CN112133869B

CN112133869B - Method for dry in-situ synthesis of diaphragm, product thereof and product application

Info

Publication number: CN112133869B
Application number: CN202010981157.2A
Authority: CN
Inventors: 马忠龙; 赵晓宁; 秦士林; 郑晓醒
Original assignee: Svolt Energy Technology Co Ltd
Current assignee: Svolt Energy Technology Co Ltd
Priority date: 2020-09-17
Filing date: 2020-09-17
Publication date: 2022-04-26
Anticipated expiration: 2040-09-17
Also published as: CN112133869A

Abstract

The invention relates to a method for synthesizing a diaphragm in situ by a dry method, a product and the application of the product; the method comprises the steps of premixing a first polymer and a fiberizable polymer or premixing the first polymer, a solid cross-linking agent and the fiberizable polymer, drawing the fiberizable polymer to form fibers under the action of shearing force, and then carrying out hot-pressing treatment and cross-linking to obtain the diaphragm; the diaphragm obtained by the method is of a networked structure, has rich pores, good thermal stability, mechanical stability and high ionic conductivity, and can greatly improve the safety performance of the battery; and the synthetic process of the method does not involve the use of any solvent, thereby simplifying the operation steps.

Description

Method for dry in-situ synthesis of diaphragm, product thereof and product application

Technical Field

The invention belongs to the field of batteries, and relates to a method for synthesizing a diaphragm in situ by a dry method, a product and application of the product.

Background

With the rapid development of new energy automobiles, the requirements on the energy density and the safety performance of the energy storage device for the automobile are continuously improved. The lithium ion battery with the advantages of high specific energy, high specific power, good cyclicity, no environmental pollution and the like is considered as the best choice. It is expected that the energy density of the power battery will reach over 500Wh/kg by 2025. With the increasing of energy density of power batteries, the safety performance of the power batteries is also under more severe examination. In addition, in recent years, since a large number of electronic products are popularized, lithium batteries used as power sources of the electronic products are more and more emphasized due to the advantages of light weight, small size, high operating voltage, high energy density, large output power, high charging efficiency, no memory effect and the like, and thus, the requirement on the safety performance of the lithium batteries is inevitably higher. The diaphragm is used as an important component of the lithium battery, and has the functions of isolating positive and negative pole pieces, preventing short circuit and providing a lithium ion transmission channel. Therefore, improving the safety performance of the battery and reducing the production cost of the diaphragm are one of the main targets of the future lithium ion battery research.

Analyzed from the existing industry development level and published patent literature, the current diaphragms on the market are mainly made of Polyethylene (PE) and polypropylene (PP), and have low melting point and high thermal shrinkage; under extreme conditions, the temperature of the battery is too high, so that the common diaphragm is easy to melt and contract, the anode and the cathode are in direct contact, and the battery is ignited and burnt. Although a layer of alumina ceramic (with the melting point of about 2000 ℃) or other material coating is coated on the base film of the diaphragm to improve some characteristics of the surface of the diaphragm, the thermal shrinkage of the diaphragm under a high-temperature environment can be improved, and the improvement of the safety performance of the battery core is helped to a certain extent; among them, beijing kawasa new energy science and technology ltd discloses a similar patent document (CN 106876633 a) which discloses that the safety performance of a cell is improved by coating an inorganic lithium salt and a ceramic material on the surface of a separator. Compared with the way of increasing coatings on PP and PE materials, the mode of treating symptoms and root causes changes the main materials such as PP and PE, and is a higher-brightness means if the main materials are replaced by high-temperature-resistant polymers with high thermal stability; zhejiang university (CN105957993A) discloses a preparation method of a thermally crosslinkable polymer electrolyte membrane, which still maintains high strength by initiating thermal crosslinking of a polymer during the formation of a gel.

Currently, the industry improves the safety of the diaphragm by coating the surface of the diaphragm with ceramic or other material, but the manufacturing cost and the manufacturing process of the diaphragm are further increased, and the improvement effect of the method is limited. In addition, the non-polar polymers (PP, PE) generally have poor wettability with the electrolyte, resulting in long electrolyte wetting time and poor ability to penetrate through the separator, which is manifested by increased internal resistance of the battery, affecting the rate and cycle performance of the battery. At present, the preparation process taking the high-temperature resistant polymer as the diaphragm is mainly to prepare a polymer solution by a liquid phase method and then dry the solvent to prepare a membrane material; in order to achieve crosslinking of the polymer, it is necessary to further dissolve the crosslinking agent in some solvent. This undoubtedly increases the production difficulty of the whole preparation process, and also increases the cost.

Therefore, the development of a preparation method of the diaphragm which is simple in preparation process and has good mechanical stability and ionic conductivity is still significant.

Disclosure of Invention

The invention aims to provide a method for synthesizing a diaphragm in situ by a dry method, a product and a product application thereof; the method comprises the steps of premixing a first polymer and a fiberizable polymer or premixing the first polymer, a solid cross-linking agent and the fiberizable polymer, drawing the fiberizable polymer to form fibers under the action of shearing force, and then carrying out hot-pressing treatment and cross-linking to obtain the diaphragm; the diaphragm obtained by the method is of a networked structure, has rich pores, good thermal stability, mechanical stability and high ionic conductivity, and can greatly improve the safety performance of the battery; and the synthetic process of the method does not involve the use of any solvent, thereby simplifying the operation steps.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a method for dry in-situ synthesis of a membrane, wherein the method comprises the following steps:

(1) premixing a first polymer and a fiberizable polymer or premixing the first polymer, a solid cross-linking agent and the fiberizable polymer, and then drawing the fiberizable polymer into fibers under the action of shearing force to obtain dry powder;

(2) carrying out hot-pressing treatment and crosslinking on the dry-process powder obtained in the step (1) to obtain a diaphragm;

wherein the first polymer comprises a high temperature resistant polymer and/or a gellable polymer.

The method comprises a plurality of crosslinking modes, wherein when the dry-process powder in the step (1) does not contain a solid crosslinking agent, the crosslinking process is self-crosslinking, the polymer can physically initiate self-crosslinking at a high temperature (60-250 ℃) to form a polymer network structure, the addition of the crosslinking agent is not needed, but the relative crosslinking rate is slow, and the polymer needs to be kept in a high-temperature environment for a long time (the self-crosslinking at the high temperature is carried out in the hot-pressing treatment process), or the polymer is crosslinked under high-energy irradiation (if the crosslinking is carried out under the high-energy irradiation, the sequence of crosslinking and hot pressing is not limited, namely the crosslinking process can be carried out before the hot-pressing treatment process, in the hot-pressing treatment process or after the hot-pressing treatment process). In addition, when the dry-process powder in the step (1) contains a solid cross-linking agent, the cross-linking process can be completed in the hot-pressing treatment process; the solid cross-linking agent is heated in the hot-pressing treatment process to form free radicals, so that the polymer is initiated to generate a cross-linking reaction, and the speed is high.

The method adopts a dry film-making technology, wherein the film-making polymers (the first polymer and the fiberizable polymer) can be drawn and fiberized to form fibers under the action of shearing force, and then the fiberized polymers are subjected to hot-pressing treatment and crosslinking, and are randomly overlapped in the hot-pressing treatment process to form a network structure with rich pores, so that the safety performance of the battery can be greatly improved; meanwhile, the mechanical strength of the membrane material is further improved by crosslinking of the polymer chain segment; the first polymer and the fiberizable polymer are polymers with different polarities, and the thermal stability and the mechanical property of the film material are further improved through the cross-linking synergy between the polymers with different polarities.

In addition, when the first polymer is selected from high-temperature-resistant polymers, the obtained diaphragm has good thermal stability, the mechanical strength is improved more obviously, and the ionic conductivity of the diaphragm is higher; when the first polymer is selected from the gellable polymers, the obtained separator has high ionic conductivity in addition to good mechanical stability, and when the separator is used as a battery separator, the addition amount of an electrolyte can be reduced appropriately, thereby improving the safety performance of the battery.

According to the method, the solid cross-linking agent is added in the premixing process, the solid cross-linking agent can be uniformly dispersed in the polymer powder under the action of shearing force, and when hot-pressing treatment is carried out, the solid cross-linking agent is heated to initiate a polymer chain segment to carry out thermal cross-linking, so that the mechanical property of a membrane material is further improved; and the cross-linking process and the hot-pressing treatment process are carried out synchronously, so that the efficiency of the preparation process is improved.

The method does not involve the use of any solvent in the whole process, reduces the preparation cost of the diaphragm, and is simpler to operate.

The method disclosed by the invention is beneficial to preparing the high-strength diaphragm with high temperature resistance and high safety.

Preferably, the high temperature resistant polymer includes at least one of Polyimide (PI) and Polyacrylonitrile (PAN), wherein the combination of the high temperature resistant polymer exemplarily includes a combination of polyimide and polyacrylonitrile.

Preferably, the gelable polymer includes at least one of polypropylene carbonate (PPC), polyethylene carbonate (PEC), and polyethylene carbonate (PVC), wherein a combination of the gelable polymer exemplarily includes a combination of polypropylene carbonate and polyethylene carbonate, a combination of polyethylene carbonate and polyethylene carbonate, or a combination of polypropylene carbonate and polyethylene carbonate, and the like.

Preferably, when the first polymer is a composition of a high temperature resistant polymer and a gellable polymer, the composition exemplarily includes a combination of polyimide and polypropylene carbonate, a combination of polyimide and polyethylene carbonate, a combination of polyacrylonitrile and polypropylene carbonate, a combination of polyacrylonitrile and polyethylene carbonate, or a combination of polyacrylonitrile and polyethylene carbonate, etc.

When the first polymer is a high-temperature-resistant polymer, the obtained diaphragm has high thermal stability (the thermal deformation temperature is more than 300 ℃), the mechanical stability is obviously improved, the tensile strength of the diaphragm can reach more than 80MPa, the elongation after fracture can be controlled to be less than 15%, and the ionic conductivity is reduced less and can reach 0.86 mS/cm.

When the first polymer is a gelable polymer, the first polymer has high ionic conductivity which can reach more than 1.03mS/cm, the mechanical stability is obviously improved, the tensile strength can reach more than 65MPa, and the elongation after fracture is less than 28.6 percent; the electrolyte has high ionic conductivity, and can be used as a battery diaphragm, so that the addition of the electrolyte can be properly reduced, and the safety of the battery is further improved.

Preferably, the fiberizable polymer is selected from Polytetrafluoroethylene (PTFE).

Preferably, the mass percentage of the first polymer is 80-96% based on 100% of the mass of the dry powder in the step (1); such as 82%, 85%, 88%, 90%, 92%, or 94%, etc.

Preferably, the mass percentage of the solid cross-linking agent is 1-3% based on 100% of the mass of the dry powder in the step (1); e.g., 1.5%, 2%, or 2.5%, etc.

Preferably, the mass percentage of the fiberizable polymer is 3-15%, for example, 5%, 7%, 9%, 10%, 12%, or 14%, based on 100% of the dry powder in step (1).

Preferably, the dry powder in the step (1) comprises the following components by mass percent based on 100 percent of the dry powder:

80-96% of the first polymer

1-3% of solid cross-linking agent

3-15% of fiberizable polymer.

In the invention, the dry-process powder in the step (1) comprises the following components by mass percent of 100 percent: the mass percentage of the first polymer is 80-96%, such as 82%, 85%, 88%, 90%, 92% or 94%; the solid cross-linking agent is 1-3% by mass, such as 1.5%, 2% or 2.5%, and the fiberizable polymer is 3-15% by mass, such as 5%, 7%, 9%, 10%, 12% or 14%; the dry method powder adopts the components, and the obtained diaphragm has good mechanical strength and higher ionic conductivity, and is beneficial to improving the safety of the diaphragm.

Preferably, the drawing of the fiberizable polymer under shear to form fibers in step (1) comprises: at least one of high-speed stirring, screw extrusion and airflow crushing, preferably high-speed stirring, wherein the high-speed stirring speed is more than or equal to 1000 rpm; for example, 2000rpm, 5000rpm, 10000rpm, 15000rpm, 20000rpm, 25000rpm, etc.

The high-speed stirring is the key for fiberizing the fiberizable polymer, in the process of high-speed stirring, the fiberizable polymer can be gradually drawn and fiberized, the first polymer and the solid cross-linking agent are bonded to form polymer powder with certain viscosity, then the diaphragm material with certain thickness is obtained through hot pressing treatment and polymer cross-linking, and in the hot pressing process, the fiberizable polymer is mutually overlapped and extruded to move to form a network structure; meanwhile, the solid cross-linking agent is heated in the hot-pressing treatment process to form free radicals, and the polymer is initiated to carry out a cross-linking reaction, so that the diaphragm is obtained; wherein, a polymer network structure is formed in the cross-linking process, and the strength of the diaphragm is further improved.

Preferably, the method for premixing the first polymer, the solid crosslinking agent and the fiberizable polymer in the step (1) comprises: the first polymer is mixed with a solid crosslinking agent, and then a fiberizable polymer is added and mixed at a speed of 100 to 25000rpm, for example, 500rpm, 1000rpm, 1500rpm, 2000rpm, 2500rpm, 3000rpm, 5000rpm, 10000rpm, 15000rpm, 20000rpm, 25000rpm, or the like, preferably 100 to 3000 rpm.

Preferably, the mixing speed of the first polymer and the solid cross-linking agent is 1000 to 25000rpm, such as 2000rpm, 5000rpm, 10000rpm, 15000rpm or 20000 rpm.

Preferably, the method for premixing the first polymer and the fiberizable polymer in step (1) comprises: the first polymer and the fiberizable polymer are mixed at a speed of 100 to 3000rpm, such as 500rpm, 1000rpm, 1500rpm, 2000rpm, 2500rpm, or the like.

According to the method, after the fiberizable polymer is added, the fiberizable polymer is stirred at a speed of 100-3000 rpm, so that the fiberizable polymer can be prevented from being drawn too early, and meanwhile, the first polymer and the fiberizable polymer or the first polymer, the solid cross-linking agent and the fiberizable polymer are uniformly mixed.

Preferably, the high-speed stirring speed is 3000-25000 rpm; for example, 5000rpm, 10000rpm, 15000rpm, 20000rpm, 25000rpm, or the like.

Preferably, the high-speed stirring method is pulse stirring.

Preferably, the time of the pulse type stirring is 2-30 min, such as 3min, 5min, 10min, 15min, 20min or 25 min.

Preferably, the intermittent time of the pulse type stirring is 0-3 min, such as 1min or 2 min.

Preferably, the crosslinking of step (2) comprises crosslinking with a crosslinking agent or self-crosslinking.

Preferably, the crosslinking process of the crosslinking agent is performed simultaneously with the thermocompression treatment process.

Preferably, the self-crosslinking is performed at a temperature of 60-250 ℃, such as 80 ℃, 100 ℃, 120 ℃, 140 ℃, 160 ℃, 180 ℃, 200 ℃, 220 ℃ or 240 ℃, preferably at 120-250 ℃, for a time of 1-60 min, such as 5min, 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min or 55min, preferably for 30-60 min, or the self-crosslinking is performed under high-energy irradiation, preferably under ultraviolet irradiation.

Preferably, the hot pressing process in the step (2) is a hot rolling process.

Preferably, the temperature of the hot pressing treatment in the step (2) is 60 to 250 ℃, such as 80 ℃, 100 ℃, 150 ℃ or 200 ℃.

Preferably, the hot pressing gap of the hot pressing treatment in the step (2) is 0-2 mm, such as 10 μm, 50 μm, 100 μm, 500 μm, 1mm or 1.5 mm.

As a preferred technical method, the method for synthesizing the diaphragm in situ by the dry method comprises the following steps:

(a) stirring the first polymer and the fiberizable polymer at a speed of 100-3000 rpm to obtain premixed powder, and stirring at a high speed of 3000-25000 rpm to obtain dry powder;

(b) carrying out hot pressing treatment and self-crosslinking on the dry powder obtained in the step (a) at the temperature of 60-250 ℃ to obtain a diaphragm;

or the method comprises the steps of:

(a') stirring and mixing the first polymer and the solid cross-linking agent at the speed of 1000-25000 rpm, then adding the fiberizable polymer, stirring at the speed of 100-3000 rpm to obtain premixed powder, and stirring at the high-speed stirring speed of 3000-25000 rpm to obtain dry powder;

(b ') carrying out hot pressing treatment at the temperature of 60-250 ℃ on the dry powder obtained in the step (a') and crosslinking by using a crosslinking agent to obtain a diaphragm;

In a second aspect, the present disclosure provides a separator comprising a first polymer and a fiberizable polymer crosslinked to form a network.

The diaphragm has good mechanical stability, and when the first polymer is a high-temperature-resistant polymer, the mechanical stability of the diaphragm is improved more obviously, and the diaphragm has good thermal stability; when the first polymer adopts the gelable polymer, the gelable polymer has good mechanical stability and high ionic conductivity, and the addition amount of the electrolyte can be properly reduced by using the gelable polymer as the battery diaphragm, so that the safety performance of the battery is improved.

Preferably, the separator is a porous structure.

Preferably, the thickness of the separator is 5 to 100 μm, for example, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, or 90 μm.

The separator is an electrolyte membrane.

Preferably, the membrane is prepared using a method as described in the first aspect, and the parameter settings relating to the first aspect are still applicable in the second aspect.

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

The battery of the present invention employs the separator of the second aspect, which has higher thermal stability and safety.

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

(1) the diaphragm prepared by the method has a network structure with rich pores, has good mechanical stability, can greatly improve the safety performance of the battery, has more obvious improvement on the mechanical strength and good thermal stability when the first polymer adopts a high-temperature-resistant polymer, and has higher ionic conductivity when the first polymer adopts a gelable polymer;

(2) the preparation method does not involve the use of any solvent, reduces the preparation cost and has simpler operation.

Drawings

FIG. 1 is a schematic diagram showing the structural change of the crosslinking process in the method of the present invention.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

The schematic diagram of the structural change in the cross-linking process of the method for synthesizing the diaphragm in situ by the dry method is shown in figure 1, and as can be seen from figure 1, the cross-linking reaction occurs among polymer chain segments in the synthesis process, and the method plays an important role in improving the mechanical stability of the diaphragm.

Example 1

The method for synthesizing the diaphragm in situ by the dry method comprises the following steps:

(1) 4.5g of polymer PAN powder and 0.05g of bis 25(2, 5-dimethyl-2, 5-di-tert-butyl hexane peroxide, solid cross-linking agent) are firstly mixed at a high speed of 20000rpm for 5min to ensure that the polymer PAN powder and the bis 25 are fully and uniformly mixed; then adding 0.25g of PTFE, stirring and dispersing for 5min at the stirring speed of 2000rpm to fully and uniformly mix the polymer powder and the solid cross-linking agent; then stirring at a high speed of 20000rpm in a pulse mode for 1min, stopping for 1min, and stirring for 20min to obtain dry powder;

the dry powder comprises the following components by mass of 100 percent:

PAN powder 93.8%

1.0 percent of solid cross-linking agent

PTFE 5.2％

(2) Taking a certain amount of dry powder, placing the dry powder on a rolling device with a roller set temperature of 150 ℃ (the device is preheated and the temperature is stabilized at about 150 ℃), and preparing a diaphragm material with the thickness of 11 microns at a rolling speed of 5rpm at a roller gap of 10 microns; mutual entanglement of polymer chain segments and cross-linking agent initiation of polymer chain segment cross-linking are carried out in the hot pressing process; obtaining a diaphragm;

and the crosslinked diaphragm is subjected to mechanical property test, the tensile strength of the diaphragm reaches 80MPa, and the mechanical property of the diaphragm is obviously improved compared with that of an uncrosslinked diaphragm.

Example 2

The present embodiment is different from embodiment 1 in that the PAN in embodiment 1 is replaced with PI of equal mass, and other parameters and conditions are exactly the same as those in embodiment 1.

Example 3

This embodiment is different from embodiment 1 in that PAN in embodiment 1 is replaced with PPC of equal quality, and other parameters and conditions are exactly the same as those in embodiment 1.

Example 4

This example is different from example 1 in that PAN in example 1 is replaced with a mixture of PPC and PAN of equal mass (mass ratio of 1:1), and other parameters and conditions are exactly the same as those in example 1.

Example 5

This example differs from example 1 in that PAN in example 1 is replaced by a mixture of equal mass of PI and PEC (mass ratio of 1:1), and other parameters and conditions are exactly the same as in example 1.

Example 6

This example differs from example 1 in that PAN in example 1 is replaced by a mixture of equal mass PVC and PEC (mass ratio 1:1), and other parameters and conditions are exactly the same as in example 1.

Example 7

The difference between the present embodiment and embodiment 1 is that the dry powder comprises the following components by mass percent of 100 percent:

PAN powder 82%

3 percent of solid cross-linking agent

PTFE 15％；

Other parameters and conditions were exactly the same as in example 1.

Example 8

PAN powder 88%

1.5% of solid cross-linking agent

PTFE 10.5％；

Other parameters and conditions were exactly the same as in example 1.

Example 9

PAN powder 69%

1% of solid cross-linking agent

PTFE 30％；

Other parameters and conditions were exactly the same as in example 1.

Example 10

This example is different from example 1 in that high-speed stirring was carried out at 20000rpm directly after addition of PTFE, and other parameters and conditions were exactly the same as those in example 1.

Example 11

This example differs from example 1 in that the high speed stirring rate was replaced with 5000rpm and the other parameters and conditions were exactly the same as in example 1.

Example 12

This example differs from example 1 in that the high speed stirring rate was replaced with 2000rpm and the other parameters and conditions were exactly the same as in example 1.

Example 13

The difference between this example and example 1 is that no solid cross-linking agent is added in step (1), high-energy irradiation (ultraviolet irradiation for 5min) is carried out during the hot-pressing treatment in step (2), and other parameters and conditions are exactly the same as those in example 1.

Example 14

This example differs from example 1 in that no solid crosslinking agent was added in step (1) and in step (2) by keeping at 150 ℃ for 45min, the other parameters and conditions being exactly the same as in example 1.

Example 15

This example is different from example 1 in that benzoyl peroxide is substituted for the solid crosslinking agent and the like, and other parameters and conditions are exactly the same as those in example 1.

Comparative example 1

The preparation method of the separator in the comparative example comprises the following steps:

(1) 4.5g of polymer PAN powder and 0.25g of PTFE are stirred and dispersed for 5min at the stirring speed of 2000rpm, so that the two polymer powders are fully and uniformly mixed; then stirring at a high speed of 20000rpm for pulse stirring for 1min, stopping for 1min, and stirring for 20 min;

(2) a certain amount of polymer powder is taken and placed on a rolling device with a roller set temperature of 100 ℃ (the device is preheated and the temperature is stabilized at about 100 ℃), and a diaphragm with the thickness of 11 microns is prepared at a rolling speed of 5rpm at a roller gap of 10 microns.

In the comparative example, no solid crosslinking agent was added, that is, no significant crosslinking reaction occurred in the polymer during hot pressing, and the tensile strength of the obtained separator was only 50 MPa.

And (3) performance testing:

the tensile strength, elongation after break, thermal stability and ionic conductivity of the separators obtained in examples 1-2, 7-15 and comparative example 1 were measured as follows:

wherein, the tensile strength and the elongation after fracture are tested: testing according to the national test standard GB/T36363-2018;

and (3) testing thermal stability: cutting a diaphragm with the size of 3 multiplied by 3cm, paving the diaphragm on a heating table, continuously raising the temperature, and observing the temperature of the diaphragm at which thermal deformation starts to occur;

and (3) ion conductivity test: soaking the diaphragm in the electrolyte to fully wet the diaphragm by the electrolyte; li// Li button cells were assembled with the separator, and EIS test was conducted.

The above test results are shown in table 1;

TABLE 1

As can be seen from the above table 1, the mechanical stability of the diaphragm obtained by the method of the invention is obviously improved, the tensile strength of the diaphragm can reach more than 80MPa, and the elongation after fracture can be controlled below 15%; and the thermal stability is good, the ionic conductivity is higher, and the ionic conductivity can reach more than 0.85 mS/cm.

As can be seen from comparison of examples 1-2, the high temperature resistant polymer is polyacrylonitrile or polyimide, and the obtained membrane has good mechanical stability and thermal stability, wherein the mechanical stability of the membrane obtained from polyacrylonitrile is better, and the ionic conductivity of the membrane obtained from polyimide is higher.

As can be seen from comparative examples 1, 7 to 9, the dry powder preferably contains the following components, based on 100% by mass of the dry powder: the mass percentage content of the first polymer is 80-96%; the mass percentage of the solid cross-linking agent is 1-3%; the mass percentage of the fiberizable polymer is 3-15%. Within the above preferred range, the resulting separator has not only good mechanical and thermal stability, but also higher ionic conductivity.

Comparing examples 1 and 10, it can be seen that the addition of the fiberizable polymer followed by direct high-speed shearing is likely to cause premature fiberization of the fiberizable polymer, which in turn affects the material dispersion uniformity and causes a decrease in mechanical stability and ionic conductivity.

It can be seen from comparative examples 1, 11 and 12 that when the high-speed stirring speed is too low, the fiberization degree of the fiberizable polymer is insufficient, and the mechanical stability and the ionic conductivity of the separator are reduced.

It can be seen from comparison of examples 1 and 13 that the polymer undergoes self-crosslinking under high-energy irradiation without the addition of a solid crosslinking agent, and the mechanical stability of the separator can be significantly improved.

It can be seen from comparison of examples 1 and 14 that, in the absence of a solid crosslinking agent, the crosslinking occurs by polymerization when the hot pressing process is maintained at a high temperature for a long time, and the mechanical stability of the separator is improved, but the improvement effect is inferior to that of the self-crosslinking by the addition of a solid crosslinking agent and high-energy radiation.

As can be seen from comparison of examples 1 and 15, the solid crosslinking agent of the present invention is preferably 2, 5-dimethyl-2, 5-di-tert-butylperoxyhexane.

Comparing example 1 and comparative example 1, it can be seen that the cross-linking of the first polymer and the fiberizable polymer in the process according to the invention leads to a significant improvement in the mechanical stability of the separator.

The tensile strength, elongation after fracture, and ionic conductivity of the separator obtained in examples 3 to 6 were measured in the same manner as described above, and the test results are shown in table 2;

TABLE 2

	Tensile strength MPa	Elongation after break/%	Ionic conductivity mS/cm
				Example 3	70	25.2	1.26
Example 4	73	21.7	1.06
				Example 5	71	23.2	1.02
Example 6	65	28.6	1.29

As can be seen from table 2 above, when the gellable polymer is included in the first polymer according to the present invention, the obtained separator has not only good mechanical properties, but also significantly improved ionic conductivity.

The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims

1. A method for dry in-situ synthesis of a membrane, comprising the steps of:

or the method comprises the steps of:

(a') stirring and mixing a first polymer and a solid cross-linking agent at the speed of 1000-25000 rpm, then adding a fiberizable polymer, stirring at the speed of 100-3000 rpm to obtain premixed powder, and stirring at a high speed of 3000-25000 rpm to obtain dry powder;

wherein the first polymer comprises a high temperature resistant polymer and/or a gellable polymer;

the high-temperature resistant polymer comprises at least one of polyimide and polyacrylonitrile;

the gellable polymer includes at least one of polypropylene carbonate, polyethylene carbonate, and polyethylene carbonate.

2. The method of claim 1, wherein the fiberizable polymer is selected from the group consisting of polytetrafluoroethylene.

3. The method of claim 1, wherein the solid crosslinking agent comprises at least one of 2, 5-dimethyl-2, 5-di-tert-butylperoxyhexane and benzoyl peroxide.

4. The method of claim 3, wherein the solid crosslinking agent is 2, 5-dimethyl-2, 5 di-tert-butylperoxyhexane.

5. The method according to claim 1, wherein the mass percentage of the first polymer is 80 to 96% based on 100% by mass of the dry powder.

6. The method according to claim 1, wherein the solid crosslinking agent is contained in an amount of 1 to 3% by mass based on 100% by mass of the dry powder.

7. The method according to claim 1, wherein the fiberizable polymer is present in an amount of 3 to 15% by mass, based on 100% by mass of the dry powder.

8. The method of claim 1, wherein the high speed agitation is pulsed agitation.

9. The method of claim 8, wherein the pulsed agitation is for a period of 2 to 30 min.

10. The method of claim 8, wherein the pulsed agitation is applied for a period of time ranging from 0 to 3 minutes.

11. The method of claim 1, wherein the crosslinking of the crosslinking agent is performed simultaneously with the autoclaving.

12. The method of claim 1, wherein the self-crosslinking is performed at a temperature of 60 to 250 ℃ for 1 to 60min, or under high energy irradiation.

13. The method of claim 12, wherein the self-crosslinking is performed at a temperature of 120 to 250 ℃.

14. The method of claim 12, wherein the self-crosslinking time is 30 to 60 min.

15. The method of claim 1, wherein the hot pressing process is a hot rolling process.

16. A separator prepared by the method for dry in-situ synthesis of a separator according to any one of claims 1 to 15, wherein the separator comprises a first polymer and a fibrillatable polymer crosslinked to form a network structure.

17. The separator of claim 16, wherein the separator is a porous structure.

18. The separator according to claim 16, wherein the thickness of the separator is 5 to 100 μm.

19. A battery comprising the separator of claim 16.