A new method for manufacturing diaphragms

Abstract

The present invention relates to a novel method for manufacturing a diaphragm, comprising the following steps: 1) dissolving a soluble barium salt in deionized water, then mixing and stirring with a binder to obtain slurry A; 2) dissolving a soluble sulfate in deionized water to obtain solution B; 3) applying slurry A to the surface of a porous substrate by roller coating, followed by spraying solution B. The sprayed porous substrate is then cured, washed, and dried to obtain the diaphragm. This invention improves the coating process for the inorganic porous layer, resolving the technical challenge of dispersing nano-inorganic materials within the coating material, enhancing the homogeneity of the coating layer, and contributing to improved quality and stability of the diaphragm.

Description

Technical Field

[0001] The invention relates to a novel diaphragm manufacturing method, belonging to the technical field of membrane material preparation. Background Art

[0002] The diaphragm is a crucial component of lithium-ion batteries, separating the positive and negative electrodes to prevent short circuits while allowing ions to pass through. It is crucial for ensuring battery safety and stability. Since lithium-ion batteries generate heat during operation, the battery temperature rises, requiring the diaphragm material to possess excellent high-temperature resistance. Dendrites can form inside lithium-ion batteries, and puncturing the diaphragm by dendrites is a major cause of battery short circuits. Therefore, the diaphragm material must also possess high strength. To ensure a high ion pass rate, a high porosity is generally required, with a pore size between 10 and 500 nm. Low porosity results in low ion pass rate, while an excessively large pore size allows dendrites to easily penetrate the diaphragm, causing a short circuit.

[0003] Current lithium-ion battery separator materials use PE and PP as the base material, and boehmite is coated on the surface of the base material to enhance its temperature resistance and strength. PE and PP are non-polar materials with poor lyophilicity and need to be coated with PVDF, which increases the cost. Even so, the temperature resistance of this type of separator can only reach 150°C, and the shrinkage rate is greater than 2% at 200°C.

[0004] In addition, coating an inorganic dielectric layer on the surface of the substrate can improve the strength and temperature resistance of the diaphragm. Nano-inorganic salt particles are used to make a slurry for coating. The inorganic salt particles accumulate to form an inorganic porous layer with a microporous structure, thereby increasing the porosity of the diaphragm. However, the quality of the inorganic porous layer places high demands on the coating process. Nano-inorganic salt particles are very prone to agglomeration. When preparing the slurry, it takes a long time to grind and disperse them in a sand mill to reduce agglomeration and improve the uniformity of the slurry. The sand milling process is time-consuming and inefficient. Even so, the homogeneity of the coated material is low and the quality stability is poor. Summary of the Invention

[0005] In view of the above problems, the present invention provides a novel diaphragm manufacturing method, the specific solution is as follows:

[0006] A novel diaphragm manufacturing method comprises the following steps:

[0007] 1) Dissolve the soluble barium salt in deionized water, and then mix and stir with the binder to obtain slurry A;

[0008] 2) Dissolving the soluble sulfate in deionized water to obtain solution B;

[0009] 3) Slurry A is roll-coated on the surface of the porous substrate, and then solution B is sprayed on the porous substrate. The sprayed porous substrate is cured, washed with water, and dried to obtain a diaphragm.

[0010] Furthermore, in step 3), the porous substrate is poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), polyoxadiazole, or a mixture thereof.

[0011] Furthermore, in step 1), the soluble barium salt is barium nitrate or barium acetate; and in step 2), the soluble sulfate is ammonium sulfate or sodium sulfate.

[0012] Furthermore, in step 1), the binder is acrylic resin.

[0013] Furthermore, in step 3), a roller coater is used to roll-coat slurry A on the surface of the porous substrate. The roller coater includes a feed roller, a coating roller, and a support roller. The feed roller is arranged in a coating tray, and a spray pipe is arranged downstream of the coating roller. The spray pipe is used to spray solution B.

[0014] Furthermore, an ultrasonic device is provided at a position downstream of the support roller.

[0015] Furthermore, a first densitometer and a second densitometer are sequentially arranged at intervals downstream of the ultrasonic device, and the power of the ultrasonic device is controlled according to the difference between the detection values ​​of the second densitometer and the first densitometer. When the difference is greater than a threshold, the power of the ultrasonic device is increased.

[0016] Furthermore, a third densitometer is set at the upstream position of the spray pipe, and a flow valve is set on the spray pipe to control the flow of the spray pipe according to the difference between the detection values ​​of the second densitometer and the third densitometer. When the difference is less than the threshold, the flow of the spray pipe is increased.

[0017] The present invention improves the coating process of the inorganic porous layer, can solve the technical problem of the difficulty in dispersing nano inorganic materials in the coating material, improve the homogeneity of the coating layer, and is conducive to improving the quality stability of the diaphragm.

[0018] The diaphragm prepared by the present invention can be used as a lithium ion battery diaphragm, an RO membrane and a hydrogen storage material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the roller coater in the embodiment. DETAILED DESCRIPTION

[0020] The following describes the solution of the present invention in detail with reference to specific examples.

[0021] In the following examples and comparative examples, the acrylic resin is styrene acrylic resin, but this is not limiting. When other acrylic resins are used, the results are similar to those of the examples presented herein. The porous substrate is poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), polyoxadiazole, or a mixture thereof. These substrates exhibit high heat resistance. In the following examples and comparative examples, poly(p-phenylene terephthalamide) is specifically selected for example. Example 1

[0022] 1) Dissolve barium nitrate in deionized water to prepare a 9% barium nitrate solution, and mix the barium nitrate solution with styrene acrylic resin in a volume ratio of 1:1 to prepare a slurry for later use;

[0023] 2) Dissolve ammonium sulfate in deionized water to prepare a 30% ammonium sulfate solution for later use;

[0024] 3) Coat the surface of the porous substrate with a slurry roller and then spray it with ammonium sulfate solution. After standing for 24 hours, the coating layer will naturally solidify. Then, immerse and wash it with deionized water and then dry it at 150°C. Example 2

[0025] 1) Dissolve barium acetate in deionized water to prepare a 30% barium acetate solution, and mix the barium acetate solution with styrene acrylic resin in a volume ratio of 1:1 to prepare a slurry for later use;

[0026] 2) Dissolve sodium sulfate in deionized water to prepare a 30% sodium sulfate solution for later use;

[0027] 3) Coat the surface of the porous substrate with a slurry roller, then spray with ammonium sulfate solution, let it stand for 12 hours, dry it at 150°C, solidify the coating layer, immerse and wash it with deionized water, and then dry it at 150°C. Example 3

[0028] 1) Dissolve barium acetate in deionized water to prepare a 30% barium acetate solution, and mix the barium acetate solution with styrene acrylic resin in a volume ratio of 1:1 to prepare a slurry for later use;

[0029] 2) Dissolve ammonium sulfate in deionized water to prepare a 30% ammonium sulfate solution for later use;

[0030] 3) Coat the surface of the porous substrate with a slurry roller, then spray with ammonium sulfate solution, let it stand for 12 hours, dry it at 150°C, solidify the coating layer, immerse and wash it with deionized water, and then dry it at 150°C.

[0031] Comparative Example 1

[0032] 1) Mix acrylic resin and deionized water in a volume ratio of 1:2, and then disperse with barium sulfate raw material using a sand mill for 12 hours to prepare a slurry for later use;

[0033] 3) Apply the slurry to the surface of the porous substrate with a roller, let it stand for 12 hours, and then dry it at 150°C to solidify the coating layer. Then, rinse it with deionized water and dry it at 150°C.

[0034] Five samples of the diaphragms prepared in Examples 1-3 and Comparative Example 1 were cut at different positions and subjected to porosity and heat resistance tests. The porosity was tested by nitrogen adsorption, and the heat resistance was tested by material shrinkage at 200°C. The results are shown in the following table:

[0035]

[0036] From the above comparison, it can be seen that the diaphragm prepared by the method of the present invention has a higher porosity and a shrinkage rate of less than 1% at 200°C. Moreover, the material has good homogeneity and stable quality. Example 4

[0037] This embodiment provides a roller coating machine that can be used to implement the method of the present invention, such as Figure 1 The roller coater includes a feeding roller 1, a coating roller 2 and a supporting roller 3. The supporting roller is a rubber roller, and the coating roller and the feeding roller are stainless steel rollers. The feeding roller is arranged in a coating tray 4. The A slurry for roller coating is placed in the coating tray. A spray pipe 5 is arranged at the downstream position of the coating roller. The spray pipe is used to spray the B solution and is connected to the spray system through a pipeline.

[0038] During operation, the substrate is conveyed along the support roller. The take-up roller picks up the slurry from the coating pan and transfers it to the coating roller. The coating roller rotates in the opposite direction to the support roller, coating the substrate. The coating thickness is adjusted by the gap between the coating roller and the support roller. After roller coating, the spray pipe sprays the substrate surface with a soluble sulfate solution onto the roller coating surface. The sulfate undergoes a double decomposition reaction with the barium salt in the roller coating to form a barium sulfate precipitate, completing the barium sulfate coating.

[0039] In this embodiment, in order to increase the reaction speed of the soluble sulfate and the barium salt, an ultrasonic device 6 is provided on the downstream side of the support roll to increase the reaction speed by using ultrasonic waves.

[0040] In addition, the first densitometer 7 and the second densitometer 8 are arranged in sequence at the downstream position of the ultrasonic device, and the power of the ultrasonic device is controlled according to the difference between the detection values ​​of the second densitometer 8 and the first densitometer 7. When the difference is greater than the threshold, the power of the ultrasonic device is increased.

[0041] An optical densitometer can measure the OD (optical density) of a material online. When barium sulfate precipitates form in the coating layer on the substrate surface, the transmittance decreases and the optical density increases. The difference between the second and first optical densitometer readings can be used as a reference for reaction rate control. If the reaction rate is too slow, the difference between the second and first optical densitometer readings is large, and the ultrasonic device power can be increased accordingly to improve the reaction rate.

[0042] Similarly, a third densitometer 9 is positioned upstream of the spray pipe, and a flow valve is installed on the spray pipe. The flow rate in the spray pipe is controlled based on the difference between the values ​​detected by the second and third densitometers. When the difference is less than a threshold, the flow rate in the spray pipe is increased. A small difference between the second and third densitometers indicates that barium sulfate precipitation is low and below expectations. If the roller coating slurry contains a sufficient amount of soluble barium salt, this indicates that insufficient soluble sulfate is being sprayed, and the spray rate can be increased.

[0043] In the above solution, the control threshold of the difference between the second densitometer and the first densitometer, and the control threshold of the difference between the second densitometer and the third photometer can be determined by empirical values ​​to ensure that the coating layer can generate the expected barium sulfate porous layer.

Claims

1. A novel diaphragm manufacturing method, characterized in that: The following steps are involved: 1) dissolving a soluble barium salt in deionized water, and then mixing and stirring with a binder to obtain slurry A; the soluble barium salt is barium nitrate or barium acetate; the binder is acrylic resin; 2) dissolving a soluble sulfate in deionized water to obtain solution B; the soluble sulfate is ammonium sulfate or sodium sulfate; 3) Slurry A is roller-coated on the surface of the porous substrate, followed by spraying solution B. The porous substrate after spraying is cured, washed with water, and dried to obtain a diaphragm; In step 3), a roller coater is used to coat the surface of the porous substrate with slurry A. The roller coater includes a feed roller, a coating roller, and a support roller. The feed roller is disposed in a coating tray, and a spray pipe is disposed downstream of the coating roller for spraying solution B. An ultrasonic device is provided at a downstream position of the support roller; A first densitometer and a second densitometer are sequentially arranged at intervals downstream of the ultrasonic device, and the power of the ultrasonic device is controlled according to the difference between the detection values ​​of the second densitometer and the first densitometer. When the difference is greater than a threshold value, the power of the ultrasonic device is increased; A third densitometer is set at the upstream position of the spray pipe, and a flow valve is set on the spray pipe. The flow of the spray pipe is controlled according to the difference between the detection values ​​of the second and third densitometers. When the difference is less than the threshold, the flow of the spray pipe is increased.

2. The novel diaphragm manufacturing method according to claim 1, characterized in that: In step 3), the porous substrate is poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), polyoxadiazole, or a mixture thereof.

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