WO2016206145A1

WO2016206145A1 - Preparation method for high-safety multilayer lithium battery diaphragm

Info

Publication number: WO2016206145A1
Application number: PCT/CN2015/084041
Authority: WO
Inventors: 朱俊; 植志飞
Original assignee: 深圳市星源材质科技股份有限公司
Priority date: 2015-06-26
Filing date: 2015-07-15
Publication date: 2016-12-29
Also published as: CN105047843A; CN105047843B

Abstract

A method for preparing a microporous diaphragm by means of multilayer coextrusion and unilateral stretching. Functional layers (1, 3) with added inorganic filler or other pore-forming filler and a polyolefin microporous membrane (2) are compounded by means of multilayer coextrusion for casting pieces, a multilayer composite microporous membrane precursor is molded at one step, and then the composite membrane precursor is subjected to heat treatment, multilayer compounding and unilateral stretching to obtain a high-performance microporous membrane. The method is perfect in technology, high in production efficiency, free from pollution, low in cost and beneficial to large-scale production; furthermore, after the method is adopted, the pore size and distribution of a microporous membrane are easily adjusted; and the microporous membrane obtained by the method is uniform in pore size distribution.

Description

Method for preparing high-safety multilayer lithium battery separator

Technical field

The present invention relates to the field of microporous membranes, and more particularly to a method for preparing a microporous membrane of a polyolefin material, and to the use of a polyolefin microporous membrane prepared by such a method.

Background technique

In recent years, polyolefin microporous membranes have been widely used in the fields of battery separators, filtration separation membranes, medical membranes and the like. In the application process, low cost and high efficiency, and the preparation of products with pore distribution and uniform pore size are a major technical difficulty. Especially in the field of battery separators, the uniform distribution of the pores and the uniform pore size are a great guarantee for the superior performance of the battery. At the same time, with the demand for clean energy and the awareness of environmental protection, the electric vehicle industry has also ushered in a period of rapid development. Therefore, high-safety, high-discharge-rate energy storage batteries have emerged as the times require, and more and more technical workers and entrepreneurs pay attention.

Multilayer composite microporous membranes are prepared through different functional layers, thereby obtaining a microporous membrane with high safety. Such techniques have been reported frequently. Chinese patent CN101779311A discloses a preparation method of a multi-layer microporous membrane, which is characterized in that a high heat resistant material is coated on a polyolefin microporous membrane to achieve the purpose of improving the safety of the microporous membrane, however, the method is The process is cumbersome, the process is numerous, the cost is high, the efficiency is low, and the process waste is environmentally polluted.

Summary of the invention

The present invention prepares a microporous membrane by a method of multi-layer coextrusion followed by uniaxial stretching. The method has the perfect process technology, and the composite layer of the inorganic filler or other pore-forming filler is mixed with the polyolefin microporous membrane by a multi-layer co-extrusion method, and the multilayer composite microporous membrane precursor is formed at one time. Thereafter, the composite film precursor is heat-treated, multi-layered, and uniaxially stretched to obtain a high-performance microporous film. The microporous membrane obtained by the method has uniform pore size distribution, high production efficiency, no pollution, low cost and is advantageous for mass production. In addition, the pore size and distribution of the method are easy to adjust.

The object of the present invention is to provide a method for preparing a multi-layer composite high-performance microporous membrane, wherein the microporous membrane prepared by the method has two layers of high-strength and high-melting functional layers for improving safety during use of the battery. performance.

The above object of the present invention can be achieved by the following technical solutions:

a, cast piece: the pore-forming additive and the functional layer resin are mixed into the functional layer resin A, wherein the pore-forming additive accounts for 20% to 80% by weight, and then is co-extruded with the polyolefin resin B, wherein A: B: A three-layer extrusion thickness ratio of 10:80:10-20:60:20, functional layer resin A is two skin layers, polyolefin resin B is an intermediate layer, the precursor film is prepared through this step;

b, heat treatment: the precursor film in step a is subjected to heat treatment at a temperature of 80 to 150 ° C for 2 to 14 hours to obtain a heat-treated film;

c, compounding: the heat-treated film prepared in step b is recombined at a compound temperature of 0 to 150 ° C;

d. Stretching: The heat-treated film composited in the step c is drawn into a hole at a stretching temperature of 25 to 150 ° C and a stretching ratio of 1 to 3 times to obtain a final microporous film.

The pore-forming additive in the step a includes the pore-forming additive being selected from the group consisting of oxides, hydroxides, sulfides, nitrides, carbides, or mixtures thereof of at least one of metal or semiconductor elements. Among them, metal elements such as Ca, Al, Si, Mg, Zn or Ba, etc., semiconductor elements such as silicon, germanium, boron, selenium, tellurium or carbon.

The functional layer resin in the step a includes: polyethylene, polypropylene, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyurethane, polymethylpentene (PMP), polyethylene terephthalate Glycol ester (PET), polycarbonate (PC), polyester, polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyoxymethylene (PMO), polymethyl methacrylate (PMMA), polyoxyethylene (PEO), or cellulose, or a mixture of two or more thereof.

The polyolefin resin in the step a is preferably polypropylene or polyethylene.

The pore-forming additive in the step a is mixed with the functional layer resin, wherein the pore-forming additive preferably has a weight ratio of 30% to 70%.

The extrusion thickness ratio of the functional layer to the polyolefin resin layer in the step a is: the functional layer and the polyolefin layer are combined into an ABA three-layer structure, and the extrusion preferably has a thickness ratio of A:B:A of 15:70:15. ~20:60:20.

The heat treatment temperature in the step b is preferably 100 to 120 ° C, and the treatment time is 5 to 10 hours.

The number of composite layers in the step c may preferably be 2 to 6 layers, and the composite temperature is preferably 80 to 120 °C.

The number of the stretched layers in the step d may preferably be 2 to 24 layers, the stretching temperature is preferably 80 to 120 ° C, and the stretching ratio is 1.5 to 2 times.

Advantageous Effects Description: The microporous membrane obtained by this method has uniform pore size distribution, high production efficiency, no pollution, low cost, low equipment input cost, and is advantageous for mass production. In addition, the pore size and distribution of the method are easy to adjust. By changing the proportion of the pore-forming filler and the stretching ratio, the porosity of the microporous membrane can be easily changed, thereby changing the pore distribution and the pore size. The invention introduces the concept of a composite process in the process, can realize multi-level synchronous stretching, and greatly increases production efficiency.

DRAWINGS

Figure 1 three-layer diaphragm structure

1 and 3 are functional layers prepared by mixing resin and pore-forming filler; 2 is a polyolefin microporous layer; 4 is a microporous structure and distribution on a functional layer; 5 is a microporous structure and distribution on a polyolefin microporous layer

Figure 2 is a schematic diagram showing the pore size distribution of the comparative sample.

detailed description

The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

In the examples, the thickness of the sample is all referenced to 16 μm. For other conditions, see the above technical solutions, and the differences will be explained in the specific examples.

Example 1

The calcium carbonate (CaCO ₃ ) powder was added to the polypropylene at a mass ratio of 30%, and then extruded with a polypropylene resin through a three-layer co-extrusion casting die to form a precursor film of the ABA three-layer structure, and the layer A was The CaCO ₃ is mixed with polypropylene, the B layer is a polypropylene layer, and the three layers are extruded to a thickness ratio of 20:60:20. The precursor film is cooled by a casting roll to complete the casting process. The precursor film was heat-treated at 140 ° C for 4 hours to obtain a heat treatment. The heat-treated film was laminated in two layers by a special composite device, and the composite temperature was 50 °C.

The heat-treated film after the two-layer composite was stretched in a pattern of 6 unwinding and 12-layer stretching, and the stretching temperature was 140 ° C, and the stretching ratio was 2 times to obtain a finished product.

Example 2

The aluminum hydroxide (Al(OH) ₃ ) powder was added to the polypropylene in a mass ratio of 50%, and then extruded with a polypropylene resin through a three-layer co-extrusion casting die to form a precursor film of the ABA three-layer structure. The layer A is a mixed layer of Al(OH) ₃ and polypropylene, the layer B is a layer of polypropylene, and the thickness ratio of the three layers is 15:70:15. The precursor film is cooled by a casting roll to complete the casting process. The precursor film was heat-treated at 130 ° C for 8 hours to obtain a heat-treated film. The heat-treated film was laminated in three layers by a special composite equipment, and the composite temperature was 30 °C.

The heat-treated film roll after the three-layer composite was stretched in a pattern of 4 unwinding and 12-layer stretching, and the stretching temperature was 120 ° C, and the stretching ratio was 1.5 times to obtain a finished product.

Example 3

The calcium carbonate (CaCO ₃ ) powder was added to the polyester in a mass ratio of 30%, and then extruded with a polypropylene resin through a three-layer co-extrusion casting die to form a precursor film of the ABA three-layer structure, and the layer A was The CaCO ₃ is mixed with the polyester layer, the B layer is a polypropylene layer, and the three layers are extruded to a thickness ratio of 10:80:10. The precursor film is cooled by a casting roll to complete the casting process. The precursor film was heat-treated at 120 ° C for 12 hours to obtain a heat-treated film. The heat-treated film was laminated in four layers by a special composite equipment, and the composite temperature was 60 °C.

The heat-treated film roll after the four-layer composite was stretched in a pattern of four unwinding and 16-layer stretching, and the stretching temperature was 100 ° C, and the stretching ratio was 2.5 times to obtain a finished product.

Example 4

The polypropylene resin is extruded through a three-layer co-extrusion casting die to form a precursor film of the ABA three-layer structure, the A layer is a polypropylene layer, the B layer is also a polypropylene layer, and the three layers are extruded to a thickness ratio of 15: 70:15. The precursor film is cooled by a casting roll to complete the casting process. The precursor film was heat-treated at 130 ° C for 8 hours to obtain a heat-treated film. The heat-treated film was laminated in three layers by a special composite equipment, and the composite temperature was 30 °C.

The performance parameters of all the embodiments are shown in Table 1.

Table 1 Example sample performance parameters

Note: "MD tensile strength" means that the sample is tested for tensile strength in a direction parallel to the direction of stretching.

As shown in Table 1, Example 4 did not add pore-forming filler and other functional layer resins, and the obtained product was similar to the existing marketed microporous membrane. From the results of the data of Example 1, Example 2, and Example 3, after the addition of the functional layer, the properties of the microporous membrane were significantly improved, especially in terms of strength, and the improvement was remarkable, and the microporous membrane was significantly improved. Safety performance in the field of lithium battery applications.

Example 4

Prepared by the method of Example 1, wherein the processing ratio, and the test results are shown in Table 2.

Table 2

As is clear from Table 2, in the case where both the porosity and the pore type distribution and the large size are taken into consideration, the preferred technical scope of the present invention has a technical effect of better tensile strength and puncture strength.

In addition, as shown in FIG. 2, the pore size distribution and size of the microporous membrane can be easily changed by changing the formulation ratio. It can also be seen from the figure that the preferred technical range can obtain a microporous membrane with a more concentrated pore size distribution and a more uniform pore size, thereby ensuring a more uniform performance of the microporous membrane. In particular, the multi-layer lithium battery separator prepared by the pore-forming additive in the range of 30% to 70% has a more remarkable technical effect. Similar technical effects are obtained for other functional layer resins and polyolefin resins.

The above embodiments are merely preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention belong to the present invention. The scope of the claim.

Claims

A method for preparing a multilayer composite lithium battery separator, comprising the steps of:

a, cast piece: the pore-forming additive and the functional layer resin are mixed into the functional layer resin A, wherein the pore-forming additive accounts for 20% to 80% by weight, and then is co-extruded with the polyolefin resin B, wherein A: B: A three-layer extrusion thickness ratio of 10:80:10-20:60:20, functional layer resin A is two skin layers, polyolefin resin B is an intermediate layer, the precursor film is prepared through this step;

b, heat treatment: the precursor film in step a is subjected to heat treatment at a temperature of 80 to 150 ° C for 2 to 14 hours to obtain a heat-treated film;

c, compounding: the heat-treated film prepared in step b is recombined at a compound temperature of 0 to 150 ° C;

d. Stretching: The heat-treated film composited in the step c is drawn into a hole at a stretching temperature of 25 to 150 ° C and a stretching ratio of 1 to 3 times to obtain a final microporous film.
The method according to claim 1, wherein the pore-forming filler preferably has a weight ratio of 30% to 70%.
The method according to claim 1, wherein the pore-forming filler is selected from at least one of a metal or a semiconductor element, an oxide, a sulfide, a nitride, a carbide, or a mixture thereof.
The method according to claim 3, wherein the metal element is selected from the group consisting of Ca, Al, Si, Mg, Zn or Ba, and the semiconductor element is selected from the group consisting of silicon, germanium, boron, selenium, tellurium or carbon.
The preparation method according to claim 1, wherein the functional layer resin is selected from the group consisting of polyethylene, polypropylene, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyurethane, and polymethylpentene ( PMP), polyethylene terephthalate (PET), polycarbonate (PC), polyester, polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyoxymethylene (PMO), polymethacrylic acid Methyl ester (PMMA), polyoxyethylene (PEO) or cellulose, or a mixture of two or more thereof.
The preparation method according to claim 1 or 2, wherein the ratio of the thickness of the functional layer in the step a to the A:B:A of the polyolefin resin layer is preferably from 15:70:15 to 20:60. :20.
The preparation method according to claim 1 or 2, wherein the heat treatment temperature in the step b is preferably 100 to 120 ° C, and the treatment time is 5 to 10 hours.
The preparation method according to claim 1 or 2, wherein the number of the composite layers in the step c is preferably 2 to 6 layers, and the composite temperature is preferably 80 to 120 °C.
The preparation method according to claim 1 or 2, wherein the number of the stretched layers in the step d is preferably 2 to 24 layers, the stretching temperature is preferably 80 to 120 ° C, and the stretching ratio is 1.5 to 2 times.
A multilayer composite lithium battery separator, characterized in that the battery separator is prepared according to the method of any of claims 1-9.