Battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery. The battery comprises a shell and a battery cell, the battery cell comprises a negative plate, the thickness of a negative current collector in the negative plate is 8-14 microns, the shell sequentially comprises a first layer, a metal layer and a second layer, the second layer is close to the battery cell, and the puncture strength of the shell is larger than or equal to 25 N; the ratio of the thickness of the first layer to the thickness of the shell is 0.25-0.35, a characteristic peak exists in an X-ray diffraction pattern of the first layer when 2 theta is equal to 20.1-23.2 degrees, the metal layer comprises crystal grains, and the number of the crystal grains with the grain size larger than or equal to 5 microns in the crystal grains is smaller than or equal to 4 in an optional area with the area being 100 microns * 100 microns in an EBSD pattern of the metal layer. The battery has high puncture resistance and high heat dissipation performance, the risk that the battery fails in advance due to poor heat dissipation performance in a falling puncture test is reduced, and the falling puncture passing rate of the battery is increased.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a battery. Background Technology

[0002] Lithium-ion batteries, with their high energy density and long cycle life, have become the core power source for consumer electronics, electric vehicles, and energy storage systems. However, their safety, especially the risk of thermal runaway under mechanical abuse conditions, remains a key challenge restricting their further development. In tests such as drop and puncture tests, external impacts can easily cause short circuits in the positive and negative electrode plates inside the cell, generating a large amount of Joule heat and causing local temperature rise. This temperature rise triggers a series of chain exothermic reactions: first, it causes the organic electrolyte to decompose, producing flammable gases such as hydrogen and methane; then, it causes the highly active positive electrode material to decompose and release oxygen; at the same time, the SEI film on the surface of the negative electrode also decomposes, further aggravating the exothermic reaction. These reactions promote each other, leading to a rapid accumulation of heat and a sudden increase in internal pressure, which may ultimately cause the battery to catch fire or even explode, resulting in an unsatisfactory pass rate in drop and puncture tests. Summary of the Invention

[0003] During drop and puncture tests, the metal puncture needle preferentially penetrates the battery casing. By increasing the casing's puncture strength, the kinetic energy during puncture can be resisted, reducing localized stress on the positive and negative electrodes. This lowers the risk of the electrodes being punctured and conducting electricity through the metal puncture needle, thus improving the battery's drop and puncture pass rate. However, while increasing the casing's thickness enhances its puncture strength, this also reduces its heat dissipation performance. This can lead to heat buildup inside the battery, potentially causing a fire and premature battery failure during drop and puncture tests.

[0004] To reduce the risk of premature battery failure due to poor heat dissipation during drop puncture tests, improve the battery drop puncture pass rate, and enhance battery safety, this invention provides a battery. The battery of this invention combines high puncture resistance with high heat dissipation performance, thereby reducing the risk of premature battery failure due to poor heat dissipation during drop puncture tests, thus improving the battery drop puncture pass rate and enhancing battery safety.

[0005] To achieve the above objectives, the present invention provides a battery comprising a casing and a cell, the cell being located within a containment space formed by the casing, the cell comprising an electrolyte and an electrode assembly formed by a positive electrode, a separator, and a negative electrode, the negative electrode comprising a negative current collector having a thickness of 8μm-14μm, the casing comprising a first layer, a metal layer, and a second layer sequentially stacked thereon, the second layer being close to the cell, and the puncture strength of the casing being greater than or equal to 25N; The thickness ratio of the first layer to the shell is 0.25-0.35. In the X-ray diffraction pattern of the first layer, there is a characteristic peak at 2θ=20.1°-23.2°. The metal layer includes grains. In any region of 100μm×100μm selected in the EBSD pattern of the metal layer, the number of grains with a diameter greater than or equal to 5μm is less than or equal to 4.

[0006] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: In the battery of this invention, the puncture strength of the casing is controlled so that the casing can resist the kinetic energy of the metal needle during puncture, reducing the local stress on the positive and negative electrodes. Simultaneously, by controlling the ratio of the thickness of the first layer to the thickness of the casing to be between 0.25 and 0.35, and by ensuring that the XRD pattern of the first layer has a characteristic peak at 2θ = 20.1°-23.2°, it is ensured that the outer layer of the casing (i.e., the first layer) has sufficient thickness to contribute to high puncture strength, while its polymer molecular chains form a specific regular arrangement and crystalline structure. This specific crystalline morphology allows it to absorb energy through micro-region deformation under impact, exhibiting excellent toughness and tear resistance. Furthermore, in the E... Within any 100μm×100μm area selected in the BSD diagram, controlling the number of grains with a diameter greater than or equal to 5μm in the metal layer ensures that the metal layer constituting the outer shell skeleton has a fine and uniform grain structure. This not only improves the overall strength and toughness of the metal layer, but more importantly, it avoids coarse grains as weak points in mechanical properties, ensuring that the shell deforms uniformly when subjected to impact and is not prone to intergranular fracture. This further reduces the piercing kinetic energy of the metal needle and further improves the drop puncture pass rate of the battery. At the same time, through the synergistic effect of the metal layer and the second layer, it effectively prevents the cracks generated when the metal needle penetrates the shell from further expanding.

[0007] Furthermore, in order to compensate for the reduced heat dissipation performance caused by the increased thickness of the polymer layer in the high-strength shell, the present invention simultaneously controls the thickness of the negative electrode current collector to be between 8μm and 14μm, thereby improving the lateral (along the foil surface) heat diffusion capability of the negative electrode current collector. When a hot spot appears in a local area, the thicker negative electrode current collector can quickly disperse the local hot spot to a larger area, avoiding heat concentration and effectively preventing premature thermal failure due to poor heat dissipation under conditions such as drop tests. Thus, the battery has both high puncture resistance and high heat dissipation performance.

[0008] Other features and advantages of the present invention will be described in detail in the following detailed description section.

[0009] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0010] Figure 1 The diagram shows the location of the puncture in the casing of the battery of the present invention after a drop puncture test. Detailed Implementation

[0011] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention. Unless otherwise specified herein, data ranges include endpoints.

[0012] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0013] This invention provides a battery comprising a casing and a battery cell, the battery cell being located within a receiving space formed by the casing. The battery cell includes an electrolyte and an electrode assembly formed by a positive electrode, a separator, and a negative electrode. The negative electrode includes a negative current collector, the thickness of which is 8μm-14μm (e.g., 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm or...). (within the range of any two of the above values), the casing includes a first layer, a metal layer, and a second layer stacked sequentially, with the second layer close to the battery cell, and the puncture strength of the casing is greater than or equal to 25N (e.g., 25N, 28N, 30N, 33N, 35N, 38N, 40N, 43N, 45N, 48N, 50N, 55N, 60N, 65N, 70N, 75N, 80N, 85N, 90N, 95N, 100N, or within the range of any two of the above values). The ratio of the thickness of the first layer to the thickness of the shell is 0.25-0.35 (e.g., 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, or within any two of the above values). In the X-ray diffraction pattern of the first layer, at 2θ = 20.1°-23.2° (e.g., 20.1°, 20.3°, 20.5°, 20.8°, 21°, 21.3°, 21.5°, 21.8°, 22°, 22.3°, 22.5°, 22.8°), the X-ray diffraction pattern is as follows: The metal layer comprises grains, and in any 100μm×100μm region in the EBSD image of the metal layer, the number of grains with a diameter greater than or equal to 5μm (e.g., 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm or within any two of the above values) is less than or equal to 4 (e.g., 4, 3, 2, 1, 0).

[0014] It is understood that if the number of grains with a diameter greater than or equal to 5 μm in any 100 μm × 100 μm region in the EBSD diagram of the metal layer is 0, it means that there are no grains with a diameter greater than or equal to 5 μm in the metal layer.

[0015] In the battery design of this invention, the puncture strength of the casing is controlled by the system to effectively resist the kinetic energy applied when the metal needle punctures, thereby significantly reducing the local stress borne by the positive and negative electrode plates. Specifically, controlling the ratio of the thickness of the first layer (outer polymer layer) to the total thickness of the casing within a reasonable range is one of the keys to ensuring the casing has excellent puncture resistance. If this ratio is too low (less than 0.25), the outer structure of the casing will be insufficient in strength, which will weaken its resistance to initial puncture, making the casing more easily punctured under impact. The kinetic energy of the metal needle will be transferred to the inner metal layer with almost no buffer. In this case, even if the negative electrode current collector has good lateral heat dissipation capacity, the heat cannot be evenly diffused in time due to the excessively violent and rapid short circuit process, which will eventually lead to thermal runaway. Conversely, if this ratio is too high (greater than 0.35), the first layer (outer polymer layer) will excessively encroach on the total thickness of the casing, forcing the thickness of the metal layer, which serves as the structural skeleton and main heat dissipation channel, to be reduced. The thinner metal layer will not only reduce its overall strength and toughness, making it more prone to tearing under the action of the needle, but will also significantly weaken the lateral heat dissipation capacity of the casing, affecting the thermal management performance of the battery.

[0016] Furthermore, the first layer is controlled to exhibit characteristic peaks in the XRD pattern within the range of 2θ = 20.1°–23.2° to ensure that the first layer (polymer layer) possesses a specific regular arrangement of molecular chains and a crystalline structure. This ordered crystalline morphology allows the first layer to effectively absorb energy through micro-region deformation when subjected to impact, thus exhibiting excellent toughness and tear resistance. Simultaneously, the grain size in the metal layer is controlled, requiring that within any randomly selected 100μm × 100μm area in the EBSD pattern of the metal layer, the number of grains with a diameter greater than or equal to 5μm does not exceed four. This ensures that the metal skeleton (metal layer) has a fine and uniform grain structure. This structure helps improve the overall strength and toughness of the metal layer, preventing coarse grains from becoming mechanical weak points that could cause uneven deformation or intergranular fracture. This allows for more uniform dissipation of the needle's kinetic energy during impact, inhibiting crack propagation and further improving the battery's drop puncture pass rate. Simultaneously, the synergistic effect of the metal layer and the second layer (inner layer) also helps prevent the further propagation of cracks caused by puncture.

[0017] To compensate for the potential decrease in heat dissipation performance caused by the increased thickness of the polymer layer in high-strength aluminum-plastic film, this invention also optimizes the thickness of the negative electrode current collector, controlling it within a reasonable range to effectively enhance the lateral heat diffusion capability of the negative electrode current collector (e.g., copper foil). If the thickness of the negative electrode current collector is too small (<8μm), the heat dissipation capacity is insufficient, and local heat accumulation during puncture can easily form hot spots, causing premature thermal failure of the battery. Conversely, if the thickness is too large (>14μm), it will reduce the battery's energy density and hinder internal stress buffering during puncture, increasing the risk of separator tearing and internal short circuits. In summary, through multi-parameter collaborative design and precise control of key structures, this invention significantly improves the safety performance of the battery under mechanical abuse conditions while maintaining high energy density.

[0018] In this invention, the puncture strength of the shell can be tested using the following method: A universal testing machine equipped with a 1.0 mm flat-headed cylindrical needle is used. The shell sample is securely fixed with a ring clamp (12.7 mm aperture); then, the needle is inserted into the sample at a constant speed of 200 mm / min until it is completely penetrated. The instrument records the force-displacement curve throughout the process, and the peak force (unit: Newtons N) is the puncture strength. It is understood that the shell consists of multiple surfaces, and the shell sample is a single-sided shell.

[0019] In this invention, the thickness of the first layer refers to the dimension of the first layer in the battery thickness direction, and the thickness of the casing refers to the dimension of the casing in the battery thickness direction.

[0020] In the present invention, the X-ray diffraction pattern of the first layer can be obtained by the following method: using a copper target (Cu Kα) light source, with a working voltage of 40 kV and a current of 40 mA. The scanning range (2θ) is set to 5° - 80°, and the scanning speed is 2° / min. The powder sample needs to be ground finely and filled evenly.

[0021] In the present invention, the number of grains with a grain size greater than or equal to 5 μm in the grains can be obtained by the following method: in the inverse pole figure plane distribution map obtained by electron backscatter diffraction (EBSD) testing on the surface of the metal layer, arbitrarily select a 100 μm × 100 μm area, and use the imageJ analysis software supporting the Oxford C-Nano+ electron backscatter diffraction instrument to count the grain sizes of the grains within this area. Take the equivalent circular diameter of the grains as the grain size, and make a number distribution map (where the number distribution map represents the relationship between the number of grains and the grain size), and directly obtain the number of grains with a grain size greater than or equal to 5 μm according to the number distribution map.

[0022] In the present invention, through the collaborative design of the above-mentioned multiple parameters, compared with the prior art, it can enable the battery to have high puncture resistance and high heat dissipation performance while maintaining a high energy density, and improve the passing rate of battery drop and puncture. To further improve the effect, one or more of the technical features can be further optimized.

[0023] In some examples, the thickness of the housing is 70 μm - 150 μm (for example, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, 125 μm, 130 μm, 135 μm, 140 μm, 145 μm, 150 μm or within the range composed of any two of the above values).

[0024] In some examples, the thickness of the first layer is 20 μm - 50 μm (for example, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm or within the range composed of any two of the above values).

[0025] According to some specific embodiments, the thickness of the housing is 70 μm - 150 μm, the thickness of the first layer is 20 μm - 50 μm, and the ratio of the thickness of the first layer to the thickness of the housing is 0.25 - 0.35.

[0026] In some examples, the component of the first layer is a first polymer, and the first polymer includes one or more of polyamide and polyethylene terephthalate.

[0027] In some instances, the molecular weight of the first polymer is between 35,000 g / mol and 45,000 g / mol (e.g., 35,000 g / mol, 36,000 g / mol, 37,000 g / mol, 38,000 g / mol, 39,000 g / mol, 40,000 g / mol, 41,000 g / mol, 42,000 g / mol, 43,000 g / mol, 44,000 g / mol, 45,000 g / mol, or within any two of the above values).

[0028] In some instances, the second layer is composed of a second polymer, which includes polypropylene (PP), cast polypropylene (CPP), polyethylene (PE), and silica-doped POE resin.

[0029] In some instances, the metal layer comprises aluminum foil.

[0030] In some instances, such as Figure 1 As shown, after the battery undergoes a drop puncture test, a bulge is formed at the puncture site on the casing. Among the bulges, the number of bulges with a height of less than 0.5 mm and a width of more than 3 mm is 4 to 7 (e.g., 4, 5, 6 or 7).

[0031] The drop puncture test conditions are as follows: in an environment with a relative humidity of 50%±10%, the battery is charged at a constant current and constant voltage of 0.2C, and charged to 100% SOC with a cutoff of 0.02C. The battery is placed 1.3m away from the tip of the steel needle and allowed to fall freely to the tip of the steel needle. The parameters of the steel needle include: material is tungsten steel, length is 15mm, needle tip diameter is 3mm, and chamfer of needle tip is 32°.

[0032] In this invention, the height of the protrusion refers to its dimension in the direction in which it extends. The direction in which the protrusion extends is the same as the direction of the steel needle puncture. The width of the protrusion refers to its dimension in the direction perpendicular to the direction in which it extends.

[0033] Protrusions with a height less than 0.5 mm and a width greater than 3 mm are short and wide in shape. This type of protrusion is less likely to cause short circuits between the positive and negative electrodes, thus reducing the risk of internal short circuits in the battery. When there are many of these short and wide protrusions, it indicates that the protrusions at the puncture site (e.g., the puncture sites on the casing and electrodes) are more regularly shaped during drop puncture tests. Regularly shaped protrusions are less likely to cause short circuits between the positive and negative electrodes, thus improving the battery's drop puncture pass rate. By controlling the number of protrusions with a height of less than 0.5 mm and a width of more than 3 mm within the above range, it can be ensured that the protrusions generated at the puncture site are more regular in shape during drop puncture testing. In drop puncture testing, the impact force received by the casing is greater than that of the electrode. When the protrusions generated at the puncture site of the casing are more regular in shape, the protrusions generated at the puncture site of the electrode will also be more regular in shape. More regular protrusions are less likely to cause short circuits between the positive and negative electrodes, thereby further improving the drop puncture pass rate of the battery.

[0034] In some instances, the elongation TD of the negative current collector in the width direction of the negative electrode sheet is 1%-15% (e.g., 1.1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or within any two of the above values).

[0035] In some instances, the elongation TD of the negative current collector is 2%-8% in the width direction of the negative electrode sheet.

[0036] In some instances, the elongation MD of the negative current collector along the length of the negative electrode sheet is 1.35%-14% (e.g., 1.36%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or within any two of the above values).

[0037] In some instances, the elongation (MD) of the negative current collector is 2.3%-7.8% along the length of the negative electrode sheet.

[0038] According to some specific implementations, the elongation TD of the negative electrode current collector is 1%-15% in the width direction of the negative electrode sheet, and the elongation MD of the negative electrode current collector is 1.35%-14% in the length direction of the negative electrode sheet. By controlling the elongation of the negative electrode current collector within the above range, it possesses sufficient flexibility to buffer cyclic stress and avoid "corner breakage," while maintaining appropriate rigidity to preserve structural integrity under mechanical abuse and synergistically improve puncture resistance. This ensures long cycle life while simultaneously optimizing safety performance. When the elongation of the negative electrode current collector is too high, the overly soft current collector will undergo excessive deformation under instantaneous impacts such as puncture, failing to provide effective support to suppress separator tearing and internal short circuits. Instead, it will hinder the uniform diffusion of stress and reduce the drop puncture pass rate. At the same time, the negative electrode current collector will amplify the stress concentration at the corners of the cell. During battery cycling, the negative electrode current collector repeatedly undergoes plastic deformation, leading to material fatigue, delamination between the negative electrode current collector and the negative electrode active layer, and cracking of the active layer itself. This can cause corner breakage during cell cycling, shortening battery life. Conversely, if the elongation is too low, the negative electrode current collector is too brittle and its deformation capacity is insufficient. It cannot absorb and dissipate energy through its own elongation deformation when subjected to impact. In the instant of needle puncture or drop, the brittle negative electrode current collector is more likely to break, immediately causing a large-area internal short circuit, which will also lead to a decrease in the puncture pass rate.

[0039] In this invention, the elongation of the negative electrode current collector can be tested by the following method: measuring the elongation of the negative electrode current collector in the empty foil area of ​​the negative electrode sheet, specifically as follows: the elongation of the negative electrode current collector can be tested by conventional methods in the art, for example, after discharging the battery to 0% SOC, disassembling and removing the negative electrode sheet, taking the negative electrode current collector in the empty foil area, soaking it in DMC solvent for 12 hours, then rinsing it with DMC solvent to remove the lithium salt adhering to the empty foil area, drying it, and then using a knife to cut the above-treated empty foil area to form a test sample; taking "the elongation of the negative electrode current collector in the length direction of the negative electrode sheet" as an example. Using a cutting tool, the treated empty foil area is cut into samples with a size of 15 mm along the width direction of the negative electrode current collector and a size exceeding 50 mm along the length direction of the negative electrode current collector. Using a WD-D3 electronic universal testing machine (accuracy class 0.5, accuracy ±1% of the indicated value), with a gauge length of 50 mm and a speed of 50 mm / min, a tensile test is performed on the above samples along the length direction to measure the elongation of the negative electrode current collector in the length direction of the negative electrode sheet. The test method for the elongation of the negative electrode current collector in the width direction of the negative electrode sheet can refer to the test method for the elongation of the negative electrode current collector in the width direction of the negative electrode sheet.

[0040] In some instances, the negative electrode sheet includes a negative current collector and a negative active layer located on at least one side of the surface of the negative current collector.

[0041] In some instances, one side surface of the negative electrode sheet includes several protrusions, which are understood to be located on the surface of the negative electrode active layer. These protrusions can be formed on the surface of the negative electrode active layer using an embossing process.

[0042] The casing effectively resists external punctures and reduces local stress in the current collector by dispersing kinetic energy, thereby suppressing plastic deformation and protrusion. However, its excessive rigidity restricts the normal expansion and contraction of the electrode during cycling, leading to internal stress concentration, causing the active material to peel off from the current collector, or even causing the current collector itself to break, thus accelerating battery capacity decay. Therefore, an embossing process is used on the negative electrode. When several protrusions are formed on the surface of the negative electrode sheet, this structure provides effective deformation buffer space during electrode expansion, thereby suppressing the shedding of active material due to volume changes. By reducing the peeling and powdering of active material, the possibility of contact between the negative electrode active material and the positive electrode current collector can be further reduced, thus suppressing internal short circuits and ultimately improving the battery's pass rate in drop and puncture tests.

[0043] In some instances, the height of the protrusion is 3μm-80μm (e.g., 3μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm or within any two of the above values).

[0044] In some instances, the average diameter of the protrusion is 2.5mm-8mm (e.g., 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 6.5mm, 7mm, 7.5mm, 8mm or within any two of the above values).

[0045] In some instances, the distance between the edges of two adjacent protrusions is 0.5mm-8mm (e.g., 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 6.5mm, 7mm, 7.5mm, 8mm or within any two of the above values).

[0046] By controlling the protrusions within the aforementioned parameter range, a stable and uniform buffer structure can be formed inside the electrode. This structure can effectively absorb the electrode expansion stress during charging and discharging, suppress the shedding of active materials, and ensure structural integrity. It can also avoid local stress concentration or insufficient support caused by excessively dense or sparse protrusions, thereby improving interface stability, significantly reducing the risk of internal short circuits, and optimizing the overall safety and cycle performance of the battery.

[0047] In some instances, the negative electrode active layer comprises a negative electrode active material, which comprises silicon-based particles with a sphericity greater than 0.85 (e.g., 0.86, 0.88, 0.9, 0.93, 0.96, 0.98, or 1).

[0048] Because silicon-based particles with high sphericity undergo approximately 300% volume expansion during charging and discharging, the isotropic stress distribution generated by their spherical geometry avoids stress concentration at the edges of irregular particles. By controlling the sphericity of the silicon-based particles within the aforementioned range, the silicon-based particles can withstand anisotropic stress, making it less likely for local stress concentration points to form during charging and discharging. This reduces the risk of powder shedding during drop puncture tests and further improves the drop puncture pass rate of the battery.

[0049] In some instances, the silicon-based material includes at least one of silicon-carbon, nano-silicon powder, and silicon oxide.

[0050] In some instances, the negative electrode active material also includes a carbon-based material, which includes artificial graphite and / or natural graphite.

[0051] In some instances, the negative electrode active layer further includes a negative electrode conductive agent and a negative electrode binder.

[0052] In some instances, the negative electrode conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, and carbon nanotubes.

[0053] In some instances, the negative electrode binder includes one or more of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, polyethylene oxide, and polyvinylidene fluoride.

[0054] In one example, based on the total weight of the negative electrode active layer, the weight content of the negative electrode active material is 80%-99.5% (e.g., 80%, 85%, 90%, 95%, 99%, 99.5%, or within any two of the above values), the weight content of the negative electrode conductive agent is 0.25%-10% (e.g., 0.25%, 0.5%, 1%, 3%, 5%, 7%, 10%, or within any two of the above values), and the weight content of the negative electrode binder is 0.25%-10% (e.g., 0.25%, 0.5%, 1%, 3%, 5%, 7%, 10%, or within any two of the above values).

[0055] In some instances, the separator is located between the positive electrode and the negative electrode, and the adhesive force between the negative electrode and the separator is greater than 6.5 N / m (e.g., 6.6 N / m, 7 N / m, 7.5 N / m, 8 N / m, 8.5 N / m, 9 N / m, 9.5 N / m, 10 N / m, 10.5 N / m, 11 N / m, 11.5 N / m, 12 N / m or within any two of the above values).

[0056] In this invention, the adhesive force between the negative electrode and the separator can be tested by the following method: the battery is dissected, the positive electrode is removed, and the complete negative electrode and separator (adhesive state) are retained. The negative electrode and separator are peeled off using a universal testing machine at a specific angle (180°) and speed (200 mm / s). The instrument records the force-displacement curve throughout the process, and the peak force (unit: Newton N / m) is the adhesive force.

[0057] In some instances, the diaphragm includes a carrier layer and an adhesive layer located on one or both surfaces of the carrier layer.

[0058] In some instances, the adhesive layer includes first particles with an average particle size of 0.5 μm-1 μm (e.g., 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, or within any two of these values). By controlling the average particle size of the first particles within this range, the first particles can effectively transform the cyclic expansion of the battery cell during cycling into controllable plastic deformation. Under pressure, the first particles deform without breaking, thereby absorbing energy during expansion, reducing the battery's expansion rate, and the porosity of the particle stack within this average particle size range also ensures the unobstructed lithium-ion transport channels.

[0059] In this invention, the average particle size of the first particle can be obtained by the following method: On a scanned image of the adhesive layer surface obtained using SEM, draw a rectangle (which can be a square) that completely surrounds the particle and has the smallest possible area. Make the edge of the particle tangent to the four sides of the rectangle. The length of the long side of the rectangle is then used as the particle size value of the first particle. Within an arbitrarily selected 10μm × 10μm area on the adhesive layer surface, measure the particle size of any 100 first particles and calculate their average value. To reduce error, repeat the above operation 5 times, and take the average of the 5 tests as the average particle size. It should be noted that if 100 first particles can be observed in the captured image, or if not, take multiple images and set the average particle size of the total 100 first particles as the average particle size. The scanned images can be obtained by observing the surface of the adhesive layer using a scanning electron microscope (S-3400N manufactured by Hitachi, Ltd.).

[0060] In some instances, the adhesive layer covers 10%-50% of the surface of the carrier layer (e.g., 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any two of the above values). Controlling the adhesive layer's surface coverage within this range effectively ensures the continuity of the diaphragm-electrode interface adhesion, reduces and eliminates stress concentration points on the electrode during cycling, and converts the electrode expansion stress into adhesive layer deformation during cyclic expansion, mitigating material wear and damage during shrinkage-expansion.

[0061] In this invention, the coverage rate of the adhesive layer on the surface of the carrier layer refers to the proportion of the orthographic projection area of ​​the adhesive layer on one side of the carrier layer to the area of ​​that side of the carrier layer (i.e., the surface of the carrier layer with the adhesive layer). When there are adhesive layers on both sides of the carrier layer, the coverage rates of the adhesive layers on the two sides can be the same or different.

[0062] In this invention, the surface coverage of the adhesive layer on the carrier layer can be tested by the following method: obtaining a microscopic image of the adhesive layer surface using SEM, and randomly dividing the image into areas with a size of 100µm. 2 The area (e.g., 100µm × 100µm) is divided into uniform squares of 400*400. If the area covered by the orthographic projection of the adhesive layer in a square exceeds half the area of ​​the square, it means that the square is occupied by the coating layer; otherwise, it means that the square is not occupied by the adhesive layer. By counting the number of squares occupied by the adhesive layer, the total number of squares occupied by the coating layer is recorded as X. Then, the coverage rate = (X / (400 × 400)) × 100%. Repeat the above operation 5 times, and take the average of the 5 times as the coverage rate of the adhesive layer on the surface of the carrier layer.

[0063] In some instances, the composition of the first particle includes polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, fluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polybutyl acrylate, polyethyl acrylate, polybutyl methacrylate, polymethyl methacrylate, methacrylate-acrylonitrile copolymer, methacrylate-ethylene copolymer, methacrylate-styrene copolymer, butadiene and isobutyl acrylate copolymer.

[0064] In some instances, the carrier layer includes a substrate layer and a coating located on one or both surfaces of the substrate layer.

[0065] In some instances, the coating includes a second particle and a second adhesive.

[0066] In some instances, the second particle comprises one or more of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium dioxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride, melamine cyanurate, 4,6-dimethyl-2-phenylpyrimidine, uracil, cytosine, 2,4-dimercaptopyrimidine, 2,4-dimercapto-5,6-diaminopyrimidine, and lithium aluminum titanium phosphate.

[0067] In some instances, the second adhesive comprises one or more of polyvinyl alcohol, styrene-butadiene rubber, ethylene-vinyl acetate copolymer, polyvinylpyrrolidone, polymethyl methacrylate, polybutyl methacrylate, styrene-acrylic latex, polyacrylonitrile, ethyl polyacrylate, polyvinyl acetate, polyacrylate, polyvinylidene fluoride polyurethane, polyvinylidene fluoride-hexafluoropropylene, or copolymer systems derived from the above polymers.

[0068] In some instances, the coating also includes dispersants and wetting agents.

[0069] In some instances, the dispersant includes sodium carboxymethyl cellulose.

[0070] In some instances, the wetting agent includes one or more of alkylnaphthalene sulfonates, alkylbenzene sulfonates, and polyoxyethylene fatty alcohol ethers.

[0071] In some instances, the second particles comprise 92%-97% of the total weight of the coating (e.g., 92%, 93%, 94%, 95%, 96%, 97% or any two of the above values), and the second adhesive comprises 3%-8% of the total weight of the coating (e.g., 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8% or any two of the above values). The weight percentage of the dispersant is 0-1.5% (e.g., 0, 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%, or within any two of the above values), and the weight percentage of the wetting agent is 0-1.5% (e.g., 0, 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%, or within any two of the above values). When the weight percentage of the dispersant in the coating is 0, it indicates that the dispersant is absent. When the weight percentage of the wetting agent in the coating is 0, it indicates that the wetting agent is absent.

[0072] In some instances, the substrate layer is composed of polyethylene.

[0073] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0074] The following examples illustrate the battery of the present invention.

[0075] Example 1 1. Positive electrode plate Lithium cobalt oxide, a conductive agent (a mixture of conductive carbon black and carbon nanotubes), and PVDF were placed in NMP at a mass ratio of 97.6:1.35:1.05 and stirred until homogeneous to obtain a positive electrode slurry. This positive electrode slurry was then uniformly coated onto both sides of an aluminum foil, with a single-sided areal density of 0.01975 g / cm³. 2 The aluminum foil was 8 μm thick and was dried and rolled to produce a positive electrode sheet with a double-sided thickness of 106 μm. The positive electrode sheet was then die-cut to obtain the positive electrode sheet.

[0076] 2. Negative electrode plate Artificial graphite, silicon carbide particles (with a sphericity of 0.96), conductive agent (conductive carbon black), and binder (styrene-butadiene rubber) were placed in deionized water at a mass ratio of 86.9:9.7:2.8:0.6. The slurry was stirred until homogeneous to obtain a negative electrode slurry. This negative electrode slurry was uniformly coated onto both sides of a negative electrode current collector (copper foil, 10 μm thick). The coating was then subjected to drying, rolling, and die-cutting processes to obtain a negative electrode sheet, wherein the thickness of the single-sided negative electrode active layer was 40 μm. The negative electrode sheet was then embossed to create several protrusions on one side of the negative electrode active layer surface. The height of each protrusion was 20 μm, the average diameter of each protrusion was 5 mm, and the distance between the edges of two adjacent protrusions was 4 mm. The elongation (TD) of the negative electrode current collector was 5.32% in the width direction and 4.38% in the length direction.

[0077] 3. Electrolyte In an argon-filled glove box (moisture <10ppm, oxygen <1ppm), ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) were mixed uniformly in a mass ratio of 2:1.5:2. LiPF6 (14wt% based on the total mass of the non-aqueous electrolyte) and fluoroethylene carbonate (FEC) (20wt% based on the total mass of the non-aqueous electrolyte) were slowly added to the mixed solution and stirred until homogeneous to obtain the non-aqueous electrolyte.

[0078] 4. Diaphragm The membrane's carrier layer comprises a substrate layer and a coating layer. The substrate layer is composed of polyethylene (8 μm thick). The coating layer is located on one side of the substrate layer, and the adhesive layer is located on the other side of the substrate layer and the surface of the coating layer furthest from the substrate layer. The first particles in the adhesive layer have an average particle size of 0.8 μm and are composed of polybutyl methacrylate. The coverage of the adhesive layer on the substrate layer surface and the coverage of the adhesive layer on the coating surface are both 30.8%. The second particles in the coating layer are composed of alumina, and the second binder is polymethyl methacrylate. The second particles account for 95% of the weight of the coating, and the second binder accounts for 5% of the weight.

[0079] 5. Lithium-ion batteries The positive electrode sheet obtained in step (1), the separator obtained in step (4), and the negative electrode sheet obtained in step (2) are prepared into a core structure in a fully automatic winding machine. The core is then packaged using a high-strength aluminum-plastic film (shell). Finally, after liquid injection (i.e., injection of the electrolyte prepared in step (3)), formation, and secondary sealing, a lithium-ion battery is obtained. The aluminum-plastic film (shell) has a puncture strength of 31N and a shell thickness of 100μm. The first layer is composed of polyamide (molecular weight 38000g / mol) with a thickness of 30μm. The metal layer is aluminum foil, and the second layer is composed of polyethylene. The thickness ratio of the first layer to the shell is 30 / 100=0.3. In the X-ray diffraction pattern of the first layer, there is a characteristic peak at 20.1°-23.2°. In the EBSD pattern of the metal layer, within any region with an area of ​​100μm×100μm, there is one grain with a particle size greater than or equal to 5μm. After the battery undergoes a drop puncture test, a bulge is generated at the puncture site on the shell. Among the bulges, there are five bulges with a height less than 0.5mm and a width greater than 3mm.

[0080] Example 2 group This set of examples illustrates the effects of changes in the thickness of the negative electrode current collector.

[0081] Example 2a The process was carried out in accordance with Example 1, except that the thickness of the negative electrode current collector was 8 μm, the elongation TD of the negative electrode current collector was 1.19% in the width direction of the negative electrode sheet, and the elongation MD of the negative electrode current collector was 1.41% in the length direction of the negative electrode sheet.

[0082] Example 2b The process was carried out in accordance with Example 1, except that the thickness of the negative electrode current collector was 14 μm, the elongation TD of the negative electrode current collector was 14.53% in the width direction of the negative electrode sheet, and the elongation MD of the negative electrode current collector was 13.50% in the length direction of the negative electrode sheet.

[0083] Example 3 Group This set of examples illustrates the effects that occur when the ratio of the thickness of the first layer in the shell to the thickness of the shell changes.

[0084] Example 3a The same procedure was performed as in Example 1, except that the thickness of the first layer was 20 μm, the thickness of the shell was 80 μm, the ratio of the thickness of the first layer to the thickness of the shell was 0.25, the puncture strength of the shell was 27 N, and after the battery underwent a drop puncture test, a protrusion was generated at the puncture site on the shell. Among the protrusions, there were 6 protrusions with a height of less than 0.5 mm and a width of more than 3 mm.

[0085] Example 3b The same procedure was performed as in Example 1, except that the thickness of the first layer was 50 μm, the thickness of the shell was 143 μm, the ratio of the thickness of the first layer to the thickness of the shell was 0.35, the puncture strength of the shell was 38 N, and after the battery underwent a drop puncture test, a protrusion was generated at the puncture site on the shell. Among the protrusions, there were 3 protrusions with a height of less than 0.5 mm and a width of more than 3 mm.

[0086] Example 3c The experiment was conducted in accordance with Example 1, except that the thickness of the first layer was 19 μm, the thickness of the shell was 75 μm, the ratio of the thickness of the first layer to the thickness of the shell was 0.25, the puncture strength of the shell was 25 N, and after the battery underwent a drop puncture test, the shell produced a protrusion at the puncture site. Among the protrusions, there were 7 protrusions with a height of less than 0.5 mm and a width of more than 3 mm.

[0087] Example 3d The experiment was conducted in accordance with Example 1, except that the thickness of the first layer was 51 μm, the thickness of the shell was 145 μm, the ratio of the thickness of the first layer to the thickness of the shell was 0.35, the puncture strength of the shell was 39 N, and after the battery underwent a drop puncture test, a protrusion was generated at the puncture site on the shell. Among the protrusions, there were 3 protrusions with a height of less than 0.5 mm and a width of more than 3 mm.

[0088] Example 4 The experiment was conducted in accordance with Example 1, except that the first polymer in the first layer was polyethylene terephthalate (PET), the molecular weight of the first polymer was 30000 g / mol, the thickness of the first layer was 30 μm, the thickness of the shell was 113 μm, the ratio of the thickness of the first layer to the thickness of the shell was 0.27, the puncture strength of the shell was 30 N, and after the battery underwent a drop puncture test, a protrusion was formed at the puncture site on the shell. Among the protrusions, there were 6 protrusions with a height of less than 0.5 mm and a width of more than 3 mm.

[0089] Example 5 The process was carried out in accordance with Example 1, except that by adjusting the process parameters for preparing the metal layer (e.g., annealing temperature, holding time, and one or more of cold rolling conditions), the number of grains with a diameter greater than or equal to 5 μm in the metal layer was selected in any 100 μm × 100 μm area in the EBSD diagram of the metal layer, and the puncture strength of the casing was 25 N. After the battery was subjected to a drop puncture test, the casing produced a protrusion at the puncture position. Among the protrusions, the number of protrusions with a height less than 0.5 mm and a width greater than 3 mm was 9.

[0090] Example 6 group This set of examples illustrates the effects of changes in the average particle size of the first particle in the adhesive layer.

[0091] Example 6a The procedure was carried out in accordance with Example 1, except that the average particle size of the first particle in the adhesive layer was 0.5 μm.

[0092] Example 6b The procedure was carried out in accordance with Example 1, except that the average particle size of the first particle in the adhesive layer was 1 μm.

[0093] Example 6c The procedure was carried out in accordance with Example 1, except that the average particle size of the first particle in the adhesive layer was 0.4 μm.

[0094] Example 6d The procedure was carried out in accordance with Example 1, except that the average particle size of the first particle in the adhesive layer was 1.2 μm.

[0095] Example 7 group This set of examples illustrates the effects of changes in the coverage of the adhesive layer on the carrier layer surface.

[0096] Example 7a The procedure was carried out in accordance with Example 1, except that the coverage of the adhesive layer on the surface of the carrier layer was 10.4%.

[0097] Example 7b The procedure was carried out in accordance with Example 1, except that the coverage of the adhesive layer on the surface of the carrier layer was 49.8%.

[0098] Example 7c The procedure was carried out in accordance with Example 1, except that the coverage of the adhesive layer on the surface of the carrier layer was 9.2%.

[0099] Example 7d The procedure was carried out in accordance with Example 1, except that the coverage of the adhesive layer on the surface of the carrier layer was 51.7%.

[0100] Example 8 group Example 8a The experiment was carried out in accordance with Example 1, except that the molecular weight of the first polymer in the first layer of the shell was 35000 g / mol, the height of the protrusion on the surface of the negative electrode active layer on one side of the negative electrode sheet was 3 μm, the average diameter of the protrusion was 2.5 mm, the distance between the edges of two adjacent protrusions was 0.5 mm, and the sphericity of the silicon-based particles was 0.86.

[0101] Example 8b The process is carried out in accordance with Example 1, except that the molecular weight of the first polymer in the first layer of the shell is 45000 g / mol, the height of the protrusion on the surface of the negative electrode active layer on one side of the negative electrode sheet is 80 μm, the average diameter of the protrusion is 8 mm, and the distance between the edges of two adjacent protrusions is 8 mm. It can be understood that the ratio of the height of the protrusion to the thickness of the negative electrode active layer on the side where the protrusion is located can be kept basically unchanged by changing the thickness of the single-sided negative electrode active layer, so as to ensure that the height of the protrusion is not greater than the thickness of the single-sided negative electrode active layer.

[0102] Comparative Example 1 The experiment was conducted in accordance with Example 1, except that the molecular weight of the first polymer was 33000 g / mol, the thickness of the first layer was 20 μm, the thickness of the shell was 96 μm, the ratio of the thickness of the first layer to the thickness of the shell was 0.21, and the puncture strength of the shell was 24 N.

[0103] Comparative Example 2 The procedure was carried out in accordance with Example 1, except that the thickness of the first layer was 37 μm, the thickness of the shell was 83 μm, the ratio of the thickness of the first layer to the thickness of the shell was 0.45, and the puncture strength of the shell was 28 N.

[0104] Comparative Example 3 The procedure was carried out in accordance with Example 1, except that the thickness of the first layer was 22 μm, the thickness of the shell was 135 μm, the ratio of the thickness of the first layer to the thickness of the shell was 0.16, and the puncture strength of the shell was 27 N.

[0105] Comparative Example 4 The process was carried out in accordance with Example 1, except that by adjusting the process parameters for preparing the metal layer (e.g., annealing temperature, holding time, and one or more of cold rolling conditions), the number of grains with a diameter greater than or equal to 5 μm in the metal layer was 6 in any 100 μm × 100 μm area in the EBSD diagram of the metal layer, and the puncture strength of the shell was 22 N.

[0106] Comparative Example 5 The process was carried out in accordance with Example 1, except that the thickness of the negative electrode current collector was 6 μm, the elongation TD of the negative electrode current collector was 1.03% in the width direction of the negative electrode sheet, and the elongation MD of the negative electrode current collector was 1.36% in the length direction of the negative electrode sheet.

[0107] Comparative Example 6 The process was carried out in accordance with Example 1, except that the thickness of the negative current collector was 16 μm, the elongation TD of the negative current collector was 14.75% in the width direction of the negative electrode sheet, and the elongation MD of the negative current collector was 13.90% in the length direction of the negative electrode sheet.

[0108] Comparative Example 7 The procedure was carried out in accordance with Example 1, except that the material of the first layer was changed to amorphous nylon PA6-3-T. In this case, there were no characteristic peaks in the X-ray diffraction pattern of the first layer at 2θ=20.1°-23.2°.

[0109] Test case The lithium-ion batteries prepared in the examples and comparative examples were tested as follows.

[0110] 1. Drop puncture test In an environment with a relative humidity of 50%±10%, the battery is charged at a constant current and constant voltage of 0.2C, and then charged to 100% SOC with a cutoff of 0.02C. The battery is placed 1.3m away from the tip of the steel needle and allowed to fall freely onto the tip of the steel needle. The parameters of the steel needle include: material is tungsten steel, length is 15mm, needle tip diameter is 3mm, and chamfer of needle tip is 32°.

[0111] If no fire or explosion occurs, the test is considered passed; if a fire and / or explosion occurs, the test is considered failed. Each embodiment and comparative example tested 20 battery samples, and the results are expressed as "number of passes / 20," for example, "5 / 20" means 5 out of 20 battery samples passed the test.

[0112] 2. Furnace temperature test The battery cell was charged at a current of 0.2 C and then fully charged to the upper limit voltage (4.53V) at a cutoff current of 0.02 C. The fully charged cell was then placed in an oven and heated at a rate of 5℃ ± 2℃ / min until the oven temperature reached 128℃ and was maintained for 60 minutes. If no fire or explosion occurred, the test was considered passed; if fire and / or explosion occurred, the test was considered failed. Twenty battery samples were tested for each example and comparative example. The results are expressed as "number of passes / 20," for example, "5 / 20" means that 5 out of 20 battery samples passed the test.

[0113] 3. Cyclic performance test at 25℃ a) At 25°C, charge the battery after capacity testing to 4.53V at a constant current and constant voltage of 1.5C, cut off current of 0.05C, and then discharge it to 3V at a constant current of 1.5C. Record the initial discharge capacity C1. b) Perform 600 charge-discharge cycles as per step a), and record the discharge capacity C2 on the 600th cycle. The calculation formula is as follows: The capacity retention rate (%) in the 1500th cycle = (C2 / C1) × 100%.

[0114] 4. Energy density At 25℃, the length L, width K, and height D of the battery were measured before charging. The battery was charged and discharged at 1C constant current and constant voltage to 4.53V, left to stand for 10 minutes, and then discharged at 1C constant current to 3V. The discharge energy at this time was measured as G Wh, and the energy density = G / (L×K×D) in Wh / L.

[0115] The results are recorded in Table 1.

[0116] Table 1 As can be seen from Table 1, by comparing the comparative example and the embodiment, the drop puncture pass rate and furnace temperature pass rate of the battery in the embodiment are significantly improved. This indicates that by controlling the puncture strength of the casing, the ratio of the thickness of the first layer to the thickness of the casing, the characteristic peak value of the first layer, the number of larger grains in the metal layer, and the thickness of the negative electrode current collector, the battery can have both high puncture resistance and high heat dissipation performance, thereby improving the drop puncture pass rate of the battery.

[0117] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A battery, characterized in that, The battery includes a casing and a cell, the cell being located within a containment space formed by the casing, the cell including an electrolyte and an electrode assembly formed by a positive electrode, a separator, and a negative electrode, the negative electrode including a negative current collector having a thickness of 8μm-14μm, the casing including a first layer, a metal layer, and a second layer stacked sequentially, the second layer being close to the cell, and the puncture strength of the casing being greater than or equal to 25N; The thickness ratio of the first layer to the shell is 0.25-0.

35. In the X-ray diffraction pattern of the first layer, there is a characteristic peak at 2θ=20.1°-23.2°. The metal layer includes grains. In any region of 100μm×100μm selected in the EBSD pattern of the metal layer, the number of grains with a diameter greater than or equal to 5μm is less than or equal to 4.

2. The battery according to claim 1, wherein, The first layer is composed of a first polymer, which includes one or more of polyamide and polyethylene terephthalate. The second layer is composed of a second polymer, which includes polypropylene, cast polypropylene, polyethylene, and silica-doped POE resin.

3. The battery according to claim 2, wherein, The molecular weight of the first polymer is 35000 g / mol to 45000 g / mol; And / or, the thickness of the first layer is 20μm-50μm; And / or, the metal layer includes aluminum foil.

4. The battery according to claim 1, wherein, In the width direction of the negative electrode sheet, the elongation TD of the negative electrode current collector is 1%-15%, preferably 2%-8%; And / or, in the length direction of the negative electrode sheet, the elongation MD of the negative electrode current collector is 1.35%-14%, preferably 2.3%-7.8%.

5. The battery according to claim 1, wherein, One side surface of the negative electrode includes several protrusions, the height of which is 3μm-80μm.

6. The battery according to claim 5, wherein, The average diameter of the protrusion is 2.5mm-8mm; And / or, the distance between the edges of two adjacent protrusions is 0.5mm-8mm.

7. The battery according to claim 1, wherein, The negative electrode sheet includes a negative current collector and a negative active layer located on at least one side of the surface of the negative current collector. The negative active layer includes silicon-based particles with a sphericity greater than 0.

85.

8. The battery according to claim 1, wherein, After the battery undergoes a drop puncture test, a bulge is formed at the puncture site on the casing. Among the bulges, there are 4 to 7 bulges with a height of less than 0.5 mm and a width of more than 3 mm. The drop puncture test conditions are as follows: in an environment with a relative humidity of 50%±10%, the battery is charged at a constant current and constant voltage of 0.2C and charged to 100% SOC with a cutoff of 0.02C. The battery is placed 1.3m away from the tip of a steel needle and allowed to fall freely to the tip of the steel needle. The parameters of the steel needle include: material is tungsten steel, length is 15mm, needle tip diameter is 3mm, and chamfer of needle tip is 32°.

9. The battery according to claim 1, wherein, The separator is located between the positive electrode and the negative electrode, and the adhesive force between the negative electrode and the separator is greater than 6.5 N / m.

10. The battery according to any one of claims 1-9, wherein, The diaphragm includes a carrier layer and an adhesive layer located on one or both surfaces of the carrier layer. The adhesive layer includes first particles with an average particle size of 0.5 μm to 1 μm. And / or, the adhesive layer has a surface coverage of 10%-50% on the carrier layer; And / or, the composition of the first particle includes polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, fluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polybutyl acrylate, polyethyl acrylate, polybutyl methacrylate, polymethyl methacrylate, methacrylate-acrylonitrile copolymer, methacrylate-ethylene copolymer, methacrylate-styrene copolymer, butadiene and isobutyl acrylate copolymer.

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