Composite current collector and method for manufacturing the same

Abstract

The present application relates to a kind of composite current collector and its preparation method, belong to secondary battery technical field.The composite current collector provided by the present application has the original structure of sharp cone for shape memory polymer support layer, and the opening of support layer is filled with foaming agent and foaming aid.A kind of composite current collector provided by the present application can reduce weight and improve the energy density of battery.Secondly, the composite current collector provided by the present application increases the heat-sensitive function, which can cut off the electrochemical reaction inside the secondary battery on one hand after the thermal runaway and external impact of battery, and can reduce the heat generation of secondary battery on the other hand when the secondary battery is at high temperature, which has a triple guarantee for the safety performance of battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of secondary batteries, and more particularly relates to a composite current collector and a preparation method thereof, in particular to a composite current collector, an electrode tab and a secondary battery. BACKGROUND

[0002] The continuous development of green energy puts higher requirements on the energy density of lithium ion batteries (LIB). In order to meet the high energy density, all battery components in lithium ion batteries, including electrochemically inactive components, have reached the limit. For example, the thickness of copper foil in the current collector is reduced from 20 μm to 6-10 μm, and the thickness of aluminum foil is reduced from 18 μm to 10-15 μm. This measure reduces the material cost and improves the energy density of the battery, but further reducing the thickness of the current collector is technically challenging (especially achieving excellent surface finish and uniformity in the winding production), and complicates the handling of battery assembly and operation. Therefore, how to further reduce the mass of the current collector has become the focus of optimizing the battery structure in the future.

[0003] In addition, with the wide application of lithium ion batteries in different fields, the safety hidden problems they show have gradually become the focus of discussion. For example, the negative electrode lithium dendrite, the shrinkage or melting of the separator, etc., which can easily cause the battery to short circuit and generate a large amount of heat. Generally speaking, when the internal temperature of the battery is about 90℃, the SEI film on the electrode surface begins to decompose, and the battery thermal runaway trigger condition begins to be established. With a series of chain exothermic reactions, the internal temperature of the battery increases exponentially, and the temperature will quickly approach the ignition point of the flammable electrolyte, thereby causing the battery to burn and explode. Therefore, preventing lithium ion battery thermal runaway and establishing a battery safety control system are important prerequisites for further upgrading and optimizing lithium ion batteries in the future.

[0004] Currently, battery researchers mainly design from the "external" and "internal" prevention and control of the battery to prevent battery safety hazards. However, when the battery experiences thermal runaway, the temperature will rise rapidly in a very short time, and external detection equipment is difficult to respond quickly. In comparison, the strategy of improving the internal structure to prevent thermal runaway is more favored by researchers. For example, in the commercial PP-PE-PP separator, the porous PE layer will first melt during the thermal runaway process, causing the pore structure to collapse and blocking mass transfer, but the overheating may still cause the separator to shrink, causing internal short circuit of the battery. In addition, adding flame retardants to flammable electrolytes or preparing non-flammable solid-state electrolytes to increase the flame retardancy is also a favorable strategy. However, the introduction of flame retardants or solid-state electrolytes reduces the lithium ion conductivity and mobility, weakening the electrochemical performance of the battery. Therefore, under the premise of not affecting the electrochemical performance of the battery, designing a battery "internal" prevention and control material that can respond quickly to thermal runaway is a necessary means to solve the battery safety problem.

[0005] Therefore, it is necessary to design a technical solution to solve the above problems of energy density and safety. SUMMARY

[0006] The shape memory polymer support layer of the composite current collector has a sharp cone original structure, and the opening of the support layer is filled with a foaming agent and a foaming aid. The composite current collector provided by the application can reduce weight and improve the energy density of the battery. In addition, the composite current collector provided by the application has a heat-sensitive function. On the one hand, the self-blocking design can cut off the electrochemical reaction inside the secondary battery after the battery appears thermal runaway or external impact. On the other hand, the heat generated by the secondary battery can be reduced at high temperature, thereby providing threefold protection for the safety performance of the battery. Thus, the problems of low battery energy density and safety of the battery against thermal runaway in the prior art are solved.

[0007] According to a first aspect of the application, a preparation method of a composite current collector is provided, comprising the following steps:

[0008] (1) a high polymer with shape memory is prepared into a film with a sharp cone structure on the surface by using a flow casting method;

[0009] (2) the film with the sharp cone structure on the surface obtained in step (1) is subjected to heat pressing and cooling treatment to obtain a shape memory polymer support layer with a flat surface;

[0010] (3) the shape memory polymer support layer with the flat surface obtained in step (2) is perforated, and then is immersed in a suspension containing a foaming agent and a foaming aid, and the foaming agent and the foaming aid are deposited into the openings. Then, the support layer is taken out of the suspension, and the solvent is evaporated by heating to complete the filling of the foaming agent and the foaming aid.

[0011] (4) an adhesive layer is prepared on the upper and lower surfaces of the support layer obtained in step (3), and a metal plating layer is prepared on the upper surface of the upper adhesive layer and the lower surface of the lower adhesive layer, thereby obtaining the composite current collector.

[0012] Preferably, the deformation temperature T of the support layer ranges from 90℃ to 120℃, and the deformation amount S after reaching the deformation temperature ranges from 100% to 300%.

[0013] Preferably, the high polymer with shape memory is at least one of polyurethane, polyvinyl alcohol, polyimide, polyether ether ketone, polystyrene and epoxy resin.

[0014] Preferably, the foaming agent is an azo compound, an N-nitroso compound, a sulfonhydrazide compound, ammonium carbonate, sodium bicarbonate, sodium carbonate, ammonium chloride or sodium nitrite.

[0015] The foaming aid of the azo compound is stearic acid, urea, benzoic acid, zinc oxide, magnesium oxide, lead oxide, metal salt or organosilicon; the foaming aid of the N-nitroso compound is stearic acid, salicylic acid, adipic acid, phthalic acid, urea or glycerol; the foaming aid of the sulfonhydrazide compound is urea or metal salt; the foaming aid of the ammonium carbonate, sodium bicarbonate, sodium carbonate, ammonium chloride and sodium nitrite is independently selected from stearic acid, phosphate, silicone, phthalic acid, glycol or metal salt.

[0016] Preferably, in step (3), the hole making is specifically that the support layer is conveyed by the roller of the film puncher to the space between the needle roller and the pad roller, and the support layer located at the intersection of the needle roller and the pad roller is imprinted into a hole during the inward rolling tangential movement of the needle roller and the pad roller.

[0017] Preferably, the film with a sharp cone aperture having a sharp cone height of 3-50 μm and a thickness of 8-30 μm is prepared on the roller with a sharp cone aperture, and a shape memory polymer support layer with a thickness of 4-20 μm is obtained after hot pressing.

[0018] Preferably, in step (3), the diameter of the hole obtained by the hole making is 10-15 μm.

[0019] According to another aspect of the present application, there is provided a composite current collector prepared by any of the above methods.

[0020] According to another aspect of the present application, there is provided an electrode tab comprising the composite current collector and an active material layer coated on the composite current collector.

[0021] According to another aspect of the present application, there is provided a secondary battery comprising the electrode tab.

[0022] In general, the above technical solutions conceived by the present application have the following technical advantages compared with the prior art:

[0023] (1) The application provides a composite current collector, an electrode sheet and a secondary battery, and relates to the technical field of batteries.The composite current collector comprises a shape memory polymer support layer, a foaming agent, a bonding layer and a metal conductive layer; the foaming agent is filled in the holes after the holes are opened in the vertical direction of the support layer; the bonding layer is located on both sides of the support layer and can stably store the foaming agent; and the metal conductive layer is located on both sides of the bonding layer. Firstly, the composite current collector can reduce the weight and improve the energy density of the battery. The bonding layer on both sides of the support layer can enhance the combination with the metal conductive layer and also enclose the foaming agent in the holes, so that the foaming agent is prevented from contacting other substances such as active substances and electrolyte in the secondary battery, and the normal performance of the secondary battery is ensured. Secondly, the current collector has three safety effects on the battery: first, in the case of mechanical abuse such as needle puncture, the polymer extension can close the short-circuit point and prevent short circuit and further thermal runaway; second, in the case of thermal abuse, the shape memory polymer support layer of the composite current collector will expand at high temperature, tear the metal conductive layer, damage the electrochemical reaction inside the secondary battery and prevent the continuous rise of the temperature inside the secondary battery; third, after the metal conductive layer is torn, the foaming agent filled in the holes of the support layer is extruded and decomposed under the action of the thermal expansion deformation stress of the support layer and releases a large amount of gas, so that oxygen is isolated, and the effect of fire retardation and explosion prevention can be achieved.

[0024] (2) The application can inhibit the short-circuit current and control the thermal runaway of the battery by supporting layer extension and open circuit effect after the secondary battery is mechanically abused to cause short circuit, and fundamentally solves the explosion and fire of the secondary battery.

[0025] (3) The shape memory polymer support layer of the composite current collector can rapidly deform at high temperature, tear the metal conductive layer, damage the electrochemical reaction inside the secondary battery and prevent the continuous rise of the temperature inside the secondary battery after the secondary battery is thermally abused to cause thermal runaway.

[0026] (4) The foaming agent filled in the holes of the support layer is extruded and decomposed under the action of the thermal expansion deformation stress of the support layer and releases inert gas after the conductive layer is torn or fused, so that the problem of thermal runaway inside the secondary battery is alleviated.

[0027] (5) The foaming agent and foaming aid provided by the application stably exist when the battery is normally working, the foaming agent is enclosed in the holes and is prevented from contacting other substances such as active substances and electrolyte in the secondary battery, and will not be corroded or swelled by the electrolyte. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a sectional view of the composite current collector in the application.

[0029] Figure 2This is a schematic cross-sectional view of the composite current collector in this invention when it is abnormally heated.

[0030] Figure 3 This is a cross-sectional schematic diagram of the secondary battery in this invention after deformation under mechanical abuse conditions.

[0031] Figure 4 The graph shows the cycle performance of the coin cells assembled from the positive electrode composite current collector in Example 1 and the conventional aluminum foil in Comparative Example 3 after coating with lithium iron phosphate positive electrode at 2.5-4.2V and 1C.

[0032] Figure 5 The graph shows the charge-discharge curves of the coin cell assembled after coating the positive electrode composite current collector with lithium iron phosphate positive electrode in Example 1, during the first cycle at 2.5-4.2V and 1C.

[0033] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-metallic conductive layer; 2-adhesive layer; 3-shape memory polymer support layer; 4-opening; 5-foaming agent and foaming aid; 6-carbon dioxide and nitrogen; 7-torn adhesive layer; 8-torn metallic conductive layer; 9-shape memory polymer support layer deformed at high temperature; 10-opening deformed at high temperature; 11-conical structure appearing on the surface of the support layer at high temperature; 12-positive electrode active material; 13-torn positive electrode active material; 14-diaphragm; 15-negative electrode active material; 16-copper foil; 17-metal nail. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0035] The present invention provides a composite current collector comprising:

[0036] A support layer, wherein holes are made in the vertical direction using a polymer film perforator;

[0037] An adhesive layer is located on both sides of the support layer and seals the openings in the support layer.

[0038] A metal conductive layer is located on both sides of the adhesive layer;

[0039] Foaming agent and foaming aid, wherein the foaming agent and foaming aid are filled into the pores of the support layer by vacuum treatment, ultrasonic treatment and heat treatment;

[0040] The support layer is made of shape memory polymer with a deformation temperature of 90–120°C and a deformation of 100%–300% after reaching the deformation temperature. The deformation properties of the support layer are controlled by the type of shape memory polymer and the parameters of the hot pressing process.

[0041] The decomposition temperature of the foaming agent is 90-120°C, and the gases produced by the decomposition of the foaming agent include one or more of nitrogen, carbon dioxide, etc.

[0042] When the temperature of the secondary battery exceeds the deformation temperature of the support layer and the decomposition temperature of the foaming agent, the support layer will deform at high temperature, damaging the metal conductive layer and blocking the internal reaction of the battery. The foaming agent filled in the pores of the support layer is squeezed out under the deformation stress of the support layer and then decomposes into inert gases such as carbon dioxide and nitrogen. This not only reduces the temperature but also isolates the secondary battery from contact with oxygen in the air, thus playing a role in flame retardancy and explosion prevention.

[0043] As in this invention Figure 1 , Figure 2 and Figure 3 As shown, Figure 1 This is a schematic diagram of the composite current collector in this invention. The shape memory polymer support layer 3 is composed of shape memory polymer, and the support layer has openings 4 inside, with foaming agent and foaming aid 5 added inside the openings. Vapor deposition / magnetron sputtering is performed on both sides of the shape memory polymer support layer 3 to form an adhesive layer 2 on the surface. Vapor deposition / magnetron sputtering / electroplated plating is then performed on both sides of the adhesive layer 2 to form a metallic conductive layer 1 on the surface.

[0044] Figure 2 This is a schematic diagram of the composite current collector in this invention during abnormal heating. When the secondary battery temperature exceeds the deformation temperature, the shape memory polymer support layer 3, after being fixed by hot pressing deformation, expands in volume, transforming into a shape memory polymer support layer 9 that deforms at high temperature. Simultaneously, the pointed cone structure 11 on the surface of the support layer rapidly appears, further forming a torn metallic conductive layer 8 and a torn adhesive layer 7. Furthermore, the foaming agent and foaming aid 5 filling the pores of the support layer are extruded under the stress of thermal expansion deformation of the support layer and the deformation stress of the openings 10 deformed at high temperature. The foaming agent decomposes into inert gases such as carbon dioxide and nitrogen 6. This rapidly switches the battery from a conductive state to an insulating state while reducing the battery temperature, significantly reducing the safety hazard of thermal runaway.

[0045] Figure 3This is a schematic diagram of the secondary battery of the present invention after deformation under mechanical abuse. When the metal nail 17 passes through the composite current collector, it penetrates the metal conductive layer 1, the adhesive layer 2, the shape memory polymer support layer 3, the positive electrode active material 12, the separator 14, the negative electrode active material 15, and the copper foil 16, forming a torn metal conductive layer 8, a torn adhesive layer 7, and a torn positive electrode active material 13, thus blocking the conduction of electrons inside the battery. Furthermore, the electron transport path from the metal conductive layer 1 to the metal nail 17 to the copper foil 16 is suppressed due to the thin metal conductive layer thickness. Ultimately, this results in localized insulation of the battery, eliminating internal short circuits.

[0046] The support layer is first prepared on a roller with pointed cone pores to form a thin film (excluding the height of the cone) with a cone height of 3-50 μm and a thickness of 8-30 μm. After hot pressing, a shape memory polymer film with a thickness of 4-20 μm is obtained. The cone height and density on the surface of the support layer are controlled by the roller pressing.

[0047] The foaming agent is filled by immersing the perforated support layer in a suspension containing foaming agent and foaming aid, and then subjecting the suspension containing the support to vacuum and ultrasonic treatment to complete the filling of foaming agent and foaming aid.

[0048] The shape memory polymer is at least one of the following polymers: polyvinyl alcohol, polystyrene, polyurethane polyetheretherketone, epoxy resin, polyimide, etc.

[0049] The deformation temperature of the support layer can be 90-100℃, 100-110℃, or 110-120℃. However, when the temperature of the secondary battery exceeds 100℃, a safety accident is likely to occur. Therefore, the optimal deformation temperature of the support layer is around 100-110℃. The deformation temperature of the support layer is controlled by the type of shape memory polymer.

[0050] The support layer has a deformation range of 100%–175%, 175%–225%, and 225%–300%, with deformation times of 2s–3s, 3s–4s, and 4s–5s. The deformation properties of the support layer are regulated by the type of shape memory aggregation.

[0051] The support layer is rapidly cooled on rollers with tapered gaps, resulting in a tapered height of 3–50 μm on the surface of the support layer and a pore density of 20,000–30,000 pores / m². 2 When a secondary battery experiences thermal runaway, it meets the requirement of rapidly destroying the metal conductive layer.

[0052] The support layer, after being output from the unwinding machine, moves between the needle roller and the pad roller. During the inward rolling and tangential process of the needle roller and the pad roller, the support layer at the intersection of the needle roller and the pad roller is pressed into a hole. The shape of the hole in the vertical direction can be divided into square column, round column, and rhomboid column according to the size of the hole needle. The hole diameter is 5-10μm, 10-15μm, and 15-20μm according to the size of the hole needle. The hole spacing is 50-300μm, 300-600μm, and 600-1000μm according to the distance between the hole needles.

[0053] When the opening shape is cylindrical, the production time, feeding time, foaming agent release and decomposition time are optimal.

[0054] When the pore size is too large, the foaming agent and foaming aid filling the pore cannot be stored stably; when the pore size is too small, the amount of foaming agent and foaming aid filling the pore is too small to play a role in cooling and flame retardancy. Therefore, an pore size of 10 to 15 μm is the optimal choice.

[0055] When the spacing between any openings is too close, the structure of the support layer becomes unstable and the deformation and deformation time are affected; when the spacing between any openings is too far apart, the amount of foaming agent and foaming aid filling the openings is too small, and they cannot play a role in cooling and flame retardancy; therefore, a spacing of 300 to 600 μm is the optimal choice.

[0056] The perforated support layer is immersed in a suspension containing a foaming agent and a foaming aid. The suspension containing the support layer is then subjected to vacuum treatment, causing the foaming agent and foaming aid to precipitate into the perforations. The vacuum-treated suspension containing the substrate is then subjected to ultrasonic treatment. The vacuum treatment and ultrasonic treatment are repeated more than three times. The support layer is then removed from the suspension, and the support is heated to 60-80°C to evaporate the solvent, thus completing the filling of the foaming agent and foaming aid.

[0057] The foaming agent is at least one of azo compounds, N-nitroso compounds, sulfonyl hydrazide compounds, ammonium carbonate, sodium bicarbonate, sodium carbonate, ammonium chloride, sodium nitrite, etc. The selection of the foaming agent can be determined according to the actual situation.

[0058] The foaming aids for the azo compounds are stearic acid, urea, benzoic acid, zinc oxide / magnesium / lead oxide, metal salts, and organosilicon compounds; the foaming aids for the N-nitroso compounds are stearic acid, salicylic acid, adipic acid, phthalic acid, urea, and glycerin; the foaming aids for the sulfonyl hydrazine compounds are urea and metal salts; and the foaming aids for ammonium carbonate, sodium bicarbonate, sodium carbonate, ammonium chloride, or sodium nitrite are stearic acid, phosphates, silicones, phthalic acid, diols, and metal salts. These are used to adjust the decomposition temperature and gas generation of the foaming agent; the selection of the foaming aid can be determined based on actual conditions.

[0059] The decomposition temperature of the foaming agent can be 90–100℃, 100–110℃, 110–120℃, or 120–130℃. However, safety accidents are more likely to occur when the temperature of the secondary battery exceeds 100℃; a decomposition temperature of around 100℃ is optimal. When the support layer deforms and the conductive layer tears, the foaming agent also decomposes simultaneously. While blocking the electrochemical reaction, the generated inert gases such as carbon dioxide and nitrogen not only lower the temperature but also isolate the secondary battery from oxygen in the air, thus providing a flame-retardant effect.

[0060] The gas production of the foaming agent can be 100-200 mL / g, 200-300 mL / g, 300-400 mL / g, or 400-500 mL / g. When the decomposition temperature is reached, if the gas production is too low, the foaming agent cannot play a role in cooling and flame retardancy. If the gas production is too high, excessive local gas production inside the secondary battery will lead to excessive gas pressure inside the secondary battery and cause an explosion.

[0061] The adhesive layer is a metal coating or a non-metal coating. When it is a metal coating, the metal is copper, nickel, chromium, or titanium. When it is a non-metal coating, the non-metal is silicon carbide, silicon nitride, aluminum oxide, or aluminum nitride. The thickness of the adhesive layer is 0.01 to 0.1 μm.

[0062] The material of the conductive metal layer is selected from at least one of aluminum, copper, nickel, titanium, silver, nickel-copper alloy, and aluminum-zirconium alloy, and the thickness of the metal coating is 0.5 to 2 μm.

[0063] The preparation process includes the following steps:

[0064] (1) First, one or more shape memory polymers are mixed, melted, cast, hot-pressed and opened to prepare support layers with various deformation temperatures, deformations, pore sizes, pore densities and opening shapes.

[0065] (2) The support layer with openings is immersed in a suspension containing foaming agent and foaming aid. The suspension containing the support is vacuum treated to allow the foaming agent and foaming aid to precipitate into the openings. The suspension containing the substrate after vacuum treatment is then ultrasonically treated. The vacuum treatment and ultrasonic treatment are repeated more than 3 times. The support layer is removed from the suspension, and the support is heated to 60-80°C to evaporate the solvent, thus completing the filling of foaming agent and foaming aid.

[0066] (3) Perform plasma cleaning on the surface of the support layer to remove surface impurities;

[0067] (4) An adhesive layer is prepared on the upper and lower surfaces of the cleaned film by means of vapor deposition, magnetron sputtering, or blade coating;

[0068] Specifically, the process involves: performing corona treatment, then placing the roll of plastic film into the vacuum chamber of a double-sided reciprocating magnetron sputtering coating machine, sealing the vacuum chamber, evacuating the vacuum chamber step by step to achieve a purity of ≥99.9%, and using magnetron sputtering to efficiently coat the plastic film on both sides. The unwinding and rewinding speeds are adjusted, and the sputtered target material forms an adhesive layer on the moving film.

[0069] Alternatively, corona treatment can be performed, and then the roll of plastic film can be placed into the vacuum chamber of a double-sided reciprocating high-frequency induction evaporation coating machine. The vacuum chamber is sealed, and vacuum is drawn step by step. High-frequency current is used to heat the target material in the high-frequency induction evaporation mechanism. The target material purity is ≥99.9%. The unwinding speed, winding speed and evaporation rate are adjusted. The target material continues to melt and evaporate in the evaporation mechanism, forming an adhesive layer on the moving film surface.

[0070] (5) The metal conductive layer is prepared on the outside of the adhesive layer by means of vapor deposition, magnetron sputtering or electroplating.

[0071] Specifically, the above-obtained bonding layer support layer is placed into the vacuum chamber of a double-sided reciprocating evaporation coating machine, the vacuum chamber is sealed, vacuum is drawn step by step, the evaporation mechanism is heated, and then the metal target is sent to the evaporation mechanism. The unwinding speed, winding speed and evaporation amount are adjusted, the target purity is ≥99.9%, the metal target continues to melt and evaporate in the evaporation mechanism, and a metal conductive layer is formed on both sides of the moving film surface.

[0072] Alternatively, the support layer of the above-obtained adhesive layer is placed in the vacuum chamber of a double-sided reciprocating magnetron sputtering coating machine, the vacuum chamber is sealed, and vacuum is drawn step by step. The purity of the target material is ≥99.9%. Magnetron sputtering is used to efficiently coat the plastic film on both sides. The unwinding speed and rewinding speed are adjusted, and the sputtered target material forms a metal conductive layer on the moving film.

[0073] Alternatively, the support layer of the above-obtained adhesive layer can be roughened and then placed in a CuSO4·5H2O solution (containing H2SO4 and Cl). - In the electrolytic cell, the applied current density is 6–10 A / dm³. -2 Copper ions in the solution gain electrons on both sides of the nickel-copper alloy film and are reduced to copper atoms, which are deposited on the surface to thicken the copper layer and form a copper metal conductive layer.

[0074] Another object of the present invention is to provide an electrode sheet, wherein the current collector is a composite current collector as described above; and an active material layer is disposed on both sides of the composite current collector.

[0075] Another object of the present invention is to provide a battery comprising: a positive electrode, a negative electrode, a separator, and an electrolyte, wherein at least one of the positive electrode and the negative electrode is an electrode as described above.

[0076] This invention heats a shape memory polymer to its melting temperature in the feed barrel of a twin-screw extruder. The molten material then enters the melt extruder and is extruded in a measured quantity. The filtered melt, after passing through a die, has a conical pore density of 20,000–30,000 pores / m³. 2 Rapid cooling on rollers with cone depths of 3–50 μm produces films with cone heights of 3–50 μm and thicknesses of 10–30 μm. The films are then compressed under preheated rollers at 90–120°C, undergoing a vertical compression of 1.5–3.0 times (to eliminate the cones on the film surface and apply stress to alter the surface morphology and thickness). After rapid cooling and shaping on cooling rollers at 40–60°C, thickness measurement, corona treatment, and flattening are performed. Thicker edge material is trimmed, and the film is then unrolled and wound into a film roll to prepare polymer films with thicknesses of 4–20 μm. When the external temperature reaches the deformation temperature of the polymer film (90–100℃, 100–110℃, and 110–120℃), after a deformation time of 2–7 seconds, the thickness of the polymer film expands from the original 4–20 μm to 10–30 μm, and the 3–50 μm long cone-shaped structures on the surface of the polymer film reappear. Depending on the application of the secondary battery under different conditions, the type and amount of shape memory polymer can be freely set, as can the deformation temperature, deformation amount, and deformation shape of the support layer.

[0077] The following are specific embodiments.

[0078] Example 1

[0079] Polyvinyl alcohol or modified polyvinyl alcohol resin was used to prepare a polymer film with a thickness of 6 μm according to the above steps. When the ambient temperature reached the deformation temperature of the polymer film (100℃), after a deformation time of 2 seconds, the thickness of the polymer film expanded from the original 6 μm to 15 μm, and the 40 μm high cones reappeared on the surface of the polymer film, with a cone density of 20,000 / m². 2 .

[0080] The prepared support layer is perforated with circular cylinders, each with a diameter of 15 μm and a spacing of 600 μm.

[0081] The prepared porous support layer is immersed in p-toluenesulfonyl hydrazine and urea, and the gas generation capacity can be 120 mL / g.

[0082] The support layer obtained above is vacuum-deposited with 100nm thick aluminum oxide layers on both sides, and then 2000nm thick metallic aluminum is vacuum-deposited on the outside of the aluminum oxide layers.

[0083] The composite current collector prepared above was used as the positive current collector (10 μm thick). Commercial lithium iron phosphate positive electrode material was coated on it to prepare the positive electrode sheet. Finally, the positive electrode sheet and separator were assembled into a soft pack battery, and the battery temperature rise was tested.

[0084] Example 2

[0085] A 4 μm thick polymer film was prepared using polyvinyl alcohol or modified polyvinyl alcohol resin according to the steps described above. When the ambient temperature reached the deformation temperature of the polymer film (100°C), after a deformation time of 2 seconds, the thickness of the polymer film expanded from the original 4 μm to 12 μm. The 40 μm high cones reappeared on the surface of the polymer film, with a cone density of 20,000 cones / m². 2

[0086] The prepared support layer is perforated with circular cylinders, each with a diameter of 15 μm and a spacing of 600 μm.

[0087] The prepared porous support layer is immersed in p-toluenesulfonyl hydrazine and urea, and the gas generation capacity can be 120 mL / g.

[0088] A 50 nm thick nickel layer was magnetron sputtered on both sides of the support layer obtained above, and a 1000 nm thick metallic copper layer was prepared on the outside of the nickel layer by electroplating.

[0089] The composite current collector prepared above was used as the negative electrode current collector (thickness of 6μm). Commercial graphite negative electrode material was coated on it to prepare the negative electrode sheet. Finally, the negative electrode sheet and separator were assembled into a pouch cell, and the battery temperature rise was tested.

[0090] Example 3

[0091] A 6 μm thick polymer film was prepared from polystyrene-isoprene or modified polystyrene-isoprene resin according to the steps described above. When the ambient temperature reached the deformation temperature of the polymer film (100°C), after a deformation time of 3 seconds, the thickness of the polymer film expanded from the original 6 μm to 15 μm. The 40 μm high cones reappeared on the surface of the polymer film, with a cone density of 20,000 / m². 2 .

[0092] The prepared support layer is perforated with circular cylindrical pores, each pore having a diameter of 12 μm and a spacing of 800 μm.

[0093] The prepared porous support layer is immersed in diisopropyl azodicarbonate and phthalic acid, and the gas generation capacity can be 250 mL / g.

[0094] The support layer obtained above is vacuum-deposited with 100nm thick aluminum oxide layers on both sides, and then 2000nm thick metallic aluminum is vacuum-deposited on the outside of the aluminum oxide layers.

[0095] The composite current collector prepared above was used as the positive current collector (10 μm thick). Commercial lithium iron phosphate positive electrode material was coated on it to prepare the positive electrode sheet. Finally, the positive electrode sheet and separator were assembled into a soft pack battery, and the battery temperature rise was tested.

[0096] Example 4

[0097] A 4 μm thick polymer film was prepared from polystyrene-isoprene or modified polystyrene-isoprene resin according to the steps described above. When the ambient temperature reached the deformation temperature of the polymer film (100℃), after a deformation time of 3 seconds, the thickness of the polymer film expanded from the original 4 μm to 12 μm. The 40 μm high cones reappeared on the surface of the polymer film, with a cone density of 20,000 / m². 2 .

[0098] The prepared support layer is perforated with circular cylindrical pores, each pore having a diameter of 12 μm and a spacing of 800 μm.

[0099] The prepared porous support layer is immersed in diisopropyl azodicarbonate and phthalic acid, and the gas generation capacity can be 250 mL / g.

[0100] A 50 nm thick nickel layer was magnetron sputtered on both sides of the support layer obtained above, and a 1000 nm thick metallic copper layer was prepared on the outside of the nickel layer by electroplating.

[0101] The composite current collector prepared above was used as the negative electrode current collector (thickness of 6μm). Commercial graphite negative electrode material was coated on it to prepare the negative electrode sheet. Finally, the negative electrode sheet and separator were assembled into a pouch cell, and the battery temperature rise was tested.

[0102] Comparative Example 1

[0103] A 50 nm thick nickel layer was magnetron sputtered onto both sides of a commercial PET polymer film, and a 1000 nm thick metallic copper layer was prepared on the outside of the nickel layer by electroplating.

[0104] The composite current collector prepared above is used as the positive current collector. Commercial lithium iron phosphate positive electrode material is coated on it to prepare the positive electrode sheet. Finally, the battery is assembled into a soft pack battery with a traditional negative electrode sheet and separator, and the battery temperature rise is tested.

[0105] Comparative Example 2

[0106] A 100nm thick alumina layer is vacuum-deposited on both sides of a commercial PET polymer film, and a 2000nm thick metallic aluminum layer is vacuum-deposited on the outside of the alumina layer.

[0107] The composite current collector prepared above is used as the negative current collector. Commercial graphite negative electrode material is coated to prepare the negative electrode sheet. Finally, the positive electrode sheet and separator are used to assemble a soft pack battery, and the battery temperature rise is tested.

[0108] Comparative Example 3

[0109] Commercially available lithium iron phosphate cathode material and graphite anode material were coated onto traditional aluminum foil and copper foil respectively to prepare cathode and anode sheets. Finally, they were assembled with a separator to form a pouch cell, and the battery temperature rise was tested.

[0110] Hot box test method:

[0111] Charge the battery at 1C current to the 4.2V cutoff voltage, then charge at a constant voltage until the current drops to 0.1C, then stop charging. Place the battery in a hot box and raise the temperature to 90℃ at 5℃ / min, then keep it at that temperature for 30 minutes. Observe whether the battery burns or explodes. If the battery does not burn or explode, repeat this process with another battery, maintaining the temperature at 5℃ higher, until a battery burns or explodes.

[0112] Acupuncture test method:

[0113] Charge the battery to 4.2V at 1C current, then charge it at constant voltage until the current drops to 0.1C, then stop charging. Use a 10mm diameter high-temperature resistant steel needle to penetrate the battery from a direction perpendicular to the battery plates at a speed of 20mm / s. The penetration point should be close to the geometric center of the pierced surface. Keep the steel needle inside the battery and observe whether the battery shows signs of burning or explosion.

[0114] Button battery cycle test method:

[0115] The batteries were subjected to cycle performance tests at 2.5-4.2V and 1C to compare the differences in cycle performance after assembling batteries with composite current collectors and conventional current collectors.

[0116] The experimental results of the examples and comparative examples are shown in Table 1. Table 1 shows the test data of temperature rise of soft-pack batteries with different current collectors.

[0117] Table 1. Test data of temperature rise of soft-pack batteries with different current collectors.

[0118] Figure 4 The graph shows the cycle performance of the coin cells assembled from the positive electrode composite current collector in Example 1 and the conventional aluminum foil in Comparative Example 3 after coating with lithium iron phosphate positive electrode at 2.5-4.2V and 1C.

[0119] Figure 5The graph shows the charge-discharge curves of the coin cell assembled after coating the positive electrode composite current collector with lithium iron phosphate positive electrode in Example 1, during the first cycle at 2.5-4.2V and 1C.

[0120] Table 1

[0121]

[0122] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a composite current collector, characterized in that, Includes the following steps: (1) A polymer with shape memory is used to prepare a thin film with a pointed cone structure on the surface by casting. (2) The thin film with a pointed cone structure obtained in step (1) is subjected to hot pressing and cooling treatment to obtain a shape memory polymer support layer with a flat surface; (3) Make holes in the smooth shape memory polymer support layer obtained in step (2), and then immerse it in a suspension containing foaming agent and foaming aid, and let the foaming agent and foaming aid precipitate into the holes; then take the support layer out of the suspension, heat and evaporate the solvent to complete the filling of foaming agent and foaming aid; the foaming agent is used to be squeezed out and decomposed to release a large amount of gas under the action of thermal expansion deformation stress of the support layer, and isolate oxygen, thereby playing a flame-retardant and explosion-proof role; (4) Prepare adhesive layers on the upper and lower surfaces of the support layer obtained in step (3); prepare metal coatings on the upper surface of the upper adhesive layer and the lower surface of the lower adhesive layer to obtain the composite current collector.

2. The method for preparing the composite current collector as described in claim 1, characterized in that, The deformation temperature T of the support layer is in the range of 90℃≤T≤120℃, and the deformation S after reaching the deformation temperature is in the range of 100%≤S≤300%.

3. The method for preparing the composite current collector as described in claim 1, characterized in that, The shape memory polymer is at least one of polyurethane, polyvinyl alcohol, polyimide, polyetheretherketone, polystyrene, and epoxy resin.

4. The method for preparing the composite current collector as described in claim 1, characterized in that, The foaming agent is an azo compound, an N-nitroso compound, a sulfonyl hydrazine compound, ammonium carbonate, sodium bicarbonate, sodium carbonate, ammonium chloride, or sodium nitrite; The foaming aids for azo compounds are stearic acid, urea, benzoic acid, zinc oxide, magnesium oxide, lead oxide, metal salts, or organosilicones; the foaming aids for N-nitroso compounds are stearic acid, salicylic acid, adipic acid, phthalic acid, urea, or glycerin; the foaming aids for sulfonyl hydrazine compounds are urea or metal salts; the foaming aids for ammonium carbonate, sodium bicarbonate, sodium carbonate, ammonium chloride, and sodium nitrite are each independently selected from stearic acid, phosphates, silicones, phthalic acid, diols, or metal salts.

5. The method for preparing the composite current collector as described in claim 1, characterized in that, In step (3), the opening is specifically: the support layer is conveyed to the space between the needle roller and the pad roller by the roller of the film punching machine, and the support layer located at the intersection of the needle roller and the pad roller is pressed into a hole during the inward rolling tangential process of the needle roller and the pad roller.

6. The method for preparing the composite current collector as described in claim 1, characterized in that, A thin film with a cone height of 3-50 μm and a thickness of 8-30 μm is prepared on a roller with a cone-shaped aperture. After hot pressing, a shape memory polymer support layer with a thickness of 4-20 μm is obtained.

7. The method for preparing the composite current collector as described in claim 1, characterized in that, In step (3), the diameter of the hole obtained by the opening is 10~15 μm.

8. The composite current collector prepared by the method according to any one of claims 1-7.

9. An electrode sheet, characterized in that, It includes the composite current collector as described in claim 8 and the active material layer coated on the composite current collector.

10. A secondary battery, characterized in that, Includes the electrode sheet as described in claim 9.

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