Calculation method for theoretical porosity of coated separator, and use of calculation method

Abstract

Provided in the present application are a calculation method for the theoretical porosity of a coated separator, and the use of the calculation method. The calculation method comprises the following steps: (1) measuring the true density of each layer of a coated separator to be tested, and calculating the theoretical porosity of each layer on the basis of the true density of each layer of said coated separator; (2) respectively calculating the ratio of the surface density of each layer of said coated separator to the surface density of said coated separator; and (3) calculating the theoretical porosity of said coated separator on the basis of the theoretical porosities of the layers of said coated separator and the ratios of the surface densities of the layers of said coated separator to the surface density of said coated separator. On the basis of a calculation method for the theoretical porosity of a base membrane, the present application provides a testing method for the theoretical porosity of a coated separator. By means of the theoretical porosity calculation method, the porosity of a coated separator can be quickly obtained, thus providing data support for parameters of the electrolyte injection volume in battery simulation.

Description

A method for calculating the theoretical porosity of coated membranes and its application

[0001] This application claims priority to an invention patent application filed on August 31, 2023, with application number 202311116099.7 and titled “A method for calculating the theoretical porosity of a coated membrane and its application,” the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the field of battery testing, for example, a method for calculating the theoretical porosity of a coated diaphragm and its application. Background Art

[0003] With the rapid development of battery technology, battery simulation is increasingly being used in early-stage battery development. This allows for the early simulation of battery operating conditions and the identification of potential issues. Battery injection volume is a crucial simulation parameter. Excessive or insufficient injection can negatively impact battery performance; only the appropriate injection volume can maximize performance. This injection volume is closely related to the porosity of the battery's separator.

[0004] CN107843533A discloses a diaphragm porosity testing method, comprising the following steps: intercepting a diaphragm sample, calculating and recording the apparent volume V1 of the diaphragm sample; placing the diaphragm sample in an oven to melt and cool to obtain a melted diaphragm block; placing the diaphragm block in a volumetric flask and placing the volumetric flask on a balance, returning the balance reading to zero, adding a solvent with a known density ρ to the volumetric flask to the scale line of the volumetric flask and ensuring that the diaphragm block is immersed in the solvent, recording the volume reading V2 of the volumetric flask contents and the balance reading M; the volume of the solvent added in the previous step V3 = M / ρ, and the volume of the diaphragm block obtained is V4 = V2-V3; and calculating the porosity of the diaphragm sample.

[0005] CN112098301A The method comprises: 1) measuring the mass m and apparent volume Vapparent of the diaphragm; 2) measuring the true density ρ of the diaphragm by gas displacement method, and obtaining the true volume Vtrue of the diaphragm according to the formula Vtrue=m / ρ; 3) obtaining the true volume Vtrue of the diaphragm according to the formula Calculate the membrane porosity.

[0006] The above method only measures the porosity of the base membrane. However, in practice, the vast majority of batteries use coated separators with functional coatings. Furthermore, technical personnel prefer theoretical calculations, which are convenient and readily available, and the theoretical calculation data is widely accepted. Currently, there are several porosity test methods for coated separators, but no theoretical porosity calculation method similar to that for base membranes exists.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] The present application provides a method for calculating the theoretical porosity of a coated diaphragm and its application. Based on the theoretical porosity calculation method of a base membrane, the present application proposes a method for testing the theoretical porosity of a coated membrane. Through this theoretical calculation method, the porosity of the coated membrane can be quickly obtained, providing data support for the battery simulation injection volume parameters.

[0010] In a first aspect, the present application provides a method for calculating the theoretical porosity of a coated diaphragm, the method comprising the following steps:

[0011] (1) measuring the true density of each layer of the coated diaphragm to be tested, and calculating the theoretical porosity of each layer based on the true density of each layer of the coated diaphragm to be tested;

[0012] (2) respectively calculating the ratio of the surface density of each layer of the coated membrane to be tested to the surface density of the coated membrane;

[0013] (3) The theoretical porosity of the coated membrane is calculated based on the theoretical porosity of each layer of the coated membrane to be tested and the proportion of the surface density of each layer to the surface density of the coated membrane.

[0014] The calculation method described in this application does not limit the calculation order of step (1) and step (2), and step (1) can be performed first or step (2) can be performed first.

[0015] This application uses a simple calculation method to calculate the porosity of the coated diaphragm, provide data support for the injection volume simulation data, obtain the optimal injection volume parameters, and the corresponding battery electrical performance is also optimal, shortening the battery design and development cycle.

[0016] Optionally, the coated membrane to be tested in step (1) includes a base membrane and a coating.

[0017] Optionally, the coating comprises a ceramic coating and / or an adhesive coating.

[0018] The coating of the diaphragm coated in the present application may be a ceramic coating, an adhesive coating or a mixture of the two, and may be a single layer or multiple layers.

[0019] Optionally, the calculation formula for the theoretical porosity in step (1) is Wherein, P is the theoretical porosity of each layer of the coated membrane, S is the theoretical surface density of each layer of the coated membrane, d is the theoretical thickness of each layer of the coated membrane, and ρ is the true density of each layer of the coated membrane.

[0020] Optionally, the unit of the theoretical surface density is g / m 2 .

[0021] Optionally, the unit of the thickness is μm.

[0022] Optionally, the unit of true density is g / cm 3 .

[0023] Optionally, the calculation formula for the ratio of the surface density of each layer of the coated membrane to be tested in step (2) to the surface density of the coated membrane is: Wherein, ω is the ratio of the surface density of each layer of the coated membrane to be measured to the surface density of the coated membrane, S is the theoretical surface density of each layer of the coated membrane, S T is the theoretical total areal density of the coated membrane.

[0024] Optionally, the unit of the theoretical surface density is g / m 2 .

[0025] Optionally, the calculation formula for the theoretical porosity of the coated membrane in step (3) is P T =∑P·ω×100%, where P T is the theoretical porosity of the coated membrane, P is the theoretical porosity of each layer of the coated membrane, and ω is the ratio of the surface density of each layer of the coated membrane to the theoretical total surface density of the membrane.

[0026] As an optional solution of this application, the calculation method includes the following steps:

[0027] (1) Measure the true density of the base film and each coating of the coated diaphragm to be tested, according to the formula The theoretical porosity of the base film and each coating layer is obtained respectively, wherein P is the theoretical porosity of the base film or each coating layer, S is the theoretical surface density of the base film or each coating layer, d is the theoretical thickness of the base film or each coating layer, and ρ is the true density of the base film or each coating layer;

[0028] (2) According to the formula Calculate the ratio of the surface density of the base film and each coating layer to the surface density of the coated membrane, and obtain the ratio of the surface density of the base film and each coating layer to the theoretical total surface density of the membrane, wherein ω is the ratio of the surface density of the base film or each coating layer to the theoretical total surface density of the membrane, S is the theoretical surface density of the base film or each coating layer, and S T is the theoretical total surface density of the base film and each coating;

[0029] (3) According to the formula P T =∑P·ω×100%, and the theoretical porosity of the coated membrane is calculated, where P T is the theoretical porosity of the coated membrane.

[0030] In a second aspect, the present application provides an application of the calculation method according to any one of claims 1 to 8, characterized in that the optimal liquid filling amount of the battery is obtained according to the calculation method.

[0031] Optionally, the optimal liquid injection volume of the battery is obtained by simulation based on theoretical porosity and battery capacity.

[0032] Compared with the related art, this application has the following beneficial effects:

[0033] This application provides a convenient and effective calculation method to calculate the porosity of the coating film according to the theoretical formula, provide data support for the injection volume simulation data, obtain the optimal injection volume parameters, and the corresponding battery electrical performance is also optimal, shortening the battery design and development cycle.

[0034] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0035] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application.

[0036] In the calculation method described in this application, the calculation and reasoning process of theoretical porosity are as follows:

[0037] First, the porosity of the base membrane is determined according to the national standard GB / T 3302-2016 Microporous Functional Film Porosity Determination Method. The specific steps are as follows. Cut the membrane to be tested into a sample with a length of not less than 10 cm and a width of not less than 5 cm, then use a caliper to accurately measure the length X and width Y of the sample, and use a thickness gauge to measure the thickness d of the sample (measure several points and take the average value), and then use an electronic balance to weigh the membrane, recorded as W1. After completely soaking the membrane in hexadecane organic solvent for about 60±5 minutes, place it between two pieces of oil-absorbing paper, and then roll it back and forth with a roller. After changing the oil-absorbing paper several times and rolling, try to remove as much hexadecane as possible from the surface of the membrane. Then weigh the weight of the membrane after soaking, recorded as W2.

[0038] The porosity of the basement membrane is calculated as follows:

[0039] In the formula

[0040] P——diaphragm porosity, unit is (%);

[0041] W2——weight of the diaphragm after fully absorbing hexadecane, unit is (g);

[0042] W1——weight of the membrane before absorbing hexadecane, in g;

[0043] ρ——density of hexadecane, take 0.7734 as unit (g / cm 3 );

[0044] X——diaphragm length, in cm;

[0045] Y——diaphragm width, in cm;

[0046] d——diaphragm thickness, in cm;

[0047] Secondly, the porosity of the basement membrane is calculated using a theoretical calculation method. The theoretical calculation formula is as follows:

[0048] In the formula

[0049] P--Theoretical porosity of the diaphragm, unit is (%)

[0050] s - Theoretical surface density of the membrane, high pore, medium pore, and general pore are 4.5, 5.1, and 5.3 respectively, the unit is (g / m 2 );

[0051] d - theoretical thickness of the diaphragm, take 9, unit is (μm);

[0052] ρ--PE true density, take 0.96, unit is (g / cm 3 )

[0053] The comparison between the basement membrane porosity test value and the theoretical calculated value is shown in Table 1:

[0054] Table 1

[0055] From Table 1, it can be seen that the porosity of the base membrane obtained according to the national standard test is at the same level as the theoretical calculated value, which proves that the method for calculating the theoretical porosity of the diaphragm described in this application is practical.

[0056] Example 1

[0057] This embodiment provides a method for calculating the theoretical porosity of a coated membrane, wherein the coated membrane includes a porous base membrane, a first PVDF coating layer, and a second PVDF coating layer. The calculation method includes the following steps:

[0058] (1) The diaphragm is divided into three parts: the base membrane, the first PVDF coating and the second PVDF coating. Then the true density of the base membrane and the PVDF coating is obtained by looking up the data, which are respectively recorded as ρ B =0.96g / cm 3 , ρ P =1.78g / cm 3 , ρ O =1.78g / cm 3 , the theoretical surface density is denoted as SB =5.3g / m 2 、S P =0.5g / m 2 、S o =0.5g / m 2 , the theoretical thickness is recorded as d B =9μm, d P =1μm, d o =1μm, according to the formula The theoretical porosity P of the base film is obtained B =39%, the theoretical porosity P of the first PVDF coating P =72% and the theoretical porosity P of the second PVDF coating o =72%;

[0059] (2) The theoretical surface densities of the base film, the first PVDF coating and the second PVDF coating are respectively denoted as S B =5.3g / m 2 、S P =0.5g / m 2 、S o =0.5g / m 2 , the theoretical total surface density of the diaphragm is recorded as S T =6.3g / m 2 , according to the formula The ratio of the surface density of the base film to the theoretical total surface density of the diaphragm is obtained. B =84%, the ratio of the surface density of the first PVDF coating to the theoretical total surface density of the diaphragm ω P =8.0% and the ratio of the surface density of the second PVDF coating to the theoretical total surface density of the diaphragm ω O =8.0%;

[0060] (3) According to the formula P T =(P B ·ω B +P P ·ω P +P o ·ω o )·100%, and the theoretical porosity P of the coated membrane is obtained. T =44%. The measured porosity of the coated membrane is 48%.

[0061] Example 2

[0062] This embodiment provides a method for calculating the theoretical porosity of a coated membrane, wherein the coated membrane includes a porous base membrane and a ceramic coating. The calculation method includes the following steps:

[0063] (1) The diaphragm is split into two parts: the base membrane and the ceramic coating. Then the true density of the base membrane and the ceramic coating is obtained by looking up the data, which are respectively recorded as ρ B =0.96g / cm 3 and ρ C =3.89g / cm 3 , the theoretical surface density is denoted as S B =5.3g / m 2 and S C =3.7g / m 2 , the theoretical thickness is recorded as d B =9μm and d C =2μm, according to the formula The theoretical porosity P of the base film is obtained B =39% and the theoretical porosity P of the ceramic coating C =52%;

[0064] (2) The theoretical surface density of the base film and ceramic coating is recorded as S B =5.3g / cm 2 and S C =3.7g / m 2 , the theoretical total surface density of the diaphragm is recorded as S T =9.0g / m 2 , according to the formula The ratio of the surface density of the base film to the theoretical total surface density of the diaphragm is obtained. B =59% and the ratio of the surface density of the ceramic coating to the theoretical total surface density of the diaphragm ω C =41%;

[0065] (3) According to the formula P T =(P B ·ω B +P C ·ω C )·100%, and the theoretical porosity P of the coated membrane is obtained. T =44%. The measured porosity of the coated membrane is 49%.

[0066] Example 3

[0067] This embodiment provides a method for calculating the theoretical porosity of a coated membrane, wherein the coated membrane includes a porous base membrane, a single-sided ceramic coating, and a double-sided PVDF coating. The calculation method includes the following steps:

[0068] (1) The diaphragm is divided into four parts: the base membrane, the ceramic coating, the first PVDF coating and the second PVDF coating. Then the true density of the base membrane, the ceramic coating and the PVDF coating is obtained by looking up the data, which are respectively recorded as ρ B =0.96g / cm 3, ρ C =3.89g / cm 3 , ρ P =1.78g / cm 3 , ρ O =1.78g / cm 3 , the theoretical surface density is denoted as S B =5.3g / m 2 、S C =3.7g / m 2 、S P =0.5g / m 2 、S O =0.5g / m 2 , the theoretical thickness is recorded as d B =9μm, d C =2μm, d P =1μm, d O =1μm, according to the formula The theoretical porosity P of the base film is obtained B =39%, the theoretical porosity of the ceramic coating P C =52%, the theoretical porosity P of the first PVDF coating P =72% and the theoretical porosity P of the second PVDF coating O =72%;

[0069] (2) The theoretical surface densities of the base film, ceramic coating and PVDF coating are respectively denoted as S B =5.3g / m 2 、S C =3.7g / m 2 、S P =0.5g / m 2 and S O =0.5g / m 2 , the theoretical total surface density of the diaphragm is recorded as S T =10.0g / m 2 , according to the formula The ratio of the surface density of the base film to the theoretical total surface density of the diaphragm is obtained. B =53%, the ratio of the surface density of the ceramic coating to the theoretical total surface density of the diaphragm ω C =37%, the ratio of the surface density of the first PVDF coating to the theoretical total surface density of the diaphragm ω P =5.0%, the ratio of the surface density of the second PVDF coating to the theoretical total surface density of the diaphragm ω O =5.0%;

[0070] (3) According to the formula P T =(P B ·ω B +PC ·ω C +P P ·ω P +P O ω O )·100%, and the theoretical porosity P of the coated membrane is obtained. T =47%. The measured porosity of the coated membrane is 51%.

[0071] Example 4

[0072] The only difference between this embodiment and embodiment 1 is that the plain porous base membrane is replaced with a high-porous base membrane. Other conditions and parameters are exactly the same as those in embodiment 1. The theoretical porosity P of the coated membrane T =51%. The measured porosity of the coated membrane is 54%.

[0073] Example 5

[0074] The only difference between this embodiment and embodiment 2 is that the plain porous base membrane is replaced with a high-porous base membrane. Other conditions and parameters are exactly the same as those in embodiment 1. The theoretical porosity P of the coated membrane T =49%. The measured porosity of the coated membrane is 53%.

[0075] Example 6

[0076] The only difference between this embodiment and embodiment 3 is that the plain porous base membrane is replaced with a high-porous base membrane. Other conditions and parameters are exactly the same as those in embodiment 1. The theoretical porosity P of the coated membrane T =52%. The measured porosity of the coated membrane is 56%.

[0077] Example 7

[0078] The only difference between this embodiment and embodiment 1 is that the pore-free base membrane is replaced with a mesoporous base membrane. Other conditions and parameters are exactly the same as those in embodiment 1. The theoretical porosity P of the coated membrane T =46%. The measured porosity of the coated membrane is 49%.

[0079] Example 8

[0080] The only difference between this embodiment and embodiment 2 is that the pore-free base membrane is replaced with a mesoporous base membrane. Other conditions and parameters are exactly the same as those in embodiment 1. The theoretical porosity P of the coated membrane is T =46%. The measured porosity of the coated membrane is 50%.

[0081] Example 9

[0082] The only difference between this embodiment and embodiment 3 is that the pore-free base membrane is replaced with a mesoporous base membrane. Other conditions and parameters are exactly the same as those in embodiment 1. The theoretical porosity P of the coated membrane T=48%. The measured porosity of the coated membrane is 51%.

[0083] Application Example 1

[0084] This application example used the coated separator described in Example 1. Based on its theoretical porosity and battery capacity simulation, the optimal injection volume was determined to be 196.1 g. Control groups with excessively high and low injection volumes were set based on the optimal injection volume. Batteries were then manufactured and tested for their electrical performance. The test results are shown in Table 2.

[0085] Application Example 2

[0086] This application example used the coated separator described in Example 2. Based on its theoretical porosity and battery capacity simulation, the optimal injection volume was determined to be 194.3 g. Control groups with excessive and low injection volumes were set based on the optimal injection volume, and batteries were manufactured to test their electrical performance. The test results are shown in Table 2.

[0087] Application Example 3

[0088] This application example used the coated separator described in Example 3. Based on its theoretical porosity and battery capacity simulation, the optimal injection volume was determined to be 207.7 g. Control groups with excessively high and low injection volumes were set based on the optimal injection volume, and batteries were manufactured to test their electrical performance. The test results are shown in Table 2.

[0089] Table 2

[0090] It can be seen from Table 2 that the injection amount obtained by the calculation method described in this application for the porosity data calculated for different coated diaphragms corresponds to the optimal battery electrical performance.

[0091] The applicant declares that the above is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Technical personnel in the relevant technical field should understand that any changes or substitutions that can be easily thought of by technical personnel in the relevant technical field within the technical scope disclosed in this application fall within the protection scope and disclosure scope of this application.

Claims

1. A method for calculating the theoretical porosity of a coated diaphragm, comprising the following steps: (1) measuring the true density of each layer of the coated diaphragm to be tested, and calculating the theoretical porosity of each layer according to the true density of each layer of the coated diaphragm to be tested; (2) respectively calculating the ratio of the surface density of each layer of the coated membrane to be tested to the surface density of the coated membrane; (3) The theoretical porosity of the coated membrane is calculated based on the theoretical porosity of each layer of the coated membrane to be tested and the proportion of the surface density of each layer to the surface density of the coated membrane.

2. The calculation method according to claim 1, wherein: The coated membrane to be tested in step (1) comprises a base membrane and a coating.

3. The calculation method according to claim 2, wherein: The coating includes a ceramic coating and / or a binder coating.

4. The calculation method according to any one of claims 1 to 3, wherein: The calculation formula of the theoretical porosity in step (1) is: Wherein, P is the theoretical porosity of each layer of the coated membrane, S is the theoretical surface density of each layer of the coated membrane, d is the theoretical thickness of each layer of the coated membrane, and ρ is the true density of each layer of the coated membrane.

5. The calculation method according to claim 4, wherein: The unit of the theoretical surface density is g / m 2 .

6. The calculation method according to claim 4, wherein: The unit of the thickness is μm.

7. The calculation method according to claim 4, wherein: The unit of true density is g / cm 3 .

8. The calculation method according to any one of claims 1 to 7, wherein: The calculation formula for the ratio of the surface density of each layer of the coated membrane to be tested in step (2) to the surface density of the coated membrane is: Wherein, ω is the ratio of the surface density of each layer of the coated membrane to be tested to the surface density of the coated membrane, S is the theoretical surface density of each layer of the coated membrane, S T is the theoretical total surface density of the coated membrane.

9. The calculation method according to claim 8, wherein: The unit of the theoretical surface density is g / m 2 .

10. The calculation method according to any one of claims 1 to 9, wherein: The calculation formula of the theoretical porosity of the coated diaphragm in step (3) is: T =∑P·ω×100%, where P T is the theoretical porosity of the coated membrane, P is the theoretical porosity of each layer of the coated membrane, and ω is the ratio of the surface density of each layer of the coated membrane to the theoretical total surface density of the membrane.

11. The calculation method according to any one of claims 1 to 10, comprising the following steps: (1) Measure the true density of the base film and each coating of the coated diaphragm to be tested, according to the formula The theoretical porosity of the base film and each coating is obtained respectively, wherein P is the theoretical porosity of the base film or each coating, S is the theoretical surface density of the base film or each coating, d is the theoretical thickness of the base film or each coating, and ρ is the true density of the base film or each coating; (2) According to the formula The ratio of the surface density of the base film and each coating to the surface density of the coated diaphragm is calculated respectively, and the ratio of the surface density of the base film and each coating to the theoretical total surface density of the diaphragm is obtained respectively, wherein ω is the ratio of the surface density of the base film or each coating to the theoretical total surface density of the diaphragm, S is the theoretical surface density of the base film or each coating, and S T is the theoretical total surface density of the base film and each coating; (3) According to the formula P T =∑P·ω×100%, and the theoretical porosity of the coated membrane is calculated, where P T is the theoretical porosity of the coated membrane.

12. An application of the calculation method according to any one of claims 1 to 11, wherein: The optimal liquid injection amount of the battery is obtained according to the calculation method.

13. The use according to claim 12, wherein: The optimal liquid injection volume of the battery is obtained by simulation based on theoretical porosity and battery capacity.

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