Glass fiber cloth coated diaphragm for lithium battery and preparation method of glass fiber cloth coated diaphragm

Abstract

The invention relates to the technical field of coated diaphragms, in particular to a glass fiber cloth coated diaphragm for a lithium battery and a preparation method of the glass fiber cloth coated diaphragm. The diaphragm comprises a glass fiber cloth base membrane layer and a composite coating coated on one side or two sides of the glass fiber cloth base membrane layer, the composite coating can be selected from one of a PVDF adhesive layer, an aramid fiber layer, a PP layer or a PE layer, and the PVDF adhesive layer is prepared by dissolving PVDF powder, polyvinyl alcohol and polyoxyethylene alkylphenol ether in N-methyl pyrrolidone. The aramid fiber layer is prepared by dissolving aramid fiber, polyurethane and sodium polyacrylate in dimethylformamide, and the PP / PE layer is prepared by dissolving PP / PE resin, polyacrylic acid and polyethylene glycol in methylbenzene; the preparation method comprises the following steps: ultrasonically cleaning the glass fiber cloth base membrane with deionized water, drying, coating selected slurry to a required thickness by using a coating machine, and finally drying and curing to obtain a finished product. Through material selection and process control, the prepared diaphragm has excellent flame retardance, electrolyte wettability and mechanical strength, and the safety performance and comprehensive performance of the lithium battery can be remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coated diaphragm, in particular to a glass fiber cloth coated diaphragm for lithium battery and a preparation method thereof. BACKGROUND

[0002] With the rapid expansion of the electric vehicle industry and the development of portable electronic devices towards high performance, lithium ion batteries are facing increasingly stringent performance requirements. As a key component inside the battery, the performance of the diaphragm is directly related to the ion transmission efficiency, electrode interface stability and battery safety mechanism. Especially in the current high energy density battery system, the diaphragm needs to meet the dimensional stability at high temperature, uniformity of electrolyte infiltration and resistance to dendrite puncture at the same time. These characteristics have become the core elements to ensure the long cycle life and safe operation of the battery.

[0003] At present, the market mainstream still uses polyolefin diaphragm. Although this kind of material has the convenience of processing, it has obvious defects: first, its heat resistance is insufficient - polyethylene melts and shrinks at about 130℃, and the heat resistance of polypropylene is slightly higher but still limited. When the battery is overcharged or short-circuited, the diaphragm shrinks easily, causing the risk of thermal runaway. Second, the compatibility with electrolyte is poor - the surface properties of the material lead to slow electrolyte infiltration, not only prolonging the production cycle, but also affecting the ion distribution uniformity during the battery charging and discharging process. Third, the mechanical strength is weak - it is easily punctured by active material particles during battery assembly or long-term cycling. In order to improve these problems, the industry has developed technical solutions such as ceramic coated diaphragm, but the addition of a large number of inorganic particles leads to a decrease in flexibility.

[0004] Therefore, it is an urgent need for the industry to develop a new type of diaphragm that has excellent flame retardancy, good electrolyte affinity, high mechanical strength and controllable cost. In recent years, glass fiber cloth based diaphragm has attracted attention due to its unique three-dimensional network structure and excellent high temperature resistance. However, untreated glass fiber based membrane has obvious shortcomings: on the one hand, the fiber surface is prone to side reactions with electrolyte, accelerating the performance degradation of the battery; on the other hand, the binding force between fibers is weak, and the structure is prone to powdering during long-term use. In view of these bottlenecks, surface modification and structure strengthening of glass fiber based membrane through functional polymer coating become an effective way to break through the technical difficulties, by precisely selecting the coating material, optimizing the interface bonding process and accurately controlling the coating thickness, so as to comprehensively improve the overall performance of the diaphragm. SUMMARY

[0005] Based on the problems in the above background art, the present application provides a glass fiber cloth coated diaphragm for lithium battery, which comprises a base film layer made of glass fiber cloth and a composite coating layer, the thickness of the glass fiber layer is 20μm, the composite coating layer is coated on one side or both sides of the base film layer, and the thickness of the composite coating layer coated on the base film layer is 3-5μm. The glass fiber cloth with a thickness of 20μm is selected as the base film to ensure that the base film has good mechanical strength and is convenient for subsequent coating process operation.

[0006] Preferably, the composite coating layer comprises but is not limited to one of a PVDF glue layer, an aramid layer, a PP layer or a PE layer.

[0007] Preferably, the composite material further comprises a ceramic material such as alumina, silicon dioxide, etc. as the main component of the coating layer.

[0008] Taking alumina as an example, 60% alumina particles and 8% polyacrylic acid are dispersed in solvent water in proportion, and stirred uniformly to form a slurry. The solid content of the slurry needs to be controlled to ensure uniformity of coating.

[0009] Preferably, the PVDF glue layer is prepared by adding 10% PVDF powder, 2% polyvinyl alcohol and 1% polyoxyethylene alkyl phenol ether into N-methyl pyrrolidone in terms of mass fraction.

[0010] Preferably, the aramid layer is prepared by adding 8% aramid fiber, 1.5% polyurethane and 0.5% sodium polyacrylate into dimethylformamide in terms of mass fraction.

[0011] Preferably, the PP layer or the PE layer is prepared by adding 12% PP or PE, 1% polyacrylic acid and 0.8% polyethylene glycol into toluene.

[0012] Preferably, a preparation method of a glass fiber cloth coated diaphragm for lithium battery comprises the following steps,

[0013] Step one, the glass fiber cloth base film layer is first cleaned with deionized water for 10-15 minutes to remove impurities and oil stains on the surface of the glass fiber base film, and then dried in an oven at 80-120℃ for 30 minutes for standby; ensure that the base film is completely dried to provide a clean and dry substrate for subsequent coating process.

[0014] Step two, each component of the composite coating layer is weighed according to a certain mass fraction, and the composite coating slurry is obtained after stirring uniformly; ensure that the glue solution has good coating performance.

[0015] Step three, the uniformly stirred composite coating slurry is uniformly coated on one side or both sides of the base film layer using a coating machine.

[0016] Step four, place the coated separator in the oven at a predetermined temperature to dry and cure to obtain the finished product.

[0017] Preferably, in step three, the coating speed of the composite coating is 0.8-1.2 m / min. Preferably, the coating speed of the PVDF glue layer in the composite coating is 1 m / min, and the coating thickness of the PVDF glue layer in the composite coating is 5 μm, which not only ensures the coating performance of the glue solution, but also ensures the density and uniformity of the PVDF glue layer. The coating thickness of the PVDF glue layer is 5 μm, which not only improves the thermal stability and electrolyte wettability of the separator, but also avoids the decrease of porosity caused by the over-thickness of the coating layer; the coating speed of the aramid layer in the composite coating is 0.8 m / min, the coating thickness of the aramid layer in the composite coating is 3 μm, and the coating speed of the PP layer or PE layer in the composite coating is 1.2 m / min. The coating thickness of the PP layer or PE layer in the composite coating is 4 μm. The thermal stability and electrolyte wettability of the separator are improved, and the decrease of porosity caused by the over-thickness of the coating layer is avoided.

[0018] Preferably, in step four, the drying temperature of the composite coating is 60-120℃, and the curing time of the composite coating is 1-2 hours.

[0019] Preferably, the drying temperature of the PVDF glue layer in the composite coating is 80℃, and the curing time is 2 hours; the drying temperature of the aramid layer in the composite coating is 120℃, and the curing time is 1 hour; the drying temperature of the PP layer or PE layer in the composite coating is 60℃, and the curing time is 1.5 hours.

[0020] Compared with the prior art, the glass fiber cloth coated separator for lithium battery and the preparation method thereof proposed by the application have achieved significant improvement in many key performance indicators and have brought significant beneficial effects.

[0021] Firstly, in terms of flame retardant performance, the application uses glass fiber cloth as the base film layer and composites a functional polymer coating layer such as a PVDF glue layer and an aramid layer, which significantly enhances the high temperature resistance and flame retardant performance of the separator, effectively prevents the safety risk caused by thermal runaway of the battery under high temperature or extreme conditions, and greatly improves the safety performance of the lithium battery.

[0022] Secondly, in terms of electrolyte wettability, the composite coating is carefully designed and optimized, so that the separator can quickly soak the electrolyte, which not only shortens the production cycle of the battery, but also improves the uniformity of ion distribution during the charging and discharging process of the battery, which helps to improve the overall performance and cycle life of the battery.

[0023] In addition, in terms of mechanical strength, the combination of the glass fiber cloth-based membrane layer and the functional coating layer significantly enhances the structural stability and puncture resistance of the separator, effectively resisting the puncture of active material particles during battery assembly or long-term cycling, preventing internal short circuit of the battery, and further improving the safety and reliability of the battery. Meanwhile, through optimization of material selection and process control, the production cost is effectively controlled while maintaining or improving the performance of the separator, making the combination of the glass fiber cloth-based membrane layer and the functional coating layer more economical and market competitive.

[0024] In summary, the glass fiber cloth-coated separator for lithium batteries and the preparation method thereof proposed by the present application have significant advantages in terms of flame retardancy, electrolyte wettability, mechanical strength, and cost controllability, providing strong protection for the safe operation and long cycle life of lithium batteries, and have broad application prospects and market value. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0026] A preparation method of a glass fiber cloth-coated separator for lithium batteries, comprising the following steps,

[0027] Step one, the glass fiber cloth-based membrane layer is first cleaned with deionized water for 10 minutes, and then dried in an oven at 80℃ for 30 minutes for standby;

[0028] Step two, 10% PVDF powder, 2% polyvinyl alcohol and 1% polyoxyethylene alkyl phenol ether are dissolved in N-methyl pyrrolidone to prepare a composite coating slurry PVDF glue layer, and then stirred uniformly for standby;

[0029] Step three, the uniformly stirred composite coating slurry is uniformly coated on one side or both sides of the base membrane layer using a coating machine; the coating speed of the PVDF glue layer is 1m / min, and the coating thickness of the PVDF glue layer is 5μm;

[0030] Step four, the coated separator is placed in an oven at a preset temperature for drying and curing, the PVDF glue layer is dried at 80℃, and the curing time is 2 hours, and the finished product is obtained.

[0031] The traditional lithium battery separator is mostly made of polyolefin material, and its limiting oxygen index (LOI) is usually less than 20%, which belongs to flammable material. When the battery overheats or thermal runaway occurs, such separators are easy to burn and release a large amount of heat, which aggravates the thermal runaway process of the battery, and even causes fire or explosion. The separator in the embodiment of the application uses glass fiber cloth as the base film layer and is coated with a PVDF glue layer composite coating. The glass fiber cloth itself has excellent high-temperature resistance, and its LOI value is as high as more than 35%, which belongs to non-combustible material. It can effectively resist the invasion of fire and maintain stable physical and chemical properties in a high-temperature environment, preventing the aggravation of battery thermal runaway caused by the burning of the separator. At the same time, the PVDF glue layer is also optimized and designed to work synergistically with the glass fiber cloth base film layer, further improving the flame retardant performance of the separator, effectively resisting the invasion of heat, maintaining stable physical and chemical properties, preventing internal short circuit of the battery caused by the thermal shrinkage or melting of the separator, thereby greatly reducing the risk of battery fire and explosion, and providing more reliable safety protection for lithium batteries.

[0032] Embodiment 2

[0033] A preparation method of a glass fiber cloth coated separator for lithium batteries, comprising the following steps,

[0034] Step one, the glass fiber cloth base film layer is first cleaned with deionized water for 15 minutes, and then dried in an oven at 120℃ for 30 minutes for standby;

[0035] Step two, 10% PVDF powder, 2% polyvinyl alcohol and 1% polyoxyethylene alkyl phenol ether are dissolved in N-methyl pyrrolidone to prepare a composite coating slurry PVDF glue layer, and then stirred uniformly for standby;

[0036] Step three, use a coating machine to uniformly coat the uniformly stirred composite coating slurry on one side or both sides of the base film layer; the coating speed of the PVDF glue layer is 1.2 m / min, and the coating thickness of the PVDF glue layer is 5 μm;

[0037] Step four, place the coated separator in a preset temperature oven for drying and curing, the PVDF glue layer drying temperature is 120℃, and the curing time is 2 hours, to obtain the finished product.

[0038] Embodiment 3

[0039] A preparation method of a glass fiber cloth coated separator for lithium batteries, comprising the following steps,

[0040] Step one, the glass fiber cloth base film layer is first cleaned with deionized water for 12 minutes, and then dried in an oven at 100℃ for 30 minutes for standby;

[0041] Step two, 10% PVDF powder, 2% polyvinyl alcohol and 1% polyoxyethylene alkyl phenol ether are dissolved in N-methyl pyrrolidone to prepare a composite coating slurry PVDF glue layer, and then stirred uniformly for standby;

[0042] Step three, the uniformly stirred composite coating slurry is uniformly coated on one side or both sides of the base film layer by using a coating machine; the coating speed of the PVDF glue layer is 0.8 m / min, and the coating thickness of the PVDF glue layer is 4 μm;

[0043] Step four, the coated separator is placed in an oven at a preset temperature for drying and curing, the PVDF glue layer is dried at 100℃, and the curing time is 1.5 hours, and the finished product is obtained.

[0044] Example 4

[0045] A preparation method of a glass fiber cloth coated separator for lithium battery, comprising the following steps,

[0046] Step one, the glass fiber cloth base film layer is first ultrasonically cleaned with deionized water for 14 minutes, and then dried in an oven at 90℃ for 30 minutes for standby;

[0047] Step two, 10% PVDF powder, 2% polyvinyl alcohol and 1% polyoxyethylene alkyl phenol ether are dissolved in N-methyl pyrrolidone to prepare a composite coating slurry PVDF glue layer, and then stirred uniformly for standby;

[0048] Step three, the uniformly stirred composite coating slurry is uniformly coated on one side or both sides of the base film layer by using a coating machine; the coating speed of the PVDF glue layer is 0.9 m / min, and the coating thickness of the PVDF glue layer is 3 μm;

[0049] Step four, the coated separator is placed in an oven at a preset temperature for drying and curing, the PVDF glue layer is dried at 70℃, and the curing time is 1 hour, and the finished product is obtained.

[0050] Example 5

[0051] A preparation method of a glass fiber cloth coated separator for lithium battery, comprising the following steps,

[0052] Step one, the glass fiber cloth base film layer is first ultrasonically cleaned with deionized water for 10 minutes, and then dried in an oven at 80℃ for 30 minutes for standby;

[0053] Step two, 8% aramid fiber, 1.5% polyurethane, and 0.5% polyacrylic acid sodium are dissolved in dimethylformamide to prepare a composite coating slurry aramid layer, and then stirred uniformly for standby;

[0054] Step three, use a coating machine to uniformly coat the uniformly stirred composite coating slurry on one side or both sides of the base film layer; the coating speed of the aramid layer in the composite coating is 0.8 m / min, and the coating thickness of the aramid layer is 3 μm;

[0055] Step four, place the coated separator in a oven at a preset temperature for drying and curing, the PVDF glue layer drying temperature is 80℃, and the curing time is 2 hours, to obtain the finished product.

[0056] The glass fiber cloth coated separator for lithium battery prepared in this embodiment has a significant advantage in flame retardancy compared to traditional materials. Traditional lithium battery separators are prone to burning and releasing a large amount of heat when the battery overheats or experiences thermal runaway, exacerbating the thermal runaway process of the battery and even causing a fire or explosion. The separator in this embodiment uses glass fiber cloth as the base film layer and is coated with an aramid layer composite coating. The glass fiber cloth itself has excellent high-temperature resistance, with an LOI value of 35% or higher, making it a difficult-to-burn material. Aramid fiber, as a high-performance flame-retardant fiber, has an LOI value of 28%-32%, which is a difficult-to-burn material (LOI = 26%-34%) with excellent flame-retardant properties. In a high-temperature environment, the separator can effectively resist the invasion of flames, maintain stable physical and chemical properties, and prevent the exacerbation of battery thermal runaway caused by separator burning, thereby greatly reducing the risk of battery fire and explosion, providing more reliable safety protection for lithium batteries.

[0057] Example 6

[0058] A method for preparing a glass fiber cloth coated separator for lithium battery, comprising the following steps,

[0059] Step one, first clean the glass fiber cloth base film layer with deionized water for 10 minutes, then dry it in an oven at 80℃ for 30 minutes for standby;

[0060] Step two, dissolve 12% PP or PE, 1% polyacrylic acid, and 0.8% polyethylene glycol in toluene to prepare a composite coating slurry PP layer or PE layer, and stir uniformly for standby;

[0061] Step three, use a coating machine to uniformly coat the uniformly stirred composite coating slurry on one side or both sides of the base film layer; the coating speed of the PP layer or PE layer in the composite coating is 1.2 m / min, and the coating thickness of the PP layer or PE layer is 4 μm;

[0062] Step four, place the coated separator in a oven at a preset temperature for drying and curing, the PVDF glue layer drying temperature is 80℃, and the curing time is 2 hours, to obtain the finished product.

[0063] The glass fiber cloth coated diaphragm for lithium battery prepared by the embodiment of the present application has a significant advantage in flame retardancy compared with traditional materials. Traditional lithium battery diaphragms use polyolefin materials such as polypropylene (PP) and polyethylene (PE), and the limiting oxygen index (LOI) of which is usually less than 20%, belonging to flammable materials. When the battery overheats or experiences thermal runaway, such diaphragms are easy to burn and release a large amount of heat, aggravating the thermal runaway process of the battery, and even causing a fire or explosion. The diaphragm in the embodiment of the present application uses glass fiber cloth as the base film layer and is coated with a PP layer or a PE layer composite coating. The glass fiber cloth itself has excellent high-temperature resistance, and the LOI value is as high as more than 35%, belonging to a difficult-to-burn material, which can effectively resist the invasion of fire and maintain stable physical and chemical properties in a high-temperature environment, preventing the aggravation of battery thermal runaway caused by diaphragm burning. At the same time, the PP or PE composite coating is also optimally designed to synergize with the glass fiber cloth base film layer, further improving the flame retardant performance of the diaphragm, thereby greatly reducing the risk of battery fire and explosion, and providing more reliable safety protection for lithium batteries.

[0064] The above is only the preferred embodiment of the present application, and it should be pointed out that the above preferred embodiment should not be regarded as a limitation of the present application, and the protection scope of the present application should be limited by the scope defined by the claims. For ordinary skilled persons in the art, several improvements and refinements can be made without departing from the spirit and scope of the present application, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A glass-fiber cloth coated separator for lithium batteries, characterized by: The base film layer is made of glass fiber cloth, the thickness of the base film layer is 20 μm, and the composite coating is coated on one side or both sides of the base film layer, and the thickness of the composite coating coated on the base film layer is 3-5 μm.

2. The glass-fiber cloth-coated separator for a lithium battery according to claim 1, characterized by: The composite coating includes but is not limited to one of a PVDF glue layer, an aramid layer, a PP layer, and a PE layer.

3. The glass-fiber cloth coated separator for lithium batteries according to claim 2, characterized in that: The PVDF glue layer is prepared by adding 10% PVDF powder, 2% polyvinyl alcohol, and 1% polyoxyethylene alkyl phenol ether into N-methyl pyrrolidone.

4. The glass-fiber cloth coated separator for lithium batteries according to claim 2, characterized by: The aramid layer is prepared by adding 8% aramid fiber, 1.5% polyurethane, and 0.5% polyacrylic acid sodium into dimethylformamide.

5. The glass-fiber cloth-coated separator for a lithium battery according to claim 2, characterized by: The PP layer or the PE layer is prepared by adding 12% PP or PE, 1% polyacrylic acid, and 0.8% polyethylene glycol into toluene.

6. A method for preparing a glass fiber cloth coated separator for lithium batteries according to any one of claims 1-5, characterized in that: The method comprises the following steps, In step one, the glass fiber cloth base film layer is first cleaned with deionized water for 10-15 minutes, and then dried in an oven at 80-120°C for 30 minutes for standby use. In step two, the components of the composite coating are weighed according to a certain mass fraction, and the composite coating slurry is obtained after stirring uniformly. In step three, the uniformly stirred composite coating slurry is uniformly coated on one side or both sides of the base film layer using a coating machine. In step four, the coated separator is placed in an oven at a preset temperature for drying and curing to obtain the finished product.

7. The method for preparing a glass fiber cloth coated separator for lithium batteries according to claim 6, characterized in that: In step three, the coating speed of the composite coating is 0.8-1.2 m / min.

8. The method for preparing a glass fiber cloth coated separator for lithium batteries according to claim 7, characterized in that: The coating speed of the PVDF glue layer in the composite coating is 1 m / min, the coating thickness of the PVDF glue layer in the composite coating is 5 μm, the coating speed of the aramid layer in the composite coating is 0.8 m / min, the coating thickness of the aramid layer in the composite coating is 3 μm, the coating speed of the PP layer or the PE layer in the composite coating is 1.2 m / min, and the coating thickness of the PP layer or the PE layer in the composite coating is 4 μm.

9. The method for preparing a glass fiber cloth coated separator for lithium batteries according to claim 6, characterized in that: In step four, the drying temperature of the composite coating is 60-120°C, and the curing time of the composite coating is 1-2 hours.

10. The method for preparing a glass fiber cloth coated separator for lithium batteries according to claim 9, characterized in that: The drying temperature of the PVDF glue layer in the composite coating is 80°C, and the curing time is 2 hours; the drying temperature of the aramid layer in the composite coating is 120°C, and the curing time is 1 hour; the drying temperature of the PP layer or the PE layer in the composite coating is 60°C, and the curing time is 1.5 hours.