Novel diaphragm manufacturing method

Abstract

The invention relates to a novel diaphragm manufacturing method which comprises the following steps: 1) dissolving soluble barium salt with deionized water, and mixing and stirring with a binder to obtain slurry A; 2) dissolving soluble sulfate with deionized water to obtain a solution B; and 3) roller-painting the slurry A on the surface of the porous base material, spraying the solution B, curing the sprayed porous base material, washing with water, and drying to obtain the diaphragm. According to the invention, the coating process of the inorganic porous layer is improved, so that the technical problem that the nano inorganic material in the coating material is difficult to disperse can be solved, the homogeneity of the coating layer is improved, and the quality stability of the diaphragm is improved.

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 an important component of lithium-ion batteries. It is used to separate the positive and negative electrodes and prevent short circuits. At the same time, it also allows ions to pass through. It is the key to ensure battery safety and stability. Since lithium-ion batteries generate heat when working and the battery temperature rises, the diaphragm material is required to have good high temperature resistance. Dendrites may be generated inside lithium-ion batteries. Dendrites piercing the diaphragm is an important cause of battery short circuits. Therefore, the diaphragm material is also required to have high strength. In order to ensure a high ion pass rate, it is generally required to have a high porosity and the pore size is required to be between 10-500nm. Low porosity means low ion pass rate. If the pore size is too large, dendrites can easily pass through the diaphragm, causing a short circuit.

[0003] The 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, which improves the porosity of the diaphragm. However, the quality of the inorganic porous layer has very high requirements on the coating process. Nano-inorganic salt particles are very easy to agglomerate. When preparing the slurry, it takes a long time to grind and disperse it through 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 scheme 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) or poly(m-phenylene isophthalamide) or polyoxadiazole, or a mixture thereof.

[0011] Furthermore, in step 1), the soluble barium salt is barium nitrate or barium acetate; 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. A spray pipe is arranged at the downstream of the coating roller. The spray pipe is used to spray solution B.

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

[0015] Furthermore, a first densitometer and a second densitometer are sequentially arranged at intervals at a 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 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 a 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 invention can be used for lithium ion battery diaphragm, RO membrane and hydrogen storage material. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0020] The scheme of the present invention is described in detail below with reference to specific examples.

[0021] In the following examples and comparative examples, the acrylic resin is selected as styrene acrylic resin, but it is not limited thereto. When other acrylic resins are selected, the effect is close to that of the examples listed in the present invention. The porous substrate is selected as poly(p-phenylene terephthalamide) or poly(m-phenylene isophthalamide) or polyoxadiazole, or a mixture of the three, and the substrate has a high temperature resistance. In the following examples and comparative examples, poly(p-phenylene terephthalamide) is specifically selected as an 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) The slurry is coated on the surface of the porous substrate with a roller, and then the ammonium sulfate solution is sprayed. After standing for 24 hours, the coating layer is naturally cured, and then immersed in deionized water for washing, and then dried 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) The slurry is coated on the surface of the porous substrate with a roller, and then the ammonium sulfate solution is sprayed. After standing for 12 hours, it is dried at 150°C. The coating layer is solidified, and it is immersed and washed with deionized water, and then dried 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) The slurry is coated on the surface of the porous substrate with a roller, and then the ammonium sulfate solution is sprayed. After standing for 12 hours, it is dried at 150°C. The coating layer is solidified, and it is immersed and washed with deionized water, and then dried at 150°C.

[0031] Comparative Example 1 1) Acrylic resin and deionized water are mixed in a volume ratio of 1:2, and then dispersed with barium sulfate raw material by a sand mill for 12 hours to prepare slurry for standby use;

[0032] 3) After roll-coating the surface of the porous substrate with a slurry, allowing it to stand for 12 hours, drying it at 150 °C, curing the coating layer, impregnating and washing it with deionized water, and then drying it at 150 °C again.

[0033] Five samples were cut from the diaphragms prepared in Examples 1-3 and Comparative Example 1 at different positions, and the porosity and heat resistance were detected respectively. The porosity was detected by the nitrogen adsorption method, and the heat resistance was detected by the material shrinkage rate at 200 °C. The results are shown in the following table:

[0034] It can be seen from the above comparison that the diaphragm prepared by the method of the present invention has a higher porosity, the shrinkage rate at 200 °C is less than 1%, and moreover, the material has good homogeneity and stable quality. Example 4

[0035] This example provides a roll coater that can be used to implement the method of the present invention. For example, Figure 1 , the roll coater includes a material-taking roll 1, a coating roll 2 and a supporting roll 3. The supporting roll is a rubber roll, and the coating roll and the material-taking roll are stainless steel rolls. The material-taking roll is arranged in a paint tray 4, and the A slurry for roll coating is placed in the paint tray. A spray pipe 5 is arranged at the downstream position of the coating roll, and the spray pipe is used to spray the B solution and is connected to the spray system through a pipeline.

[0036] During operation, the substrate is conveyed along the supporting roll. The material-taking roll dips the slurry from the paint tray and then transfers the slurry to the coating roll. The coating roll rotates reversely relative to the supporting roll to coat the substrate, and the coating thickness is adjusted by the gap between the coating roll and the supporting roll. After roll coating, the spray pipe sprays the surface of the substrate, spraying the soluble sulfate solution on the roll-coated layer. The sulfate reacts with the barium salt in the roll-coated layer through a metathesis reaction to generate barium sulfate precipitate, realizing the coating of barium sulfate.

[0037] In this example, in order to improve the reaction rate between the soluble sulfate and the barium salt, an ultrasonic device 6 is arranged on the downstream side of the supporting roll to increase the reaction rate by using ultrasonic waves.

[0038] In addition, a first densitometer 7 and a second densitometer 8 are arranged at intervals in sequence at the downstream position of the ultrasonic device. 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 value, the power of the ultrasonic device is increased.

[0039] The optical densitometer can detect the OD value (optical density) of the material online. When barium sulfate precipitation is generated in the coating layer on the surface of the substrate, the transmittance decreases and the optical density value increases. The difference between the second optical densitometer and the first optical densitometer can be used as a reference for reaction speed control. When the reaction speed is too slow, the difference between the second optical densitometer and the first optical densitometer is large, and the power of the ultrasonic device can be increased accordingly to increase the reaction speed.

[0040] Similarly, a third densitometer 9 is provided at the upstream position of the spray pipe, and a flow valve is provided on the spray pipe. The flow of the spray pipe is controlled according to the difference between the detection values ​​of the second densitometer and the third densitometer. When the difference is less than the threshold value, the flow of the spray pipe is increased. When the difference between the second densitometer and the third photometer is small, it means that less barium sulfate precipitation is generated, which is lower than expected. Under the condition that the soluble barium salt mixed in the roller coating slurry is sufficient, it means that the soluble sulfate sprayed is insufficient, and the spraying amount can be increased.

[0041] In the above scheme, 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) Dissolve the soluble barium salt in deionized water, and then mix and stir with the binder to obtain slurry A; 2) dissolving the soluble sulfate in deionized water to obtain solution B; 3) Slurry A is roll-coated on the surface of the porous substrate, and then solution B is sprayed on the porous substrate. The porous substrate after spraying is cured, washed with water, and dried to obtain a diaphragm.

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

3. The novel diaphragm manufacturing method according to claim 1 is characterized in that: In step 1), the soluble barium salt is barium nitrate or barium acetate; in step 2), the soluble sulfate is ammonium sulfate or sodium sulfate.

4. The novel diaphragm manufacturing method according to claim 1 is characterized in that: In step 1), the binder is acrylic resin.

5. The novel diaphragm manufacturing method according to claim 1 is characterized in that: In step 3), a roller coater is used to roll 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. A spray pipe is arranged downstream of the coating roller. The spray pipe is used to spray solution B.

6. The novel diaphragm manufacturing method according to claim 5 is characterized in that: An ultrasonic device is provided at a position downstream of the support roll.

7. The novel diaphragm manufacturing method according to claim 6 is characterized in that: A first densitometer and a second densitometer are arranged in sequence at a 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 and the first densitometer. When the difference is greater than a threshold, the power of the ultrasonic device is increased.

8. The novel diaphragm manufacturing method according to claim 7 is characterized in that: 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 densitometer and the third densitometer. When the difference is less than the threshold, the flow of the spray pipe is increased.

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