Composite current collector, method for preparing the same, and use thereof

Abstract

The application provides a composite current collector and a preparation method and application thereof, relates to the technical field of lithium ion batteries, and the composite current collector comprises a polymer film and copper conductive layers deposited on two sides of the polymer film; the polymer film comprises 1-30% of copper sulfate pentahydrate and 70-99% of a polymer in terms of mass percentage. The application provides a three-layer sandwich type composite current collector formula, and the polymer material can effectively enhance the toughness and insulation of the current collector relative to the copper material. A self-destroying agent is added in the polymer material in the middle layer, when the battery is in a high-temperature environment or thermal runaway occurs, the self-destroying agent is dehydrated at a specific temperature, the water removed by the self-destroying agent can be reacted with lithium ions in the negative electrode in advance, so that the lithium in the negative electrode is consumed in advance, the established thermal runaway reaction time sequence is broken, and the generation amount of reducing gas is reduced, so that the purpose of reducing the reaction intensity is achieved, and finally the safety performance of the battery cell is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a composite current collector, its preparation method, and its application. Background Technology

[0002] Benefiting from increased demand in fields such as new energy vehicles, energy storage, and 3C digital products, the demand for lithium-ion batteries is growing rapidly, and the safety of lithium batteries is also a major concern. Currently, lithium-ion batteries commonly use current collectors made of high-purity electrolytic copper or aluminum, which are prone to burrs during processing, resulting in poor tensile and compressive strength.

[0003] In addition, lithium-ion batteries can experience exothermic reactions during overcharging, short circuits, and heating. These side reactions generate a large amount of heat, which can easily lead to thermal runaway if not dissipated in time. During the thermal runaway process, the separator may melt, causing a short circuit between the positive and negative electrodes. This can trigger more intense heat-generating reactions, easily leading to thermal runaway and ultimately causing the lithium-ion battery to burn or explode.

[0004] Based on this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a composite current collector, its preparation method, and its application. It provides a three-layer sandwich composite current collector structure. The polymer material effectively enhances the toughness and insulation of the current collector compared to copper. A self-destructing agent is added to the middle layer of the polymer material. When the battery is in a high-temperature environment or experiences thermal runaway, the self-destructing agent loses water at a specific temperature, allowing the released water to react prematurely with lithium ions in the negative electrode. This prematurely consumes the lithium in the negative electrode, disrupting the predetermined thermal runaway reaction sequence and reducing the generation of reducing gases, thereby reducing the intensity of the reaction and ultimately improving the safety performance of the battery cell. This invention uses a self-destructing agent—copper sulfate pentahydrate—added to the polymer material layer. When the temperature rises to a specific temperature, this hydrate begins to decompose into crystal water. The released water reacts prematurely with lithium ions in the negative electrode, reducing the intensity of the reaction and lowering the maximum temperature during thermal runaway, ultimately preventing thermal runaway.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The present invention provides a composite current collector, comprising a polymer film and copper conductive layers deposited on both sides of the polymer film;

[0008] The polymer film comprises, by weight percentage, 1-30% copper sulfate pentahydrate and 70-99% polymer.

[0009] Furthermore, based on the above technical solution, the thickness of the polymer film is 2-6 μm.

[0010] Furthermore, based on the above technical solution, the polymer includes one or more of polybutylene terephthalate, polyethylene terephthalate, polyethylene, polypropylene, polyamide, polyimide, polyvinyl chloride, and polystyrene.

[0011] Furthermore, based on the above technical solution, copper plating layers are also deposited on the copper conductive layers on both sides of the polymer film.

[0012] The thickness of the copper conductive layer on one side is 45-55 nm.

[0013] The total thickness of the copper plating and copper conductive layer on one side is 0.5-5μm.

[0014] Furthermore, based on the above technical solution, the thickness of the composite current collector is 2.5-11 μm.

[0015] The present invention also provides a method for preparing the composite current collector as described above, comprising the following steps:

[0016] S1: Preparation of polymer thin films;

[0017] S2: Copper conductive layers are deposited on both sides of the polymer film by magnetron sputtering;

[0018] S3: Optionally, a copper plating layer is prepared on the copper conductive layer by electroplating to obtain polymer copper foil;

[0019] S4: After washing the polymer film with copper conductive layer deposited in step S2 or the polymer copper foil obtained in step S3 with water, a composite current collector is obtained.

[0020] Furthermore, based on the above technical solution, in step S1, the method for preparing the polymer film includes:

[0021] Copper sulfate pentahydrate powder and granular polymer are mixed evenly at a stirring speed of 400-900 r / min according to a certain ratio. The mixture is then extruded through a twin-screw extruder to obtain a polymer sheet. The polymer sheet is then stretched to obtain the polymer film.

[0022] Furthermore, based on the above technical solution, the conditions of the twin-screw extruder include: a screw diameter of 10-15cm, a screw speed of 200-400r / min, and a screw extrusion temperature of 120-180℃;

[0023] The stretching is performed simultaneously in both the transverse and longitudinal directions, with the stretching temperature being 120-130℃ and the setting temperature being 120℃.

[0024] Furthermore, based on the above technical solution, in step S3, the pH value of the electroplating solution is 1-3, the working temperature of the plating solution is 20℃-35℃, and the current density is 1-4Asd.

[0025] The present invention also provides an application of the composite current collector as described above or the composite current collector prepared by the preparation method as described above, which can be used to prepare the negative electrode sheet of lithium-ion battery cells.

[0026] The lithium-ion battery cell is assembled from the negative electrode, the separator, and the positive electrode.

[0027] The composite current collector, its preparation method, and its applications provided by this invention have the following beneficial effects:

[0028] 1. This invention provides a three-layer sandwich composite current collector. The polymer material effectively enhances the toughness and insulation of the current collector compared to pure copper foil. A self-destructing agent is added to the middle polymer layer. When the battery is in a high-temperature environment or experiences thermal runaway, the self-destructing agent loses water at a specific temperature, allowing the released water to react prematurely with lithium ions in the negative electrode. This prematurely consumes the lithium in the negative electrode, disrupting the predetermined thermal runaway reaction sequence and reducing the generation of reducing gases, thereby reducing the intensity of the reaction and ultimately improving the safety performance of the battery cell. This invention uses a self-destructing agent—copper sulfate pentahydrate—added to the polymer material layer. When the temperature rises to a specific temperature, this hydrate begins to decompose into crystal water. The released water reacts prematurely with lithium ions in the negative electrode, reducing the intensity of the reaction and lowering the maximum temperature during thermal runaway, ultimately preventing thermal runaway.

[0029] 2. This invention employs melt extrusion to mix the self-destructing agent and polymer together. This method not only ensures that the self-destructing agent is firmly held within the composite current collector film layer under normal battery use conditions, but also prevents the release of crystal water from the self-destructing agent within the normal battery operating temperature range, thus avoiding damage to the battery. The twin-screw extrusion temperature of this invention is 120-180℃. During the polymer film preparation process, the self-destructing agent will lose at least two loosely bound non-hydrogen-bonded crystal water molecules, thereby preventing the self-destructing agent from dehydrating and affecting battery performance and safety during normal battery use. The remaining crystal water on the copper sulfate will only detach when the battery reaches a specific temperature, such as when thermal runaway is triggered, and further react with lithium on the negative electrode. Specifically, under conditions of 120-180℃, the self-destructing agent will first decompose to release some crystal water that is easily detached at low temperatures, ensuring that no water is generated during normal battery use. The undissociated crystal water on the copper sulfate can dissociate after the battery reaches a sufficiently high temperature, playing a cooling role at appropriate times and preventing battery combustion and explosion. Attached Figure Description

[0030] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 This is a comparison diagram of the large-area temperature curves of the thermal runaway process provided in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0033] The endpoints and any values ​​of the ranges disclosed in this invention 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 in this invention.

[0034] According to a first aspect of the present invention, a composite current collector is provided, comprising a polymer film and a copper conductive layer deposited on both sides of the polymer film;

[0035] By weight percentage, the polymer film comprises 1-30% (e.g., 5%, 10%, 15%, 20%, 22%, 24%, 26%, 28%, etc.) of copper sulfate pentahydrate and 70-99% (e.g., 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, etc.) of polymer.

[0036] Specifically, this invention provides a three-layer sandwich composite current collector. The polymer material effectively enhances the toughness and insulation of the current collector compared to copper. A self-destructing agent is added to the middle polymer layer. When the battery is in a high-temperature environment or experiences thermal runaway, the self-destructing agent loses water at a specific temperature, allowing the released water to react prematurely with lithium ions in the negative electrode. This prematurely consumes the lithium in the negative electrode, disrupting the predetermined thermal runaway reaction sequence and reducing the generation of reducing gases, thereby reducing the intensity of the reaction and ultimately improving the safety performance of the battery cell. This invention uses copper sulfate pentahydrate as a self-destructing agent added to the polymer material layer. When the temperature rises to a specific temperature, this hydrate begins to decompose, releasing water that reacts prematurely with lithium ions in the negative electrode, reducing the intensity of the reaction and lowering the maximum temperature during thermal runaway, ultimately preventing thermal runaway.

[0037] Furthermore, this invention limits the content of copper sulfate pentahydrate in the polymer film to the range of 1-30% to ensure that the material possesses the necessary thermal runaway prevention function without adversely affecting the film's molding and tensile properties. Excessive copper sulfate pentahydrate can affect the film's flexibility and uniformity, and reduce the tensile strength of the composite foil, which contradicts the current trend towards thinner and lighter designs in materials science and electronics manufacturing. By precisely controlling the content of copper sulfate pentahydrate, this invention aims to achieve the optimal balance between the self-destruct agent function and the physical properties of the composite foil, thereby meeting the requirements of battery safety and thinner design.

[0038] As an optional embodiment of the present invention, the thickness of the polymer film is 2-6 μm (e.g., 3 μm, 4 μm, 5 μm, etc.).

[0039] Specifically, as part of the battery composite current collector, the thin film needs to possess certain mechanical strength and insulation properties to ensure the safety of the battery under normal use and potential thermal runaway conditions. A thickness of 2-6 μm provides sufficient strength and insulation to prevent short circuits and electrolyte leakage. If the film thickness exceeds 6 μm, it will reduce cell space utilization, lower battery energy density, and offer no application advantages.

[0040] As an optional embodiment of the present invention, the polymer includes one or more of polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC) and polystyrene (PS).

[0041] As an optional embodiment of the present invention, copper conductive layers on both sides of the polymer film are further plated with copper plating layers.

[0042] The thickness of the copper conductive layer on one side is 45-55nm (e.g., 46nm, 47nm, 48nm, 49nm, 50nm, 51nm, 52nm, 53nm, 54nm, etc.), preferably 50nm.

[0043] The total thickness of the copper plating and copper conductive layer on one side is 0.5-5μm (e.g., 1μm, 2μm, 3μm, 4μm, etc.).

[0044] Specifically, electroplating refers to the process of forming a copper coating on the surface of a polymer film through an oxidation-reduction reaction using an electric current. First, a copper coating is formed on the polymer film surface using methods such as magnetron sputtering or vacuum evaporation, giving it a certain degree of conductivity; at this stage, the thickness is 45-55 nm. Then, the polymer film is placed in the electroplating solution as the anode, using the copper plate as the cathode, and a DC power supply is applied. Under the influence of the external current, an oxidation-reduction reaction occurs. The copper plate at the anode transforms into copper ions, which dissolve into the electroplating solution. These copper ions are then reduced to metallic copper at the cathode, forming a micron-sized copper coating on the polymer film surface.

[0045] Furthermore, the copper conductive layer primarily provides the basic conductivity of the polymer film. It is formed through physical deposition methods such as magnetron sputtering and vacuum evaporation, providing the initial foundation for conductivity. In addition, the uniform coverage of the copper conductive layer on the polymer film surface ensures uniform deposition of the copper plating during subsequent electroplating, while also enhancing the mechanical adhesion between the copper plating and the polymer film, improving the stability and durability of the plating, and reducing the overall resistance of the composite current collector, thereby increasing its conductivity. The copper plating layer further enhances conductivity based on the copper conductive layer. The electroplating process thickens the plating layer, significantly improving the conductivity of the polymer film. The copper plating layer also increases the mechanical strength and wear resistance of the film, improves its oxidation resistance and chemical stability, and can resist the corrosion of chemicals such as electrolytes. In battery applications, the copper plating layer, as part of the current collector, plays a crucial role in collecting and conducting current.

[0046] As an optional embodiment of the present invention, the thickness of the composite current collector is 2.5-11μm (e.g., 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc.).

[0047] According to a second aspect of the present invention, a method for preparing the composite current collector as described above is provided, comprising the following steps:

[0048] S1: Preparation of polymer thin films;

[0049] S2: Copper conductive layers are deposited on both sides of the polymer film by magnetron sputtering;

[0050] S3: Optionally, a copper plating layer is prepared on the copper conductive layer by electroplating to obtain polymer copper foil;

[0051] S4: After washing the polymer film with copper conductive layer deposited in step S2 or the polymer copper foil obtained in step S3 with water, a composite current collector is obtained.

[0052] As an optional embodiment of the present invention, in step S1, the method for preparing the polymer film includes:

[0053] Copper sulfate pentahydrate powder and granular polymer are mixed evenly at a stirring speed of 400-900 r / min (e.g., 500 r / min, 600 r / min, 800 r / min, etc.) according to a certain ratio. The mixture is then extruded through a twin-screw extruder to obtain a polymer sheet. The polymer sheet is then stretched to obtain the polymer film.

[0054] As an optional embodiment of the present invention, the conditions of the twin-screw extruder include: a screw diameter of 10-15 cm, a screw speed of 200-400 r / min, and a screw extrusion temperature of 120-180℃ (e.g., 125℃, 130℃, 135℃, 140℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, etc.).

[0055] The stretching is performed simultaneously in both transverse and longitudinal directions, with the stretching temperature being 120-130℃ (e.g., 122℃, 124℃, 126℃, 128℃, etc.); the setting temperature is 120℃.

[0056] Specifically, this invention employs melt extrusion to mix the self-destructing agent and polymer together. This method not only ensures that the self-destructing agent is firmly held within the composite current collector film layer under normal battery use conditions, but also prevents the release of water of crystallization from the self-destructing agent within the normal battery operating temperature range, thus avoiding damage to the battery. The twin-screw extrusion temperature of this invention is 120-180℃. During the polymer film preparation process, the self-destructing agent will lose at least two loosely bound non-hydrogen-bonded water molecules of crystallization, thereby preventing the self-destructing agent from dehydrating and affecting battery performance and safety during normal battery use. The remaining water of crystallization on the copper sulfate will only detach when the battery reaches a specific temperature, such as when thermal runaway is triggered, and further react with lithium on the negative electrode. Specifically, under conditions of 120-180℃, the self-destructing agent will first decompose to release some water of crystallization that is easily detached at low temperatures, ensuring that no water is generated during normal battery use. The undissociated water of crystallization on the copper sulfate can dissociate after the battery reaches a sufficiently high temperature, playing a cooling role at appropriate times and preventing battery combustion and explosion.

[0057] Specifically, in step S2, magnetron sputtering utilizes a magnetic field to confine electron movement for sputtering, which features low temperature and high speed, and does not trigger the self-destructing agent contained in the thin film during sputtering.

[0058] As an optional embodiment of the present invention, in step S3, the electroplating is performed by applying an electric current in an aqueous solution to reduce and deposit metal ions on the substrate to be plated, thereby forming a metal coating on the surface of the substrate.

[0059] The main component of the electroplating solution is copper sulfate, and the pH value of the solution is 1-3. The pH value of the solution is an important factor affecting the electroplating reaction rate and the coating quality. Too high a pH value will inhibit the deposition rate of the coating metal, while too low a pH value will cause hydrogen ions in the solution to compete with the coating metal ions, reducing the deposition efficiency of the coating metal. Therefore, the pH value of the solution should be controlled within the range of 1-3.

[0060] The working temperature of the plating solution is 20℃-35℃. The working temperature of the plating solution affects the rate of the electroplating reaction and the crystallization state of the coating. Increasing the plating solution temperature can accelerate the electroplating rate, but it may also lead to an increase in coating roughness. Therefore, the working temperature of the plating solution should be controlled within the range of 20℃-35℃.

[0061] The current density should be between 1 and 4 Asd. Current density refers to the current intensity passing through a unit area, which directly affects the deposition rate and quality of the coating. Excessive current density may lead to a rough or burnt coating; insufficient current density may result in a slow deposition rate and a thin coating. Therefore, the current density should be controlled within the range of 1 to 4 Asd.

[0062] According to a third aspect of the present invention, an application is provided of the composite current collector as described above or the composite current collector prepared by the preparation method as described above, which can be used to prepare the negative electrode sheet of a lithium-ion battery cell.

[0063] The lithium-ion battery cell is assembled from the negative electrode, the separator, and the positive electrode.

[0064] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0065] Example 1

[0066] S1: Copper sulfate pentahydrate powder and polyethylene granules are mixed evenly at a mass ratio of 1:9 and stirred at a stirring speed of 600r / min. The mixture is then extruded through a twin-screw extruder to obtain a polymer sheet. The polymer sheet is then stretched to obtain a polymer film with a thickness of 3μm.

[0067] The conditions of the twin-screw extruder include: a screw diameter of 13 cm, a screw speed of 300 r / min, and a screw extrusion temperature of 160 °C.

[0068] The stretching is performed simultaneously in both the transverse and longitudinal directions, with a stretching temperature of 125°C and a setting temperature of 120°C.

[0069] S2: Copper conductive layers are deposited on both sides of the polymer film by magnetron sputtering, with the thickness of the copper conductive layer on each side being 50 nm.

[0070] S3: A copper plating layer is prepared on the copper conductive layer by electroplating. The total thickness of the copper plating layer and the copper conductive layer on one side is 2μm, and a polymer copper foil is obtained.

[0071] The main component of the electroplating solution is copper sulfate, the pH value of the solution is 1, the working temperature of the solution is 30℃, and the current density is 3Asd.

[0072] S4: After washing the polymer copper foil multiple times with water, a composite current collector with a thickness of 7μm is obtained.

[0073] Example 2

[0074] S1: Copper sulfate pentahydrate powder and polyvinyl chloride (PVC) granules are mixed evenly at a stirring speed of 600 r / min according to a mass ratio of 2:8. The mixture is then extruded through a twin-screw extruder to obtain a polymer sheet. The polymer sheet is then stretched to obtain a polymer film with a thickness of 2 μm.

[0075] The conditions of the twin-screw extruder include: a screw diameter of 13 cm, a screw speed of 200 r / min, and a screw extrusion temperature of 140 °C.

[0076] The stretching is performed simultaneously in both the transverse and longitudinal directions, with a stretching temperature of 125°C and a setting temperature of 120°C.

[0077] S2: Copper conductive layers are deposited on both sides of the polymer film by magnetron sputtering, with the thickness of the copper conductive layer on each side being 50 nm.

[0078] S3: A copper plating layer is prepared on the copper conductive layer by electroplating with water. The total thickness of the copper plating layer and the copper conductive layer on one side is 0.5 μm, and a polymer copper foil is obtained.

[0079] The main component of the electroplating solution is copper sulfate, the pH value of the solution is 2, the working temperature of the solution is 25℃, and the current density is 2Asd.

[0080] S4: After washing the polymer copper foil multiple times with water, a composite current collector with a thickness of 3μm is obtained.

[0081] Example 3

[0082] S1: Copper sulfate pentahydrate powder and polypropylene granules are mixed evenly at a stirring speed of 600 r / min in a mass ratio of 3:7. The mixture is then extruded through a twin-screw extruder to obtain a polymer sheet. The polymer sheet is then stretched to obtain a polymer film with a thickness of 6 μm.

[0083] The conditions of the twin-screw extruder include: a screw diameter of 13 mm, a screw speed of 400 r / min, and a screw extrusion temperature of 150 °C.

[0084] The stretching is performed simultaneously in both the transverse and longitudinal directions, with a stretching temperature of 125°C and a setting temperature of 120°C.

[0085] S2: Copper conductive layers are deposited on both sides of the polymer film by magnetron sputtering, with the thickness of the copper conductive layer on each side being 50 nm.

[0086] S3: A copper plating layer is prepared on the copper conductive layer by electroplating with water. The total thickness of the copper plating layer and the copper conductive layer on one side is 1 μm, and a polymer copper foil is obtained.

[0087] The main component of the electroplating solution is copper sulfate, the pH value of the solution is 3, the working temperature of the solution is 35℃, and the current density is 1Asd.

[0088] S4: After washing the polymer copper foil multiple times with water, a composite current collector with a thickness of 8μm is obtained.

[0089] Comparative Example 1

[0090] The main difference between this comparative example and Example 1 is that copper sulfate pentahydrate is not added to the polymer film; that is, only the polymer is added. The remaining steps and technical parameters are the same as in Example 1.

[0091] Comparative Example 2

[0092] The main difference between this comparative example and Example 1 is that 40% copper sulfate pentahydrate by mass is added to the polymer film, that is, 60% polymer by mass. The remaining steps and technical parameters are the same as those in Example 1.

[0093] Compared with Comparative Example 2, Example 1 had an excessively high content of copper sulfate pentahydrate, which affected the flexibility and uniformity of the polymer film. The polymer sheet obtained by extrusion could not be stretched to obtain a film of the required thickness, and therefore could not be tested for thermal runaway.

[0094] Performance testing

[0095] The fabrication of lithium-ion battery cells:

[0096] 1) A 9-series ternary cathode material, PVDF, SP, and CNT were mixed uniformly in a ratio of 96.5:2.0:1.0:0.5 and coated evenly onto a 13μm carbon-coated aluminum foil to obtain an areal density of 340g / m³. 2 The positive electrode plate;

[0097] 2) Graphite, SP, CMC, and SBR were mixed uniformly in a ratio of 96.0:0.8:1.4:1.8, and then uniformly coated onto the composite copper foils prepared in the examples and comparative examples, respectively, to obtain an areal density of 190 g / m². 2 The negative electrode plate;

[0098] 3) The composite copper foil negative electrode sheet is transferred to a copper foil with a width of 18mm by ultrasonic roll welding;

[0099] 4) The negative electrode sheet, positive electrode sheet, and separator prepared by the current collectors of the different embodiments and comparative examples above are wound, assembled, and injected with liquid to obtain a square aluminum shell cell with a capacity of 140Ah and a size of 33300113.

[0100] Performance tests were conducted on the lithium-ion cells prepared using the current collectors from the examples and comparative examples:

[0101] 1. Perform DCR testing on the battery cell according to the following method:

[0102] 1) Charging: Charge to 4.2V with constant current and constant voltage at 0.33C, with a cutoff current of 0.05C;

[0103] 2) Let stand for 30 minutes;

[0104] 3) Discharge: Discharge at a constant current of 0.33C to 50% SOC;

[0105] 4. Let stand for 120 minutes;

[0106] 5) Discharge: 2C constant current discharge for 10s (50% SOC discharge DCR).

[0107] 2. Use an ACR tester to test the ACR value of the battery cell.

[0108] 3. Perform thermal runaway testing on the battery cell using the following method:

[0109] a) Use a planar or rod-shaped heating device with a ceramic, metal, or insulating layer on its surface. The heating power of the heating device should be greater than 600W. Assemble the battery cell with the heating device, ensuring direct contact between the heating device and the battery. The size of the heating device should be smaller than the heated surface of the battery cell. Install a temperature monitor with the temperature sensor located on the side away from heat conduction (opposite to the heating device). The temperature data sampling interval should be no greater than 1 second, with an accuracy of ±2℃. The diameter of the temperature sensor tip should be less than 1mm.

[0110] b) After initial charging of the battery cells, continue charging with constant current at 1C for 12 minutes;

[0111] c) Start the heating device and continuously heat the test object at its maximum power. When thermal runaway occurs or the temperature at the monitoring point reaches 300°C, turn off the heating device.

[0112] d) Record the test results.

[0113] Whether thermal runaway has occurred should be determined according to the following conditions:

[0114] a) The test object experiences a voltage drop;

[0115] b) The temperature at the monitoring point reaches the battery's protection temperature;

[0116] c) The temperature rise rate at the monitoring point is >1℃ / s;

[0117] d) When a)+c) or b)+c) occurs, the battery cell is determined to have thermal runaway;

[0118] e) If fire or explosion occurs during the heating process or within 1 hour after the heating ends, the test should be terminated and determined to be a case of thermal runaway.

[0119] Results data

[0120] Table 1

[0121]

[0122]

[0123] As shown in Table 1 and Figure 1 As shown, before and after the test, the composite current collector in Example 1 with the addition of the self-destructing agent passed the thermal runaway test, and its maximum temperature was also lower during the thermal runaway process, proving that the addition of the self-destructing agent to the composite current collector can reduce the severity of thermal runaway.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite current collector, characterized in that, It consists of a polymer film, copper conductive layers deposited on both sides of the polymer film, and copper plating layers respectively plated on the copper conductive layers on both sides of the polymer film. The polymer film comprises, by weight percentage, 1-30% copper sulfate pentahydrate and 70-99% polymer; The method for preparing the composite current collector includes the following steps: S1: Preparation of polymer thin films; S2: Copper conductive layers are deposited on both sides of the polymer film by magnetron sputtering; S3: Prepare a copper plating layer on the copper conductive layer by electroplating to obtain polymer copper foil; S4: After washing the polymer copper foil obtained in step S3 with water, a composite current collector is obtained; In step S1, the method for preparing the polymer film includes: Copper sulfate pentahydrate powder and granular polymer are mixed evenly at a stirring speed of 400-900 r / min according to a certain ratio. The mixture is then extruded through a twin-screw extruder to obtain a polymer sheet. The polymer sheet is then stretched to obtain a polymer film. The screw extrusion temperature is 120-180℃.

2. The composite current collector according to claim 1, characterized in that, The thickness of the polymer film is 2-6 μm.

3. The composite current collector according to claim 1, characterized in that, The polymer includes one or more of polyethylene, polypropylene, polyvinyl chloride, and polystyrene.

4. The composite current collector according to claim 1, characterized in that, The thickness of the copper conductive layer on one side is 45-55 nm; The total thickness of the copper plating and copper conductive layer on one side is 0.5-5μm.

5. The composite current collector according to claim 1, characterized in that, The thickness of the composite current collector is 2.5-11 μm.

6. The composite current collector according to claim 1, characterized in that, The conditions for the twin-screw extruder include: a screw diameter of 10-15 cm and a screw speed of 200-400 r / min; The stretching is performed simultaneously in both the transverse and longitudinal directions, with the stretching temperature being 120-130℃ and the setting temperature being 120℃.

7. The composite current collector according to claim 1, characterized in that, In step S3, the pH value of the electroplating solution is 1-3, the working temperature of the solution is 20℃-35℃, and the current density is 1-4 Asd.

8. An application of the composite current collector as described in any one of claims 1-7, characterized in that, It can be used to prepare negative electrode sheets for lithium-ion battery cells; The lithium-ion battery cell is assembled from the negative electrode, the separator, and the positive electrode.

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