Negative electrode sheet, battery, and electric device

Abstract

The present application discloses a negative electrode sheet, a battery, and an electric device. The negative electrode sheet comprises: a negative electrode current collector; a first negative electrode active material layer, the first negative electrode active material layer being provided on at least one side of the negative electrode current collector, and the first negative electrode active material layer comprising a first negative electrode active material; and a second negative electrode active material layer, the second negative electrode active material layer being provided on the side of the first negative electrode active material layer away from the negative electrode current collector, and the second negative electrode active material layer comprising a second negative electrode active material, wherein under the pressure of 20000 N, the compaction density of the first negative electrode active material is P1, the compaction density of the second negative electrode active material is P2, and P1-P2≥0.09 g / cm3. Thus, the probability of deformation of the negative electrode current collector can be reduced, and then the risk of brittle damage of the negative electrode sheet during cycles is reduced.

Description

Negative electrode, battery and electrical equipment Technical Field

[0001] The present application relates to the field of batteries, and in particular to negative electrode plates, batteries, and electrical equipment. Background Art

[0002] Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power stations, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric vehicles, as well as in a variety of fields such as military equipment and aerospace. To meet the demand for high energy density, the energy density of the battery can be increased by increasing the coating weight per unit area of ​​the negative electrode sheet and the pressure during cold pressing of the negative electrode sheet. However, when the cold pressing pressure is increased, the brittleness of the negative electrode sheet increases, and the risk of brittle damage to the negative electrode sheet increases during the battery cycle, thereby reducing the cycle life of the battery.

[0003] Summary of the Invention

[0004] In view of the technical problems existing in the background technology, the present application provides a negative electrode plate, which reduces the risk of brittle damage to the negative electrode plate, thereby improving the cycle life of the battery.

[0005] The first aspect of the present application provides a negative electrode sheet, comprising: a negative electrode current collector; a first negative electrode active material layer, the first negative electrode active material layer being disposed on at least one side of the negative electrode current collector, the first negative electrode active material layer comprising a first negative electrode active material; a second negative electrode active material layer, the second negative electrode active material layer being disposed on a side of the first negative electrode active material layer away from the negative electrode current collector, the second negative electrode active material layer comprising a second negative electrode active material; under a pressure of 20000N, the compaction density of the first negative electrode active material is P1, the compaction density of the second negative electrode active material is P2, and P1-P2≥0.09g / cm 3 Therefore, by making the difference in compaction density between the first negative electrode active material and the second negative electrode active material within the above range, the ability of the first negative electrode active material layer to bear external forces is improved, and the transmission of external forces to the negative electrode current collector is reduced, thereby reducing the risk of brittle damage to the negative electrode sheet during the cycle process, reducing the risk of the negative electrode sheet breaking during the battery cycle, reducing the probability of the negative electrode active material falling off, and improving the cycle life of the battery.

[0006] According to some embodiments of the present application, under a pressure of 20000N, 0.09g / cm 3 ≤P1-P2≤0.22g / cm 3Therefore, by making the difference in compaction density between the first negative electrode active material and the second negative electrode active material within the above range, the ability of the first active material layer to bear external forces can be improved, thereby reducing the transmission of force from the first negative electrode active material layer to the negative electrode current collector, thereby reducing the risk of brittle damage to the negative electrode sheet during the cycle.

[0007] According to some embodiments of the present application, under a pressure of 20000N, 0.12g / cm 3 ≤P1-P2≤0.20g / cm 3 Therefore, by making the difference in compaction density between the first negative electrode active material and the second negative electrode active material within the above range, the ability of the first active material layer to bear external forces can be improved, thereby reducing the transmission of force from the first negative electrode active material layer to the negative electrode current collector, thereby reducing the risk of brittle damage to the negative electrode sheet during the cycle.

[0008] According to some embodiments of the present application, under a pressure of 20000N, the values ​​of P1 and P2 meet one or more of the following conditions: 1.84g / cm 3 ≤P1≤1.90g / cm 3 ;1.70g / cm 3 ≤P2≤1.75g / cm 3 Therefore, by setting the values ​​of P1 and P2 within the above range, the energy density of the battery can be increased while reducing the brittleness of the negative electrode sheet.

[0009] According to some embodiments of the present application, the compaction density of the negative electrode sheet is 1.75 g / cm 3 -1.85g / cm 3 . Thus, the energy density of the battery can be improved.

[0010] According to some embodiments of the present application, the coating weight of the negative electrode sheet is 11.0 mg / cm 2 -13.0mg / cm 2 . Thus, the energy density of the battery can be improved.

[0011] According to some embodiments of the present application, the volume average particle size Dv50 of the powder of the first negative electrode active material layer satisfies the following conditions: 15 μm ≤ Dv50 ≤ 20 μm, and the volume average particle size Dv50 of the powder of the second negative electrode active material layer satisfies the following conditions: 13 μm ≤ Dv50 ≤ 18 μm. Thus, by making the compaction density of the first negative electrode active material greater than the compaction density of the second negative electrode active material, the ability of the first negative electrode active material layer to withstand external forces can be improved.

[0012] According to some embodiments of the present application, the first negative electrode active material includes at least one of a first artificial graphite or a natural graphite, and the second negative electrode active material includes a second artificial graphite. This can improve the energy density and fast charging performance of the battery.

[0013] According to some embodiments of the present application, both the first artificial graphite and the second artificial graphite include secondary graphite particles, thereby improving the energy density and fast charging performance of the battery.

[0014] According to some embodiments of the present application, the negative electrode sheet meets one or more of the following conditions: the volume average particle size Dv50 of the second artificial graphite meets the following conditions: 13 μm ≤ Dv50 ≤ 18 μm; the volume average particle size Dv50 of the first artificial graphite meets the following conditions: 13 μm ≤ Dv50 ≤ 17 μm; and the volume average particle size Dv50 of the natural graphite meets the following conditions: 15 μm ≤ Dv50 ≤ 25 μm. Thus, by increasing the compaction density of the first negative electrode active material to be greater than the compaction density of the second negative electrode active material, the ability of the first negative electrode active material layer to withstand external forces can be improved, thereby reducing the risk of brittle damage to the negative electrode current collector.

[0015] The second aspect of the present application provides a battery comprising the negative electrode plate provided in the first aspect of the present application, thereby providing the battery with excellent fast charging capability, high energy density, and excellent cycle performance.

[0016] The third aspect of the present application provides an electrical device, including the negative electrode provided by the first aspect of the present application or the battery provided by the second aspect of the present application.

[0017] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0019] FIG1 is a schematic structural diagram of a negative electrode sheet according to an embodiment of the present application;

[0020] FIG2 is a schematic diagram of a battery according to an embodiment of the present application.

[0021] FIG3 is an exploded view of the battery shown in FIG2 according to one embodiment of the present application.

[0022] FIG4 is a schematic diagram of a battery module according to an embodiment of the present application.

[0023] FIG5 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0024] FIG. 6 is an exploded view of the battery pack shown in FIG. 5 according to an embodiment of the present application.

[0025] FIG7 is a schematic diagram of an electrical device using a battery as a power source according to an embodiment of the present application.

[0026] Description of reference numerals:

[0027] 10 negative electrode plate; 11 negative electrode current collector; 12 first negative electrode active material layer; 13 second negative electrode active material layer;

[0028] 1. Battery pack; 2. Upper case; 3. Lower case; 4. Battery module; 5. Battery; 5.1. Shell; 5.2. Electrode assembly; 5.3. Top cover assembly. DETAILED DESCRIPTION

[0029] The following embodiments of the technical solution of the present application are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only used as examples and are not intended to limit the scope of protection of the present application.

[0030] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0031] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0032] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0033] Unless otherwise specified, all steps of the present 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 may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0034] Currently, market developments indicate that batteries are increasingly being used. They are not only used in energy storage systems such as hydropower, thermal, wind, and solar power plants, but are also widely used in electric vehicles like electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. As battery applications continue to expand, market demand is also growing.

[0035] To meet the demand for high battery energy density, the energy density of the battery can be increased by increasing the coating weight of the negative electrode sheet. As the energy density of the negative electrode sheet increases, the cold pressing pressure increases during the cold pressing process, and the brittleness of the negative electrode sheet increases after cold pressing. Due to the limited space in the battery shell, after the battery is fully charged, the electrodes may be squeezed together, resulting in brittle damage to the negative electrode sheet. For example, during battery preparation, the positive electrode sheet, negative electrode sheet, and diaphragm can be wound around a winding needle of a certain shape and then placed in a shell of fixed size. If the negative electrode sheet is relatively brittle, the corners of the inner ring of the negative electrode sheet are prone to brittle damage after the battery is fully charged.

[0036] During the cold pressing process of the electrode sheet, force is distributed across the different film layers on the electrode sheet. The negative electrode sheet proposed in this application improves the ability of the first negative electrode active material layer to withstand external forces by ensuring that the difference in compaction density between the first negative electrode active material and the second negative electrode active material falls within a certain range. When the battery is fully charged, even if compression occurs between the electrode sheets, the transmission of external forces to the negative electrode current collector is reduced, reducing the probability of brittle damage to the negative electrode current collector. This reduces the risk of negative electrode sheet fracture during battery cycling, reduces the probability of negative electrode active material shedding, and improves the battery's cycle life.

[0037] The negative electrode plate proposed in this application can be used for lithium-ion batteries, and the battery disclosed in the embodiments of this application can be used in electrical equipment that uses batteries as power sources or various energy storage systems that use batteries as energy storage elements. Electrical equipment may include but is not limited to mobile phones, tablets, laptops, electric toys, power tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0038] In a first aspect, the present application provides a negative electrode sheet. Referring to FIG1 , the negative electrode sheet 10 includes: a negative electrode current collector 11; a first negative electrode active material layer 12, wherein the first negative electrode active material layer 12 is provided on at least one side of the negative electrode current collector 11, and the first negative electrode active material layer 12 includes a first negative electrode active material; a second negative electrode active material layer 13, wherein the second negative electrode active material layer 13 is provided on a side of the first negative electrode active material layer 12 away from the negative electrode current collector 11, and the second negative electrode active material layer 13 includes a second negative electrode active material; under a pressure of 20000N, the compaction density of the first negative electrode active material is P1, the compaction density of the second negative electrode active material is P2, and P1-P2≥0.09g / cm 3 .

[0039] The negative electrode plate proposed in the present application, even if a relatively high pressure is used to cold press the plate, when the negative electrode plate is subjected to external force during the cold pressing process, by making the compaction density difference between the first negative electrode active material and the second negative electrode active material within the above-mentioned range, the degree of deformation that the first negative electrode active material layer 12 can withstand can be increased. The external force during cold pressing mainly acts on the first negative electrode active material and causes it to deform, thereby reducing the probability of the external force being transmitted to the negative electrode collector 11 through the first negative electrode active material layer 12, reducing the force on the negative electrode current collector 11, and further reducing the probability of deformation of the negative electrode current collector 11, reducing the risk of brittle damage of the negative electrode plate 10 during the cycle, reducing the probability of microcracks in the negative electrode current collector 11 or shedding of the negative electrode active material, and thus improving the cycle life of the battery.

[0040] In the present application, the first negative electrode active material layer 12 and the second negative electrode active material layer 13 are layered as follows: the overall thickness of the negative electrode active material layer is recorded as H, the thickness range from the surface of the negative electrode active material layer away from the negative electrode current collector to 0.3H can be regarded as the second negative electrode active material layer, and the film layer with a thickness of 0.3H from the surface of the negative electrode current collector 11 to the negative electrode current collector 11 can be regarded as the first negative electrode active material layer. The powders of the second negative electrode active material layer and the first negative electrode active material layer are scraped off in turn, and the powders are sintered at a sintering temperature greater than or equal to 400°C. The binder in the powder of the first negative electrode active material layer and the powder of the second negative electrode active material layer is removed, and the remaining powder of the first negative electrode active material layer and the second negative electrode active material layer is tested for compaction density, which can represent the compaction density of the first negative electrode active material and the second negative electrode active material.

[0041] In the present application, the test method for the compaction density of the first negative electrode active material layer powder and the second negative electrode active material layer powder is: take a certain amount of powder and place it in a compaction mold, use a pressure of 20,000 N, record the thickness of the powder after pressure relief, and the compaction density of the powder under a pressure of 20,000 N can be calculated by ρ = m / v.

[0042] According to some embodiments of the present application, under a pressure of 20000N, 0.09g / cm 3 ≤P1-P2≤0.22g / cm 3 For example, P1-P2≤ can be 0.09 g / cm 3 , 0.1g / cm 3 , 0.11g / cm 3 , 0.12g / cm 3 , 0.13g / cm 3 , 0.14g / cm 3 , 0.15g / cm 3 , 0.16g / cm 3 , 0.17g / cm 3 , 0.18g / cm 3 , 0.19g / cm 3 , 0.2g / cm 3 or 0.22g / cm 3 According to some specific embodiments of the present application, under a pressure of 20000N, 0.12g / cm 3 ≤P1-P2≤0.20g / cm 3 .

[0043] According to some embodiments of the present application, under a pressure of 20000N, 1.84g / cm 3 ≤P1≤1.90g / cm 3 , for example, can be 1.84 g / cm 3 , 1.85g / cm 3 , 1.86g / cm 3 , 1.87g / cm 3 , 1.88g / cm 3 , 1.89g / cm 3 or 1.90g / cm 3 etc., or can be within the range of any of the above numerical values.

[0044] According to some embodiments of the present application, under a pressure of 20000N, 1.70g / cm 3 ≤P2≤1.75g / cm 3 For example, it can be 1.70g / cm 3 、1.71g / cm 3 , 1.72g / cm 3 , 1.73g / cm 3 , 1.74g / cm 3 or 1.75g / cm 3 etc., or can be within the range of any of the above numerical values.

[0045] Therefore, since P1 is greater than P2, by setting the values ​​of P1 and P2 within the above range, the ability of the first negative electrode active material layer 12 to bear external forces can be improved while the energy density of the battery can be increased.

[0046] According to some embodiments of the present application, the compaction density of the negative electrode sheet 10 can be 1.75 g / cm 3 -1.85g / cm 3 For example, it can be 1.75g / cm 3 , 1.76g / cm 3 , 1.77g / cm 3 , 1.78g / cm 3 , 1.79g / cm 3 , 1.80g / cm 3 、1.81g / cm 3 , 1.82g / cm 3 , 1.83g / cm 3 、1.84g / cm 3 or 1.85g / cm 3 etc., or can be within a range consisting of any of the above values. Thus, the compacted density of the negative electrode sheet 10 is relatively high. By making P1 greater than P2, the ability of the first negative electrode active material layer 12 to bear external forces can be improved, thereby reducing the transmission of force from the first negative electrode active material layer 12 to the negative electrode current collector 11, thereby reducing the risk of brittle damage to the negative electrode sheet 10 during cycling, reducing the risk of fracture of the negative electrode sheet during battery cycling, reducing the probability of active material on the negative electrode sheet falling off, and improving the cycle life of the battery.

[0047] In the present application, the compaction density of the negative electrode sheet refers to the compaction density of the negative electrode active material layer (including the first negative electrode active material layer and the second negative electrode active material layer).

[0048] In the present application, the test method for the compaction density of the negative electrode plate 10 is as follows: the coated area and the empty foil area in the plate are punched into fixed sizes, and the thickness of the plate is measured as H1 and the thickness of the negative electrode collector is measured as H0 using a micrometer; the weight of the cut negative electrode plate is weighed as M1 and the weight of the negative electrode collector is weighed as M0, and the compaction density of the negative electrode plate can be calculated as (M1-M0) / (H1-H0).

[0049] According to some embodiments of the present application, the volume average particle size Dv50 of the powder of the first negative electrode active material layer 12 satisfies the following conditions: 15 μm ≤ Dv50 ≤ 20 μm. For example, the Dv50 of the powder of the first negative electrode active material layer 12 may be 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm, or may be a range consisting of any of the above values. The volume average particle size Dv50 of the powder of the second negative electrode active material layer 13 satisfies the following conditions: 13 μm ≤ Dv50 ≤ 18 μm. For example, the Dv50 of the powder of the second negative electrode active material layer 13 may be 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, or 18 μm, or may be a range consisting of any of the above values. Thus, the fast charging capability of the battery is improved.

[0050] In this application, the volume average particle size Dv50 refers to the particle size corresponding to the cumulative volume distribution percentage reaching 50%, for example, with reference to the standard GB / T 19077-2016 / ISO 13320:2009, using a laser particle size analyzer (Malvern Master Size 2000). The specific testing process is as follows: scrape off the powder of the first negative electrode active material layer 12, take an appropriate amount of sample (the sample concentration is sufficient to ensure 8%-12% light shielding), add 20ml of deionized water, and ultrasonicate for 5 minutes (53KHz / 120W) to ensure that the sample is completely dispersed. Then, the sample is measured according to the GB / T19077-2016 / ISO 13320:2009 standard.

[0051] According to some embodiments of the present application, the coating weight of the negative electrode sheet 10 can be 11.0 mg / cm 2 -13.0mg / cm 2 For example, it can be 11.0 mg / cm 2 、11.5mg / cm 2 、12.0mg / cm 2 、12.5mg / cm 2 or 13.0 mg / cm 2 Thus, the negative electrode sheet is coated thickly to increase the energy density of the battery.

[0052] According to some embodiments of the present application, the compaction density of the negative electrode sheet can be 1.75 g / cm 3 -1.85g / cm 3 ， The coating weight of the negative electrode plate 10 can be 11.0 mg / cm 2 -13.0mg / cm 2That is, the negative electrode plate adopts high pressure density and thick coating. When the negative electrode plate is subjected to external force during the cold pressing process, since the compaction density of the second negative electrode active material is less than the compaction density of the first negative electrode active material, the deformation degree that the first negative electrode active material layer 12 can withstand can be increased. The external force during cold pressing mainly acts on the first negative electrode active material and causes it to deform, thereby reducing the probability of the external force being transmitted to the negative electrode current collector 11 through the first negative electrode active material layer 12, reducing the force on the negative electrode current collector 11, and further reducing the probability of deformation of the negative electrode current collector 11, reducing the risk of brittle damage of the negative electrode plate 10 during the cycle, and reducing the probability of microcracks in the negative electrode current collector 11 or shedding of the negative electrode active material.

[0053] In the present application, the test method for the coating weight of the negative electrode plate 10 is to punch out the coated area and the empty foil area in the negative electrode plate into fixed sizes, weigh the weight of the cut negative electrode plate as M1, and the weight of the negative electrode collector as M0, and then calculate the coating weight of the negative electrode plate as: (M1-M0) / plate area after punching.

[0054] According to some embodiments of the present application, the ratio of the coating weight of the first negative electrode active material layer 12 to the coating weight of the second negative electrode active material layer 13 can be 0.65-1.5, for example, it can be 0.65, 0.75, 0.85, 0.95, 1.05, 1.15, 1.25, 1.35, 1.45 or 1.5, etc., or it can be a range consisting of any of the above values.

[0055] According to some embodiments of the present application, the coating weight of the first negative electrode active material layer 12 and the coating weight of the second negative electrode active material layer 13 may be the same.

[0056] According to some embodiments of the present application, the first negative electrode active material includes at least one of a first artificial graphite or a natural graphite, and the second negative electrode active material includes a second artificial graphite. This improves the battery's energy density while also enhancing its fast-charging performance. According to some specific embodiments of the present application, both the first artificial graphite and the second artificial graphite may include secondary graphite particles.

[0057] According to some embodiments of the present application, the first negative electrode active material includes a first artificial graphite and natural graphite, and the second negative electrode active material includes a second artificial graphite, wherein the first artificial graphite and the second artificial graphite are both secondary graphite particles.

[0058] According to some embodiments of the present application, when the first negative electrode active material layer 12 includes a first artificial graphite and a natural graphite, the ratio of the mass of the first artificial graphite to the mass of the natural graphite can be 1-1.5, for example, it can be 1, 1.1, 1.2, 1.3, 1.4 or 1.5, etc., or it can be a range consisting of any of the above numerical values.

[0059] According to some embodiments of the present application, the mass proportion of the first artificial graphite may be 50%-60% based on the total mass of the first negative electrode active material layer 12. For example, it may be 50%, 52%, 54%, 56%, 58%, or 60%, or any range thereof.

[0060] According to some embodiments of the present application, the mass proportion of the natural graphite may be 40%-50% based on the total mass of the first negative electrode active material layer 12. For example, it may be 40%, 42%, 44%, 46%, 48%, or 50%, or may be within a range consisting of any of the above values.

[0061] It should be noted that when the first negative electrode active material layer 12 includes both the first artificial graphite and the natural graphite, the compaction density of the first negative electrode active material can be calculated according to the content of the first artificial graphite and the natural graphite. For example, the compaction density of the first negative electrode active material = X1 × P 11 +X2×P 12 , wherein X1 is the mass proportion of the first artificial graphite based on the total mass of the first artificial graphite and natural graphite, in %; P 11 is the compacted density of the first artificial graphite, in g / cm 3 ; X2 is the mass proportion of natural graphite based on the total mass of the first artificial graphite and natural graphite, in %; P 12 is the compacted density of natural graphite, in g / cm 3 .

[0062] According to some embodiments of the present invention, under a pressure of 20000N, the compaction density of the first artificial graphite can be 1.84g / cm 3 ≤P1≤1.90g / cm 3 , for example, can be 1.84 g / cm 3 , 1.85g / cm 3 , 1.86g / cm 3 , 1.87g / cm 3 , 1.88g / cm 3 , 1.89g / cm 3 or 1.90g / cm 3 etc., or can be within the range of any of the above numerical values. Thus, the energy density of the battery can be improved.

[0063] According to some embodiments of the present invention, the compacted density of natural graphite can be 1.84 g / cm2 under a pressure of 20,000 N. 3 ≤P1≤1.90g / cm 3 , for example, can be 1.84 g / cm 3 , 1.85g / cm 3 , 1.86g / cm 3 , 1.87g / cm 3 , 1.88g / cm 3 , 1.89g / cm 3 or 1.90g / cm 3 etc., or can be within the range of any of the above numerical values. Thus, the energy density of the battery can be improved.

[0064] According to some embodiments of the present application, the volume average particle size Dv50 of the second artificial graphite satisfies the following: 13 μm ≤ Dv50 ≤ 18 μm. For example, the volume average particle size Dv50 may be 13 μm, 15 μm, 17 μm, or 18 μm, or may be within a range consisting of any of the aforementioned values. This can improve the energy density of the battery.

[0065] According to some embodiments of the present application, the volume average particle size Dv50 of the first artificial graphite satisfies the following: 13 μm ≤ Dv50 ≤ 17 μm. For example, the volume average particle size Dv50 may be 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, or any range thereof. This improves the energy density of the battery.

[0066] According to some embodiments of the present application, the volume average particle size Dv50 of the natural graphite satisfies the following: 15 μm ≤ Dv50 ≤ 25 μm. For example, the volume average particle size Dv50 may be 15 μm, 17 μm, 19 μm, 21 μm, 23 μm, or 25 μm, or may be within a range consisting of any of the above values. This improves the energy density of the battery.

[0067] The second aspect of the present application provides a battery, comprising the negative electrode plate 10 provided in the first aspect of the present application. Thus, during the battery cycle, the probability of brittle damage to the negative electrode plate 10 can be reduced, thereby increasing the cycle life of the battery.

[0068] Typically, a battery includes a positive electrode sheet, a negative electrode sheet 10, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrode sheets 10. The electrolyte conducts ions between the positive and negative electrode sheets 10. The separator is positioned between the positive and negative electrode sheets 10, primarily preventing short circuits between the positive and negative electrodes while allowing ions to pass through.

[0069] [Positive electrode]

[0070] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode active material of the first aspect of the present application.

[0071] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0072] In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0073] In some embodiments, when the battery is a lithium-ion battery, the positive electrode active material may adopt the positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries 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 may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0074] The modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0075] In some embodiments, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0076] In some embodiments, the positive electrode active material layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0077] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0078] [Negative electrode]

[0079] 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 base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0080] In some embodiments, the first negative electrode active material layer and the second negative electrode active material layer may further include a binder. The binder may be selected from at least one of 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).

[0081] In some embodiments, the first negative electrode active material layer and the second negative electrode active material layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0082] In some embodiments, the first negative electrode active material layer and the second negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0083] [Electrolytes]

[0084] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. This application has no specific restrictions on the type of electrolyte, and it can be selected according to needs.

[0085] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0086] In some embodiments, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0087] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0088] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0089] [Isolation film]

[0090] In some embodiments, the battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0091] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven 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.

[0092] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0093] In some embodiments, the battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0094] In some embodiments, the battery outer packaging may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the battery outer packaging may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0095] The present application has no particular limitation on the shape of the battery, which can be cylindrical, square, or any other shape. For example, FIG2 shows a square-shaped battery 5 as an example.

[0096] In some embodiments, referring to FIG3 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0097] In some embodiments, batteries may be assembled into a battery module. The number of batteries contained in the battery module may be one or more. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0098] FIG4 illustrates an exemplary battery module 4. Referring to FIG4 , within the battery module 4, multiple batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, the arrangement may also be arranged in any other manner. Furthermore, the multiple batteries 5 may be secured together using fasteners.

[0099] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of batteries 5 are received in the receiving space.

[0100] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0101] Figures 5 and 6 illustrate an example battery pack 1. Referring to Figures 5 and 6 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0102] The third aspect of the present application provides an electric device, which includes at least one of the batteries, battery modules, or battery packs provided in the present application. The battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0103] As the electrical device, a battery, a battery module or a battery pack can be selected according to its usage requirements.

[0104] Figure 7 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the battery, a battery pack or battery module can be used.

[0105] Another example device may be a mobile phone, a tablet computer, a laptop computer, etc. Such a device is usually required to be light and thin, and may use a battery as a power source.

[0106] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0107] Example 1

[0108] 1. Preparation of positive electrode sheet

[0109] The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an appropriate amount of solvent N-methylpyrrolidone (NMP) in a mass ratio of 80:15:5 to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode sheet is obtained.

[0110] 2. Preparation of negative electrode sheet

[0111] The negative electrode active materials artificial graphite and natural graphite (the mass ratio of artificial graphite to natural graphite is 1:1), the conductive agent Super P, the thickener CMC, and the binder styrene-butadiene rubber are mixed in a mass ratio of 96.4:1:1.2:1.4, and deionized water solvent is added. The mixture is stirred evenly under the action of a vacuum mixer, coated on the negative electrode current collector copper foil, and dried in an oven to form a first negative electrode active material layer.

[0112] The negative electrode active material artificial graphite, conductive agent Super P, thickener CMC, and binder styrene-butadiene rubber are mixed in a mass ratio of 96.4:1:1.2:1.4, and deionized water is added as a solvent. The mixture is stirred evenly under the action of a vacuum mixer and coated on the side of the first negative electrode active material layer away from the copper foil. The mixture is dried in an oven and cold pressed to obtain a negative electrode sheet.

[0113] 3. Prepare electrolyte

[0114] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. The fully dried electrolyte salt LiPF6 was dissolved in the above solvent and mixed evenly to obtain an electrolyte solution with a concentration of 1 mol / L.

[0115] 4. Isolation film

[0116] A porous polyethylene film was used as the separator.

[0117] 5. Preparation of batteries

[0118] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried lithium-ion battery. After vacuum packaging, standing, formation, and shaping processes, a lithium-ion battery is obtained.

[0119] The preparation methods of the batteries in Examples 2 to 13 and Comparative Example 1 are the same as those in Example 1, with the differences detailed in Table 1.

[0120] In the present application, the compaction density of the negative electrode sheet can be adjusted by adjusting the pressure of the roller during the cold pressing process.

[0121] In the present application, the coating weight of the negative electrode sheet can be adjusted by adjusting the gap between the coating blades during the coating process.

[0122] Table 1

[0123] Performance Testing

[0124] 1. Pole brittle damage test

[0125] After fully charging the battery obtained above, disassemble it and separate the fully charged negative electrode. Fold the electrode in half along the radial direction and squeeze it with a 35cm×15cm glass plate with a mass of about 600g to completely fold it in half. After opening it, observe whether the electrode is broken. The degree of lithium precipitation is determined by the ratio of light leakage or breakage length at the fold to the entire length. Complete breakage is classified as first-level brittle damage, light leakage or breakage ratio greater than 1 / 2 is classified as second-level brittle damage, light leakage or breakage ratio between 1 / 4 and 1 / 2 is classified as third-level brittle damage, light leakage or breakage ratio less than 1 / 4 is classified as fourth-level brittle damage, and no light leakage or breakage is classified as zero-level damage. In addition, for the electrode that is not completely broken, fold it back and forth until it breaks, and record the number of times it is completely broken, where one positive fold and one negative fold of the electrode is counted as one time.

[0126] It should be noted that graphite-based negative electrode materials are highly flexible, and after cold pressing, the negative electrode sheets are expanded after extrusion, making it difficult for the current collector to break or separate from the active material. This application aims to avoid possible brittle damage during cycling, so fully charged electrode sheets (which are more brittle) are used as the research object.

[0127] The test results of Examples 1 to 13 and Comparative Example 1 are shown in Table 2.

[0128] Table 2

[0129] Conclusion: Compared with Example 1-13 and Comparative Example 1, it can be seen that the present invention achieves the following results by making P1-P2≥0.09g / cm 3 , which can reduce the degree of damage to the negative electrode sheet, thereby reducing the risk of the negative electrode sheet breaking during the battery cycle, reducing the probability of the negative electrode active material falling off, and improving the cycle life of the battery.

[0130] It can be seen from Examples 1 to 13 of the present application that when the negative electrode sheet adopts high density and high coating, by making P1-P2≥0.09g / cm 3 , which can reduce the degree of damage to the negative electrode sheet, thereby reducing the risk of the negative electrode sheet breaking during the battery cycle, reducing the probability of the negative electrode active material falling off, and improving the cycle life of the battery.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A negative electrode sheet, wherein: include: negative electrode current collector; a first negative electrode active material layer, the first negative electrode active material layer being disposed on at least one side of the negative electrode current collector, the first negative electrode active material layer comprising a first negative electrode active material; a second negative electrode active material layer, the second negative electrode active material layer being disposed on a side of the first negative electrode active material layer away from the negative electrode current collector, the second negative electrode active material layer comprising a second negative electrode active material; Under a pressure of 20000N, the compaction density of the first negative electrode active material is P1, the compaction density of the second negative electrode active material is P2, and P1-P2≥0.09g / cm 3 .

2. The negative electrode sheet according to claim 1, wherein: 0.09g / cm2 under 20000N pressure 3 ≤P1-P2≤0.22g / cm 3 .

3. The negative electrode sheet according to claim 1 or 2, wherein: 0.12g / cm2 under 20000N pressure 3 ≤P1-P2≤0.20g / cm 3 .

4. The negative electrode sheet according to any one of claims 1 to 3, wherein: Under a pressure of 20,000 N, the values ​​of P1 and P2 meet one or more of the following conditions: 1.84 g / cm 3 ≤P1≤1.90g / cm 3 ; 1.70g / cm 3 ≤P2≤1.75g / cm 3 。 5. The negative electrode sheet according to any one of claims 1 to 4, wherein: The compaction density of the negative electrode sheet is 1.75 g / cm 3 -1.85g / cm 3 .

6. The negative electrode sheet according to any one of claims 1 to 5, wherein: The coating weight of the negative electrode sheet is 11.0 mg / cm 2 -13.0mg / cm 2 .

7. The negative electrode sheet according to any one of claims 1 to 6, wherein: The volume average particle size Dv50 of the first negative electrode active material layer powder satisfies: 15 μm≤Dv50≤20 μm, and the volume average particle size Dv50 of the second negative electrode active material layer powder satisfies: 13 μm≤Dv50≤18 μm.

8. The negative electrode sheet according to any one of claims 1 to 7, wherein: The first negative electrode active material includes at least one of a first artificial graphite or a natural graphite, and the second negative electrode active material includes a second artificial graphite.

9. The negative electrode sheet according to claim 8, wherein: The first artificial graphite and the second artificial graphite both include secondary graphite particles.

10. The negative electrode sheet according to claim 9, wherein: Meet one or more of the following conditions: The volume average particle size Dv50 of the second artificial graphite satisfies: 13 μm≤Dv50≤18 μm; The volume average particle size Dv50 of the first artificial graphite satisfies: 13 μm≤Dv50≤17 μm; The volume average particle size Dv50 of the natural graphite satisfies: 15 μm≤Dv50≤25 μm.

11. A battery, wherein: The invention comprises the negative electrode sheet according to any one of claims 1 to 10.

12. An electrical device, wherein: Including the battery according to claim 11.

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