A gel-state PMMA slurry, a separator, a lithium battery and a preparation method thereof

Abstract

The application discloses a kind of gel PMMA slurry, diaphragm lithium battery and preparation method thereof.Gel PMMA slurry preparation method includes the following steps: step 1: methyl methacrylate is added to N-methyl pyrrolidone, and stirred uniformly;Then initiator azobisisobutyronitrile is added, and stirred min;Subsequently, temperature is raised to 50-70℃, and the heating rate is 3-5℃ / min, keep 30-50min, then continue to heat to 80-90℃, keep 2-4h, and the heating rate is 3-5℃ / min, then cool to room temperature to obtain PMMA gel;Step 2: alumina powder is added to N-methyl pyrrolidone, and stirred 30-40min;Then use bar pin type sand mill to sand mill to obtain inorganic powder solution;Step 3: PMMA gel prepared in step 1 is added to the inorganic powder solution obtained in step 2, and stirred to mix uniformly;Then dimethyl carbonate is added, and stirred to obtain gel PMMA slurry.The prepared gel PMMA coated diaphragm has great adhesion to pole piece and higher liquid absorption rate and liquid retention rate.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separator technology, and in particular to a gel-state PMMA slurry, a separator, a lithium battery, and a method for preparing the same. Background Technology

[0002] Polymethyl methacrylate (PMMA) has a very flexible molecular chain and relatively high strength, making it a promising new material that has attracted much attention.

[0003] Our earlier application (Publication No.: CN109378431B) used PMMA with a higher molecular weight. Higher molecular weight PMMA is not conducive to forming a network structure on the separator, resulting in a slower wetting speed during electrolyte injection and significantly reducing the efficiency of battery manufacturing. Furthermore, due to its high molecular weight, the intramolecular bonds are tightly connected, and its melting point is above 150℃. During battery manufacturing, the electrode and separator need to be hot-pressed together at a temperature of at least 130℃ to achieve adhesion, greatly increasing the difficulty of battery manufacturing. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies where high molecular weight PMMA-supported diaphragms have slow wetting speeds and are not easy to adhere to electrodes, by providing a method for preparing gel-state PMMA slurry.

[0005] Another object of the present invention is to provide a diaphragm formed by coating the above-mentioned gel-state PMMA slurry.

[0006] Another object of the present invention is to provide the application of the above-described gel-state PMMA separator in lithium batteries.

[0007] The technical solution adopted to achieve the purpose of this invention is:

[0008] A method for preparing a gelled PMMA slurry includes the following steps:

[0009] Step 1: Polymethyl methacrylate polymerization

[0010] Methyl methacrylate was added to N-methylpyrrolidone and stirred for 5-10 minutes until homogeneous. Then, the initiator azobisisobutyronitrile was added and stirred for 2-3 minutes. The temperature was then raised to 50-70°C at a rate of 3-5°C / min and held for 30-50 minutes. The temperature was then raised to 80-90°C and held for 2-4 hours at a rate of 3-5°C / min. Finally, the temperature was lowered to room temperature to obtain PMMA gel.

[0011] The mass ratio of methyl methacrylate, N-methylpyrrolidone and azobisisobutyronitrile is (10-30):(65-89):(1-5).

[0012] Step 2: Add alumina powder to N-methylpyrrolidone and stir for 30-40 minutes; then grind the mixture in a pin mill for 15-30 minutes to obtain an inorganic powder solution; wherein the mass ratio of alumina powder to N-methylpyrrolidone is (25-35):(65-75); the milling speed is 500 r / min;

[0013] Step 3: Add the PMMA gel prepared in Step 1 to the inorganic powder solution obtained in Step 2 and stir for 30-50 min to mix it evenly; then add dimethyl carbonate and stir for 20-30 min to obtain a gelled PMMA slurry; wherein, the mass ratio of PMMA gel, inorganic powder solution and dimethyl carbonate is (55-70):(25-35):(5-10).

[0014] In the above preparation process, azobisisobutyronitrile (AIBN) was used as the initiator for the polymerization of methyl methacrylate (MMA). AIBN is characterized by a relatively stable decomposition reaction, producing only one type of free radical and essentially avoiding induced decomposition. This allows for effective control of the reaction rate during polymerization, preventing explosive polymerization. The reaction rate was controlled primarily using N-methylpyrrolidone (NMP) as a retarder for MMA polymerization. NMPN is highly polar and an effective solvent for MMA, increasing the distance between molecules and slowing down the polymerization rate. Dimethyl carbonate was added to the resulting PMMA solution as a pore-forming agent. During extraction, this effectively helps the PMMA form a network structure, increasing adhesion to the electrode and improving charge / discharge efficiency during the injection process.

[0015] In another aspect of the present invention, a gel-state PMMA coated diaphragm includes a base film and a coating formed by the aforementioned gel-state PMMA slurry coated on one or both sides of the base film.

[0016] In the preparation process of the above-mentioned gel-state PMMA coated diaphragm, the extraction is carried out through the following steps: the extraction tank is divided into 10 small tanks, each with a depth of 1m. The first three tanks contain an extraction solution of deionized water and N-methylpyrrolidone mixed in different mass ratios to form a coagulation bath. The mass ratio of N-methylpyrrolidone to water in the first tank is 3:2, the mass ratio of N-methylpyrrolidone to water in the second tank is 1:1, and the mass ratio of N-methylpyrrolidone to water in the third tank is 2:3. The remaining tanks contain deionized water. The diaphragm is allowed to pass through each tank and sequentially pass through three coagulation baths of different concentrations and deionized water for extraction.

[0017] In another aspect of the present invention, the above-described gel-state PMMA-coated separator is used in lithium batteries.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. In the preparation process provided by the present invention, azobisisobutyronitrile is used as the initiator for the polymerization of methyl methacrylate, and N-methylpyrrolidone solvent is used as the retarder for the polymerization of methyl methacrylate. This can effectively control the reaction rate and the polymerization reaction time during the polymerization process, preventing it from reacting fully, and ultimately achieving a controllable molecular weight.

[0020] 2. The gel-state PMMA-coated diaphragm provided by this invention has a strong adhesion to the electrode and a higher liquid absorption and retention rate.

[0021] 3. The gel-state PMMA-coated separator provided by this invention can quickly absorb electrolyte during injection, increasing the electrolyte injection efficiency of the battery and improving the battery production efficiency. Attached Figure Description

[0022] Figure 1 The image shown is a scanning electron microscope image of the gel-state PMMA-coated diaphragm in Example 1. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0024] Example 1

[0025] A method for preparing a gelled PMMA slurry includes the following steps:

[0026] Step 1: Polymethyl methacrylate polymerization

[0027] Methyl methacrylate was added to N-methylpyrrolidone and stirred for 5 min; then the initiator azobisisobutyronitrile was added and stirred for 2 min; subsequently, the temperature was raised to 50 °C at a rate of 3 °C / min and held for 30 min, then the temperature was raised to 80 °C and held for 2 h at a rate of 3 °C / min, and then cooled to room temperature to obtain PMMA gel; wherein the mass ratio of methyl methacrylate, N-methylpyrrolidone and azobisisobutyronitrile was 10:89:1.

[0028] Step 2: Add alumina powder to N-methylpyrrolidone and stir for 30 min; then use a pin mill to grind for 15 min to obtain an inorganic powder solution; wherein, the mass ratio of alumina powder to N-methylpyrrolidone is 35:65; the milling speed is 500 r / min;

[0029] Step 3: Add the PMMA gel prepared in Step 1 to the inorganic powder solution obtained in Step 2, and stir for 30 min to mix it evenly; then add dimethyl carbonate and stir for 20 min to obtain a gelled PMMA slurry; wherein, the mass ratio of PMMA gel, inorganic powder solution and dimethyl carbonate is 70:25:5.

[0030] A gel-state PMMA coated membrane includes a PE base film and a coating formed by the aforementioned gel-state PMMA slurry coated on one side of the base film, the coating thickness being 2 μm.

[0031] In the above-mentioned preparation process of the gel-state PMMA coated diaphragm, the extraction is carried out through the following steps: the extraction tank is divided into 10 small tanks, each with a depth of 1m. The first three tanks contain an extraction solution of deionized water and N-methylpyrrolidone mixed in different mass ratios to form a coagulation bath. The mass ratio of N-methylpyrrolidone to water in the first tank is 3:2, the mass ratio of N-methylpyrrolidone to water in the second tank is 1:1, and the mass ratio of N-methylpyrrolidone to water in the third tank is 2:3. The remaining tanks contain deionized water. The diaphragm is allowed to pass through each tank and sequentially pass through three coagulation baths of different concentrations and deionized water for extraction.

[0032] Scanning electron microscope image of the prepared gel-state PMMA-coated diaphragm is shown below. Figure 1 As shown in the electron microscope, the polymethyl methacrylate network structure is relatively three-dimensional and has a high porosity.

[0033] Example 2

[0034] A method for preparing a gelled PMMA slurry includes the following steps:

[0035] Step 1: Polymethyl methacrylate polymerization

[0036] Methyl methacrylate was added to N-methylpyrrolidone and stirred for 7 min; then the initiator azobisisobutyronitrile was added and stirred for 2 min; subsequently, the temperature was raised to 60 °C at a rate of 4 °C / min and held for 40 min, then the temperature was further raised to 85 °C and held for 3 h at a rate of 4 °C / min, and then cooled to room temperature to obtain PMMA gel; wherein the mass ratio of methyl methacrylate, N-methylpyrrolidone and azobisisobutyronitrile was 15:82:3.

[0037] Step 2: Add alumina powder to N-methylpyrrolidone and stir for 35 min; then grind with a pin mill for 20 min to obtain an inorganic powder solution; wherein, the mass ratio of alumina powder to N-methylpyrrolidone is 30:70; the milling speed is 500 r / min;

[0038] Step 3: Add the PMMA gel prepared in Step 1 to the inorganic powder solution obtained in Step 2, and stir for 40 min to mix it evenly; then add dimethyl carbonate and stir for 25 min to obtain a gelled PMMA slurry; wherein, the mass ratio of PMMA gel, inorganic powder solution and dimethyl carbonate is 63:30:7.

[0039] A gel-state PMMA coated membrane includes a PE base film and a coating formed by the aforementioned gel-state PMMA slurry coated on one side of the base film, the coating thickness being 2 μm.

[0040] Example 3

[0041] A method for preparing a gelled PMMA slurry includes the following steps:

[0042] Step 1: Polymethyl methacrylate polymerization

[0043] Methyl methacrylate was added to N-methylpyrrolidone and stirred for 10 min; then the initiator azobisisobutyronitrile was added and stirred for 3 min; subsequently, the temperature was raised to 70 °C at a rate of 5 °C / min and held for 50 min, then the temperature was further raised to 90 °C and held for 4 h at a rate of 5 °C / min, and then cooled to room temperature to obtain PMMA gel; wherein the mass ratio of methyl methacrylate, N-methylpyrrolidone and azobisisobutyronitrile was 30:65:5.

[0044] Step 2: Add alumina powder to N-methylpyrrolidone and stir for 40 min; then use a pin mill to grind for 30 min to obtain an inorganic powder solution; wherein, the mass ratio of alumina powder to N-methylpyrrolidone is 25:75; the milling speed is 500 r / min;

[0045] Step 3: Add the PMMA gel prepared in Step 1 to the inorganic powder solution obtained in Step 2, and stir for 50 min to mix it evenly; then add dimethyl carbonate and stir for 30 min to obtain a gelled PMMA slurry; wherein, the mass ratio of PMMA gel, inorganic powder solution and dimethyl carbonate is 55:35:10.

[0046] A gel-state PMMA coated membrane includes a PE base film and a coating formed by the aforementioned gel-state PMMA slurry coated on one side of the base film, the coating thickness being 2 μm.

[0047] Comparative Example 1

[0048] The difference between this comparative example and Example 3 is that PVDF is used instead of PMMA gel, while maintaining the same parameters.

[0049] A method for preparing PVDF slurry includes the following steps:

[0050] Step 1: Add alumina powder to N-methylpyrrolidone and stir for 40 min; then use a pin mill to grind for 30 min to obtain an inorganic powder solution; wherein, the mass ratio of alumina powder to N-methylpyrrolidone is 25:75; the milling speed is 500 r / min.

[0051] Step 2: Add PVDF to the inorganic powder solution prepared in Step 1 and stir for 50 min to mix it evenly; then add dimethyl carbonate and stir for 30 min to obtain PVDF slurry; wherein the mass ratio of PVDF, inorganic powder solution and dimethyl carbonate is 55:35:10.

[0052] A PVDF-coated separator includes a PE base film and a coating formed by coating the aforementioned PVDF slurry onto one side of the base film. The coating thickness is 2 μm.

[0053] Comparative Example 2

[0054] The difference between this comparative example and Example 3 is that polymethyl methacrylate particles are used instead of PMMA gel, while maintaining the same parameters.

[0055] A method for preparing PMMA slurry includes the following steps:

[0056] Step 1: Add alumina powder to N-methylpyrrolidone and stir for 40 min; then use a pin mill to grind for 30 min to obtain an inorganic powder solution; wherein, the mass ratio of alumina powder to N-methylpyrrolidone is 25:75; the milling speed is 500 r / min.

[0057] Step 2: Add PMMA particles to the inorganic powder solution prepared in Step 1 and stir for 50 min to mix evenly; then add dimethyl carbonate and stir for 30 min to obtain PVDF slurry; wherein the mass ratio of PMMA particles, inorganic powder solution and dimethyl carbonate is 55:35:10.

[0058] A PMMA-coated separator includes a PE base film and a coating formed by coating the aforementioned PMMA slurry onto one side of the base film. The coating thickness is 2 μm.

[0059] Adhesion test:

[0060] The electrodes (positive and negative) and the separators to be tested (Examples 1-3 and Comparative Examples 1-2) were cut into shapes with a width of 12 mm and a length of 100 mm, respectively. They were then stacked together and tested using a battery electrode press at a pressure of 0.8 MPa, a temperature of 70°C, and a time of 20 seconds to create test samples. Next, a tensile testing machine was used to test the force required to tear the electrodes from the separator, representing the adhesion between the separator and the electrodes. The test results are shown in the table below:

[0061]

[0062]

[0063] The data above shows that the polymethyl methacrylate (PMMA) used in Examples 1-3 exhibits a high degree of adhesion to the electrode sheets after controlling the molecular weight during the synthesis process. This adhesion is significantly stronger than that of the diaphragm coated with the PVDF slurry prepared in Comparative Example 1. In contrast, the high molecular weight PMMA in Comparative Document 2, due to its larger molecular weight and weaker plasticity, results in lower adhesion.

[0064] Liquid absorption and retention rate tests:

[0065] Liquid absorption rate: Cut the diaphragm to be tested into a fixed size, immerse it in the electrolyte for 30 minutes, take it out and weigh it, and calculate the liquid absorption rate.

[0066] Liquid retention rate: The diaphragm to be tested, after being soaked in electrolyte for 30 minutes, is taken out, suspended for 30 minutes, and then weighed to calculate the liquid retention rate.

[0067] The test results are shown in the table below:

[0068]

[0069] Based on the test data, the gel-state PMMA-coated separators prepared in Examples 1-3 have higher liquid absorption and liquid retention rates, which can significantly improve the charge and discharge efficiency in the battery.

[0070] Electrolyte injection efficiency during battery assembly:

[0071] The separator to be tested is wound together with the battery electrode to form a stack, which is then hot-pressed into a fixed volume. A certain amount of electrolyte is then injected. Since the wound electrode almost fills the space inside the battery, the electrolyte needs to be immersed in the stack. The time for the electrolyte to be injected into the battery is the injection efficiency. The shorter the time, the higher the injection efficiency.

[0072] The wound battery model is NCM606090. Each battery has a thickness of 3.5mm, a width of 78mm, a height of 131mm, a nominal capacity of 4000mAh, an internal resistance of less than 40mΩ, a nominal voltage of 3.7V, a positive electrode material of lithium iron phosphate, a negative electrode material of graphite, an electrolyte of lithium hexafluorophosphate, a solvent of carbonate, and an electrolyte concentration of 6mol / L.

[0073] The test results are shown in the table below:

[0074]

[0075]

[0076] The data above show that the gel-state PMMA-coated separators prepared in Examples 1-3 have a good immersion rate and can quickly absorb electrolyte during electrolyte injection, thereby increasing the electrolyte injection efficiency of the battery.

[0077] By adjusting the process parameters according to the content of this invention, the gel-state PMMA slurry of this invention can be prepared and exhibits properties that are basically the same as those in Example 1.

[0078] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of preparing a gelatinous PMMA slurry, characterized by: Includes the following steps: Step 1: Polymethyl methacrylate polymerization Methyl methacrylate was added to N-methylpyrrolidone and stirred until homogeneous. Then, the initiator azobisisobutyronitrile was added and stirred for 2-3 minutes. The temperature was then raised to 50-70°C at a rate of 3-5°C / min and held for 30-50 minutes. The temperature was then raised to 80-90°C and held for 2-4 hours at a rate of 3-5°C / min. Finally, the temperature was lowered to room temperature to obtain PMMA gel. Step 2: Add alumina powder to N-methylpyrrolidone and stir for 30-40 minutes; then grind it with a pin mill to obtain an inorganic powder solution. Step 3: Add the PMMA gel prepared in Step 1 to the inorganic powder solution obtained in Step 2 and stir to mix it evenly; then add dimethyl carbonate and stir to obtain a gelled PMMA slurry.

2. The production method according to claim 1, characterized by: In step 1, the mass ratio of methyl methacrylate, N-methylpyrrolidone and azobisisobutyronitrile is (10-30):(65-89):(1-5).

3. The production method according to claim 1, wherein: In step 2, the mass ratio of alumina powder to N-methylpyrrolidone is (25-35):(65-75).

4. The production method according to claim 1, wherein: In step 2, the grinding time is 15-30 minutes; the grinding speed is 500 r / min.

5. The production method according to claim 1, wherein: In step 3, the mass ratio of PMMA gel, inorganic powder solution and dimethyl carbonate is (55-70):(25-35):(5-10).

6. A gelled PMMA slurry prepared by the preparation method according to any one of claims 1-5.

7. A gel state PMMA coated separator characterized in that, It includes a base film and a coating formed by coating one or both sides of the base film with the gel-state PMMA slurry as described in claim 6.

8. The gelated PMMA-coated separator of claim 7, wherein, The extraction method involves dividing the extraction tank into 10 smaller tanks, each 1m deep. The first three tanks contain an extract solution of deionized water and N-methylpyrrolidone mixed in different mass ratios to form a coagulation bath. In the first tank, the mass ratio of N-methylpyrrolidone to water is 3:2; in the second tank, it is 1:1; and in the third tank, it is 2:

3. The remaining tanks contain deionized water. A diaphragm is passed through each tank, sequentially through three different concentrations of coagulation bath and deionized water for extraction.

9. A lithium battery, characterized by It includes a positive electrode, a negative electrode, an electrolyte, and a gel-state PMMA-coated separator as described in claim 7.

10. The lithium battery of claim 9, wherein the electrolyte comprises 0.1 to 5 wt% of the lithium salt. The positive electrode material is lithium iron phosphate, the negative electrode material is graphite, the electrolyte is lithium hexafluorophosphate, the solvent is carbonate, and the concentration of the electrolyte in the electrolyte is 6 mol / L.

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