A method for preparing a lithium battery separator with low closure temperature and high strength

Abstract

The present invention relates to the technical field of lithium battery separators and proposes a method for preparing a lithium battery separator with low closure temperature and high strength. The method comprises the following steps: mixing raw materials, extruding, tape casting, longitudinal stretching, primary transverse stretching, extraction, secondary transverse stretching, and film formation. The raw materials for the lithium battery separator include the following components by weight: 15-27 parts ultra-high molecular weight polyethylene, 1-6 parts pyrolysis polyethylene wax, 0.4-1.5 parts toughening agent, and 70-80 parts solvent oil. This technical solution solves the problems of high closure temperature and low strength of lithium battery separators in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery separators, and in particular to a method for preparing a lithium battery separator with low closing temperature and high strength. Background Art

[0002] With the booming development of the new energy vehicle industry, my country's lithium battery industry has become a core player in the global supply chain. However, with the continuous emergence of new models, consumers are increasingly concerned about vehicle safety performance, especially in the key technical link of lithium battery separators, whose strength has become an important safety criterion.

[0003] Lithium battery separators must possess both high strength and a low pore temperature to ensure structural stability while enabling rapid response at relatively low temperatures to prevent thermal runaway. However, the challenge is that conventional high-strength lithium battery separators, such as ultra-high molecular weight polyethylene (UHMWPE), have pore temperatures exceeding 135°C, which runs counter to the goal of achieving a lower pore temperature.

[0004] Currently, the industry is trying to add low-melting-point materials to high-strength lithium battery separators. Although this helps to reduce the closed-cell temperature to a certain extent, it also significantly reduces the strength of the lithium battery separator. Therefore, it is of great significance to develop a method for preparing a lithium battery separator with a low closed-cell temperature and high strength. Summary of the Invention

[0005] The present invention provides a method for preparing a lithium battery separator with low closed-pore temperature and high strength, which solves the problem of high closed-pore temperature and low strength of lithium battery separators in related technologies.

[0006] The technical solutions of the present invention are as follows:

[0007] The present invention provides a low-closure-temperature high-strength lithium battery separator, 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 cracked polyethylene wax, 0.4-1.5 parts of a toughening agent, and 70-80 parts of solvent oil.

[0008] As a further technical solution, the mass ratio of the ultra-high molecular weight polyethylene to the cracked polyethylene wax is 4-5:1.

[0009] In the present invention, when the mass ratio of ultra-high molecular weight polyethylene to cracked polyethylene wax is 4 to 5:1, it helps to further improve the strength of the lithium-ion battery separator.

[0010] As a further technical solution, the weight average molecular weight of the ultra-high molecular weight polyethylene is 1.5 million to 5 million.

[0011] In the present invention, the ultra-high molecular weight polyethylene can improve the strength of the lithium-ion battery separator. The weight average molecular weight of the ultra-high molecular weight polyethylene is preferably 1.5 million to 5 million, more preferably 3 million to 5 million.

[0012] As a further technical solution, the softening point of the cracked polyethylene wax is 105-115°C.

[0013] In the present invention, the cracked polyethylene wax can effectively reduce the closed-cell temperature of the lithium-ion battery separator. The softening point of the cracked polyethylene wax is preferably 105-115°C, more preferably 105-110°C.

[0014] As a further technical solution, the toughening agent is one or more of 35BA40 toughening agent, AX8900 toughening agent, and 28MA07 toughening agent.

[0015] In the present invention, the addition of a toughening agent effectively improves the strength of the lithium-ion battery separator. The toughening agent can be selected from Arkema's 35BA40 toughening agent, AX8900 toughening agent, and 28MA07 toughening agent, and is preferably 35BA40 toughening agent.

[0016] As a further technical solution, the solvent oil includes one of white oil, castor oil, rapeseed oil, peanut oil, paraffin oil, and mineral oil.

[0017] As a further technical solution, the raw materials further include 0.1 to 0.3 parts of dihydroxyamino aluminum acetate and 0.1 to 1 parts of nano calcium carbonate.

[0018] In the present invention, by adding dihydroxyaminoaluminum acetate and nano-calcium carbonate, the crystallization effect of ultra-high molecular weight polyethylene can be enhanced in an organic-inorganic synergistic manner, thereby further improving the strength of the lithium-ion battery separator.

[0019] As a further technical solution, the weight ratio of the dihydroxyaminoaluminum acetate to nano-calcium carbonate is 1:2~3.

[0020] In the present invention, when the weight ratio of dihydroxyaminoaluminum acetate to nano-calcium carbonate is 1:2-3, it helps to further improve the strength of the lithium-ion battery separator.

[0021] As a further technical solution, the nano calcium carbonate is microencapsulated nano calcium carbonate;

[0022] In the microencapsulated nano-calcium carbonate, the core material is nano-calcium carbonate and the wall material is polyaniline.

[0023] In the present invention, the use of microencapsulated nano calcium carbonate can effectively prevent a large amount of agglomeration 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.

[0024] As a further technical solution, the preparation method of the microencapsulated nano calcium carbonate comprises the following steps:

[0025] S1, dissolving polyaniline in N-methylpyrrolidone, adding nano calcium carbonate, and dispersing uniformly to obtain a mixed solution;

[0026] S2. The mixed liquid is atomized and dried to obtain the microencapsulated nano-calcium carbonate.

[0027] As a further technical solution, the weight ratio of the nano-calcium carbonate to polyaniline is 10:1-3.

[0028] In the present invention, when the weight ratio of nano-calcium carbonate to polyaniline is 10:1-3, it helps to further improve the strength of the lithium-ion battery separator.

[0029] As a further technical solution, the particle size of the nano calcium carbonate is 50-100 nm.

[0030] The present invention also proposes a method for preparing the low-closure-temperature high-strength lithium battery separator, which includes the following steps: mixing raw materials, extruding, casting, longitudinal stretching, primary transverse stretching, extraction, secondary transverse stretching, and forming a film.

[0031] As a further technical solution, during the mixing, the temperature is 40-70°C.

[0032] As a further technical solution, the temperature during the extrusion is 180-220°C.

[0033] As a further technical solution, during the longitudinal stretching, the temperature is 100-120° C. and the stretching ratio is 6-10 times.

[0034] As a further technical solution, during the one-time transverse stretching, the temperature is 100-120° C. and the stretching ratio is 6-12 times.

[0035] As a further technical solution, during the extraction, the temperature is 15-25°C.

[0036] As a further technical solution, during the secondary transverse stretching, the temperature is 125-135° C. and the stretching ratio is 1.2-1.5 times.

[0037] The working principle and beneficial effects of the present invention are:

[0038] In the present invention, by combining low-melting-point, low-molecular-weight pyrolyzed polyethylene wax with ultra-high molecular-weight polyethylene, the pyrolyzed polyethylene wax can be evenly distributed within the lithium battery separator. When the lithium battery separator is heated to a certain temperature, the pyrolyzed polyethylene wax melts, closing the entire pores of the separator, thereby lowering the pore-closing temperature to below 130°C. The addition of a toughening agent can effectively prevent the poor crystallization of the ultra-high molecular-weight polyethylene due to the low melting point and low molecular weight of the pyrolyzed polyethylene wax. It can also accelerate and tighten the cross-linking of the molecular chains of the ultra-high molecular-weight polyethylene during crystallization, significantly improving the strength of the lithium-ion battery separator. DETAILED DESCRIPTION

[0039] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0040] In the following examples and comparative examples, unless otherwise specified, the particle size of nano-calcium carbonate is 50 nm; the product number of 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.

[0041] Example 1

[0042] A low-shutdown-temperature, high-strength lithium battery separator, comprising the following components in parts by weight: 15 parts of ultra-high molecular weight polyethylene (weight-average molecular weight 5,000,000), 1 part of cracked polyethylene wax (model DP0109F, softening point 115°C), 0.4 parts of a toughening agent, and 70 parts of paraffin oil.

[0043] The preparation method includes the following steps: mixing the components at 45°C for 1 hour, extruding at 190°C, casting a sheet, longitudinally stretching at 110°C (stretching ratio of 9 times), transversely stretching once at 118°C (stretching ratio of 10 times), extracting in dichloromethane at 20°C for 10 minutes, transversely stretching twice at 134°C (stretching ratio of 1.3 times), forming a film, and obtaining a lithium-ion battery separator.

[0044] Example 2

[0045] A low-shutdown-temperature, high-strength lithium battery separator, comprising 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 cracked polyethylene wax (model DP0020F, softening point 110°C), 0.6 parts of a toughening agent, and 75 parts of paraffin oil.

[0046] The preparation method includes the following steps: mixing the components at 45°C for 1 hour, extruding at 190°C, casting a sheet, longitudinally stretching at 110°C (stretching ratio of 9 times), transversely stretching once at 118°C (stretching ratio of 10 times), extracting in dichloromethane at 20°C for 10 minutes, transversely stretching twice at 134°C (stretching ratio of 1.3 times), forming a film, and obtaining a lithium-ion battery separator.

[0047] Example 3

[0048] A low-shutdown-temperature, high-strength lithium battery separator, comprising the following components in parts by weight: 27 parts of ultra-high molecular weight polyethylene (weight-average molecular weight 3,000,000), 6 parts of cracked polyethylene wax (model EP620F, softening point 105°C), 1.5 parts of a toughening agent, and 80 parts of paraffin oil;

[0049] The preparation method includes the following steps: mixing the components at 45°C for 1 hour, extruding at 190°C, casting a sheet, longitudinally stretching at 110°C (stretching ratio of 9 times), transversely stretching once at 118°C (stretching ratio of 10 times), extracting in dichloromethane at 20°C for 10 minutes, transversely stretching twice at 134°C (stretching ratio of 1.3 times), forming a film, and obtaining a lithium-ion battery separator.

[0050] Example 4

[0051] The only difference between this embodiment and embodiment 2 is that, in this embodiment, the weight portion of the cracked polyethylene wax is 6 parts.

[0052] Example 5

[0053] The only difference between this embodiment and embodiment 2 is that, in this embodiment, the weight portion of the cracked polyethylene wax is 4.5 parts.

[0054] Example 6

[0055] The only difference between this embodiment and embodiment 2 is that, in this embodiment, the weight portion of the cracked polyethylene wax is 3.6 parts.

[0056] Example 7

[0057] The only difference between this embodiment and embodiment 6 is that, in this embodiment, the raw materials further include 0.2 parts of dihydroxyamino aluminum acetate.

[0058] Example 8

[0059] The only difference between this embodiment and embodiment 6 is that, in this embodiment, the raw materials further include 0.2 parts of nano-calcium carbonate.

[0060] Example 9

[0061] The only difference between this embodiment and embodiment 6 is that, in this embodiment, the raw materials further include 0.1 parts of dihydroxyamino aluminum acetate and 0.1 parts of nano calcium carbonate.

[0062] Example 10

[0063] The only difference between this embodiment and embodiment 9 is that, in this embodiment, the weight portion of dihydroxyamino aluminum acetate is 0.3 parts, and the weight portion of nano-calcium carbonate is 1 part.

[0064] Example 11

[0065] The only difference between this embodiment and embodiment 9 is that, in this embodiment, the weight portion of dihydroxyamino aluminum acetate is 0.25 parts, and the weight portion of nano-calcium carbonate is 0.35 parts.

[0066] Example 12

[0067] The only difference between this embodiment and embodiment 11 is that, in this embodiment, the weight portion of dihydroxyamino aluminum acetate is 0.1 parts, and the weight portion of nano-calcium carbonate is 0.5 parts.

[0068] Example 13

[0069] The only difference between this embodiment and embodiment 11 is that, in this embodiment, the weight portion of dihydroxyamino aluminum acetate is 0.2 parts, and the weight portion of nano-calcium carbonate is 0.4 parts.

[0070] Example 14

[0071] The only difference between this embodiment and embodiment 11 is that, in this embodiment, the weight portion of dihydroxyamino aluminum acetate is 0.15 parts, and the weight portion of nano-calcium carbonate is 0.45 parts.

[0072] Example 15

[0073] The only difference between this embodiment and embodiment 14 is that, in this embodiment, the nano calcium carbonate is microencapsulated nano calcium carbonate, and the preparation method of microencapsulated nano calcium carbonate comprises the following steps:

[0074] S1, dissolving polyaniline in N-methylpyrrolidone, adding nano calcium carbonate, and dispersing uniformly to obtain a mixed solution;

[0075] S2, after the mixed solution is atomized and dried, microencapsulated nano calcium carbonate is obtained;

[0076] The weight ratio of nano-calcium carbonate to polyaniline is 20:1.

[0077] Example 16

[0078] The only difference between this embodiment and Example 15 is that in this embodiment, the weight ratio of nano-calcium carbonate to polyaniline in the microencapsulated nano-calcium carbonate is 10:4.

[0079] Example 17

[0080] The only difference between this embodiment and Example 15 is that in this embodiment, the weight ratio of nano-calcium carbonate to polyaniline in the microencapsulated nano-calcium carbonate is 10:1.

[0081] Example 18

[0082] The only difference between this embodiment and embodiment 15 is that in this embodiment, the weight ratio of nano-calcium carbonate to polyaniline in the microencapsulated nano-calcium carbonate is 10:3.

[0083] Comparative Example 1

[0084] The only difference between this comparative example and Example 2 is that in this comparative example, no cracked polyethylene wax is added.

[0085] Comparative Example 2

[0086] The only difference between this comparative example and Example 2 is that no toughening agent is added in this comparative example.

[0087] Comparative Example 3

[0088] The only difference between this comparative example and Example 2 is that in this comparative example, no cracked polyethylene wax and toughening agent were added.

[0089] Comparative Example 4

[0090] The only difference between this comparative example and Example 2 is that in this comparative example, the cracked polyethylene wax is replaced by an equal amount of low-melting-point polyethylene wax (model P-200, softening point 110° C.).

[0091] Comparative Example 5

[0092] The only difference between this comparative example and Example 2 is that in this comparative example, the cracked polyethylene wax is replaced by an equal amount of low-melting-point polyethylene (model LA0710, melting point 107° C.).

[0093] The closed-cell temperatures of the lithium-ion battery separators prepared in Examples 1-18 and Comparative Examples 1-5 were measured using a differential scanning calorimeter (DZ-DSC300) at a heating rate of 10°C / min, a cutoff temperature of 220°C, and a nitrogen atmosphere flow rate of 50 mL / min. The closed-cell 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.

[0094] 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." The tensile strength test was conducted at a speed of 250 mm / min, while the puncture strength test was conducted at a speed of 100 mm / min. The test results are shown in Table 1 below.

[0095] Table 1 Test results

[0096]

[0097] Comparison of Example 2 and Comparative Example 2 shows that the addition of a toughening agent to a lithium-ion battery separator can significantly eliminate the negative effects of pyrolysis polyethylene wax and significantly improve the strength of the lithium-ion battery separator. Comparison of Example 2 and Comparative Examples 4-5 shows that, compared to ordinary low-melting-point polyethylene wax and low-melting-point polyethylene, the combined use of pyrolysis polyethylene wax and ultra-high molecular weight polyethylene can reduce the closed-cell temperature while improving the strength of the lithium-ion battery separator.

[0098] Comparison of Examples 3-4 with Examples 5-6 shows that when the mass ratio of ultra-high molecular weight polyethylene to cracked polyethylene wax is 4-5:1, it helps to further improve the strength of the lithium-ion battery separator. Comparison of Examples 6-8 with Example 9 shows that the addition of dihydroxyaminoacetic acid aluminum and nano-calcium carbonate can further improve the strength of the lithium-ion battery separator. Comparison of Examples 11-12 with Examples 13-14 shows that when the weight ratio of dihydroxyaminoacetic acid aluminum and nano-calcium carbonate is 1:2-3, it helps to further improve the strength of the lithium-ion battery separator. Comparison of Example 14 with Examples 15-18 shows that microencapsulation of nano-calcium carbonate helps to further improve the strength of the lithium-ion battery separator. Comparison of Examples 15-16 with Examples 17-18 shows that when the weight ratio of nano-calcium carbonate to polyaniline is 10:1-3, it helps to further improve the strength of the lithium-ion battery separator.

[0099] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A low-closure-temperature, high-strength lithium battery separator, 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 cracked polyethylene wax, 0.4-1.5 parts of toughening agent, and 70-80 parts of solvent oil.

2. The low-closure-temperature, high-strength lithium battery separator according to claim 1, characterized in that: The mass ratio of the ultra-high molecular weight polyethylene to the cracked 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 cracked 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 0.1-0.3 parts of dihydroxyamino aluminum acetate and 0.1-1 parts of nano calcium carbonate.

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

8. The 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. The low-closure-temperature, high-strength lithium battery separator according to claim 8, characterized in that: The preparation method of the microencapsulated nano calcium carbonate comprises the following steps: S1, dissolving polyaniline in N-methylpyrrolidone, adding nano calcium carbonate, and dispersing uniformly to obtain a mixed solution; S2. The mixed liquid is atomized and dried to obtain the microencapsulated nano-calcium carbonate.

10. A method for preparing a low-shutdown-temperature, high-strength lithium battery separator according to any one of claims 1 to 9, characterized in that: The following steps are involved: The raw materials are mixed, extruded, cast into sheets, longitudinally stretched, transversely stretched once, extracted, transversely stretched twice, and then formed into a film.

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