Methods for measuring the shrinkage rate of lithium-ion battery separators

Abstract

This invention relates to the field of lithium-ion battery separator testing technology, specifically providing a method for measuring the shrinkage rate of lithium-ion battery separators. The method involves assembling the separator into a simulated battery, then baking the simulated battery at different temperatures, obtaining the dimensions of the separator after baking, and comparing these dimensions with the dimensions before baking to obtain the separator shrinkage rate at different temperatures. This invention's measurement method can measure the separator shrinkage rate at different temperatures, and more importantly, it can effectively measure the shrinkage rate of the separator in the finished battery at high temperatures, with high measurement accuracy, accurately reflecting the shrinkage performance of the separator in actual use.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery separator testing technology, and particularly relates to a method for measuring the shrinkage rate of lithium-ion battery separators. Background Technology

[0002] Lithium-ion batteries are commonly used energy storage and conversion devices in modern life. With the development of renewable energy and electric vehicles, increasingly higher demands are being placed on the energy density of lithium-ion batteries. While meeting these energy density requirements, costs have actually decreased, leading to their wider application. However, the safety of lithium-ion batteries remains a significant concern, especially since the commercialization of high-capacity and power-type lithium-ion batteries, making their safety performance even more crucial.

[0003] The safety of lithium-ion batteries ultimately depends on the thermal stability of the battery materials. Lithium-ion battery materials mainly include the positive electrode, negative electrode, separator, and electrolyte. The main component of the separator is polyolefin, and the most commonly used type is the coated separator, which involves coating a layer of high-temperature resistant, high-mechanical-strength material onto the surface of a polyolefin membrane (single-sided or double-sided). The separator acts between the positive and negative electrodes, preventing direct contact and short circuits, while allowing ions to pass freely but preventing electrons. Common separators have a microporous structure, which acts as a carrier for the electrolyte, adsorbing a certain amount of electrolyte.

[0004] Lithium-ion batteries typically undergo the following exothermic reactions during thermal failure: decomposition of the SEI film → thermal decomposition of the positive electrode material → thermal decomposition of the negative electrode material → thermal decomposition of the electrolyte on the positive electrode and redox reactions of the organic electrolyte on both the positive and negative electrodes. This is followed by battery failure and explosion. The cause of instantaneous failure is either the separator shrinking due to heat, causing a short circuit between the positive and negative electrodes, or the separator losing its original insulating function due to the combined effects of high temperature and high pressure inside the cell. Therefore, testing the shrinkage rate of the separator in finished battery cells is particularly important.

[0005] However, current methods for evaluating the shrinkage rate of lithium-ion battery separators primarily involve directly baking the supplier-supplied separators in an oven for a certain period. This method fails to reflect the true shrinkage performance of the separator in the finished battery. Some companies also assemble the separator and positive / negative electrode sheets into an electrode assembly for testing. However, due to the external tension applied to the separator during winding and the support provided by the positive and negative electrode sheets, and the fact that fully charged cells are prone to explosion at 150°C, separators in depleted cells are easily ejected at 160°C, and separators in electrolyte-free cells are difficult to separate from the electrodes at 145°C, dimensional measurement becomes challenging. The discrepancy between conventional separator test results and the shrinkage rate of the separator in the finished battery cell also prevents effective detection of the separator shrinkage rate at high temperatures. Summary of the Invention

[0006] This invention provides a method for measuring the shrinkage rate of lithium-ion battery separators, aiming to solve the problem that existing testing methods detect a large difference between the shrinkage rate of lithium-ion battery separators and the shrinkage rate of finished battery separators, thus failing to accurately reflect the shrinkage rate of lithium-ion battery separators during application.

[0007] This invention is implemented as follows:

[0008] A method for measuring the shrinkage rate of a lithium-ion battery separator, wherein the method involves assembling the separator into a simulated battery, then baking the simulated battery at different temperatures, obtaining the separator size at each baking temperature, and comparing it with the separator size before baking, thereby obtaining the separator shrinkage rate at different temperatures.

[0009] The beneficial effects of this invention are as follows:

[0010] Compared with existing technologies, the method for measuring the shrinkage rate of lithium-ion battery separators provided by this invention simulates the battery environment by assembling the separator into a simulated battery before testing the shrinkage rate of the separator. This ensures that the measurement results of the separator shrinkage rate can truly reflect the shrinkage performance of the finished battery during use, and the measurement accuracy is high with small deviation. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a schematic diagram of the longitudinal section of the assembled lithium-ion battery in the method for measuring the shrinkage rate of the lithium-ion battery separator provided by the present invention.

[0013] Figure 2 These are the shrinkage curves of the lithium-ion battery separator as a function of temperature, measured by the method for measuring the shrinkage rate of the separator in Examples 1 and 2 provided by this invention.

[0014] Among them, 1-lithium-ion battery casing; 2-first gasket; 3-second gasket; 4-separator; 5-positive electrode sheet; 6-negative electrode sheet. Detailed Implementation

[0015] To make the technical problem to be solved, the technical solution, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0016] It is worth noting that the present invention Figure 1 The longitudinal section shown is a cross-sectional view of the simplified structure of a lithium-ion battery along the center of the battery. Since it is necessary to observe the internal structure of the lithium-ion battery, those skilled in the art know that the cutting position is the center position, so it is no longer necessary to draw a top view or give the cutting line along the top view structure.

[0017] This invention provides a method for measuring the shrinkage rate of lithium-ion battery separators.

[0018] The measurement method involves assembling the separator into a simulated battery, then baking the simulated battery at different temperatures, obtaining the separator size at each baking temperature, and comparing it with the separator size before baking, thereby obtaining the separator shrinkage rate at different temperatures.

[0019] The simulated battery assembled with a separator involves winding the positive electrode, negative electrode, and separator into an electrode assembly and then fitting it into a lithium-ion battery casing. The positive and negative electrodes used in the simulated battery are those employed in the field of lithium-ion battery technology, while the electrolyte is replaced by a solvent.

[0020] Preferably, the measurement method includes the following steps:

[0021] Step S01. Place the first gasket inside the lithium-ion battery case and assemble the battery terminals into the lithium-ion battery case;

[0022] Step S02. Inject a solvent with a boiling point higher than the maximum baking temperature into the lithium-ion battery casing, place a second gasket on the upper surface of the electrode assembly, seal the casing, and allow it to stand and age to allow the solvent to fully wet the electrode assembly, thereby obtaining the simulated battery.

[0023] Step S03. The simulated battery is baked at different temperatures. A batch of separators from the simulated battery is taken out at each baking temperature and their size is measured and compared with the size of the separators before baking, thereby obtaining data on the separator shrinkage rate at different temperatures.

[0024] In the specific measurement process, tests can be conducted separately according to the battery model, battery separator, lithium-ion battery casing, and assembly pressure. Alternatively, a common lithium-ion battery casing model can be used as the standard.

[0025] Please see Figure 1 Taking the battery casing of an 18650 lithium-ion battery as an example. In step S01, an 18650 lithium-ion battery casing 1 is taken, and a first gasket 2 is placed inside the casing 1. Then, according to the manufacturing process of the 18650 lithium-ion battery, the wound electrode assembly is installed into the casing 1. The electrode assembly includes a separator 4, a positive electrode 5, and a negative electrode 6. After the electrode assembly is installed, a second gasket 3 is placed on top of the electrode assembly to ensure that the first gasket 2 and the second gasket 3 clamp the electrode assembly from top to bottom. This ensures that the gasket does not melt when the separator melts, avoiding the gasket melting and sticking to the melted separator at high temperatures, which would make separator separation difficult. Of course, the measurement method of this invention is not limited to the 18650 lithium-ion battery.

[0026] The first gasket 2 and the second gasket 3 of this invention both have melting points higher than the maximum baking temperature. Preferably, the first gasket 2 is any one of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and glass fiber. PET has a melting point of 260°C, PBT has a melting point between 225°C and 235°C, and glass fiber has a softening temperature above 500°C; all of these can be used as gaskets in diaphragm shrinkage rate testing. Of course, the first gasket 2 of this invention is not limited to these listed types and can also be other materials that meet the requirements for melting point and softening point.

[0027] Preferably, the second gasket 3 is any one of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and glass fiber. PET has a melting point of 260°C, PBT has a melting point between 225°C and 235°C, and glass fiber has a softening temperature above 500°C, all of which meet the requirements. Of course, the second gasket 3 of the present invention is not limited to these listed types and can also be made of other materials that meet the requirements for melting point or softening point.

[0028] In step S02, to avoid the inconvenience of disassembly and interference with the measurement due to the presence of electrolyte during the measurement process, a solvent is injected into the battery cell instead of the electrolyte in the measurement of the shrinkage rate of the lithium-ion battery separator. Since the shrinkage rate needs to be measured at different temperatures, it is necessary to ensure that the injected solvent does not boil, evaporate, explode, or spray out at the highest temperature. Therefore, it is essential to ensure that the solvent is liquid at room temperature and its boiling point is higher than the highest baking temperature. Preferably, a boiling point ≥180℃ of the solvent is sufficient to meet the testing requirements. In actual testing, a solvent with a boiling point that meets the requirements is selected based on the highest baking temperature. The solvent used should be liquid at room temperature and should not undergo a chemical reaction during the baking heating process.

[0029] Preferably, the solvent is N-methylpyrrolidone (NMP) or dimethyl sulfoxide (DMSO), wherein NMP has a boiling point of 203°C and DMSO has a boiling point of 189°C, both of which meet the requirements of the present invention. Of course, the solvent of the present invention is not limited to the above two solvents, and may also be other solvents with a boiling point higher than 180°C.

[0030] It is worth noting that in this invention, there are no special requirements for the order of solvent injection and the second gasket 3. The second gasket 3 can be placed directly after the electrode assembly is installed in the shell, or the solvent can be injected first and then the second gasket 3 can be placed after the electrode assembly is installed in the shell.

[0031] The amount of solvent injected should be as similar as possible to the amount of electrolyte injected into the corresponding model of lithium-ion battery during conventional lithium-ion battery production. Preferably, the amount of solvent injected is 70% to 100% of the amount of electrolyte injected into the corresponding model of lithium-ion battery. Taking the 18650 type as an example, the amount of solvent injected is the same as the amount of electrolyte injected into the 18650 type lithium-ion battery. In addition to ensuring wetting, this can also reduce the difference from the actual injected electrolyte and improve its simulation accuracy. Furthermore, the maximum amount of some solvents injected may not reach the amount injected into the corresponding model of lithium-ion battery. In this case, the maximum amount of solvent injected shall prevail.

[0032] The sealing process described above is the same as the sealing process in general lithium-ion battery production, which involves triple sealing. The aging process is also consistent with the aging process in general lithium-ion battery production. The purpose of aging is to ensure that the electrode is fully impregnated.

[0033] Preferably, the aging time is 24–48 hours.

[0034] In step S03, the simulated battery obtained in step S02 can be placed in an oven for baking, or other baking equipment can be used.

[0035] To save on the number of baking cycles and baking time, and to improve measurement efficiency, a batch of finished products obtained in step S02 can be placed in the baking equipment simultaneously and baked in sequence from low temperature to high temperature. At each measurement point, a batch of simulated batteries is removed, allowed to cool naturally to room temperature, and then the cells are disassembled, the separator 4 is separated, and the dimensions of the separated separator 4 are measured. The remaining simulated batteries remain in the baking equipment and continue to be heated to the next measurement point temperature. Then, another batch of simulated batteries is removed, cooled to room temperature, and the dimensions of the separator 4 are measured following the same procedure.

[0036] By comparing the diaphragm dimensions measured at each temperature with the diaphragm dimensions before winding (before baking), the shrinkage rate of the diaphragm at different temperatures can be obtained. To better compare the shrinkage rate, the dimensions of the diaphragm to be wound can be measured before winding, or a batch of diaphragms of the same size can be cut as a blank control before winding, and the dimensions of the blank control diaphragms can be measured.

[0037] The preferred baking temperature is 105–200°C, more preferably 160–200°C. Within this temperature range, the shrinkage rate of the separator can be obtained. Following the aforementioned baking sequence from low to high temperature, the temperature can first be raised to 105°C and baked at a constant temperature of 105°C for 30–60 minutes. A batch of simulated batteries is then removed and allowed to cool naturally to room temperature. The separator dimensions of this batch are measured, and the average value is calculated. Subsequently, the temperature is sequentially raised to 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 190°C, 195°C, and 200°C, and held at each measurement temperature for 30–60 minutes. There are no special requirements for the heating rate or the temperature points used for measurement. The listed temperature intervals and points are merely general measurements. Those skilled in the art, based on the concept provided by this invention, can also measure the diaphragm dimensions at other temperature points, as long as the boiling point of the solvent and the melting points of the first gasket 2 and the second gasket 3 are both higher than the highest baking temperature during the measurement process. For example, if the highest baking temperature is 150°C, then the selected solvent must have a boiling point higher than 150°C, and the melting points of the first gasket 2 and the second gasket must be higher than 150°C; similarly, if the highest baking temperature is 160°C, then the selected solvent must have a boiling point higher than 160°C, and the melting points of the first gasket 2 and the second gasket must be higher than 160°C; furthermore, if the highest baking temperature is 170°C, then the selected solvent must have a boiling point higher than 170°C, and the melting points of the first gasket 2 and the second gasket must be higher than 170°C. For example, if the maximum baking temperature is 180℃, then the boiling point of the selected solvent is higher than 180℃, and the melting point of the first gasket 2 and the second gasket is higher than 180℃; if the maximum baking temperature is 190℃, then the boiling point of the selected solvent is higher than 190℃, and the melting point of the first gasket 2 and the second gasket is higher than 190℃; if the maximum baking temperature is 200℃, then the boiling point of the selected solvent is higher than 200℃, and the melting point of the first gasket 2 and the second gasket is higher than 200℃.

[0038] Specifically, the membrane shrinkage rate of the present invention can be calculated using the following formula (I):

[0039]

[0040] Where L0 represents the original size of the diaphragm, which can be the original size of the diaphragm in the blank control or the size before winding;

[0041] L1 represents the size of the diaphragm after shrinkage.

[0042] In this invention, the positive and negative electrode sheets are general electrode sheets in the field of lithium-ion battery technology. For example, the positive electrode sheet can be an active material such as lithium iron phosphate attached to a copper foil according to the general positive electrode sheet production process, and the negative electrode sheet can be an active material such as graphite attached to an aluminum foil according to the general negative electrode sheet production process. To save space, the positive and negative electrode sheets will not be described in detail here.

[0043] Because the high-melting-point upper and lower gaskets used in this invention have relatively high melting points, exceeding the maximum baking temperature, they do not melt or soften at high temperatures and will not act as adhesives to the diaphragm, thus avoiding errors in the measurement of diaphragm shrinkage dimensions. The high-boiling-point solvent used in this invention replaces the electrolyte and will not boil or decompose at high temperatures, having little impact on diaphragm performance. The diaphragm can be easily separated from the positive and negative electrodes after disassembly, making the measurement of the shrunken diaphragm dimensions more accurate.

[0044] To better illustrate the technical solution of the present invention, specific embodiments are described below.

[0045] Example 1

[0046] This embodiment 1 provides a method for measuring the shrinkage rate of a lithium-ion battery separator. The separator involved is a 12+4 model separator produced by Donggao. Taking an 18650 lithium-ion battery as an example, the method includes the following steps.

[0047] (1) Take 15 18650 type lithium-ion battery cases, place the first PET sheet at the bottom of each battery case so that the first PET sheet just covers the bottom of the battery case; cut a batch of separators of the same size, and use part of them to wind with the positive electrode and negative electrode to form an electrode group, while the other part is used as a reference group. Put the wound electrode group into the case, and place the second PET sheet on the top of the electrode group so that the second PET sheet just covers the top of the electrode group.

[0048] (2) Inject 5.0g NMP into each battery case and use a vacuum chamber to quickly wet the electrode sheets with NMP. Then, seal the battery case three times and let it stand at room temperature for 24 hours to allow the positive and negative electrode sheets to be further fully wetted.

[0049] (3). Place the 15 finished products obtained in step (2) above in an oven and bake them at 105°C for 30 minutes. Then take out 3 finished products and let them cool naturally to room temperature. Disassemble and separate the positive electrode, negative electrode and separator. Use vernier calipers to measure the size of the obtained separator, record the data and compare it with the size of the separator in the reference group. Calculate the shrinkage rate, calculate the average value based on the shrinkage rate and record it in Table 1.

[0050] The remaining 12 finished products in the oven were heated to 130°C and kept warm for 30 minutes. Then, 3 finished products were taken out and allowed to cool naturally to room temperature. The positive electrode, negative electrode and separator were disassembled and separated. The size of the obtained separator was measured with vernier calipers, the data was recorded and compared with the size of the separator of the reference group. The shrinkage rate was calculated, the average value was calculated based on the shrinkage rate and recorded in Table 1.

[0051] The remaining 9 finished products in the oven were heated to 145℃ and kept warm for 30 minutes. Then, 3 finished products were taken out and allowed to cool naturally to room temperature. The positive electrode, negative electrode and separator were disassembled and separated. The size of the obtained separator was measured with vernier calipers, the data was recorded and compared with the size of the separator of the reference group. The shrinkage rate was calculated, the average value was calculated based on the shrinkage rate and recorded in Table 1.

[0052] The remaining 6 finished products in the oven were heated to 160℃ and kept warm for 30 minutes. Then, 3 finished products were taken out and allowed to cool naturally to room temperature. The positive electrode, negative electrode and separator were disassembled and separated. The size of the obtained separator was measured with vernier calipers, the data was recorded and compared with the size of the separator of the reference group. The shrinkage rate was calculated, the average value was calculated based on the shrinkage rate and recorded in Table 1.

[0053] The remaining three finished products in the oven were heated to 180°C and kept warm for 30 minutes. After that, the three finished products were taken out and allowed to cool naturally to room temperature. The positive electrode, negative electrode and separator were disassembled and separated. The size of the obtained separator was measured with vernier calipers, the data was recorded and compared with the size of the separator of the reference group. The shrinkage rate was calculated, the average value was calculated based on the shrinkage rate and recorded in Table 1.

[0054] Table 1. Shrinkage rate (%) of Donggao 12+4 type diaphragm

[0055]

[0056]

[0057] Example 2

[0058] This embodiment 2 provides a method for measuring the shrinkage rate of a lithium-ion battery separator. The separator involved is a 14+2 model separator produced by Donggao. Taking an 18650 lithium-ion battery as an example, the method includes the following steps:

[0059] (1) Take 15 18650 type lithium-ion battery cases, place the first PET sheet at the bottom of each battery case so that the first PET sheet just covers the bottom of the battery case; cut a batch of separators of the same size, and use part of them to wind with the positive electrode and negative electrode to form an electrode group, while the other part is used as a reference group. Put the wound electrode group into the case, and place the second PET sheet on the top of the electrode group so that the second PET sheet just covers the top of the electrode group.

[0060] (2) Inject 5.0g NMP into each battery case and use a vacuum chamber to quickly wet the electrode sheets with NMP. Then, seal the battery case three times and let it stand at room temperature for 24 hours to allow the positive and negative electrode sheets to be further fully wetted.

[0061] (3). Place the 15 finished products obtained in step (2) above in an oven and bake them at 105°C for 30 minutes. Then take out 3 finished products and let them cool naturally to room temperature. Disassemble and separate the positive electrode, negative electrode and separator. Use vernier calipers to measure the size of the obtained separator, record the data and compare it with the size of the separator in the reference group. Calculate the shrinkage rate, calculate the average value based on the shrinkage rate and record it in Table 1.

[0062] The remaining 12 finished products in the oven were heated to 130°C and kept warm for 30 minutes. Then, 3 finished products were taken out and allowed to cool naturally to room temperature. The positive electrode, negative electrode and separator were disassembled and separated. The size of the obtained separator was measured with vernier calipers, the data was recorded and compared with the size of the separator of the reference group. The shrinkage rate was calculated, the average value was calculated based on the shrinkage rate and recorded in Table 2.

[0063] The remaining 9 finished products in the oven were heated to 145℃ and kept warm for 30 minutes. Then, 3 finished products were taken out and allowed to cool naturally to room temperature. The positive electrode, negative electrode and separator were disassembled and separated. The size of the obtained separator was measured with vernier calipers, the data was recorded and compared with the size of the separator of the reference group. The shrinkage rate was calculated, the average value was calculated based on the shrinkage rate and recorded in Table 2.

[0064] The remaining 6 finished products in the oven were heated to 160℃ and kept warm for 30 minutes. Then, 3 finished products were taken out and allowed to cool naturally to room temperature. The positive electrode, negative electrode and separator were disassembled and separated. The size of the obtained separator was measured with vernier calipers, the data was recorded and compared with the size of the separator of the reference group. The shrinkage rate was calculated, the average value was calculated based on the shrinkage rate and recorded in Table 2.

[0065] The remaining three finished products in the oven were heated to 180°C and kept warm for 30 minutes. After that, the three finished products were taken out and allowed to cool naturally to room temperature. The positive electrode, negative electrode and separator were disassembled and separated. The size of the obtained separator was measured with vernier calipers, the data was recorded and compared with the size of the separator of the reference group. The shrinkage rate was calculated, the average value was calculated based on the shrinkage rate and recorded in Table 2.

[0066] Table 2. Shrinkage rate (%) of Donggao 14+2 type diaphragm

[0067]

[0068] The diaphragm shrinkage rate data obtained in Examples 1 and 2 were plotted as curves, specifically as follows: Figure 2 As shown. By Figure 2 It can be seen that as the temperature increases, the shrinkage rate of the diaphragm also increases. After the temperature rises to a certain level, the shrinkage rate of the diaphragm no longer continues to increase, indicating that it has reached its maximum shrinkage rate.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for measuring the shrinkage rate of a lithium-ion battery separator, characterized in that, The measurement method involves assembling the separator into a simulated battery, then baking the simulated battery at different temperatures, obtaining the separator size at each baking temperature, and comparing it with the separator size before baking, thereby obtaining the separator shrinkage rate at different temperatures. The simulated battery assembled with the separator is made by winding the positive electrode, negative electrode and separator into an electrode assembly and then putting it into a lithium-ion battery case. The simulated battery is obtained through the following steps: A first gasket is placed inside the lithium-ion battery casing, and the battery electrode assembly is then inserted into the lithium-ion battery casing. A solvent is injected into the lithium-ion battery casing, and a second gasket is placed on the upper surface of the electrode assembly. The casing is then sealed and allowed to stand and age, allowing the solvent to fully wet the electrode assembly, thus obtaining the simulated battery.

2. The method for measuring the shrinkage rate of a lithium-ion battery separator as described in claim 1, characterized in that, The solvent has a boiling point higher than the maximum baking temperature.

3. The method for measuring the shrinkage rate of a lithium-ion battery separator as described in claim 1, characterized in that, The melting point temperatures of the first and second gaskets are higher than the maximum baking temperature.

4. The method for measuring the shrinkage rate of a lithium-ion battery separator as described in claim 1, characterized in that, The solvent is either N-methylpyrrolidone or dimethyl sulfoxide.

5. The method for measuring the shrinkage rate of a lithium-ion battery separator as described in claim 1, characterized in that, The first gasket is any one of polyethylene terephthalate, polybutylene terephthalate, and glass fiber; and / or the second gasket is any one of polyethylene terephthalate, polybutylene terephthalate, and glass fiber.

6. The method for measuring the shrinkage rate of a lithium-ion battery separator as described in claim 1, characterized in that, The baking temperature shall not be lower than 160°C.

7. The method for measuring the shrinkage rate of a lithium-ion battery separator as described in claim 6, characterized in that, The baking temperature range is 160~200℃.

8. The method for measuring the shrinkage rate of a lithium-ion battery separator as described in claim 1, characterized in that, The baking method involves baking in sequence from low temperature to high temperature.

9. The method for measuring the shrinkage rate of a lithium-ion battery separator as described in claim 1, characterized in that, The amount of solvent injected is 70% to 100% of the amount of electrolyte injected for the corresponding model of lithium-ion battery.

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