A method for improving short circuit safety performance of a battery

Abstract

The application relates to the technical field of batteries, in particular to a method for improving the short-circuit safety performance of a battery, which comprises the following steps: preparing test batteries with different tab sizes and other consistent process parameters, short-circuiting the test batteries, measuring the maximum temperature T of the tabs, obtaining a plurality of data points of the tab sizes L and the corresponding maximum temperatures T of the tabs; fitting the tab size L-tab maximum temperature T relationship according to the plurality of data points; substituting the film breaking temperature T1 of the diaphragm into the tab size L-tab maximum temperature T relationship to obtain a tab size reference value Y; and preparing the battery according to the tab size reference value Y; when the prepared battery is short-circuited in the connected external circuit, the maximum temperature that can be reached by the tab is less than the tab film breaking temperature, the diaphragm of the battery is not prone to melting, the battery is not prone to fire or explosion, and the safety performance of the battery can be improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a method for improving the short-circuit safety performance of batteries. Background Technology

[0002] Lithium-ion batteries, as a new type of rechargeable battery, have advantages such as high energy density and power density, high operating voltage, light weight, small size, long cycle life, good safety, and environmental friendliness. They are widely used as power sources in various electrical appliances. As batteries are widely used in multiple fields, it is necessary to improve their safety performance. To ensure battery safety, the battery must not catch fire or explode under both internal and external short circuits. The main reason for a battery explosion under external short circuit is that the battery tabs and current collectors heat up, causing heat accumulation in the battery. This leads to an increase in battery temperature, melting of the battery separator, and internal short circuit, resulting in an explosion.

[0003] Existing technologies mainly use special formulas and materials to prepare batteries to increase their heat resistance. However, this method is costly and has a certain impact on other properties of the battery cell.

[0004] Therefore, there is an urgent need to invent a method to improve the short-circuit safety performance of batteries to solve the aforementioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a method to improve the short-circuit safety performance of batteries. This method can balance the heat dissipation of the electrode tabs and the heat generated during a short circuit, control the temperature of the electrode tabs within a suitable range, reduce the risk of battery fire or explosion, and improve the safety performance of batteries during short circuits.

[0006] To solve the above-mentioned technical problems, this application adopts the following technical solution:

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

[0008] A test battery with different tab sizes but consistent other process parameters was prepared. The test battery was short-circuited, and the highest temperature T of the tab was measured to obtain multiple data points of the tab size L and the highest temperature T corresponding to the tab.

[0009] The relationship between the tab size L and the highest tab temperature T is obtained by fitting multiple data points;

[0010] Substituting the membrane rupture temperature T1 into the relationship between the tab size L and the highest tab temperature T, we obtain the tab size reference value Y.

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

[0012] Specifically, the step of fitting the relationship between the tab size L and the highest tab temperature T based on multiple data points includes: the relationship between the tab size L and the highest tab temperature T is T=aln(L)+b;

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

[0014] Specifically, substituting the diaphragm rupture temperature T1 into the relationship between the tab size L and the highest tab temperature T to obtain the tab size reference value Y includes: the calculation formula for the tab size reference value Y is as follows:

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

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

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

[0018] Specifically, manufacturing 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 electrode tab is 100% to 200% of the reference value Y for electrode tab size.

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

[0021] Specifically, the electrode tab is rectangular in shape.

[0022] The beneficial effects of this invention are as follows: This application provides a method that can derive the relationship between battery tabs and the battery's maximum temperature based on limited experiments. This relationship can accurately determine the maximum temperature that the tabs will reach due to the heat generated when a large current is generated by a short circuit outside the battery, resulting in batteries made with tabs of different sizes. The main reason for a battery fire due to a short circuit in the external circuit is that the excessively high temperature of the tabs causes the separator of the negative electrode to melt, leading to a short circuit between the positive and negative electrodes inside the battery. This exacerbates heat generation, causing thermal runaway and potentially resulting in a fire or even an explosion. This application, by selecting tabs of appropriate sizes based on the melting temperature of the separator, ensures that the maximum temperature reached by the tabs when a short circuit occurs in the connected external circuit is lower than the tab rupture temperature. This reduces the likelihood of the separator melting and the battery catching fire or exploding, improving battery safety and solving the problem of the empirical and blind nature of tab size selection methods. Attached Figure Description

[0023] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0024] Figure 1 This is a schematic diagram of the electrode tab structure in this invention;

[0025] Wherein: 1-Electrode tab; 2-Electrode plate; L-Length of the welding end electrode tab. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terminology used in the specification of this application is for the purpose of describing specific embodiments only and is not intended to limit this application.

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

[0028] The applicant has discovered that when a battery experiences an external short circuit—that is, a short circuit occurs in the external circuit connected to the tabs, causing a short circuit between the positive and negative terminals—the current flowing from the battery generates a large amount of heat in the tabs, leading to an increase in the tab temperature. The main reason for fires or even explosions during external short circuits is that the excessively high tab temperature causes the battery separator to melt, preventing the positive and negative electrodes from being insulated by the separator, resulting in an internal short circuit. This causes rapid heat generation and thermal runaway, leading to a fire or explosion. Therefore, existing technologies use new materials for the separator or incorporate heat insulation layers to prevent the tab temperature from melting the separator. However, these methods all compromise battery performance. The applicant has discovered that the tab temperature can be controlled by controlling the tab's heat dissipation. In one embodiment of this application, the heat dissipation of the tab is controlled by adjusting its size, thereby balancing the current-generated heat and the heat dissipation of the tab. By controlling the battery size, the melting of the separator can be prevented, overcoming the problems of existing measures that generally use special formulas and materials, resulting in higher costs and impacting other cell performance.

[0029] Implementation Method 1

[0030] This embodiment provides a method for improving the short-circuit safety performance of a battery, comprising: preparing a test battery with different tab sizes but consistent other process parameters, short-circuiting the test battery, measuring the highest temperature T of the tabs, and obtaining multiple data points of tab size L and the corresponding highest temperature T; fitting the multiple data points to obtain a relationship between tab size L and highest temperature T; substituting the membrane rupture temperature T1 of the separator into the relationship between tab size L and highest temperature T to obtain a reference value Y for the tab size; and preparing a battery based on the tab size reference value Y.

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

[0032] Specifically, the relationship between tab size L and tab maximum temperature T obtained by fitting multiple data points includes: the relationship between tab size L and tab maximum temperature T is T=aln(L)+b; by substituting multiple tab sizes L and the corresponding maximum temperature T into the relationship between tab size L and tab maximum temperature T, the values ​​of parameters a and b are obtained. For example, after preparing at least two batteries with different tab sizes, the positive and negative electrodes of the batteries are short-circuited to simulate the external circuit short circuit of the battery, and the maximum temperature of the tabs is measured. Substituting the measured maximum temperature data of the tabs and the surface area of ​​the tabs into the relationship T=aln(L)+b, the parameters a and b in the formula can be calculated. After calculation, the maximum temperature of the tabs under external short circuit can be obtained from the tab size, and the tab size can be obtained from the maximum temperature of the tabs under external short circuit.

[0033] Specifically, substituting the diaphragm rupture temperature T1 into the relationship between the tab size L and the highest tab temperature T, we obtain the tab size reference value Y. The formula for calculating the tab size reference value Y is as follows: The maximum temperature of the tab and the rupture temperature of the diaphragm are the same for the tab size reference value Y. The size of the tab can be set according to the tab size reference value Y.

[0034] Preferably, the battery is prepared according to the tab size reference value Y, wherein 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 separator.

[0035] Preferably, the size of the tab is 100% to 200% of the tab size reference value Y. Within this range, the tab will not be too large, thus occupying too much space in the battery, nor will it be too small, causing the tab to overheat during an external short circuit, thus affecting the safety performance of the battery.

[0036] Preferably, the data points are taken when the battery does not burn or explode. When the battery burns or explodes, the temperature at the tab is not only caused by the heat generated by the battery current, but also partly by the heat generated by the battery combustion, which makes the data inaccurate and makes it impossible to obtain an accurate relationship between tab size L and tab maximum temperature T.

[0037] Implementation Method 2

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

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

[0040] Preferably, the shape of the tab is rectangular. When the tab is rectangular, the length of the tab is proportional to the heat dissipation capacity of the tab, making the relationship between the tab size L and the highest temperature T of the tab in this application more accurate.

[0041] Example 1

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

[0043] Example 2

[0044] Unlike Example 1, the length of the tab was calculated to be 90.7 mm when the maximum temperature was 250°C. The length of the tab at the welding end was selected to be 100 mm, and the battery with a membrane breaking temperature of 250°C was prepared.

[0045] Example 3

[0046] Unlike Example 1, the length of the tab was calculated to be 218.7 mm when the maximum temperature was 200°C. The length of the tab at the welding end was selected to be 230 mm, and the battery with a membrane breaking temperature of 200°C was prepared.

[0047] Comparative Example 1

[0048] Unlike Example 1, a battery with a tab length of 11 mm at the welding end and a membrane rupture temperature of 300°C was selected.

[0049] Comparative Example 2

[0050] Unlike Example 1, a battery with a tab length of 31 mm at the welding end and a membrane rupture temperature of 300°C was selected.

[0051] Comparative Example 3

[0052] Unlike Example 1, a battery with a tab length of 50 mm at the welding end and a membrane rupture temperature of 250°C was selected.

[0053] Comparative Example 4

[0054] Unlike Example 1, a battery with a tab length of 80 mm at the welding end and a membrane rupture temperature of 250°C was selected.

[0055] Comparative Example 5

[0056] Unlike Example 1, a battery with a tab length of 150 mm at the welding end and a membrane rupture temperature of 200°C was selected.

[0057] Battery external circuit short circuit test

[0058] Prepare 10 sets of batteries in each embodiment and comparative example and charge them to 4.0 V. 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 maintain for 5 minutes, and then place for 30 minutes. Observe the changes in the battery. If the battery does not catch fire or explode, it passes. The passing rates of the batteries in each embodiment and comparative example are shown in Table 1.

[0059] Table 1

[0060]

[0061] From the comparison between Examples 1-3 and Comparative Examples 2, 4, and 5, it can be seen that when the film-breaking temperature of the separator decreases, the size of the tab does not increase, and the passing rate of the external circuit short-circuit test of the battery decreases. This is because when the film-breaking temperature of the separator decreases, the maximum temperature of the tab also needs to decrease to ensure that the tab does not melt the separator. 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. However, as mentioned above, 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. Instead, it can be used in various other combinations, modifications, and environments, and can be changed within the scope of the inventive concept of the present invention through the above teachings or the technology or knowledge in the relevant field. Any changes and modifications made by those skilled in the art without departing from the spirit and scope of the present invention shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for improving the short-circuit safety performance of a battery, characterized in that, include: A test battery with different tab sizes but consistent other process parameters was prepared. The test battery was short-circuited, and the highest temperature T of the tab was measured. Multiple data points of the tab size L and the highest temperature T corresponding to the tab were obtained. The tab size L is the length of the welded end of the tab along the width direction of the electrode sheet. The relationship between tab size L and tab maximum temperature T is obtained by fitting multiple data points; the relationship between tab size L and tab maximum temperature T is T=aln(L)+b; the values ​​of parameters a and b are obtained by substituting multiple tab sizes L and the corresponding maximum temperature T into the relationship between tab size L and tab maximum temperature T. Substituting the membrane rupture temperature T1 into the relationship between the tab size L and the highest tab temperature T, we obtain the tab size reference value Y. The formula for calculating the reference value Y for the tab size is as follows: ; The battery is manufactured according to the tab size reference value Y, including the tab size being larger than the tab size reference value Y; The thickness of the tab is less than 1 / 10 of the length of the tab, and the width of the tab is more than 4 times the thickness of the tab; the shape of the tab is rectangular; the data point is the value at which the battery does not burn or explode.

2. The method for improving battery short-circuit safety performance according to claim 1, characterized in that: The size of the electrode tab is 100% to 200% of the reference value Y for electrode tab size.

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