Preparation method of battery safety coating and aluminum foil modification application of battery safety coating

Abstract

The invention relates to the technical field of batteries, and particularly discloses a preparation method of a battery safety coating and aluminum foil modification application of the battery safety coating, and the battery safety coating comprises the following components: 20-55 wt% of a solvent, 20-45 wt% of an adhesive and 15-30 wt% of a conductive additive, according to the formula of the safe coating, common solvents, adhesives and conductive additives are adopted as main components, the raw materials are easy to obtain, the cost is low, the preparation process is simple and efficient, secondly, the safe coating which is extremely thin, uniform and compact can be formed on the surface of the aluminum foil by accurately controlling the proportion of all the components and the coating process, and the service life of the safe coating is prolonged. The safe coating has a unique temperature response characteristic and shows excellent conductivity in a normal working temperature range of the battery, and when the temperature of the battery rises to a dangerous threshold due to abnormal conditions, the resistance of the coating is increased in an exponential level, so that a current path is quickly cut off, a thermal runaway chain reaction is effectively prevented, and the service life of the battery is prolonged. Serious safety accidents such as battery combustion and explosion are fundamentally avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and particularly relates to a preparation method of a battery safety coating and an aluminum foil modification application thereof. Background Art

[0002] With the vigorous development of the new energy industry, lithium-ion batteries, as the mainstream energy storage device, play a vital role in electric vehicles, portable electronic devices and other fields. The safety performance of batteries has always been one of the key factors restricting their widespread application. Especially under abnormal conditions such as high temperature and short circuit, thermal runaway inside the battery may lead to serious safety accidents such as combustion and explosion, posing a huge threat to personal safety and property. Therefore, improving the safety performance of batteries, especially in terms of thermal runaway protection, has become an important issue that needs to be urgently addressed in the current field of battery technology.

[0003] At present, a variety of technical means have been proposed and applied to improve the safety performance of batteries. Among them, a common method is to coat a layer of coating with specific functions on the key parts of the battery, such as the surface of the current collector. These coating materials usually have good thermal stability and electrochemical properties. They are designed to respond quickly when the battery temperature rises abnormally through physical or chemical mechanisms, cut off the current path or inhibit the electrochemical reaction inside the battery, thereby effectively preventing the occurrence of thermal runaway. However, existing coating materials and their preparation technologies still have many shortcomings. For example, although some coating materials can improve the safety performance of the battery to a certain extent, their raw material costs are high and the preparation process is complicated, which is not conducive to large-scale industrial production. Other coating materials, although low in cost and simple in preparation process, have less than ideal thermal response characteristics and often require higher temperatures to trigger the protection mechanism, resulting in the battery being unable to respond in time when facing the risk of initial thermal runaway, thereby reducing the overall safety performance of the battery. In addition, some coating materials may have a negative impact on the electrochemical performance of the battery during the coating process, such as reducing the energy density of the battery and increasing the internal resistance. These problems limit the application effect of existing coating materials in the field of battery safety, so staff need to improve them. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a battery safety coating and its aluminum foil modification application, so as to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A battery safety coating comprising the following components:

[0007] Solvent: 20-55wt%, adhesive: 20-45wt%, conductive additive: 15-30wt%.

[0008] Preferably, the solvent is selected from one or more of N-methylpyrrolidone, dimethylformamide, ether, acetone, toluene, dichloromethane, isophorone, and dibasic acid esters.

[0009] Preferably, the adhesive is selected from one or more of polyvinylidene fluoride, styrene-butadiene rubber, polyester, polyurethane, polyethylene, polythiophene, polyaniline, polypyrrole, and polyacetylene.

[0010] Preferably, the conductive additive is selected from one or more of conductive carbon black, carbon nanotubes, graphene, and graphite powder.

[0011] A method for preparing a battery safety coating comprises the following steps:

[0012] The solvent, adhesive and conductive additive are mixed and stirred evenly to obtain the battery safety coating.

[0013] A modified aluminum foil comprising:

[0014] Aluminum foil substrate;

[0015] A safety coating is provided on the surface of the aluminum foil substrate, wherein the safety coating is formed by adhering the battery safety coating according to any one of claims 1 to 4 to the surface of the aluminum foil through a dipping or scraping process and drying. The thickness of the safety coating is 300-700 nm.

[0016] Preferably, the resistance of the safety coating increases rapidly after the temperature exceeds a specific threshold, thereby hindering the electrochemical reaction in the battery cell.

[0017] Preferably, the specific threshold is 90-120°C.

[0018] The modified aluminum foil described in the above solution is used in lithium batteries.

[0019] A lithium battery comprises the modified aluminum foil as a current collector.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The formula of the safety coating of the present invention uses common solvents, adhesives and conductive additives as main components. Not only are the raw materials easily available and low in cost, but the preparation process is simple and efficient. A uniform and stable coating can be obtained only through conventional mixing and stirring, which greatly facilitates industrial production. Secondly, by precisely controlling the ratio of each component and the coating process, an extremely thin, uniform and dense safety coating can be formed on the surface of the aluminum foil. This ultra-thin coating will not have any negative impact on the energy density and electrochemical performance of the battery while ensuring the normal operation efficiency of the battery. More importantly, the safety coating has unique temperature response characteristics. It exhibits excellent electrical conductivity within the operating temperature range, and when the battery temperature rises to a dangerous threshold due to abnormal conditions, the coating resistance will increase exponentially, thereby quickly cutting off the current path and effectively preventing the occurrence of thermal runaway chain reactions, fundamentally avoiding serious safety accidents such as battery combustion and explosion; in addition, the coating construction process of the present invention is highly compatible with existing battery production lines, and conventional methods such as dipping, scraping, and micro-gravure coating are applicable. There is no need to purchase additional expensive equipment or change the existing production process, which not only ensures the consistency of product quality, but also greatly reduces production costs, providing reliable guarantees for large-scale commercial applications. Overall, the present invention not only significantly improves the safety performance of lithium batteries, but also has outstanding advantages in process adaptability, production costs, and industrial promotion, providing a new solution for the development of power battery safety technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a flow chart of the present invention;

[0023] Figure 2 The relationship between resistance, voltage and temperature of the half-cell assembled using aluminum foil coated with a safety coating and pure aluminum foil as current collectors in Example 1;

[0024] Figure 3 This is a half-cell cycle performance test using aluminum foil coated with a safety coating and pure aluminum foil as current collectors in Example 1. DETAILED DESCRIPTION

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0026] Example 1:

[0027] (1) Preparation of battery safety coating

[0028] N-methylpyrrolidone (20 wt%), dibasic acid ester (25 wt%), polyurethane (20 wt%), polythiophene (15 wt%), conductive carbon black (13 wt%) and carbon nanotubes (7 wt%) were put into a stirring kettle and stirred at 800 rpm at room temperature for 2 hours until the mixture was uniformly mixed to obtain a viscous black slurry, which is the battery safety coating.

[0029] (2) Preparation of modified aluminum foil

[0030] The battery safety coating prepared above was evenly coated on a 12μm-thick aluminum foil using a knife-coating process at a coating speed of 3m / min, with a coating gap of 3μm. After coating, the aluminum foil was dried in a 100°C oven for 1.5 hours to completely evaporate the solvent, resulting in a safety coating with a thickness of 320nm. This modified aluminum foil (denoted as Al-PTC) was then obtained.

[0031] (3) Performance testing

[0032] Resistance-temperature characteristics testing: Al-PTC was cut into 12mm diameter electrode sheets, assembled into button-type half-cells using lithium cobalt oxide as the positive electrode active material and a lithium metal sheet as the counter electrode. The cell's resistance change at different temperatures was tested. The results showed that at 120°C, the Al-PTC's resistance rose sharply to over one million times its initial value, effectively blocking the electrochemical reaction and preventing thermal runaway.

[0033] Cycling performance test: In the charge and discharge cycle test at a 1C rate, the Al-PTC assembled battery had an initial efficiency of 91.7%, and the capacity retention rate was still above 95% after 100 cycles. The battery assembled with uncoated pure aluminum foil had an initial efficiency of only 88.4%, and the capacity decayed to 1 / 3 of the initial value after 100 cycles.

[0034] Example 2:

[0035] (1) Preparation of battery safety coating

[0036] N-methylpyrrolidone (15 wt%), isophorone (27 wt%), polyester (20 wt%), polyaniline (20 wt%), conductive carbon black (15 wt%) and graphene (3 wt%) were mixed and stirred at 1000 rpm in a 60 °C water bath for 1.5 h to form a uniformly dispersed coating.

[0037] (2) Preparation of modified aluminum foil

[0038] Aluminum foil was dipped into the coating using a dipping process for 10 seconds at a pull-out speed of 2 mm / s. The foil was then dried in a 100°C oven for 1.5 hours, ultimately forming a safety coating with a thickness of 407 nm.

[0039] (3) Performance testing

[0040] Temperature response test: When assembling a half-cell test, it was found that when the temperature exceeded 100°C, the coating resistance rapidly increased to more than 1 million times the initial value, effectively inhibiting further reaction of the battery.

[0041] Electrochemical performance test: The battery's initial efficiency is 90.2%, and there is no capacity decay after 100 cycles at 1C, indicating that the coating significantly improves the long-term stability of the battery.

[0042] Example 3:

[0043] (1) Preparation of battery safety coating

[0044] Dimethylformamide (25 wt %), dibasic acid ester (30 wt %), polyvinylidene fluoride (10 wt %), polypyrrole (30 wt %), graphene (5 wt %) and carbon nanotubes (10 wt %) were mixed and stirred at 500 rpm for 3 h under ultrasound assistance to ensure that the components were fully dispersed.

[0045] (2) Preparation of modified aluminum foil

[0046] The coating was applied to the surface of the aluminum foil using a micro-gravure coating process, with the coating thickness controlled at 2 μm. It was then dried at 90°C for 2.5 hours to obtain a modified aluminum foil with a safety coating thickness of 510 nm.

[0047] (3) Performance testing

[0048] Thermal stability test: The coating exhibits a significant PTC effect (positive temperature coefficient effect) at 90°C, with a sudden increase in resistance, effectively preventing the battery from overheating.

[0049] Cycle test: The battery's initial efficiency is 90.7%, and the capacity retention rate exceeds 98% after 100 cycles at 1C, which is much better than the battery performance of uncoated aluminum foil.

[0050] Example 4:

[0051] (1) Preparation of battery safety coating

[0052] The same formulation as in Example 1 was used, but the coating process parameters were adjusted so that the coating thicknesses were 300 nm, 500 nm, and 700 nm, respectively.

[0053] (2) Performance comparison

[0054] 300nm coating: The resistance response temperature is slightly higher (130℃), but it has minimal impact on battery energy density.

[0055] 500nm coating: Best balanced performance, trigger temperature of 110℃, and excellent cycle stability.

[0056] 700nm coating: The resistance response is the fastest (triggering at 90°C), but slightly reduces the battery energy density (about 2%).

[0057] Conclusion: Coating thicknesses in the range of 300-700 nm can achieve effective temperature protection, with 500 nm being the optimal choice.

[0058] Embodiment 5:

[0059] (1) Formula comparison

[0060] Formula A: conductive carbon black (20wt%) + graphene (5wt%)

[0061] Formula B: carbon nanotubes (15wt%) + graphite powder (10wt%)

[0062] (2) Test results

[0063] The coating resistance response temperature of formula A is 105℃, and the cycle performance is more stable.

[0064] The coating of Formulation B triggers protection at 95°C, but the cost is higher.

[0065] Application recommendations: Formula B is used for scenarios with high safety requirements, while Formula A is preferred for general applications.

[0066] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A battery safety coating, characterized in that: Includes the following components: Solvent: 20-55wt%, adhesive: 20-45wt%, conductive additive: 15-30wt%.

2. The battery safety coating according to claim 1, characterized in that: The solvent is selected from one or more of N-methylpyrrolidone, dimethylformamide, ether, acetone, toluene, dichloromethane, isophorone, and dibasic acid esters.

3. The battery safety coating according to claim 1, characterized in that: The adhesive is selected from one or more of polyvinylidene fluoride, styrene-butadiene rubber, polyester, polyurethane, polyethylene, polythiophene, polyaniline, polypyrrole, and polyacetylene.

4. The battery safety coating according to claim 1, characterized in that: The conductive additive is selected from one or more of conductive carbon black, carbon nanotubes, graphene, and graphite powder.

5. A method for preparing a battery safety coating, applicable to a battery safety coating according to any one of claims 1 to 4, characterized in that: The following steps are involved: The solvent, adhesive and conductive additive are mixed and stirred evenly to obtain the battery safety coating.

6. A modified aluminum foil, characterized in that: include: Aluminum foil substrate; A safety coating is provided on the surface of the aluminum foil substrate, wherein the safety coating is formed by adhering the battery safety coating according to any one of claims 1 to 4 to the surface of the aluminum foil through a dipping or scraping process and drying. The thickness of the safety coating is 300-700 nm.

7. The modified aluminum foil according to claim 6, characterized in that: The resistance of the safety coating increases rapidly when the temperature exceeds a certain threshold, hindering the electrochemical reaction in the battery cell.

8. The modified aluminum foil according to claim 7, characterized in that: The specific threshold value is 90-120°C.

9. Use of the modified aluminum foil according to any one of claims 6 to 8 in lithium batteries.

10. A lithium battery, characterized in that: The modified aluminum foil according to any one of claims 6 to 8 is used as a current collector.

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