CN113146911B - A kind of high temperature resistant diaphragm, its dry preparation method and use - Google Patents

Abstract

The invention discloses a method for preparing a diaphragm. The method comprises the following steps: 1) mixing a fiberizable polymer powder and a high temperature resistant polymer, and under the action of shearing force, the fiberizable polymer powder is mixed Wire drawing to form fibers to obtain a mixture; 2) heat-pressing the mixture to a preset thickness to obtain a diaphragm; wherein, the high temperature-resistant polymer is a polymer that exists stably at the operating temperature of the diaphragm. It solves the problems that the existing PP and PE type polyolefin materials are not resistant to high temperature, the wettability of the electrolyte is poor, and the problems of the high preparation cost of the existing diaphragm.

Description

A kind of high temperature resistant diaphragm, its dry preparation method and use

technical field

The invention relates to the technical field of batteries, relates to a separator, a preparation method and uses thereof, and in particular relates to a high temperature resistant separator, a dry preparation method thereof and a battery.

Background technique

With the rapid development of new energy vehicles, the requirements for energy density and safety performance of automotive energy storage devices are constantly increasing. Lithium-ion batteries with the advantages of high specific energy, high specific power, good cyclability, and no environmental pollution are considered to be the best choice. It is expected that by 2025, the energy density of power batteries will reach more than 500Wh/kg. With the continuous improvement of the energy density of power batteries, their safety performance is also facing more severe tests. In addition, in recent years, electronic products have been widely popularized. Lithium batteries as their power sources have received more and more attention due to their advantages of light weight, small size, high operating voltage, high energy density, high output power, high charging efficiency and no memory effect. . As a result, the requirements for the safety and performance of lithium batteries are becoming higher and higher.

As an important component of lithium batteries, the separator has the functions of isolating the positive and negative plates, preventing short circuits and providing lithium ion transport channels. Therefore, improving the battery safety performance and reducing the production cost of separators is one of the main goals of future lithium-ion battery research.

At present, the marketed lithium battery separators are all based on polypropylene (PP) or polyethylene (PE). However, PP and PE polyolefin materials have low surface energy and lyophobic properties, which lead to poor wettability of such separators to the electrolyte, which affects the cycle life of the battery. In addition, the thermal deformation temperature of these two materials is relatively low (PP thermal deformation temperature is 80-85 °C, PP is 100 °C), and if the temperature is too high, serious thermal shrinkage will occur, so this type of diaphragm is not suitable for high temperature environments. At the same time, the separator, as a critical component in the safe operation of the battery, needs to protect the safety of the battery under special circumstances. In special circumstances such as accidents, punctures, and battery abuse, the separator is partially damaged or deformed, which will directly lead to positive and negative electrodes. contact, which will cause a violent battery reaction and cause the battery to catch fire and explode.

Therefore, in order to improve the safety of lithium-ion batteries and ensure the safe and smooth operation of batteries, it is necessary to find a safer separator system.

CN101974828 discloses a technology of polyimide nanofiber lithium ion battery separator prepared by electrospinning. The PI separator prepared by this technology has the characteristics of high porosity and high temperature resistance, but the electrospinning process is complicated and the production efficiency is low , is not conducive to large-scale industrial production.

CN101645497A prepares a polyamic acid film by mixing a polyamic acid solution and a pore-forming agent, then takes out the pore-forming agent from the film through a non-solvent, and finally prepares a porous polyimide lithium battery diaphragm by thermal imidization. Compared with electrospinning, this scheme relatively improves the production efficiency, but requires multiple chemical reactions in the experimental process, which involves long-term stirring and drying. It is difficult to ensure that the added monomers have just completed the reaction to generate polyimide, and it is also difficult to ensure that the pore-forming agent is removed cleanly. In addition, the process of using the solvent will also affect the experimenter and surrounding areas. The overall purpose of environmental protection is not to use lithium-ion batteries to cause harm to the environment.

SUMMARY OF THE INVENTION

In view of the above problems existing in the prior art, the purpose of the present invention is to provide a separator, its preparation method and use, and in particular to a high temperature resistant separator, its dry method preparation method and battery. It solves the problems that the existing PP and PE type polyolefin materials are not resistant to high temperature, the wettability of the electrolyte solution is poor, and the problems of the high preparation cost of the existing diaphragm are solved.

The applicant's previous application (application number: 202010723671.6) provides a composite separator and a preparation method thereof, which utilizes thermoplastic polymers to be fibrillated under high-speed shear to construct a polymer network with abundant pores and is used to disperse fillers, but its It does not have high temperature resistance. When the cell works in an extremely high temperature environment, the polymer will reach the glass transition temperature and undergo deformation such as bending and curling, resulting in the short circuit between the positive and negative electrodes of the cell, resulting in dangers such as burning and explosion. This patent uses PI type high temperature resistant polymer material as the main material of the diaphragm, which greatly improves the temperature application range of the diaphragm and effectively improves the safety of the battery.

For achieving the above object, the present invention adopts the following technical solutions:

In a first aspect, the present invention provides a method for preparing a diaphragm, the method comprising the following steps:

(1) mixing the fiberizable polymer powder and the high temperature resistant polymer, and drawing the fiberizable polymer powder under the action of shearing force to form fibers to obtain a mixture;

(2) hot-pressing the mixture described in step (1) to a preset thickness to obtain a diaphragm;

Wherein, the high temperature resistant polymer is a polymer that exists stably at the operating temperature of the separator.

The invention proposes to use a dry film-making technology to prepare a diaphragm, specifically to prepare a self-supporting diaphragm. The fiberized polymer is fiberized by drawing, and then hot-pressed to form a film. The polymer fibers converted from the fiberizable polymer are randomly overlapped during the hot-pressed film-forming process to form a polymer network structure with rich pores. The high temperature resistant polymer particles are dispersed and bonded on the polymer network structure to obtain a separator. The existence of high temperature resistant polymeric ions increases the service temperature of the diaphragm, avoids the shortage of low hot-melt temperature of conventional PP and PE diaphragms, and greatly enriches the types of optional materials for the diaphragm (the conventional wet process is only suitable for PE, and most of PP dry process). In the preparation process of the method of the present invention, the material ratio and the hot pressing parameters can be adjusted to adjust the porosity of the diaphragm.

Specifically, in step (1), dry mixing is performed, and the fiberizable polymer and the high-temperature resistant polymer are mixed at a high speed according to a certain ratio to make a dry powder with a certain viscosity. During the high-speed stirring process , the fiberizable polymer is drawn and fiberized, and the high temperature resistant polymer particles are bonded to give the powder a certain viscosity. In step (2), hot pressing the film is performed, and the powder obtained by dry mixing is pressed into a diaphragm material of a certain thickness by a certain hot pressing method; The pressure moves to form a network structure, and at the same time, the bonding effect between the substances is increased.

In the present invention, the form of the raw material high temperature resistant polymer is not limited, for example, it may be a high temperature resistant polymer powder. The following are the preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical purposes and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

In the present invention, the type of the fiberizable polymer powder is not particularly limited, as long as it can be drawn into fiber under the action of high-speed stirring force. Including but not limited to at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR) and polyacrylic acid (PAA), preferably PTFE.

Preferably, the fiberizable polymer powder in step (1) is a high-temperature-resistant fiberizable polymer powder, which exists stably at the operating temperature of the separator. This kind of polymer that can be both fiberized and high temperature resistant is used in combination with the above high temperature resistant polymer to synergistically improve the service temperature of the diaphragm.

In the present invention, the "use temperature of the diaphragm" refers to the temperature of the environment where the diaphragm is located, and the use temperature is generally -40°C to 300°C.

Preferably, the high temperature resistant polymer in step (1) includes polyimide PI, polyethylene terephthalate PET, polyamide PA, polyacrylonitrile PAN, polymetaphenylene isophthalamide PMIA , any one or a combination of at least two in polyparaphenylene terephthalamide PPTA, polyvinyl alcohol or polyparaphenylene benzodiazole PBO, such as the combination of PI and PET, the combination of PI and PA , the combination of PI and PAN, the combination of PI and PNIA, the combination of PI, PET and PPTA, the combination of PET, PA and PBO, the combination of PAN, PMIA and PPTA, etc., preferably PI. PI not only has good high temperature resistance, but also has excellent electrolyte wettability, which can effectively improve the liquid absorption rate and liquid retention rate of the diaphragm.

Preferably, in the mixture described in step (1), the mass ratio of the high temperature resistant polymer to the fiberizable polymer powder is 70:30-98:2, for example 70:30, 75:25, 77:3: 23, 80:20, 85:15, 90:10, 92:8 or 95:5, etc., preferably 90:10-95:5. Within the above range, a high temperature resistant separator with excellent performance can be obtained on the premise of forming a polymer network structure and exerting its good bonding effect.

Preferably, in the mixture of step (1), the fiberizable polymer powder is PTFE, and the content is 5%-10% (for example, 5%, 6%, 7%, 8%, 9% or 10%, etc. ); the high temperature resistant polymer is PI with a content of 90%-95% (eg 90%, 92%, 94%, 94.5% or 95%, etc.). In the mixture, the higher the PTFE content, the higher the mechanical strength of the diaphragm, but at the same time, the liquid absorption rate and porosity of the diaphragm will decrease. Within the above preferred range, good mechanical properties, liquid absorption properties and higher porosity can be better combined.

The types of fiberizable polymer powders are different, and their preferred addition amounts are different. The addition amount of fiberizable polymer powders with better high temperature resistance can be selected in a wide range; while the fiberizable polymer powders with poor high temperature resistance performance The material powder is preferably added in a small amount on the premise of forming a polymer network structure and exerting its good binding effect.

Preferably, the method of drawing the fiberizable polymer powder to form fibers under the action of shearing force in step (1) includes: at least one of high-speed stirring, screw extrusion and air-jet pulverization. The equipment includes masher, high-speed disperser, twin-screw extruder and jet mill.

Preferably, the method of drawing the fiberizable polymer powder to form fibers under the action of shearing force in step (1) is high-speed stirring, and the speed of the high-speed stirring is ≥1000rpm (for example, 2000rpm, 3000rpm, 4000rpm, 5000rpm) , 6000rpm, 7000rpm, 8000rpm, 9000rpm, 10000rpm, 12000rpm, 12500rpm, 13500rpm, 15000rpm, 16500rpm, 18000rpm, 20000rpm, 21000rpm, 22500rpm, 26000rpm or 28000rpm, etc.). However, it is not limited to the methods listed above, and other methods that can achieve the purpose of fiberization are also applicable to the present invention.

Preferably, the speed of the high-speed stirring in step (1) is 8000rpm-25600rpm, such as 8000rpm, 9000rpm, 10000rpm, 11000rpm, 12000rpm, 13000rpm, 15000rpm, 17500rpm, 18500rpm, 20000rpm, 21000rpm, 22500rpm, 23500rpm, 25000rpm, 25530rpm, 25500rpm, etc. Preferably it is 17000rpm-21000rpm.

Preferably, the high-speed stirring and mixing time of step (1) is 2min-2h, such as 2min, 5min, 10min, 15min, 17min, 20min, 25min, 28min, 30min, 40min, 50min, 1h, 1.1h, 1.2h, 1.3h, 1.5h, 1.8h or 2h, etc., preferably 10min-30min.

In the present invention, the purpose of high-speed shearing, on the one hand, is to achieve uniform mixing of materials, and on the other hand, it is also more important to draw the fiberizable polymer under the action of super high-speed dispersion to achieve fiberization. If the shear rate is too low, on the one hand, the mixing time will be too long, which will increase the time cost, and on the other hand, the fibrillation effect will be unsatisfactory; , and the second is that the performance of temperature-sensitive raw materials may be degraded due to heat generation problems.

Preferably, the high-speed stirring and mixing in step (1) is pulse stirring, and the interval time is 0-30min, such as 0.5min, 1min, 3min, 5min, 10min, 15min, 20min, 25min or 30min, etc.

The present invention does not limit the form of the hot pressing treatment in step (2), for example, a rolling press can be used to perform hot rolling at a certain temperature.

Preferably, the temperature of the hot pressing treatment in step (2) is 25°C-300°C, such as 25°C, 30°C, 35°C, 40°C, 50°C, 65°C, 80°C, 100°C, 115°C, 130°C °C, 150°C, 180°C, 200°C, 220°C, 230°C, 240°C, or 250°C, etc., preferably 60°C-250°C, more preferably 180°C-220°C.

Preferably, in the hot pressing process of step (2), the hot pressing speed is 5rpm-50rpm, such as 5rpm, 7rpm, 10rpm, 15rpm, 20rpm, 30rpm, 35rpm, 40rpm or 50rpm, etc. Preferably 5rpm-10rpm.

Preferably, the preset thickness in step (2) is 15um-70um, such as 15um, 20um, 25um, 30um, 35um, 40um, 45um, 50um, 55um, 60um, 65um or 70um.

As a further preferred technical solution of the method of the present invention, the method comprises the following steps:

(1) Mix PTFE and PI, carry out pulsed stirring at a speed of ≥10000rpm, the gap time is 0-30min and does not contain 0, and the time of pulsed stirring is 2min-2h to obtain a well-mixed mixture, and the mixing In the material, the mass proportion of PI is 70%-98%, and the mass proportion of PTFE is 2%-30%;

(2) Hot pressing the mixture described in step (1), the hot pressing temperature is 60°C-250°C, the hot pressing speed is 5rpm-50rpm, and the thickness is 15um-70um to obtain a self-supporting diaphragm.

As one of the polymers with good comprehensive properties, polyimide (PI) has excellent thermal stability, which can effectively avoid the melting and thermal shrinkage of the separator, and greatly improve the high temperature safety performance of the battery. Polyolefin material, PI has excellent electrolyte wettability, which can effectively improve the rate performance and cycle life of lithium-ion batteries.

This preferred technical solution uses PI as the high temperature resistant polymer, which has excellent electrolyte wettability, which can effectively improve the washing rate and liquid retention rate of the diaphragm, and both PI and PTFE have high temperature resistance properties, thereby improving the The operating temperature range of the battery enhances the safety features of the battery.

In a second aspect, the present invention provides a separator, the separator is prepared by the method described in the first aspect, and the separator comprises: a network formed by overlapping polymer fibers converted from a fiberizable polymer. structure, and a high temperature polymer dispersed and bound in the network structure.

In a third aspect, the present invention provides a battery comprising the separator of the second aspect.

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

Different from other preparation methods and technologies such as wet preparation, dry drawing and electrospinning of lithium battery separators, the present invention selects two types of polymers, fibrillizable polymer powder and high temperature resistant polymer, as the main material to be used together. The diaphragm is prepared by dry method under the action of super high-speed dispersion. The fiberizable polymer powder is fiberized by high-speed shearing and mixed with high-temperature resistant polymer, and the fibers formed by the subsequent hot-pressing process are randomly lapped to form A network structure in which the high temperature resistant polymer is dispersed and bound. This structure is beneficial for the separator to obtain suitable porosity, good mechanical properties and high temperature resistance. The method of the invention has a simple preparation process and is convenient for commercial expansion; the preparation process does not need to go through multiple steps such as mixing, homogenizing, coating, drying, etc., and the use of solvents is not involved in the whole process, which reduces material costs at the same time. It also effectively achieves green environmental protection, and solves the problems that processes such as electrospinning process and wet-process polyamic acid conversion are not easy to industrialize and are not environmentally friendly.

The method of the invention can not only simplify the process and improve the consistency of the diaphragm, but also can easily control the process and save the cost.

Description of drawings

FIG. 1 is a photo of the liquid absorption test of the diaphragm prepared in Example 1 of the present invention.

FIG. 2 is an optical photograph of the diaphragm prepared in Example 1 of the present invention.

Detailed ways

The technical solutions of the present invention are further described below with reference to the accompanying drawings and through specific embodiments.

Example 1

In a room temperature environment, the PI powder and PTFE powder were weighed in a mass ratio of 70:30, placed in a high-speed disperser, and pulsed at 20,000 rpm for 5 minutes, and then the mixed material was placed in a roller press. The temperature is 200°C, the rotation speed is 10rpm, and the powder is rolled into a self-supporting diaphragm.

Example 2

In the room temperature environment, the PI powder and the PTFE powder were weighed in a mass ratio of 90:5, placed in a high-speed disperser, and pulsed at 20,000 rpm for 5 minutes, and then the mixed material was placed in a roller press. The temperature is 200°C, the rotation speed is 10rpm, and the powder is rolled into a self-supporting diaphragm.

Example 3

In a room temperature environment, the PI powder and the PTFE powder were weighed in a mass ratio of 80:20, placed in a high-speed disperser, and stirred in a pulsed manner at 10,000 rpm for 30 minutes, and then the mixed material was placed in a roller press. The temperature is 180°C, the rotation speed is 5rpm, and the powder is rolled into a self-supporting diaphragm.

Example 4

In a room temperature environment, the PI powder and PTFE powder were weighed in a mass ratio of 75:25, placed in a high-speed disperser, and pulsed at 17500 rpm for 20 minutes, and then the mixed material was placed in a roller press. The temperature is 135°C, the rotation speed is 3rpm, and the powder is rolled into a self-supporting diaphragm.

Example 5

In a room temperature environment, PMIA powder and PTFE powder were weighed in a mass ratio of 75:25, placed in a high-speed disperser, and pulsed at 17,500 rpm for 20 minutes, and then the mixed material was placed in a roller press. The temperature is 135°C, the rotation speed is 3rpm, and the powder is rolled into a self-supporting diaphragm.

Example 6

In a room temperature environment, PI powder, PET powder and PTFE powder were weighed in a mass ratio of 80:5:15 and placed in a high-speed disperser. After pulsed stirring at 8000rpm for 60min, the mixed material was placed in a roller press In the machine, the temperature of the roller press is 90 °C and the rotation speed is 2 rpm, and the powder is rolled into a self-supporting diaphragm.

Example 7

In a room temperature environment, the PI powder and PVDF powder were weighed in a mass ratio of 98:2, placed in a high-speed disperser, and pulsed at 18,000 rpm for 10 minutes, then the mixed material was placed in a roller press. The temperature is 170°C and the rotation speed is 8rpm, and the powder is rolled into a self-supporting diaphragm.

Example 8

The difference from Example 1 is that the mass ratio of PI powder and PTFE powder is 50:50.

Example 9

The difference from Example 1 is that the mass ratio of PI powder and PTFE powder is 99:1.

Comparative Example 1

Purchased Celgard PP single-layer separator.

Comparative Example 2

The difference from Example 1 is that PTFE powder is not added, but only PI powder is used (the usage amount is the same as the total mass of PI powder and PTFE powder in Example 1).

Comparative Example 3

The difference from Example 1 is that PI powder is not added, but only PTFE powder is used (the usage amount is the same as the total mass of PI powder and PTFE powder in Example 1).

test:

The separators of each example and comparative example were tested, and their mechanical strength was tested by tensile ratio, and their thickness, porosity, liquid absorption rate, liquid retention rate and 150°C high temperature resistance were tested. The results are shown in Table 1.

FIG. 1 is a photo of the liquid absorption test of the separator prepared in Example 1. FIG. FIG. 2 is an optical photograph of the separator prepared in Example 1. FIG.

Table 1

As can be seen from the above table, the diaphragm of the present invention has higher porosity, liquid absorption rate and liquid retention rate,

From the comparison between Examples 8-9 and Example 1, it can be seen that when the PTFE content is too high, the porosity, liquid absorption rate and liquid retention rate of the diaphragm will decrease, while the elongation rate will increase. On the contrary, when the PI content is too high , the porosity, liquid absorption and liquid retention rate of the separator will increase, while the elongation rate will decrease.

It can be seen from the comparison between Comparative Example 1 and Example 1 that the diaphragms made of PTFE and PI high temperature resistant materials will not deform at 150°C, and are not flammable, while the conventional PP diaphragms have been melted and curled at 150°C, and flammable.

From the comparison between Comparative Example 2 and Example 1, it can be seen that when there is only PI powder and no PTFE binder, the diaphragm mainly reflects the characteristics of PI material and has high porosity and liquid absorption rate, but the mechanical strength is very poor, and the elongation rate is poor. Low.

From the comparison between Comparative Example 3 and Example 1, it can be seen that when there is only PTFE and no PI material, the diaphragm mainly reflects the characteristics of PTFE material and has high mechanical strength, but the porosity and liquid absorption rate are very low.

The applicant declares that the present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims (13)

1. a dry preparation method of diaphragm, is characterized in that, described method comprises the following steps: (1) Mix the fiberizable polymer powder and the high temperature resistant polymer, and draw the fiberizable polymer powder to form fibers under the action of shearing force to obtain a mixture; In the mixture described in step (1), the fiberizable polymer powder is PTFE, and the mass ratio is 5%-10%; the high temperature resistant polymer is PI, and the mass ratio is 90%-95%; In step (1), the method of drawing the fiberizable polymer powder to form fibers under the action of shearing force is high-speed stirring, and the speed of the high-speed stirring is 8000rpm-25600rpm; (2) hot-pressing the mixture described in step (1) to a preset thickness to obtain a diaphragm; The preset thickness in step (2) is 15 μm-70 μm; Wherein, the high temperature resistant polymer is a polymer that exists stably at the operating temperature of the diaphragm; The fiberizable polymer powder exists stably at the operating temperature of the diaphragm; The separator comprises: a network structure formed by overlapping polymer fibers converted from a fiberizable polymer, and a high temperature resistant polymer dispersed and bonded in the network structure; The network structure is formed by the fiberizable polymer powder under the action of shearing force to form fibers, which are overlapped with each other during the hot pressing process. 2 . The dry preparation method according to claim 1 , wherein the speed of the high-speed stirring in step (1) is 17000rpm-21000rpm. 3 . 3 . The dry preparation method according to claim 1 , wherein the high-speed stirring and mixing time in step (1) is 2min-2h. 4 . 4 . The dry preparation method according to claim 3 , wherein the high-speed stirring and mixing time in step (1) is 10min-30min. 5 . 5 . The dry preparation method according to claim 1 , wherein the high-speed stirring and mixing in step (1) is pulsed stirring, and the gap time is 0-30 min. 6 . 6 . The method according to claim 1 , wherein the hot pressing treatment in step (2) is hot rolling. 7 . 7 . The dry preparation method according to claim 1 , wherein the temperature of the hot-pressing treatment in step (2) is 25°C-300°C. 8 . 8 . The dry preparation method according to claim 1 , wherein the temperature of the hot-pressing treatment in step (2) is 60° C.-250° C. 9 . 9 . The dry preparation method according to claim 1 , wherein the temperature of the hot-pressing treatment in step (2) is 180°C-220°C. 10 . 10 . The dry preparation method according to claim 1 , wherein, in the hot pressing process of step (2), the hot pressing speed is 5 rpm-50 rpm. 11 . 11 . The dry preparation method according to claim 1 , wherein, in the hot pressing process of step (2), the hot pressing speed is 5 rpm-10 rpm. 12 . 12. A separator prepared by the method of any one of claims 1-11. 13. A battery comprising the separator of claim 12.

Images