby extending battery life. Furthermore, it improves the battery's short-term discharge and recharge power at low temperatures. On the other hand, designing the d1 / d2 ratio range helps reduce battery life degradation caused by excessive d1 thickness and mitigates the impact on kinetic performance caused by excessive d1 thinness. Therefore, controlling the d1 / d2 ratio within this range helps balance battery kinetic characteristics and lifespan.

[0007] In one possible implementation, d1:d2 = (0.03~0.1):1.

[0008] In this embodiment of the application, setting the ratio of d1 to d2 within this range is beneficial to further improve the performance of the battery cell.

[0009] In one possible implementation, d1 satisfies: 1μm≤d1≤10μm, and d2 satisfies: 40μm≤d2≤80μm.

[0010] In the embodiments of this application, on the one hand, the thickness of the first negative electrode active layer should not be too large compared to the second negative electrode active layer, which is beneficial to the service life of the battery cell; on the other hand, the thickness of the first negative electrode active layer should not be too small, which is beneficial to the dynamic performance of the battery cell.

[0011] In one possible implementation, 2μm≤d1≤5μm, 50μm≤d2≤70μm.

[0012] In the embodiments of this application, setting d1 and d2 within this range is beneficial to further improve the performance of the battery cells.

[0013] In one possible implementation, the mass per unit area of ​​the first negative electrode active layer is in the range of 0.002 mg / mm². 2 -0.02mg / mm 2 The mass range per unit area of ​​the second negative electrode active layer is 0.065 mg / mm². 2 -0.18mg / mm 2 .

[0014] In this embodiment, setting the mass range per unit area of ​​the first and second negative electrode active layers helps to reduce the decrease in battery kinetic performance caused by excessively low content of negative electrode active material, while also reducing the decrease in electrode porosity caused by excessively high content, which in turn affects ion transport and battery rate performance. Furthermore, compared to the second negative electrode active layer, the first negative electrode active layer has a lower mass per unit area, providing more migration channels and shorter diffusion paths for lithium ions, thereby improving the battery rate performance.

[0015] In one possible implementation, the mass per unit area of ​​the first negative electrode active layer is in the range of 0.005 mg / mm². 2 -0.015mg / mm 2 .

[0016] In this embodiment, setting the mass per unit area of ​​the first negative electrode active layer within this range is beneficial for further improving the performance of the battery cell.

[0017] In one possible implementation, the specific surface area S1 of the first negative electrode active material satisfies: S1 ≥ 8m² 2 / g, the specific surface area S2 of the second negative electrode active material satisfies: S2≤S1.

[0018] In this embodiment of the application, the specific surface area S1 of the first negative electrode active layer is greater than or equal to 8m². 2 At a density of / g, this design provides more reaction sites, enhancing the battery's electrochemical performance and charge storage capacity. Furthermore, during the initial charge / discharge cycle, the electrolyte reacts with the negative electrode active material to form an SEI film, which affects battery performance. The smaller specific surface area S2 in the second negative electrode active layer helps reduce irreversible lithium consumption. Simultaneously, the smaller S2 design reduces the contact area with the electrolyte, minimizing SEI film formation and electrolyte consumption, thereby improving the battery's initial charge / discharge efficiency and long-term lifespan.

[0019] In one possible implementation, the porosity P1 of the first negative electrode active layer and the porosity P2 of the second negative electrode active layer satisfy: P1≥P2.

[0020] In this embodiment, ensuring the porosity of the negative electrode film satisfies P1≥P2 not only improves the electrolyte's wetting rate on the electrode but also reduces the tortuosity of lithium ion migration, shortening the lithium ion transport path and thus improving the battery's rate performance. Furthermore, since P1 is greater than or equal to P2, the effective transport distance of lithium ions in the first negative electrode active layer is reduced, accelerating the lithium ion insertion process and thereby improving the battery's charging efficiency.

[0021] In one possible implementation, the first negative electrode active material comprises hard carbon, and the mass ratio ω1 of the hard carbon to the first negative electrode active material satisfies: ω1≥0.8.

[0022] In this embodiment, hard carbon material exhibits excellent kinetic performance and rapid lithium-ion intercalation capability. Therefore, hard carbon is used as the main material of the first negative electrode active material, and the mass range of ω1 is designed. This design can improve the kinetic performance of the first negative electrode active layer, expand the surface pulse rate window, and achieve high-rate pulse self-heating, thereby accelerating the charging process in low-temperature environments.

[0023] In one possible implementation, the first negative electrode active material further includes at least one of graphite, silicon carbon, and soft carbon.

[0024] In this embodiment, since hard carbon materials have low initial charge-discharge efficiency, combining them with other materials can optimize SEI film formation, reduce electrolyte consumption, and thus improve the battery's initial charge-discharge efficiency and stability. For example, graphite is beneficial for improving initial charge-discharge efficiency, silicon-carbon can enhance specific capacity, and soft carbon is beneficial for improving compatibility with electrolyte and cycle performance. Combining the advantages of these materials helps to improve the overall performance of the battery.

[0025] In one possible implementation, the second negative electrode active material comprises graphite, and the mass ratio ω2 of the graphite to the second negative electrode active material satisfies: ω2≥0.8.

[0026] In this embodiment, graphite possesses excellent conductivity and uniform lithium-ion insertion / extraction characteristics, which can reduce the contact resistance between the electrode and the current collector, thereby accelerating electron transport. Therefore, using graphite as the main material for the second negative electrode active material promotes the formation rate of a stable SEI film, helps reduce electrolyte decomposition, and decreases irreversible capacity loss during the first charge-discharge cycle, thus improving the battery's first charge-discharge efficiency.

[0027] In one possible implementation, the second negative electrode active material further includes a silicon-based material, which includes at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy.

[0028] In this embodiment, silicon-based materials possess a higher theoretical specific capacity compared to graphite, which helps improve battery energy density. Simultaneously, the high specific capacity of silicon-based materials accelerates lithium intercalation, enhancing the battery's rate performance. However, the initial charge-discharge efficiency of silicon-based materials is relatively low. Therefore, a suitable second negative electrode active material can be selected based on the actual application requirements of the battery.

[0029] In one possible implementation, the binder in the negative electrode film layer includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0030] In the embodiments of this application, the above-mentioned oil-based binder or water-based binder can be selected according to the actual usage requirements of the negative electrode sheet.

[0031] In one possible implementation, the binder in the first negative electrode active layer comprises polyvinylidene fluoride.

[0032] In this embodiment, polyvinylidene fluoride (PVDF) can linearly connect the active material and the current collector, thereby enhancing the contact between the active material, the conductive agent, and the current collector. Simultaneously, the microporous structure of PVDF increases the lithium-ion transport channels, which is beneficial for increasing the lithium-ion migration path and thus reducing charge transfer impedance, thereby enhancing the kinetic performance of the first negative electrode active layer.

[0033] In one possible implementation, the binder in the second negative electrode active layer includes at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0034] In this embodiment, the second negative electrode active layer uses the above-mentioned water-based binder, which is different from the oil-based binder of the first layer. This not only enhances the stability of the second negative electrode active layer, but also helps to reduce manufacturing costs.

[0035] In one possible implementation, the first negative electrode active layer is a single-layer structure, and the second negative electrode active layer is a multi-layer structure.

[0036] In this embodiment, the single-layer design of the first negative electrode active layer is beneficial for improving the lithium-ion transport speed and electron conductivity, thereby enhancing the battery's kinetic performance. The second negative electrode active layer employs a multi-layer structure; due to the interlocking effect between the active materials in the layers, a lower binder content is sufficient to meet stability requirements. This not only reduces the total binder content but also adapts to different particle size application scenarios. Thus, it is beneficial for further improving fast-charging performance while also ensuring a long battery lifespan.

[0037] In one possible implementation, the absolute value of the difference in interlayer binder content in the second negative electrode active layer is ≤1%.

[0038] In this embodiment, setting the absolute value of the difference in binder content between the layers in the second negative electrode active layer within this range helps improve the consistency of the negative electrode structure and the stability of battery performance. This design reduces localized stress concentration and electrochemical performance inhomogeneity, and also reduces the uneven distribution of internal electrode resistance. Simultaneously, the uniform distribution of the binder also helps maintain the long-term mechanical stability of the electrode.

[0039] Secondly, a method for preparing a battery cell is provided, comprising: providing a negative electrode sheet to prepare the battery cell; wherein providing the negative electrode sheet includes: providing a first negative electrode active material to prepare a first negative electrode slurry; wherein the volumetric particle size distribution of the first negative electrode active material is Dv50. 1 Satisfying: Dv50 1 ≤2μm, the volumetric particle size distribution Dv99 of the first negative electrode active material 1 Satisfying: Dv99 1 ≤5μm; providing a second negative electrode active material to prepare a second negative electrode slurry; wherein, the volumetric particle size distribution Dv50 of the second negative electrode active material is... 2 Satisfying: Dv50 2 ≥Dv99 1 The second negative electrode slurry is coated on at least one side of the negative electrode current collector to obtain a second negative electrode active layer; the first negative electrode slurry is coated on the surface of the second negative electrode active layer to obtain a first negative electrode active layer, thereby preparing the negative electrode sheet; wherein, the thickness d1 of the first negative electrode active layer and the thickness d2 of the second negative electrode active layer satisfy: d1:d2=(0.023~0.25):1.

[0040] In this embodiment, by setting the average particle size distribution and thickness of the first and second negative electrode active layers, the performance of the battery cell can be improved. Specifically, the volumetric particle size distribution Dv50 of the first negative electrode active material... 1 ≤2μm, Dv99 1 A diameter of ≤5μm helps reduce the ion transport distance of the first negative electrode active layer, improving kinetic performance. This expands the surface pulse rate window of the pulse battery, enhancing the self-heating effect of high-rate pulses. Furthermore, it improves the battery's short-term discharge and recharge power in low-temperature environments. Simultaneously, by designing the ratio of d1 to d2, it helps balance battery kinetic characteristics and lifespan.

[0041] In one possible implementation, d1:d2 = (0.03~0.1):1.

[0042] In this embodiment of the application, setting the ratio of d1 to d2 within this range can further improve the performance of the battery cell.

[0043] In one possible implementation, the method further includes: performing at least one of cold pressing, hot pressing, rolling pressing and ultrasonic treatment on the second negative electrode active layer, so that the porosity P1 of the first negative electrode active layer and the porosity P2 of the second negative electrode active layer satisfy: P1≥P2.

[0044] In this embodiment, ensuring the porosity of the negative electrode film layer satisfies P1≥P2 is beneficial for improving the rate performance and charging efficiency of the battery. Furthermore, the above solution allows for the selection of an appropriate porosity treatment method for the second negative electrode active layer based on the specific requirements and material characteristics of the battery, thus meeting the needs of different application scenarios.

[0045] In one possible implementation, the first negative electrode active material comprises hard carbon, and the mass ratio ω1 of the hard carbon to the first negative electrode active material satisfies: ω1≥0.8.

[0046] In this embodiment, hard carbon with high kinetics is used as the main material of the first negative electrode active material, which is beneficial to achieving a battery that balances kinetics and lifespan.

[0047] Thirdly, a battery is provided, comprising a battery cell according to the first aspect and any possible implementation thereof, and / or a battery cell obtained by a preparation method according to the second aspect and any possible implementation thereof.

[0048] Fourthly, an electrical device is provided, including the battery described in the third aspect. Attached Figure Description

[0049] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0050] Figure 1 is a schematic diagram of the negative electrode material according to an embodiment of this application;

[0051] Figure 2 is a schematic diagram of a battery cell according to an embodiment of this application;

[0052] Figure 3 is a schematic diagram of the structure of a battery cell according to another embodiment of this application;

[0053] Figure 4 is a flowchart of the preparation process of a battery cell according to an embodiment of this application;

[0054] Figure 5 is another process flow diagram of the preparation of a battery cell according to one embodiment of this application;

[0055] Figure 6 is a schematic diagram of a battery according to an embodiment of this application;

[0056] Figure 7 is a schematic diagram of the structure of a battery according to an embodiment of this application;

[0057] Figure 8 is a schematic diagram of the structure of an electrical device according to an embodiment of this application. Detailed Implementation

[0058] The following detailed description of the battery cell, its preparation method, battery, and power-consuming device of this application, with appropriate reference to the accompanying drawings, may omit unnecessary details. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0059] 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 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 "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.

[0060] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application 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 description, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the description, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a specific order or hierarchy.

[0061] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0062] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0063] Unless otherwise specified, all steps in 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.

[0064] The development of battery technology requires consideration of various design factors, such as energy density, cycle life, storage performance, charge / discharge rate, and reliability. However, when batteries are used in low-temperature environments, their charging rate, charging efficiency, and lifespan all decrease. Specifically, batteries exhibit higher impedance and correspondingly lower charging current at low temperatures. According to Joule's law, current significantly impacts heat generation. Therefore, the lower current at low temperatures leads to lower heating efficiency, thus affecting the battery's charging capability.

[0065] In view of this, this application provides a battery cell, a method for preparing the same, a battery, and an electrical device. The battery cell includes: a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer disposed on at least one side surface of the negative current collector, the negative electrode film layer including a first negative electrode active layer and a second negative electrode active layer, the second negative electrode active layer being located between the negative current collector and the first negative electrode active layer, the first negative electrode active layer including a first negative electrode active material, the second negative electrode active layer including a second negative electrode active material, wherein the volumetric particle size distribution of the first negative electrode active material is Dv50.1 Satisfying: Dv50 1 ≤2μm, the volumetric particle size distribution of the first negative electrode active material is Dv99 1 Satisfying: Dv99 1 ≤5μm; Volumetric particle size distribution Dv50 of the second negative electrode active material 2 Satisfying: Dv50 2 ≥Dv99 1 The thickness d1 of the first negative electrode active layer and the thickness d2 of the second negative electrode active layer satisfy: d1:d2=(0.023~0.25):1; optionally, d1:d2=(0.03~0.1):1.

[0066] Dv50 can refer to the particle size at which the cumulative particle size distribution number (CPD) of a sample reaches 50%, meaning that 50% of the particles are smaller than Dv50. Similarly, Dv99 can refer to the particle size at which the CPD of a sample reaches 99%, meaning that 99% of the particles are smaller than Dv99. Here, Dv50... 1 Dv50 2 and Dv99 1 It is only for distinguishing the volume average particle size of different substances.

[0067] In the above technical solution, by designing a layered negative electrode film layer, the volume particle size distribution of the first and second negative electrode active materials satisfies: Dv50. 2 ≥Dv99 1 Compared to the second negative electrode active material, the first negative electrode active material has a smaller average particle size. Therefore, the ion transport distance of the first negative electrode active material, which is farther from the current collector, is shorter, resulting in higher kinetic performance of the first negative electrode active layer. This improves the surface pulse rate window of the pulse battery, facilitating high-rate pulse self-heating. Simultaneously, the larger particle size of the second negative electrode active material reduces its specific surface area and the number of reaction sites on the surface. This reduces irreversible lithium consumption during film formation, thus benefiting battery lifespan. Furthermore, it improves the battery's short-term discharge and recharge power at low temperatures. Moreover, by setting d1:d2 = (0.023~0.25):1, the battery life is not affected by an excessively thick d1, nor is the kinetic performance affected by an excessively thin d1. Therefore, setting the d1:d2 ratio within this range is beneficial for balancing battery kinetics and lifespan. Furthermore, when the thickness of the negative electrode film is set to d1:d2 = (0.03~0.1):1, the negative electrode film has a more suitable thickness ratio, which is beneficial to further improve the performance of the battery.

[0068] The following description, with reference to the accompanying drawings, illustrates the battery cell, its preparation method, the battery, and the power-consuming device of this application.

[0069] Furthermore, the technical solution of this application can be applied to various batteries, such as lithium-ion batteries, lithium metal batteries, sodium-ion batteries, potassium-ion batteries, zinc-ion batteries, magnesium batteries, calcium batteries, zinc batteries, aluminum batteries, etc. This application does not limit them; for the sake of convenience, lithium-ion batteries will be used as an example for the following description.

[0070] [Battery cell]

[0071] This application provides a single battery cell. Typically, a single battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During the charging and discharging process of the battery cell, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte, acting as a conductor for the active ions, lies between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing the passage of active ions. In some embodiments, the above-mentioned battery cell is also referred to as a secondary battery, and the battery cell can be the smallest possible battery unit.

[0072] Next, the negative electrode, positive electrode, electrolyte, and separator of this application will be described with appropriate reference to the accompanying drawings.

[0073] [Negative electrode plate]

[0074] The negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one side surface of the negative current collector, wherein the negative electrode film layer includes a first negative electrode active layer and a second negative electrode active layer.

[0075] Figure 1 is a schematic diagram of the material of a negative electrode 121 according to an embodiment of this application. As shown in Figure 1, the negative electrode 121 includes a negative current collector 1211 and a negative electrode film layer disposed on at least one side surface of the negative current collector. The negative electrode film layer includes a first negative electrode active layer 1212 and a second negative electrode active layer 1213.

[0076] It should be noted that the negative electrode current collector 1211 has two opposite sides along its own thickness direction (z direction in Figure 1), the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector 1211, and the second negative electrode active layer 1213 is disposed between the negative electrode current collector 1211 and the first negative electrode active layer 1212, with the second negative electrode active layer 1213 located on the side closer to the negative electrode current collector 1211.

[0077] As one example, the negative electrode film layer is disposed on one side surface of the negative electrode current collector 1211. As another example, the negative electrode film layer is disposed on both sides surface of the negative electrode current collector 1211.

[0078] In embodiments of this application, the first negative electrode active layer 1212 comprises a first negative electrode active material, and the second negative electrode active layer 1213 comprises a second negative electrode active material. The volumetric particle size distribution Dv50 of the first negative electrode active material is... 1 Satisfying: Dv50 1 ≤2μm, the volumetric particle size distribution of the first negative electrode active material is Dv99 1 Satisfying: Dv99 1 ≤5μm; Volumetric particle size distribution Dv50 of the second negative electrode active material 2 Satisfying: Dv50 2 ≥Dv99 1 .

[0079] The above technical solution uses Dv50. 1 ≤2μm and Dv99 1 A first negative electrode active material with a diameter ≤5μm can reduce the ion diffusion distance of the first negative electrode active material, which is beneficial to improving the rate performance and kinetic characteristics of the battery. Furthermore, Dv50 is set... 2 ≥Dv99 1 Compared to the second negative electrode active material, the first negative electrode active material has a smaller average particle size. Therefore, the ion transport distance of the first negative electrode active material is shorter, further improving the kinetic performance of the first negative electrode active layer 1212. This design helps to expand the surface pulse rate window of the pulse battery, thereby promoting high-rate pulse self-heating. Furthermore, it also helps to improve the battery's short-term discharge power and recharge power in low-temperature environments.

[0080] On the other hand, the use of negative electrode active materials with different particle sizes in the above-mentioned technical solution is beneficial to battery life. Specifically, although the particle size of the second negative electrode active material is larger, resulting in lower kinetic performance than the first negative electrode active material, the larger particle size can reduce the specific surface area of ​​the second negative electrode active material, reducing the number of reaction sites on the surface. This helps to reduce irreversible lithium consumption during film formation, thereby extending battery life. Therefore, using negative electrode active materials with different particle sizes is beneficial for balancing battery kinetic performance and lifespan.

[0081] In the embodiments of this application, the thickness d1 of the first negative electrode active layer 1212 and the thickness d2 of the second negative electrode active layer 1213 satisfy the following ratio: d1:d2 = (0.023~0.25):1. For example, d1:d2 can be 0.023:1, 0.025:1, 0.03:1, 0.08:1, 0.13:1, 0.18:1, 0.25:1, or any value within the above range. Setting the ratio of d1 to d2 within the above range in the embodiments of this application is beneficial in reducing the impact on battery life due to excessively thick d1, and also beneficial in reducing the impact on battery dynamic performance due to excessively thin d1. Therefore, setting the range of the d1:d2 ratio is beneficial in balancing battery dynamics and lifespan.

[0082] Optionally, d1:d2 = (0.03 to 0.1):1. For example, d1:d2 can be 0.03:1, 0.05:1, 0.06:1, 0.08:1, 0.09:1, 0.1:1, or any value within the above range. In this way, the negative electrode film layer has a more suitable thickness ratio, which is beneficial to further improving the performance of the battery cell.

[0083] In some embodiments, d1 satisfies: 1μm≤d1≤10μm; d2 satisfies: 40μm≤d2≤80μm. For example, d1 is 1μm, 2μm, 3μm, 5μm, 6μm, 7μm, 8μm, 10μm or any value within the above range; d2 is 40μm, 45μm, 50μm, 55μm, 60μm, 70μm, 80μm or any value within the above range.

[0084] Optionally, 2μm ≤ d1 ≤ 5μm, and 50μm ≤ d2 ≤ 70μm. For example, d1 can be 2μm, 2.5μm, 3μm, 4μm, 5μm, or any value within the above range; d2 can be 50μm, 52μm, 55μm, 60μm, 65μm, 70μm, or any value within the above range. This results in a more suitable thickness ratio for the negative electrode film, which is beneficial for further improving the performance of the battery cell.

[0085] In some embodiments, the mass per unit area of ​​the first negative electrode active layer 1212 ranges from 0.002 mg / mm². 2 -0.02mg / mm 2 The mass range per unit area of ​​the second negative electrode active layer 1213 is 0.065 mg / mm². 2 -0.18mg / mm 2 For example, the mass per unit area of ​​the first negative electrode active layer 1212 ranges from 0.002 mg / mm². 2 0.004 mg / mm 2 0.006 mg / mm 2 0.008 mg / mm 20.01 mg / mm 2 0.015 mg / mm 2 0.02 mg / mm 2 Or any value within the above range; the mass range per unit area of ​​the second negative electrode active layer 1213 is 0.065 mg / mm². 2 0.1 mg / mm 2 0.11 mg / mm 2 0.12 mg / mm 2 0.13 mg / mm 2 0.15 mg / mm 2 0.17 mg / mm 2 0.18 mg / mm 2 Or any value within the above range.

[0086] In the above technical solution, the mass per unit area of ​​the first negative electrode active layer 1212 and the second negative electrode active layer 1213 is set within this range. This ensures that the battery's kinetic performance is not affected by excessively low content of negative electrode active material, nor is the electrode porosity reduced due to excessively high content of negative electrode active material, thus affecting ion transport and the battery's rate performance. Furthermore, setting the mass per unit area of ​​the first negative electrode active layer 1212 to be lower than that of the second negative electrode active layer 1213 helps the first negative electrode active layer 1212 provide more migration channels and shorter diffusion paths for lithium ions, thereby improving the battery's rate performance.

[0087] In some embodiments, the mass per unit area of ​​the first negative electrode active layer 1212 ranges from 0.005 mg / mm². 2 -0.015mg / mm 2 For example, the mass per unit area of ​​the first negative electrode active layer 1212 ranges from 0.005 mg / mm². 2 0.006 mg / mm 2 0.008 mg / mm 2 0.01 mg / mm 2 0.015 mg / mm 2 Or any value within the aforementioned range. In this way, the first negative electrode active layer 1212 has a more suitable mass range per unit area, which can further improve the performance of the battery cell.

[0088] In some embodiments, the specific surface area S1 of the first negative electrode active material satisfies: S1 ≥ 8m² 2 / g, the specific surface area S2 of the second negative electrode active material satisfies: S2≤S1. When S1 meets this range, it can provide more reaction sites and adsorption sites for the first negative electrode active layer 1212 to participate in electrochemical reactions, thereby improving the electrochemical performance of the battery. Furthermore, S1≥8m2 In the case of / g, the contact area between the first negative electrode active layer 1212 and the electrolyte can be increased, thereby improving the charge storage capacity and electrochemical reaction rate.

[0089] On the other hand, during the first charge and discharge of the battery, the electrolyte and the negative electrode active material react at the solid-liquid interface to form a stable solid electrolyte interface (SEI) film. However, the formation of the SEI film affects battery performance. For example, in lithium-ion batteries, this process inevitably consumes some lithium ions, and this consumption is irreversible. If the consumption of lithium ions exceeds a reasonable range, the overall performance of the battery will be significantly affected. The formation of the SEI film is related to the specific surface area of ​​the negative electrode film layer; a smaller specific surface area reduces excessive irreversible lithium consumption. Since the particle size of the first negative electrode active layer is small, it can meet the requirements for fast charging performance. The second negative electrode active layer 1213 is located on the side close to the negative electrode current collector 1211, and its smaller specific surface area S2 reduces the surface area in contact with the electrolyte, thereby reducing the formation of the overall negative electrode SEI film and electrolyte consumption, improving the battery's first charge and discharge efficiency and long-term lifespan.

[0090] During the charging process of a lithium-ion battery, lithium ions are released from the positive electrode active material, move and embed into the negative electrode material; while during the discharging process, lithium ions are released from the negative electrode material, move and embed into the positive electrode active material.

[0091] In some embodiments, the porosity P1 of the first negative electrode active layer 1212 and the porosity P2 of the second negative electrode active layer 1213 satisfy: P1 ≥ P2. Compared with the second negative electrode active layer 1213, the porosity P1 of the first negative electrode active layer 1212 is higher. This not only improves the electrolyte wetting rate but also reduces the tortuosity of lithium ion migration, thereby reducing the length of the lithium ion transport path and improving the rate performance of the battery. Simultaneously, due to the higher porosity of the first negative electrode active layer 1212, the effective transport distance of lithium ions is reduced, thereby accelerating the lithium ion insertion speed and improving the charging efficiency of the battery.

[0092] It should be understood that the “intercalation” process described in this application refers to the process in which lithium ions are intercalated in the positive electrode active material and the negative electrode material due to an electrochemical reaction, and the “deintercalation” and “deintercalation” processes described in this application refer to the process in which lithium ions are deintercalated in the positive electrode active material and the negative electrode material due to an electrochemical reaction.

[0093] In some embodiments, the first negative electrode active material includes hard carbon, and the mass ratio ω1 of hard carbon to the first negative electrode active material satisfies: ω1≥0.8. Specifically, hard carbon material has excellent kinetic performance and rapid lithium-ion intercalation capability. For pulse charging, it has a short charging time. Therefore, using hard carbon material in the first negative electrode active layer 1212 and designing a mass ratio ω1≥0.8 is beneficial to improve the surface high kinetics, thereby increasing the surface pulse rate window to achieve high-rate pulse self-heating.

[0094] In some embodiments, the first negative electrode active material further includes at least one of graphite, silicon carbon, and soft carbon. Since hard carbon materials have low initial charge-discharge efficiency, combining them with other materials can optimize SEI film formation, reduce electrolyte consumption, and improve the battery's initial charge-discharge efficiency and cycle stability. Graphite can improve the battery's initial charge-discharge efficiency, silicon carbon is beneficial for high specific capacity, and soft carbon, due to its good compatibility with the electrolyte, can improve cycle performance. Therefore, the first negative electrode active material uses hard carbon as the main material, and combines it with other carbon materials according to actual application requirements. This combines the advantages of various materials, thereby improving the battery's kinetic performance, cycle stability, and rate performance.

[0095] In some embodiments, the mass ratio of graphite to the first negative electrode active material is ≥0.8. Compared to hard carbon materials, graphite has lower kinetic performance, but higher initial charge-discharge efficiency. Furthermore, compared to the second negative electrode active layer 1213, the first negative electrode active layer 1212 has smaller particle size and a larger specific surface area, thus widening the lithium intercalation channels and improving the battery's kinetic performance. In other words, selecting a mass ratio of graphite to the first negative electrode active material ≥0.8 allows for maintaining the cell's initial charge-discharge efficiency without deterioration while improving the surface pulse rate window.

[0096] Therefore, the first negative electrode active material in this application embodiment can be selected as the main material according to actual usage requirements. For example, in scenarios requiring high kinetics, hard carbon material can be selected as the main material of the first negative electrode active material; in scenarios requiring high initial charge-discharge efficiency, graphite material can be selected as the main material of the first negative electrode active material. Through material selection and design, it is beneficial to improve the overall performance of the battery to meet different usage scenarios.

[0097] In some embodiments, the first negative electrode active material is a pre-lithiated negative electrode active material. Pre-lithiation treatment can improve the first charge-discharge efficiency of the battery. Specifically, pre-lithiation treatment improves the first charge-discharge efficiency of the battery by reducing irreversible lithium consumption during the first charge-discharge process. In the embodiments of this application, the pre-lithiation treatment includes at least one of chemical pre-lithiation, electrochemical pre-lithiation, mechanical pre-lithiation, and vacuum thermal treatment pre-lithiation. Pre-lithiation treatment can replenish lithium to the first negative electrode active material in different ways to compensate for the irreversible lithium consumption during the first charge-discharge process, thereby improving the overall performance of the battery.

[0098] In some embodiments, the second negative electrode active material includes graphite, and the mass ratio ω2 of graphite to the second negative electrode active material satisfies: ω2 ≥ 0.8. Since hard carbon, the main material in the first negative electrode active material, has low initial charge-discharge efficiency and poor cycle life, its large-area application would reduce battery performance. Therefore, the main material of the second negative electrode active material does not include hard carbon, but is instead graphite. Graphite has good conductivity and uniform lithium-ion insertion / extraction characteristics, which helps reduce the contact resistance between the electrode and the current collector, thereby promoting rapid electron transport. Simultaneously, this helps to quickly form a stable SEI film, reduce electrolyte decomposition, and reduce irreversible capacity loss during the first charge-discharge process, thereby improving the initial charge-discharge efficiency. Therefore, using graphite as the main material of the second negative electrode active layer 1213 is beneficial for improving the battery's initial charge-discharge efficiency.

[0099] In some embodiments, the second negative electrode active material further includes a silicon-based material, comprising at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Compared to graphite materials, silicon-based materials have a higher theoretical specific capacity but a lower initial charge-discharge efficiency. This means that silicon-based materials can improve the energy density of the battery. Furthermore, the higher specific capacity offered by silicon-based materials accelerates lithium intercalation, which is beneficial for improving the rate performance of the battery.

[0100] Therefore, depending on the specific application requirements of the battery, different material mass ratios can be selected in the second negative electrode active material. For example, when a higher initial charge-discharge efficiency is required, the mass ratio of graphite in the second negative electrode active material can be increased; when a higher battery energy density and rate performance are required, the mass ratio of graphite in the second negative electrode active material can be decreased. In some embodiments, the binder in the negative electrode film layer includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan. Depending on the actual application requirements of the negative electrode sheet, suitable oil-based or water-based binders can be used.

[0101] In some embodiments, the binder in the first negative electrode active layer 1212 comprises polyvinylidene fluoride (PVDF). PVDF can linearly connect the active material and the current collector to enhance the contact between the active material, the conductive agent, and the current collector. Furthermore, the PVDF binder contains micropores, which can provide channels for lithium ion conduction, increasing the lithium ion transport path and thereby reducing charge transfer resistance. Therefore, providing a PVDF binder in the first negative electrode active layer 1212 can improve the kinetics of the first negative electrode active layer 1212.

[0102] In the negative electrode 121, although PVDF has high kinetic performance, as an oily binder, it relies on oily solvents (such as N-methyl pyrrolidone (NMP)) during application. Extensive use of PVDF binder not only increases the cost of exhaust gas treatment, but the presence of PVDF in the negative electrode may also affect the overall stability of the battery. For example, PVDF thermal decomposition, chemical reactions, electrochemical instability, and mechanical property degradation during long-term cycling may lead to electrode material detachment, affecting battery performance and lifespan.

[0103] Based on this, in some embodiments, the binder in the second negative electrode active layer 1213 includes at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethyl methacrylate (PMAA), and carboxymethyl chitosan (CMCS). Therefore, the binder in the second negative electrode active layer 1213 differs from that in the first negative electrode active layer 1212, employing the aforementioned aqueous binder. For example, styrene-butadiene rubber is a commonly used binder in aqueous negative electrode slurries; it is water-soluble and, when used as a binder, works in conjunction with sodium carboxymethyl cellulose to achieve a binding effect and reduce slurry settling. The use of this aqueous binder helps improve the stability of the second negative electrode active layer 1213 and reduces production costs.

[0104] In some embodiments, the first negative electrode active layer 1212 is a single-layer structure, and the second negative electrode active layer 1213 is a multi-layer structure. This single-layer design of the first negative electrode active layer 1212 can provide a faster lithium-ion transport rate and better electronic conductivity, thereby improving the battery's kinetic performance. Furthermore, designing the second negative electrode active layer 1213 as a multi-layer structure allows for a lower binder content to meet stability requirements due to the interlocking effect between the active materials in the layers, thus reducing the total binder content in the negative electrode active layer. On the other hand, it also allows for the application of materials with different particle sizes, which is beneficial for further improving fast-charging performance and ensuring a long battery life.

[0105] It should be noted that the aforementioned lower binder content is also beneficial to battery performance. Specifically, during the coating and drying process of the negative electrode 121, due to moisture evaporation, a certain degree of binder migration to the upper layer of the electrode will occur. In the embodiments of this application, the upper layer of the electrode is the first negative electrode active layer 1212. However, excessive binder content in the first negative electrode active layer 1212 will reduce battery kinetics, thereby deteriorating its fast-charging capability. Therefore, using a lower binder content is also beneficial to battery performance.

[0106] In some embodiments, the absolute value of the difference in the content of the interlayer binder in the second negative electrode active layer 1213 is ≤1%. The uniformity of binder distribution in the electrode affects battery performance. Designing the absolute value of the difference in the content of the interlayer binder within this range is beneficial to the uniformity of the internal structure of the negative electrode 121 and the consistency of battery performance. Specifically, this difference in binder content can reduce local stress concentration or electrochemical performance inhomogeneity, and can also reduce the non-uniform distribution of internal resistance of the electrode. In addition, the uniform distribution of binder content helps maintain the long-term mechanical stability of the electrode structure and reduces material shedding or structural damage that may occur during cycling.

[0107] 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 substrate and a metal layer formed on at least one surface of the polymer 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0108] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0109] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0110] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0111] [Positive electrode plate]

[0112] The positive electrode sheet may include a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0113] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0114] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0115] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following: lithium-containing transition metal oxides, lithium phosphates with an olivine structure, or materials with a spinel structure. 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 transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNiO2). 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 Mn0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, 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 manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0116] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0117] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0118] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, 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.

[0119] [Electrolytes]

[0120] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0121] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0122] 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.

[0123] 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.

[0124] 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 may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0125] [Isolation membrane]

[0126] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0127] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0128] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0129] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0130] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0131] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 is a schematic diagram of a battery cell according to one embodiment of this application.

[0132] Figure 3 is a schematic diagram of the structure of a battery cell according to another embodiment of this application. As shown in Figure 3, the outer packaging of the battery cell 100 includes a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The shell 11 has an opening communicating with the receiving cavity, and the cover plate 13 can cover the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 100 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0133] In some embodiments, the battery cells 100 can also be assembled into a battery module. The number of battery cells 100 contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0134] [Preparation methods for battery cells]

[0135] Figure 4 is a flowchart illustrating the preparation process of a single battery cell according to an embodiment of this application. As shown in Figure 4, the method 200 for preparing the negative electrode sheet includes the following steps:

[0136] S210 provides a negative electrode 121 for preparing a battery cell.

[0137] As shown in Figure 5, step S210 above may specifically include:

[0138] S211, providing a first negative electrode active material to prepare a first negative electrode slurry; wherein, the volumetric particle size distribution of the first negative electrode active material is Dv50. 1 Satisfying: Dv50 1 ≤2μm, the volumetric particle size distribution of the first negative electrode active material is Dv99 1 Satisfying: Dv99 1 ≤5μm;

[0139] S212 provides a second negative electrode active material to prepare a second negative electrode slurry; wherein the volumetric particle size distribution of the second negative electrode active material is Dv50. 2 Satisfying: Dv50 2 ≥Dv99 1 ;

[0140] S213, the second negative electrode slurry is coated on at least one side surface of the negative electrode current collector 1211 to obtain the second negative electrode active layer 1213;

[0141] S214, the first negative electrode slurry is coated on the surface of the second negative electrode active layer to obtain the first negative electrode active layer 1212, so as to prepare the negative electrode sheet 121; wherein, the thickness d1 of the first negative electrode active layer 1212 and the thickness d2 of the second negative electrode active layer 1213 satisfy: d1:d2=(0.023~0.25):1.

[0142] Specifically, in S211, the first negative electrode active material adopts a volume particle size distribution of Dv50. 1 ≤2μm and Dv99 1 ≤5μm helps reduce the ion diffusion distance of the first negative electrode active material, thereby improving the rate performance and kinetic characteristics of the battery.

[0143] In S212, the average particle size of the first negative electrode active material is smaller than that of the second negative electrode active material. This design helps to reduce the ion transport distance of the first negative electrode active material, thereby improving the kinetic performance of the first negative electrode active layer 1212. In other words, this design can expand the surface pulse rate window of the pulse battery, thereby promoting high-rate pulse self-heating. Furthermore, Dv50 is set... 2 ≥Dv99 1 The negative electrode film layer helps to improve the battery's lifespan.

[0144] In S213, as an example, the negative electrode film layer is disposed on one side surface of the negative electrode current collector 1211. As another example, the negative electrode film layer is disposed on both sides surface of the negative electrode current collector 1211.

[0145] In some embodiments, step S213 further includes drying the second negative electrode active layer 1213 to remove the solvent from it. The drying process includes at least one of forced-air drying, hot-air drying, vacuum drying, freeze-drying, constant-temperature drying, and microwave drying. Different drying methods are suitable for different production needs and material properties. Specifically, forced-air drying uses a circulating fan to blow hot air, balancing the temperature inside the chamber to achieve the drying effect; hot-air drying uses heated airflow to improve drying efficiency and accelerate solvent evaporation; vacuum drying is suitable for drying heat-sensitive electrodes, reducing material degradation caused by high temperatures; freeze-drying is suitable for electrodes that are extremely sensitive to temperature, maintaining the electrode's structure and activity; constant-temperature drying is suitable for electrodes requiring precise control of drying conditions, maintaining consistent electrode quality; microwave drying is fast, efficient, and can penetrate materials, making it suitable for uniformly drying electrodes.

[0146] Therefore, in the embodiments of this application, appropriate drying technology can be selected according to the needs of various types of second negative electrode active layers 1213 to efficiently and accurately remove the solvent and moisture from the second negative electrode active layer 1213.

[0147] In S214, the thickness of the first negative electrode active layer 1212 is thinner than the thickness of the second negative electrode active layer 1213. For example, d1:d2 is 0.023:1, 0.025:1, 0.03:1, 0.08:1, 0.13:1, 0.18:1, 0.25:1, or any value within the above range. Setting the ratio of d1 to d2 within the above range is beneficial to reduce the impact on battery life due to excessively thick d1, and also beneficial to reduce the impact on battery kinetic performance due to excessively thin d1. Therefore, setting the range of the d1:d2 ratio is beneficial to balance battery kinetics and lifespan.

[0148] Optionally, d1:d2 = (0.03 to 0.1):1. For example, d1:d2 can be 0.03:1, 0.05:1, 0.06:1, 0.08:1, 0.09:1, 0.1:1, or any value within the above range. In this way, the negative electrode film layer has a more suitable thickness ratio, which is beneficial to further improving the performance of the battery cell.

[0149] In some embodiments, step S214 further includes drying the first negative electrode active layer 1212 to remove solvent from the negative electrode sheet 121. The drying process includes at least one of forced-air drying, hot-air drying, vacuum drying, freeze-drying, constant-temperature drying, and microwave drying. During the preparation of the electrode sheet 121, a suitable drying method can be selected according to the specific needs of different application scenarios.

[0150] In some embodiments, the preparation method 200 further includes: performing at least one of cold pressing, hot pressing, rolling pressing and ultrasonic treatment on the second negative electrode active layer 1213, so that the porosity P1 of the first negative electrode active layer 1212 and the porosity P2 of the second negative electrode active layer 1213 satisfy: P1≥P2.

[0151] Specifically, by setting P1≥P2, not only can the wetting rate of the electrolyte be improved, but the tortuosity of lithium-ion migration can also be reduced, thereby shortening the length of the lithium-ion transport path and improving the rate performance of the battery. Furthermore, setting the first negative electrode active layer 1212 to have higher porosity shortens the effective transport distance of lithium ions, thereby increasing the lithium-ion insertion speed and improving the battery's charging efficiency.

[0152] It should be noted that the porosity treatment of the second negative electrode active layer 1213 in this embodiment includes at least one of cold pressing, hot pressing, rolling pressing, and ultrasonic treatment. Each method has its own characteristics and applicable scope.

[0153] Specifically, cold pressing involves compressing the negative electrode active material at room temperature to increase its density and reduce its porosity. This method is characterized by its simplicity, low cost, and suitability for materials that are not easily altered at high temperatures. However, cold pressing may not achieve very high compaction densities, making it potentially less than ideal for batteries requiring high energy density.

[0154] Hot pressing involves compressing the negative electrode active material under heating conditions, which increases the material's compaction density and reduces porosity. The advantage of hot pressing is that it achieves higher compaction density, thereby increasing the battery's energy density. This method is suitable for materials that are stable at high temperatures and do not easily decompose. However, hot pressing requires more expensive equipment and has higher operating costs.

[0155] Roll pressing involves continuously rolling the negative electrode active layer with rollers to achieve a uniform distribution and reduction of porosity. This method is characterized by high production efficiency, suitability for large-scale production, and the ability to achieve relatively uniform compaction. Roll pressing is suitable for materials with a certain degree of plasticity, but may cause fracture in excessively brittle materials.

[0156] Ultrasonic treatment utilizes high-frequency vibrations to improve the pore structure of the negative electrode active layer. This method is characterized by its non-contact processing, which avoids mechanical damage to the material and enables microscopic porosity adjustment. Ultrasonic treatment is suitable for applications requiring precise pore structure control, but it may require more complex equipment and incur higher costs. Therefore, depending on the specific requirements of the battery design and the characteristics of the material, different porosity treatment methods can be selected for the second negative electrode active layer 1213 to adapt to diverse application scenarios.

[0157] In some embodiments, the preparation method 200 further includes: performing at least one of cold pressing, hot pressing, rolling pressing, and ultrasonic treatment on the first negative electrode active layer 1212. It should be noted that during the preparation of the negative electrode sheet, the first negative electrode active layer 1212 can be treated as described above first, or the second negative electrode active layer 1213 can be treated as described above first; this application does not impose any limitation on this.

[0158] In some embodiments, the first negative electrode active material includes hard carbon, and the mass ratio ω1 of hard carbon to the first negative electrode active material satisfies: ω1≥0.8. By using hard carbon, which has excellent kinetic performance, as the main component of the first negative electrode active material, it is beneficial to achieve a battery with high kinetic requirements and long lifespan.

[0159] In some embodiments, the preparation method 200 further includes: pre-lithiation treatment of the first negative electrode active material to obtain a pre-lithiation treated first negative electrode active material. Pre-lithiation treatment refers to reacting the negative electrode material with lithium metal or lithium compounds before battery assembly, thereby pre-intercalating lithium ions into the negative electrode material to improve battery performance.

[0160] In some embodiments, the pre-lithiation treatment includes pre-lithiation of the hard carbon in the first anode active material. This is beneficial for improving the initial charge-discharge efficiency of the main material in the first anode active material. It should be noted that, in the embodiments of this application, the pre-lithiation treatment includes at least one of chemical pre-lithiation, electrochemical pre-lithiation, mechanical pre-lithiation, and vacuum thermal treatment pre-lithiation.

[0161] Chemical pre-lithiation involves preparing pre-lithiated positive and negative electrode materials by adding a lithium source to a mixed solution containing an aromatic composition and an organic solvent to form a lithiation solution. The negative electrode powder is then added to the lithiation solution and dried to obtain the pre-lithiated negative electrode material. Electrochemical pre-lithiation involves forming an SEI film through an electrochemical reaction during the construction of a temporary battery or electrochemical device. This electrochemical pre-lithiation method can effectively improve the lithium insertion depth and efficiency, reduce irreversible capacity loss, and increase battery capacity. Mechanical pre-lithiation involves physically mixing lithium powder with the negative electrode active material and then pressing or coating it onto the negative electrode during battery manufacturing. Vacuum heat treatment pre-lithiation refers to mixing the negative electrode material with lithium metal or lithium compounds under vacuum conditions and then performing heat treatment to allow lithium to diffuse uniformly into the negative electrode material. In practical battery applications, appropriate pre-lithiation methods can be selected based on different requirements.

[0162] This application also provides a battery and an electrical device. The battery and electrical device of this application will now be described with appropriate reference to the accompanying drawings.

[0163] [Battery]

[0164] This application provides a battery, including the battery cell described in the above embodiments.

[0165] Figure 6 is a schematic diagram of a battery according to one embodiment of this application, and Figure 7 is a structural schematic diagram of a battery according to one embodiment of this application. Referring to Figures 6 and 7, the battery 400 may include a battery case and a plurality of battery cells 100 disposed in the battery case. The battery case includes an upper case 401 and a lower case 402, the upper case 401 being able to cover the lower case 402 and forming a closed space for accommodating the battery cells 100. The plurality of battery cells 100 may be arranged in the battery case in any manner.

[0166] [Electrical appliances]

[0167] This application also provides an electrical device that includes the battery described in the foregoing embodiments. The electrical device includes at least one of the battery cell 100 or battery 400 provided in this application. The battery cell 100 or battery 400 can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0168] For example, Figure 8 is a schematic diagram of the structure of an electrical device according to one embodiment of this application. As shown in Figure 8, the electrical device is a vehicle 1, which can be a gasoline vehicle, a natural gas vehicle, or a new energy vehicle. A new energy vehicle can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. A motor 500, a controller 600, and a battery 400 can be installed inside the vehicle 1. The controller 600 controls the battery 400 to supply power to the motor 500. For example, the battery 400 can be installed at the bottom, front, or rear of the vehicle 1. The battery 400 can be used to power the vehicle 1; for example, the battery 400 can serve as the operating power source for the vehicle 1's electrical system, such as meeting the power requirements for starting, navigation, and operation of the vehicle 1. In another embodiment of this application, the battery 400 can not only serve as the operating power source for the vehicle 1 but also as the driving power source for the vehicle 1, replacing or partially replacing gasoline or natural gas to provide driving power to the vehicle 1.

[0169] As the electrical device, either battery cell 100 or battery 400 can be selected according to its usage requirements.

[0170] The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the battery for this electrical device, a 100-cell battery or a 400-cell battery can be used.

[0171] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell (100) as their power source.

[0172] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0173] [Examples and Comparative Examples]

[0174] [Example 1]

[0175] (1) Preparation of the positive electrode sheet:

[0176] Lithium iron phosphate powder, conductive carbon, polyvinylidene fluoride, and surfactant were mixed uniformly in a mass ratio of 97.2%:0.5%:1.8%:0.5%. NMP was then added and stirred thoroughly to prepare a positive electrode slurry. This slurry was then coated on both sides of a positive electrode current collector. After drying, cold pressing, and die-cutting, the positive electrode active layer was obtained to prepare the positive electrode sheet. The mass per unit area of ​​the positive electrode active layer was 0.16 mg / mm². 2 .

[0177] (2) Preparation of negative electrode sheet:

[0178] The slurry for the second negative electrode active layer is prepared by dissolving artificial graphite, conductive carbon, sodium carboxymethyl cellulose, and styrene-butadiene rubber in deionized water at a mass ratio of 95%:2.5%:1%:1.5%. After thorough mixing, the second negative electrode slurry is coated onto both sides of the negative electrode current collector, and then dried and cold-pressed to obtain the second negative electrode active layer. The second negative electrode active layer, designed as a single layer, has a thickness of 65 μm and contains 1.5% styrene-butadiene rubber as a binder. The Dv50 of the artificial graphite is... 2 The thickness is 10 μm, and the initial charge / discharge efficiency is 93%; the mass per unit area of ​​the second negative electrode active layer is 0.07 mg / mm². 2 Specific surface area is 10m² 2 / g.

[0179] The slurry for the first negative electrode active layer is prepared by mixing hard carbon, conductive carbon, polyvinylidene fluoride (PVDF), and surfactant in a mass ratio of 95%, 2.5%, 2%, and 0.5%, respectively. NMP is then added and the mixture is thoroughly stirred to prepare the first negative electrode slurry. This first negative electrode slurry is then coated onto both sides of the second negative electrode active layer. After drying, it is die-cut into strips to obtain the negative electrode sheet. The thickness of the first negative electrode active layer is 2 μm, the d1:d2 ratio is 0.031:1, and the binder is PVDF. The hard carbon has a Dv50 content. 1 1μm, Dv99 1 The thickness is 2μm, and the initial charge / discharge efficiency is 75%; the mass per unit area of ​​the first negative electrode active layer is 0.005mg / mm². 2 Specific surface area is 10m² 2 / g.

[0180] (3) Separating membrane:

[0181] A 7μm thick polypropylene membrane is used, comprising a 2μm thick ceramic coating disposed on either side of the base membrane, and an adhesive layer disposed on both sides of the base membrane, wherein the mass per unit area of ​​the adhesive layer is 1.5mg / 1540.25mm². 2 .

[0182] (4) Preparation of electrolyte:

[0183] The film-forming additives used are vinylene carbonate (VC), solvent ethylene carbonate (EC), and dimethyl carbonate (DMC).

[0184] A mixed solution of lithium hexafluorophosphate, vinylene carbonate (VC), ethylene carbonate solvent (EC), and dimethyl carbonate (DMC) in a mass ratio of 15%:2%:13%:70% was used as the electrolyte.

[0185] (5) Preparation of lithium-ion batteries:

[0186] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an aluminum shell (300 mm long, 101.5 mm high, and 52.5 mm thick), and the electrolyte prepared above is added. After processes such as encapsulation, electrolyte injection, formation, and degassing, a lithium-ion battery is obtained.

[0187] [Example 2]

[0188] The difference between Example 2 and Example 1 is that the hard carbon Dv50 1 and Dv99 1 different.

[0189] [Example 3]

[0190] The difference between Example 3 and Example 2 is that the Dv50 of graphite... 2 different.

[0191] [Examples 4-7]

[0192] The difference between Examples 4-7 and Example 1 is that the thickness of the first negative electrode active layer is different, and the ratio d1 to d2 is different.

[0193] [Examples 8-9]

[0194] The difference between Examples 8-9 and Example 1 is that the thickness of the second negative electrode active layer is different, and the ratio d1 to d2 is different.

[0195] [Examples 10-11]

[0196] The difference between Examples 10-11 and Example 1 is that the mass per unit area of ​​the first negative electrode active layer is different.

[0197] [Example 12]

[0198] The difference between Example 12 and Example 1 is that the specific surface area of ​​the second negative electrode active layer is different.

[0199] [Example 13]

[0200] The difference between Example 13 and Example 1 is that the specific surface area of ​​the first negative electrode active layer is different.

[0201] [Examples 14-15]

[0202] The difference between Examples 14-15 and Example 1 is that the mass per unit area of ​​the second negative electrode active layer is different.

[0203] [Example 16]

[0204] The difference between Example 16 and Example 1 is that the first negative electrode active layer undergoes pre-lithiation treatment using a chemical pre-lithiation method. Specifically, pre-lithiated positive and negative electrode materials are prepared by adding a lithium source to a mixed solution containing an aromatic composition and an organic solvent to form a lithiation solution. Then, the negative electrode powder material is added to the lithiation solution and dried to obtain the pre-lithiated negative electrode material, which has an initial charge-discharge efficiency of 93%.

[0205] [Example 17]

[0206] The difference between Example 17 and Example 1 is that the adhesive material of the second negative electrode active layer is different, and polyacrylic acid adhesive is used.

[0207] [Examples 18-19]

[0208] The difference between Examples 18-19 and Example 1 is that the number of layers in the second negative electrode active layer is different, and the content of binder in the second negative electrode active layer is different.

[0209] [Example 20]

[0210] The difference between Example 20 and Example 1 is that the first negative electrode active material is different; graphite material is used, and its initial charge-discharge efficiency is 93%.

[0211] [Example 21]

[0212] The difference between Example 21 and Example 20 is that the first negative electrode active material is different, using hard carbon and graphite materials, and its first charge-discharge efficiency is 93%.

[0213] [Example 22]

[0214] The difference between Example 22 and Example 20 is that the first negative electrode active material is different, using hard carbon, soft carbon and silicon carbon materials.

[0215] [Example 23]

[0216] The difference between Example 23 and Example 1 is that the second negative electrode active material is different, using graphite and silicon carbide materials.

[0217] [Comparative Example 1]

[0218] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not have a first negative electrode active layer.

[0219] [Comparative Example 2]

[0220] The difference between Comparative Example 2 and Example 1 is that there is no first negative electrode active layer, and the number of layers and the content of binder in the second negative electrode active layer are different.

[0221] Table 1 shows the specific parameters of the first negative electrode active layer during the preparation of the battery cell; Table 2 shows the specific parameters of the second negative electrode active layer during the preparation of the battery cell; Table 3 shows the relevant test results of the battery cell.

[0222] Table 1. Specific parameters of Examples 1-23 and Comparative Examples 1-2

[0223] In Table 1, Dv50 1 The particle size at which the cumulative particle size distribution of the first negative electrode active material reaches 50% can be defined as the particle size at which 50% of the particles are smaller than Dv99. 1 The particle size at which the cumulative particle size distribution of the first negative electrode active material reaches 99% can be defined as the particle size at which 99% of the particles are smaller than this value.

[0224] Table 2 Specific parameters of Examples 1-23 and Comparative Examples 1-2

[0225] In Table 2, Dv50 2 The particle size at which the cumulative particle size distribution of the second negative electrode active material reaches 50% can be defined as the particle size at which 50% of the particles are smaller than this value.

[0226] [Physical Characterization of Electrodes]

[0227] (1) Thickness measurement

[0228] The thickness of the first negative electrode active layer and the second negative electrode active layer were measured using a micrometer.

[0229] (2) Test of volumetric particle size distribution

[0230] Volume average particle size can be determined using a particle size analyzer-laser diffraction method. Specifically, refer to standard GB / T19077-2016, using a laser diffraction scattering particle size analyzer, and measure according to the manufacturer's instructions. As an example, take an appropriate amount of composite material and test the volume average particle size of the material using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer. Specifically, take an appropriate amount of the sample to be tested (sample concentration of 8-12% opacity is sufficient), add 20 ml of deionized water, and simultaneously sonicate externally for 5 min (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, measure the sample according to GB / T19077-2016 / ISO 13320:2009 standard.

[0231] (3) Measurement of mass per unit area

[0232] The sample to be weighed is cut into pieces with an area of ​​1540.25 mm² using a punching die. 2 The discs were then weighed using an electronic balance, and the weight was recorded. The mass per unit area was then calculated.

[0233] (4) Measurement of specific surface area

[0234] The tests were performed directly using the American Mach Gemini VII 239 multi-station fully automated specific surface area and porosity analyzer.

[0235] (5) Porosity measurement

[0236] GB / T 24586-2009 Measurement of Porosity. This includes pretreatment: using tweezers, select more than 20 original samples with good appearance and no powder shedding from the edges, place them in a sample cup, record the number of samples, and calculate the apparent volume; measurement: place the sample cup containing the sample in a true density analyzer within a closed testing system, introduce helium gas according to the procedure, detect the gas pressure in the sample chamber and expansion chamber, and then calculate the true volume according to Bohr's Law (PV = nRT), thus obtaining the porosity of the sample to be tested.

[0237] [Lithium-ion Battery Performance Characterization]

[0238] (1) Measurement of volumetric energy density

[0239] The lithium-ion battery was placed at 25°C and charged at a constant current rate of 0.33C to 3.8V, then charged at a constant voltage of 3.8V until the current rate dropped to 0.05C. After resting for 10 minutes, it was discharged at a constant current rate of 0.33C to 2.0V. The corresponding capacity at this point was recorded as the battery's discharge capacity C0. The length, width, and height of the lithium-ion battery were measured using calipers, and the volume V of the single cell was calculated to be 300mm * 101.5mm * 52.5mm. The volumetric energy density of the battery cell, VED, is calculated as (C0 × discharge plateau voltage of the lithium-ion battery) / V, in Wh / L. During this process, the battery's chemical system remained consistent, and the plateau voltage U was 3.22V. It should be understood that the discharge plateau voltage of lithium-ion batteries with different positive and negative electrode systems varies, and this can be obtained by testing their charge-discharge curves or referring to existing literature.

[0240] (2) DC internal resistance test

[0241] Direct current resistance (DCR) characterizes a battery's power performance. Generally, the lower the DCR, the better the battery's power performance.

[0242] The lithium-ion battery was placed at 25℃ and charged at a constant current rate of 0.33C to 3.8V, then charged at a constant voltage of 3.8V until the current rate dropped to 0.05C. After resting for 10 minutes, it was discharged at a constant current rate of 0.33C to 2.0V, and the discharge capacity C0 was recorded. Then, it was charged at a constant current rate of 0.33C to 3.8V, then charged at a constant voltage of 3.8V until the current rate dropped to 0.05C, at which point the battery's SOC was 100%. After resting for 10 minutes, it was discharged at a constant current rate of 0.33C to a capacity of 0.9C0Ah, adjusting the battery's SOC to 10%, and the cutoff voltage V1 was recorded. Next, the battery was placed in an environment of -20℃. After the battery cooled to -20℃, it was discharged at a rate of 2C for 0.5s, and the cutoff voltage V2 after 0.5s was recorded. The DC internal resistance DCR was calculated using (V1-V2) / 2C.

[0243] (3) Detection of lithium plating by pulse cycling

[0244] The lithium-ion battery was placed at 25℃ and charged at a constant current rate of 0.33C to 3.8V, then charged at a constant voltage of 3.8V until the current rate dropped to 0.05C. After resting for 10 minutes, it was discharged at a constant current rate of 0.33C to 2.0V, and the discharge capacity C0 was recorded. After resting for 10 minutes, it was charged at a constant current rate of 0.33C to 3.8V, then charged at a constant voltage of 3.8V until the current rate dropped to 0.05C. After resting for 10 minutes, it was discharged at a constant current rate of 0.33C to a capacity of 0.9C0Ah, adjusting the battery's SOC to 10%. Subsequently, the battery was placed in an environment of -20℃. After the battery cooled to -20℃, a pulse cycle test was performed at a 2C rate (0.5s discharge, 0.5s recharge, 3000 cycles). Next, place the battery at 25°C. After the battery reaches 25°C, charge it at a constant current rate of 0.33C to 3.8V, then charge it at a constant voltage rate of 3.8V until the current rate drops to 0.05C. Let it stand for 10 minutes, then discharge it at a constant current rate of 0.33C to 2.0V. Record the discharge capacity Cn at this time and calculate the capacity retention rate Cn / C0 after the cycle. Finally, charge it at a constant current rate of 0.33C to 3.8V, then charge it at a constant voltage rate of 3.8V until the current rate drops to 0.05C. Fully charge the battery, disassemble the battery cell and record whether lithium plating occurs on the negative electrode.

[0245] (4) Capacity retention test

[0246] The lithium-ion battery was placed at 25°C and charged at a constant current rate of 0.33C to 3.8V, then charged at a constant voltage of 3.8V until the current rate dropped to 0.05C. After resting for 10 minutes, it was discharged at a constant current rate of 0.33C to 2.0V, and the discharge capacity C0 was recorded. Then, it was charged at a constant current rate of 0.33C to 3.8V, and then charged at a constant voltage of 3.8V until the current rate dropped to 0.05C. At this point, the battery's state of charge (SOC) was 100%. After resting for 10 minutes, discharge at a constant current rate of 0.33C to a capacity of 0.9C0Ah, adjusting the battery SOC to 10%. Next, place the battery in an environment of -20℃. After the battery cools down to -20℃, charge it at 2C for 0.5s, then discharge it for 0.5s, recording this as one cycle. After 10,000 cycles, adjust the ambient temperature to 25℃. After the battery surface temperature reaches 25℃, charge it at a constant current rate of 0.33C to 3.8V, then charge it at a constant voltage of 3.8V until the current rate drops to 0.05C. Let it rest for 10 minutes, then discharge it at a constant current rate of 0.33C to 2.0V. Record this actual discharge capacity C1, and calculate the capacity retention rate based on C1 / C0.

[0247] Table 3 Test results of Examples 1-23 and Comparative Examples 1-2

[0248] In Table 3, VED is the volumetric energy density of a single battery cell, and DCR is the DC internal resistance.

[0249] In this application, capacity retention rate is used to characterize the cycle performance of a battery. The higher the capacity retention rate, the higher the capacity is retained after the battery has cycled to a specific number of times, which means that the battery has better cycle performance and lifespan.

[0250] As shown in Table 3, based on Example 1 and Comparative Example 1, the technical solution of this application, by setting a first negative electrode active layer and a single-layer second negative electrode active layer, and designing different particle sizes and thicknesses of the negative electrode active layers within a certain range, is beneficial to reduce the DCR of the battery cell, and can improve the capacity retention rate while reducing lithium plating.

[0251] As shown in Table 3, based on Example 18 and Comparative Example 2, the technical solution of this application, by setting a first negative electrode active layer and a double-layered second negative electrode active layer, and designing different particle sizes and thicknesses of the negative electrode active layers within a certain range, is beneficial to reduce the DCR of the battery cell, and can improve the capacity retention rate while reducing lithium plating.

[0252] Referring to Table 3, and based on Examples 2 and 1, it can be seen that when the first negative electrode active material is set within a suitable range, Dv50 1 and Dv99 1 The smaller the value, the better it is to reduce the DCR of individual battery cells, and while reducing lithium plating, it can also improve capacity retention.

[0253] Referring to Table 3, and based on Examples 3 and 2, it can be seen that when the second negative electrode active material is set within a suitable range, Dv50 2 Smaller size is beneficial for increasing volumetric energy density, reducing the DCR of individual cells, and improving capacity retention while reducing lithium plating.

[0254] As shown in Table 3, based on Examples 4-7 and Example 1, the d1:d2 ratio varies with the thickness of the first negative electrode active layer. Within a certain range, the thinner the first negative electrode active layer, the smaller the d1:d2 ratio, which is beneficial for improving the volumetric energy density. When d1 is 2μm to 5.2μm and d1:d2 is 0.03 to 0.1, the DCR of the battery cell can be reduced, and the capacity retention rate can be improved.

[0255] As shown in Table 3, based on Examples 8-9 and Example 1, the ratio of d1 to d2 varies depending on the thickness of the second negative electrode active layer. Within a certain range, a thinner second negative electrode active layer results in a larger d1:d2 ratio, which is beneficial for improving volumetric energy density. Conversely, a thicker second negative electrode active layer results in a smaller d1:d2 ratio, which is beneficial for reducing the DCR of individual battery cells and improving capacity retention. By further adjusting the ranges of d2 and d1:d2, it is possible to balance volumetric energy density, reduce the DCR of individual battery cells, and improve capacity retention while reducing lithium plating.

[0256] Referring to Table 3, and based on Examples 10-11 and Example 1, it is evident that the mass per unit area of ​​the first negative electrode active layer varies. Within a certain range, reducing the mass per unit area of ​​the first negative electrode active layer is beneficial for increasing the volumetric energy density. Conversely, increasing the mass per unit area of ​​the first negative electrode active layer is beneficial for reducing the DCR of the battery cells, minimizing lithium plating, and improving capacity retention. Further adjusting the mass per unit area of ​​the first negative electrode active layer is beneficial for simultaneously increasing the volumetric energy density, reducing the DCR of the battery cells, minimizing lithium plating, and maintaining capacity retention.

[0257] As shown in Table 3, based on Examples 12 and 1, the specific surface area of ​​the second negative electrode active layer differs. Within a certain range, provided S2 ≤ S1, a smaller specific surface area of ​​the second negative electrode active layer is beneficial for improving volumetric energy density. Within a certain range, increasing the specific surface area of ​​the second negative electrode active layer helps reduce lithium plating, lowers the DCR of the battery cell, and improves capacity retention.

[0258] As shown in Table 3, based on Examples 13 and 1, the specific surface area of ​​the first negative electrode active layer is different. Within a certain range, when S2≤S1 is satisfied, the smaller the specific surface area of ​​the first negative electrode active layer, the better it is to improve the volumetric energy density, reduce the DCR of the battery cell, and improve the capacity retention rate.

[0259] Referring to Table 3, and based on Examples 14-15 and Example 1, it is evident that the mass per unit area of ​​the second negative electrode active layer varies. Within a certain range, increasing the mass per unit area of ​​the second negative electrode active layer is beneficial for improving the volumetric energy density, while decreasing the mass per unit area of ​​the second negative electrode active layer is beneficial for reducing the DCR of the battery cells, reducing lithium plating, and improving capacity retention. By further adjusting the mass per unit area of ​​the first negative electrode active layer, it is possible to balance the volumetric energy density while reducing the DCR of the battery cells, reducing lithium plating, and maintaining capacity retention.

[0260] As shown in Table 3, according to Examples 16 and 1, the first negative electrode active layer is pre-lithiated, which helps to improve the first charge and discharge efficiency of the first negative electrode active layer and increase the volumetric energy density.

[0261] As shown in Table 3, based on Examples 17 and 1, the binder material of the second negative electrode active layer is different, using polyacrylic acid binder, which helps to reduce the DCR of the battery cell and improve the capacity retention rate.

[0262] As shown in Table 3, based on Examples 18-19 and Example 1, the number of layers in the second negative electrode active layer varies, as does the binder content in the second negative electrode active layer. Compared to a single-layer second negative electrode active layer, a double-layer second negative electrode active layer can increase the volumetric energy density while reducing the DCR of the battery cell and improving the capacity retention rate. Furthermore, reducing the binder content in the second negative electrode active layer, which is located further away from the current collector layer, is beneficial for further improving the performance of the battery cell.

[0263] As shown in Table 3, based on Examples 20 and 1, the first negative electrode active material is different; graphite is used, which is beneficial for improving the volumetric energy density.

[0264] As shown in Table 3, according to Examples 21 and 20, the first negative electrode active material is different, using hard carbon and graphite materials. This is beneficial to reduce the DCR of the battery cell, reduce lithium plating, and improve the volumetric energy density.

[0265] As shown in Table 3, according to Examples 22 and 20, the first negative electrode active material is different, using hard carbon, soft carbon and silicon carbon materials, which is beneficial to reducing the DCR of the battery cell.

[0266] As shown in Table 3, based on Examples 23 and 1, the second negative electrode active material is different, using graphite and silicon-carbon materials, which is beneficial to improving the volumetric energy density.

[0267] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

A battery cell, characterized in that, include: A negative electrode sheet, comprising 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 comprising a first negative electrode active layer and a second negative electrode active layer, the second negative electrode active layer being located between the negative current collector and the first negative electrode active layer, the first negative electrode active layer comprising a first negative electrode active material, and the second negative electrode active layer comprising a second negative electrode active material, wherein... The volumetric particle size distribution Dv50 of the first negative electrode active material 1 Satisfying: Dv50 1 ≤2μm, the volumetric particle size distribution Dv99 of the first negative electrode active material 1 Satisfying: Dv99 1 ≤5μm; The volumetric particle size distribution Dv50 of the second negative electrode active material 2 Satisfying: Dv50 2 ≥Dv99 1 ; The thickness d1 of the first negative electrode active layer and the thickness d2 of the second negative electrode active layer satisfy: d1:d2=(0.023~0.25):

1. The battery cell according to claim 1 is characterized in that, d1:d2 = (0.03~0.1):

1. The battery cell according to claim 1 or 2 is characterized in that, The d1 satisfies: 1μm≤d1≤10μm, and the d2 satisfies: 40μm≤d2≤80μm. The battery cell according to claim 3 is characterized in that, 2μm≤d1≤5μm, 50μm≤d2≤70μm. The battery cell according to any one of claims 1 to 4 is characterized in that, The mass range per unit area of ​​the first negative electrode active layer is 0.002 mg / mm². 2 -0.02mg / mm 2 The mass range per unit area of ​​the second negative electrode active layer is 0.065 mg / mm². 2 -0.18mg / mm 2 . The battery cell according to claim 5 is characterized in that, The mass range per unit area of ​​the first negative electrode active layer is 0.005 mg / mm². 2 -0.015mg / mm 2 . The battery cell according to any one of claims 1 to 6 is characterized in that, The specific surface area S1 of the first negative electrode active material satisfies: S1≥8m 2 / g, the specific surface area S2 of the second negative electrode active material satisfies: S2≤S1. The battery cell according to any one of claims 1 to 7 is characterized in that, The porosity P1 of the first negative electrode active layer and the porosity P2 of the second negative electrode active layer satisfy: P1≥P2. The battery cell according to any one of claims 1 to 8 is characterized in that, The first negative electrode active material includes hard carbon, and the mass ratio ω1 of the hard carbon to the first negative electrode active material satisfies: ω1≥0.

8. The battery cell according to claim 9 is characterized in that, The first negative electrode active material also includes at least one of graphite, silicon carbide, and soft carbon. The battery cell according to any one of claims 1 to 10 is characterized in that, The second negative electrode active material includes graphite, and the mass ratio ω2 of the graphite to the second negative electrode active material satisfies: ω2≥0.

8. The battery cell according to claim 11 is characterized in that, The second negative electrode active material further includes a silicon-based material, which includes at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The battery cell according to any one of claims 1 to 12 is characterized in that, The binder in the negative electrode film layer includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan. The battery cell according to claim 13 is characterized in that, The binder in the first negative electrode active layer includes polyvinylidene fluoride. The battery cell according to claim 13 is characterized in that, The binder in the second negative electrode active layer includes at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan. The battery cell according to any one of claims 1 to 15 is characterized in that, The first negative electrode active layer is a single-layer structure, and the second negative electrode active layer is a multi-layer structure. The battery cell according to claim 16 is characterized in that, In the second negative electrode active layer, the absolute value of the difference in the content of interlayer binder is ≤1%. A method for preparing a single battery cell, characterized in that, include: A negative electrode sheet is provided to prepare the battery cell; The negative electrode sheet includes: A first negative electrode active material is provided to prepare a first negative electrode slurry; wherein the volumetric particle size distribution of the first negative electrode active material is Dv50. 1 Satisfying: Dv50 1 ≤2μm, the volumetric particle size distribution Dv99 of the first negative electrode active material 1 Satisfying: Dv99 1 ≤5μm; A second negative electrode active material is provided to prepare a second negative electrode slurry; wherein the volumetric particle size distribution of the second negative electrode active material is Dv50. 2 Satisfying: Dv50 2 ≥Dv99 1 ; The second negative electrode slurry is coated on at least one side surface of the negative electrode current collector to obtain the second negative electrode active layer; The first negative electrode slurry is coated onto the surface of the second negative electrode active layer to obtain the first negative electrode active layer, thereby preparing the negative electrode sheet; wherein... The thickness d1 of the first negative electrode active layer and the thickness d2 of the second negative electrode active layer satisfy: d1:d2=(0.023~0.25):

1. The preparation method according to claim 18 is characterized in that, d1:d2 = (0.03~0.1):

1. The preparation method according to claim 18 or 19 is characterized in that, The method further includes: The second negative electrode active layer is subjected to at least one of cold pressing, hot pressing, rolling pressing and ultrasonic treatment, so that the porosity P1 of the first negative electrode active layer and the porosity P2 of the second negative electrode active layer satisfy: P1≥P2. The preparation method according to any one of claims 18 to 20 is characterized in that, The first negative electrode active material includes hard carbon, and the mass ratio ω1 of the hard carbon to the first negative electrode active material satisfies: ω1≥0.

8. A battery characterized in that, include: The battery cell according to any one of claims 1 to 17, and / or the battery cell obtained by the preparation method according to any one of claims 18 to 21. An electrical device, characterized in that, Includes the battery as described in claim 22.

Images