Ultrafast-charge electrostatic spinning lithium battery diaphragm, preparation method and application

Abstract

The invention discloses an ultra-fast charge electrostatic spinning lithium battery diaphragm, a preparation method and application, and belongs to the field of lithium battery diaphragms. The ultra-fast charge electrostatic spinning lithium battery diaphragm is a composite diaphragm and comprises a polyvinyl base membrane, polyvinylidene fluoride bonding layers located on the two side faces of the polyvinyl base membrane and polyacrylonitrile functional layers located on the two side faces of the polyvinylidene fluoride bonding layers from inside to outside. The characteristics of high melting point and easy modification of polyacrylonitrile are utilized, and spinning modification is carried out on two sides of a commercial polyethylene diaphragm by using an electrostatic spinning technology. The obtained composite diaphragm has the characteristics of high rate performance, high porosity, super infiltration speed and extremely high heat resistance by controlling electrostatic spinning technical parameters. The preparation method can be used for preparing the diaphragm of the fast-charging lithium battery, not only can meet high rate performance required by fast charging, but also can keep good physical structure and thermal stability at high temperature generated by fast charging, and can effectively improve the safety of the lithium battery.

Description

Technical Field

[0001] The present invention belongs to the field of lithium battery separators, and specifically provides a method for preparing an ultrafast charging electrostatic spinning lithium battery separator. Background Art

[0002] With the rapid development of electric vehicles and electronic devices, the development of energy storage devices with high energy density, high safety, and fast charging speeds has become an urgent need. Lithium metal batteries, due to their excellent theoretical capacity and operating potential, dominate the energy storage market. However, in the field of fast-charging batteries, current commercial lithium batteries use polyolefin materials as battery separators. Their excellent cycling performance, high mechanical strength, and low production cost make polyolefin separators difficult to replace in the short term. However, polyolefin materials also have significant disadvantages: poor wettability and thermal stability. On the one hand, the inherent low polarity and surface energy of polyolefins result in poor wettability of the separator, making it difficult for the electrolyte to quickly penetrate. This makes it difficult for polyolefin materials to meet the mass transfer requirements of high-rate fast charging, thereby limiting charging speed. On the other hand, poor thermal stability can easily cause thermal shrinkage and deformation of the separator, which can easily cause short circuits at high charging rates and even cause battery explosion, which is a potential danger.

[0003] Electrospinning is an effective technique for producing nanofiber membranes with high porosity, high surface area, and tunable microstructure and thickness, as well as good pore connectivity and high electrolyte wettability. The high electrolyte wettability of electrospun separators can effectively improve the lithium ion transport efficiency of lithium batteries and accelerate battery charging. Polyacrylonitrile, with its high melting point (317°C) and easy modifiability, can be used as a spinning modifier layer, enhancing both separator wettability and heat resistance. Summary of the Invention

[0004] Aiming at the defects of existing lithium battery separators, the present invention provides a method for preparing an ultra-fast charging electrostatic spinning lithium battery separator.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] A super-fast charging electrostatic spinning lithium battery separator, which is a composite separator, comprising, from the inside to the outside, a polyethylene base film, a polyvinylidene fluoride adhesive layer located on both sides of the polyethylene base film, and a polyacrylonitrile functional layer located on both sides of the polyvinylidene fluoride adhesive layer.

[0007] Furthermore, the thickness of the polyethylene-based film is 4 μm to 6 μm; the thickness of the polyvinylidene fluoride adhesive layer is 1 μm to 2 μm; and the thickness of the polyacrylonitrile functional layer is 3 μm to 4 μm.

[0008] A method for preparing an ultrafast charging electrospun lithium battery separator comprises the following steps:

[0009] Step 1: dissolving polyacrylonitrile powder in dimethylformamide, stirring and mixing uniformly to obtain a polyacrylonitrile functional layer spinning solution.

[0010] Step 2: dissolving polyvinylidene fluoride powder in dimethylformamide, stirring and mixing uniformly to obtain polyvinylidene fluoride bonding layer spinning solution.

[0011] Step 3: Use the polyvinylidene fluoride adhesive layer spinning solution of step 2 to perform electrospinning on both sides of the polyethylene base film to form a double-sided polyvinylidene fluoride adhesive layer, thereby obtaining a double-sided composite diaphragm with adhesion.

[0012] Step 4: Using the polyacrylonitrile functional layer spinning solution of step 1, electrospinning is performed on both sides of the double-sided composite membrane to form double-sided polyacrylonitrile functional layers, thereby obtaining an electrospun composite membrane.

[0013] Step 5: hot-press the electrospun composite membrane obtained in step 4, and dry it to remove the residual dimethylformamide to obtain an ultra-fast charging electrospun lithium battery membrane.

[0014] Furthermore, in step 1 and step 2, the mass fractions of the polyacrylonitrile functional layer spinning solution and the polyvinylidene fluoride adhesive layer spinning solution are both 12 wt.% to 15 wt.%.

[0015] Furthermore, in steps 3 and 4, the electrospinning needle models 19 to 21 are applicable, the positive voltage of electrospinning is 12kV to 15kV, the negative voltage of electrospinning is 2kV to 5kV, the electrospinning speed is 100rpm to 150rpm, and the distance between the electrospinning transmitter and the receiving substrate is 20cm to 24cm.

[0016] Furthermore, in step 3, the spinning solution flow rate of the polyvinylidene fluoride bonding layer is 0.005 L / min~0.01 mL / min.

[0017] Furthermore, in step 4, the flow rate of the polyacrylonitrile functional layer spinning solution is 0.005 mL / min~0.008 mL / min.

[0018] Furthermore, in step 5, the temperature of the hot pressing treatment is 80°C to 120°C, the pressure of the hot pressing treatment is 3MPa to 5MPa, and the time of the hot pressing treatment is 5 minutes to 10 minutes. The drying temperature is 45°C to 60°C, and the drying time is 2 hours to 4 hours.

[0019] In terms of application, the lithium battery separator prepared by the above-mentioned method for preparing an ultra-fast charging electrospinning lithium battery separator is applied to lithium-ion batteries.

[0020] The present invention utilizes electrospinning to modify both sides of a base film. Polyacrylonitrile (PAN, melting point 317°C) is a high-melting-point material used as the functional layer, and polyvinylidene fluoride (PVDF) serves as the adhesive between the base film and the PAN. The resulting ultra-fast-charge electrospun lithium battery separator exhibits excellent electrolyte wettability and high-rate fast-charging performance. Furthermore, the high-melting-point PAN effectively prevents the separator from melting under the high temperatures generated by rapid charging, thereby enhancing the safety of lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a rate performance comparison chart.

[0022] Figure 2 A comparison diagram of electrolyte wetting and diffusion. DETAILED DESCRIPTION

[0023] The present invention will be described in further detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto. For process parameters not particularly noted, conventional techniques may be used.

[0024] Example 1:

[0025] This embodiment provides a method for preparing an ultrafast charging electrospinning lithium battery separator, comprising the following steps:

[0026] Step 1: Dissolve polyacrylonitrile powder in dimethylformamide according to a preset ratio, stir in a water bath at 80° C. for 5 hours until the mixture is uniform, and obtain a polyacrylonitrile functional layer spinning solution. The concentration of the polyacrylonitrile functional layer spinning solution is 15 wt %.

[0027] Step 2: Dissolve the polyvinylidene fluoride powder in dimethylformamide according to a preset ratio, stir in a 60° C. water bath for 5 hours until the mixture is uniform, and obtain a polyvinylidene fluoride adhesive layer spinning solution. The concentration of the polyvinylidene fluoride adhesive layer spinning solution is 15 wt %.

[0028] Step 3: Load the polyvinylidene fluoride adhesive layer spinning solution into a syringe and electrospin onto both sides of the polyethylene film to form a double-sided polyvinylidene fluoride adhesive layer. The electrospinning parameters were set as follows: a model 20 electrospinning needle, a positive voltage of 15kV, a negative voltage of 3kV, a rotation speed of 100rpm, a distance of 24cm between the emitter and the receiving substrate, and a polyvinylidene fluoride adhesive layer spinning solution flow rate of 0.01mL / min. The polyethylene film was a commercially available polyethylene film with a thickness of 5μm, and the polyvinylidene fluoride adhesive layer had a thickness of 1μm. This resulted in a double-sided composite membrane with good adhesion.

[0029] Step 4: Load the polyacrylonitrile functional layer spinning solution into a syringe and electrospin the solution onto both sides of the double-sided composite membrane to form a double-sided polyacrylonitrile functional layer. The electrospinning parameters were as follows: a Model 20 electrospinning needle was used, the positive voltage was 12 kV, the negative voltage was 3 kV, the spin speed was 120 rpm, the distance between the emitter and the receiving substrate was 20 cm, and the flow rate of the polyacrylonitrile functional layer spinning solution was 0.005 mL / min. The resulting electrospun composite membrane had a polyacrylonitrile functional layer thickness of 3 μm.

[0030] Step 5: The obtained electrospun composite membrane was hot-pressed at 120°C and 5 MPa pressure for 5 minutes, and dried in an oven at 50°C for 2 hours to remove residual dimethylformamide to obtain an ultra-fast charging electrospun lithium battery membrane.

[0031] The prepared ultrafast-charge electrospun lithium battery separator has a total thickness of 9.8 μm. Thermal rupture tests at 200°C revealed no significant damage after two hours. The electrolyte infiltration and diffusion rate were rapid.

[0032] The ultra-fast charging electrospun lithium battery separator was assembled into a single-layer soft-pack lithium battery according to the existing process for testing. The lithium battery performance test results showed that at a current of 8C, the lithium battery capacity retention rate was as follows: Figure 1 As shown. The electrolyte infiltration and diffusion contrast Figure 2 shown.

[0033] Example 2:

[0034] This example uses the same method as Example 1 to prepare an ultrafast-charge electrospun lithium battery separator, except that in steps 1 and 2, the concentrations of the polyacrylonitrile functional layer spinning solution and the polyvinylidene fluoride adhesive layer spinning solution are both 12 wt %. In steps 3 and 4, a model 19 electrospinning needle is used, and the polyvinylidene fluoride adhesive layer spinning solution flow rate is 0.005 mL / min; the polyacrylonitrile functional layer spinning solution flow rate is 0.008 mL / min. The electrospinning positive voltage in steps 3 and 4 is 12 kV, and the negative voltage is 2 kV. The spinning collection roller rotates at 100 rpm.

[0035] The ultrafast charging electrospun lithium battery separator prepared in Example 2 had a total thickness of 10.2 μm. A thermal break test at 200°C for 2 hours revealed no significant damage. The electrolyte infiltration and diffusion rate was rapid.

[0036] The ultra-fast charging electrospun lithium battery separator was assembled into a single-layer soft-pack lithium battery according to the existing process for testing. The lithium battery performance test results showed that at a current of 8C, the lithium battery capacity retention rate was as follows: Figure 1 As shown. The electrolyte infiltration and diffusion contrast Figure 2 shown.

[0037] Example 3:

[0038] This example uses the same method as Example 1 to prepare an ultrafast charging electrospun lithium battery separator, except that in steps 1 and 2, the concentrations of the polyacrylonitrile functional layer spinning solution and the polyvinylidene fluoride adhesive layer spinning solution are both 12 wt %. In steps 3 and 4, a model 21 electrospinning needle is used. The electrospinning positive voltage in steps 3 and 4 is 15 kV, and the negative voltage is 5 kV. The spinning collection roller rotates at 130 rpm.

[0039] The ultrafast charging electrospun lithium battery separator prepared in Example 3 had a total thickness of 10.2 μm. A thermal break test at 200°C for 2 hours revealed no significant damage. The electrolyte infiltration and diffusion rate was rapid.

[0040] The ultra-fast charging electrospun lithium battery separator was assembled into a single-layer soft-pack lithium battery according to the existing process for testing. The lithium battery performance test results showed that at a current of 8C, the lithium battery capacity retention rate was as follows: Figure 1 As shown. The electrolyte wetting and diffusion contrast Figure 2 shown.

[0041] Example 4:

[0042] This example uses the same method as Example 1 to prepare an ultrafast-charging electrospun lithium battery separator, with the following differences: In step 3 of Example 4, the thickness of the polyvinylidene fluoride adhesive layer is controlled to 2 μm, and in step 4, the thickness of the polyacrylonitrile functional layer is controlled to 4 μm. In step 5, the hot pressing pressure is 3 MPa and the hot pressing time is 10 minutes. The drying temperature is 50°C and the drying time is 3 hours.

[0043] The ultrafast-charge electrospun lithium battery separator prepared in Example 4 had a total thickness of 14.5 μm. A thermal break test at 200°C for 2 hours revealed no significant damage. The electrolyte infiltration and diffusion rate was rapid.

[0044] The ultra-fast charging electrospun lithium battery separator was assembled into a single-layer soft-pack lithium battery according to the existing process for testing. The lithium battery performance test results showed that at a current of 8C, the lithium battery capacity retention rate was as follows: Figure 1 shown.

[0045] Example 5:

[0046] This example uses the same method as Example 4 to prepare an ultrafast charging electrospun lithium battery separator, except that in step 5, the hot pressing pressure is 4 MPa, the hot pressing time is 10 minutes, and the drying temperature is 60°C, and the drying time is 4 hours.

[0047] The ultrafast-charge electrospun lithium battery separator prepared in Example 5 had a total thickness of 14.5 μm. A thermal break test at 200°C for 2 hours revealed no significant damage. The electrolyte infiltration and diffusion rate was rapid.

[0048] The ultra-fast charging electrospun lithium battery separator was assembled into a single-layer soft-pack lithium battery according to the existing process for testing. The lithium battery performance test results showed that at a current of 8C, the lithium battery capacity retention rate was as follows: Figure 1 shown.

[0049] Comparative Example 1:

[0050] This comparative example provides a single-sided spinning membrane, and the preparation method is the same as the steps in Example 1, except that: in steps 3 and 4, only single-sided electrospinning is performed to obtain a single-sided spinning membrane.

[0051] The obtained single-sided spinning membrane broke in 3 minutes in the thermal membrane breaking experiment at 200℃; in addition, its rate performance was weaker than that of Examples 1, 2, 3, 4, and 5. Figure 1 shown.

[0052] Comparative Example 2:

[0053] This comparative example provides a PVDF-free spinning membrane, and the preparation method is the same as the steps in Example 1, except that: during the electrospinning process, the electrospinning of the polyvinylidene fluoride bonding layer is not performed.

[0054] The PVDF-free spinning membrane produced: The electrospun polypropylene functional layer is severely separated from the polyethylene base membrane and cannot be loaded with lithium batteries for testing.

[0055] Comparative Example 3:

[0056] This comparative example provides a double-sided spinning membrane with the same structure as Example 1. The preparation method is the same as the steps in Example 1, except that: during the electrospinning process, the thickness of the polyacrylonitrile functional layer is controlled at 6 μm.

[0057] The obtained double-sided spinning membrane: the PVDF spinning layer cannot adhere to all the polypropylene functional layers, and the polypropylene functional layers will self-separate.

[0058] The above embodiments are preferred implementations of the present invention, but the implementation of the present invention is not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. An ultrafast charging electrospinning lithium battery separator, characterized in that: The ultrafast charging electrospun lithium battery separator is a composite separator, which includes, from the inside to the outside, a polyethylene base film, a polyvinylidene fluoride adhesive layer located on both sides of the polyethylene base film, and a polyacrylonitrile functional layer located on both sides of the polyvinylidene fluoride adhesive layer; The thickness of the polyethylene-based film is 4 μm to 6 μm; the thickness of the polyvinylidene fluoride adhesive layer is 1 μm to 2 μm; and the thickness of the polyacrylonitrile functional layer is 3 μm to 4 μm.

2. The method for preparing an ultrafast charging electrospinning lithium battery separator according to claim 1, characterized in that: The specific steps include: Step 1, dissolving polyacrylonitrile powder in dimethylformamide, stirring and mixing uniformly to obtain a polyacrylonitrile functional layer spinning solution; Step 2, dissolving polyvinylidene fluoride powder in dimethylformamide, stirring and mixing uniformly to obtain a polyvinylidene fluoride bonding layer spinning solution; Step 3: Using the polyvinylidene fluoride adhesive layer spinning solution of step 2, electrospinning is performed on both sides of the polyethylene base film to form a double-sided polyvinylidene fluoride adhesive layer, thereby obtaining a double-sided composite diaphragm with adhesion; Step 4: using the polyacrylonitrile functional layer spinning solution of step 1, electrospinning is performed on both sides of the double-sided composite membrane to form a double-sided polyacrylonitrile functional layer, thereby obtaining an electrospun composite membrane; Step 5: hot-press the electrospun composite membrane obtained in step 4 and dry it to remove the residual dimethylformamide to obtain an ultra-fast charging electrospun lithium battery membrane.

3. The method for preparing an ultrafast charging electrospinning lithium battery separator according to claim 2, characterized in that: In step 1 and step 2, the mass fractions of the polyacrylonitrile functional layer spinning solution and the polyvinylidene fluoride adhesive layer spinning solution are both 12 wt.% to 15 wt.%.

4. The method for preparing an ultrafast charging electrospinning lithium battery separator according to claim 2, characterized in that: In steps 3 and 4, the electrospinning needle models are 19 to 21, the positive voltage of electrospinning is 12kV to 15kV, the negative voltage of electrospinning is 2kV to 5kV, the electrospinning speed is 100rpm to 150rpm, and the distance between the electrospinning transmitter and the receiving substrate is 20cm to 24cm.

5. The method for preparing an ultrafast charging electrospinning lithium battery separator according to claim 2, characterized in that: In step 3, the flow rate of the polyvinylidene fluoride bonding layer spinning solution is 0.005 L / min~0.01 mL / min.

6. The method for preparing an ultrafast charging electrospinning lithium battery separator according to claim 2, characterized in that: In step 4, the flow rate of the polyacrylonitrile functional layer spinning solution is 0.005 mL / min~0.008 mL / min.

7. The method for preparing an ultrafast charging electrospinning lithium battery separator according to claim 2, characterized in that: In step 5, the temperature of the hot pressing treatment is 80°C to 120°C, the pressure of the hot pressing treatment is 3MPa to 5MPa, and the time of the hot pressing treatment is 5 minutes to 10 minutes; the drying temperature is 45°C to 60°C, and the drying time is 2 hours to 4 hours.

8. The ultrafast charging electrospun lithium battery separator according to claim 1 is used in lithium-ion batteries.

9. An ultrafast charging electrospun lithium battery separator prepared by the preparation method according to any one of claims 3 to 7 is used in lithium-ion batteries.

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