Composite current collector of adjustable resistor and preparation method thereof

Abstract

The invention provides a composite current collector of an adjustable resistor. The composite current collector comprises a macromolecule layer, metal layers attached to the two sides of the macromolecule layer and functional layers attached to the surfaces of the metal layers. The macromolecule layer can be made of various organic matter membrane materials, and the metal layers are uniformly distributed on the two sides of the macromolecule layer; the functional layer uniformly covers the metal layer and has the capability of conducting electrons, and meanwhile, the resistance of the functional layer is changed along with the change of states such as temperature and voltage of the functional layer. The thickness of the composite current collector is 1-40 [mu] m, the functional layer, the metal layer and the polymer film layer are tightly combined, the composite current collector is resistant to electrochemical corrosion and not prone to falling off, the composite current collector has the advantages of being light, thin, high in strength and good in toughness, and the metal current collector film can be effectively improved to provide an electronic path for short circuit in a battery when the battery is subjected to thermal runaway; and the safety problem of heat release of the battery is aggravated.

Description

Technical Field

[0001] The present invention relates to the technical field of composite current collectors, and particularly relates to an adjustable-resistance composite current collector and a preparation method thereof. Background Art

[0002] Lithium-ion batteries, as energy storage devices, have been widely used in various consumer devices and the field of electric vehicles. The market's pursuit of the energy density and safety of lithium-ion batteries is also continuously increasing. It is urgent to develop lithium-ion batteries with high energy density and high safety. Compared with metal current collectors, composite current collectors are lighter in weight and lower in cost. At the same time, as an emerging safety component for lithium batteries, composite current collectors can show excellent performance in preventing thermal runaway of batteries caused by mechanical abuse without sacrificing the battery's energy density. All aspects of data indicate that composite current collectors have broad prospects in lithium battery applications. However, in the face of the increasing energy density of lithium batteries, composite current collectors seem to be increasingly unable to cope. Simply using composite current collectors has become increasingly difficult to ensure the mechanical abuse safety of batteries. At the same time, there is still a question mark as to whether composite current collectors can maintain their safety in the face of thermal abuse of batteries. This poses new and higher safety requirements for composite current collectors.

[0003] Patent CN116565215A discloses a flame-retardant current collector, a preparation method thereof, and an electrochemical energy storage device. Its design idea is based on adding a layer of flame-retardant medium on the surface of the composite current collector. In the initial stage of thermal runaway induced by a thermal failure cause in the electrochemical energy storage device, the local current and voltage in the electrochemical energy storage device increase, the flame-retardant current collector suddenly heats up, the outer shell of the heat-conducting resistance medium contained in the heat-conducting resistance coating is thermally detached, the conductive material chain is disconnected, and the core of the heat-conducting resistance medium contained in the heat-conducting resistance coating is exposed. The core directly contacts the external heat source. Since the core of the heat-conducting resistance medium contained in the heat-conducting resistance coating is a heat-resistant material, the resistance of the heat-resistant material increases rapidly when heated, thereby achieving internal open circuit and ensuring battery safety.

[0004] Patent CN109119637A discloses a current collector coating, a pole piece, and a preparation method thereof. The current collector coating includes: a conductive agent, a binder, and a hyperbranched oligomer. When the battery temperature rises abnormally, the hyperbranched oligomer molecules in the current collector coating can form an insulating film, which plays a role in blocking the chemical reaction current inside the battery, thereby improving the safety of the battery. However, the hyperbranched polymer molecules in the current collector coating will affect the conductive performance of the current collector coating, resulting in a decrease in the conductive performance of the current collector.

[0005] However, the currently disclosed flame-retardant designs still have certain limitations, such as poor conductivity of the flame-retardant current collector or slow response of the flame-retardant method, and high cost of the flame-retardant method. In particular, it is worth noting that the flame-retardant coatings in most patents are based on temperature-responsive designs, and the temperature thresholds are mostly set at around 100°C, with disadvantages such as a single response method and a fixed response temperature. Therefore, it is crucial to design a new type of safety current collector with a novel response method in combination with a composite current collector. Based on this, the present invention provides an adjustable-resistance composite current collector and a preparation method thereof. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides an adjustable-resistance composite current collector, which makes different safety designs for the battery safety capabilities under different working conditions while ensuring the conductivity of the current collector itself; at the same time, the functional layer structure described in this design is simple and the production cost is low, which is suitable for large-scale production and promotion using roll-to-roll.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides an adjustable-resistance composite current collector, which includes a polymer layer, metal layers attached to both sides of the polymer layer, and a functional layer attached to the surface of the metal layers.

[0009] Further, the polymer layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyethylene naphthalate, polymethyl methacrylate, and polyphenylene sulfide, and the thickness of the polymer layer is 1-30 μm.

[0010] Further, the metal layer includes at least one of zinc, copper, aluminum, silver, tin, iron, cobalt, nickel, and titanium, and the thickness of the metal layer is 10-10,000 nm.

[0011] Further, the construction method of the metal layer includes vacuum evaporation deposition method, electroplating deposition method, or magnetron sputtering deposition method.

[0012] Further, the functional layer is composed of a substrate and conductive particle fillers, wherein the mass ratio of the substrate to the fillers is 100:(5-40), and the thickness of the functional layer is 0.001-1 μm.

[0013] Further, the areal density of the functional layer is 0.001-0.3 g / cm 2 .

[0014] Further, the composition of the substrate includes at least one of polypyrrole, polythiophene, polyaniline, polyacetylene, poly(p-phenylene vinylene), and poly(p-phenylene) and derivatives of the foregoing materials; typical but non-limiting substrate compositions include polypyrrole, polythiophene and its derivatives, and polyaniline.

[0015] Furthermore, the composition of the filler includes at least one of carbon black, carbon nanotubes, resin carbon, organic polymer pyrolytic carbon, and nano metal powder, and the nano metal powder includes any one of copper, aluminum, iron, cobalt, nickel, and titanium; typical but non-limiting combinations include the combination of conductive carbon black and carbon nanotubes, the combination of acetylene black and carbon nanotubes, and the combination of conductive carbon black, carbon nanotubes, and acetylene black.

[0016] Furthermore, the functional layer substrate is polypyrrole and the filler is nano aluminum particles.

[0017] Among them, polypyrrole has a positive temperature coefficient effect, that is, its own resistance increases when the temperature rises. At the same time, polypyrrole itself has a certain conductivity, which can improve the conductivity of the functional layer, and polypyrrole does not participate in the side reactions of the battery and can stably exist in the electrolyte. At the same time, it has the characteristics of simple processing and easy replication. Therefore, polypyrrole is used as the substrate of the functional layer; nano aluminum particles have low cost, do not participate in the side reactions of the battery, can stably exist in the electrolyte, and are easy to form a conductive path. Therefore, nano aluminum particles are used as the filler.

[0018] Furthermore, the functional layer further includes a binder, and the binder satisfies at least one of the following conditions:

[0019] (1) The binder includes any one of polyvinylidene fluoride, polytetrafluoroethylene, and polyvinylidene dichloride;

[0020] (2) The mass percentage of the binder in the functional layer is 0.5% - 10%.

[0021] On the other hand, the present invention provides a method for preparing an adjustable resistance composite current collector, and the steps include: performing corona surface roughening treatment on the polymer layer, depositing a metal layer on both sides of the polymer layer by vacuum evaporation deposition, electroplating deposition, or magnetron sputtering deposition, preparing a functional layer slurry, coating the functional layer slurry by micro gravure coating, and drying to obtain a functional layer attached to the surface of the metal layer, thereby preparing the adjustable resistance composite current collector.

[0022] Furthermore, in the vacuum evaporation deposition method, the current magnitude is 50 - 60A, the wire feeding speed of the aluminum wire is 300 - 600 mm / min, and the winding speed is 4.5 - 6.5 m / s.

[0023] The advantages of the present invention are:

[0024] The composite current collector design with adjustable resistance provided by the present invention has good conductivity and electrochemical stability of the substrate (polymer) and filler (conductive particles) contained in the functional layer under the temperature conditions of normal operation of the electrochemical energy storage device, and can maintain the integrity of the structure. Among them, the substrate itself has good conductivity, which makes up for the resistance generated by the electrode sheet after the additional structure is added. By changing the potential of the substrate, it can be controlled to be in a conductive state or a polarized state. The functional layer in the conductive state has a low resistance, the electronic path between the composite current collector and the electrode active material is smooth, and the electrochemical energy storage device works normally; the functional layer in the polarized state loses its conductivity, the resistance between the composite current collector and the electrode active material increases sharply, and a short circuit is formed inside the electrochemical energy storage device. At the same time, the filler dispersed in the functional layer can form a conductive path, and the electronic conductivity of the functional layer is realized through the direct contact of these conductive particles or the close-range electron tunneling effect.

[0025] In the initial stage of thermal runaway caused by mechanical or thermal abuse of electrochemical energy storage devices, the local temperature inside the electrochemical energy storage device rises. On the one hand, due to the thermal expansion effect of the polymer, the polymer substrate will undergo a huge volume expansion, which increases the distance between the dispersed fillers that were originally in close contact in the functional layer, and the electron tunneling effect basically disappears; on the other hand, the diaphragm will shrink at high temperature, causing an internal short circuit inside the battery. The potential of the functional layer quickly decreases from the high potential under normal working conditions to the 0 potential during the short circuit, and changes from the conductive state to the polarized state. The original electronic path is destroyed, and the resistance between the composite current collector and the electrode active material increases sharply, forming a short circuit inside the electrochemical energy storage device, thereby preventing further internal short circuits from occurring at the internal thermal runaway location, avoiding the continuous development of thermal runaway, and enhancing the safety of the electrochemical energy storage device. At the same time, when facing mechanical abuse, the composite current collector can further cover the short circuit area with the excellent ductility of its internal polymer layer to ensure the electrical insulation of the broken part, adding double insurance to battery safety.

[0026] In addition, the functional layer of the present invention has a simple structure, a thickness generally between 0.001-1 μm, a small surface density, and a small proportion of the cathode / anode electrode mass (typically 0.5% by mass), and does not affect the energy density of the electrochemical energy storage device; and the coating process of the functional layer of the present invention is mature, and the thickness and surface density of the functional layer on the composite current collector can be well controlled by using the coating-drying technology, and the thickness of the functional layer can be accurately controlled within a few hundred nanometers by using the micro-gravure printing technology; further, the functional layer material composition is simple, and large-scale slurry configuration can be achieved by simple mixing equipment, eliminating the granulation, drying, screening and other processes in the previous flame retardant coating;

[0027] In the present invention, the prepared functional layer can flexibly adjust its corresponding resistance according to requirements. By controlling the proportion of the filler, the temperature response threshold can be controlled, and no additional materials or processes are required. Compared with the fixed response temperature threshold (about 110 °C) of the previous flame-retardant coating, its usability and flexibility are greatly improved. For example, after increasing the temperature response threshold, the coating can be freely deployed in electrochemical energy storage devices operating in high-temperature environments; in addition to the temperature response mechanism, a voltage response function is added. Through the de / doping of certain polymer macromolecules and the potential range of their own oxidation and reduction states, the functional layer can conduct electricity normally under the normal operating voltage of the electrochemical energy storage device. Once an internal short circuit occurs and the potential of the functional layer decreases, it can be transformed into a non-conductive state, promptly realizing the internal open circuit of the electrochemical device and preventing further thermal runaway of the electrochemical energy storage device.

[0028] By further optimizing the materials of the functional layer in the present invention, such as adding branched chains of appropriate length to the substrate and adjusting the proportion of the filler, the voltage response threshold can be further adjusted to a lower voltage, which further broadens the application range of the functional layer. For example, the typical operating voltage range of lithium-ion batteries is 3-4.5V, and the typical operating voltage range of sodium-ion batteries is 2-4V. This is of great significance for broadening the application range of this process. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0030] Figure 1 It is a schematic diagram of a composite current collector with adjustable resistance according to the present invention. Among them, 1 is the functional layer, 2 is the metal layer, and 3 is the polymer layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] The present invention provides a composite current collector with adjustable resistance, including a polymer layer, metal layers attached to both sides of the polymer layer, and a functional layer attached to the surface of the metal layer; as Figure 1As shown, where 1 is the functional layer, 2 is the metal layer, and 3 is the polymer layer.

[0033] Among them, the polymer layer includes but is not limited to at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyethylene naphthalate, polymethyl methacrylate, and polyphenylene sulfide, and the thickness of the polymer layer is 1 - 30 μm; the metal layer includes but is not limited to at least one of zinc, copper, aluminum, silver, tin, iron, cobalt, nickel, and titanium, and the thickness of the metal layer is 10 - 10,000 nm; the construction method of the metal layer includes but is not limited to vacuum evaporation deposition method, electroplating deposition method, or magnetron sputtering deposition method;

[0034] The functional layer is composed of a substrate and conductive particle fillers. Among them, the mass ratio of the substrate to the fillers is 100:(5 - 40). The mass ratio of the substrate to the fillers can be 100:10, 100:15, 100:20, 100:25, 100:30, or 100:40, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0035] And the thickness of the functional layer is 0.001 - 1 μm, which can be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 400 nm, 500 nm, or 600 nm, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0036] The surface density of the functional layer is 0.001 - 0.3 g / cm 2 . In a further embodiment, it can be 0.1 g / cm 2 , 0.11 g / cm 2 , 0.12 g / cm 2 , 0.13 g / cm 2 , 0.14 g / cm 2 , 0.15 g / cm 2 , 0.16 g / cm 2 , 0.17 g / cm 2 , 0.18 g / cm 2 , 0.19 g / cm 2 or 0.2 g / cm 2 , but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0037] Among them, the composition of the substrate includes but is not limited to at least one of polypyrrole, polythiophene, polyaniline, polyacetylene, poly(phenylene vinylene), and poly(phenylene) and derivatives of the foregoing materials; typical but non - limiting substrate compositions include polypyrrole, polythiophene and its derivatives, and polyaniline.

[0038] Among them, the functional layer further includes a bonding material, and the bonding material satisfies at least one of the following conditions: (1) the bonding material includes any one of polyvinylidene fluoride, polytetrafluoroethylene, and polyvinylidene dichloride; (2) the mass percentage of the bonding material in the functional layer is 0.5% - 10%.

[0039] The preparation method of this adjustable resistance composite current collector includes the following steps: corona surface roughening treatment is carried out on the polymer layer, the metal layer is deposited on both sides of the polymer layer by vacuum evaporation deposition method, electroplating deposition method or magnetron sputtering deposition method, the functional layer slurry is configured, the functional layer slurry is coated by microgravure coating method, and after drying, the functional layer attached to the surface of the metal layer is obtained, thus preparing the adjustable resistance composite current collector. When the vacuum evaporation deposition method is selected, the current size during operation is controlled to be 50 - 60A, the wire feeding speed of the aluminum wire is 300 - 600mm / min, and the winding speed is 4.5 - 6.5m / s.

[0040] The test materials and reagents used in the following examples, unless otherwise specified, can all be obtained from commercial channels. For those not specified in the examples regarding specific technologies or conditions, they can all be carried out according to the technologies or conditions described in the literature in this field or according to the product instructions.

[0041] Example 1

[0042] The preparation method of the composite current collector with adjustable resistance in this example is as follows:

[0043] (1) The middle polymer layer uses a polyethylene terephthalate (PET) film with a thickness of 6μm, and the PET film is first subjected to corona surface roughening treatment at 60kW.

[0044] (2) Using the vacuum evaporation deposition technology, with the aluminum wire as the metal source, the evaporation boat (aluminum nitride / aluminum oxide ceramic) is heated to 500°C by direct current, the aluminum wire is continuously sent to the surface of the evaporation boat to melt and evaporate, and when it contacts the colder PET base film, it cools and solidifies to form a conductive metal with strong adhesion. As the number of evaporation times increases, the thickness of the finally obtained conductive metal layer is 1μm. Among them, the current size is controlled at 55A, the wire feeding speed of the aluminum wire is 450mm / min, and the winding speed is 5.5m / s.

[0045] (3) Dissolve 1 part of pyrrole monomer in 100 parts of ethanol aqueous solution (volume ratio of ethanol to water is 1:1), stir in an ice bath until completely dissolved, and gradually add 20 parts of ammonium persulfate solution with a concentration of 0.7mol / L. After reacting for 24h, black polypyrrole powder can be obtained.

[0046] (4) Dissolve 3 parts of polypyrrole in 100 parts of toluene solvent by stirring at 30°C. Add nano-aluminum particles with a mass fraction of 20% relative to polypyrrole. The particle size of the nano-aluminum particles is 20 - 30 nm. After stirring evenly, remove bubbles under vacuum to obtain the functional layer slurry;

[0047] (5) Add the functional layer slurry into the feeding bucket of the gravure coater, use micro-gravure coating, and then bake and dry in an 80°C oven. The coating speed is 20 m / min, and the finished product is wound up. The thickness of the functional layer is 600 nm, and the surface density is 0.12 g / cm 2 .

[0048] Example 2

[0049] The preparation method of the current collector in Example 2 is the same as that in Example 1, except that the composition ratio of its functional layer is different, and the mass fraction of the nano-aluminum particles becomes 40%.

[0050] Example 3

[0051] The preparation method of the current collector in Example 3 is the same as that in Example 1, except that the composition ratio of its functional layer is different, and no nano-aluminum particles are added.

[0052] Example 4

[0053] The preparation method of the current collector in Example 4 is the same as that in Example 1, except that the composition ratio of its functional layer is different, and the nano-aluminum particles are replaced by carbon nanotubes, and the mass fraction of both is 20%.

[0054] Example 5

[0055] The preparation method of the current collector in Example 5 is the same as that in Example 1, except that the composition ratio of its functional layer is different. The preparation method of its functional layer is as follows:

[0056] (1) Mix 3 parts of 3,3'-methoxythiophene with 7 parts of triethylene glycol methyl ether and dissolve them in 150 parts of toluene solution. Add 0.5 part of p-toluenesulfonic acid and reflux for 24 hours under a nitrogen atmosphere. After cooling to room temperature, quench with water and extract with ethyl acetate. After drying, 3-triethylene glycol thiophene can be obtained.

[0057] (2) Dissolve 1 part of ferric chloride in n - hexane to prepare a 1.9 mol / L solution. Add 1 part of the prepared 3 - triethylene glycol thiophene powder to it. Set the reaction temperature at 10 °C. After stirring for 1 hour, add MeOH solution. Dissolve the precipitate in 2 L of THF at 60 °C for 5 hours. Add a certain amount of MeOH solution to the dissolved solution to further remove Fe ions. Wash the obtained powder three times with MeOH solution to obtain pure polythiophene powder.

[0058] (3) Stir and dissolve 3 parts of polythiophene and 100 parts of toluene solvent at 30 °C. Add nano - aluminum particles with a mass fraction of 20% relative to polythiophene to it. The particle size of the nano - aluminum particles is 20 - 30 nm. After stirring evenly, remove air bubbles under vacuum to obtain the functional layer slurry.

[0059] (4) Add the functional layer slurry into the feeding bucket of the gravure coater. Use micro - gravure coating, and then bake and dry it in an 80 °C oven. The coating speed is 20 m / min. The finished product is wound up. The thickness of the functional layer is 600 nm, and the surface density is 0.13 g / cm 2 .

[0060] Example 6

[0061] The preparation method of the current collector in Example 6 is the same as that in Example 5, except that the composition ratio of its functional layer is different, and the mass fraction of the nano - aluminum particles is 40%.

[0062] Comparative Example

[0063] This example provides an adjustable - resistance composite current collector, which includes a polymer layer, metal layers attached to both sides of the polymer layer, and a functional layer attached to the surface of the metal layer. Its preparation method is as follows:

[0064] (1) The middle polymer layer uses a polyethylene terephthalate (PET) film with a thickness of 6 μm. First, perform a 60 KW corona surface roughening treatment on the PET film.

[0065] (2) Adopt the vacuum evaporation deposition technology. Use aluminum wire as the metal source. Heat the evaporation boat (aluminum nitride / aluminum oxide ceramic) to 500 °C with direct - current heating. Continuously send the aluminum wire to the surface of the evaporation boat to melt and evaporate. When it contacts the colder PET base film, it cools and solidifies to form a conductive metal with strong adhesion. As the number of evaporation times increases, the thickness of the finally obtained conductive metal layer is 1 μm. Among them, control the current size at 55 A, the aluminum wire feeding speed at 450 mm / min, and the winding speed at 5.5 m / s.

[0066] (3) Add 5 parts of polyvinylidene fluoride (PVDF) powder (M W(1000000) was dissolved in 100 parts of N-methylpyrrolidone (NMP), stirred at room temperature until completely dissolved, and then carbon nanotube powder with a mass fraction of 40% relative to PVDF was added, and stirring was continued until fully mixed to obtain the functional layer coating;

[0067] (4) The functional layer slurry was added to the feed bucket of the gravure coater, micro-gravure coating was used, and then baking and drying were carried out in an 80 °C oven. The coating speed was 20 m / min, and the finished product was wound up. The thickness of the functional layer was 600 nm, and the areal density was 0.16 g / cm 2 .

[0068] To test the performance of the composite current collectors of the above several examples and comparative examples, the lithium cobaltate positive electrode slurry was coated on the composite current collectors prepared in Examples 1, 2, 3, 4 and the comparative example by a transfer coater, dried in an oven and then rolled by a rolling press to finally obtain the electrode sheets.

[0069] The electrochemical performance of the prepared electrode sheets was detected. The temperature-resistance test is as follows:

[0070] 1. Assembly of the resistance test device: The obtained electrode sheet was cut into a standard circular sheet with a diameter of 19 mm. The test platform was a CR2025 button cell. After the positive electrode shell, gasket, electrode sheet, gasket, shrapnel, and negative electrode shell were assembled in sequence, they were encapsulated using a button cell encapsulation machine. The encapsulation pressure was 550 kg. A small amount of liquid was injected into the button cell, and the injection volume was 10 μL. The injection composition was 1 mol LiPF6 dissolved in diethyl carbonate (DEC): ethylene carbonate (EC) = 1:1 Vol%, and fluoroethylene carbonate (FEC) with a total volume fraction of 5% relative to the total volume of diethyl carbonate (DEC) and ethylene carbonate (EC) was added.

[0071] 2. The assembled button cell was placed in a test oven, the heating rate was controlled at 1 °C / min, and the resistance of the battery was tested and recorded using a resistance tester (BEICH CH2515). The obtained temperature-resistance data are shown in Table 1;

[0072] Table 1 Temperature-resistance test results of examples and comparative examples

[0073]

[0074] It can be seen from the temperature-resistance test that by controlling the content of nano-aluminum metal powder in the examples (0% - 40%), we can further control the threshold of the thermal response of the functional layer to increase from 90 °C when the addition is 0% to 110 °C when the addition is 40%, and the control range reaches 30 °C. Further, the content of the conductive filler can be precisely adjusted for temperature response control at the degree Celsius level.

[0075] When the conductive additive was replaced with carbon nanotubes, Example 4 still achieved a thermal response at 100 °C, indicating that different types of conductive fillers can all achieve the expected performance, which greatly broadens our choice of conductive filler materials. At the same time, we can see that because the added carbon nanotubes have weaker conductivity than nano-aluminum particles, the resulting functional layer exhibits a greater resistance under normal working conditions, indicating that we can control the type of conductive particles to regulate the working resistance.

[0076] When the substrate of the functional layer was replaced with polythiophene, which has a similar structure to polypyrrole, a sharp increase in resistance was exhibited at a similar temperature, demonstrating that the material selection of the functional layer has great extensibility, which is conducive to trying more combinations of functional layer materials in the future.

[0077] Compared with the comparative example, the examples used self-conductive polypyrrole and polythiophene as substrates, resulting in a lower resistance of the examples at normal working temperatures, hardly affecting the normal operation of the electrode sheet. In contrast, the PVDF substrate used in the comparative example is not conductive itself, causing the functional layer to rely solely on the filled conductive particles to achieve electron conduction, with a relatively large self-resistance, which will affect the electrochemical performance of the final electrode sheet.

[0078] The electrochemical performance test is as follows:

[0079] 1. Assembly of the electrical performance test device: The obtained electrode sheet was cut into standard circular discs with a diameter of 12 mm. The test platform was a CR2025 coin cell. After assembling the positive electrode shell, electrode sheet, separator, lithium sheet, gasket, spring sheet, and negative electrode shell in sequence, it was encapsulated using a coin cell encapsulation machine. The encapsulation pressure was 550 kg, the injection volume was 40 μL, and the electrolyte composition was 1 mol LiPF6 dissolved in diethyl carbonate (DEC): ethylene carbonate (EC) = 1:1 Vol%, and 5% fluoroethylene carbonate (FEC) was added relative to the total volume fraction of diethyl carbonate (DEC) and ethylene carbonate (EC).

[0080] 2. Activate the assembled coin cell. The program was set to charge at a constant current of 0.05C to 4.5V, then discharge at a constant current of 0.05C to 2.9V and cycle 3 times.

[0081] 3. Perform stepped charging on the assembled battery. Charge at a constant current of 0.1C, and measure the internal resistance of the battery every 0.2V and record the internal resistance value. The obtained voltage-resistance data is shown in Table 2.

[0082] Table 2 Voltage-resistance test results of the examples and the comparative example

[0083]

[0084] From the voltage-resistance test, it can be seen that for the embodiments, regardless of the type and mass fraction of the conductive filler, the functional layer will exhibit a large resistance at low voltages. This is due to the de / doping phenomenon of polypyrrole polymers with the change of their own potential. At low potentials, due to de-doping, polypyrrole itself loses its conductive properties, resulting in a sharp increase in the resistance of the functional layer and achieving the purpose of open circuit. In the comparative example, PVDF does not have the corresponding de / doping phenomenon, and its structure remains constant, unable to achieve the change of resistance with potential.

[0085] When the conductive additive is replaced with carbon nanotubes, Example 4 still realizes a sharp increase in resistance at low potentials, indicating that the type of conductive filler only affects the resistance during normal operation and does not affect the overall voltage-current response trend of the functional layer. In Example 4, since the conductivity of carbon nanotubes themselves is lower than that of nano-aluminum particles, its resistance is slightly greater than that of Example 1.

[0086] When the substrate of the functional layer is replaced with polythiophene with a similar structure, polythiophene also produces a similar resistance effect at different potentials, and the circuit is still blocked at low potentials.

[0087] Compared with the comparative example, the use of polypyrrole as the substrate in the embodiment makes the resistance of the embodiment lower under the normal working voltage and hardly affects the normal operation of the electrode sheet. At low potentials, polypyrrole can hardly conduct electricity due to its own de / doping characteristics, which enables the electrode sheet to cut off its own circuit when a short circuit occurs in the battery. However, the functional layer made of the PVDF substrate used in the comparative example does not have the ability to respond to resistance due to the change of potential, resulting in almost no effect on isolating the short circuit in the battery for the comparative example.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the present invention and do not limit the technical solutions described in the present invention; those of ordinary skill in the art should understand that the present invention can still be modified or equivalently replaced; and all technical solutions and their improvements that do not depart from the spirit and scope of the present invention should be covered by the scope of the claims of the present invention.

Claims

1. A composite current collector with adjustable resistance, characterized in that: It includes a polymer layer, a metal layer attached to both sides of the polymer layer, and a functional layer attached to the surface of the metal layer.

2. The composite current collector with adjustable resistance according to claim 1, characterized in that: The polymer layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, polyethylene naphthalate, polymethyl methacrylate, and polyphenylene sulfide, and the thickness of the polymer layer is 1-30 μm.

3. The composite current collector with adjustable resistance according to claim 1, characterized in that: The metal layer includes at least one of zinc, copper, aluminum, silver, tin, iron, cobalt, nickel and titanium, and the thickness of the metal layer is 10-10000nm.

4. The composite current collector with adjustable resistance according to claim 1, characterized in that: The method for constructing the metal layer includes vacuum evaporation deposition, electroplating deposition or magnetron sputtering deposition.

5. The composite current collector with adjustable resistance according to claim 1, characterized in that: The functional layer is composed of a substrate and conductive particle fillers, wherein the mass ratio of the substrate to the filler is 100:(5-40), and the thickness of the functional layer is 0.001-1 μm.

6. The composite current collector with adjustable resistance according to claim 5, characterized in that: The substrate comprises at least one of polypyrrole, polythiophene, polyaniline, polyacetylene, polyparaphenylene vinylene and polyparaphenylene and derivatives thereof.

7. The composite current collector with adjustable resistance according to claim 5, characterized in that: The filler comprises at least one of carbon black, carbon nanotubes, resin carbon, organic polymer pyrolytic carbon, and nano metal powder, and the nano metal powder comprises any one of copper, aluminum, iron, cobalt, nickel, and titanium.

8. The composite current collector with adjustable resistance according to claim 5, characterized in that: The functional layer further comprises a bonding material, and the bonding material satisfies at least one of the following conditions: (1) The bonding material includes any one of polyvinylidene fluoride, polytetrafluoroethylene and polyvinylidene chloride; (2) The mass percentage of the bonding material in the functional layer is 0.5% to 10%.

9. A method for preparing a composite current collector with adjustable resistance according to any one of claims 1 to 8, characterized in that the steps include: The polymer layer is subjected to corona surface roughening treatment, a metal layer is deposited on both sides of the polymer layer by vacuum evaporation deposition, electroplating deposition or magnetron sputtering deposition, a functional layer slurry is prepared, the functional layer slurry is coated by micro-gravure coating, and after drying, a functional layer attached to the surface of the metal layer is obtained, thereby preparing the composite current collector with adjustable resistance.

10. The method for preparing a composite current collector with adjustable resistance according to claim 9, characterized in that: In the vacuum evaporation deposition method, the current is 50-60A, the aluminum wire feeding speed is 300-600mm / min, and the coil feeding speed is 4.5-6.5m / s.

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