CN116625907A - Method for testing porosity of lithium ion battery diaphragm - Google Patents
Method for testing porosity of lithium ion battery diaphragm Download PDFInfo
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- CN116625907A CN116625907A CN202310904198.5A CN202310904198A CN116625907A CN 116625907 A CN116625907 A CN 116625907A CN 202310904198 A CN202310904198 A CN 202310904198A CN 116625907 A CN116625907 A CN 116625907A
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- 238000000034 method Methods 0.000 title claims abstract description 45
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 26
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 26
- 238000012360 testing method Methods 0.000 title claims abstract description 23
- 230000003287 optical effect Effects 0.000 claims abstract description 30
- 239000012528 membrane Substances 0.000 claims description 17
- 239000007788 liquid Substances 0.000 claims description 12
- 239000011521 glass Substances 0.000 claims description 11
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 claims description 9
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical group C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 claims description 9
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 claims description 9
- 229910052708 sodium Inorganic materials 0.000 claims description 9
- 239000011734 sodium Substances 0.000 claims description 9
- XTHFKEDIFFGKHM-UHFFFAOYSA-N Dimethoxyethane Chemical compound COCCOC XTHFKEDIFFGKHM-UHFFFAOYSA-N 0.000 claims description 6
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 6
- 230000003204 osmotic effect Effects 0.000 claims description 6
- 230000000284 resting effect Effects 0.000 claims description 5
- XDTMQSROBMDMFD-UHFFFAOYSA-N Cyclohexane Chemical compound C1CCCCC1 XDTMQSROBMDMFD-UHFFFAOYSA-N 0.000 claims description 3
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 3
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 3
- HPXRVTGHNJAIIH-UHFFFAOYSA-N cyclohexanol Chemical compound OC1CCCCC1 HPXRVTGHNJAIIH-UHFFFAOYSA-N 0.000 claims description 3
- DCAYPVUWAIABOU-UHFFFAOYSA-N hexadecane Chemical compound CCCCCCCCCCCCCCCC DCAYPVUWAIABOU-UHFFFAOYSA-N 0.000 claims description 3
- 238000004364 calculation method Methods 0.000 abstract description 5
- 239000004743 Polypropylene Substances 0.000 description 12
- 229920001155 polypropylene Polymers 0.000 description 12
- 239000004698 Polyethylene Substances 0.000 description 8
- 229920000573 polyethylene Polymers 0.000 description 8
- -1 Polyethylene Polymers 0.000 description 6
- 239000000463 material Substances 0.000 description 5
- 238000005520 cutting process Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 230000035699 permeability Effects 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 239000002356 single layer Substances 0.000 description 4
- 230000003321 amplification Effects 0.000 description 3
- 239000005357 flat glass Substances 0.000 description 3
- 238000005305 interferometry Methods 0.000 description 3
- 238000003199 nucleic acid amplification method Methods 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- 239000002131 composite material Substances 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 239000010410 layer Substances 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 239000012153 distilled water Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000011010 flushing procedure Methods 0.000 description 1
- 238000003703 image analysis method Methods 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 239000012982 microporous membrane Substances 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 229920000098 polyolefin Polymers 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N5/00—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid
- G01N5/02—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid by absorbing or adsorbing components of a material and determining change of weight of the adsorbent, e.g. determining moisture content
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Chemical & Material Sciences (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Dispersion Chemistry (AREA)
- Length Measuring Devices By Optical Means (AREA)
Abstract
The invention discloses a method for testing the porosity of a lithium ion battery diaphragm, which relates to the technical field of lithium ion battery energy, and comprises the following steps: measuring the thickness of the diaphragm sample by adopting a wedge interference optical method, and determining the volume of the diaphragm sample according to the length, the width and the thickness of the diaphragm sample; measuring the mass of the diaphragm sample by using an electronic balance; obtaining the overflow quality of the high-permeability solution of the standard component which is not wrapped with the diaphragm sample and the overflow quality of the high-permeability solution of the standard component which is wrapped with the diaphragm sample; and determining the mass of the high-permeability solution stopped on the diaphragm sample according to the mass of the diaphragm sample, the overflow mass of the high-permeability solution of the standard part which is not wrapped with the diaphragm sample and the overflow mass of the high-permeability solution of the standard part which is wrapped with the diaphragm sample, and determining the porosity of the diaphragm sample according to the mass of the high-permeability solution stopped on the diaphragm sample and the volume of the diaphragm sample. The method can improve the accuracy of the calculation result of the porosity of the diaphragm sample.
Description
Technical Field
The invention relates to the technical field of lithium ion battery energy, in particular to a method for testing the porosity of a lithium ion battery diaphragm.
Background
The lithium ion battery is widely applied to the energy storage market and the new energy industry due to the advantages of high energy density, long cycle life, high withstand voltage and the like. The diaphragm is an important component of the lithium ion battery, plays a role in separating positive and negative plates from ion conduction and insulation, and has excellent performance in determining interface structure, internal resistance and the like of the lithium ion battery, and has an important effect on improving the comprehensive service life of the lithium ion battery.
The porosity of the diaphragm affects the performances of the lithium ion battery such as internal resistance, multiplying power, high-temperature storage, normal-temperature circulation and the like. The diaphragm needs higher porosity to ensure the migration and transmission efficiency of ions, improve the charge and discharge performance, and simultaneously ensure the reduction of internal resistance under the condition of higher puncture strength. Therefore, the method has higher requirements on the porosity test of the lithium ion battery separator.
Currently, the porosity of a lithium ion battery diaphragm can be obtained through a liquid absorption method, a calculation method, an instrument measurement method and an image analysis method; the pore size and distribution are generally measured by scanning electron microscope observation, and can also be measured by combining an instrument with a Laplace equation. The thickness of the diaphragm is mostly measured by a micro amplification method, but the method can apply contact pressure to the diaphragm when the diaphragm is folded for a plurality of times, so that the diaphragm is deformed to a certain extent, and the thickness measurement is inaccurate.
Disclosure of Invention
The invention aims to provide a method for testing the porosity of a diaphragm of a lithium ion battery, which can improve the accuracy of a diaphragm sample porosity calculation result.
In order to achieve the above object, the present invention provides the following solutions:
a method for testing porosity of a lithium ion battery separator, comprising:
acquiring the length and the width of a diaphragm sample;
measuring the thickness of the diaphragm sample by adopting a wedge interference optical method, and determining the volume of the diaphragm sample according to the length, the width and the thickness of the diaphragm sample; the wedge interference optical method is that firstly, two optical plane glass plates are stacked together, and a diaphragm sample is inserted into one end of the optical plane glass plates, so that an air wedge is formed between the two optical plane glass plates, and a wedge end and a sample clamping end are formed at two ends of the air wedge; then when the monochromatic light irradiates, the monochromatic light is reflected and overlapped on the two surfaces of the air wedge to generate two light beam interference fringes, and the interference condition and the optical path difference are combined to determine the thickness of the diaphragm sample;
measuring the mass of the diaphragm sample by using an electronic balance;
obtaining the overflow quality of the high-permeability solution of the standard component which is not wrapped with the diaphragm sample and the overflow quality of the high-permeability solution of the standard component which is wrapped with the diaphragm sample; the method comprises the steps of firstly placing a standard component into an overflow cup containing high-permeability solution, conveying the high-permeability solution flowing out of an overflow port to a beaker, and then placing the beaker containing the high-permeability solution in an electronic balance to obtain the high-permeability solution overflow mass of the standard component of the non-wrapped diaphragm sample; the method comprises the steps of firstly placing a standard component wrapped with a diaphragm sample into an overflow cup containing high-permeability solution, conveying the high-permeability solution flowing out of an overflow port to a beaker, and then placing the beaker containing the high-permeability solution in an electronic balance to obtain the high-permeability solution overflow mass of the standard component wrapped with the diaphragm sample; the liquid level of the overflow cup containing the high-permeability solution is level with the overflow port of the overflow cup;
and determining the mass of the high-permeability solution stopped on the diaphragm sample according to the mass of the diaphragm sample, the overflow mass of the high-permeability solution of the standard part which is not wrapped with the diaphragm sample and the overflow mass of the high-permeability solution of the standard part which is wrapped with the diaphragm sample, and determining the porosity of the diaphragm sample according to the mass of the high-permeability solution stopped on the diaphragm sample and the volume of the diaphragm sample.
Optionally, the calculation formula of the thickness of the diaphragm sample is:
；
wherein N is the number of interference fringes; l (L) n The length of the n dark stripes is nm;the wavelength of monochromatic light is in nm; h is the thickness of the membrane sample in nm.
Optionally, the monochromatic light is sodium yellow light.
Optionally, the high-permeability solution is N-butanol solution, absolute ethanol solution, cyclohexane solution, hexadecane solution, ethylene glycol solution, isopropanol solution, ethylene glycol dimethyl ether solution, cyclohexanol solution or N-methyl pyrrolidone solution.
Alternatively, the mass of the high-permeability solution resting on the membrane sample is calculated as:
M 4 =M 0 -M 3 +M 2 ；
wherein M is 4 The mass of the high-permeability solution, in g, that is resting on the membrane sample; m is M 0 The mass of the diaphragm sample is expressed as g; m is M 2 The standard component of the non-coated diaphragm sample has high osmotic solution overflow mass, and the unit is g; m is M 3 The standard piece coated with the diaphragm sample has high osmotic solution overflow mass in g.
Alternatively, the porosity of the separator sample is calculated as:
；
wherein P is the porosity of the membrane sample in units of;is the density of the high-permeability solution, and the unit is g/cm 3 ；V 0 For the volume of the diaphragm sample in mm 3 。
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention adopts wedge interference optics method, namely, the thickness of the diaphragm sample is measured by utilizing optical property, and meanwhile, an overflow cup is used as a liquid container for containing liquid, so that the accuracy of the aperture ratio calculation result of the diaphragm sample is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic flow chart of a method for testing porosity of a lithium ion battery separator according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The method for testing the porosity of the lithium ion battery diaphragm has the defects of higher cost, complicated steps, poor precision, no universality of the diaphragm material to be tested and the like.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
As shown in fig. 1, the method for testing the porosity of the lithium ion battery separator provided in this embodiment includes the following steps.
Step 100: the length and width of the septum samples were taken.
In this example, a smooth, complete diaphragm sample was cut from a piece of irregular material using a high precision cutting knife, and the length L and width D of the diaphragm sample were measured using a screw micrometer.
The diaphragm sample is obtained by adopting a high-precision cutting knife, so that the effects of quick cutting and smooth cutting surface can be realized; the measuring range of the level bar of the high-precision screw micrometer is 1m, and the precision is 0.001m.
Step 200: the thickness of the diaphragm sample is measured using wedge interferometry, and the volume of the diaphragm sample is determined based on the length, width and thickness of the diaphragm sample.
In this embodiment, the wedge interferometry is: firstly, two optical plane glass plates are stacked together, and a diaphragm sample is inserted into one end of the optical plane glass plates, so that an air wedge (air gap) is naturally formed between the two optical plane glass plates, and a wedge end and a sample clamping end are formed at two ends of the air wedge; when the monochromatic light irradiates, the monochromatic light is reflected and overlapped on the two surfaces of the air wedge to generate two light beam interference fringes, wherein the interference fringes are a cluster of equidistant straight lines parallel to the wedge, and the thickness of the diaphragm sample is determined by combining interference conditions and optical path differences.
The wedge interferometry described above, in combination with the interference conditions and the optical path difference, is as follows:
。
wherein e k Thickness at the kth level of interference fringes;is the wavelength of the incident light; />Is half-wave loss (k=0, 1,2 … …).
Can be arranged to obtainIf a k=n-scale stripe is present at the membrane sample, the thickness of the membrane sample is。
For the convenience of measurement, only the length L corresponding to the n interference fringes is measured n And the total length from the cleaving tip to the sample clamping endIt can be seen that:
。
wherein N is the number of interference fringes; l (L) n The length of the n dark stripes is nm;the wavelength of monochromatic light is in nm; h is the thickness of the membrane sample in nm.
Obtaining interference conditions and optical path difference by adopting a wedge interference optical method, further calculating the thickness H of the diaphragm sample, and accurately obtaining a micrometer position according to the result, so as to avoid errors generated by direct measurement by a micro amplification method; the method is more accurate and precise than the conventional micro amplification method.
Further, sodium yellow light is selected as monochromatic light when the diaphragm sample is measured by using a wedge interference optical method. When the sodium yellow light irradiates, the sodium yellow light is ensured to aim in a straight line direction, and the sodium yellow light is reflected and overlapped on two surfaces of the wedge position to generate two light beam interference fringes. When the diaphragm sample is measured by the wedge interference optical method, the main reason for selecting sodium yellow light is that the wavelength of the sodium yellow light is 589.3nm, the sodium yellow light belongs to monochromatic light, all levels of fringes are not overlapped, and all levels of interference fringes can be conveniently observed.
Furthermore, when the diaphragm sample is measured by adopting a wedge interference optical method, a glass plate with moderate thickness and flat and smooth surface is selected.
Further, in the process of inserting the diaphragm sheet into the two optical flat glass plates, the diaphragm sample is ensured to be fully placed between the two optical flat glass plates and the two optical flat glass plates are kept to be attached; when the diaphragm sample is measured by adopting the wedge interference optical method, the tabletop is kept stable and is not vibrated, and the optical plane glass plate cannot be touched.
In the present embodiment, the volume V of the diaphragm sample can be calculated from the length L, width D and thickness H of the diaphragm sample 0 。
Step 300: the mass of the diaphragm sample was measured using an electronic balance.
In the present embodiment, the mass M of the thin and light diaphragm sample can be accurately weighed by measuring the mass of the diaphragm sample using an electronic balance with a precision of 0.0001g 0 。
In this example, the surface of the membrane sample was wiped clean before it was weighed using an electronic balance, avoiding the effect of residual stains on the weighing results.
Step 400: and obtaining the overflow quality of the high-permeability solution of the standard component which is not wrapped with the diaphragm sample and the overflow quality of the high-permeability solution of the standard component which is wrapped with the diaphragm sample.
The method comprises the steps of firstly placing a standard component into an overflow cup containing high-permeability solution, conveying the high-permeability solution flowing out of an overflow port to a beaker, and then placing the beaker containing the high-permeability solution in an electronic balance to obtain the high-permeability solution overflow mass of the standard component of the non-wrapped diaphragm sample; the determination process of the overflow mass of the high-permeability solution of the standard component wrapped with the diaphragm sample comprises the steps of firstly placing the standard component wrapped with the diaphragm sample into an overflow cup containing the high-permeability solution, conveying the high-permeability solution flowing out of the overflow port to a beaker, and then placing the beaker containing the high-permeability solution in an electronic balance to obtain the overflow mass of the high-permeability solution of the standard component wrapped with the diaphragm sample.
Wherein the liquid level of the overflow cup containing the high-permeability solution is equal to the overflow port of the overflow cup.
In this embodiment, step 400 specifically includes:
(1) Taking known parameters (qualityAnd volume->) The length, width and height of the standard component are smaller than those of the overflow cup, and the standard component can be completely immersed into the solution of the overflow cup.
(2) To a known density ofAnd a proper amount of high-permeability solution is injected into the overflow cup, so that the liquid level is leveled with the overflow port, and the overflow cup is stably placed on an electronic balance, and the indication number is M 1 。
(3) The standard was gently placed in the overflow cup to be completely immersed in the high permeability solution. Then part of the high-permeability solution overflows to an empty beaker, and the electronic balance is denoted as M 2 。
(4) Repeating the step (2), taking out the standard component and wiping the standard component, simultaneously adding the high-permeability solution into the overflow cup again to make the liquid level and the overflow gap be level, and displaying the number M by an electronic balance 1 。
(5) Wrapping the membrane sample outside a clean standard part, completely immersing the standard part wrapped by the membrane sample into an overflow cup filled with high-permeability solution, and overflowing part of the high-permeability solution into an empty beaker, wherein the electronic balance is denoted by M 3 。
In this embodiment, the high-permeability solution may be selected from N-butanol solution, absolute ethanol solution, cyclohexane solution, hexadecane solution, ethylene glycol solution, isopropanol solution, ethylene glycol dimethyl ether solution, cyclohexanol solution, N-methylpyrrolidone solution, etc.
In this embodiment, the standard component is smaller than the overflow cup, so that the standard component can not be in contact with the wall of the overflow cup in the process of being placed into the overflow cup, and can be completely immersed into the overflow cup, and the condition that the standard component is suspended above the overflow cup can not occur.
The reason that the overflow cup is selected for the container for containing the high-permeability solution is as follows: the overflow cup can enable the solution discharged after the standard component is placed to smoothly flow into the empty beaker, so that the electronic balance cannot be wetted, even if the overflowed solution is smoothly discharged, the accuracy of a measurement result is improved.
In order to ensure that the overflow cup does not contain irrelevant residual liquid, distilled water is used for flushing the overflow cup before the overflow cup is used, and the overflow cup is placed into a drying oven for full drying; when the high-permeability solution is injected, the liquid level is leveled with the overflow port, so that the purpose of stable placement without solution overflow is achieved.
When the discharged solution overflows to the empty beaker, part of the solution can be hung on the middle pipeline of the container and the wall of the beaker, and the liquid in the empty beaker is not directly weighed to improve the accuracy of the result.
After the standard component is taken out from the overflow cup, the surface residual solution is wiped by using a dry paper towel without scraps, so that the surface of the standard component is ensured to have no solution residue, and the subsequent experimental result is not influenced.
And adding the high-permeability solution into the overflow cup again to make the liquid level and the overflow gap be equal, so that the high-permeability solution content in the overflow cup is ensured to be the same as before.
Step 500: and determining the mass of the high-permeability solution stopped on the diaphragm sample according to the mass of the diaphragm sample, the overflow mass of the high-permeability solution of the standard part which is not wrapped with the diaphragm sample and the overflow mass of the high-permeability solution of the standard part which is wrapped with the diaphragm sample, and determining the porosity of the diaphragm sample according to the mass of the high-permeability solution stopped on the diaphragm sample and the volume of the diaphragm sample.
In this example, the mass of the high permeability solution resting on the membrane sample was calculated as:
M 4 =M 0 -M 3 +M 2 。
wherein M is 4 The mass of the high-permeability solution, in g, that is resting on the membrane sample; m is M 0 The mass of the diaphragm sample is expressed as g; m is M 2 The standard component of the non-coated diaphragm sample has high osmotic solution overflow mass, and the unit is g; m is M 3 The standard piece coated with the diaphragm sample has high osmotic solution overflow mass in g.
In this embodiment, the porosity of the separator sample is calculated as:
。
wherein P is the porosity of the membrane sample in units of;is the density of the high-permeability solution, and the unit is g/cm 3 ；V 0 For the volume of the diaphragm sample in mm 3 。
In this embodiment, to avoid that the diaphragm sample is less gravitationally buoyant than it is in the high permeability solution, it cannot be completely immersed in the high permeability solution, so the diaphragm sample is wrapped around the clean standard. Wherein, the diaphragm sample needs to be completely wrapped outside the standard component, has no overlapping, and can not be separated from the standard component when immersed in the high-permeability solution.
The current separator of the lithium ion battery is mainly a polyolefin microporous membrane, and three types of separator samples of lithium ion batteries with different materials are sequentially Polyethylene (PE) single-layer films, polypropylene (PP) single-layer films and polypropylene/polyethylene/polypropylene (PP/PE/PP) three-layer composite films. All equipment used in the test can be recovered, cleaned and reused.
The same sample is subjected to multiple experiments, so that the experimental process is more objective and fair, accidental errors are reduced, and the accuracy of the test result is improved.
Table 1 shows the results of a 30 μm roll of Polyethylene (PE) monolayer separator with different sections of porosity (the hypertonic solvent used was n-butanol solution)
Table 2 shows the results of a 30 μm roll of polypropylene (PP) single layer separator with different sections of porosity (the hypertonic solvent used was n-butanol solution)
Table 3 shows the results of the porosity test of a roll of 30 μm polypropylene/polyethylene/polypropylene (PP/PE/PP) three-layer composite membrane at different sections (the hypertonic solvent used was n-butanol solution)
The thicknesses of the diaphragm samples are measured by the wedge interference optical method in the tables 1-3, the calculated porosity is compared with the known porosity of the diaphragm sample in the inspection report, the difference value of the calculated porosity and the known porosity of the diaphragm sample is less than 1%, the average number of the difference values is less than 0.5%, the consistency is better, the error of the result obtained by the testing method is smaller, the testing method is applicable to the testing of the porosity of the diaphragm made of any material, the application range is wide, and the accuracy is high.
In conclusion, the test method provided by the invention has the advantages of simple operation, easiness in mastering, short time consumption, no special equipment requirement, convenience in material acquisition, convenience in implementation, less time and place limitation, high test data accuracy and small error.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (6)
1. The method for testing the porosity of the lithium ion battery diaphragm is characterized by comprising the following steps of:
acquiring the length and the width of a diaphragm sample;
measuring the thickness of the diaphragm sample by adopting a wedge interference optical method, and determining the volume of the diaphragm sample according to the length, the width and the thickness of the diaphragm sample; the wedge interference optical method is that firstly, two optical plane glass plates are stacked together, and a diaphragm sample is inserted into one end of the optical plane glass plates, so that an air wedge is formed between the two optical plane glass plates, and a wedge end and a sample clamping end are formed at two ends of the air wedge; then when the monochromatic light irradiates, the monochromatic light is reflected and overlapped on the two surfaces of the air wedge to generate two light beam interference fringes, and the interference condition and the optical path difference are combined to determine the thickness of the diaphragm sample;
measuring the mass of the diaphragm sample by using an electronic balance;
obtaining the overflow quality of the high-permeability solution of the standard component which is not wrapped with the diaphragm sample and the overflow quality of the high-permeability solution of the standard component which is wrapped with the diaphragm sample; the method comprises the steps of firstly placing a standard component into an overflow cup containing high-permeability solution, conveying the high-permeability solution flowing out of an overflow port to a beaker, and then placing the beaker containing the high-permeability solution in an electronic balance to obtain the high-permeability solution overflow mass of the standard component of the non-wrapped diaphragm sample; the method comprises the steps of firstly placing a standard component wrapped with a diaphragm sample into an overflow cup containing high-permeability solution, conveying the high-permeability solution flowing out of an overflow port to a beaker, and then placing the beaker containing the high-permeability solution in an electronic balance to obtain the high-permeability solution overflow mass of the standard component wrapped with the diaphragm sample; the liquid level of the overflow cup containing the high-permeability solution is level with the overflow port of the overflow cup;
and determining the mass of the high-permeability solution stopped on the diaphragm sample according to the mass of the diaphragm sample, the overflow mass of the high-permeability solution of the standard part which is not wrapped with the diaphragm sample and the overflow mass of the high-permeability solution of the standard part which is wrapped with the diaphragm sample, and determining the porosity of the diaphragm sample according to the mass of the high-permeability solution stopped on the diaphragm sample and the volume of the diaphragm sample.
2. The method for testing the porosity of a lithium ion battery diaphragm according to claim 1, wherein the thickness of the diaphragm sample is calculated according to the formula:
；
wherein N is the number of interference fringes; l (L) n The length of the n dark stripes is nm;the wavelength of monochromatic light is in nm; h is the thickness of the membrane sample in nm.
3. The method for testing the porosity of a lithium ion battery separator according to claim 1, wherein the monochromatic light is sodium yellow light.
4. The method for testing the porosity of the lithium ion battery diaphragm according to claim 1, wherein the high-permeability solution is N-butanol solution, absolute ethanol solution, cyclohexane solution, hexadecane solution, ethylene glycol solution, isopropanol solution, ethylene glycol dimethyl ether solution, cyclohexanol solution or N-methyl pyrrolidone solution.
5. The method for testing the porosity of a lithium ion battery separator according to claim 1, wherein the mass of the high-permeability solution which stays on the separator sample is calculated as:
M 4 =M 0 -M 3 +M 2 ；
wherein M is 4 The mass of the high-permeability solution, in g, that is resting on the membrane sample; m is M 0 The mass of the diaphragm sample is expressed as g; m is M 2 High osmotic solution overflow quality for standard components of uncoated septum samples, singleThe position is g; m is M 3 The standard piece coated with the diaphragm sample has high osmotic solution overflow mass in g.
6. The method for testing the porosity of a lithium ion battery separator according to claim 4, wherein the porosity of the separator sample is calculated according to the formula:
；
wherein P is the porosity of the membrane sample in units of;is the density of the high-permeability solution, and the unit is g/cm 3 ；V 0 For the volume of the diaphragm sample in mm 3 。
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