Carbon-coated aluminum foil current collector based on polymer functional coating and preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly discloses a carbon-coated aluminum foil current collector based on a polymer functional coating as well as a preparation method and application of the carbon-coated aluminum foil current collector. The current collector comprises a carbon-coated aluminum foil base material and a polymer functional coating coated on the surface of the carbon-coated aluminum foil base material; the high-molecular functional coating comprises the following components: a high-molecular base material, a conductive filler, a binder and a solvent; wherein the polymer base material is one or more of polypropylene, acrylic acid and polyvinylidene fluoride, the conductive filler is one or more of carbon black, metal particles and graphite, the binder is one or more of acrylate, polyurethane and polyvinylidene fluoride, and the solvent is N-methyl pyrrolidone. According to the invention, the functional polymer coating is added on the carbon-coated aluminum foil, and the coating can automatically adjust the resistance through a temperature sensitive effect under an overheating condition, so that an effective overheating protection effect is achieved, the service life of the battery is prolonged, and the safety of the battery is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a carbon-coated aluminum foil current collector with self-power-off protection function and a preparation method thereof, which is suitable for power batteries, energy storage batteries and consumer electronic batteries with high safety requirements. BACKGROUND

[0002] Lithium batteries have rapidly become mainstream power sources due to their high energy density, long cycle life, and relatively light weight, and are widely used in consumer electronics, electric vehicles (EV), energy storage systems, and other fields. However, with the introduction of high-energy density materials, especially high-nickel ternary positive electrode materials and silicon-based negative electrode materials, the energy storage capacity of the battery has been greatly improved, but this has also brought higher safety risks. These new high-energy density materials have made significant progress in improving battery performance, but the risk of thermal runaway they cause has also increased significantly. Factors such as overcurrent, overheating, or external short circuits can cause the internal temperature of the battery to rise sharply, further causing electrolyte decomposition, gas accumulation, and even explosions or fires in extreme cases. Therefore, how to effectively prevent and control thermal runaway has become a key focus of current lithium battery technology research.

[0003] To address this challenge, engineers are constantly optimizing battery design and manufacturing processes, adopting more advanced overcurrent and overheating protection technologies, improving battery management systems (BMS), introducing intelligent temperature control systems, using phase change materials and high thermal conductivity materials, and other measures to improve battery performance while ensuring safety in various operating environments. While these technologies can effectively improve the safety of lithium batteries, they also come with challenges such as high cost, low response efficiency, and stability. For example, CN202311517286.6 introduces an image processing module to calculate the area of high-temperature regions and estimate battery abnormalities, which is a complex process, and it can only monitor and alarm for thermal runaway in real time, not fundamentally solving the problem; CN201910478574.2 uses a ceramic coating to improve the heat resistance of the separator, but it cannot actively cut off the current. SUMMARY

[0004] In view of the above technical drawbacks, the present application aims to provide a carbon-coated aluminum foil current collector based on a high molecular coating and a preparation method and application thereof. The high molecular coating can self-adjust the resistance through temperature sensitivity effect under overheating conditions, effectively protecting against overheating and improving the service life and safety of the battery.

[0005] To achieve the above-mentioned purposes, the specific technical solutions adopted by the present application are as follows:

[0006] In a first aspect, the present application provides a carbon-coated aluminum foil current collector based on a polymer functional coating, comprising a carbon-coated aluminum foil substrate and a polymer functional coating coated on the surface thereof; the polymer functional coating comprises the following components: a polymer substrate, a conductive filler, a binder, and a solvent; the polymer substrate is one or more of polypropylene, acrylic acid, and polyvinylidene fluoride; the conductive filler is one or more of carbon black, metal particles, and graphite; the binder is one or more of acrylate, polyurethane, and polyvinylidene fluoride; and the solvent is N-methyl pyrrolidone.

[0007] Further, the polymer functional coating comprises the following components by mass percentage: 20-50% of the polymer substrate, 30-60% of the conductive filler, 5-15% of the binder, and the balance of the solvent. More preferably, the polymer functional coating comprises the following components by mass percentage: 25-40% of the polymer substrate, 40-55% of the conductive filler, 5-10% of the binder, and 10-30% of the solvent, with the total being 100%.

[0008] Further, the functionalized polymer coating has a thickness of 1-3 μm, a normal resistance of <1 Ω·cm, a triggering temperature of 60-120 °C, a triggering current of 1.2-3 times the maximum working current, and a resistance change rate of >1000%.

[0009] In a second aspect, the present application provides a method for preparing the above-mentioned carbon-coated aluminum foil current collector based on a polymer functional coating, comprising the following steps:

[0010] S1. Dry the components of the coating raw material, i.e., the polymer substrate and the conductive filler, in order to fully remove moisture and reduce the impact of moisture on battery performance;

[0011] S2. Add the polymer substrate, the conductive filler, and the binder to the solvent in the appropriate proportions, and use a planetary mixer for preliminary mixing;

[0012] S3. Use a sand mill for nanoscale dispersion;

[0013] S4. Apply the slurry to the carbon-coated aluminum foil and then dry it.

[0014] Further, in step S1, the drying is performed at 80-100 °C under vacuum for 4-6 hours.

[0015] Further, in step S2, the planetary mixer is operated at a speed of 500-1000 rpm for 2-4 hours.

[0016] Further, in step S3, the sand mill is used to grind the particles to a particle size of ≤100 nm, with a grinding time of 1-2 hours and a control of the slurry discharge viscosity to be 2000-5000 mPa·s (25 °C).

[0017] Further, in step S4, the wet film thickness of the slurry coating is 50-100 μm, and the dry film thickness after drying is 1-3 μm.

[0018] In a third aspect, the application provides application of the above-mentioned carbon-coated aluminum foil current collector based on a high-molecular functional coating in lithium battery power-off protection. The current collector has a self-power-off protection function, and a battery assembled therefrom can achieve lithium battery power-off protection.

[0019] The application has the following beneficial effects:

[0020] The application adopts a method of adding a functional high-molecular coating on the carbon-coated aluminum foil, realizes integrated design of the coating and the carbon-coated aluminum foil, and in a normal state, the electrical resistance of the functional coating is 0.1-1 Ω·cm (25℃). When the current exceeds a threshold value of 1-15 A / cm 2 or the temperature reaches 60-120℃, the Joule heating effect causes the high-molecular matrix to expand, the conductive network to break, and the electrical resistance to suddenly increase to >1 kΩ·cm, thereby cutting off the local current path and realizing self-power-off protection. When the fault is eliminated, the material also cools and shrinks, the conductive network is rebuilt, and the electrical resistance returns to the initial value, effectively realizing battery overheat protection and providing a low-cost and effective safety solution.

[0021] The integrated design of the functional coating and the carbon-coated aluminum foil of the application saves external protection elements and reduces internal resistance. The functional coating can be selectively coated on the tab or the hot spot area of the electrode, and the operation is simple. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 : Structure diagram of the functional coating carbon-coated aluminum foil of the application.

[0023] Figure 2 : Partial enlarged diagram of the functional coating of the application.

[0024] Figure 3 : Working mechanism diagram of the functional coating of the application. DETAILED DESCRIPTION

[0025] The current collector structure of the application is shown in Figure 1 , which comprises a carbon-coated aluminum foil substrate and a high-molecular functional coating coated on the surface thereof. The current collector has a self-power-off protection function, and the principle is as follows: the high-molecular functional coating is directly integrated on the carbon-coated aluminum foil to realize self-protection of the current collector, simplify the structure, and improve the response speed. That is, when the temperature rises, the high-molecular coating expands to cause the conductive path to break, and the electrical resistance sharply rises to limit the current. After the fault is eliminated, the coating shrinks after cooling to realize recovery of the electrical resistance, as shown in Figures 2-3 .

[0026] The slurry formula of the high polymer functional coating is shown in the following table:

[0027]

[0028] The preparation method of the carbon-coated aluminum foil current collector is as follows:

[0029] S1. Dry the raw materials such as the polymer matrix and the conductive filler at 80-100℃ for 4-6 hours in vacuum to fully remove the moisture and reduce the influence of the moisture on the battery performance;

[0030] S2. Add the polymer matrix, the conductive filler and the binder into the solvent in proportion, and use a planetary mixer (speed 500-1000 rpm, time 2-4 h) to preliminarily mix;

[0031] S3. Use a sand mill to perform nanoscale dispersion (particle size ≤100 nm, grinding time 1-2 h), and control the slurry discharge viscosity at 2000-5000 mPa·s (25℃);

[0032] S4. Apply the slurry on the carbon-coated aluminum foil, and the wet film thickness is 50-100 μm. After drying, it is used to assemble a battery.

[0033] The application is further described below in combination with specific examples according to the above formula and preparation method.

[0034] Example 1

[0035] A carbon-coated aluminum foil current collector based on a high polymer coating is prepared by the following steps: take polypropylene (PP) 35%, carbon black 50%, acrylic ester binder 5%, and solvent N-methyl pyrrolidone 10% by mass fraction, disperse in a double planetary mixer at 800 rpm for 4 h, and then continue to disperse in a sand mill for 1 h. After the dispersion is completed, the slurry discharge viscosity is 3200 mPa·s, which is called slurry A. Apply A on the carbon-coated aluminum foil, and the wet film thickness is 50 μm.

[0036] After drying, assemble into a battery. The positive electrode material is lithium iron phosphate (specifically, coat lithium iron phosphate and a binder on the high polymer coating of the carbon-coated aluminum foil current collector of the application to form a positive electrode coating, and combine the carbon-coated aluminum foil, the high polymer coating and the positive electrode coating into a positive electrode sheet). The negative electrode is graphite, and the electrolyte is LiPF6 / EC+EMC. Perform overcharge test (4.8 V, 1C): the ordinary battery has thermal runaway in 30 minutes; the battery of the present example has a sudden increase in resistance and a current drop to 5% of the initial value when the current density reaches 4.5 A / cm 2 , temperature 110℃, the resistance jumps from 0.5 Ω·cm to 1.2 kΩ·cm, and no thermal runaway occurs.

[0037] Example 2

[0038] A kind of carbon-coated aluminum foil current collector based on polymer coating is prepared by the following steps: PP:PVDF=6:4 (total 35%) by mass fraction, carbon black 50%, acrylic binder 5%, solvent N-methyl pyrrolidone 10%, after 4h dispersion in double planetary mixer at 800rpm, continue to disperse in sand mill for 1h, after dispersion is completed, the slurry discharge viscosity is 2800mPa·s, called slurry B, B is coated on carbon-coated aluminum foil, wet film 50 μm;

[0039] After drying, assemble into a battery, the positive electrode material is lithium iron phosphate, the negative electrode is graphite, the electrolyte is LiPF6 / EC+EMC, and overcharge test (4.8V, 1C) is carried out: the current density of the battery in this embodiment reaches 10A / cm 2 , the functional coating triggers within 5 seconds, the battery surface temperature stabilizes below 90℃, and the resistance jumps from 0.5Ω·cm to 1.6kΩ·cm, without thermal runaway.

[0040] Example 3

[0041] A kind of carbon-coated aluminum foil current collector based on polymer coating is prepared by the following steps: PP:PVDF=6:4 (total 35%) by mass fraction, carbon black 50%, polyurethane binder 5%, solvent N-methyl pyrrolidone 10%, after 4h dispersion in double planetary mixer at 800rpm, continue to disperse in sand mill for 1h, after dispersion is completed, the slurry discharge viscosity is 3800mPa·s, called slurry C, C is coated on carbon-coated aluminum foil, wet film 50 μm;

[0042] After drying, assemble into a battery, the positive electrode material is lithium iron phosphate, the negative electrode is graphite, the electrolyte is LiPF6 / EC+EMC, and overcharge test (4.8V, 1C) is carried out: the current density of the battery in this embodiment reaches 5A / cm 2 , the functional coating triggers within 12 seconds, the battery surface temperature stabilizes below 100℃, and the resistance jumps from 0.5Ω·cm to 1.2kΩ·cm, without thermal runaway.

[0043] Compared with slurry A, slurry C uses PP and PVDF composite, which enhances the dispersion of fillers by the polarity of PVDF, and at the same time reduces the crystallinity of PE to improve the response speed of triggering; compared with slurry B, slurry C uses different binders, and it is found that the discharge viscosity of polyurethane binder is high, and the apparent difference is high, and acrylic ester as a binder can improve the flexibility of slurry and inhibit high temperature phase separation.

[0044] Example 4

[0045] A kind of carbon-coated aluminum foil current collector based on polymer coating is prepared by the following steps: taking PP:PVDF=5:5 (40% in total) by mass fraction, carbon black 40%, acrylic ester binder 5%, solvent N-methyl pyrrolidone 15%, dispersing in double planetary mixer at 800 rpm for 4h, then continue to disperse in sand mill for 1h, after dispersion is completed, the slurry discharge viscosity is 3000 mPa·s, called slurry D, apply D on carbon-coated aluminum foil, wet film 50 μm;

[0046] After drying, assemble into a battery, the positive electrode material is lithium iron phosphate, the negative electrode is graphite, the electrolyte is LiPF6 / EC+EMC, and overcharge test (4.8V, 1C) is carried out: the current density of the battery of the application reaches 7.5A / cm 2 , the functional coating triggers within 12 seconds, the battery surface temperature stabilizes below 120℃, the resistance jumps from 0.4Ω·cm to 1.3kΩ·cm, and no thermal runaway occurs.

[0047] Compared with the slurry D, the slurry D increases the proportion of polymer matrix, which can effectively control the triggering temperature. The role of polymer matrix is to provide structural support and stability. These materials are superior to certain low molecular materials in thermal stability. Therefore, as the content of polymer matrix increases, the thermal stability of the slurry is enhanced, resulting in an increase in the triggering temperature.

[0048] Record the resistance and surface temperature (infrared thermal imager) of the above formula, define the triggering current as the minimum current density when the resistance rises to 10 times the initial value, and the results are shown in the following table. It can be seen that the functional coating of examples 1-4 can effectively play the role of power-off protection.

[0049]

[0050] This specific embodiment is only an explanation of the application and is not a limitation of the application. Any changes made by those skilled in the art after reading the specification of the application will be protected by the patent law as long as it is within the scope of the claims of the application.

Claims

1. A carbon-coated aluminum foil current collector based on a polymer functional coating, characterized in that: It includes a carbon-coated aluminum foil substrate and a polymer functional coating coated on the surface thereof; the polymer functional coating includes the following components: a polymer substrate, a conductive filler, a binder and a solvent; the polymer substrate is one or more of polypropylene, acrylic acid, and polyvinylidene fluoride; the conductive filler is one or more of carbon black, metal particles, and graphite; the binder is one or more of acrylate, polyurethane, and polyvinylidene fluoride; and the solvent is N-methylpyrrolidone.

2. The carbon-coated aluminum foil current collector based on polymer functional coating according to claim 1, characterized in that: The polymer functional coating comprises the following components by mass percentage: 20-50% of polymer base material, 30-60% of conductive filler, 5-15% of binder, and the balance is solvent.

3. The carbon-coated aluminum foil current collector based on polymer functional coating according to claim 2, characterized in that: The polymer functional coating comprises the following components by mass percentage: 25-40% of polymer base material, 40-55% of conductive filler, 5-10% of adhesive, 10-30% of solvent, and the total amount is 100%.

4. The carbon-coated aluminum foil current collector according to claim 3, characterized in that: The functionalized polymer coating has a thickness of 1 to 3 μm, a normal resistance of less than 1Ω·cm, a trigger temperature of 60 to 120° C., a trigger current of 1.2 to 3 times the maximum operating current, and a resistance change rate of more than 1000%.

5. The method for preparing a carbon-coated aluminum foil current collector based on a polymer functional coating according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. The coating raw material components polymer substrate and conductive filler are dried; S2. The polymer substrate, conductive filler, and binder are added to the solvent in proportion and initially mixed using a planetary mixer; S3. Nano-scale dispersion using a sand mill; S4. The slurry is coated on a carbon-coated aluminum foil and then dried.

6. The preparation method according to claim 5, characterized in that In step S1, the drying is performed under vacuum at 80-100° C. for 4-6 hours.

7. The preparation method according to claim 5, characterized in that In step S2, the stirring conditions of the planetary mixer are: a rotation speed of 500-1000 rpm and a time of 2-4 hours.

8. The preparation method according to claim 5, characterized in that In step S3, a sand mill is used to grind the particles to a particle size of ≤100 nm for 1-2 h, and the viscosity of the slurry discharge is controlled at 2000-5000 mPa·s.

9. The preparation method according to claim 5, characterized in that In step S4, the wet film thickness of the slurry coating is 50-100 μm.

10. Use of the carbon-coated aluminum foil current collector based on a polymer functional coating according to any one of claims 1 to 4 in power-off protection of a lithium battery.

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