Method for testing thermal stability of lithium ion battery diaphragm

文档序号：807212 发布日期：2021-03-26 浏览：21次中文

阅读说明：本技术 一种锂离子电池隔膜热稳定性的测试方法 (Method for testing thermal stability of lithium ion battery diaphragm ) 是由魏岩巍杨艳陈世培于 2019-09-26 设计创作，主要内容包括：本公开涉及一种锂离子电池隔膜热稳定性测试方法,该方法包括：a、将待测隔膜与极片进行压合,得到隔膜/极片组件,其中,所述压合的条件包括：压力为0.2-1.0MPa,温度为45-90℃；b、使用高温热针刺穿所述隔膜/极片组件,然后测量刺穿孔周围隔膜的热收缩面积；并且根据所述热收缩面积的大小判断所述待测隔膜的热稳定性的高低。通过上述技术方案,将待测隔膜与极片进行压合得到隔膜/极片组件后后,测量得到的隔膜/极片组件中隔膜的热稳定性,可以真实反应隔膜在工作环境下的热稳定性,测试结果更加准确；而且利用高温热针作为测试工具,能够支持更高且更宽范围的测试温度。(The disclosure relates to a method for testing thermal stability of a lithium ion battery diaphragm, which comprises the following steps: a. and pressing the diaphragm to be tested and the pole piece to obtain a diaphragm/pole piece assembly, wherein the pressing conditions comprise: the pressure is 0.2-1.0MPa, and the temperature is 45-90 ℃; b. piercing the membrane/pole piece assembly using a high temperature hot needle, and then measuring the heat shrinkage area of the membrane around the pierced hole; and judging the thermal stability of the diaphragm to be tested according to the size of the thermal shrinkage area. According to the technical scheme, after the diaphragm to be tested and the pole piece are laminated to obtain the diaphragm/pole piece assembly, the thermal stability of the diaphragm in the obtained diaphragm/pole piece assembly is measured, the thermal stability of the diaphragm in a working environment can be truly reflected, and a test result is more accurate; and the high-temperature hot needle is used as a test tool, so that higher and wider test temperature range can be supported.)

1. A method for testing thermal stability of a lithium ion battery diaphragm is characterized by comprising the following steps:

a. and pressing the diaphragm to be tested and the pole piece to obtain a diaphragm/pole piece assembly, wherein the pressing conditions comprise: the pressure is 0.2-1.0MPa, and the temperature is 45-90 ℃;

b. piercing the membrane/pole piece assembly using a high temperature hot needle, and then measuring the heat shrinkage area of the membrane around the pierced hole; and judging the thermal stability of the diaphragm to be tested according to the size of the thermal shrinkage area.

2. The method of testing of claim 1, further comprising:

and c, placing the diaphragm/pole piece assembly in electrolyte to be soaked for 5-10min, then taking out, and then performing the operation of the step b.

3. The method of testing of claim 1, further comprising:

4. The test method according to claim 3, wherein the time interval between the disassembling operation in step a and the high temperature needling operation in step b is not more than 30 min.

5. The test method according to any one of claims 1 to 4, wherein the separator/pole piece assembly comprises at least one of a separator/positive pole piece assembly, a separator/negative pole piece assembly, and a positive pole piece/separator/negative pole piece assembly.

6. The test method as claimed in any one of claims 1 to 4, wherein the temperature of the high temperature hot pin is 200-450 ℃.

7. The test method according to any one of claims 1 to 4, wherein the high temperature hot pin has a diameter of 1 to 5 mm.

8. The test method according to any one of claims 1 to 4, further comprising:

in the step b, after the high-temperature hot needle pierces the diaphragm/pole piece assembly and keeps static for 5-60s, the high-temperature hot needle is drawn out, and then the thermal shrinkage area of the diaphragm around the pierced hole is measured.

9. The test method according to any one of claims 1 to 4, further comprising:

and after the type of the pole piece is changed, repeating the operation of the step a-b for N times, wherein N is a positive integer greater than or equal to 1.

10. The test method according to any one of claims 1 to 4, wherein the heat shrinkage area of the membrane to be tested around the pierced hole is measured by an imager.

Technical Field

The disclosure relates to the technical field of battery performance testing, in particular to a method for testing thermal stability of a battery diaphragm.

Background

With the development of lithium ion battery technology, the safety performance test of lithium ion batteries is also increasingly emphasized. The lithium ion battery generally comprises a positive electrode, a negative electrode, electrolyte, a diaphragm and the like, wherein the diaphragm is generally made of a high-strength film, and the diaphragm is mainly used for separating the positive electrode and the negative electrode of the battery and preventing the two electrodes from being contacted to cause short circuit and is a key component for ensuring the safety performance of the lithium ion battery. When the temperature of the battery is increased due to long-term use or abnormal conditions, the diaphragm has certain thermal stability so as to continuously play a role in isolating the positive electrode and the negative electrode.

The method for testing the thermal stability of the battery separator in the industry at present mainly comprises the following steps: and (3) performing a heating test after extruding the diaphragm by using a flat plate, or directly placing the diaphragm on a high-temperature iron plate for a heating test, and the like.

However, the test result of the above test method can only characterize the intrinsic thermal stability of the diaphragm to a certain extent, and the test result cannot truly reflect the thermal stability of the diaphragm in the working environment.

Disclosure of Invention

The purpose of the disclosure is to solve the problem that the test result of the existing diaphragm thermal stability test method cannot truly reflect the thermal stability of the diaphragm in the working environment, and provide a method for testing the thermal stability of the battery diaphragm.

In order to achieve the above object, the present disclosure provides a method for testing thermal stability of a lithium ion battery separator, including:

Optionally, the method further comprises:

and c, placing the diaphragm/pole piece assembly in electrolyte to be soaked for 5-10min, then taking out, and then performing the operation of the step b.

Optionally, the method further comprises:

Optionally, the time interval between the disassembling operation in the step a and the high-temperature needling operation in the step b is not more than 30 min.

Optionally, the separator/pole piece assembly comprises at least one of a separator/positive pole piece assembly, a separator/negative pole piece assembly, and a positive pole piece/separator/negative pole piece assembly.

Optionally, the temperature of the high-temperature hot needle is 200-.

Optionally, the diameter of the high temperature hot needle is 1-5 mm.

Optionally, the method further comprises:

and after the type of the pole piece is changed, repeating the operation of the step a-b for N times, wherein N is a positive integer greater than or equal to 1.

Optionally, the heat shrinkage area of the membrane to be measured around the pierced hole is measured by an imager.

According to the technical scheme, after the diaphragm to be tested and the pole piece are laminated to obtain the diaphragm/pole piece assembly, the thermal stability of the diaphragm in the obtained diaphragm/pole piece assembly is measured, the thermal stability of the diaphragm in a working environment can be truly reflected, and a test result is more accurate; and the high-temperature hot needle is used as a test tool, so that higher and wider test temperature range can be supported.

Additional features and advantages of the disclosure will be set forth in the detailed description which follows.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure without limiting the disclosure. In the drawings:

fig. 1 is a schematic simulation diagram of a thermal stability testing method of a battery separator provided in an embodiment of the present disclosure.

Fig. 2 is a schematic diagram of thermal shrinkage of a separator after testing a separator/pole piece assembly by using a method for testing thermal stability of a battery separator provided by an embodiment of the disclosure.

Fig. 3 is a schematic diagram of the thermal shrinkage of a separator after another separator/pole piece assembly is tested by using the method for testing the thermal stability of a battery separator provided by the embodiment of the disclosure.

Fig. 4 is a schematic view of an apparatus for a method of testing thermal stability of a battery separator used in a comparative example.

Description of the reference numerals

1 high temperature hot needle 2 diaphragm

3 Pole piece 4 operation table

5 metal guide plate body 6 glass plate

Detailed Description

The following describes in detail specific embodiments of the present disclosure. It should be understood that the detailed description and specific examples, while indicating the present disclosure, are given by way of illustration and explanation only, not limitation.

The present disclosure provides a method for testing thermal stability of a lithium ion battery separator, the method comprising:

Further, the smaller the thermal shrinkage area of the diaphragm to be measured is measured by the method, the higher the thermal stability of the diaphragm to be measured is, and conversely, the larger the measured thermal shrinkage area of the diaphragm to be measured is, the lower the thermal stability of the diaphragm to be measured is.

The inventor of the present disclosure finds that, in the actual application process of the diaphragm, the diaphragm and the pole piece need to be pressed together to form a diaphragm/pole piece assembly (generally, a battery cell), and the adhesive force existing between the pressed diaphragm and the pole piece may affect the thermal shrinkage performance of the diaphragm under the high temperature condition, so that the thermal stability of the diaphragm in the working environment cannot be truly reflected by the test result obtained by only performing a thermal stability test on the diaphragm alone. In addition, when the thermal stability of the whole diaphragm is separately tested, if the temperature is higher than 150 ℃, the surface of the diaphragm can generate anisotropic thermal shrinkage, and the real thermal shrinkage rate of the diaphragm is difficult to accurately measure.

The diaphragm/pole piece assembly is formed by pressing a diaphragm to be tested and a pole piece, then the diaphragm/pole piece assembly is pierced by a high-temperature hot needle, the thermal shrinkage area of the diaphragm to be tested around the pierced hole is measured, and the thermal stability of the diaphragm to be tested is judged according to the size of the thermal shrinkage area. Before testing, the diaphragm to be tested and the pole piece are pressed to form a diaphragm/pole piece assembly, so that the working state of the diaphragm to be tested in the battery can be simulated, the testing environment of the diaphragm to be tested is closer to the real working environment of the diaphragm to be tested, the testing result can reflect the thermal stability of the diaphragm to be tested in the working environment more truly, and the testing result is more accurate; meanwhile, a high-temperature hot needle is used for puncturing the diaphragm/pole piece assembly for measurement, so that the phenomenon that the whole to-be-measured diaphragm is in high temperature and is subjected to anisotropic thermal shrinkage is avoided, and higher and wider test temperature range can be supported.

In addition, as shown in fig. 1, in the testing method of the present disclosure, the high-temperature hot pin is in a suspended state after penetrating through the membrane/pole piece assembly, and does not contact other heat-conducting media, and the temperature of the high-temperature hot pin is not affected by external media other than the testing assembly in the testing process, so that the testing temperature can be controlled more accurately, and the accuracy of the testing result is further increased.

According to the present disclosure, in order to further increase the accuracy of the test result, the method may preferably further include:

and c, placing the diaphragm/pole piece assembly in electrolyte to be soaked for 5-10min, then taking out, and then performing the operation of the step b. The electrolyte is an important component in the battery, the diaphragm/pole piece assembly is placed in the electrolyte to be soaked for a period of time, the working environment of the diaphragm to be tested, which is in contact with the electrolyte, in the battery is further simulated, the test result is closer to the real thermal stability of the diaphragm to be tested in the working environment, and the accuracy of the test result is further improved.

According to the disclosure, in order to further improve the accuracy of the test result of the above test method and enable the test result and the thermal stability of the diaphragm to be tested in the working environment, the method may further include:

in the step a, assembling the diaphragm, the pole piece and the electrolyte into a lithium ion battery, and disassembling the diaphragm/pole piece assembly used for carrying out the high-temperature hot needling in the step b from the lithium ion battery after the lithium ion battery is formed by high-temperature pressurization. In the technical scheme, the diaphragm/pole piece assembly disassembled from the lithium ion battery is used as a test object of thermal stability, and the test environment of the diaphragm to be tested is basically the same as the working environment of the diaphragm to be tested in the battery just after the diaphragm is disassembled from the lithium ion battery, so that the test result can fully reflect the real thermal stability of the diaphragm to be tested in the working environment, and the accuracy of the test result is higher.

According to the present disclosure, in order to further increase the accuracy of the test result, it is preferable that the time interval between the disassembling operation in the step a and the high temperature needling operation in the step b is not more than 30 min. Under the preferable condition, the phenomenon that the electrolyte is dried up due to the fact that the time for disassembling the diaphragm/pole piece assembly from the battery is too long can be avoided, and the accuracy of the test result is influenced.

The type of composition of the separator/pole piece assembly may be selected within a wide range in accordance with the present disclosure, for example, the separator/pole piece assembly may include at least one of a separator/positive pole piece assembly, a separator/negative pole piece assembly, and a positive pole piece/separator/negative pole piece assembly.

According to the present disclosure, the temperature of the high temperature hot pin may vary within a wide range, for example, the temperature of the high temperature hot pin may be 200-450 ℃.

According to the present disclosure, the diameter of the high temperature hot pin may be selected from a wide range, for example, the diameter of the high temperature hot pin may be 1-5 mm.

According to the present disclosure, in order to further control the time of the thermal stability test of the membrane to be tested, the method may preferably further include:

According to the present disclosure, the method may further comprise:

and after the type of the pole piece is changed, repeating the operation of the step a-b for N times, wherein N is a positive integer greater than or equal to 1. The testing method disclosed by the invention can be used for more accurately testing the thermal stability of the diaphragm to be tested, and also has multiple purposes, for example, the types of pole pieces in the diaphragm/pole piece assembly can be changed for multiple times in the testing process, and the thermal shrinkage performance of the diaphragm to be tested after being pressed with each pole piece is tested, so that the bonding effect of the diaphragm to be tested after being pressed with each pole piece is evaluated, and if the testing result shows that the thermal shrinkage performance is better, the bonding effect of the diaphragm to be tested after being pressed with the corresponding pole piece is better. The results of the testing of the present disclosure on different separator/pole piece assemblies are shown in fig. 2 and 3.

According to the present disclosure, the thermal shrinkage area of the membrane to be measured may be measured in various ways, for example, the thermal shrinkage area of the membrane to be measured around the pierced hole may be measured by an imager.

The present disclosure is further illustrated by the following examples and comparative examples, but the present disclosure is not limited thereto in any way.

In the following examples and comparative examples, the electrode sheet used was a positive electrode sheet (aluminum foil thickness 10 μm, material formulation: lithium cobaltate: conductive agent: binder: 94:3:3 wt%, compacted density 3.8 g/cm)³) (ii) a The formula of the electrolyte is EC, EMC and DMC 1:1:1 v%; the diaphragm is 7 in total (1, FZA0902, imperial; 2, FZA0903, imperial; 3, ZCP9LK, Shenzhen Zhongxing new material; 4, ZCP12LK, Shenzhen Zhongxing new material; 5, MC92S1D-01, Jeli new energy; 6, MC112S1D-01, Jeli new energy; 7, MC132S1D-01, Jeli new energy).

Examples

(1) And respectively laminating the No. 1-7 diaphragm to be tested and the pole piece to obtain 7 groups of diaphragm/pole piece assemblies, wherein the laminating conditions comprise: the pressure is 0.5MPa, and the temperature is 75 ℃; respectively placing the 7 groups of diaphragm/pole piece assemblies in electrolyte for soaking for 5min, and then taking out the assemblies to obtain 7 groups of diaphragm/pole piece assemblies to be tested;

(2) heating the high-temperature hot needle to 400 ℃, respectively placing the 7 groups of to-be-tested diaphragm/pole piece assemblies on an operation platform after the temperature is stable, wherein a through hole with the diameter larger than that of the high-temperature hot needle is arranged in an area, which is opposite to the high-temperature hot needle, on the operation platform, the diameter of the high-temperature hot needle is 2.50mm, adjusting the height of the high-temperature hot needle to ensure that the high-temperature hot needle completely pierces the to-be-tested diaphragm/pole piece assembly, then, the high-temperature hot needle was kept still for 10 seconds, the height of the high-temperature hot needle was adjusted to draw out the high-temperature hot needle from the pierced hole, the thermal shrinkage areas of the No. 1 to No. 7 separators to be tested around the pierced hole were measured respectively by the imager OMM (in fig. 2 or fig. 3, the thermal shrinkage area of the separator to be tested was the area of the circle after the contraction of the separator minus the pierced hole), and the thermal expansion rates of the No. 1 to No. 7 separators to be tested were calculated respectively (the thermal shrinkage area of the separator was the area of the pierced hole).

Examples the thermal contraction area and the thermal expansion rate of the above-mentioned separators to be tested No. 1 to 7 were measured as shown in table 1.

TABLE 1

Diaphragm numbering	Area of thermal contraction in mm²	Thermal expansion rate,%
			1	0.61	12.4％
2	0.86	17.5％
			3	0.28	5.7％
4	0.20	4.0％
			5	6.97	142.1％
6	9.21	187.6％
			7	9.74	198.6％

Comparative example

Comparative example measurement of the thermal contraction area and the thermal expansion rate of the separator was performed using the apparatus shown in fig. 4.

(1) Taking the No. 1-7 membranes to be measured, and cutting the membranes into samples with the size of 100 x 50mm respectively;

(2) flatly paving an aluminum foil with the thickness of 20 mu m on a smooth glass plate, then flatly paving a diaphragm on the aluminum foil, and pressing two ends of the diaphragm by using a pressing block to prevent the diaphragm from moving in the testing process;

(3) heating a soldering iron with the diameter of 1.27mm to 400 ℃, after the temperature is stabilized, vertically pricking the soldering iron to the diaphragm, keeping the diaphragm still for 10s, then moving the soldering iron along the vertical direction, respectively measuring the heat shrinkage area (the area of the punctured hole is subtracted from the circular area after the diaphragm shrinks) of the No. 1-7 diaphragms to be tested around the punctured hole by using an imager OMM, and respectively calculating the heat expansion rate (the area of the heat shrinkage area of the diaphragm is larger than the area of the punctured hole) of the No. 1-7 diaphragms to be tested.

Comparative example the thermal shrinkage area and thermal expansion rate of the separator to be tested nos. 1 to 7 described above were measured and are shown in table 2.

TABLE 2

Diaphragm numbering	Area of thermal contraction in mm²	Thermal expansion rate,%
			D-1	6.55	517.4％
D-2	6.61	521.8％
			D-3	0.26	20.4％
D-4	0.23	18.1％
			D-5	0.18	14.1％
D-6	0.20	15.6％
			D-7	0.19	14.7％

Test example

4 types of diaphragms to be tested (diaphragm numbers 1, 2, 3 and 4) with the minimum thermal expansion rate in the test results of the embodiment are utilized to manufacture lithium ion batteries to be used as test groups of lithium ion batteries; and 4 membranes (membrane numbers D-4, D-5, D-6 and D-7) with the lowest thermal expansion rate in the comparative example test results are used for manufacturing the lithium ion batteries as the control group lithium ion batteries. And according to UL1642 standard, respectively carrying out impact safety test on the lithium ion batteries of the test group and the lithium ion batteries of the comparison group, and detecting and recording the safety test passing rate of each lithium ion battery. The safety test pass rate of each lithium ion battery is shown in table 3.

TABLE 3

As can be seen from table 3, after the lithium ion battery is manufactured by using the separator with better thermal stability screened by the testing method of the present disclosure, the impact safety test throughput of the lithium ion battery is significantly higher than that of the lithium ion battery manufactured by using the separator screened by the method of the comparative example, which shows that the testing result of the testing method of the thermal stability of the lithium ion battery separator provided by the present disclosure can reflect the thermal stability of the separator in the working environment better, and the testing result is more accurate and has more guiding significance.

The preferred embodiments of the present disclosure have been described in detail above, however, the present disclosure is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present disclosure within the technical idea of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

It should be noted that, in the foregoing embodiments, various features described in the above embodiments may be combined in any suitable manner, and in order to avoid unnecessary repetition, various combinations that are possible in the present disclosure are not described again.

In addition, any combination of various embodiments of the present disclosure may be made, and the same should be considered as the disclosure of the present disclosure, as long as it does not depart from the spirit of the present disclosure.

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