Preparation method of lithium ion battery separator with high viscosity and high safety

Abstract

The application relates to the technical field of battery diaphragm, and discloses a lithium ion battery diaphragm with high viscosity and high safety, which is prepared from the following components in parts by weight: 15-20 parts of polyolefin, 80-85 parts of pore-forming agent and 2-4 parts of filler; the viscosity average molecular weight of the polyolefin is 1-4 million; the raw material of the filler comprises component A and component B in a mass ratio of 1:19-19:1; the component A comprises barium stearate; and the component B comprises one or more of lithium molybdate, lithium tungstate and lithium tantalate. Through the technical scheme, the problem of low strength of the lithium battery diaphragm in the related art is solved.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, specifically to a method for preparing a high-viscosity and high-safety lithium-ion battery separator. Background Technology

[0002] With the rapid development of lithium battery separators, the strength requirements for lithium battery separators are becoming increasingly stringent. Generally, higher strength means stronger resistance to dendrite penetration, resulting in a safer battery. Lithium-ion battery separators with insufficient strength are easily punctured during battery charging and discharging due to the expansion and contraction of the electrodes, causing short circuits between the positive and negative electrodes and leading to safety accidents such as battery overheating and fire.

[0003] Common polyolefin lithium battery separators, while possessing good chemical stability and ion conductivity, have certain shortcomings in mechanical properties. The arrangement of their molecular structure makes the intermolecular forces weak when subjected to external forces, making them prone to chain slippage and breakage, thus resulting in insufficient strength of the lithium battery separator.

[0004] Therefore, it is necessary to improve the strength of lithium-ion battery separators to ensure higher safety when they are used in lithium batteries. Summary of the Invention

[0005] This invention proposes a method for preparing a high-viscosity and high-safety lithium-ion battery separator, which solves the problem of low strength of lithium battery separators in related technologies.

[0006] The technical solution of the present invention is as follows:

[0007] This invention proposes a high-viscosity and high-safety lithium-ion battery separator, the raw materials of which include the following components by weight: 15-20 parts of polyolefin, 80-85 parts of pore-forming agent, and 2-4 parts of filler;

[0008] The viscosity-average molecular weight of the polyolefin is 1 million to 4 million.

[0009] The raw materials for the filler include component A and component B in a mass ratio of 1:19 to 19:1;

[0010] Component A includes barium stearate;

[0011] Component B includes one or more of lithium molybdate, lithium tungstate, and lithium tantalate.

[0012] As a further technical solution, the raw materials of the filler include component A and component B in a mass ratio of 1:4 to 7:3.

[0013] As a further technical solution, the polyolefin includes one or both of polyethylene and polypropylene; the pore-forming agent includes white oil.

[0014] In this invention, the strength of the lithium-ion battery separator is further improved by adjusting the mass ratio of component A to component B to 1:4 to 7:3.

[0015] As a further technical solution, the raw material of the filler also includes component C;

[0016] Component C comprises a coupling agent and 1,2-vinyl diphosphonic acid in a mass ratio of 1:1 to 0.5.

[0017] As a further technical solution, the mass ratio of component C to component B is 0.1~0.2:1.

[0018] As a further technical solution, the coupling agent includes one or both of silane coupling agents and titanate coupling agents.

[0019] This invention also proposes a method for preparing a high-viscosity and high-safety lithium-ion battery separator, comprising the following steps:

[0020] S1. Dissolve component C, mix it with component B, and dry to obtain a composite material;

[0021] S2. The composite material is mixed with the remaining components of the lithium-ion battery separator, extruded, cast, cast, biaxially stretched, extracted, and heat-treated to obtain the lithium-ion battery separator.

[0022] In this invention, during the preparation of the lithium-ion battery separator, a coupling agent and 1,2-vinyl diphosphonic acid are used as component C and mixed with component B to prepare a composite material. Then, the composite material is mixed with other components to obtain the lithium battery separator. The composite material prepared by mixing component C and component B improves the compatibility of component B with the polyolefin matrix. Then, it is mixed with other components to obtain the lithium battery separator. In addition to having excellent strength, the heat resistance of the lithium battery separator is also improved.

[0023] As a further technical solution, during the dissolution process, the mass-to-volume ratio of component C to solvent is 1g:50~100mL.

[0024] As a further technical solution, during the extrusion process, the temperature of the extrusion mixing section is 100~160℃, the temperature of the shearing section is 180~220℃, the temperature of the conveying section is 190~220℃, and the extrusion rate is 150~700kg / h.

[0025] The ratio of the extrusion rate to the screw speed is 2.5 to 5.0.

[0026] In this invention, the extrusion mixing section temperature is 100~160℃, the shearing section temperature is 180~220℃, the conveying section temperature is 190~220℃, the extrusion rate is 150~700kg / h, and the ratio of extrusion rate to screw speed is 2.5~5.0. This allows the polyolefin to be fully and evenly mixed with other raw materials, and ensures stable material extrusion, thus guaranteeing the uniformity of the diaphragm.

[0027] As a further technical solution, the casting temperature is 200~250℃.

[0028] As a further technical solution, the casting temperature is 10~30℃.

[0029] In this invention, using a casting temperature of 200~250℃ allows the material to spread evenly during the casting process, forming a uniform film layer. At a casting temperature of 10~30℃, the diaphragm can be rapidly cooled and shaped, reducing internal stress and preventing the generation of diaphragm defects.

[0030] As a further technical solution, the stretching ratio of the longitudinal stretching and the stretching ratio of the transverse stretching during bidirectional stretching are both ≤6 times.

[0031] The extraction was followed by a second transverse stretching; the stretching ratio of the second transverse stretching was ≤1.2 times.

[0032] The ratio of the outlet velocity to the inlet velocity during the heat treatment is ≤1.1.

[0033] In this invention, the longitudinal and transverse stretching ratios are both ≤6 times during biaxial stretching, which avoids the breakage of polyolefin molecular chains and structural damage caused by excessive stretching. While expanding the pores, sufficient strength is retained. After extraction, a second transverse stretching is performed with a stretching ratio of ≤1.2 times, which can further optimize the membrane pore structure.

[0034] The working principle and beneficial effects of this invention are as follows:

[0035] In this invention, polyolefin is the main component of lithium-ion battery separator. Its viscosity-average molecular weight is between 1 million and 4 million, which has the characteristics of high viscosity. The polyolefin molecular chains are long and tightly entangled with each other, forming a stable structural network, reducing the risk of damage during battery operation and improving the safety of lithium-ion batteries.

[0036] Barium stearate, as component A, can improve the processability of polyolefins and, when dispersed in the polyolefin matrix, plays a reinforcing role. Lithium molybdate, lithium tungstate, lithium tantalate, etc., as component B, fill the polyolefin structure with these lithium salt compounds, enhancing the skeletal strength of the separator. Components A and B work synergistically to improve the strength of the lithium-ion battery separator. Detailed Implementation

[0037] 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.

[0038] In the following examples and comparative examples, the coupling agent is KH560, the particle size of barium stearate is 1 μm, the particle size of lithium molybdate is 1 μm, the particle size of lithium tungstate is 100 nm, and the particle size of lithium tantalate is 500 nm.

[0039] Example 1

[0040] The high-viscosity and high-safety lithium-ion battery separator is made of the following components by weight: 15 parts polyethylene, 85 parts white oil, and 2 parts filler.

[0041] The viscosity-average molecular weight of polyethylene is 1 million.

[0042] The raw materials for the filler include component A and component B in a mass ratio of 1:19;

[0043] Component A includes barium stearate;

[0044] Component B includes lithium molybdate;

[0045] A method for preparing a high-viscosity and high-safety lithium-ion battery separator includes the following steps:

[0046] The components of the lithium-ion battery separator are mixed and extruded (extrusion mixing section temperature 100℃, shearing section temperature 180℃, conveying section temperature 190℃, extrusion rate 150kg / h, extrusion rate to screw speed ratio 2.5), cast at 200℃, cast to a 10℃ shaping roller for casting, and then subjected to longitudinal stretching (stretch ratio 6 times), first transverse stretching (stretch ratio 6 times), extraction of white oil with dichloromethane, and then a second transverse stretching (stretch ratio 1.2 times), followed by heat treatment (the outlet speed during heat treatment is 1.1 times the inlet speed) to obtain the lithium-ion battery separator.

[0047] Example 2

[0048] The high-viscosity and high-safety lithium-ion battery separator is made of the following components by weight: 17 parts polyethylene, 83 parts white oil, and 3 parts filler.

[0049] The viscosity-average molecular weight of polyethylene is 2 million.

[0050] The raw materials for the filler include component A and component B in a mass ratio of 1:19;

[0051] Component A includes barium stearate;

[0052] Component B includes lithium tungstate;

[0053] A method for preparing a high-viscosity and high-safety lithium-ion battery separator includes the following steps:

[0054] The components of the lithium-ion battery separator are mixed and extruded (extrusion mixing section temperature 150℃, shearing section temperature 210℃, conveying section temperature 200℃, extrusion rate 300kg / h, extrusion rate to screw speed ratio 3.2), cast at 233℃, cast to a 30℃ shaping roller for sheet casting, and then subjected to longitudinal stretching (stretch ratio 5.5 times), first transverse stretching (stretch ratio 5.5 times), extraction of white oil with dichloromethane, and then a second transverse stretching (stretch ratio ≤ 1.1 times), followed by heat treatment (the outlet speed during heat treatment is 1.05 times the inlet speed) to obtain the lithium-ion battery separator.

[0055] Example 3

[0056] The high-viscosity and high-safety lithium-ion battery separator is made of the following components by weight: 20 parts polyethylene, 80 parts white oil, and 4 parts filler.

[0057] The viscosity-average molecular weight of polyethylene is 4 million.

[0058] The raw materials for the filler include component A and component B in a mass ratio of 1:19;

[0059] Component A includes barium stearate;

[0060] Component B includes lithium tungstate and lithium tantalate in a mass ratio of 1:1;

[0061] A method for preparing a high-viscosity and high-safety lithium-ion battery separator includes the following steps:

[0062] The components of the lithium-ion battery separator are mixed and extruded (extrusion mixing section temperature 160℃, shearing section temperature 220℃, conveying section temperature 220℃, extrusion rate 700kg / h, extrusion rate to screw speed ratio 5.0), cast at 250℃, cast to a 15℃ shaping roller for casting, and then subjected to longitudinal stretching (stretch ratio 5.5 times), first transverse stretching (stretch ratio 5.5 times), extraction of white oil with dichloromethane, and then a second transverse stretching (stretch ratio 1.05 times), followed by heat treatment (the outlet speed during heat treatment is 1.05 times the inlet speed) to obtain the lithium-ion battery separator.

[0063] Example 4

[0064] The only difference between this embodiment and Embodiment 3 is that the raw materials for the filler include component A and component B in a mass ratio of 19:1.

[0065] Example 5

[0066] The only difference between this embodiment and Embodiment 3 is that the raw materials for the filler include component A and component B in a mass ratio of 7:3.

[0067] Example 6

[0068] The only difference between this embodiment and Embodiment 3 is that the raw materials for the filler include component A and component B in a mass ratio of 1:4.

[0069] Example 7

[0070] The only difference between this embodiment and Embodiment 6 is that the raw material of the filler also includes component C;

[0071] Component C is 1,2-vinyl diphosphonic acid;

[0072] The mass ratio of component C to component B is 0.1:1.

[0073] Example 8

[0074] The only difference between this embodiment and Embodiment 6 is that the raw material of the filler also includes component C;

[0075] Component C is 1,2-vinyl diphosphonic acid;

[0076] The mass ratio of component C to component B is 0.1:1;

[0077] A method for preparing a high-viscosity and high-safety lithium-ion battery separator includes the following steps:

[0078] S1. Dissolve component C in water, mix it with component B, and dry to obtain a composite material; wherein the mass-volume ratio of component C to water is 1g:100mL.

[0079] S2. The composite material and the remaining components of the lithium-ion battery separator are mixed and extruded (extrusion mixing section temperature is 160℃, shearing section temperature is 220℃, conveying section temperature is 220℃, extrusion rate is 700kg / h, and the ratio of extrusion rate to screw speed is 5.0). The mixture is then cast at 250℃ and cast onto a 15℃ shaping roller. The mixture is then subjected to longitudinal stretching (stretch ratio 5.5 times), first transverse stretching (stretch ratio 5.5 times), extraction of white oil with dichloromethane, and a second transverse stretching (stretch ratio 1.05 times). Finally, the mixture is heat-treated (the outlet speed during heat treatment is 1.05 times the inlet speed) to obtain the lithium-ion battery separator.

[0080] Example 9

[0081] The only difference between this embodiment and Embodiment 8 is that component C is a coupling agent.

[0082] Example 10

[0083] The only difference between this embodiment and Example 8 is that component C is a coupling agent and 1,2-vinyl diphosphonic acid in a mass ratio of 1:1.

[0084] Example 11

[0085] The only difference between this embodiment and Example 10 is that component C is a coupling agent and 1,2-vinyl diphosphonic acid in a mass ratio of 1:0.5;

[0086] The mass ratio of component C to component B is 0.2:1;

[0087] In step S1 of the method for preparing a high-viscosity and high-safety lithium-ion battery separator, the mass-volume ratio of component C to water is 1 g: 50 mL.

[0088] Comparative Example 1

[0089] The only difference between this comparative example and Example 1 is that the raw material for the filler is component B.

[0090] Comparative Example 2

[0091] The only difference between this comparative example and Example 1 is that the raw material for the filler is component A.

[0092] Experimental Example 1

[0093] The tensile strength (separator size: length × width × thickness = 150 mm × 15 mm × 9 μm) of the lithium-ion battery separators prepared in Examples 1-6 and Comparative Examples 1-2 were tested using a Shimadzu AGS-50N intelligent electronic tensile testing machine. The results are shown in Table 1 below.

[0094] Table 1 Tensile strength test results

[0095]

[0096] Compared with Comparative Examples 1-2, the lithium battery separators prepared in Examples 1-3 have higher longitudinal tensile strength, indicating that the lithium-ion battery separator uses polyolefin as the matrix and introduces and adjusts components A and B to improve the strength of the lithium battery separator.

[0097] Experiment Example 2

[0098] The lithium battery separators (9 μm thick) prepared in Examples 6 to 11 were placed in an oven and the thermal shrinkage rate at 120°C for 1 hour was tested. The results are shown in Table 2.

[0099] Table 2 Results of heat shrinkage test

[0100]

[0101] Compared with Examples 6-9, the lithium battery separators prepared in Examples 10-11 have a lower longitudinal thermal shrinkage rate, indicating that when preparing lithium-ion battery separators, the coupling agent and 1,2-vinyl diphosphonic acid are mixed with component B as component C to prepare a composite material, and then mixed with other components to obtain lithium battery separators, which have better heat resistance.

[0102] Experimental Example 3

[0103] The lithium battery separators prepared in Examples 1-3 were tested for areal density, needle penetration strength, air permeability, liquid absorption rate, and liquid retention rate.

[0104] Needle penetration strength: tested using Shimadzu AGS-50N intelligent electronic tensile testing machine (diaphragm dimensions: length × width × thickness = 100mm × 100mm × 9μm).

[0105] Air permeability: The test was conducted using an EG01-55-1MR tester, and the time required for 100 mL of nitrogen gas to pass through the diaphragm was recorded.

[0106] Liquid absorption rate and liquid retention rate tests:

[0107] Cut three diaphragm samples with an area of ​​50mm×50mm, weigh the cut samples and record the weight as m1. Immerse the weighed diaphragm in the electrolyte for 30 minutes, then remove and dry it. Weigh the dried sample as m2, let it stand for one hour, weigh it again and record the weight as m3.

[0108] The diaphragm liquid absorption rate and liquid retention rate are calculated according to the following formulas:

[0109] Liquid absorption rate = [(m2-m1) / m1] × 100%;

[0110] Liquid retention rate = [(m3-m1) / m1]×100%;

[0111] In the formula:

[0112] m1 is the weight of the diaphragm after it has been cut;

[0113] m2 is the weight of the diaphragm after soaking;

[0114] m3 is the weight of the diaphragm after soaking and standing for 1 hour; the result is the average value of 3 parallel samples.

[0115] The results are shown in Table 3.

[0116] Table 3 Performance Test Results

[0117]

[0118] 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-viscosity and high-safety lithium-ion battery separator, characterized in that, The raw materials include the following components in parts by weight: 15-20 parts polyolefin, 80-85 parts pore-forming agent, and 2-4 parts filler; The viscosity-average molecular weight of the polyolefin is 1 million to 4 million. The raw materials for the filler include component A and component B in a mass ratio of 1:19 to 19:1; Component A includes barium stearate; Component B includes one or more of lithium molybdate, lithium tungstate, and lithium tantalate. The raw material for the filler also includes component C; Component C comprises a coupling agent and 1,2-vinyl diphosphonic acid in a mass ratio of 1:1 to 0.5; The mass ratio of component C to component B is 0.1~0.2:1; The method for preparing the lithium-ion battery separator includes the following steps: S1. Dissolve component C, mix it with component B, and dry to obtain a composite material; S2. The composite material is mixed with the remaining components of the lithium-ion battery separator, extruded, cast, cast, biaxially stretched, extracted, and heat-treated to obtain the lithium-ion battery separator.

2. The high viscosity and high safety lithium-ion battery separator according to claim 1, characterized in that, The raw materials for the filler include component A and component B in a mass ratio of 1:4 to 7:

3.

3. The high-viscosity and high-safety lithium-ion battery separator according to claim 1, characterized in that, The coupling agent includes one or both of silane coupling agents and titanate coupling agents.

4. A method for preparing a high-viscosity and high-safety lithium-ion battery separator according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Dissolve component C, mix it with component B, and dry to obtain a composite material; S2. The composite material is mixed with the remaining components of the lithium-ion battery separator, extruded, cast, cast, biaxially stretched, extracted, and heat-treated to obtain the lithium-ion battery separator.

5. The method for preparing a high-viscosity and high-safety lithium-ion battery separator according to claim 4, characterized in that, During the dissolution process, the mass-to-volume ratio of component C to solvent is 1g:50~100mL.

6. The method for preparing a high-viscosity and high-safety lithium-ion battery separator according to claim 4, characterized in that, During the extrusion process, the temperature of the extrusion mixing section is 100~160℃, the temperature of the shearing section is 180~220℃, the temperature of the conveying section is 190~220℃, and the extrusion rate is 150~700 kg / h. The ratio of the extrusion rate to the screw speed is 2.5 to 5.

0.

7. The method for preparing a high-viscosity and high-safety lithium-ion battery separator according to claim 4, characterized in that, The casting temperature is 200~250℃.

8. The method for preparing a high-viscosity and high-safety lithium-ion battery separator according to claim 4, characterized in that, The casting temperature is 10~30℃.

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