Composite current collector and preparation method and application thereof

Abstract

The invention provides a composite current collector and a preparation method and application thereof, and relates to the technical field of lithium ion batteries, the composite current collector comprises a polymer film and copper conductive layers deposited on two sides of the polymer film; the polymer film comprises the following components in percentage by mass: 1-30% of copper sulfate pentahydrate and 70-99% of polymer. The invention provides a three-layer sandwich type composite current collector formula, the high polymer material can effectively enhance the toughness and insulativity of the current collector compared with a copper material, a self-destruction agent is added into the middle layer high polymer material, and when a battery is in a high-temperature environment or thermal runaway occurs, the self-destruction agent can effectively destroy the current collector by utilizing the characteristic that the self-destruction agent loses water at a specific temperature. And the water removed by the reaction kettle can react with lithium ions in the negative electrode in advance, so that lithium in the negative electrode is consumed in advance, a set thermal runaway reaction time sequence is broken, the generation amount of reducing gas is reduced, the purpose of reducing the reaction intensity is achieved, and the safety performance of the battery cell is finally improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a composite current collector and a preparation method and application thereof. Background Art

[0002] Benefiting from the increasing demand in new energy vehicles, energy storage, 3C digital and other fields, the demand for lithium-ion batteries has grown rapidly, and the safety of lithium batteries has also attracted much attention. At present, the current collector commonly used in lithium-ion batteries is made of electrolytic copper or aluminum metal with high purity, which is prone to burrs during processing, resulting in poor tensile and compressive deformation resistance.

[0003] In addition, lithium-ion batteries may cause exothermic reactions during overcharging, short circuiting and heating. The side reactions generate a lot of heat. If the heat cannot be dissipated in time, it is easy to cause thermal runaway. During the thermal runaway of the battery, the diaphragm will melt, the positive and negative electrodes will short-circuit, and more intense heat generation reactions will occur later, which can easily trigger thermal runaway of the battery, 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 the present invention is to provide a composite current collector and its preparation method and application, and to provide a three-layer sandwich composite current collector structure. The polymer material can effectively enhance the toughness and insulation of the current collector relative to the copper material. A self-destructing agent is added to the polymer material in the middle layer. When the battery is in a high temperature environment or thermal runaway occurs, the self-destructing agent loses water at a specific temperature, so that the water released can react with the lithium ions in the negative electrode in advance, thereby consuming the lithium in the negative electrode in advance, breaking the established thermal runaway reaction sequence, and reducing the amount of reducing gas generated, thereby achieving the purpose of reducing the severity of the reaction, and ultimately improving the safety performance of the battery cell. The present invention selects to add a self-destructing agent-copper sulfate pentahydrate to the polymer material layer. When the temperature rises to a specific temperature, the hydrate will begin to decompose the crystal water, and the decomposed water will react with the lithium ions in the negative electrode in advance, thereby reducing the severity of the reaction, so that the maximum temperature in the thermal runaway process is reduced, and ultimately achieving the purpose of avoiding thermal runaway.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

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

[0008] In terms of mass percentage, the polymer film includes 1-30% of copper sulfate pentahydrate and 70-99% of polymer.

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

[0010] Further, on the basis of 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, on the basis of the above technical solution, the copper conductive layers on both sides of the polymer film are plated with copper plating layers respectively;

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

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

[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 film;

[0017] S2: depositing copper conductive layers on both sides of the polymer film by magnetron sputtering;

[0018] S3: optionally preparing a copper plating layer on the copper conductive layer by water electroplating to obtain a polymer copper foil;

[0019] S4: Wash the polymer film deposited with a copper conductive layer obtained in step S2 or the polymer copper foil obtained in step S3 with water to obtain a composite current collector.

[0020] Further, 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 stirred and mixed uniformly at a stirring speed of 400-900 r / min according to a proportion, extruded through a twin-screw extruder to obtain a polymer slab, and then the polymer slab is stretched to obtain the polymer film.

[0022] Further, on the basis of the above technical solution, 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°C;

[0023] The stretching is performed in both transverse and longitudinal directions at the same time, wherein the stretching temperature is 120-130°C; and the shaping temperature is 120°C.

[0024] Further, on the basis of the above technical solution, in step S3, the pH value of the water electroplating solution is 1-3, the working temperature of the plating solution is 20° C.-35° C., 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 a negative electrode sheet of a lithium ion battery cell;

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

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

[0028] 1. The present invention provides a three-layer sandwich composite current collector. Compared with a simple copper foil, the polymer material can effectively enhance the toughness and insulation of the current collector. A self-destructing agent is added to the polymer material of the middle layer. When the battery is in a high temperature environment or thermal runaway occurs, the self-destructing agent loses water at a specific temperature, so that the water released can react with the lithium ions in the negative electrode in advance, thereby consuming the lithium in the negative electrode in advance, breaking the established thermal runaway reaction sequence, and reducing the amount of reducing gas generated, thereby achieving the purpose of reducing the intensity of the reaction, and ultimately improving the safety performance of the battery cell. The present invention selects to add a self-destructing agent-copper sulfate pentahydrate to the polymer material layer. When the temperature rises to a specific temperature, the hydrate will begin to decompose the crystal water, and the decomposed water will react with the lithium ions in the negative electrode in advance, thereby reducing the intensity of the reaction, so that the maximum temperature in the thermal runaway process is reduced, and ultimately achieving the purpose of avoiding thermal runaway.

[0029] 2. The present invention adopts the method of melt extrusion to mix the self-destructing agent and the polymer together. This method not only ensures that the self-destructing agent can be firmly held in the film layer of the composite current collector under normal use conditions, but also does not release the crystal water in the self-destructing agent within the normal use temperature range of the battery, causing damage to the battery. The temperature of the twin-screw extrusion of the present invention is 120-180°C. During the preparation of the polymer film, the self-destructing agent will lose at least two non-hydrogen bonded crystal waters that are not firmly bound, thereby avoiding the dehydration of the self-destructing agent during normal use of the battery to affect the battery performance and safety. The remaining crystal water on the copper sulfate will only be separated when a specific temperature is reached inside the battery, such as when thermal runaway is triggered, and further react with the lithium on the negative electrode. Specifically, under the condition of 120-180°C, the self-destructing agent will first decompose a part of the crystal water that is easy to fall off at low temperature, ensuring that no water is generated during the normal use of the battery. The crystal water that has not dissociated on the copper sulfate can be dissociated after the temperature inside the battery reaches a sufficiently high temperature, and play a cooling role at an appropriate time to avoid battery combustion and explosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 A comparison diagram of large-surface temperature curves during the thermal runaway process provided by Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0033] The endpoints and any values ​​of the ranges disclosed in the present 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

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

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

[0036] Specifically, the present invention provides a three-layer sandwich composite current collector. The polymer material can effectively enhance the toughness and insulation of the current collector relative to the copper material. A self-destructing agent is added to the middle layer polymer material. When the battery is in a high temperature environment or thermal runaway occurs, the self-destructing agent loses water at a specific temperature, so that the water released can react with the lithium ions in the negative electrode in advance, thereby consuming the lithium in the negative electrode in advance, breaking the established thermal runaway reaction sequence, and reducing the amount of reducing gas generated, thereby achieving the purpose of reducing the intensity of the reaction, and ultimately improving the safety performance of the battery cell. The present invention selects to add a self-destructing agent-copper sulfate pentahydrate to the polymer material layer. When the temperature rises to a specific temperature, the hydrate will begin to decompose the crystal water, and the decomposed water will react with the lithium ions in the negative electrode in advance, thereby reducing the intensity of the reaction, so that the maximum temperature in the thermal runaway process is reduced, and ultimately achieving the purpose of avoiding thermal runaway.

[0037] Furthermore, the present invention limits the content of copper sulfate pentahydrate in the polymer film to within the range of 1-30% in order to ensure that the material has the necessary thermal runaway prevention function while not adversely affecting the film's forming and tensile properties. Too much copper sulfate pentahydrate will affect the film's flexibility and uniformity, and reduce the tensile strength of the composite foil, which is contrary to the current trend of lightweight development in the fields of materials science and electronic manufacturing. By precisely controlling the content of copper sulfate pentahydrate, the present invention aims to achieve an optimal balance between the self-destructing agent function and the physical properties of the composite foil to meet the requirements of battery safety performance and lightweight design.

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

[0039] Specifically, as part of the battery composite current collector, the film needs to have certain mechanical strength and insulation to ensure the safety of the battery in normal use and potential thermal runaway conditions. A thickness of 2-6μm can provide sufficient strength and insulation to prevent short circuits and electrolyte leakage. If the film thickness exceeds 6μm, it will reduce the space utilization of the battery cell and reduce the battery energy density, and there will be 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, the copper conductive layers on both sides of the polymer film are also plated with copper plating layers respectively;

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

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

[0044] Specifically, water electroplating refers to the process of forming a copper coating on the surface of a polymer film through an oxidation-reduction reaction by using the electrolysis of electric current. First, a copper coating is formed on the surface of the polymer film by means of magnetron sputtering, vacuum evaporation, etc., so that it has a certain conductivity, and the thickness is 45-55nm at this time. Then, the polymer film is used as the cathode and the copper plate is used as the anode, and they are placed in the electroplating solution and connected to a DC power supply. Under the action of external current, an oxidation-reduction reaction occurs, and the copper plate at the anode becomes copper ions and dissolves into the electroplating solution. The copper ions are reduced to metallic copper at the cathode, and a micron-level copper coating is formed on the surface of the polymer film.

[0045] Furthermore, the role of the copper conductive layer is mainly reflected in providing basic conductivity for the polymer film. It is formed by physical deposition methods such as magnetron sputtering and vacuum evaporation, providing the initial conductivity basis for the film. In addition, the copper conductive layer is evenly covered on the surface of the polymer film, ensuring the uniform deposition of the copper plating layer in the subsequent electroplating process, while enhancing the mechanical adhesion between the copper plating layer and the polymer film, improving the stability and durability of the plating layer, and being able to reduce the resistance of the entire composite current collector, thereby improving its conductivity. The role of the copper plating layer is to further increase the conductivity on the basis of the copper conductive layer, thicken the plating layer through the electroplating process, and significantly improve 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 erosion of chemical substances such as electrolytes. At the same time, in battery applications, the copper plating layer, as part of the current collector, undertakes the important function of collecting and conducting current.

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

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

[0048] S1: Preparation of polymer film;

[0049] S2: depositing copper conductive layers on both sides of the polymer film by magnetron sputtering;

[0050] S3: optionally preparing a copper plating layer on the copper conductive layer by water electroplating to obtain a polymer copper foil;

[0051] S4: Wash the polymer film deposited with a copper conductive layer obtained in step S2 or the polymer copper foil obtained in step S3 with water to obtain a composite current collector.

[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 stirred and mixed uniformly at a stirring speed of 400-900 r / min (such as 500 r / min, 600 r / min, 800 r / min, etc.) in proportion, and extruded through a twin-screw extruder to obtain a polymer thick sheet, and then the polymer thick sheet is 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°C (such as 125°C, 130°C, 135°C, 140°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, etc.);

[0055] The stretching is performed simultaneously in transverse and longitudinal directions, wherein the stretching temperature is 120-130°C (such as 122°C, 124°C, 126°C, 128°C, etc.); the setting temperature is 120°C.

[0056] Specifically, the present invention adopts the method of melt extrusion to mix the self-destructing agent and the polymer together. This method not only ensures that the self-destructing agent can be firmly held in the film layer of the composite current collector under normal use conditions, but also does not release the crystal water in the self-destructing agent within the normal use temperature range of the battery, causing damage to the battery. The temperature of the twin-screw extrusion of the present invention is 120-180°C. During the preparation of the polymer film, the self-destructing agent will lose at least two non-hydrogen bonded crystal waters that are not firmly bound, thereby avoiding the dehydration of the self-destructing agent during normal use of the battery to affect the battery performance and safety. The remaining crystal water on the copper sulfate will only be separated when a specific temperature is reached inside the battery, such as when thermal runaway is triggered, and further react with the lithium on the negative electrode. Specifically, under the condition of 120-180°C, the self-destructing agent will first decompose a part of the crystal water that is easy to fall off at low temperature, ensuring that no water is generated during the normal use of the battery. The crystal water that has not dissociated on the copper sulfate can be dissociated after the temperature inside the battery reaches a sufficiently high temperature, and play a cooling role at an appropriate time to avoid battery combustion and explosion.

[0057] Specifically, in step S2, magnetron sputtering is performed by using a magnetic field to constrain the movement of electrons, which has the characteristics of low temperature and high speed, and does not trigger the self-destructive agent contained in the film during sputtering.

[0058] As an optional embodiment of the present invention, in step S3, the water electroplating is to apply electric current in the aqueous solution to cause metal ions to be reduced and deposited on the substrate to be plated, thereby forming a metal coating on the surface of the substrate;

[0059] Among them, the main component of the electroplating solution is copper sulfate, and the pH value of the plating solution is 1-3. The pH value of the plating solution is an important factor affecting the electroplating reaction rate and the quality of the coating. Too high a pH value will inhibit the deposition rate of the plated metal, and too low a pH value will cause the hydrogen ions in the plating solution to compete with the plating metal ions, reducing the deposition efficiency of the plated metal. Therefore, the pH value of the plating 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 will affect the rate of the electroplating reaction and the crystallization state of the coating. Increasing the temperature of the plating solution can speed up the electroplating rate, but it may also increase the roughness of the coating. Therefore, the working temperature of the plating solution is controlled within the range of 20℃-35℃.

[0061] The current density is 1-4Asd. Current density refers to the current intensity passing through a unit area, which directly affects the deposition rate and quality of the coating. Too high a current density may cause the coating to be rough and burnt; too low a current density may cause the deposition rate to be too slow and the coating to be too thin, so the current density should be controlled within the range of 1-4Asd.

[0062] According to a third aspect of the present invention, there is provided 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 a negative electrode sheet of a lithium-ion battery cell;

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

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

[0065] Example 1

[0066] S1: mixing copper sulfate pentahydrate powder and polyethylene particles at a mass ratio of 1:9 at a stirring speed of 600 r / min, extruding through a twin-screw extruder to obtain a polymer slab, and then stretching the polymer slab to obtain the polymer film, wherein the thickness of the polymer film is 3 μm;

[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 in both transverse and longitudinal directions at the same time, wherein the stretching temperature is 125°C and the shaping temperature is 120°C.

[0069] S2: depositing copper conductive layers on both sides of the polymer film by magnetron sputtering, wherein the thickness of the copper conductive layer on one side is 50 nm;

[0070] S3: preparing a copper plating layer on the copper conductive layer by water electroplating, wherein the total thickness of the copper plating layer and the copper conductive layer on one side is 2 μm, to obtain a polymer copper foil;

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

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

[0073] Example 2

[0074] S1: Copper sulfate pentahydrate powder and polyvinyl chloride (PVC) particles are stirred and mixed at a mass ratio of 2:8 at a stirring speed of 600 r / min, extruded through a twin-screw extruder to obtain a polymer slab, and then stretched the polymer slab to obtain the polymer film, wherein the thickness of the polymer film is 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 in both transverse and longitudinal directions at the same time, wherein the stretching temperature is 125°C and the shaping temperature is 120°C.

[0077] S2: depositing copper conductive layers on both sides of the polymer film by magnetron sputtering, wherein the thickness of the copper conductive layer on one side is 50 nm;

[0078] S3: preparing a copper plating layer on the copper conductive layer by water electroplating, wherein the total thickness of the copper plating layer and the copper conductive layer on one side is 0.5 μm, to obtain a polymer copper foil;

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

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

[0081] Example 3

[0082] S1: mixing copper sulfate pentahydrate powder and polypropylene particles at a mass ratio of 3:7 at a stirring speed of 600 r / min, extruding through a twin-screw extruder to obtain a polymer slab, and then stretching the polymer slab to obtain the polymer film, wherein the thickness of the polymer film is 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 in both transverse and longitudinal directions at the same time, wherein the stretching temperature is 125°C and the shaping temperature is 120°C.

[0085] S2: depositing copper conductive layers on both sides of the polymer film by magnetron sputtering, wherein the thickness of the copper conductive layer on one side is 50 nm;

[0086] S3: preparing a copper plating layer on the copper conductive layer by water electroplating, wherein the total thickness of the copper plating layer and the copper conductive layer on one side is 1 μm, to obtain a polymer copper foil;

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

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

[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, and the remaining steps and technical parameters are the same as those of Example 1.

[0091] Comparative Example 2

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

[0093] Compared with Example 2, Example 1 has a too high content of copper sulfate pentahydrate added in Example 2, which affects the flexibility and uniformity of the polymer film. The thick polymer sheet obtained by extrusion cannot be stretched to obtain a film of the desired thickness, and therefore the thermal runaway experiment cannot be tested.

[0094] Performance Testing

[0095] Preparation of lithium-ion batteries:

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

[0097] 2) Graphite, SP, CMC and SBR were mixed in a ratio of 96.0:0.8:1.4:1.8 and uniformly coated on the composite copper foil prepared in the embodiment and the comparative example to obtain a composite copper foil with an area density of 190 g / m 2 The negative electrode;

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

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

[0100] The performance of the lithium-ion battery cells prepared by the current collectors prepared in the examples and comparative examples was tested:

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

[0102] 1) Charging: Charge to 4.2V at 0.33C constant current and constant voltage, cut-off current 0.05C;

[0103] 2) Let stand for 30 minutes;

[0104] 3) Discharge: Discharge at 0.33C constant current 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 test on the battery cell according to the following method:

[0109] a) Use a flat or rod-shaped heating device, and its surface is covered with ceramic, metal or insulating layer, and the heating power of the heating device is greater than 600W. Complete the assembly of the battery cell and the heating device, the heating device is in direct contact with the battery, and the size of the heating device is smaller than the heated surface of the battery cell; install the temperature monitor, and the monitoring point temperature sensor is arranged on the side away from heat conduction, that is, installed on the opposite side of the heating device, the sampling interval of the temperature data is not more than 1s, the accuracy is ±2℃, and the diameter of the temperature sensor tip is less than 1mm;

[0110] b) After the battery monomer is initially charged, continue charging at 1C constant current for 12 minutes;

[0111] c) Start the heating device and continue to 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 occurs should be determined according to the following conditions:

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

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

[0116] c) The temperature rise rate of the monitoring point is greater than 1°C / s;

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

[0118] e) If fire or explosion occurs during the heating process or within 1 hour after the end of heating, the test should be terminated and it should be determined that thermal runaway has occurred.

[0119] Performance data

[0120] Table 1

[0121]

[0122]

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

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 includes a polymer film and a copper conductive layer deposited on both sides of the polymer film; In terms of mass percentage, the polymer film includes 1-30% of copper sulfate pentahydrate and 70-99% of polymer.

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 copper conductive layers on both sides of the polymer film are also plated with copper plating layers respectively; The thickness of the copper conductive layer on one side is 45-55 nm; The total thickness of the copper plating layer and the copper conductive layer on one side is 0.5-5 μm.

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

6. A method for preparing a composite current collector according to any one of claims 1 to 5, characterized in that: The steps include: S1: Preparation of polymer film; S2: depositing copper conductive layers on both sides of the polymer film by magnetron sputtering; S3: optionally preparing a copper plating layer on the copper conductive layer by water electroplating to obtain a polymer copper foil; S4: Wash the polymer film deposited with a copper conductive layer obtained in step S2 or the polymer copper foil obtained in step S3 with water to obtain a composite current collector.

7. The method for preparing a composite current collector according to claim 6, characterized in that: In step S1, the method for preparing the polymer film includes: Copper sulfate pentahydrate powder and granular polymer are stirred and mixed uniformly at a stirring speed of 400-900 r / min according to a proportion, extruded through a twin-screw extruder to obtain a polymer slab, and then the polymer slab is stretched to obtain the polymer film.

8. The method for preparing a composite current collector according to claim 7, characterized in that: 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° C.; The stretching is performed in both transverse and longitudinal directions at the same time, wherein the stretching temperature is 120-130°C; and the shaping temperature is 120°C.

9. The method for preparing a composite current collector according to claim 6, characterized in that: In step S3, the pH value of the water electroplating solution is 1-3, the working temperature of the plating solution is 20° C.-35° C., and the current density is 1-4 Asd.

10. An application of the composite current collector according to any one of claims 1 to 5 or the composite current collector prepared by the preparation method according to any one of claims 6 to 9, characterized in that: Can be used to prepare negative electrode sheets for lithium-ion batteries; The lithium-ion battery cell is assembled from the negative electrode sheet, the separator and the positive electrode sheet.

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