Method for improving short-circuit safety performance of battery

Abstract

The invention relates to the technical field of batteries, in particular to a method for improving battery short circuit safety performance, which comprises the following steps: preparing a test battery with different tab sizes and consistent other process parameters, performing short circuit on the test battery, and measuring the highest temperature T of tabs to obtain a plurality of tab sizes L and data points of the highest temperature T corresponding to the tabs; fitting according to the plurality of data points to obtain a relational expression between the tab size L and the tab maximum temperature T; substituting the diaphragm rupture temperature T1 of the diaphragm into a relational expression between the tab size L and the maximum tab temperature T to obtain a tab size reference value Y; the battery is prepared according to the tab size reference value Y. When the external circuit connected with the prepared battery is short-circuited, the highest temperature that the tab can reach is lower than the tab membrane rupture temperature, the diaphragm of the battery is not easy to melt, the battery is not easy to fire or explode, and the safety performance of the battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a method for improving the short-circuit safety performance of a battery. Background Art

[0002] As a new type of secondary battery, lithium-ion battery has the advantages of high energy density and power density, high operating voltage, light weight, small size, long cycle life, good safety, and green environmental protection. It is widely used in many kinds of electrical appliances as a power source. As batteries are widely used in many fields, it is necessary to improve the safety performance of batteries. To ensure the safety performance of batteries, it is necessary to prevent fire and explosion during internal short circuit and external short circuit of the battery. The main reason for the explosion of the battery during external short circuit is that the heat of the battery's ears and collectors causes heat accumulation in the battery, causing the battery temperature to rise and the battery's diaphragm to melt, resulting in an internal short circuit of the battery, causing the battery to explode.

[0003] In the prior art, the heat resistance of batteries is mainly increased by using special formulas and materials to prepare batteries. However, this method is costly and has a certain impact on other properties of the battery cell.

[0004] Based on this, it is urgent to invent a method for improving the short-circuit safety performance of a battery to solve the aforementioned technical problems. Summary of the invention

[0005] The purpose of the present invention is to provide a method for improving the short-circuit safety performance of a battery in view of the deficiencies in the prior art. The method can balance the heat dissipation of the tabs and the heat generated by the short circuit when the battery is short-circuited, control the temperature of the tabs within a suitable range, reduce the fire or explosion of the battery, and improve the safety performance of the battery when it is short-circuited.

[0006] In order to solve the above technical problems, this application adopts the following technical solutions:

[0007] A method for improving short-circuit safety performance of a battery is provided, comprising:

[0008] Prepare test batteries with different tab sizes and other consistent process parameters, short-circuit the test batteries, measure the maximum temperature T of the tabs, and obtain multiple data points of the tab sizes L and the maximum temperature T corresponding to the tabs;

[0009] According to the plurality of data points, a relationship between the size of the tab L and the maximum temperature of the tab T is obtained by fitting;

[0010] Substituting the membrane rupture temperature T1 of the diaphragm into the relationship between the tab size L and the tab maximum temperature T, the tab size reference value Y is obtained;

[0011] A battery is manufactured according to the tab size reference value Y.

[0012] Specifically, the fitting and obtaining of the relationship between the lug size L and the lug maximum temperature T according to the plurality of data points includes: the relationship between the lug size L and the lug maximum temperature T is T=aln(L)+b;

[0013] Substitute the multiple tab sizes L and the corresponding maximum temperatures T of the tabs into the relationship between tab size L and tab maximum temperature T to obtain the values ​​of parameter a and parameter b.

[0014] Specifically, the step of substituting the membrane rupture temperature T1 of the diaphragm into the relationship between the tab size L and the tab maximum temperature T to obtain the tab size reference value Y includes: the calculation formula of the tab size reference value Y is,

[0015] Specifically, the tab size L is the surface area of ​​the tab.

[0016] Specifically, the tab size L is the length of the welding end of the tab along the X direction.

[0017] Specifically, the thickness of the pole lug is less than 1 / 10 of the length of the pole lug, and the width of the pole lug is greater than 4 times the thickness of the pole lug.

[0018] Specifically, preparing a battery according to the tab size reference value Y includes: the size of the tab is larger than the tab size reference value Y.

[0019] Specifically, the size of the pole lug is 100% to 200% of the reference value Y of the pole lug size.

[0020] Specifically, the data point is a value at which the battery does not burn or explode.

[0021] Specifically, the shape of the pole ear is rectangular.

[0022] The beneficial effects of the present invention are as follows: the present application provides a method by which a relationship between a battery tab and the maximum temperature of a battery can be derived based on limited experiments, and the maximum temperature that the tab will reach due to the heat generated when a short circuit occurs outside the battery to generate a large current can be accurately derived from the relationship. The main reason for the short circuit and fire of the external circuit of the battery is that the temperature of the tab is too high, causing the diaphragm of the negative electrode of the tab to melt, resulting in a short circuit between the positive and negative electrode sheets inside the battery, aggravating the heat generation of the battery and causing the battery to form a thermal runaway, resulting in a fire or even an explosion of the battery. The present application prepares a battery by selecting a tab of a suitable size according to the melting temperature of the diaphragm. When a short circuit occurs in the connected external circuit of the prepared battery, the maximum temperature that the tab can reach is less than the tab rupture temperature, the diaphragm of the battery is not easy to melt, and the battery is not easy to catch fire or explode, which can improve the safety performance of the battery and solve the problems of empiricism and blindness in the tab size selection method. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0024] Figure 1 It is a schematic diagram of the structure of the electrode ear in the present invention;

[0025] Wherein: 1-pole ear; 2-pole piece; L-length of the welding end pole ear. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by technicians in the technical field of the present application. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings, but this is not intended to limit the present invention.

[0028] The applicant has found that when the external short circuit of the battery occurs, that is, the external circuit connected to the tab is short-circuited, causing the positive and negative electrodes of the battery to be short-circuited, at this time, since there is no electrical appliance connected, the current flowing out of the battery will generate a large amount of heat in the tab of the battery, causing the tab temperature to rise. The main reason why the battery will catch fire or even explode when the external short circuit occurs is that the tab temperature is too high, causing the battery diaphragm to melt, so that the positive and negative electrodes of the battery cannot be insulated by the diaphragm, causing the battery to have an internal short circuit, causing the battery to generate heat rapidly and then thermal runaway, the battery catching fire or exploding. Therefore, in order to prevent the temperature of the tab from causing the battery diaphragm to melt, the existing technology chooses to use a diaphragm of a new material or set a heat insulation layer, and these methods will cause the performance of the battery to be impaired. The applicant has found that the temperature of the tab can be controlled by controlling the heat dissipation of the tab. In one embodiment of the present application, the heat dissipation of the tab is controlled by controlling the size of the tab, so as to control the temperature of the tab when the current heat generation of the battery and the heat dissipation of the tab are balanced. The tab melting diaphragm can be prevented by controlling the size of the battery, overcoming the problem that the existing measures generally use special formulas and high material costs, and have a certain impact on other properties of the battery cell.

[0029] Implementation Method 1

[0030] In the present embodiment, a method for improving the short-circuit safety performance of a battery is provided, including: preparing test batteries with different tab sizes but the same other process parameters, and short-circuiting the test batteries, measuring the maximum temperature T of the tabs, and obtaining a plurality of data points of the tab sizes L and the maximum temperature T corresponding to the tabs; obtaining a relationship between the tab size L and the maximum temperature T of the tabs according to fitting of the plurality of data points; substituting the membrane rupture temperature T1 of the diaphragm into the relationship between the tab size L and the maximum temperature T of the tabs to obtain a reference value Y for the tab size; and preparing a battery according to the reference value Y for the tab size.

[0031] Specifically, the tab size L is the surface area of ​​the tab. Since the maximum temperature of the tab is related to the heat dissipation of the tab, and the heat dissipation of the tab is related to the size of the tab, the larger the surface area of ​​the tab, the better the heat dissipation effect of the tab. By obtaining the relationship between the surface area of ​​the tab and the maximum temperature of the tab, the tab of appropriate size can be selected according to the rupture temperature of the diaphragm, that is, the melting temperature of the diaphragm, so that the maximum temperature of the tab is lower than the rupture temperature of the diaphragm, so that even if a short circuit occurs in the external circuit connected to the battery, the temperature of the tab will not be higher than the rupture temperature of the diaphragm, thereby reducing the possibility of melting of the battery diaphragm and improving the safety performance of the battery.

[0032] Specifically, the relationship between the lug size L and the maximum lug temperature T is obtained by fitting multiple data points, including: the relationship between the lug size L and the maximum lug temperature T is T=aln(L)+b; the multiple lug sizes L and the corresponding maximum temperatures T of the lugs are substituted into the relationship between the lug size L and the maximum lug temperature T to obtain the values ​​of parameters a and b. Exemplarily, after preparing at least two batteries with different lug sizes, the positive and negative electrodes of the batteries are short-circuited to simulate the short circuit of the external circuit of the battery, and the maximum temperature of the lug is measured. The data of the measured maximum lug temperature and the size of the surface area of ​​the lug are substituted into the relationship T=aln(L)+b to calculate the a and b parameters in the formula. After the calculation, the maximum temperature of the lug during the external short circuit can be obtained through the size of the lug, and the size of the lug can also be obtained through the maximum temperature of the lug during the external short circuit.

[0033] Specifically, substituting the membrane rupture temperature T1 of the diaphragm into the relationship between the tab size L and the tab maximum temperature T to obtain the tab size reference value Y includes: the calculation formula of the tab size reference value Y is, The maximum temperature of the pole lug with the reference value Y of the pole lug size is the same as the rupture temperature of the diaphragm, and the size of the pole lug can be set according to the reference value Y of the pole lug size.

[0034] Preferably, preparing a battery according to the tab size reference value Y includes: the tab size is larger than the tab size reference value Y, when the tab size is larger than the tab size reference value Y, the heat dissipation capacity of the tab is enhanced, the maximum temperature of the tab decreases, and the maximum temperature of the tab is lower than the membrane rupture temperature of the diaphragm.

[0035] Preferably, the size of the tab is 100% to 200% of the tab size reference value Y. Within this range, the tab is neither too large to occupy too much space in the battery, nor too small to cause the tab to have too high a temperature during an external short circuit, affecting the safety performance of the battery.

[0036] Preferably, the data point is taken as the value when the battery does not burn or explode. When the battery burns or explodes, the temperature at the pole ear is not only formed by the heat generated by the current of the battery, but also partly due to the heat generated by the combustion of the battery, resulting in inaccurate data, and it is impossible to obtain an accurate relationship between the pole ear size L and the pole ear maximum temperature T.

[0037] Implementation Method 2

[0038] like Figure 1 As shown, the difference between this embodiment and embodiment 1 is that the lug size L is the length of the welding end of the lug along the X direction. Since the shape of the lug is generally a thin sheet, the area of ​​the side of the lug is relatively small in the surface area of ​​the lug and is difficult to measure. Therefore, the length of the lug can be directly selected as the lug size. Since the lug mainly generates heat at the welding end and the temperature at this position is the highest, the position with the highest temperature needs to be selected as the highest temperature of the lug. Therefore, the length of the lug at the welding end is selected as the standard of the lug size.

[0039] Preferably, the thickness of the lug is less than 1 / 10 of the length of the lug, and the width of the lug is greater than 4 times the thickness of the lug. When the size of the lug is within this range, the heat dissipation of the lug is mainly carried out by the surface of the lug away from the pole piece. Therefore, choosing this method can reduce the error of the relationship between the lug size L and the maximum lug temperature T.

[0040] Preferably, the shape of the pole ear is a rectangle. When the pole ear is a rectangle, the length of the pole ear is proportional to the heat dissipation capacity of the pole ear, so that the relationship between the pole ear size L and the pole ear maximum temperature T of the present application is more accurate.

[0041] Example 1

[0042] Test batteries with different lengths of the battery tabs at the welding end were prepared, short-circuit tests were performed, and the maximum temperature at the tabs was measured. The tab length L and the maximum temperature at the tabs were substituted into the formula T = aln(L) + b to obtain the correlation formula for the maximum temperature at the tab and the length of the tab at the welding end: maximum temperature = -57.66ln(tab welding area length) + 385.27. The tab length was calculated to be 38.3 mm when the maximum temperature was 300°C. A battery with a tab length of 41 mm at the welding end and a diaphragm rupture temperature of 300°C was selected.

[0043] Example 2

[0044] The difference from Example 1 is that the length of the pole ear is calculated to be 90.7 mm when the maximum temperature is 250°C, the length of the pole ear at the welding end is selected to be 100 mm and the membrane rupture temperature of the prepared diaphragm is 250°C.

[0045] Example 3

[0046] The difference from Example 1 is that the length of the pole ear is calculated to be 218.7 mm when the maximum temperature is 200°C, the length of the pole ear at the welding end is selected to be 230 mm and the membrane rupture temperature of the prepared diaphragm is 200°C.

[0047] Comparative Example 1

[0048] The difference from Example 1 is that the length of the pole ear at the welding end is selected to be 11 mm and the membrane rupture temperature of the prepared diaphragm is 300°C.

[0049] Comparative Example 2

[0050] The difference from Example 1 is that the length of the pole ear at the welding end is selected to be 31 mm and the membrane rupture temperature of the prepared diaphragm is 300°C.

[0051] Comparative Example 3

[0052] The difference from Example 1 is that the length of the electrode tab at the welding end is 50 mm and the membrane rupture temperature of the prepared diaphragm is 250° C. for the battery.

[0053] Comparative Example 4

[0054] The difference from Example 1 is that the length of the electrode tab at the welding end is selected to be 80 mm and the membrane rupture temperature of the prepared diaphragm is 250° C. for the battery.

[0055] Comparative Example 5

[0056] The difference from Example 1 is that the length of the electrode tab at the welding end is 150 mm and the membrane rupture temperature of the prepared diaphragm is 200° C. for the battery.

[0057] Battery external circuit short circuit test

[0058] Prepare 10 groups of batteries in each embodiment and comparative example and charge them to 4.0V, short-circuit the positive and negative terminals of the battery through a low-impedance wire to ensure that the short-circuit current is large enough, and keep it for 5 minutes, and leave it for 30 minutes, observe the changes of the battery, and pass when the battery does not catch fire or explode. The pass rate of the battery in each embodiment and comparative example is shown in Table 1.

[0059] Table 1

[0060]

[0061] By comparing Examples 1-3 with Comparative Examples 2, 4, and 5, it can be seen that when the rupture temperature of the diaphragm decreases, the size of the tab does not increase, and the pass rate of the battery external circuit short-circuit test decreases. This is because when the rupture temperature of the diaphragm decreases, the maximum temperature of the tab must also decrease to ensure that the tab does not melt the diaphragm. Therefore, it is necessary to increase the size of the tab and reduce the maximum temperature of the tab.

[0062] The above description shows and describes several preferred embodiments of the present invention, but as before, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept of this article through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for improving the short-circuit safety performance of a battery, characterized in that: include: Prepare test batteries with different tab sizes and other consistent process parameters, short-circuit the test batteries, measure the maximum temperature T of the tabs, and obtain multiple data points of the tab sizes L and the maximum temperature T corresponding to the tabs; According to the plurality of data points, a relationship between the size of the tab L and the maximum temperature of the tab T is obtained by fitting; Substituting the membrane rupture temperature T1 of the diaphragm into the relationship between the tab size L and the tab maximum temperature T, the tab size reference value Y is obtained; A battery is manufactured according to the tab size reference value Y.

2. The method for improving the short-circuit safety performance of a battery according to claim 1, characterized in that: The fitting method of obtaining the relationship between the size of the pole lug L and the maximum temperature of the pole lug T according to the plurality of data points includes: the relationship between the size of the pole lug L and the maximum temperature of the pole lug T is T=aln(L)+b; Substitute the multiple tab sizes L and the corresponding maximum temperatures T of the tabs into the relationship between tab size L and tab maximum temperature T to obtain the values ​​of parameter a and parameter b.

3. The method for improving the short-circuit safety performance of a battery according to claim 2, characterized in that: Substituting the membrane rupture temperature T1 of the diaphragm into the relationship between the tab size L and the tab maximum temperature T to obtain the tab size reference value Y includes: the calculation formula of the tab size reference value Y is:

4. The method for improving the short-circuit safety performance of a battery according to claim 3, characterized in that: The tab size L is the surface area of ​​the tab.

5. The method for improving the short-circuit safety performance of a battery according to claim 4, characterized in that: The tab size L is the length of the welding end of the tab along the X direction.

6. The method for improving the short-circuit safety performance of a battery according to claim 5, characterized in that: The thickness of the pole lug is less than 1 / 10 of the length of the pole lug, and the width of the pole lug is greater than 4 times the thickness of the pole lug.

7. The method for improving the short-circuit safety performance of a battery according to claim 1, characterized in that: Preparing a battery according to the tab size reference value Y includes: the size of the tab is larger than the tab size reference value Y.

8. The method for improving the short-circuit safety performance of a battery according to claim 7, characterized in that: The size of the pole lug is 100% to 200% of the reference value Y of the pole lug size.

9. The method for improving the short-circuit safety performance of a battery according to claim 1, characterized in that: The data point is a value at which the battery does not burn or explode.

10. The method for improving the short-circuit safety performance of a battery according to claim 4 or 5, characterized in that: The shape of the pole ear is rectangular.

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