Battery cell, battery device and electric device

Abstract

The present application relates to a battery cell, a battery device and an electric device. The negative electrode sheet of the battery cell comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode material layer comprises a first negative electrode film layer close to the negative electrode current collector and a second negative electrode film layer away from the negative electrode current collector; the first negative electrode film layer comprises first graphite and a first conductive agent; the second negative electrode film layer comprises second graphite and a second conductive agent; and the particle size Dv50 of the first graphite is less than the particle size Dv50 of the second graphite, and the mass percentage of the first conductive agent in the first negative electrode film layer is less than the mass percentage of the second conductive agent in the second negative electrode film layer. The battery cell can exhibit good cycle performance when used for high-rate charging and discharging.

Description

A battery cell, a battery device, and an electrical device.

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202510329423.6, filed on March 19, 2025, entitled “A Battery Cell, Battery Device and Power Consumption Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, specifically to a battery cell, a battery device, and an electrical device. Background Technology

[0004] In recent years, secondary batteries, represented by lithium-ion 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.

[0005] With the development of secondary battery applications, the requirements for battery power performance are also getting higher and higher. Summary of the Invention

[0006] The purpose of this application is to provide a battery cell, a battery device, and an electrical device, wherein the battery cell has good cycle performance under high-rate charge and discharge conditions.

[0007] Therefore, the first aspect of this application provides a battery cell, which includes a positive electrode, a separator, and a negative electrode;

[0008] The negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector; the negative electrode material layer includes a first negative electrode film layer and a second negative electrode film layer; the first negative electrode film layer is closer to the negative current collector than the second negative electrode film layer.

[0009] The first negative electrode film layer includes a first graphite and a first conductive agent; the second negative electrode film layer includes a second graphite and a second conductive agent; the particle size Dv50 of the first graphite is smaller than the particle size Dv50 of the second graphite; the mass percentage of the first conductive agent in the first negative electrode film layer is smaller than the mass percentage of the second conductive agent in the second negative electrode film layer.

[0010] The cycle performance of a battery under high-rate charge-discharge conditions is closely related to both ion and electron transport capabilities, and is also affected by side reactions in the electrolyte. In the embodiments of this application, the second negative electrode film layer is located close to the electrolyte, and larger-diameter graphite particles are used in the second negative electrode film layer. These particles have a relatively small specific surface area, resulting in a smaller contact area with the electrolyte. This reduces the number of active sites on the material surface that could lead to side reactions with the electrolyte, thereby reducing side reactions and improving cycle performance. Furthermore, the porous structure formed by the large-particle graphite helps shorten the migration path of ions in the electrolyte, reducing concentration polarization, and significantly improving the diffusion rate of ions to the first negative electrode film layer, especially at high rates.

[0011] In the negative electrode, the electron pathway first passes through the current collector and then is transferred to the negative electrode material layer. Therefore, the conductivity of the negative electrode film layer, which is far from the current collector, may become a bottleneck for electron transport. In the embodiments of this application, by using a higher mass ratio of conductive agent in the second negative electrode film layer, the conductivity of the second negative electrode film layer is improved, thereby balancing and enhancing the conductivity of the entire negative electrode material layer.

[0012] For the first negative electrode film, since it is close to the current collector, its conductivity is often not a bottleneck limiting high-rate charging, and a relatively smaller amount of conductive agent can be used compared to the second negative electrode film. Furthermore, using smaller-diameter graphite particles in the first negative electrode film provides a larger contact surface with the current collector, which is beneficial for providing a stable electron transport network and supporting high-rate charge and discharge. Therefore, through the aforementioned arrangement of the first and second negative electrode films, ion and electron transport can be comprehensively improved, electrolyte side reactions can be reduced, and thus the cycle performance of the battery under high-rate charge and discharge conditions can be enhanced.

[0013] In some embodiments, the particle size Dv50 of the first graphite is 5–12 μm.

[0014] The first negative electrode film layer is far from the electrolyte. When the first graphite adopts the above-mentioned particle size range, the particle size is small, and after cold pressing, it has a suitable compaction density and porosity, which improves the electrode's liquid absorption rate and liquid retention capacity, thereby helping to further improve the power performance of the battery cell.

[0015] In some embodiments, the particle size Dv50 of the second graphite is 10–20 μm.

[0016] When the second graphite has the above-mentioned particle size, it helps to make the negative electrode material layer have a high overall compaction density, so that the energy density of the battery is not lost while having good power performance.

[0017] In some embodiments, the specific surface area of ​​the first graphite is 0.2–1.2 m². 2 / g.

[0018] The first negative electrode film is relatively far from the electrolyte. When the specific surface area of ​​the first graphite is within the aforementioned range, there are more contact sites with the electrolyte. On the one hand, this increases the diffusion path of lithium ions, promoting rapid ion diffusion; on the other hand, it also helps to increase the effective transport of electrons, further reducing the internal resistance of the battery. Therefore, this is beneficial for improving the overall kinetics of the negative electrode.

[0019] In some embodiments, the tap density of the first graphite is 0.8–1.2 g / cm³. 3 ; and / or,

[0020] The particle size Dn10 of the first graphite is 0.2–0.9 μm.

[0021] When the tap density of the first graphite is within the above range, it is easy for the first negative electrode film layer to have a suitable tap density after cold pressing, thereby having a good electrode wetting effect, which is beneficial to improving the power performance of the battery.

[0022] When the particle size Dn10 of the first graphite is within the above range, the quantity distribution shows that it contains a certain amount of micro-particles with smaller particle sizes. These micro-particles have a larger surface area and more active sites, which is beneficial for fast charging and power performance.

[0023] In some embodiments, the specific surface area of ​​the second graphite is 0.4–0.9 m². 2 / g.

[0024] When the second graphite has the aforementioned smaller specific surface area, there are relatively fewer contact sites with the electrolyte, which helps to further mitigate side reactions with the electrolyte, reduce repeated growth of the SEI film during cyclic storage, and improve kinetic and power performance.

[0025] In some embodiments, the tap density of the second graphite is 1.2–1.6 g / cm³. 3 ; and / or,

[0026] The particle size Dn10 of the second graphite is 0.8–1.5 μm.

[0027] When the tap density of the second graphite is within the above range, it is easy for the negative electrode material layer to have a large compaction density after cold pressing, which helps to improve the overall energy density of the battery.

[0028] When the particle size Dn10 of the second graphite is within the above range, the quantity distribution shows that there are fewer micro-particles, thus resulting in fewer side reactions between the second graphite and the electrolyte.

[0029] In some embodiments, the second conductive agent constitutes 0.1% to 1.5% by mass in the second negative electrode film; and / or,

[0030] The first conductive agent accounts for 0.05% to 0.5% of the mass percentage in the first negative electrode film layer.

[0031] When the mass ratio of the second conductive agent and the first conductive agent in their respective film layers is within the above range, it is beneficial to make the battery as a whole have good conductivity, thereby reducing the electrode resistance.

[0032] In some embodiments, both the first conductive agent and the second conductive agent comprise carbon nanotubes; and the mass percentage of carbon nanotubes in the first negative electrode film is less than the mass percentage of carbon nanotubes in the second negative electrode film.

[0033] Carbon nanotubes possess excellent electrical conductivity. Applying carbon nanotubes in both the first and second anode film layers offers at least one of the following advantages: it comprehensively improves the conductivity of the anode electrode; or, because carbon nanotubes exhibit high conductivity, the amount of other conductive agents can be reduced, increasing the mass proportion of graphite and thus improving energy density. A higher mass proportion of carbon nanotubes in the second anode film helps prevent it from becoming a bottleneck limiting conductivity, thus balancing the conductivity of the entire anode material layer.

[0034] In some embodiments, the mass percentage of carbon nanotubes in the second negative electrode film is 0.1% to 1%, based on the mass of the second negative electrode film; and / or,

[0035] Based on the mass of the first negative electrode film, the mass percentage of carbon nanotubes in the first negative electrode film is 0.05% to 0.15%.

[0036] When using carbon nanotubes, the above-mentioned dosage can be used due to their excellent conductivity and cost considerations. Even with such a small amount, the conductivity can be significantly improved.

[0037] In some implementations, carbon nanotubes include single-walled carbon nanotubes.

[0038] Compared to multi-walled carbon nanotubes, single-walled carbon nanotubes are smaller in size, have fewer defects, a higher aspect ratio, superior mechanical properties, and better electrical conductivity, which are more conducive to power performance.

[0039] In some embodiments, the aspect ratio of the carbon nanotubes is 2500 to 15000.

[0040] Carbon nanotubes have a linear structure. When they have the above-mentioned aspect ratio, carbon nanotubes are easy to entangle with each other to form a network structure, which plays a certain role in binding the graphite material. This helps to reduce the volume expansion of the graphite material during the lithium intercalation process and improve the structural stability of the negative electrode during cycling.

[0041] The aspect ratio, or length-to-diameter ratio, is the ratio of length to diameter and can be measured in the following ways:

[0042] By imaging the negative electrode sheet with a scanning electron microscope (SEM), the carbon nanotubes appear as slender and continuous linear structures. By measuring their length and diameter, the aspect ratio can be calculated.

[0043] In some embodiments, the diameter of the carbon nanotubes is 0.4–2 nm; and / or,

[0044] The length of carbon nanotubes ranges from 0.5 to 20 μm.

[0045] When the linear conductive agent has the aforementioned suitable length, it can achieve both good dispersibility and long-range conductivity. When the diameter of the linear conductive agent is within the aforementioned range, it exhibits good mechanical properties, which is beneficial for improving the restraining effect on the expansion of graphite materials.

[0046] In some embodiments, the thickness ratio of the first negative electrode film layer to the second negative electrode film layer is 4–6:4–6. In some embodiments, the thickness of the first negative electrode film layer is 55–100 μm, and the thickness of the second negative electrode film layer is 55–100 μm.

[0047] When the thickness of the second negative electrode film is greater than that of the first negative electrode film, the use of larger-diameter graphite particles in the second negative electrode film increases the compaction density of the electrode material layers, thus better enabling the cell to achieve high energy density. Conversely, if the thickness of the first negative electrode film is greater than that of the second negative electrode film, it is more conducive to achieving high power performance. When the thickness ratio of the first and second negative electrode films is within the above range, both energy density and power performance can be well balanced.

[0048] In some embodiments, the compaction density of the negative electrode material layer is 1.5–1.75 g / cm³. 3 .

[0049] In the embodiments of this application, the aforementioned high electrode compaction can be achieved, which is beneficial for improving the energy density of the battery cell. Furthermore, even with the aforementioned electrode compaction, the battery can still maintain excellent power performance.

[0050] A second aspect of this application provides a battery device comprising the battery cell of the first aspect of this application.

[0051] A third aspect of this application provides an electrical device that includes a battery cell according to the first aspect of this application, or a battery device according to the second aspect of this application.

[0052] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application, it can be implemented according to the contents of the specification. In order to make the above and other objects, features and advantages of this application more obvious and understandable, the specific implementation methods of this application are listed below. Attached Figure Description

[0053] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. In the drawings:

[0054] Figure 1 is a schematic diagram of a battery cell according to an embodiment of this application;

[0055] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1;

[0056] Figure 3 is a schematic diagram of a battery module according to an embodiment of this application;

[0057] Figure 4 is a schematic diagram of a battery pack according to an embodiment of this application;

[0058] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4;

[0059] Figure 6 is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to an embodiment of this application.

[0060] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 End cap. Detailed Implementation

[0061] Exemplary embodiments of this disclosure will now be described in more detail. It should be understood that this disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0062] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0063] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0064] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0065] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0066] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0067] In recent years, secondary batteries have made great progress. With the development of related technologies and the increase in demand, the requirements for the cycle performance and power performance of secondary batteries are also getting higher and higher. It is hoped that the batteries can have good cycle performance under high-rate charge and discharge conditions.

[0068] In the embodiments of this application, the power performance of the battery is improved by applying a layered coating structure in the negative electrode sheet and using graphite with different particle sizes and conductive agents with different mass ratios in different layers.

[0069] The solutions described in the embodiments of this application are applicable to battery cells, battery devices using the battery cells, and electrical devices using the battery cells or battery devices.

[0070] battery cell

[0071] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0072] The battery cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc. In some embodiments, the battery cell is a lithium-ion battery.

[0073] [Electrode Assembly]

[0074] A single battery cell typically includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator positioned between the positive and negative electrodes. During the charging and discharging process of a single battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0075] [Negative electrode plate]

[0076] In some embodiments, a battery cell is provided, which includes a positive electrode, a separator, and a negative electrode;

[0077] The negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector; the negative electrode material layer includes a first negative electrode film layer and a second negative electrode film layer; the first negative electrode film layer is closer to the negative current collector than the second negative electrode film layer.

[0078] The first negative electrode film layer includes a first graphite and a first conductive agent; the second negative electrode film layer includes a second graphite and a second conductive agent; the particle size Dv50 of the first graphite is smaller than the particle size Dv50 of the second graphite; the mass percentage of the first conductive agent in the first negative electrode film layer is smaller than the mass percentage of the second conductive agent in the second negative electrode film layer.

[0079] In this application, the particle size Dv50 of the first and second graphite has a meaning known in the art (the volume average particle size Dv50 has a meaning known in the art, referring to the particle size value corresponding to the cumulative volume distribution reaching 50% in the particle size distribution). It can be detected using equipment and methods known in the art. The specific test method is as follows: A small amount of powder from the second negative electrode film layer is scraped from the side of the negative electrode sheet away from the current collector. The negative electrode film is completely peeled off from the current collector using strong adhesive tape, and powder from the first negative electrode film layer is scraped from the side of the negative electrode film closer to the current collector. 50 mg of the collected first region sample and second region sample are weighed respectively. The first region sample or the second region sample is filtered, dried, and then sintered at 400℃ for 2 hours to remove the binder and conductive agent, thus obtaining the first graphite of the first negative electrode film layer or the second graphite of the second negative electrode film layer. Then, according to GB / T 19077-2016, the particle size is measured using a laser particle size analyzer. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0080] In this application, the mass content of the first and second conductive agents can be detected using equipment and methods known in the art. Specific instruments include: a thermogravimetric analyzer (such as a TA Instruments TGA 2050 or Netzsch STA 449F3 Jupiter), a high-precision balance (resolution ≤0.1μg), and a high-temperature furnace (temperature range up to 1200℃). Testing procedure: Place 5-10mg of the first region sample obtained above in a crucible and place it in the thermogravimetric analyzer. Run the program according to the set conditions (temperature range: 200-1200℃; heating rate: 5-10℃ / min (determined based on DSC pre-experiment to ensure clear separation of decomposition peaks); atmosphere: inert gas (such as nitrogen, flow rate 50-100mL / min) to avoid oxidation interference), and record the TG curve (mass versus temperature curve). Data Analysis: Determining the Decomposition Temperature Range and Establishing Calibration Curves: The decomposition temperature range of CNTs (typically 800-1000℃) is determined using the TG curve. The percentage of mass loss (%Δm) is calculated to deduce the CNT content in the first region. Similarly, the CNT content in the second region can be measured.

[0081] The cycle performance of a battery under high-rate charge-discharge conditions is closely related to both ion and electron transport capabilities, and is also affected by side reactions in the electrolyte. In the embodiments of this application, the second negative electrode film layer is located close to the electrolyte, and larger-diameter graphite particles are used in the second negative electrode film layer. These particles have a relatively small specific surface area, resulting in a smaller contact area with the electrolyte. This reduces the number of active sites on the material surface that could lead to side reactions with the electrolyte, thereby reducing side reactions and improving cycle performance. Furthermore, the porous structure formed by the large-particle graphite helps shorten the migration path of ions in the electrolyte, reducing concentration polarization, and significantly improving the diffusion rate of ions to the first negative electrode film layer, especially at high rates.

[0082] In the negative electrode, the electron pathway first passes through the current collector and then is transferred to the negative electrode material layer. Therefore, the conductivity of the negative electrode film layer, which is far from the current collector, may become a bottleneck for electron transport. In the embodiments of this application, by using a higher mass ratio of conductive agent in the second negative electrode film layer, the conductivity of the second negative electrode film layer is improved, thereby balancing and enhancing the conductivity of the entire negative electrode material layer.

[0083] For the first negative electrode film, since it is close to the current collector, its conductivity is often not a bottleneck limiting high-rate charging, and a relatively smaller amount of conductive agent can be used compared to the second negative electrode film. Furthermore, using smaller-diameter graphite particles in the first negative electrode film provides a larger contact surface with the current collector, which is beneficial for providing a stable electron transport network and supporting high-rate charge and discharge. Therefore, through the aforementioned arrangement of the first and second negative electrode films, ion and electron transport can be comprehensively improved, electrolyte side reactions can be reduced, and thus the cycle performance of the battery under high-rate charge and discharge conditions can be enhanced.

[0084] In some embodiments, the particle size Dv50 of the first graphite is 5 to 12 μm, for example, it can be about 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, etc.

[0085] The first negative electrode film layer is far from the electrolyte. When the first graphite adopts the above-mentioned particle size range, the particle size is small, and after cold pressing, it has a suitable compaction density and porosity, which improves the electrode's liquid absorption rate and liquid retention capacity, thereby helping to further improve the power performance of the battery cell.

[0086] In some embodiments, the particle size Dv50 of the second graphite is 10 to 20 μm, for example, it can be about 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc.

[0087] When the second graphite has the above-mentioned particle size, it helps to make the negative electrode material layer have a high overall compaction density, so that the energy density of the battery is not lost while having good power performance.

[0088] In some embodiments, the specific surface area of ​​the first graphite is 0.2–1.2 m². 2 / g, which can be selected from 0.6 to 1.0m 2 / g, for example, can be about 0.2m 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1m 2 / g, 1.1m 2 / g, 1.2m 2 / g etc.

[0089] The first negative electrode film is relatively far from the electrolyte. When the specific surface area of ​​the first graphite is within the aforementioned range, there are more contact sites with the electrolyte. On the one hand, this increases the diffusion path of lithium ions, promoting rapid ion diffusion; on the other hand, it also helps to increase the effective transport of electrons, further reducing the internal resistance of the battery. Therefore, this is beneficial for improving the overall kinetics of the negative electrode.

[0090] The specific surface area of ​​graphite materials can be measured by using a specific surface area and porosity analyzer (such as the ASAP 2460 specific surface area and porosity analyzer), measuring the amount of nitrogen adsorbed on the graphite surface using the static volumetric method, and then calculating the specific surface area using the BET equation.

[0091] In some embodiments, the tap density of the first graphite is 0.8–1.2 g / cm³. 3 The concentration can be selected as 1–1.1 g / cm³. 3 For example, it can be approximately 0.8 g / cm³. 3 0.9g / cm 3 1g / cm 3 1.1g / cm 3 1.2g / cm 3 etc.; and / or,

[0092] The particle size Dn10 of the first graphite is 0.2 to 0.9 μm, and can be selected from 0.4 to 0.8 μm, for example, it can be about 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, etc.

[0093] When the tap density of the first graphite is within the above range, it is easy for the first negative electrode film layer to have a suitable tap density after cold pressing, thereby having a good electrode wetting effect, which is beneficial to improving the power performance of the battery.

[0094] When the particle size Dn10 of the first graphite is within the above range, the quantity distribution shows that it contains a certain amount of micro-particles with smaller particle sizes. These micro-particles have a larger surface area and more active sites, which is beneficial for fast charging and power performance.

[0095] The tapped density of graphite refers to the mass per unit volume of powder in a container after tapping under specified conditions. Tapped density can be determined using a specialized tapped density instrument. For example, the ZS703 powder density tester can be used, manufactured according to the national standard GB / T 5162-2006 / ISO3953:1993 (Determination of tapped density of metal powders). Accurately weighed sample powder is loaded into the measuring cylinder of the tester. The instrument is then started, allowing the sample to be tapped under specified conditions (vibration amplitude 3 mm). The volume of the powder is read when it no longer decreases. To calculate the tapped density, divide the weight of the powder by the tapped volume.

[0096] Particle size Dn10 is a well-known term in the art, referring to the particle size value corresponding to a cumulative particle size distribution percentage of 10%. Physically, it means that particles smaller than Dn10 account for 10% of the total particles, and is commonly used to represent the particle size index of the fine end of powders.

[0097] In some embodiments, the specific surface area of ​​the second graphite is 0.4–0.9 m². 2 / g, which can be selected from 0.5 to 0.8m 2 / g, for example, can be about 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g etc.

[0098] When the second graphite has the aforementioned smaller specific surface area, there are relatively fewer contact sites with the electrolyte, which helps to further mitigate side reactions with the electrolyte, reduce repeated growth of the SEI film during cyclic storage, and improve kinetic and power performance.

[0099] In some embodiments, the tap density of the second graphite is 1.2–1.6 g / cm³. 3 The concentration can be selected as 1.2–1.4 g / cm³. 3 For example, it can be approximately 1.2 g / cm³. 3 1.3g / cm3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 etc.; and / or,

[0100] The particle size Dn10 of the second graphite is 0.8 to 1.5 μm, and can be selected from 0.9 to 1.2 μm, for example, it can be about 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, etc.

[0101] When the tap density of the second graphite is within the above range, it is easy for the negative electrode material layer to have a large compaction density after cold pressing, which helps to improve the overall energy density of the battery.

[0102] When the particle size Dn10 of the second graphite is within the above range, the quantity distribution shows that there are fewer micro-particles, thus resulting in fewer side reactions between the second graphite and the electrolyte.

[0103] In some embodiments, based on the mass of the second negative electrode film, the mass percentage of the second conductive agent in the second negative electrode film is 0.1% to 1.5%, for example, it can be about 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.; and / or,

[0104] The first conductive agent accounts for 0.05% to 0.5% of the mass percentage in the first negative electrode film layer, for example, about 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc.

[0105] When the mass ratio of the second conductive agent and the first conductive agent in their respective film layers is within the above range, it is beneficial to make the battery as a whole have good conductivity, thereby reducing the electrode resistance.

[0106] In some embodiments, both the first conductive agent and the second conductive agent comprise carbon nanotubes; and the mass percentage of carbon nanotubes in the first negative electrode film is less than the mass percentage of carbon nanotubes in the second negative electrode film.

[0107] Carbon nanotubes possess excellent electrical conductivity. Applying carbon nanotubes in both the first and second anode film layers offers at least one of the following advantages: it comprehensively improves the conductivity of the anode electrode; or, because carbon nanotubes exhibit high conductivity, the amount of other conductive agents can be reduced, increasing the mass proportion of graphite and thus improving energy density. A higher mass proportion of carbon nanotubes in the second anode film helps prevent it from becoming a bottleneck limiting conductivity, thus balancing the conductivity of the entire anode material layer.

[0108] In some embodiments, based on the mass of the second negative electrode film, the mass percentage of carbon nanotubes in the second negative electrode film is 0.1% to 1%, for example, it can be about 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.; and / or,

[0109] Based on the mass of the first negative electrode film, the mass percentage of carbon nanotubes in the first negative electrode film is 0.05% to 0.1%, for example, it can be about 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, etc.

[0110] When using carbon nanotubes, the above-mentioned dosage can be used due to their excellent conductivity and cost considerations. Even with such a small amount, the conductivity can be significantly improved.

[0111] In some implementations, carbon nanotubes include single-walled carbon nanotubes.

[0112] Compared to multi-walled carbon nanotubes, single-walled carbon nanotubes are smaller in size, have fewer defects, a higher aspect ratio, superior mechanical properties, and better electrical conductivity, which are more conducive to power performance.

[0113] In some embodiments, the aspect ratio of the carbon nanotubes is 2500 to 15000, for example, it can be about 2500, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, etc.

[0114] Carbon nanotubes have a linear structure. When they have the above-mentioned aspect ratio, carbon nanotubes are easy to entangle with each other to form a network structure, which plays a certain role in binding the graphite material. This helps to reduce the volume expansion of the graphite material during the lithium intercalation process and improve the structural stability of the negative electrode during cycling.

[0115] The aspect ratio, or length-to-diameter ratio, is the ratio of length to diameter and can be measured in the following ways:

[0116] By imaging the negative electrode sheet with a scanning electron microscope (SEM), the carbon nanotubes appear as slender and continuous linear structures. By measuring their length and diameter, the aspect ratio can be calculated.

[0117] In some embodiments, the diameter of the carbon nanotubes is 0.4–2 nm, for example, it can be about 0.4 nm, 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1 nm, 1.2 nm, 1.5 nm, 1.7 nm, 1.8 nm, 2 nm, etc.; and / or,

[0118] The length of carbon nanotubes ranges from 0.5 to 20 μm, for example, approximately 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc.

[0119] When the linear conductive agent has the aforementioned suitable length, it can achieve both good dispersibility and long-range conductivity. When the diameter of the linear conductive agent is within the aforementioned range, it exhibits good mechanical properties, which is beneficial for improving the restraining effect on the expansion of graphite materials.

[0120] In some embodiments, the thickness ratio of the first negative electrode film layer to the second negative electrode film layer is 4–6:4–6, for example, it can be about 1:1, 4:5, 2:3, 5:4, 5:6, 3:2, 6:5, etc. In some embodiments, the thickness of the first negative electrode film layer is 55–100 μm, and the thickness of the second negative electrode film layer is 55–100 μm. For example, the thicknesses of the first negative electrode film layer and the second negative electrode film layer can each be independently selected from 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, etc.

[0121] When the thickness of the second negative electrode film is greater than that of the first negative electrode film, the use of larger-diameter graphite particles in the second negative electrode film increases the compaction density of the electrode material layers, thus better enabling the cell to achieve high energy density. Conversely, if the thickness of the first negative electrode film is greater than that of the second negative electrode film, it is more conducive to achieving high power performance. When the thickness ratio of the first and second negative electrode films is within the above range, both energy density and power performance can be well balanced.

[0122] In some embodiments, the compaction density of the negative electrode material layer is 1.5–1.75 g / cm³. 3 For example, it can be approximately 1.5 g / cm³. 3 1.55g / cm 3 1.6g / cm3 1.61 g / cm 3 1.62g / cm 3 1.63g / cm 3 1.64 g / cm 3 1.65g / cm 3 1.66 g / cm 3 1.67 g / cm 3 1.68g / cm 3 1.69 g / cm 3 1.7g / cm 3 1.71 g / cm 3 1.72g / cm 3 1.73g / cm 3 1.74 g / cm 3 1.75g / cm 3 wait.

[0123] In the embodiments of this application, the aforementioned high electrode compaction can be achieved, which is beneficial for improving the energy density of the battery cell. Furthermore, even with the aforementioned electrode compaction, the battery can still maintain excellent power performance.

[0124] In some implementations, the film resistance of the negative electrode is ≤0.0011Ω.

[0125] In the embodiments of this application, the negative electrode can achieve the aforementioned low film resistance, thereby exhibiting excellent power performance.

[0126] The film resistance of the negative electrode can be measured using a film resistance meter. For example, cut the negative electrode to an appropriate size (e.g., 5cm × 5cm), place it between the two electrodes of the film resistance meter, start the test, and read the resistance data.

[0127] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0128] In some embodiments, the negative electrode sheet further includes a base coating layer disposed between the negative electrode current collector and the negative electrode material layer. The base coating layer can be a battery base coating layer known in the art, typically formed from a base coating slurry comprising a conductive agent, a binder, a dispersant, and deionized water. The conductive agent, binder, and dispersant can be conductive agents, binders, and dispersants known in the art for use in batteries. By further including the base coating layer, the adhesion between the active material and the current collector can be increased, making the electrode sheet less prone to powder shedding or delamination during charging and discharging.

[0129] In some embodiments, the negative electrode material layer includes an adhesive, which may be a material known in the art, such as at least one selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0130] In some embodiments, the negative electrode material layer uses only the first graphite and the second graphite as the negative electrode active material. In some embodiments, the negative electrode material layer also includes other negative electrode active materials, such as at least one of the following: soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0131] In some embodiments, the first and second conductive agents may optionally include other conductive agents besides carbon nanotubes, such as at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, and carbon dots.

[0132] In some embodiments, the negative electrode material layer may optionally also include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0133] In some embodiments, the negative electrode sheet can be prepared by providing a slurry for forming a first negative electrode film layer, which includes dispersing a first graphite, a first conductive agent and any other components (e.g., a binder) in a solvent (e.g., deionized water), thereby preparing the first negative electrode slurry;

[0134] A slurry for forming a second negative electrode film is provided, which includes dispersing a second graphite, a second conductive agent and any other components (e.g., a binder) in a solvent (e.g., deionized water) to prepare the second negative electrode slurry;

[0135] The first negative electrode slurry is coated onto the negative electrode current collector, dried, and then coated with the second negative electrode slurry. After drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0136] [Positive electrode plate]

[0137] The positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector, the positive electrode material layer including a positive electrode active material.

[0138] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0139] 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.).

[0140] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, sodium transition metal oxides, polyanionic compounds, Prussian blue compounds, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium 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 LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), 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.

[0141] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 <x≤1。

[0142] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The price state.

[0143] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0144] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n-Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0145] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3, NaM'PO4F (where M' is one or more of V, Fe, Mn, and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0146] Prussian blue compounds can be a class of compounds containing sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Examples of Prussian blue compounds include Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 <a≤2,0<b<1,0<c<1。

[0147] In some embodiments, the positive electrode material 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.

[0148] In some embodiments, the positive electrode material layer 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.

[0149] 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.

[0150] [Electrolytes]

[0151] 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.

[0152] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] [Isolation Component]

[0157] In some embodiments, the electrode assembly further includes a spacer disposed between the positive electrode and the negative electrode.

[0158] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0159] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator.

[0160] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0161] [Structure of the electrode assembly]

[0162] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0163] In some implementations, the electrode assembly is a wound structure. The positive and negative electrode sheets are wound into a wound structure.

[0164] In some implementations, the electrode assembly is a stacked structure.

[0165] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0166] As an example, multiple positive electrode sheets can be set, and negative electrode sheets are folded to form multiple stacked folded segments, with a positive electrode sheet sandwiched between adjacent folded segments.

[0167] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0168] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0169] As an example, the separator can be continuously arranged between any adjacent positive or negative electrode plates by folding or rolling.

[0170] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0171] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0172] [shell]

[0173] In some embodiments, the battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0174] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations. For example, Figure 1 shows a prismatic battery cell 5 as an example.

[0175] In some embodiments, referring to FIG2, the housing includes an end cap 53 and a housing 51. The housing 51 has an opening, and the end cap 53 covers the opening. The housing 51 may have one or more openings. The end cap 53 may also be provided one or more times. The positive electrode, the negative electrode, and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within a receiving cavity formed by the housing 51 and the end cap 53. The electrolyte is immersed in the electrode assembly 52.

[0176] [Electrode terminals]

[0177] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab, or it can be indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0178] [Pressure relief mechanism]

[0179] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the battery cell.

[0180] As an example, the internal pressure or temperature of a battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is broken, thereby forming an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell.

[0181] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0182] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0183] The term "actuation" as used in this application refers to the activation or actuation of the pressure relief mechanism to a certain state, thereby releasing the internal pressure and temperature of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is activated, the high-temperature, high-pressure substances inside the battery cell are discharged as waste from the activated portion. This method allows for pressure and temperature relief of the battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0184] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for venting gas inside the battery cell.

[0185] The emissions from battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of separators, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0186] Battery device

[0187] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0188] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0189] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As an example, a battery module can be formed by bundling multiple battery cells together with cable ties. Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other arbitrary way.

[0190] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0191] As an example, the battery cell assembly can be a battery module, which can be housed within a housing by fixing the battery module within the housing. Figures 4 and 5 show an example battery pack 1. Referring to Figures 4 and 5, the battery pack 1 can include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3, with the upper housing 2 covering the lower housing 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery housing.

[0192] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0193] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0194] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0195] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0196] Electrical appliances

[0197] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft. Figure 6 shows an example electrical device. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

[0198] Example 1

[0199] This embodiment provides a lithium-ion battery, the preparation method of which includes:

[0200] (a) Negative electrode plate

[0201] 1. Preparation of negative electrode slurry

[0202] First negative electrode slurry:

[0203] Graphite (particle size Dv50 of 5 μm and specific surface area of ​​1.2 m²) was used as the negative electrode active material. 2 / g, tap density is 0.8g / cm³ 3 The first negative electrode slurry was prepared by mixing and stirring graphite (Dn10 with a particle size of 0.2 μm), single-walled carbon nanotubes (2 μm in length, 0.5 nm in diameter, and an aspect ratio of 4000), carbon black conductive agent SP, carboxymethyl cellulose (CMC) as a thickener, styrene-butadiene rubber (SBR) as a binder, and deionized water. The mass ratio of graphite, carbon nanotubes, SP, thickener, and binder was 96.85:0.05:0.4:0.7:2.

[0204] Second negative electrode slurry:

[0205] Graphite (particle size Dv50 of 10 μm and specific surface area of ​​0.9 m²) was used as the negative electrode active material. 2 / g, tap density is 1.1g / cm³ 3 The first negative electrode slurry was prepared by mixing and stirring graphite (Dn10 with a particle size of 0.8 μm), single-walled carbon nanotubes (2 μm in length, 0.5 nm in diameter, and an aspect ratio of 4000), carbon black conductive agent SP, carboxymethyl cellulose (CMC) as a thickener, styrene-butadiene rubber (SBR) as a binder, and deionized water. The mass ratio of graphite, carbon nanotubes, SP, thickener, and binder was 97.8:0.1:0.7:0.6:0.8.

[0206] 2. Preparation of negative electrode sheet

[0207] A first negative electrode slurry for forming the first negative electrode film is coated onto the surface of a copper foil serving as the negative electrode current collector, and then dried to obtain the first negative electrode sheet. A second negative electrode slurry for forming the second negative electrode film is then coated onto the surface of the first negative electrode sheet, and after drying, cold pressing, and slitting, the negative electrode sheet is obtained. The thickness of both the first and second negative electrode films is 80 μm; the compaction density of the negative electrode material layers is 1.61 g / cm³. 3 .

[0208] (II) Positive electrode plate

[0209] Lithium iron phosphate (LiFePO4) as the positive electrode active material, single-walled carbon nanotubes as the conductive agent, and PVDF as the binder are dispersed and dissolved in N-methyl-2-pyrrolidone (NMP) as the solvent in a mass ratio of 97.8:0.4:1.8 to form a uniformly dispersed positive electrode slurry. The positive electrode slurry is then uniformly coated onto aluminum foil as the positive electrode current collector. After drying, cold pressing, and slitting, the positive electrode sheet is obtained.

[0210] (III) Electrolyte

[0211] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly at a volume ratio of 3:7. LiPF6 with a final concentration of 12.5% ​​was then added and dissolved in the organic solvent and stirred evenly.

[0212] (iv) Separating membrane

[0213] Polypropylene film is used as the separator.

[0214] (V) Lithium-ion batteries

[0215] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. They are then wound to obtain a bare cell. Tabs are welded onto the bare cell, which is then placed in an aluminum casing and baked at 60°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product.

[0216] Perform the following tests,

[0217] 1. DCR test

[0218] At room temperature, charge the battery cell to 3.65V with a constant current of 0.33C, then charge it to 0.05C with a constant voltage of 3.65V, let it stand for 30 minutes, and discharge it to 2.0V with a constant current of 0.33C. Record the discharge capacity A0 at this time in Ah. Then charge it to 0.5A0 Ah with a constant current of 0.33C and adjust the SOC to 50%.

[0219] After placing the battery cells at -20℃ for 2 hours, they were discharged at a constant current of 1C for 10 seconds. The discharge values ​​ΔU and ΔI were recorded. The discharge DCR data of the lithium-ion battery were calculated using the following formula: R discharge = ΔU discharge / ΔI discharge.

[0220] Wherein, ΔU discharge represents the voltage change within 10 seconds of the start of discharge, and ΔI discharge represents the current value within 10 seconds of the start of discharge.

[0221] 2. Loop testing

[0222] At room temperature, the battery was subjected to stepped charge-discharge cycles (equivalent to 2.2C). The details for each charge-discharge cycle are as follows:

[0223] (1) Stepped charging:

[0224] 3.0Cn CC 0.1CnAh 0-10% SOC

[0225] 2.93Cn CC 0.05CnAh 10-15% SOC

[0226] 2.63Cn CC 0.05CnAh 15-20% SOC

[0227] 2.40Cn CC 0.05CnAh 20~25% SOC

[0228] 2.39Cn CC 0.05CnAh 25~30% SOC

[0229] 2.39Cn CC 0.05CnAh 30~35% SOC

[0230] 2.23Cn CC 0.05CnAh 35~40% SOC

[0231] 2.04Cn CC 0.05CnAh 40~45% SOC

[0232] 1.60Cn CC 0.05CnAh 45~50% SOC

[0233] 1.45Cn CC 0.05CnAh 50~55% SOC

[0234] 1.35Cn CC 0.05CnAh 55~60% SOC

[0235] 1.25Cn CC 0.05CnAh 60~65% SOC

[0236] 1.1Cn CC 0.05CnAh 65-70% SOC

[0237] 0.95Cn CC 0.05CnAh 70-75% SOC

[0238] 0.85Cn CC 0.05CnAh 75-80% SOC

[0239] Rest for 1 min, depolarization

[0240] 0.61Cn CC 0.05CnAh 80-85% SOC

[0241] 0.52Cn CC 0.05CnAh 85-90% SOC

[0242] 0.36Cn CC 0.05CnAh or 3.8V 85-95% SOC

[0243] 0.33Cn CC 0.03CnAh or 3.8V 95-98% SOC, proceed to the next step after the voltage reaches 3.8V.

[0244] 0.1Cn CC 3.8V 98-100% SOC

[0245] Rest 30min 25 30

[0246] (2) Discharge:

[0247] 1Cn DC 2.0V

[0248] Discharge with a small current of 0.33Cn DC 2.0VF to 0% SOC.

[0249] Rest for 30 minutes

[0250] The above process is divided according to the SOC range of the battery cell, and each range applies a corresponding charging protocol. Taking "3.0Cn CC 0.1CnAh 0-10% SOC" as an example, within the 0-10% SOC range, the following applies: 3.0C constant current charging, after reaching the upper voltage limit (3.8V), constant voltage charging continues until the current drops to 0.1C and charging stops.

[0251] During the discharge phase, the main discharge uses a constant current of 1C to discharge to 2.0V, followed by a deep discharge using a constant current of 0.33C to discharge to 2.0V, and then a small current discharge to discharge to 0% SOC.

[0252] Record the capacity of the first cycle as the discharge capacity of the first cycle, and repeat the above process for 2000 cycles. The capacity retention rate after n cycles = discharge capacity of n cycles / discharge capacity of the first cycle × 100%.

[0253] Comparative Example 1

[0254] Except that it does not contain a second negative electrode film layer and the thickness of the first negative electrode film layer is 160 μm, it was prepared and tested in the same way as in Example 1. The test results are shown in Table 1.

[0255] Comparative Example 2

[0256] Except that it does not contain a first negative electrode film layer and the thickness of the second negative electrode film layer is 160 μm, it was prepared and tested in the same way as in Example 1. The test results are shown in Table 1.

[0257] Comparative Example 3

[0258] Except for changing the coating order of the first negative electrode slurry and the second negative electrode slurry, that is, first coating the second negative electrode slurry on the negative electrode current collector to form the second negative electrode film layer, and then coating the first negative electrode slurry on the second negative electrode film layer to form the first negative electrode film layer, the preparation and testing were carried out in the same way as in Example 1, and the test results are shown in Table 1.

[0259] Comparative Example 4

[0260] Except for adjusting the mass ratio of each component in the first negative electrode slurry to be the same as that in the second negative electrode slurry, the preparation and testing were carried out in the same way as in Example 1, and the test results are shown in Table 1.

[0261] Specifically, in this comparative example, the mass ratio of graphite, carbon nanotubes, SP, thickener, and binder in the first negative electrode slurry is 97.8:0.1:0.7:0.6:0.8.

[0262] Table 1

[0263] The batteries prepared in Examples 1 and Comparative Examples 1-4 were all charged at the same equivalent rate, making the cycle performance and DCR of each secondary battery comparable. The comparison showed that when a uniform negative electrode material layer was used (Comparative Examples 1 and 2), the cycle performance of the secondary battery was poor and the DCR value was high. Using larger particle size graphite and a higher mass percentage of conductive agent in the negative electrode film layer near the current collector (Comparative Example 3) further deteriorated the aforementioned performance. By adopting a layered design and using smaller particle size graphite and a lower mass percentage of conductive agent in the negative electrode film layer near the current collector (Example 1), the DCR of the individual battery cells was significantly reduced, which improved the battery's power performance and also improved the cycle capacity retention to some extent. Furthermore, Comparative Example 4 showed that if only smaller particle size graphite was used in the negative electrode film layer near the current collector without a lower mass percentage of conductive agent, the improvement in the aforementioned performance was extremely limited.

[0264] Examples 2-4

[0265] Except for the parameters of graphite in the first negative electrode slurry (hereinafter referred to as first graphite), the parameters of graphite in the second negative electrode slurry (hereinafter referred to as second graphite), and the compaction density of the negative electrode material layer as shown in Table 2, the preparation and testing were carried out in the same manner as in Example 1, and the results are shown in Table 2.

[0266] Table 2

[0267] The above results indicate that when the parameters are adjusted within a suitable range, the battery exhibits good cycle performance under high-rate charge and discharge conditions.

[0268] Examples 5-7

[0269] Except for the mass ratios of carbon nanotubes and carbon black conductive agent SP in the first and second negative electrode films as shown in Table 3 (when the above mass ratios are changed, the mass ratios of thickener and binder remain unchanged, and the mass ratio of negative electrode active material is changed accordingly), the preparation and testing were carried out in the same manner as in Example 1, and the results are shown in Table 3.

[0270] Table 3

[0271] The above results demonstrate that the batteries exhibit good cycle performance when the amount of conductive agent is adjusted within a suitable range. In particular, a comparison of Examples 5-6 with Examples 1 and 7 shows that further optimization of the amount of carbon nanotubes can further improve the battery's capacity retention.

[0272] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A battery cell, characterized by, Includes positive electrode, separator, and negative electrode; The negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector; the negative electrode material layer includes a first negative electrode film layer and a second negative electrode film layer; the first negative electrode film layer is closer to the negative current collector than the second negative electrode film layer. The first negative electrode film layer includes a first graphite and a first conductive agent; the second negative electrode film layer includes a second graphite and a second conductive agent; the particle size Dv50 of the first graphite is smaller than the particle size Dv50 of the second graphite; the mass percentage of the first conductive agent in the first negative electrode film layer is smaller than the mass percentage of the second conductive agent in the second negative electrode film layer.

2. The battery cell of claim 1, wherein, The particle size Dv50 of the first graphite is 5–12 μm.

3. The battery cell according to claim 1 or 2, wherein The particle size Dv50 of the second graphite is 10-20 μm.

4. The battery cell according to any one of claims 1 to 3, wherein The specific surface area of the first graphite is 0.2-1.2 m 2 / g.

5. The battery cell according to any one of claims 1 to 4, wherein The tap density of the first graphite is 0.8-1.2 g / cm 3 ; and / or, The particle size Dn10 of the first graphite is 0.2 to 0.9 μm.

6. The battery cell according to any one of claims 1 to 5, wherein The specific surface area of the second graphite is 0.4-0.9 m 2 / g.

7. The battery cell according to any one of claims 1 to 6, wherein The tap density of the second graphite is 1.2 to 1.6 g / cm 3 ; and / or, The particle size Dn10 of the second graphite is 0.8–1.5 μm.

8. The battery cell according to any one of claims 1 to 7, wherein Based on the mass of the second negative electrode film, the second conductive agent accounts for 0.1% to 1.5% of the mass percentage in the second negative electrode film; and / or, Based on the mass of the first negative electrode film, the mass percentage of the first conductive agent in the first negative electrode film is 0.05% to 0.5%.

9. The battery cell according to any one of claims 1 to 8, wherein Both the first conductive agent and the second conductive agent include carbon nanotubes; and the mass percentage of carbon nanotubes in the first negative electrode film is less than the mass percentage of carbon nanotubes in the second negative electrode film.

10. The battery cell of claim 9, wherein the cathode comprises a lithium metal oxide. Based on the mass of the second negative electrode film, the mass percentage of carbon nanotubes in the second negative electrode film is 0.1% to 1%; and / or, Based on the mass of the first negative electrode film, the mass percentage of carbon nanotubes in the first negative electrode film is 0.05% to 0.15%.

11. The battery cell according to any one of claims 9 to 10, wherein The carbon nanotubes include single-walled carbon nanotubes.

12. The battery cell according to any one of claims 9 to 11, wherein The aspect ratio of the carbon nanotubes is 2500 to 15000.

13. The battery cell according to any one of claims 9 to 12, wherein The carbon nanotubes have a diameter of 0.4–2 nm; and / or, The length of the carbon nanotubes is 0.5–20 μm.

14. The battery cell according to any one of claims 1 to 13, wherein The thickness ratio of the first negative electrode film layer to the second negative electrode film layer is 4-6:4-6.

15. The battery cell according to any one of claims 1 to 14, wherein The thickness of the first negative electrode film is 55–100 μm, and the thickness of the second negative electrode film is 55–100 μm.

16. The battery cell according to any one of claims 1 to 15, wherein The compacted density of the negative electrode material layer is 1.5-1.75 g / cm 3 .

17. A battery device characterized by comprising: Includes the battery cell according to any one of claims 1 to 16.

18. An electrical device, comprising: Includes the battery cell according to any one of claims 1 to 16 or the battery device according to claim 17.

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