A method for accelerating the maturation of lithium battery separator

Abstract

The present invention discloses a method for accelerating the maturation of lithium battery diaphragms, the method comprising the following steps: S1, using a large tube core wrapped with a buffer material to roll up the diaphragm for the first time before slitting; S2, subjecting the rolled diaphragm in step S1 to a first high-temperature rapid maturation treatment; S3, slitting and rolling up the diaphragm after the maturation treatment; S4, subjecting the diaphragm rolled up in step S3 to a second high-temperature rapid maturation treatment. The process method for rapid maturation of the diaphragm of the present invention can accelerate the release of internal stress, reduce the maturation time, and reduce the deformation after maturation, that is, reduce the depth of the wave edge. The above-mentioned method for rapid maturation of the diaphragm optimizes the maturation environment on the basis of the process route of traditional diaphragm preparation, without the need to adjust the existing equipment and production lines.

Description

Technical Field

[0001] The invention belongs to the technical field of production and preparation of lithium batteries, and in particular relates to a method for accelerating the maturation of a lithium battery separator. Background Art

[0002] Lithium battery separator is a key component of lithium battery. The main function of the separator is to separate the positive and negative electrodes inside the battery to prevent the positive and negative electrodes from contacting and causing a short circuit. At the same time, it has good ion permeability. The performance of the separator determines the internal resistance, cycle, capacity, safety and other performance of the battery. At present, the mainstream separator material in the market is polyolefin (polyethylene, polypropylene) material (also called base film). In order to further improve the safety characteristics of use in high-power lithium-ion batteries, a layer of inorganic coating is generally added to the surface of the polyolefin separator, such as boehmite, alumina, etc. (also called coated separator). During the production and preparation process, the separator product is wound on the tube core by a winding process for storage and transportation. During the production and preparation process, the diaphragm products are subjected to stretching, traction and other forces. The aging process after winding is to release the internal stress. During this process, the diaphragm will slowly release the stress and the membrane surface will deform. The deformation will increase with the extension of the aging time. The current aging time of the product is about 3-5 days. It can be shipped only after passing the inspection after aging. Long-term aging leads to extended product delivery cycle and increased storage pressure. The longer the aging time, the greater the membrane surface deformation, the more defective products, and the higher the production cost of the enterprise. Summary of the invention

[0003] The purpose of the present invention is to solve the technical problem that the current lithium battery separator products have a long aging time and a large deformation, and need to reduce the aging time and the deformation through a rapid aging method. A method for accelerating the aging of lithium battery separators is provided to solve the problem that the existing products have a long aging time and a large deformation.

[0004] The purpose of the present invention can be achieved through the following technical solutions:

[0005] A method for accelerating the ripening of a lithium battery separator, the method comprising the following steps:

[0006] S1. Use a large tube core wrapped with buffer material to roll up the diaphragm for the first time before slitting;

[0007] S2, subjecting the rolled-up diaphragm in step S1 to a first high-temperature rapid aging treatment;

[0008] S3, slitting and rolling the diaphragm after the curing treatment;

[0009] S4, subjecting the membrane rolled up in step S3 to a second high-temperature rapid aging treatment.

[0010] As a preferred technical solution, the cushioning material in step S1 is a foam cushioning material (EVA material). Further preferably, the outer diameter of the large tube core is 400-650 mm.

[0011] As a preferred technical solution, the temperature range of the first high-temperature rapid aging treatment in step S2 is 40-60°C, the humidity range is 10%-60%, and the aging time is 2-4h;

[0012] As a preferred technical solution, the tube core used for slitting and rolling the aging treated diaphragm in step S3 is a tube core wrapped with a buffer material; the buffer material is a foam cotton buffer material (EVA material); the outer diameter of the tube core is 150 to 300 mm.

[0013] As a preferred technical solution, the temperature range of the second high-temperature rapid aging treatment in step S4 is 40-60° C., the humidity range is 10%-60%, and the aging time is 3-5 hours.

[0014] At present, lithium battery separators have the problems of long aging time and large deformation. The rapid aging method of the present invention can achieve the purpose of reducing aging time and reducing deformation. Lithium battery separators are a type of ultra-high molecular weight polyethylene microporous film material. In the production process, polyethylene is melt-extruded, stretched, shaped, and wound to obtain a separator product. The transformation process is very complicated. During the production process, the separator is affected by the temperature field and tensile stress. Although the stress accumulation in the production process is partially eliminated, due to the characteristics of the polymer itself, a large amount of stress remains in the finished film. In the later aging process, the internal stress is gradually released, resulting in deformation of the membrane surface. The macroscopic manifestation is that the edges and the middle of the membrane surface cannot be flattened, forming a wavy edge defect. Therefore, there is a aging process in the production process of the diaphragm. Traditional aging refers to placing the cut products in a space environment with a temperature of about 25°C and a humidity of about 45% for 3-5 days. During this period, the internal stress of the product is fully released to ensure that the product will not be deformed when it reaches the client. Generally speaking, long-term aging leads to an extension of the product delivery cycle and increased storage pressure. The longer the aging time, the greater the deformation of the membrane surface, and the more defective products there are, resulting in an increase in the production cost of the enterprise. The rapid aging method of the present invention is to perform the first step of aging the diaphragm product under high temperature (40-60°C) conditions for 2-4 hours before slitting, and the finished product after slitting is subjected to the second step of high temperature (40-60°C) aging for 3-5 hours, so that the product can fully release the internal stress in a short time and no longer deform in the later stage. At the same time, the high-temperature aging process needs to be combined with a tube core covered with a buffer material to achieve the best effect.

[0015] Beneficial effects of the present invention:

[0016] The process method for rapid aging of the diaphragm of the present invention first rolls up the diaphragm on a tube core with a buffer material for high-temperature aging treatment, so as to quickly achieve the initial release of the stress inside the diaphragm. The high-temperature environment at this time can accelerate the movement of the polymer chain segments, and cooperate with the buffer material on the tube core to ensure that the stress of the diaphragm is released without deformation of the appearance. The diaphragm after aging is then cut and rolled up, and after slitting, a second high-temperature aging treatment is performed. The product will reach the membrane surface state of the traditional aging for 3-5 days in a short time. This method accelerates the release of internal stress, reduces the aging time, and reduces the deformation after aging, that is, the depth of the wave edge is reduced. The above-mentioned method for rapid aging of the diaphragm optimizes the aging environment on the basis of the process route of traditional diaphragm preparation, without the need to adjust the existing equipment and production lines. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0018] Example 1

[0019] S1. Wrap the surface of the tube core with an outer diameter of 600 mm with foam cotton cushioning material (EVA material), and roll up the diaphragm with a width of 4000 mm for the first time;

[0020] S2, placing the membrane rolled up in step S1 in an environment with a temperature of 43-45° C. and a humidity of 40%-45% for 2 hours for maturation;

[0021] S3, the film processed in step S2 is cut and rolled up, the outer diameter of the rolled tube core is 203 mm, and wrapped with foam cotton cushioning material (EVA material);

[0022] S4, placing the membrane rolled up in step S3 in an environment with a temperature of 46-48° C. and a humidity of 30%-35% for 3 hours for maturation.

[0023] Example 2

[0024] S1. Wrap the surface of the tube core with an outer diameter of 600 mm with foam cotton cushioning material (EVA material), and roll up the diaphragm with a width of 4000 mm for the first time;

[0025] S2, placing the membrane rolled up in step S1 in an environment with a temperature of 48-50° C. and a humidity of 30%-35% for 3 hours for maturation;

[0026] S3, the film processed in step S2 is cut and rolled up, the outer diameter of the rolled tube core is 203 mm, and wrapped with foam cotton cushioning material (EVA material);

[0027] S4, placing the membrane rolled up in step S3 in an environment with a temperature of 50-52° C. and a humidity of 20%-25% for 4 hours for maturation.

[0028] Comparative Example

[0029] S1. Wrap the surface of the tube core with an outer diameter of 600 mm with foam cotton cushioning material (EVA material), and roll up the diaphragm with a width of 4000 mm for the first time;

[0030] S2, the film processed in step S1 is cut and rolled up, the outer diameter of the rolled tube core is 203 mm, and wrapped with foam cotton cushioning material (EVA material);

[0031] S3, placing the membrane rolled up in step S2 in an environment with a temperature of 25° C. and a humidity of 35% for 4 days for maturation.

[0032] Table 1 Diaphragm wave edge test results

[0033]

[0034] The test results of the wave edges of Examples 1 and 2 and the comparative example are shown in Table 1. The wave edges (left), (middle), and (right) of Examples 1 and 2 were all lower than those of the comparative example after the test was performed 1 day after the aging was completed. The wave edges (left), (middle), and (right) of Examples 1 and 2 and the comparative example did not undergo significant changes after the test was performed 3 days after the aging was completed, proving that the internal stress was fully released. The test results show that Examples 1 and 2 can reach a stable state in a short time. Comparing Examples 1 and 2, it is better to use a temperature of 43 to 45°C for the first winding aging and a time of 2h, and a high temperature aging of 46 to 48°C for the second aging and a time of 3h.

Claims

1. A method for accelerating the ripening of a lithium battery separator, characterized in that: The method comprises the following steps: S1. Use a large tube core wrapped with buffer material to roll up the diaphragm for the first time before slitting; S2, subjecting the rolled diaphragm in step S1 to a first high-temperature rapid aging treatment: the temperature range is 40-60° C., the humidity range is 10%-60%, and the aging time is 2-4 hours; S3, slitting and rolling the diaphragm after the curing treatment; S4. The membrane rolled up in step S3 is subjected to a second high-temperature rapid aging treatment: the temperature range is 40-60° C., the humidity range is 10%-60%, and the aging time is 3-5 hours.

2. The method for accelerating the ripening of a lithium battery separator according to claim 1, characterized in that: The cushioning material described in step S1 is a foam cushioning material.

3. The method for accelerating the ripening of a lithium battery separator according to claim 1 or 2, characterized in that: The outer diameter of the large tube core in step S1 is 400-650 mm.

4. The method for accelerating the ripening of a lithium battery separator according to claim 1, characterized in that: In step S3, the tube core used when slitting and rolling the aging treated diaphragm is the tube core wrapped with the buffer material.

5. The method for accelerating the ripening of a lithium battery separator according to claim 4, characterized in that: The cushioning material is a foam cushioning material; the outer diameter of the tube core is 150-300 mm.

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