Lithium ion battery fusing protection current test method

Abstract

The invention discloses a lithium ion battery fusing protection current test method. The method comprises the following steps: directly and electrically connecting a battery cover plate fusing protection device with charging and discharging equipment; charging and discharging equipment is started for testing, the fusing state and the equipment current value of the battery cover plate overcurrent protection device are monitored in real time, and the fusing protection time of the battery cover plate and the corresponding short-circuit current value are obtained; stopping the test after the current value of the equipment is reduced to zero or the discharge time reaches a set cut-off time; fitting the collected data to obtain a fitting relational expression between the fusing protection time and the short-circuit current; and predicting the fusing protection time corresponding to any short-circuit current in the preset current range interval based on the fitting relational expression. According to the method, the fusing protection time corresponding to any short-circuit current value within a certain range can be predicted by directly and electrically connecting the fusing protection device of the battery cover plate with the charging and discharging equipment for testing and deducing the power function relationship between the short-circuit current and the fusing time.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery fuse protection current testing, and in particular to a lithium ion battery fuse protection current testing method. Background Art

[0002] In order to reduce the use of traditional fossil energy and reduce greenhouse gas emissions, lithium-ion batteries, as a high-tech product, have been rapidly applied and developed in the field of electric vehicles. At the same time, battery safety has become the primary issue that needs to be addressed in the design process of automotive lithium-ion batteries. External short circuits in lithium-ion batteries will generate large currents and rapid temperature rise in a short period of time. High temperatures can easily trigger a series of chemical reactions inside the battery. In particular, the instability of the high-temperature structure of the ternary positive electrode material will increase the risk of thermal runaway and the severity of thermal runaway. In the case of an external short circuit, when the discharge current of the lithium-ion battery reaches a certain value and duration, the overcurrent protection device in the battery cover structure will automatically fuse, and then cut off the current circuit to prevent the battery from continuing to heat up and causing thermal runaway. Therefore, the maximum current and duration test of the fuse protection has become a key reference for guiding the size design of the battery cover overcurrent protection device.

[0003] At present, the conventional short-circuit test method for automotive lithium-ion batteries is to set different external circuit resistance values ​​(generally less than 5mΩ) after the battery is charged to a certain state of charge, and the positive and negative terminals of the test object are externally short-circuited for 10 minutes. During this period, the battery status is continuously monitored, and data such as current and temperature rise are collected using a data acquisition device. This test method regulates the size of the battery short-circuit current by setting different external circuit resistance values. However, affected by the voltage change during the discharge process, the battery discharge current continues to decrease under this test condition, and the current flowing through the battery overcurrent protection device cannot be guaranteed to be stable at a certain value. The test accuracy is low and the sample data volume is single. After the battery short-circuit test is completed, in order to observe the fuse state of the overcurrent protection device, the battery needs to be further dissected and analyzed, and the overall test cycle is relatively long. At the same time, the conventional fuse current test method uses finished battery samples, and the material cost is high when the sample data demand is large.

[0004] CN107367668A proposes a method for directly testing the lithium-ion battery cover plate and then evaluating the fuse protection current. This method requires manually flipping the flip plate on the battery cover plate to form a path for the positive and negative poles of the cover plate. However, during the external short circuit of the battery, the flip plate is not accompanied by a flipping action, and the current does not flow through the flip plate. The current flow path of this method is inconsistent with the actual situation. In addition, this method requires the addition of a battery module in the series circuit to supply a large current, which poses certain safety hazards and the cost of test materials is also higher. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings and defects of the prior art and provide a lithium-ion battery fuse protection current testing method to provide important data support for the safety design of lithium-ion batteries. The testing method is accurate, the component materials used are low-cost, and the testing operation is simple and easy.

[0006] A method for testing the fuse protection current of a lithium-ion battery comprises the following steps:

[0007] Directly electrically connect the battery cover fuse protection device to the charging and discharging equipment;

[0008] Start the charging and discharging equipment for testing, monitor the fusing status of the overcurrent protection device of the battery cover and the current value of the equipment in real time, and obtain the fusing protection time of the battery cover and the corresponding short-circuit current value;

[0009] The collected data are fitted to obtain a fitting relationship between the fuse protection time and the short-circuit current;

[0010] The fuse protection time corresponding to any short-circuit current within a predetermined current range is predicted based on the fitting relationship.

[0011] Wherein, an external aluminum bar is welded to the outer side of the positive electrode column of the battery cover plate, and the negative power line of the charging and discharging equipment is bolted to the external aluminum bar.

[0012] The thickness of the external aluminum bar is 1.5-2.0 mm, and the welding point track is circular.

[0013] Among them, a positive electrode aluminum foil is welded at the positive electrode connecting piece or lead piece of the battery cover, and the positive electrode power line of the charging and discharging equipment is bolted to the aluminum foil.

[0014] Wherein, the welding mark between the positive electrode aluminum foil and the positive electrode connecting piece or lead piece of the battery cover is located at the center position of the connecting piece or lead piece.

[0015] Wherein, a straight circular hole is punched on the positive electrode aluminum foil so as to be bolted and connected with the charging and discharging equipment.

[0016] Wherein, the positive electrode aluminum foil is plain aluminum foil or carbon-coated aluminum foil.

[0017] The positive electrode aluminum foil is multi-layered, and the number of layers of the positive electrode aluminum foil is consistent with the number of layers of the positive electrode sheet of the battery electrode group.

[0018] Wherein, the thickness of the positive electrode aluminum foil is 10 to 15 μm.

[0019] Among them, the types of battery cover plates include flat battery cover plates and lead-type battery cover plates.

[0020] The present invention tests the battery cover fuse protection device by directly electrically connecting it to the charging and discharging equipment. The short-circuit test current is stable and the value is controllable, thereby improving the accuracy of sample data. By deriving the power function relationship between the short-circuit current and the fuse time, the fuse protection time corresponding to any short-circuit current value within a certain range can be predicted, thereby providing important data support for the design of the battery cover structure.

[0021] The test object of the present invention is a battery cover, which can quickly and intuitively analyze the fusing state of the overcurrent protection device of the battery cover without dissecting the finished battery sample, shortening the test cycle and reducing the test cost.

[0022] The test current of the present invention flows directly through the fuse via the battery pole and the positive lead, and the same number of layers of aluminum foil as the battery pole group are welded to the positive lead. The current flow path is consistent with the battery external short process, and there is no need for the battery module to supply large current to the series circuit, thereby reducing the test risk. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention is a flow chart of a lithium-ion battery fuse protection current testing method.

[0024] Figure 2 It is a schematic diagram of the connection between the battery and the charging and discharging equipment during the fuse protection current test of the lithium ion battery of the present invention.

[0025] Figure 3 It is a characteristic curve diagram of the fuse protection time and the short-circuit current of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] See also Figure 1 , 2 As shown, a method for testing the fuse protection current of a lithium-ion battery in the present invention comprises the following steps:

[0028] S1. The battery cover 1 fuse protection device 4 is directly electrically connected to the charging and discharging device 5;

[0029] S2. Start the charging and discharging equipment 5 for testing, monitor the fuse status of the overcurrent protection device 4 of the battery cover 1 and the current value of the device in real time, and obtain the fuse protection time of the battery cover 1 and the corresponding short-circuit current value;

[0030] S3. Fitting the collected data to obtain a fitting relationship between the fuse protection time and the short-circuit current;

[0031] S4. Predict the fuse protection time corresponding to any short-circuit current within a predetermined current range based on the fitting relationship.

[0032] Among them, during the test, when the current value of the equipment drops to zero or the discharge time reaches the set cut-off time, the test is stopped, and then the test sample is replaced, a larger test current is selected, and the power-on test is restarted. And so on, increasing test currents are selected successively until all tests are completed and the test is stopped. The fuse protection time under different test currents can be obtained.

[0033] In some embodiments, an external aluminum bar 2 is welded to the outer side of the positive electrode column of the battery cover plate 1, such as by laser welding, and the negative power line of the charging and discharging device is bolted to the external aluminum bar.

[0034] In some embodiments, according to the set short-circuit current value, the thickness of the external aluminum bar is 1.5-2.0 mm, and can be selected for use within this range. The welding point track is a circle with a diameter of 8-10 mm, and can be selected for use within this range.

[0035] In some embodiments, a positive electrode aluminum foil 3 is welded to the positive electrode connecting piece or lead of the battery cover plate 1, and the positive electrode power line of the charging and discharging device is bolted to the aluminum foil.

[0036] In some embodiments, the weld mark between the positive electrode aluminum foil and the positive electrode connecting piece or lead of the battery cover is located in the center of the connecting piece or lead, and the welding area is 150-200 mm 2 You can choose to use it within this range, or adjust it according to the actual size of the connecting piece and the guide piece.

[0037] In some embodiments, a straight circular hole with a diameter of 6 to 8 mm is punched on the positive electrode aluminum foil, and can be selected within this range for use so as to be bolted to the charging and discharging device.

[0038] In some embodiments, the positive electrode aluminum foil is a plain aluminum foil or a carbon-coated aluminum foil, or other available aluminum foils, but is not limited thereto.

[0039] In some embodiments, the positive electrode aluminum foil is multi-layered, and the number of layers of the positive electrode aluminum foil is consistent with the number of layers of the positive electrode sheet of the battery electrode group. Specifically, according to the actual number of layers of the positive electrode sheet of the battery electrode group, the corresponding number of layers of aluminum foil can be folded in half or cut and stacked, and then welded to the positive electrode connecting sheet or lead sheet of the battery cover by ultrasonic welding.

[0040] In some embodiments, according to the battery design requirements, the thickness of the positive electrode aluminum foil is 10-15 μm, and can be selected and used within this range.

[0041] In some embodiments, the battery cover types include flat battery cover and lead-type battery cover, or other covers including battery cover fuse protection devices, but are not limited thereto.

[0042] It should be noted that, during implementation, the charging and discharging equipment may be used in parallel in multiple units according to the maximum target current.

[0043] During the test, the positive power line of the charging and discharging device 5 is bolted to the aluminum foil, and the negative power line of the charging and discharging device is bolted to the external aluminum bar. Write the test program, set the test current and duration, and start the charging and discharging device.

[0044] During the test, the fuse status of the battery cover overcurrent protection device 4 and the device current value are monitored in real time. When the device current value drops to zero or the discharge time reaches the set cutoff time, the test is stopped. Data is collected and analyzed and fitted with a power function.

[0045] Test example:

[0046] 1. Preparation of raw materials for test samples:

[0047] Select a lead-type battery cover with an overcurrent fuse protection device, a 2.0mm thick external test aluminum busbar with holes, and a 15μm thick carbon-coated aluminum foil.

[0048] 2. Test sample assembly steps:

[0049] The external aluminum is welded to the outside of the positive pole of the battery cover, and the laser welding point track is a circle with a diameter of 8mm. After the corresponding number of layers of aluminum foil are folded in half, they are welded to the center of the lead of the battery cover by ultrasonic welding, and the welding area is 5mm×30mm. Use a puncher to punch a 6mm diameter circular hole on the surface of the aluminum foil.

[0050] 3. Sample testing steps:

[0051] Connect the positive power line of the charging and discharging equipment to the aluminum foil bolt, and the negative power line to the external aluminum bar bolt. Set the test starting current to 600A and the overcurrent cut-off time to 120s. Monitor the fuse status and current value of the battery cover overcurrent protection device in real time. After 112s, the current value drops to zero and the discharge stops.

[0052] The test sample was replaced, the current was increased to 800A, and the power-on test was restarted.

[0053] The test is then stopped by analogy when the maximum target test current reaches 2600A.

[0054] Thus, a set of corresponding data of battery cover fuse protection time and current value is obtained (see Table 1)

[0055] Table 1 Correspondence between battery cover fuse protection time and short-circuit current

[0056]

[0057] By fitting and analyzing the above data, the relationship between the fuse protection time y and the short-circuit current x is derived:

[0058] y=7E+13x -4.278 .

[0059] By using this expression, the fuse protection time corresponding to any short-circuit current between 600 and 2600A can be calculated (see Figure 2 ).

[0060] The lithium-ion battery fuse protection current testing method of the present invention directly connects the battery cover fuse protection device to the charging and discharging equipment for charging test, obtains the corresponding data of the battery cover fuse protection time and the current value, fits the fuse protection time and the corresponding current value data, and derives the mathematical relationship expression between the fuse protection time and the short-circuit current. Through the expression, the corresponding fuse protection time of any short-circuit current within a certain current range can be predicted, providing important data support for the design of the battery cover structure.

[0061] Compared with the prior art, the test method of the present invention is scientifically designed, overcomes the uncontrollable shortcomings of the existing short-circuit test current, improves the accuracy of sample data, and quantifies the linear relationship between the fusing current and the fusing time through mathematical expressions. The test current of this scheme flows directly through the fuse through the battery pole and the positive lead. The same number of layers of aluminum foil as the battery pole group are welded to the positive lead, and the current flow path is more in line with the actual current loop of the battery short circuit. The lithium-ion battery fuse protection current test method of the present invention is easy to operate, and can quickly and intuitively analyze the fusing state of the battery cover overcurrent protection device. There is no need to dissect the finished battery sample, which further shortens the test cycle, saves material costs, and reduces testing costs. In summary, the lithium-ion battery fuse protection current test method of the present invention provides important data support for the design of the lithium-ion battery cover structure, and has great practical significance for battery safety design.

[0062] The basic principles and main features of the present invention and the advantages of the present invention are shown and described above. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0063] Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is therefore intended that all changes falling within the meaning and range of equivalent elements of the claims are included in the present invention.

[0064] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for testing the fuse protection current of a lithium-ion battery, characterized in that: include: Directly electrically connect the battery cover fuse protection device to the charging and discharging equipment; Start the charging and discharging equipment for testing, monitor the fusing status of the overcurrent protection device of the battery cover and the current value of the equipment in real time, and obtain the fusing protection time of the battery cover and the corresponding short-circuit current value; The collected data are fitted to obtain a fitting relationship between the fuse protection time and the short-circuit current; The fuse protection time corresponding to any short-circuit current within a predetermined current range is predicted based on the fitting relationship.

2. The method for testing the fuse protection current of a lithium-ion battery according to claim 1, characterized in that: An external aluminum bar is welded to the outer side of the positive pole of the battery cover plate, and the negative power line of the charging and discharging equipment is bolted to the external aluminum bar.

3. The method for testing the fuse protection current of a lithium-ion battery according to claim 1, characterized in that: The thickness of the external aluminum bar is 1.5-2.0 mm, and the welding point track is circular.

4. The method for testing the fuse protection current of a lithium-ion battery according to claim 1, characterized in that: A positive aluminum foil is welded at the positive electrode connecting piece or lead piece of the battery cover, and the positive power line of the charging and discharging equipment is bolted to the aluminum foil.

5. The method for testing the fuse protection current of a lithium-ion battery according to claim 4, characterized in that: The welding mark between the positive electrode aluminum foil and the positive electrode connecting piece or lead piece of the battery cover is located at the center of the connecting piece or lead piece.

6. The method for testing the fuse protection current of a lithium-ion battery according to claim 4, characterized in that: A straight circular hole is punched on the positive electrode aluminum foil so as to be bolted and connected to the charging and discharging equipment.

7. The method for testing the fuse protection current of a lithium-ion battery according to claim 4, characterized in that: The positive electrode aluminum foil is a plain aluminum foil or a carbon-coated aluminum foil.

8. The method for testing the fuse protection current of a lithium-ion battery according to claim 4, characterized in that: The positive electrode aluminum foil is multi-layered, and the number of layers of the positive electrode aluminum foil is consistent with the number of layers of the positive electrode sheet of the battery electrode group.

9. The method for testing the fuse protection current of a lithium-ion battery according to claim 4, characterized in that: The thickness of the positive electrode aluminum foil is 10-15 μm.

10. The method for testing the fuse protection current of a lithium-ion battery according to claim 1, characterized in that: The battery cover types include flat battery cover and lead-type battery cover.

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