Preparation method of high-viscosity and high-safety lithium ion battery diaphragm

Abstract

The invention relates to the technical field of battery diaphragms, and provides a high-viscosity and high-safety lithium ion battery diaphragm, which is prepared from the following raw materials in parts by weight: 15 to 20 parts of polyolefin, 80 to 85 parts of pore-forming agent and 2 to 4 parts of filler, the viscosity average molecular weight of the polyolefin is 1,000,000 to 4,000,000; the raw materials of the filler comprise a component A and a component B in a mass ratio of (1: 19)-(19: 1); the component A comprises barium stearate; the component B comprises one or more of lithium molybdate, lithium tungstate and lithium tantalate. According to the technical scheme, the problem that the strength of the lithium battery diaphragm in the related technology is relatively low is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and in particular to a method for preparing a lithium-ion battery separator with high viscosity and high safety. Background Art

[0002] With the rapid development of lithium battery separators, the battery end has higher and higher requirements for the strength of lithium battery separators. Generally speaking, the higher the strength, the stronger the resistance to dendrite puncture, and the safer the battery. Lithium-ion battery separators with insufficient strength are easily punctured during the battery charging and discharging process due to the expansion and contraction of the electrodes, causing a short circuit between the positive and negative electrodes, leading to safety accidents such as battery overheating and fire.

[0003] Although common polyolefin lithium battery separators have good chemical stability and ion conductivity, they have certain shortcomings in mechanical properties. The arrangement of their molecular structure makes the intermolecular force weak when subjected to external forces, and chain segments are prone to slippage and breakage, resulting in insufficient strength of the lithium battery separator.

[0004] Therefore, it is necessary to improve the strength of lithium-ion battery separators so that the lithium-ion battery separators have higher safety when used in lithium batteries. Summary of the invention

[0005] The present invention provides a method for preparing a lithium ion battery separator with high viscosity and high safety, which solves the problem of low strength of the lithium battery separator in the related art.

[0006] The technical solution of the present invention is as follows: The present invention provides a high-viscosity and high-safety lithium-ion battery separator, wherein the raw materials include the following components in parts by weight: 15 to 20 parts of polyolefin, 80 to 85 parts of pore-forming agent, and 2 to 4 parts of filler; The viscosity average molecular weight of the polyolefin is 1 to 4 million; The raw materials of the filler include component A and component B in a mass ratio of 1:19 to 19:1; The component A comprises barium stearate; The component B includes one or more of lithium molybdate, lithium tungstate, and lithium tantalate.

[0007] As a further technical solution, the raw material of the filler includes component A and component B in a mass ratio of 1:4 to 7:3.

[0008] As a further technical solution, the polyolefin includes one or both of polyethylene and polypropylene; and the pore-forming agent includes white oil.

[0009] In the present invention, the strength of the lithium ion battery separator is further improved by adjusting the mass ratio of component A to component B to 1:4-7:3.

[0010] As a further technical solution, the raw material of the filler further includes component C; The component C comprises a coupling agent and 1,2-vinyl diphosphonic acid in a mass ratio of 1:1 to 0.5.

[0011] As a further technical solution, the mass ratio of the component C to the component B is 0.1~0.2:1.

[0012] As a further technical solution, the coupling agent includes one or both of a silane coupling agent and a titanate coupling agent.

[0013] The present invention also provides a method for preparing a high-viscosity and high-safety lithium-ion battery separator, comprising the following steps: S1, dissolving the component C, mixing it with the component B, and drying it to obtain a composite material; S2. Mixing the composite material with the remaining components of the lithium-ion battery separator, extruding, casting, biaxially stretching, extracting, and heat treating to obtain a lithium-ion battery separator.

[0014] In the present invention, when preparing a lithium-ion battery separator, a coupling agent and 1,2-vinyl diphosphonic acid are used as component C to mix with component B to prepare a composite material, and then the composite material is mixed with other components to prepare a lithium battery separator. Component C and component B are mixed to prepare a composite material, and after improving the compatibility of component B with a polyolefin matrix, the composite material is mixed with other components to prepare a lithium battery separator. In addition to having excellent strength, the heat resistance of the lithium battery separator is also improved.

[0015] As a further technical solution, during the dissolution, the mass volume ratio of the component C to the solvent is 1g:50~100mL.

[0016] As a further technical solution, during the extrusion, the temperature of the extrusion mixing section is 100-160°C, the temperature of the shearing section is 180-220°C, the temperature of the conveying section is 190-220°C, and the extrusion rate is 150-700kg / h; The ratio of the extrusion volume to the screw speed is 2.5-5.0.

[0017] In the present invention, during extrusion, the temperature of the extrusion mixing section is 100-160°C, the temperature of the shearing section is 180-220°C, the temperature of the conveying section is 190-220°C, the extrusion amount is 150-700kg / h, and the ratio of the extrusion amount to the screw speed is 2.5-5.0, which can make the polyolefin and other raw materials fully uniform, ensure the stable extrusion of the materials, and ensure the uniformity of the diaphragm.

[0018] As a further technical solution, the casting temperature is 200-250°C.

[0019] As a further technical solution, the temperature during the casting is 10-30°C.

[0020] In the present invention, the casting temperature is 200-250°C, so that the material can be evenly spread during the casting process to form a uniform film layer. At a casting temperature of 10-30°C, the diaphragm can be quickly cooled and shaped, reducing internal stress and preventing the generation of diaphragm defects.

[0021] As a further technical solution, the stretching ratio of the longitudinal stretching and the stretching ratio of the transverse stretching during the biaxial stretching are both ≤6 times; After the extraction, a second transverse stretching is performed; the stretching ratio of the second transverse stretching is ≤1.2 times; During the heat treatment, the ratio of the outlet velocity to the inlet velocity is ≤1.1.

[0022] In the present invention, the longitudinal and transverse stretching ratios during biaxial stretching are both ≤6 times, which avoids the breakage of polyolefin molecular chains and structural damage caused by excessive stretching, retains sufficient strength while expanding the pores, and performs a second transverse stretching after extraction, with a stretching ratio of ≤1.2 times, which can further optimize the pore structure of the diaphragm.

[0023] The working principle and beneficial effects of the present invention are: In the present invention, polyolefin is used as the main component of the lithium-ion battery separator, and its viscosity average molecular weight is between 1 and 4 million, and it has the characteristics of high viscosity. The polyolefin molecular chain is long and tightly entangled with each other, so as to build a stable structural network, reduce the risk of damage during battery operation, and improve the safety of the lithium-ion battery; Barium stearate as component A can improve the processability of polyolefins. At the same time, it is dispersed in the polyolefin matrix to play a reinforcing role. Lithium molybdate, lithium tungstate, lithium tantalate, etc. are used as component B. These lithium salt compounds are filled into the polyolefin structure to enhance the skeleton strength of the diaphragm. Component A and component B work together to improve the strength of lithium-ion battery diaphragms. DETAILED DESCRIPTION

[0024] 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 described embodiments 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 creative work are within the scope of protection of the present invention.

[0025] In the following examples and comparative examples, the coupling agent model 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.

[0026] Example 1 A high-viscosity and high-safety lithium-ion battery separator, the raw materials include the following components in parts by weight: 15 parts of polyethylene, 85 parts of white oil, and 2 parts of filler; The viscosity average molecular weight of polyethylene is 1 million; The raw materials of the filler include component A and component B in a mass ratio of 1:19; Component A includes barium stearate; Component B includes lithium molybdate; A method for preparing a high-viscosity and high-safety lithium-ion battery separator comprises the following steps: The components of the lithium-ion battery separator are mixed, extruded (the temperature of the extrusion mixing section is 100°C, the temperature of the shear section is 180°C, the temperature of the conveying section is 190°C, the extrusion amount is 150kg / h, and the ratio of the extrusion amount to the screw speed is 2.5), cast at 200°C, cast to a 10°C shaping roller for sheet casting, longitudinal stretching (stretching ratio 6 times), the first transverse stretching (stretching ratio 6 times) are sequentially performed, the white oil is extracted with dichloromethane, and then the secondary transverse stretching (stretching ratio 1.2 times) is performed, and heat treatment is performed (the outlet speed during heat treatment is 1.1 times the inlet speed) to obtain a lithium-ion battery separator.

[0027] Example 2 A high-viscosity and high-safety lithium-ion battery separator, the raw materials include the following components in parts by weight: 17 parts of polyethylene, 83 parts of white oil, and 3 parts of filler; The viscosity-average molecular weight of polyethylene is 2 million; The raw materials of the filler include component A and component B in a mass ratio of 1:19; Component A includes barium stearate; Component B includes lithium tungstate; A method for preparing a high-viscosity and high-safety lithium-ion battery separator comprises the following steps: The components of the lithium-ion battery separator are mixed, extruded (the temperature of the extrusion mixing section is 150°C, the temperature of the shear section is 210°C, the temperature of the conveying section is 200°C, the extrusion amount is 300kg / h, and the ratio of the extrusion amount to the screw speed is 3.2), cast at 233°C, cast to a 30°C shaping roller for sheet casting, longitudinal stretching (stretching ratio 5.5 times), the first transverse stretching (stretching ratio 5.5 times) are sequentially performed, white oil is extracted with dichloromethane, and then secondary transverse stretching (stretching ratio ≤1.1 times) is performed, and heat treatment is performed (the outlet speed during heat treatment is 1.05 times the inlet speed) to obtain a lithium-ion battery separator.

[0028] Example 3 A high-viscosity and high-safety lithium-ion battery separator, the raw materials include the following components in parts by weight: 20 parts of polyethylene, 80 parts of white oil, and 4 parts of filler; The viscosity-average molecular weight of polyethylene is 4 million; The raw materials of the filler include component A and component B in a mass ratio of 1:19; Component A includes barium stearate; Component B includes lithium tungstate and lithium tantalate in a mass ratio of 1:1; A method for preparing a high-viscosity and high-safety lithium-ion battery separator comprises the following steps: The components of the lithium-ion battery separator are mixed, extruded (the temperature of the extrusion mixing section is 160°C, the temperature of the shear section is 220°C, the temperature of the conveying section is 220°C, the extrusion amount is 700kg / h, and the ratio of the extrusion amount to the screw speed is 5.0), cast at 250°C, cast to a 15°C shaping roller for sheet casting, longitudinal stretching (stretching ratio 5.5 times), the first transverse stretching (stretching ratio 5.5 times) are sequentially performed, the white oil is extracted with dichloromethane, and then the secondary transverse stretching (stretching ratio 1.05 times) is performed, and heat treatment is performed (the outlet speed during heat treatment is 1.05 times the inlet speed) to obtain a lithium-ion battery separator.

[0029] Example 4 The only difference between this embodiment and embodiment 3 is that the raw materials of the filler include component A and component B in a mass ratio of 19:1.

[0030] Example 5 The only difference between this embodiment and embodiment 3 is that the raw materials of the filler include component A and component B in a mass ratio of 7:3.

[0031] Example 6 The only difference between this embodiment and embodiment 3 is that the raw materials of the filler include component A and component B in a mass ratio of 1:4.

[0032] Example 7 The difference between this embodiment and embodiment 6 is that the raw material of the filler also includes component C; Component C is 1,2-vinyl diphosphonic acid; The mass ratio of component C to component B is 0.1:1.

[0033] Example 8 The difference between this embodiment and embodiment 6 is that the raw material of the filler also includes component C; Component C is 1,2-vinyl diphosphonic acid; The mass ratio of component C to component B is 0.1:1; A method for preparing a high-viscosity and high-safety lithium-ion battery separator comprises the following steps: S1. Dissolving component C in water, mixing with component B, and drying to obtain a composite material; wherein the mass volume ratio of component C to water is 1 g:100 mL; S2. The composite material and the remaining components of the lithium-ion battery separator are mixed, extruded (the temperature of the extrusion mixing section is 160°C, the temperature of the shear section is 220°C, the temperature of the conveying section is 220°C, the extrusion amount is 700kg / h, and the ratio of the extrusion amount to the screw speed is 5.0), cast at 250°C, cast to a 15°C shaping roller for sheet casting, longitudinal stretching (stretching ratio 5.5 times), the first transverse stretching (stretching ratio 5.5 times) are sequentially performed, the white oil is extracted with dichloromethane, and then the secondary transverse stretching (stretching ratio 1.05 times) is performed, and heat treatment is performed (the outlet speed during heat treatment is 1.05 times the inlet speed) to obtain a lithium-ion battery separator.

[0034] Example 9 The only difference between this embodiment and embodiment 8 is that component C is a coupling agent.

[0035] Example 10 The only difference between this embodiment and embodiment 8 is that component C comprises a coupling agent and 1,2-vinyl diphosphonic acid in a mass ratio of 1:1.

[0036] Embodiment 11 The difference between this embodiment and embodiment 10 is that component C is a coupling agent and 1,2-vinyl diphosphonic acid in a mass ratio of 1:0.5; The mass ratio of component C to component B is 0.2:1; 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.

[0037] Comparative Example 1 The difference between this comparative example and Example 1 is that the raw material of the filler is component B.

[0038] Comparative Example 2 The difference between this comparative example and Example 1 is that the raw material of the filler is component A.

[0039] Experimental Example 1 The tensile strength (diaphragm size: length × width × thickness = 150 mm × 15 mm × 9 μm) of the lithium ion battery separators prepared in Examples 1 to 6 and Comparative Examples 1 to 2 was tested using a Shimadzu intelligent electronic tensile testing machine AGS-50N. The results are shown in Table 1 below.

[0040] Table 1 Tensile strength test results

[0041] Compared with Comparative Examples 1-2, the longitudinal tensile strength of the lithium battery separators prepared in Examples 1-3 is higher, indicating that the lithium-ion battery separator is based on polyolefin, and component A and component B are introduced and adjusted to improve the strength of the lithium battery separator.

[0042] Experimental Example 2 The lithium battery separators (separator thickness 9 μm) prepared in Examples 6 to 11 were placed in an oven and tested for thermal shrinkage at 120° C. for 1 h. The results are shown in Table 2.

[0043] Table 2 Thermal shrinkage test results

[0044] Compared with Examples 6 to 9, the longitudinal thermal shrinkage of the lithium battery separators prepared in Examples 10 to 11 is lower, indicating that when preparing the lithium-ion battery separator, the coupling agent and 1,2-vinyl diphosphonic acid are mixed as component C with component B to prepare a composite material, and then mixed with other components to prepare a lithium battery separator, which has better heat resistance.

[0045] Experimental Example 3 The lithium battery separators prepared in Examples 1 to 3 were tested for surface density, needle puncture strength, air permeability, liquid absorption rate and liquid retention rate: Puncture strength: tested using Shimadzu intelligent electronic tensile testing machine AGS-50N (diaphragm size: length × width × thickness = 100 mm × 100 mm × 9 μm); Air permeability: Use EG01-55-1MR tester to test and record the time required for 100mL nitrogen to pass through the diaphragm; Liquid absorption rate and liquid retention rate test: Cut 3 diaphragm samples with an area of ​​50mm×50mm, weigh the cut samples and record them as m1, soak the weighed diaphragm in electrolyte for 30 minutes, take out and wipe dry, weigh the mass of the dried sample m2, leave it aside for one hour, weigh it and record it as m3.

[0046] The liquid absorption rate and liquid retention rate of the diaphragm are calculated according to the following formulas: Liquid absorption rate = [(m2-m1) / m1] × 100%; Liquid retention rate = [(m3-m1) / m1] × 100%; Where: m1 is the weight of the diaphragm after cutting; m2 is the weight of the diaphragm after immersion; m3 is the weight of the diaphragm after being soaked and left for 1 hour; the result is the average value of 3 parallel sample tests; The results are shown in Table 3.

[0047] Table 3 Performance test results

[0048] The above are only 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 in 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 of polyolefin, 80-85 parts of pore former, and 2-4 parts of filler; The viscosity average molecular weight of the polyolefin is 1 to 4 million; The raw materials of the filler include component A and component B in a mass ratio of 1:19 to 19:1; The component A comprises barium stearate; The component B includes one or more of lithium molybdate, lithium tungstate, and lithium tantalate.

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

3.

3. A high-viscosity and high-safety lithium-ion battery separator according to claim 1, characterized in that: The raw materials of the filler also include component C; The component C comprises a coupling agent and 1,2-vinyl diphosphonic acid in a mass ratio of 1:1 to 0.

5.

4. A high-viscosity and high-safety lithium-ion battery separator according to claim 3, characterized in that: The mass ratio of the component C to the component B is 0.1-0.2:

1.

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

6. The method for preparing a high-viscosity and high-safety lithium-ion battery separator according to any one of claims 3 to 5, characterized in that: The following steps are involved: S1, dissolving the component C, mixing it with the component B, and drying it to obtain a composite material; S2. Mixing the composite material with the remaining components of the lithium-ion battery separator, extruding, casting, biaxially stretching, extracting, and heat treating to obtain a lithium-ion battery separator.

7. The method for preparing a high-viscosity and high-safety lithium-ion battery separator according to claim 6, characterized in that: During the dissolution, the mass volume ratio of the component C to the solvent is 1g:50-100mL.

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

0.

9. The method for preparing a high-viscosity and high-safety lithium-ion battery separator according to claim 6, characterized in that: The casting temperature is 200-250°C.

10. The method for preparing a high-viscosity and high-safety lithium-ion battery separator according to claim 6, characterized in that: The temperature during the casting is 10-30°C.

Images