A phase change material composite fiber separator, a preparation method and applications thereof

Abstract

This invention discloses a phase change material composite fiber separator, its preparation method, and its application. The separator's main components are fibers and a phase change material. In this invention, the fibers act as a skeletal support in the separator, exhibiting non-shrinkage at high temperatures and a high porosity. The phase change material in the separator is characterized by a set temperature point; it can absorb a large amount of heat and then undergo a phase change. When a lithium battery malfunctions and the temperature continues to rise to a certain level, the phase change material begins to absorb a large amount of heat, thereby lowering the lithium battery temperature. If the lithium battery cannot cool down after the phase change material absorbs heat, the phase change material will transition from a solid to a liquid state. The gaps between the solid phase change materials will be closed, achieving pore sealing and cutting off the internal ion channels of the lithium battery, thus preventing thermal runaway and providing safety protection.

Description

Technical Field

[0001] This invention relates to the field of energy storage material production, specifically to a phase change material composite fiber membrane, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, while boasting advantages such as high energy density and long cycle life, have experienced numerous fires in lithium-ion energy storage power stations and lithium-ion pure electric vehicles during their large-scale deployment in recent years. These safety incidents have become a key factor limiting the widespread adoption of lithium-ion batteries. Currently, lithium-ion battery separators are primarily made from stretched polyolefin materials. While these materials can close their pores when heated, thus preventing thermal runaway to some extent, polyolefin separators have low thermal shrinkage temperatures, with minimal difference between their pore-closing and shrinkage temperatures. This makes them highly susceptible to shrinkage during use, potentially causing short circuits between the positive and negative electrodes and leading to thermal runaway. Fiber separators, on the other hand, do not shrink when overheated. However, in the event of overheating, they cannot block ion conduction between the positive and negative electrodes, failing to prevent thermal runaway and thus offering less effective safety protection.

[0003] Phase change materials (PCCs) are materials that require the absorption or release of a large amount of latent heat at their phase change temperature to undergo a phase change. Chinese patent application 201710376305.6 discloses a high-heat-resistant lithium-ion battery composite separator and its preparation method. The preparation method involves adding polyvinyl alcohol powder to deionized water, allowing it to swell at room temperature for 10–12 hours, and then stirring at 85–95°C for 4–5 hours to obtain a polyvinyl alcohol solution. Tetraethyl orthosilicate, anhydrous ethanol, and deionized water are mixed and stirred, and ammonia is added dropwise. The mixture is stirred at 40–45°C for 0.5–1 hour to obtain a mixture. This mixture, along with alumina powder, is added to the obtained polyvinyl alcohol solution and stirred at 40–45°C for 10–12 hours to obtain a coating slurry. The slurry is then coated onto the surface of a pretreated polyolefin microporous membrane using a coating method, dried at room temperature, and then vacuum dried to obtain the high-heat-resistant lithium-ion battery composite separator. However, this method requires an extremely complicated process for preparing the modified slurry, with a long production cycle. Moreover, due to the small amount of inorganic heat-resistant material added, it has limited effect on improving the mechanical properties of the diaphragm.

[0004] It should be noted that some existing phase change material membrane patents are based on polyolefin membranes. Although they can utilize phase change materials to absorb latent heat, they cannot change the disadvantage of thermal shrinkage of the membrane at high temperatures, thus having great technical limitations.

[0005] Therefore, it is still necessary to develop a composite membrane that can achieve cooling through phase change and overcome the disadvantages of thermal shrinkage. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a phase change material composite fiber membrane and its preparation method.

[0007] Another object of the present invention is to provide the application of such phase change material composite fiber separator in lithium batteries.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0009] A phase change material composite fiber membrane, the membrane comprising fibers and a phase change material.

[0010] In one specific implementation, the fiber is selected from any one or a combination of plant cellulose, PET fiber, PI fiber, and PA fiber.

[0011] In one specific embodiment, the phase change material is selected from one or more combinations of paraffin, acetic acid, or organic phase change materials; preferably, the phase change temperature of the phase change material is 100℃-500℃.

[0012] In one specific implementation, the phase change material composite fiber membrane contains 10%-90% phase change material by mass.

[0013] On the other hand, the aforementioned method for preparing a phase change material composite fiber membrane includes the following steps:

[0014] S1. Mix the fiber and phase change material evenly in a solvent in a certain proportion to form a mixture;

[0015] S2. Add the mixture to the refiner to refine the fibers and phase change materials into nano-sized particles and mix them thoroughly to form a slurry;

[0016] S3. Apply the slurry evenly onto the filter screen in a certain amount, remove the solvent, and dry to form the shape.

[0017] S4. Roll the S3 material flat to a certain thickness to obtain the finished phase change material composite fiber diaphragm.

[0018] In one specific implementation, the solvent in step S1 is selected from one or more combinations of water, ethanol, acetic acid, acetone, and NMP; preferably, the solid content of the mixture in S1 is 1%-50%.

[0019] In one specific implementation, after grinding in step S2, the fineness of the fibers in the slurry is 30nm-500nm, and the particle size of the phase change material is 10nm-500nm.

[0020] In one specific implementation, the solvent removed in step S3 can be recycled.

[0021] In one specific implementation, the rolling process in step S4 uses a rubber roller or a metal roller; preferably, the rolling thickness is 10μm-100μm.

[0022] In another aspect of the present invention, the application of the aforementioned phase change material composite fiber membrane or the phase change material composite fiber membrane prepared by the aforementioned method in lithium batteries.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] The composite separator of the present invention can absorb heat at the phase change point. After the phase change material absorbs heat and undergoes a phase change, it transforms into an elastic body state, which can seal the pores and cut off the internal ion channels of the lithium battery, thereby preventing thermal runaway. Moreover, even at higher temperatures, the separator will not shrink, and the safety hazards of the separator are completely eliminated.

[0025] This invention utilizes the characteristic of phase change materials to absorb a large amount of heat and undergo a phase change at a specific temperature point. When a lithium battery malfunctions and the temperature continues to rise to a certain level, the phase change material begins to absorb a large amount of heat, thereby reducing the temperature of the lithium battery. If the lithium battery still cannot cool down after the phase change material absorbs heat, the phase change material will transform from a solid state to an elastic state. The gaps between the solid phase change materials will be closed, achieving pore closure and cutting off the internal ion channels of the lithium battery, thereby preventing thermal runaway and providing safety protection. Detailed Implementation

[0026] To make the technical problem to be solved by the present invention, the technical solution, and the beneficial effects clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0027] A method for preparing a phase change material composite fiber membrane includes the following steps:

[0028] S1. The fiber and phase change material are uniformly mixed in a solvent at a certain mass ratio to form a mixture;

[0029] S2. Add the mixture to the refiner to refine the fibers and phase change materials into nano-sized particles and mix them thoroughly to form a slurry;

[0030] S3. Apply the slurry evenly onto the filter screen in a certain amount, remove the solvent, and dry to form the shape.

[0031] S4. Roll S3 flatten it to a certain thickness to obtain the finished phase change material composite fiber diaphragm.

[0032] In step S1, the fiber can be one or more of the following fibers: plant cellulose, PET fiber, PI fiber, PA fiber, etc., preferably plant cellulose. The phase change material can be one or more of the following materials: paraffin wax, acetic acid, or other organic phase change materials, preferably paraffin wax. Specifically, the phase change temperature of the phase change material can be 100℃-500℃, for example, including but not limited to 100℃, 150℃, 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, and 500℃.

[0033] In step S1, the mass percentage of the phase change material can be 10%-90% based on the total mass of the fiber and the phase change material, for example, including but not limited to 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90%; correspondingly, the remaining 90% to 10% is fiber.

[0034] The solvent in step S1 can be one or more combinations of solvents such as water, ethanol, acetic acid, acetone, and NMP, preferably water. The amount of solvent added is such that the solid content of the mixture in S1 is 1%-50%, for example, including but not limited to 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, and 50%.

[0035] After grinding in step S2, the fineness of the fibers in the slurry is 30nm-500nm, such as 30nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, etc.; the particle size of the phase change material is 10nm-500nm, such as 10nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, etc.

[0036] In step S3, the filter screen is composed of multiple layers of mesh, and the coating can be done using conventional processes in the field, such as roller coating or brush coating. After coating, the solvent is removed, for example by vacuum removal, and the removed solvent can be recycled. The drying temperature for drying and shaping can be determined according to the solvent used, for example, the drying temperature is slightly higher than the boiling point of the solvent.

[0037] In step S4, the roller used for rolling can be a rubber roller or a metal roller; the final target thickness for rolling can be 10μm-100μm, for example, including but not limited to 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, and 100μm.

[0038] The above preparation method involves simultaneously grinding and refining fibers and phase change materials (PCMs) into a fine powder, followed by papermaking to form a separator. The PCM composite fiber separator prepared by this invention primarily consists of fibers and PCMs. The fibers in the separator act as a skeletal support, exhibiting non-shrinkage at high temperatures and possessing a high porosity. The PCM in the separator is characterized by its ability to absorb a large amount of heat at a set temperature point before undergoing a phase change. When a lithium battery malfunctions and its temperature continues to rise to a certain level, the PCM begins to absorb a large amount of heat, thereby lowering the lithium battery temperature. If the lithium battery cannot cool down after the PCM absorbs heat, the PCM will transition from a solid to a liquid state, closing the gaps between the solid PCM components, achieving pore closure, and cutting off the internal ion channels of the lithium battery, thus preventing thermal runaway and providing safety protection.

[0039] The phase change material composite fiber membrane prepared by the above method can be used as a membrane in lithium batteries.

[0040] The present invention will be further explained and illustrated below through more specific embodiments, but these do not constitute any limitation.

[0041] Example 1

[0042] 1) Mix plant cellulose and 180℃ phase change paraffin in an aqueous solution at a mass ratio of 1:1, with a solid content of 8%;

[0043] 2) Add the mixture from step 1 to a pulp refiner for refining. Set the refining speed to 1000 r / min and the refining time to 8 h. Control the fineness of the cellulose pulp to about 150 nm and the particle size of the phase change paraffin material to about 50 nm.

[0044] 3) According to the dressing's solid content of 60g / m 2 The surface density is coated and dried to form the shape;

[0045] 4) Roll press to a thickness of 20μm to obtain the finished product.

[0046] Example 2

[0047] 1) PET fibers and 250℃ phase change paraffin were mixed in an aqueous solution at a mass ratio of 1:1, with a solid content of 48%;

[0048] 2) Add the mixture from step 1 to a pulp refiner for refining. Set the refining speed to 2000 r / min and the refining time to 4 h. Control the fineness of the cellulose pulp to be about 450 nm and the particle size of the phase change paraffin material to be about 450 nm.

[0049] 3) According to the dressing's solid content of 60g / m 2 The surface density is coated and dried to form the shape;

[0050] 4) Roll press to a thickness of 80μm to obtain the finished product.

[0051] Example 3

[0052] 1) PA fiber and 480℃ phase change paraffin are mixed in an aqueous solution at a mass ratio of 1:1, with a solid content of 8%;

[0053] 2) Add the mixture from step 1 to a pulp refiner for refining. Set the refining speed to 1500 r / min and the refining time to 6 h. Control the fineness of the cellulose pulp to about 50 nm and the particle size of the phase change paraffin material to about 200 nm.

[0054] 3) According to the dressing's solid content of 60g / m 2 The surface density is coated and dried to form the shape;

[0055] 4) Roll press to a thickness of 50μm to obtain the finished product.

[0056] Comparative Example

[0057] 1) Polypropylene (Dushanzi Petrochemical T98F) is melt-extruded at 180°C using two screw extruders, then calendered through a T-die to obtain two layers of separator substrate, which are then rolled and further biaxially stretched, with a longitudinal stretch of 5 times and a transverse stretch of 3 times, and wound to obtain a heat buffer fiber modified separator for lithium batteries.

[0058] Diaphragm heat resistance test:

[0059] The lithium battery separator samples from Examples 1-3 and the comparative examples were cut into circular pieces with a diameter of 5 cm and placed in an oven at 100°C for heat treatment. The shrinkage of the separator was observed after 10 min and 30 min of heat treatment. The shrinkage rate was calculated as (1 - area of ​​the sample after treatment / area of ​​the sample before treatment) × 100%. As shown in Table 1.

[0060]

[0061] Compared to existing polyolefin separators, this separator allows for a significant increase in baking temperature to approximately 175°C during the battery cell manufacturing process. This reduces baking time, greatly improves efficiency, and significantly reduces moisture content after baking. In battery cells containing this separator, under overcharging or other special conditions, when the temperature rises to 180°C, the phase change material absorbs a large amount of heat, inhibiting further temperature increases. After the phase change material completes its phase change, it transforms from a solid to a liquid state and is evenly distributed around the cellulose, blocking the pores and preventing further lithium ion migration.

[0062] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A phase change material composite fiber diaphragm, characterized in that, The diaphragm comprises fibers and a phase change material; The fiber includes any one or more combinations of plant cellulose, PET fiber, PI fiber, and PA fiber; the phase change material is selected from one or more combinations of paraffin, acetic acid, or organic phase change materials; the phase change temperature of the phase change material is 100℃-500℃. In phase change material composite fiber membranes, the mass percentage of phase change material ranges from 10% to 90%. The fiber and phase change material are uniformly mixed in a solvent in a certain proportion to form a mixture. The mixture is then added to a pulper for pulping, which makes the fiber and phase change material nano-sized. The fineness of the fibers in the slurry is 30nm-500nm, and the particle size of the phase change material is 10nm-500nm.

2. The method for preparing the phase change material composite fiber membrane according to claim 1, characterized in that, Includes the following steps: S1. Mix the fiber and phase change material evenly in a solvent in a certain proportion to form a mixture; S2. Add the mixture to the refiner to refine the fibers and phase change materials into nano-sized particles and mix them thoroughly to form a slurry; S3. The slurry is evenly coated on the filter screen, the solvent is removed, and the slurry is dried and shaped. S4. Roll the membrane blank obtained in S3 to a certain thickness to obtain the finished phase change material composite fiber membrane.

3. The preparation method according to claim 2, characterized in that, The solvent used in step S1 is selected from one or more combinations of water, ethanol, acetic acid, acetone, and NMP.

4. The preparation method according to claim 3, characterized in that, The solid content of the mixture in S1 is 1%-50%.

5. The preparation method according to claim 2, characterized in that, The solvent removed in step S3 can be recycled.

6. The preparation method according to claim 2, characterized in that, The rolling process described in step S4 uses either rubber rollers or metal rollers.

7. The preparation method according to claim 6, characterized in that, The roll-pressed thickness is 10μm-100μm.

8. The application of the phase change material composite fiber separator according to claim 1 or the phase change material composite fiber separator prepared by the method according to any one of claims 2 to 7 in lithium batteries.

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