Preparation method for lithium battery separator having low shutdown temperature and high strength

Abstract

A preparation method for a lithium battery separator having a low shutdown temperature and high strength, comprising the following steps: mixing raw materials, extruding, casting a cast piece, longitudinal stretching, first transverse stretching, extracting, second transverse stretching, and film forming, to obtain a lithium battery separator. The raw materials of the lithium battery separator comprise the following components in parts by weight: 15-27 parts of ultra-high molecular weight polyethylene, 1-6 parts of pyrolyzed polyethylene wax, 0.4-1.5 parts of a toughening agent, and 70-80 parts of solvent oil. By means of the described technical solution, the problems in the prior art of lithium battery separators having high shutdown temperatures and low strength are solved.

Description

A method for preparing a high-strength lithium battery separator with low pore-closure temperature Technical Field

[0001] This invention relates to the field of lithium battery separator technology, specifically to a method for preparing a high-strength lithium battery separator with low pore-closing temperature. Background Technology

[0002] With the booming development of the new energy vehicle industry, my country's lithium battery industry has risen to a core position in the global supply chain. However, with the continuous emergence of new models, consumers are paying increasing attention to vehicle safety performance, especially in the key technology of lithium battery separators, where their strength has become an important standard for measuring safety.

[0003] Lithium-ion battery separators need to possess both high strength and low pore-closure temperature to ensure the structural stability of the lithium-ion battery while enabling rapid response at relatively low temperatures to prevent thermal runaway. However, the practical challenge lies in the fact that traditional high-strength lithium-ion battery separators, such as ultra-high molecular weight polyethylene, have pore-closure temperatures exceeding 135°C, which contradicts the goal of achieving even lower pore-closure temperatures.

[0004] Currently, the industry is attempting to incorporate low-melting-point materials into high-strength lithium-ion battery separators. While this helps lower the pore-closing temperature to some extent, it also significantly reduces the strength of the lithium-ion battery separator. Therefore, developing a method for preparing a high-strength lithium-ion battery separator with a low pore-closing temperature is of great significance. Summary of the Invention

[0005] This invention proposes a method for preparing a high-strength lithium battery separator with low pore-closure temperature, which solves the problems of high pore-closure temperature and low strength in related technologies.

[0006] The technical solution of the present invention is as follows: The present invention proposes a high-strength lithium battery separator with low pore temperature, the raw materials of which include the following components in parts by weight: 15-27 parts of ultra-high molecular weight polyethylene, 1-6 parts of pyrolytic polyethylene wax, 0.4-1.5 parts of toughening agent, and 70-80 parts of solvent oil.

[0007] As a further technical solution, the mass ratio of ultra-high molecular weight polyethylene to pyrolytic polyethylene wax is 4-5:1.

[0008] In this invention, when the mass ratio of ultra-high molecular weight polyethylene to pyrolytic polyethylene wax is 4 to 5:1, it helps to further improve the strength of the lithium-ion battery separator.

[0009] As a further technical solution, the weight-average molecular weight of the ultra-high molecular weight polyethylene is 1.5 million to 5 million.

[0010] In this invention, ultra-high molecular weight polyethylene can improve the strength of lithium-ion battery separators. The weight-average molecular weight of ultra-high molecular weight polyethylene is preferably 1.5 million to 5 million, and more preferably 3 million to 5 million.

[0011] As a further technical solution, the softening point of the pyrolytic polyethylene wax is 105-115℃.

[0012] In this invention, pyrolytic polyethylene wax can effectively reduce the pore-closing temperature of lithium-ion battery separators. The softening point of pyrolytic polyethylene wax is preferably 105-115°C, and more preferably 105-110°C.

[0013] As a further technical solution, the toughening agent is one or more of 35BA40 toughening agent, AX8900 toughening agent, and 28MA07 toughening agent.

[0014] In this invention, the addition of toughening agent effectively improves the strength of lithium-ion battery separator. The toughening agent can be selected from Arkema's 35BA40 toughening agent, AX8900 toughening agent and 28MA07 toughening agent, etc., and is preferably 35BA40 toughening agent.

[0015] As a further technical solution, the solvent oil includes one of white oil, castor oil, rapeseed oil, peanut oil, paraffin oil, and mineral oil.

[0016] As a further technical solution, the raw materials also include 0.1 to 0.3 parts of aluminum dihydroxyaminoacetate and 0.1 to 1 part of nano-calcium carbonate.

[0017] In this invention, by adding aluminum dihydroxyaminoacetate and nano-calcium carbonate, the organic and inorganic processes can synergistically enhance the crystallization effect of ultra-high molecular weight polyethylene, thereby further improving the strength of the lithium-ion battery separator.

[0018] As a further technical solution, the weight ratio of aluminum dihydroxyaminoacetate and nano-calcium carbonate is 1:2 to 3.

[0019] In this invention, when the weight ratio of aluminum dihydroxyaminoacetate to nano-calcium carbonate is 1:2 to 3, it helps to further improve the strength of the lithium-ion battery separator.

[0020] As a further technical solution, the nano-calcium carbonate is microencapsulated nano-calcium carbonate; in the microencapsulated nano-calcium carbonate, the core material is nano-calcium carbonate and the wall material is polyaniline.

[0021] In this invention, the use of microencapsulated nano-calcium carbonate can effectively prevent the large-scale aggregation caused by the large specific surface area of ​​nano-calcium carbonate, thereby improving the uniformity of the lithium-ion battery separator and further improving the strength of the lithium-ion battery separator.

[0022] As a further technical solution, the preparation method of the microencapsulated nano-calcium carbonate includes the following steps: S1, dissolving polyaniline in N-methylpyrrolidone, adding nano-calcium carbonate, dispersing evenly to obtain a mixed solution; S2, after atomizing and drying the mixed solution, obtaining the microencapsulated nano-calcium carbonate.

[0023] As a further technical solution, the weight ratio of the nano-calcium carbonate to polyaniline is 10:1 to 3.

[0024] In this invention, when the weight ratio of nano-calcium carbonate to polyaniline is 10:1 to 3, it helps to further improve the strength of the lithium-ion battery separator.

[0025] As a further technical solution, the particle size of the nano-calcium carbonate is 50-100 nm.

[0026] The present invention also proposes a method for preparing the low-closure-temperature high-strength lithium battery separator, comprising the following steps: mixing raw materials, extruding, casting, longitudinal stretching, first transverse stretching, extraction, second transverse stretching, and obtaining the film after film formation.

[0027] As a further technical solution, the temperature during mixing is 40–70°C.

[0028] As a further technical solution, the temperature during extrusion is 180-220°C.

[0029] As a further technical solution, the temperature during longitudinal stretching is 100-120℃, and the stretching ratio is 6-10 times.

[0030] As a further technical solution, during the first transverse stretching, the temperature is 100-120℃ and the stretching ratio is 6-12 times.

[0031] As a further technical solution, the extraction temperature is 15-25℃.

[0032] As a further technical solution, the temperature during the secondary transverse stretching is 125-135℃, and the stretching ratio is 1.2-1.5 times.

[0033] The working principle and beneficial effects of this invention are as follows: In this invention, by using low-melting-point, low-molecular-weight pyrolytic polyethylene wax and ultra-high molecular weight polyethylene (UHMWPE) together, the pyrolytic polyethylene wax can be uniformly distributed inside the lithium-ion battery separator. When the lithium-ion battery separator is heated to a certain temperature, the pyrolytic polyethylene wax melts, attracting the entire separator's closed pores, thereby reducing the separator's closed-pore temperature to below 130°C. The addition of a toughening agent can effectively prevent the poor crystallization effect of UHMWPE due to the low melting point and low molecular weight of the pyrolytic polyethylene wax. Furthermore, it can make the molecular chains cross-link faster and more tightly during the UHMWPE crystallization process, thereby significantly improving the strength of the lithium-ion battery separator. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] Unless otherwise specified, in the following examples and comparative examples, the particle size of nano-calcium carbonate is 50 nm; the polyaniline is DH11918, purchased from Hubei Dahao Chemical Co., Ltd.; the toughening agent is 35BA40 toughening agent; and the paraffin oil is 50# paraffin oil.

[0036] Example 1 A high-strength lithium-ion battery separator with low closed-cell temperature, the raw materials include the following components in parts by weight: 15 parts of ultra-high molecular weight polyethylene (weight average molecular weight 5 million), 1 part of pyrolytic polyethylene wax (model DP0109F, softening point 115℃), 0.4 parts of toughening agent, and 70 parts of paraffin oil; the preparation method includes the following steps: mixing the components at 45℃ for 1 hour, extruding at 190℃, casting, longitudinally stretching at 110℃ (stretch ratio of 9 times), transversely stretching once at 118℃ (stretch ratio of 10 times), extracting in dichloromethane at 20℃ for 10 minutes, transversely stretching twice at 134℃ (stretch ratio of 1.3 times), forming a film to obtain a lithium-ion battery separator.

[0037] Example 2 A high-strength lithium-ion battery separator with low closed-cell temperature, the raw materials include the following components in parts by weight: 18 parts of ultra-high molecular weight polyethylene (weight average molecular weight 1.5 million), 3 parts of pyrolytic polyethylene wax (model DP0020F, softening point 110℃), 0.6 parts of toughening agent, and 75 parts of paraffin oil; the preparation method includes the following steps: mixing the components at 45℃ for 1 hour, extruding at 190℃, casting, longitudinally stretching at 110℃ (stretch ratio of 9 times), transversely stretching once at 118℃ (stretch ratio of 10 times), extracting in dichloromethane at 20℃ for 10 minutes, transversely stretching twice at 134℃ (stretch ratio of 1.3 times), forming a film to obtain a lithium-ion battery separator.

[0038] Example 3 A high-strength lithium-ion battery separator with low closed-cell temperature, the raw materials include the following components in parts by weight: 27 parts of ultra-high molecular weight polyethylene (weight average molecular weight 3 million), 6 parts of pyrolytic polyethylene wax (model EP620F, softening point 105℃), 1.5 parts of toughening agent, and 80 parts of paraffin oil; the preparation method includes the following steps: mixing the components at 45℃ for 1 hour, extruding at 190℃, casting, longitudinally stretching at 110℃ (stretch ratio of 9 times), transversely stretching once at 118℃ (stretch ratio of 10 times), extracting in dichloromethane at 20℃ for 10 minutes, transversely stretching twice at 134℃ (stretch ratio of 1.3 times), forming a film to obtain a lithium-ion battery separator.

[0039] Example 4 The only difference between this example and Example 2 is that in this example, the weight of the pyrolyzed polyethylene wax is 6 parts.

[0040] Example 5 The only difference between this example and Example 2 is that in this example, the weight of the pyrolyzed polyethylene wax is 4.5 parts.

[0041] Example 6 The only difference between this example and Example 2 is that in this example, the weight of the pyrolyzed polyethylene wax is 3.6 parts.

[0042] Example 7 The only difference between this example and Example 6 is that in this example, the raw materials also include 0.2 parts of aluminum dihydroxyaminoacetate.

[0043] Example 8 The only difference between this example and Example 6 is that in this example, the raw materials also include 0.2 parts of nano calcium carbonate.

[0044] Example 9 The only difference between this example and Example 6 is that in this example, the raw materials also include 0.1 parts of aluminum dihydroxyaminoacetate and 0.1 parts of nano calcium carbonate.

[0045] Example 10 The only difference between this example and Example 9 is that in this example, the weight of aluminum dihydroxyaminoacetate is 0.3 parts and the weight of nano calcium carbonate is 1 part.

[0046] Example 11 The only difference between this example and Example 9 is that in this example, the weight of aluminum dihydroxyaminoacetate is 0.25 parts and the weight of nano calcium carbonate is 0.35 parts.

[0047] Example 12 The only difference between this example and Example 11 is that in this example, the weight of aluminum dihydroxyaminoacetate is 0.1 parts and the weight of nano calcium carbonate is 0.5 parts.

[0048] Example 13 The only difference between this example and Example 11 is that in this example, the weight parts of aluminum dihydroxyaminoacetate are 0.2 parts and the weight parts of nano calcium carbonate are 0.4 parts.

[0049] Example 14 The only difference between this example and Example 11 is that in this example, the weight of aluminum dihydroxyaminoacetate is 0.15 parts and the weight of nano calcium carbonate is 0.45 parts.

[0050] Example 15 The only difference between this example and Example 14 is that in this example, the nano-calcium carbonate is microencapsulated nano-calcium carbonate. The preparation method of microencapsulated nano-calcium carbonate includes the following steps: S1, dissolving polyaniline in N-methylpyrrolidone, adding nano-calcium carbonate, dispersing evenly to obtain a mixed solution; S2, after atomizing and drying the mixed solution, microencapsulated nano-calcium carbonate is obtained; The weight ratio of nano-calcium carbonate to polyaniline is 20:1.

[0051] Example 16 The only difference between this example and Example 15 is that in this example, the weight ratio of nano-calcium carbonate to polyaniline in the microencapsulated nano-calcium carbonate is 10:4.

[0052] Example 17 The only difference between this example and Example 15 is that in this example, the weight ratio of nano-calcium carbonate to polyaniline in the microencapsulated nano-calcium carbonate is 10:1.

[0053] Example 18 The only difference between this example and Example 15 is that in this example, the weight ratio of nano-calcium carbonate to polyaniline in the microencapsulated nano-calcium carbonate is 10:3.

[0054] Comparative Example 1: The only difference between this comparative example and Example 2 is that no pyrolytic polyethylene wax was added in this comparative example.

[0055] Comparative Example 2: The only difference between this comparative example and Example 2 is that no toughening agent was added in this comparative example.

[0056] Comparative Example 3: The only difference between this comparative example and Example 2 is that no pyrolytic polyethylene wax and toughening agent were added in this comparative example.

[0057] Comparative Example 4: The only difference between this comparative example and Example 2 is that the pyrolytic polyethylene wax is replaced with an equal amount of low-melting-point polyethylene wax (model P-200, softening point 110°C).

[0058] Comparative Example 5: The only difference between this comparative example and Example 2 is that the pyrolytic polyethylene wax was replaced with an equal amount of low-melting-point polyethylene (model LA0710, melting point 107°C).

[0059] The pore-closure temperatures of the lithium-ion battery separators prepared in Examples 1-18 and Comparative Examples 1-5 were measured using a differential scanning calorimeter (model DZ-DSC300). The heating rate was 10 °C / min, the cutoff temperature was 220 °C, and the flow rate of the nitrogen atmosphere was 50 mL / min. The measured pore-closure temperatures of the lithium-ion battery separators in Examples 1-18 and Comparative Examples 2, 4, and 5 were 125-129 °C, the temperature of the lithium-ion battery separator in Comparative Example 1 was 135 °C, and the temperature of the lithium-ion battery separator in Comparative Example 3 was 136 °C.

[0060] The tensile strength and puncture strength of the lithium-ion battery separators prepared in Examples 1-18 and Comparative Examples 1-5 were tested according to GB / T 36363-2018 "Polyolefin Separators for Lithium-ion Batteries". For the tensile strength test, the test speed was 250 mm / min; for the puncture strength test, the test speed was 100 mm / min. The test results are shown in Table 1 below.

[0061] Table 1 Test Results

[0062] A comparison between Example 2 and Comparative Example 2 shows that the addition of a toughening agent to the lithium-ion battery separator can significantly eliminate the negative impact of pyrolytic polyethylene wax and significantly improve the strength of the lithium-ion battery separator. A comparison between Example 2 and Comparative Examples 4-5 shows that, compared with ordinary low-melting-point polyethylene wax and low-melting-point polyethylene, the combined use of pyrolytic polyethylene wax and ultra-high molecular weight polyethylene can improve the strength of the lithium-ion battery separator while reducing the pore-closure temperature.

[0063] A comparison of Examples 3-4 and Examples 5-6 shows that a mass ratio of ultra-high molecular weight polyethylene to pyrolytic polyethylene wax of 4-5:1 helps to further improve the strength of the lithium-ion battery separator. A comparison of Examples 6-8 and Examples 9 shows that the addition of aluminum dihydroxyaminoacetate and nano-calcium carbonate can further improve the strength of the lithium-ion battery separator. A comparison of Examples 11-12 and Examples 13-14 shows that a weight ratio of aluminum dihydroxyaminoacetate to nano-calcium carbonate of 1:2-3 helps to further improve the strength of the lithium-ion battery separator. A comparison of Examples 14 and Examples 15-18 shows that microencapsulation of nano-calcium carbonate helps to further improve the strength of the lithium-ion battery separator. A comparison of Examples 15-16 and Examples 17-18 shows that a weight ratio of nano-calcium carbonate to polyaniline of 10:1-3 helps to further improve the strength of the lithium-ion battery separator.

[0064] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-strength lithium battery separator with low pore-closure temperature, characterized in that, The raw materials include the following components in parts by weight: 15-27 parts of ultra-high molecular weight polyethylene, 1-6 parts of pyrolyzed polyethylene wax, 0.4-1.5 parts of toughening agent, and 70-80 parts of solvent oil.

2. A high-strength lithium battery separator with low pore-closure temperature, characterized in that, The mass ratio of ultra-high molecular weight polyethylene to pyrolytic polyethylene wax is 4-5:

1.

3. The low-closure-temperature, high-strength lithium battery separator according to claim 1, characterized in that, The weight-average molecular weight of the ultra-high molecular weight polyethylene is 1.5 million to 5 million.

4. The low-closure-temperature, high-strength lithium battery separator according to claim 1, characterized in that, The softening point of the pyrolytic polyethylene wax is 105–115°C.

5. The low-closure-temperature, high-strength lithium battery separator according to claim 1, characterized in that, The toughening agent is one or more of 35BA40 toughening agent, AX8900 toughening agent, and 28MA07 toughening agent.

6. The low-closure-temperature, high-strength lithium battery separator according to claim 1, characterized in that, The raw materials also include 0.1 to 0.3 parts of aluminum dihydroxyaminoacetate and 0.1 to 1 part of nano-calcium carbonate.

7. A low-closure-temperature, high-strength lithium battery separator according to claim 6, characterized in that, The weight ratio of aluminum dihydroxyaminoacetate to nano-calcium carbonate is 1:2 to 3.

8. A low-closure-temperature, high-strength lithium battery separator according to claim 6, characterized in that, The nano-calcium carbonate is microencapsulated nano-calcium carbonate. In the microencapsulated nano-calcium carbonate, the core material is nano-calcium carbonate and the wall material is polyaniline.

9. A low-closure-temperature, high-strength lithium battery separator according to claim 8, characterized in that, The preparation method of the microencapsulated nano-calcium carbonate includes the following steps: S1. Dissolve polyaniline in N-methylpyrrolidone, add nano-calcium carbonate, and disperse evenly to obtain a mixture; S2. The mixture is dried by atomization to obtain the microencapsulated nano calcium carbonate.

10. A method for preparing a low-closure-temperature, high-strength lithium battery separator as described in any one of claims 1 to 9, characterized in that, Includes the following steps: The raw materials are mixed, extruded, cast into sheets, stretched longitudinally, stretched once laterally, extracted, stretched twice laterally, and then the film is obtained.

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