A method for preparing a macroporous PET film skeleton composite diaphragm

Abstract

The invention discloses a method for preparing a macroporous PET film skeleton composite diaphragm. The PET film sold in the market can be used as the raw material for preparing the skeleton. Laser drilling is adopted, and the skeleton preparation process is simple and the cost is low. The size range of the PET film drilling is 0.03mm. 2 ‑20mm 2 The porosity range is 40%-90%. Not only are the pores large in size but also numerous in number. While retaining the high temperature resistance advantage of the PET skeleton, it eliminates the impact on the electrical performance of the battery cell. The PET skeleton composite ceramic diaphragm, combined with the advantages of the PET skeleton's high temperature resistance and the ceramic coating's strong puncture resistance, has greatly improved the safety performance of the battery cell. Conventional lithium iron phosphate batteries usually cannot pass 500℃ hot needle puncture and 150℃ / 3h hot box, but the PET skeleton composite ceramic diaphragm can easily pass such harsh safety tests.

Description

Technical Field

[0001] The invention belongs to the field of lithium batteries and relates to a composite diaphragm, and in particular to a method for preparing an extremely high-temperature-resistant and puncture-resistant macroporous PET film skeleton composite diaphragm. Background Art

[0002] Lithium batteries are widely used due to their large capacity and almost no memory effect. A layer of membrane is needed between the positive and negative electrodes of lithium batteries to allow ions to pass smoothly, but electrons cannot pass through and can only move from the negative electrode to the positive electrode through an external circuit.

[0003] The diaphragm is one of the key components of lithium-ion batteries. The main methods used in the production of lithium battery diaphragms are: 1. Stretching method (dry method): The plastic film is heated to a certain temperature and stretched by physical methods to create larger gaps in the molecular chain. This method is difficult to control the pore density and pore size, and the uniformity of the micropores is poor; 2. Wet method: The plastic film is in a liquid state, and another liquid substance with a different boiling point is added, and the temperature is changed to allow the intermediary substance to precipitate out. The space left on the remaining film after the intermediary is precipitated is the micropore. This method has a slow production speed, high cost, and high process difficulty.

[0004] For commercial relatively high-temperature resistant and puncture-resistant diaphragms, PP or PE base films are generally coated with ceramics (single or double sides). The rigidity of the ceramic layer is used to upgrade the puncture resistance of the diaphragm, and there is also a small improvement in the shrinkage or melting of the high-temperature diaphragm. PET is more difficult to make directly into a diaphragm. The current pore size and porosity required for producing battery diaphragms are relatively difficult to produce using PET as a raw material, and the cost is also high. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for preparing a macroporous PET film skeleton composite diaphragm. The method of the present invention is to punch holes in a commercially available PET film by a laser machine to obtain a macroporous PET film skeleton, which is then composited with a ceramic diaphragm to obtain a macroporous PET film skeleton composite diaphragm that is extremely resistant to high temperature and puncture.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a macroporous PET film skeleton composite diaphragm comprises the following steps

[0008] 1) preparing a PET film skeleton, punching holes on the surface of the PET film to obtain a PET film skeleton;

[0009] 2) The macroporous PET membrane skeleton obtained in step 1) is laminated with a diaphragm, wherein one side of the diaphragm is coated with an adhesive and the other side is coated with a ceramic layer to obtain a laminated sample;

[0010] 3) performing heat pressing treatment on the bonded sample obtained in step 2);

[0011] 4) After the hot pressing in step 3) is completed, the macroporous PET membrane skeleton composite diaphragm is obtained by cooling.

[0012] As a preferred solution of the present invention, in step 1), the punching method is laser punching.

[0013] As a preferred embodiment of the present invention, in step 1), the thickness of the PET film is 10 μm-100 μm.

[0014] As a preferred embodiment of the present invention, in step 1), the thickness of the PET film is 19 μm-50 μm.

[0015] As a preferred embodiment of the present invention, in step 1), the width of the PET film is 50 mm-1500 mm.

[0016] As a preferred embodiment of the present invention, in step 1), the width of the PET film is 120 mm-280 mm.

[0017] As a preferred embodiment of the present invention, in step 1), the size of the holes on the PET film skeleton is 0.03 mm 2 -20mm 2 .

[0018] As a preferred solution of the present invention, in step 1), the porosity of the pores on the PET film skeleton is 40%-90%.

[0019] As a preferred embodiment of the present invention, in step 2), the PET film skeleton and the diaphragm are double-layered.

[0020] As a preferred embodiment of the present invention, in step 3), the temperature of the hot pressing treatment is 70°C-150°C, the pressure is 0.01-0.5 MPa, and the hot pressing time is 1s-20s.

[0021] As a preferred embodiment of the present invention, in step 3), the temperature of the hot pressing treatment is 90°C-115°C, the pressure is 0.01-0.03MPa, and the hot pressing time is 1.5s-3s.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) The present invention uses commercially available PET film as a raw material for preparing the skeleton, and uses laser drilling, so the skeleton preparation process is simple and the cost is low;

[0024] 2) The size range of PET film punching is 0.03mm 2 -20mm 2The porosity range is 40%-90%. Not only are the pores large in size but also in number, which not only retains the high temperature resistance of the PET skeleton but also eliminates the impact on the electrical performance of the battery cell. If the size and porosity are set too small, the impedance of the battery cell will increase sharply, affecting the electrical performance of the battery cell. If they are set too large, the strength of the PET film skeleton will be affected, affecting the safety performance of the battery cell.

[0025] 3) PET skeleton composite ceramic diaphragm, combined with the advantages of PET skeleton's high temperature resistance and ceramic coating's strong puncture resistance, has greatly improved the safety performance of the battery cell. Conventional lithium iron phosphate battery cells usually cannot pass 500℃ hot needle puncture and 150℃ / 3h hot box, but PET skeleton composite ceramic diaphragm can easily pass such harsh safety tests. DETAILED DESCRIPTION

[0026] 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 making creative work are within the scope of protection of the present invention.

[0027] In the present invention, the PET film used can be purchased from the market, the laser drilling used is a prior art, and the ceramic diaphragm used is a prior art, which will not be described in detail below.

[0028] Example 1

[0029] This embodiment provides a method for preparing a macroporous PET film skeleton composite diaphragm, comprising the following steps:

[0030] Step 1: Prepare the PET film skeleton, select a PET film with a width of 120 mm and a thickness of 25 μm, and use a laser machine to punch holes through the belt conveyor. The size of the holes is adjusted to 1 mm. 2 , the porosity is adjusted to 50%;

[0031] Step 2: Lamination of the macroporous PET membrane skeleton and the diaphragm. The macroporous PET membrane skeleton sample prepared above is laminated with a commercially available diaphragm coated with PVDF on one side and ceramic on the other side. The diaphragm is made of 12μm PE film coated with 4μm ceramic and 1μm PVDF. It is necessary to ensure that the PVDF-coated surface is opposite to the macroporous PET membrane skeleton.

[0032] Step 3: hot pressing: hot pressing the above-mentioned bonded sample with a hot press machine, and the hot pressing parameters are set as follows: temperature is 90°C, pressure is 0.02MPa, and time is 3S;

[0033] Step 4: After cooling, a macroporous PET membrane skeleton composite diaphragm is prepared.

[0034] Embodiment 2:

[0035] This embodiment provides a method for preparing a macroporous PET film skeleton composite diaphragm, comprising the following steps:

[0036] Step 1: Prepare the PET film skeleton, select a PET film with a width of 280 mm and a thickness of 19 μm, and use a laser machine to punch holes through the belt conveyor. The size of the holes is adjusted to 2 mm. 2 , the porosity was adjusted to 71%;

[0037] Step 2: Lamination of the macroporous PET membrane skeleton and the diaphragm. The macroporous PET membrane skeleton sample prepared above is laminated with a commercially available diaphragm coated with PVDF on one side and ceramic on the other side. The diaphragm is made of 16μm PP film coated with 4μm ceramic and 1μm PVDF. It is necessary to ensure that the PVDF-coated surface is opposite to the macroporous PET membrane skeleton.

[0038] Step 3: hot pressing: hot pressing the above-mentioned bonded sample using a hot press machine, and the hot pressing parameters are set as follows: temperature is 100°C, pressure is 0.01MPa, and time is 2S;

[0039] Step 4: After cooling, a macroporous PET membrane skeleton composite diaphragm is prepared.

[0040] Embodiment 3:

[0041] This embodiment provides a method for preparing a macroporous PET film skeleton composite diaphragm, comprising the following steps:

[0042] Step 1: Prepare the PET film skeleton, select a PET film with a width of 165mm and a thickness of 19μm, and use a laser machine to punch holes through the belt conveyor. The size of the holes is adjusted to 5mm. 2 , the porosity is adjusted to 75%;

[0043] Step 2: Lamination of the macroporous PET membrane skeleton and the diaphragm. The macroporous PET membrane skeleton sample prepared above is laminated with a commercially available diaphragm coated with PVDF on one side and ceramic on the other side. The diaphragm is made of 20 μm PP film coated with 4 μm ceramic and 1 μm PVDF. It is necessary to ensure that the PVDF-coated surface is opposite to the macroporous PET membrane skeleton.

[0044] Step 3: hot pressing: hot pressing the above-mentioned bonded sample with a hot press machine, and the hot pressing parameters are set as follows: temperature is 105°C, pressure is 0.01MPa, and time is 2S;

[0045] Step 4: After cooling, a macroporous PET membrane skeleton composite diaphragm is prepared.

[0046] Embodiment 4:

[0047] This embodiment provides a method for preparing a macroporous PET film skeleton composite diaphragm, comprising the following steps:

[0048] Step 1: Prepare the PET film skeleton, select a PET film with a width of 140mm and a thickness of 50μm, and use a laser machine to punch holes through the belt conveyor. The size of the holes is adjusted to 8mm. 2 , the porosity is adjusted to 80%;

[0049] Step 2: Lamination of the macroporous PET membrane skeleton and the diaphragm. The macroporous PET membrane skeleton sample prepared above is laminated with a commercially available diaphragm coated with PVDF on one side and ceramic on the other side. The diaphragm is made of 12μm PP film coated with 4μm ceramic and 1μm PVDF. It is necessary to ensure that the PVDF-coated surface is opposite to the macroporous PET membrane skeleton.

[0050] Step 3: hot pressing: hot pressing the above-mentioned bonded sample with a hot press machine, and the hot pressing parameters are set as follows: temperature is 115°C, pressure is 0.03MPa, and time is 1.5S;

[0051] Step 4: After cooling, a macroporous PET membrane skeleton composite diaphragm is prepared.

[0052] The present invention uses commercially available PET film as the raw material for preparing the skeleton, and adopts laser punching, so the skeleton preparation process is simple and the cost is low; the size range of the PET film punching is 0.03mm 2 -20mm 2 The porosity range is 40%-90%. Not only are the pores large in size but also in number. While retaining the high temperature resistance advantage of the PET skeleton, the impact on the electrical performance of the battery cell is eliminated. In terms of the two parameters of size and porosity, if the settings are too small, the impedance of the battery cell will increase sharply, affecting the electrical performance of the battery cell. If the settings are too large, the strength of the PET film skeleton will be affected, affecting the safety performance of the battery cell. The PET skeleton composite ceramic diaphragm, combined with the advantages of the PET skeleton's high temperature resistance and the ceramic coating's strong puncture resistance, has greatly improved the safety performance of the battery cell. Conventional lithium iron phosphate batteries usually cannot pass 500°C hot needle puncture and 150°C / 3h hot box, but the PET skeleton composite ceramic diaphragm can easily pass such harsh safety tests.

[0053] The above is only a preferred embodiment of the present invention, and is not any formal or substantial limitation of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any technician familiar with this profession, without departing from the spirit and scope of the present invention, can make some changes, modifications and evolutions of the technical content disclosed above, which are equivalent embodiments of the present invention; at the same time, any changes, modifications and evolutions of any equivalent changes made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a macroporous PET film skeleton composite diaphragm, characterized in that: The following steps are included 1) Prepare a PET film skeleton, punch holes on the surface of the PET film to obtain a PET film skeleton; the size of the holes on the PET film skeleton is 0.03 mm 2 -20mm 2 ; The porosity of the pores on the PET film skeleton is 40%-90%; The thickness of the PET film is 10μm-100μm; 2) The macroporous PET membrane skeleton obtained in step 1) is laminated with a diaphragm, wherein one side of the diaphragm is coated with an adhesive and the other side is coated with a ceramic layer to obtain a laminated sample; the material of the diaphragm is PE or PP; 3) performing heat pressing treatment on the bonded sample obtained in step 2); 4) After the hot pressing in step 3) is completed, the macroporous PET membrane skeleton composite diaphragm is obtained by cooling.

2. The method for preparing a macroporous PET film skeleton composite diaphragm according to claim 1, characterized in that: In step 1), the punching method is laser punching.

3. The method for preparing a macroporous PET film skeleton composite diaphragm according to claim 1, characterized in that: In step 1), the thickness of the PET film is 19 μm-50 μm.

4. The method for preparing a macroporous PET film skeleton composite diaphragm according to claim 1, characterized in that: In step 1), the width of the PET film is 50 mm-1500 mm.

5. The method for preparing a macroporous PET film skeleton composite diaphragm according to claim 4, characterized in that: In step 1), the width of the PET film is 120 mm-280 mm.

6. The method for preparing a macroporous PET film skeleton composite diaphragm according to claim 1, characterized in that: In step 3), the temperature of the hot pressing treatment is 70°C-150°C, the pressure is 0.01-0.5MPa, and the hot pressing time is 1s-20s.

7. The method for preparing a macroporous PET film skeleton composite diaphragm according to claim 6, characterized in that: In step 3), the temperature of the hot pressing treatment is 90°C-115°C, the pressure is 0.01-0.03MPa, and the hot pressing time is 1.5s-3s.