Battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery. The battery comprises an aluminum-plastic film and an electrode assembly, the electrode assembly is located in a containing space formed by the aluminum-plastic film, the electrode assembly comprises a positive plate, a diaphragm and a negative plate, and the sum B of the puncture strength of the diaphragm and the aluminum-plastic film is 25N-51N after the diaphragm and the aluminum-plastic film are stacked and thermally compounded. In a drop puncture test, the battery can resist kinetic energy in the puncture process, the puncture force of the metal probe is rapidly reduced, and the risk of internal short circuit caused by conduction of the metal probe is reduced, so that the drop puncture passing rate of the battery is improved, and meanwhile, the furnace temperature performance can also be improved.

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 (LIBS) are widely used in consumer electronics, electric vehicles, and intelligent robots, but the requirements for their safety performance are becoming increasingly stringent.

[0003] As lithium-ion battery capacity increases, high-safety cells have garnered significant attention from battery and mobile phone manufacturers. Battery safety relies on a sealed and layered physical structure, such as the stable separation of the casing, electrodes, and separator. Drop-puncture tests directly disrupt this balance. The positive and negative electrodes inside the battery are separated by a separator (an insulating material that allows only lithium ions to pass through, preventing electron flow). If this physical structure is damaged, causing direct contact between the positive and negative electrodes (e.g., through a metal puncture needle or detached electrode powder), an internal short circuit can occur, which is the "trigger" for fire. In drop-puncture tests, the complexity of internal short-circuit points significantly increases the probability of fire, severely impacting the safety performance of lithium-ion batteries. Summary of the Invention

[0004] To improve drop puncture pass rate, existing technologies typically increase the puncture strength of the separator. However, excessively high separator puncture strength can lead to an increase in the separator's pore temperature, reducing the battery's furnace temperature performance. Therefore, it is crucial to invent a battery that can achieve both a high drop puncture pass rate and high furnace temperature performance.

[0005] In view of this, in order to solve the problem that existing batteries cannot simultaneously achieve high drop puncture pass rates and high furnace temperature performance, this invention provides a battery. In drop puncture tests, the battery of this invention can resist the kinetic energy during the puncture process, quickly reduce the puncture force of the metal probe, and reduce the risk of internal short circuits caused by metal probe conduction, thereby improving the battery's safety performance. Simultaneously, the battery of this invention also has a high energy density, enabling the battery to simultaneously achieve both high drop puncture pass rates and high energy density.

[0006] To achieve the above objectives, the present invention provides a battery comprising an aluminum-plastic film and an electrode assembly, wherein the electrode assembly is located in a receiving space formed by the aluminum-plastic film, and the electrode assembly comprises a positive electrode, a separator, and a negative electrode, wherein the sum of the puncture strength B of the separator and the aluminum-plastic film after being laminated and thermally bonded is 25N-51N.

[0007] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: In the battery of the present invention, by controlling the sum of the puncture strength B of the separator and the aluminum-plastic film after thermal lamination to be 25N-51N, the battery can resist the kinetic energy during the puncture process, reduce the risk of internal short circuit caused by metal needle conduction, and at the same time reduce the stress on the electrode sheet, reduce the risk of electrode powder falling off, thereby reducing the risk of positive and negative electrode conduction caused by electrode powder falling off, improving the drop puncture pass rate of the battery, and ensuring that the battery has a high furnace temperature pass rate, achieving the effect of both high drop puncture pass rate and high furnace temperature pass rate.

[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 image shows the protrusion on the positive electrode at the puncture site after a drop puncture test of the battery of the present invention. 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] The present invention provides a battery comprising an aluminum-plastic film and an electrode assembly, wherein the electrode assembly is located in a receiving space formed by the aluminum-plastic film, and the electrode assembly comprises a positive electrode, a separator, and a negative electrode. The sum B of the puncture strengths B of the separator and the aluminum-plastic film after being laminated and thermally bonded is 25N-51N (for example, 25N, 28N, 30N, 33N, 35N, 38N, 40N, 43N, 45N, 48N, 50N, 51N, or within any two of the above values).

[0014] In this invention, the sum of the puncture strengths of the separator and the aluminum-plastic film after thermal lamination refers to the puncture strength of the first laminate formed by sequentially stacking one layer of the aluminum-plastic film and two layers of the separator, wherein the structure of the first laminate is "aluminum-plastic film-separator-separator". It is understood that the aluminum-plastic film and separator in the first laminate are the same as those in the battery, but in the battery structure, the aluminum-plastic film and separator do not exist in the structure of the first laminate. In the battery of this invention, the battery includes an aluminum-plastic film and an electrode assembly, the electrode assembly being located within the accommodating space formed by the aluminum-plastic film, and the electrode assembly including a positive electrode, a separator, and a negative electrode, with the separator located between the positive and negative electrode.

[0015] In this invention, the test method for the sum of the puncture strengths B of the separator and the aluminum-plastic film after thermal lamination is as follows: The finished battery is disassembled, and one layer of aluminum-plastic film and two layers of separator are laminated in the order of aluminum-plastic film, separator, separator to form a first laminated sample. The thermal lamination conditions include: temperature of 85°C, pressure of 1.1 MPa, and time of 30 min. Then, a universal testing machine is used for testing. Specifically, the universal testing machine is equipped with a 1.0 mm flat-head cylindrical needle. The first laminated sample is firmly fixed with a ring clamp (hole diameter of 12.7 mm). Subsequently, the needle is inserted into the first laminated sample at a constant speed of 200 mm / min until it is completely penetrated. Complete penetration means that the needle is inserted from the insertion side of the aluminum-plastic film of the first laminated sample until its tip is completely exited from the opposite side of the laminate. The instrument records the force-displacement curve throughout the process, and the peak force (unit: Newton N) is the puncture strength.

[0016] Research has shown that by controlling the sum of the puncture strengths of the separator and aluminum-plastic film after thermal lamination within the aforementioned range, the kinetic energy dissipation rate of the metal needle can be effectively improved in drop puncture tests. This mechanism causes the kinetic energy of the needle to decay rapidly during puncture, thereby significantly enhancing the battery's resistance to puncture kinetic energy. The rapid decrease in kinetic energy prevents the needle from completely destroying the layered physical structure inside the battery, avoiding the formation of a connection between the positive and negative electrodes, reducing the risk of internal short circuits caused by needle conduction, and improving battery safety. Furthermore, it also alleviates the stress on the electrodes during puncture, reducing the shedding of active electrode materials, thus preventing secondary short circuits caused by bridging the positive and negative electrodes with detached material, further enhancing battery safety. Moreover, by controlling the sum of the puncture strengths of the separator and aluminum-plastic film after thermal lamination within the aforementioned range, the puncture strength of the separator will not be too high, allowing the battery to also achieve a high furnace temperature pass rate. Furthermore, since the puncture intensity parameter controlled by this invention has minimal or no impact on the overall volume of the battery, this solution can significantly improve the battery's drop puncture test pass rate and furnace temperature pass rate while ensuring high energy density, thus achieving synergistic optimization of safety and energy density.

[0017] In optimizing battery puncture resistance, relying solely on increasing the puncture strength of the separator to resist the kinetic energy impact of metal needles requires the separator to possess extremely high puncture strength. However, excessively high separator puncture strength often leads to an increase in closed-cell temperature, negatively impacting the battery's furnace temperature performance. If puncture resistance is achieved solely by enhancing the puncture strength of the aluminum-plastic film, the required strength of the aluminum-plastic film will also significantly increase. This not only greatly increases the difficulty of the heat-sealing process but also necessitates higher encapsulation temperatures and pressures, ultimately adversely affecting production yield. To address the limitations of single-material optimization, this invention proposes controlling the sum of the puncture strengths of the separator and aluminum-plastic film after thermal lamination within a specific range. This approach fully leverages the synergistic puncture resistance of both materials in their structure, effectively dissipating the kinetic energy of the metal needles while avoiding process or performance problems caused by excessively high strength of a single material. Therefore, while maintaining high energy density, the battery can achieve better drop puncture test pass rates and furnace temperature performance, thus achieving a good balance between safety and overall performance.

[0018] In this invention, the aluminum-plastic film and two layers of separator are thermally composited into a "first laminate" and its puncture strength is defined as a sum. This test structure effectively simulates the penetration path and stress state of a metal needle when it actually punctures a battery. In the actual battery structure, during the puncture process by an external sharp object, the needle will sequentially penetrate the aluminum-plastic film and the internal multiple layers of separator. By controlling this composite puncture strength within a specific range, the overall energy dissipation capability of the battery against external impacts is essentially optimized: the aluminum-plastic film acts as the first barrier to withstand the initial impact, while the separators act as subsequent barriers to continue absorbing and dispersing the needle's kinetic energy. This gradient dissipation mechanism avoids the aforementioned side effects caused by simply increasing the strength of a single material, while ensuring that the needle's kinetic energy is rapidly attenuated before damaging the core electrode structure. This not only effectively prevents short circuits caused by physical penetration between the positive and negative electrodes but also reduces the risk of electrode stress and active material shedding. By defining and controlling this composite puncture strength, this invention achieves a synergistic improvement in puncture resistance safety and furnace temperature performance without changing the internal spatial layout of the battery.

[0019] In this invention, by controlling the sum of the puncture strengths of the separator and the aluminum-plastic film after thermal lamination, compared with the prior art, the drop safety performance and furnace temperature performance of the battery can be balanced without degrading the energy density. To further improve the effect, one or more of the technical features can be further optimized.

[0020] In some instances, the aluminum-plastic film comprises a first layer, a metal layer, and a second layer stacked sequentially, with the second layer close to the battery cell.

[0021] In some instances, the first layer is composed of a first polymer, which includes polyamide.

[0022] In some instances, the thickness of the first layer is 15 μm-35 μm (e.g., 15 μm, 18 μm, 20 μm, 23 μm, 25 μm, 28 μm, 30 μm, 33 μm, 35 μm, or within any two of the above values). In this invention, the thickness of the first layer refers to the dimension of the first layer in the thickness direction of the battery.

[0023] In some instances, the second layer is composed of a second polymer, which includes one or more of polypropylene, cast polypropylene, polyethylene, and silica-doped POE resin.

[0024] In some instances, the metal layer comprises aluminum foil.

[0025] In some instances, the positive electrode includes a positive current collector.

[0026] In some instances, the positive current collector comprises aluminum foil.

[0027] In some instances, the sum of the puncture strengths D of the positive current collector and the separator after thermal bonding is 8N-18N (e.g., 8N, 8.5N, 9N, 9.5N, 10N, 10.5N, 11N, 11.5N, 12N, 12.5N, 13N, 13.5N, 14N, 14.5N, 15N, 15.5N, 16N, 16.5N, 17N, 17.5N, 18N, or within any two of the above values). Since the positive current collector has a low Young's modulus, controlling the sum of the puncture strengths D of the positive current collector and the separator within the above range can reduce the localized stress on the positive current collector during drop puncture tests, thereby preventing large plastic deformation of the positive current collector and fully utilizing the synergistic puncture resistance of the separator and the positive current collector in their structure, thus further improving the battery's drop puncture pass rate.

[0028] In this invention, the sum of the puncture strengths D of the positive electrode current collector and the separator after thermal bonding refers to the puncture strength of the second laminate formed by stacking one layer of the positive electrode current collector and one layer of the separator. It is understood that the positive electrode current collector and separator in the second laminate are the same as those in the battery, but in the battery structure, the positive electrode current collector and separator do not exist as a second laminate. In the battery structure of this invention, the positive electrode sheet encapsulates the positive electrode current collector and a positive electrode active layer located on one or both surfaces of the positive electrode current collector, and the separator is located between the positive electrode sheet and the negative electrode sheet.

[0029] In this invention, the sum D of the puncture strengths of the positive electrode current collector and the separator after thermal bonding can be obtained as follows: The finished battery is disassembled, and the positive electrode current collector is peeled off from the positive electrode sheet. The separated separator and positive electrode current collector are then thermally bonded together to form a second laminated sample. The thermal bonding conditions include: a temperature of 60°C, a pressure of 0.7 MPa, and a time of 15 min. A universal testing machine is then used for testing. Specifically, the universal testing machine is equipped with a 1.0 mm flat-headed cylindrical needle. The second laminated sample is firmly fixed with a ring clamp (12.7 mm aperture). Subsequently, the needle is inserted into the second laminated sample at a constant speed of 200 mm / min until it is completely penetrated. Complete penetration means that the needle enters from the separator side of the second laminated sample and its tip completely exits from the opposite side of the laminate. The instrument records the force-displacement curve throughout the process, and the peak force (unit: Newtons N) is the puncture strength.

[0030] In some instances, after the battery undergoes a drop-puncture test, the positive electrode plate develops a protrusion at the puncture site. The number A of protrusions with a height greater than 0.7 mm satisfies the condition: 3 ≤ A ≤ 5 (e.g., 3, 4, or 5). After the battery undergoes a drop-puncture test, the positive electrode plate is prone to forming protrusions at the puncture site. This invention has found that a large number of sharp protrusions significantly increases the risk of internal short circuits caused by contact between the positive and negative electrodes. Therefore, this invention controls the number of protrusions with a height greater than 0.7 mm within the aforementioned range, effectively reducing the probability of internal short circuits caused by sharp protrusions penetrating the separator. It also suppresses internal heat generation in the battery under short-circuit conditions, further reducing the risk of battery fire and systematically improving the overall safety performance of the battery in drop-puncture tests.

[0031] In this invention, the height of the protrusion refers to its dimension in the direction of its extension. The direction of the protrusion's extension is the same as the direction of the metal needle's piercing. It can be understood that the piercing position of the positive electrode plate mentioned above refers to the piercing position on the first fold of the positive electrode plate pierced by the steel needle, that is, the positive electrode plate closest to the tip of the steel needle at the initial stage of piercing (see...). Figure 1 ).

[0032] In some instances, the battery also includes an electrolyte comprising lithium bis(trifluoromethanesulfonyl)imide (LITFSI).

[0033] In some instances, the weight percentage C of the lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is 1%-5% (e.g., 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or within any two of the above values).

[0034] In some instances, the battery satisfies the following relationship: 80 ≤ A / C ≤ 460 (e.g., 80, 100, 130, 150, 180, 200, 230, 250, 280, 300, 330, 350, 380, 400, 430, 450, 460, or any two of the above values), where C is the weight percentage of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte. After the battery undergoes a drop puncture test, a protrusion is formed on the positive electrode at the puncture site, and A is the number of protrusions with a height greater than 0.7 mm. The puncture site of the positive electrode refers to the puncture location on the first fold of the positive electrode pierced by the steel needle.

[0035] 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°.

[0036] After a battery drop-puncture test, if the height of the protrusion at the positive electrode current collector is large (i.e., the protrusion is long), it increases the risk of direct contact between the positive and negative electrodes, thereby reducing the drop-puncture pass rate. To address the short-circuit risk caused by large protrusions, this invention adds lithium bis(trifluoromethanesulfonyl)imide to the electrolyte, utilizing its electrochemical properties to achieve controlled corrosion of the protrusion. Specifically, at the battery operating voltage, the TFSI⁻ anions dissociated from LiTFSI effectively destroy the passivation film on the surface of the positive electrode aluminum current collector, initiating pitting corrosion and metal dissolution. This reduces the height of the protrusion and can also corrode away protrusions that were originally small, thereby further reducing complex short-circuit points and lowering the risk of short circuits between the positive and negative electrodes caused by the protrusion. However, while lithium bis(trifluoromethanesulfonyl)imide helps to corrode the protrusions, shortening the height of higher protrusions and corroding lower protrusions to reduce complex short-circuit points, an excessively high weight content of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte can also corrode the positive electrode current collector and aluminum-plastic film, reducing their strength and affecting the battery's drop puncture pass rate. Therefore, controlling the battery to satisfy the following relationship: 80≤A / C≤460 can improve the matching degree between the number of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte and the number of protrusions with a height greater than 0.7mm. This avoids the corrosion of the positive electrode current collector and aluminum-plastic film due to an excessively high weight proportion of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte, which would reduce the battery's drop puncture test pass rate and affect its safety performance.

[0037] In some instances, the battery satisfies the following relationship: 100 ≤ A / C ≤ 400.

[0038] According to some specific implementation methods, A is 3-5, C is 0.01-0.05, and the battery satisfies the following relationship: 80≤A / C≤460.

[0039] According to some specific implementation methods, A is 3-5, C is 0.01-0.05, and the battery satisfies the following relationship: 100≤A / C≤400.

[0040] In some instances, the electrolyte comprises lithium hexafluorophosphate, organic solvents, and additives.

[0041] In some instances, the organic solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), dimethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, diethyl carbonate (DMC), ethyl formate, ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), and ethyl butyrate (EB).

[0042] In some instances, the additives include one or more of the following: fluoroethylene carbonate, 1,3-propanesulfonate lactone, ethylene sulfate, succinic acid, glutaronitrile, adiponitrile, 1,3,6-hexanetrionitrile, 1,2,6-hexanetrionitrile, tris(trimethylsilane) phosphate, and tris(trimethylsilane) borate.

[0043] In some instances, based on the total weight of the electrolyte, the lithium hexafluorophosphate accounts for 10%-15% by weight (e.g., 10%, 11%, 12%, 13%, 14%, 15%, or any two of the above values), the organic solvent accounts for 83%-89% by weight (e.g., 83%, 84%, 85%, 86%, 87%, 88%, 89%, or any two of the above values), and the additives account for 0%-5% by weight (e.g., 0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any two of the above values).

[0044] In some instances, the difference ΔT between the closure temperature and the rupture temperature of the diaphragm is 25°C to 150°C (e.g., 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, or any combination of the above values).

[0045] Research has shown that when the difference ΔT between the pore-closure temperature and the rupture temperature of the separator is too small, the separator will rupture rapidly within seconds after pore closure, leading to increased internal short circuits, faster heat accumulation inside the battery, and a further increase in the risk of thermal failure. When the difference ΔT is too large, an irreversible exothermic reaction may occur inside the battery before the separator closes, increasing the risk of thermal runaway. Furthermore, it directly reduces the ionic conductivity of the separator, hindering lithium-ion transport, increasing DCIR internal resistance, causing rapid degradation of the battery's rate performance, deteriorating electrolyte wettability, excessively high surface energy, and shortening the battery's cycle life. Therefore, controlling the difference ΔT between the pore-closure temperature and the rupture temperature of the separator within the aforementioned range allows the separator to maintain high ionic conductivity while retaining a relatively intact structure during thermal runaway, preventing large-area short circuits between the positive and negative electrodes, which could further exacerbate thermal runaway and worsen battery safety.

[0046] In this invention, the pore-closing temperature of the separator refers to the temperature threshold at which the micropores inside the separator close due to the melting and contraction of the material when the temperature rises to a specific critical value, thereby blocking the passage of lithium ions and cutting off the ion conduction channels inside the battery. The membrane rupture temperature of the separator refers to the temperature threshold at which the physical structure of the separator undergoes irreversible damage (e.g., tearing, cracking, melting and collapse) under continuous high temperature, completely losing its insulating separation function between the positive and negative electrodes.

[0047] In this invention, the pore-closure temperature of the diaphragm can be obtained by the following method: the diaphragm sample is placed in a thermomechanical analyzer (TMA) and heated at 5 °C / min, while its dimensional changes are monitored in real time. When the temperature reaches the melting point of the base membrane material, the pores close due to melting and shrinkage, causing a sudden change in the diaphragm thickness; this temperature is the pore-closure temperature.

[0048] In this invention, the rupture temperature of the diaphragm can be obtained by the following method: a 0.2 N stress is applied to the diaphragm using a 0.5 mm puncture probe, and the diaphragm is heated at 5 °C / min. The mechanical strength of the diaphragm decreases as the temperature increases. When the temperature is so high that the diaphragm cannot withstand the stress brought by the puncture probe, it will puncture the diaphragm, causing the displacement data recorded by the instrument to suddenly increase. The temperature corresponding to the point of sudden displacement increase is the rupture temperature.

[0049] In some instances, the diaphragm includes a substrate layer and a coating on at least one side surface of the substrate layer.

[0050] In some instances, the coating comprises first particles and a first binder.

[0051] In some instances, the first 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.

[0052] In some instances, the first 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.

[0053] In some instances, the coating also includes dispersants and wetting agents.

[0054] In some instances, the dispersant includes sodium carboxymethyl cellulose.

[0055] In some instances, the wetting agent includes one or more of alkylnaphthalene sulfonates, alkylbenzene sulfonates, and polyoxyethylene fatty alcohol ethers.

[0056] In some instances, the weight percentage of the first particles is 92%-97% (e.g., 92%, 93%, 94%, 95%, 96%, 97% or within any two of the above values) based on the total weight of the coating, and the weight percentage of the first adhesive is 3%-8% (e.g., 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8% or within any two of the above values) based on the total weight of the coating. 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.

[0057] In some instances, the substrate layer is composed of one or more of polyethylene (PE), polypropylene (PP), modified polyethylene, and modified polypropylene.

[0058] In some instances, the substrate layer includes a composite substrate layer, such as a polypropylene-polyethylene-polypropylene composite substrate layer.

[0059] In some instances, the molecular weight of the polyethylene is between 800,000 and 1,500,000 (e.g., 800,000, 900,000, 1,000,000, 1,100,000, 1,200,000, 1,300,000, 1,400,000, or 1,500,000). Using high molecular weight PE can effectively improve the diaphragm's puncture strength. Increased puncture strength improves the pass rate of drop puncture safety tests. However, a higher PE molecular weight leads to an increased pore-closure temperature of the diaphragm, resulting in a decrease in the overall furnace temperature performance of the battery cell. Conversely, a lower PE molecular weight results in a lower diaphragm puncture strength, failing to meet drop puncture safety requirements. Controlling the molecular weight of the polyethylene within the aforementioned range allows the diaphragm to possess both high puncture strength and a suitable pore-closure temperature.

[0060] In some instances, the diaphragm further includes an adhesive layer located on the surface of the substrate layer and / or on another surface of the coating away from the substrate layer.

[0061] In some instances, the adhesive layer comprises a third polymer and optionally filler particles.

[0062] In one example, the third polymer includes one or more of the following: polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene modified and copolymerized thereof, polyacrylonitrile, polymethyl methacrylate, polyacrylic acid, styrene-butadiene rubber, polyvinyl alcohol and its copolymerized polyvinyl alcohol, polyvinyl acetate, polyacrylamide, phenolic resin, epoxy resin, waterborne polyurethane, ethylene-vinyl acetate copolymer, multi-component acrylic copolymer, lithium polystyrene sulfonate, pure styrene latex, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene, polyvinylpyrrolidone, polyethylene oxide, cellulose acetate, cellulose butyl acetate, cellulose propyl acetate, cyanoethyl amylopectin, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, and cyanoethyl sucrose.

[0063] In one example, the filler particles are composed of one or more of the following: alumina, boehmite, magnesium oxide, magnesium hydroxide, barium sulfate, barium titanate, zinc oxide, calcium oxide, silicon dioxide, silicon carbide, melamine, melamine cyanurate, melamine polyphosphate, aluminum diethyl phosphite, and modified melamine salts.

[0064] In one example, based on the total weight of the adhesive layer, the weight content of the third polymer is 20%-100% (e.g., 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or within any two of the above values), and the weight content of the filler particles is 0-80% (e.g., 0, 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or within any two of the above values). When the weight content of the filler particles in the adhesive layer is 0, it indicates that the filler particles are absent in the adhesive layer.

[0065] According to one specific embodiment, the diaphragm includes a substrate layer, a coating layer, and an adhesive layer, wherein the coating layer is located on one side surface of the substrate layer, and the adhesive layer is located on the surface of the coating layer away from the substrate layer.

[0066] According to one specific embodiment, the diaphragm includes a substrate layer, a coating layer, and an adhesive layer, wherein the coating layer is located on one side surface of the substrate layer, and the adhesive layer is located on the other side surface of the substrate layer.

[0067] According to one specific embodiment, the diaphragm includes a substrate layer, a coating layer, and an adhesive layer, wherein the coating layer is located on one side surface of the substrate layer, the adhesive layer is located on the other side surface of the substrate layer, and the coating layer is located on the surface away from the substrate layer.

[0068] According to one specific embodiment, the diaphragm includes a substrate layer, a coating layer, and an adhesive layer, wherein the adhesive layer is located on both sides of the substrate layer and on one side of the coating layer.

[0069] According to one specific embodiment, the diaphragm includes a substrate layer, a coating layer, and an adhesive layer, wherein the coating layer is located on both sides of the substrate layer, and the adhesive layer is located on both sides of the coating layer.

[0070] In some instances, the negative electrode sheet includes a negative current collector and a negative active layer located on one or both sides of the surface of the negative current collector.

[0071] In some instances, the negative electrode active layer comprises a negative electrode material, which comprises a silicon-based material, including at least one of silicon-carbon, nano-silicon powder, and silicon oxide.

[0072] In some instances, the K-value of batteries containing silicon-based materials in the negative electrode is between 0.001 mV / H and 0.5 mV / H (e.g., 0.001 mV / H, 0.005 mV / H, 0.1 mV / H, 0.2 mV / H, 0.3 mV / H, 0.4 mV / H, 0.5 mV / H, or any two of the above values). Due to the high hardness of silicon-based materials, these particles often puncture the separator during cell fabrication, leading to minor internal short circuits within the cell. The separator described in this application possesses high puncture strength, thereby reducing the risk of the separator being punctured by silicon-based materials, decreasing internal short circuit points, and lowering the battery's K-value. Furthermore, the higher the weight percentage of silicon in the negative electrode active layer, the more significant the improvement in the battery's K-value.

[0073] In some instances, the negative electrode material also includes a carbon-based material, which includes artificial graphite and / or natural graphite.

[0074] In some instances, the weight percentage of silicon in the negative electrode active layer is 2%-80% (e.g., 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or within any two of the above values).

[0075] In this invention, the weight content of element Si in the negative electrode active material can be determined by conventional testing methods in the art, for example, by the following method: disassemble the battery, remove the negative electrode sheet, soak and clean it with DMC and then dry it, remove the copper foil to obtain the negative electrode active layer powder, place the negative electrode active layer powder in an argon atmosphere, and heat it to 250°C at a rate of 10°C / min. The weight of the negative electrode active layer powder at this point is taken as the initial weight W. 1 Then, the atmosphere was switched to air, and the temperature was increased to 900℃ at 10℃ / min and held for 8 hours to obtain the final weight W of the negative electrode active layer powder. 2 According to the formula α=7×W 2 / (15×W 1 The silicon content in the negative electrode active material can be calculated.

[0076] In some instances, the negative electrode active layer further includes a negative electrode conductive agent and a negative electrode binder.

[0077] 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.

[0078] In some instances, the negative electrode binder includes one or more of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, polyethylene oxide, and polyvinylidene fluoride.

[0079] In one example, based on the total weight of the negative electrode active layer, the weight content of the negative electrode 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).

[0080] In some instances, the battery cell is a wound battery cell or a laminated battery cell. When the battery cell is a laminated battery cell, the two outermost electrodes of the battery cell are single-sided positive electrodes. The single-sided positive electrode includes a positive current collector and a positive active layer located on one side of the positive current collector. The positive electrode also includes a double-sided positive electrode, which includes a positive current collector and positive active layers located on both sides of the positive current collector.

[0081] In some instances, the battery is a lithium-ion rechargeable battery.

[0082] 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.

[0083] The following examples illustrate the battery of the present invention.

[0084] Example 1 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 prepare a positive electrode slurry. This positive electrode slurry was then uniformly coated onto both sides of an aluminum foil, with a coating 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.

[0085] 2. Negative electrode plate Artificial graphite, silicon carbide particles, conductive agent (conductive carbon black), and binder (styrene-butadiene rubber) are placed in deionized water at a mass ratio of 86.9:9.7:2.8:0.6. The above slurry is stirred evenly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on both sides of the negative electrode current collector (copper foil), and then dried, rolled, and die-cut to obtain a negative electrode sheet.

[0086] 3. Electrolyte The electrolyte consists of lithium salt LiPF6 and solvents. The solvents include ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC), with a molar ratio of DEC:EC:EMC = 1:1:1. Fluorinated ethylene carbonate accounts for 5% of the weight of the electrolyte, and lithium bis(trifluoromethanesulfonyl)imide accounts for 2% of the weight of the electrolyte.

[0087] 4. Diaphragm The diaphragm comprises a substrate layer, a coating layer, and an adhesive layer. The substrate layer is a composite substrate layer of polypropylene-polyethylene-polypropylene (polyethylene has a molecular weight of 1.1 million). 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 away from the substrate layer. The first particle in the coating is alumina, and the first binder is polybutyl methacrylate. The first particle accounts for 95% of the weight of the coating, and the first binder accounts for 5% of the weight. The adhesive layer is formed by a third polymer, which is polymethyl methacrylate. The difference between the closure temperature and the rupture temperature of the diaphragm is 90°C. 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 used to prepare a core structure battery cell in a fully automatic winding machine. The battery cell is then packaged using a high-strength aluminum-plastic film. Finally, after treatments such as electrolyte injection (i.e., injection of the electrolyte prepared in step (3)), formation, and secondary sealing, a lithium-ion battery is obtained. The parameters of the battery are shown in Table 1.

[0088] Example 2 group This set of embodiments illustrates the effect of changing at least one of the sum of puncture strengths B and D of the positive electrode current collector and the diaphragm after thermal lamination. Specifically, changing the thickness of the aluminum-plastic film and / or the material of the substrate layer in the diaphragm can alter the sum of puncture strengths B of the diaphragm and the aluminum-plastic film after thermal lamination, and changing the material of the substrate layer in the diaphragm and / or the thickness of the positive electrode current collector can alter the sum of puncture strengths D of the positive electrode current collector and the diaphragm after thermal lamination.

[0089] This embodiment group is carried out with reference to Embodiment 1, and see Table 1 for details.

[0090] Example 3 Group This set of examples illustrates the effects of changes in A / C.

[0091] This embodiment group is based on Embodiment 1, except that A / C is changed, as detailed in Table 1.

[0092] Example 4 group This set of examples illustrates the effects of changing the difference between the pore closure temperature and the rupture temperature of the diaphragm by altering the composition of the substrate layer or the coating in the diaphragm.

[0093] This embodiment is based on Embodiment 1, except that the difference between the pore closure temperature and the rupture temperature of the diaphragm is changed.

[0094] Comparative Example 1 The procedure was carried out in accordance with Example 1, except that the sum of the puncture strengths B of the diaphragm and the aluminum-plastic film after thermal lamination was changed by altering the thickness of the aluminum-plastic film or the material of the substrate layer in the diaphragm. See Table 1 for details.

[0095] Comparative Example 2 The procedure was carried out in accordance with Example 1, except that the sum of the puncture strengths B of the diaphragm and the aluminum-plastic film after thermal lamination was changed by altering the thickness of the aluminum-plastic film or the material of the substrate layer in the diaphragm. See Table 1 for details.

[0096] Table 1 Test case The lithium-ion batteries prepared in the examples and comparative examples were tested as follows.

[0097] 1. Drop and needle penetration performance 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°.

[0098] 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 samples passing / 20," for example, "5 / 20" means 5 out of 20 battery samples passed the test.

[0099] 2. Furnace temperature performance 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 were expressed as "number of passing samples / 20", for example, "5 / 20" means that 5 out of 20 battery samples passed the test.

[0100] 3. K-value test At 25℃, the open circuit potential of the lithium-ion batteries after sorting is measured to obtain V1. After standing for 24 hours, the open circuit potential of the battery is measured again to obtain V2. The K value of the battery is obtained by subtracting V2 from V1 and dividing the difference by the standing time.

[0101] The results are recorded in Table 2.

[0102] Table 2 As can be seen from Table 2, by comparing the comparative examples and the embodiments, it can be found that the drop puncture pass rate and furnace temperature pass rate of the battery in the embodiments are significantly improved. Therefore, it can be seen that by controlling the sum B of the puncture strength of the separator and the aluminum-plastic film after thermal lamination to be within the protection range, the battery can achieve both high drop safety performance and good furnace temperature safety performance.

[0103] 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 an aluminum-plastic film and an electrode assembly. The electrode assembly is located in the accommodating space formed by the aluminum-plastic film. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The puncture strength B of the separator and the aluminum-plastic film after being laminated and thermally bonded is 25N-51N.

2. The battery according to claim 1, wherein, The positive electrode includes a positive current collector, and the sum of the puncture strength D of the positive current collector and the separator after being thermally composited in layers is 8N-18N.

3. The battery according to claim 1, wherein, The difference between the closure temperature and the rupture temperature of the diaphragm is 25℃-150℃.

4. The battery according to claim 1, wherein, The battery also includes an electrolyte comprising lithium bis(trifluoromethanesulfonyl)imide. The battery satisfies the following relationship: 80 ≤ A / C ≤ 460, where C is the weight percentage of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte. After the battery undergoes a drop puncture test, a protrusion is generated at the puncture site on the positive electrode plate, and A is the number of protrusions with a height greater than 0.7 mm. The drop puncture test is conducted under the following conditions: 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 then 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 the needle tip is 32°.

5. The battery according to claim 4, wherein, A satisfies: 3 ≤ A ≤ 5; And / or, 100≤A / C≤400.

6. The battery according to claim 1, wherein, The negative electrode sheet includes a negative current collector and a negative active layer located on one or both sides of the negative current collector. The negative active layer includes a silicon-based material, which includes at least one of silicon-carbon, nano-silicon powder, and silicon oxide.

7. The battery according to claim 6, wherein, The weight percentage of silicon in the negative electrode active layer is 2%-80%.

8. The battery according to any one of claims 1-7, wherein, The diaphragm includes a substrate layer and a coating located on at least one side surface of the substrate layer. The coating includes first particles and a first binder. The first particles are composed of one or more of the following: 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. And / or, the substrate layer is composed of polyethylene, and the molecular weight of the polyethylene is 800,000 to 1,500,000.

9. The battery according to claim 1, wherein, The aluminum-plastic film includes a first layer, a metal layer, and a second layer stacked sequentially. The second layer is close to the battery cell. The first layer is composed of a first polymer, which includes polyamide. The second layer is composed of a second polymer, which includes one or more of polypropylene, cast polypropylene, polyethylene, and silica-doped POE resin.

10. The battery according to claim 9, wherein, The thickness of the first layer is 15μm-35μm.

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