Method for evaluating thermal stability of battery cell

Abstract

The invention provides a battery cell thermal stability evaluation method. The battery cell thermal stability evaluation method comprises the following steps: preparing a battery cell which has a predetermined SOH and a predetermined SOC and is provided with an opened anti-explosion valve as a to-be-evaluated battery cell; heating the to-be-evaluated cell in a predetermined mode until thermal runaway occurs, and collecting corresponding measurement data; and comparing the related measurement data of the to-be-evaluated battery cell when the thermal runaway occurs with a corresponding threshold value so as to evaluate the thermal stability of the to-be-evaluated battery cell. According to some embodiments of the invention, an effective assessment method for the thermal stability of the battery cell after the explosion-proof valve is opened can be provided, the battery cell to be assessed is heated in the predetermined mode until thermal runaway occurs, and the related measurement data of the battery cell to be assessed when thermal runaway occurs are compared with the predetermined threshold value, so that the thermal stability of the battery cell to be assessed is evaluated. The thermal runaway risk of the to-be-evaluated cell with the opened anti-explosion valve can be quantitatively evaluated, and the cell thermal stability evaluation method has high operability and repeatability.

Description

Technical Field

[0001] The present invention relates to the technical field of battery testing, and in particular to a method for evaluating thermal stability of a battery cell. Background Art

[0002] In the current market, the proportion of electric vehicles is increasing. As the core component of electric vehicles, the safety requirements for on-board power batteries during use are very high, and thermal stability evaluation of power batteries is particularly important to ensure the battery safety of electric vehicles.

[0003] When too much heat is generated inside the battery cell, the temperature inside the battery cell rises and the heat is difficult to dissipate, which will eventually cause the battery cell to thermally run away and explode. On the other hand, the battery cell explosion-proof valve is a safety device used to prevent the battery cell from exploding. When the internal pressure of the battery cell exceeds the threshold, the explosion-proof valve will open to release the pressure, thereby effectively preventing the pressure from continuing to increase and causing the battery to explode, ensuring the safety of users.

[0004] When the battery cell ages to the end of its life cycle, the explosion-proof valve will open, and the aged battery cell may still be used. Therefore, it is necessary to conduct thermal stability assessment on the aged battery cell with the explosion-proof valve open to gain control over its thermal runaway risk, thereby helping to improve battery safety. However, existing technologies are still insufficient in this regard. Summary of the invention

[0005] The object of the present invention is to provide a method for evaluating thermal stability of a battery cell, so as to at least partially solve the above-mentioned problems existing in the prior art.

[0006] According to an aspect of the present invention, a method for evaluating thermal stability of a battery cell is provided, comprising:

[0007] Preparing a battery cell with a predetermined SOH and a predetermined SOC and an open explosion-proof valve as a battery cell to be evaluated;

[0008] Performing a predetermined mode of heating on the battery cell to be evaluated until thermal runaway occurs and collecting corresponding measurement data; and

[0009] Compare the relevant measurement data of the battery cell to be evaluated when thermal runaway occurs with the corresponding threshold value to evaluate the thermal stability of the battery cell to be evaluated.

[0010] In an exemplary embodiment, the predetermined SOH value corresponds to the SOH value at the end of the life cycle of the battery cell to be evaluated, in particular, 64%.

[0011] In an exemplary embodiment, the predetermined SOC value is 100%.

[0012] In an exemplary embodiment, the predetermined mode of heating is performed on the reference cell until thermal runaway occurs and corresponding reference measurement data is collected, and the relevant reference measurement data when thermal runaway occurs in the reference cell is used as the corresponding threshold.

[0013] In an exemplary embodiment, the reference cell has a SOH higher than the predetermined SOH value, in particular, more than 70%.

[0014] In an exemplary embodiment, the explosion-proof valve of the reference battery cell is in a non-opened state.

[0015] In an exemplary embodiment, the reference cell also has the predetermined SOC.

[0016] In an exemplary embodiment, after the battery cell is charged to the predetermined SOC, it is left for a predetermined time, in particular, for 6 hours, and then the heating in the predetermined mode is performed.

[0017] In an exemplary embodiment, the predetermined mode of heating is heating at a predetermined temperature increasing rate starting from a normal temperature.

[0018] In an exemplary embodiment, the predetermined heating rate is selected from the range of 0.01 to 2° C. / min, preferably 1° C. / min.

[0019] In an exemplary embodiment, the predetermined pattern of heating includes synchronous heating of the surroundings of the battery cell.

[0020] In an exemplary embodiment, the collected measurement data includes time data, temperature data and cell voltage data collected at a predetermined sampling frequency.

[0021] In an exemplary embodiment, the temperature data includes a positive pole temperature, a negative pole temperature, a bottom center temperature, an explosion-proof valve temperature, and an ambient temperature of the battery cell.

[0022] In an exemplary embodiment, the predetermined sampling frequency is 10 Hz.

[0023] In an exemplary embodiment, a sudden drop in the cell voltage is used as a sign of thermal runaway of the cell.

[0024] In an exemplary embodiment, the relevant measurement data includes the accumulated heating time when the battery cell experiences thermal runaway.

[0025] In an exemplary embodiment, the relevant measurement data includes the ambient temperature of the battery cell when thermal runaway occurs in the battery cell.

[0026] In an exemplary embodiment, the method for evaluating thermal stability of a battery cell further includes continuously collecting the measurement data after thermal runaway occurs until the temperature drops to normal temperature.

[0027] The beneficial effect of the present invention according to the above aspects of the present invention is that it is possible to provide an effective evaluation method for the thermal stability of a battery cell after the explosion-proof valve is opened, wherein the battery cell to be evaluated is heated in a predetermined mode until thermal runaway occurs, and the relevant measurement data of the battery cell to be evaluated when thermal runaway occurs is compared with a predetermined threshold value, so that the thermal runaway risk of the battery cell to be evaluated with the explosion-proof valve opened can be quantitatively evaluated, and the evaluation method has high operability and repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be described in more detail below with reference to the accompanying drawings, so that the principles, features and advantages of the present invention can be better understood. The accompanying drawings include:

[0029] Figure 1 A flow chart showing the main steps of a method for evaluating thermal stability of a battery cell according to an exemplary embodiment of the present invention;

[0030] Figure 2 A schematic diagram showing the arrangement of thermocouples on a battery cell in a method for evaluating thermal stability of a battery cell according to an exemplary embodiment of the present invention; and

[0031] Figure 3 A schematic diagram showing the installation of a mounting fixture on a battery cell in a method for evaluating thermal stability of a battery cell according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to make the technical problems, technical solutions and beneficial technical effects to be solved by the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and multiple exemplary embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the scope of protection of the present invention.

[0033] Figure 1 The flowchart schematically shows the main steps of the method for evaluating the thermal stability of a battery cell according to an exemplary embodiment of the present invention. Figure 1 As shown, a method for evaluating thermal stability of a battery cell according to an exemplary embodiment of the present invention mainly includes the following steps:

[0034] S1: Prepare a battery cell with a predetermined SOH and a predetermined SOC and an open explosion-proof valve as a battery cell to be evaluated;

[0035] S2: performing a predetermined mode of heating on the battery cell to be evaluated until thermal runaway occurs and collecting corresponding measurement data; and

[0036] S3: Compare the relevant measurement data of the battery cell to be evaluated when thermal runaway occurs with the corresponding threshold value to evaluate the thermal stability of the battery cell to be evaluated.

[0037] In step S1, the battery cell to be evaluated is particularly a battery cell that has aged to the end of its life cycle, so the predetermined SOH value corresponds to the SOH value of the battery cell at the end of its life cycle, which value varies according to the battery cell model, and is 64% here, for example. In addition, the predetermined SOC is preferably 100%, and preferably after the battery cell to be evaluated is charged to the predetermined SOC, it is left for a predetermined time to stabilize before performing step S2, and the predetermined time can be tens of minutes or hours, especially 6 hours.

[0038] In step S2, the heating in the predetermined mode is heating at a predetermined heating rate starting from normal temperature, such as room temperature, and the predetermined heating rate is selected from the range of 0.01 to 2°C / min, preferably 1°C / min. In this way, the battery cell can be heated slowly to ensure that the heating rates inside and outside the battery cell are substantially the same, so that relatively accurate temperature data can be easily collected as measurement data at various stages of the heating process.

[0039] Preferably, if Figure 2 As shown, thermocouples can be arranged at corresponding positions of the positive and negative poles, explosion-proof valve and the center of the bottom 201 of the battery cell 200 to collect the positive pole temperature T-1, explosion-proof valve temperature T-2, negative pole temperature T-3 and bottom center temperature T-4 of the battery cell 200 as temperature data during the heating process, wherein the temperature line uses, for example, a GG-K-30 temperature line probe. Of course, the temperature side measurement is not limited to the use of thermocouples, and thermistors and the like can also be used, as long as the corresponding temperature measurement can be achieved within a sufficient temperature range. In addition, the predetermined mode of heating also includes synchronous heating of the surrounding environment of the battery cell 200, and the collected temperature data also includes the surrounding environment temperature T-5 of the battery cell, so that the surrounding environment temperature T-5 when the battery cell 200 has thermal runaway can be obtained as one of the relevant measurement data.

[0040] The battery cell and its surroundings can be heated by an oven, which can be an air supply oven, a circulating hot air oven, a constant temperature oven, etc., as long as it can perform the above-mentioned predetermined mode of heating on the battery cell and its surroundings. Figure 3 As shown, the battery cell 300 is placed in the oven with the aid of a mounting fixture 310. The mounting fixture 310 is clamped on two large surfaces of the battery cell 300, and a heat insulation cotton 320 is used therebetween to protect the large surfaces of the battery cell 300 and ensure uniform heating, wherein the torque is controlled to be, for example, 8Nm.

[0041] In addition to the above-mentioned temperature data, the collected measurement data may also include time data t and cell voltage data U (as shown in Tables 1 and 2 below), wherein a sudden drop in cell voltage U is used as a sign of thermal runaway of the cell, and the accumulated heating time t when the cell voltage U suddenly drops and / or the above-mentioned cell surrounding temperature T-5 may be used as relevant measurement data when thermal runaway occurs in the cell. Here, these data are collected at a predetermined sampling frequency, and the predetermined sampling frequency is preferably 10 Hz, that is, measurement data is collected every 0.1 s, so as to obtain relatively accurate relevant measurement data.

[0042] When thermal runaway occurs in the battery cell, the temperature rise is stopped immediately, and in step S3, the relevant measurement data of the battery cell to be evaluated when thermal runaway occurs is compared with the corresponding threshold value to evaluate the thermal stability of the battery cell to be evaluated.

[0043] The thresholds described here are the relevant measurement data obtained by pre-executing the same heating procedure on the reference cell until thermal runaway. The reference cell is of the same model as the cell to be evaluated, and may be one cell or may include multiple cells with different health states. For example, it may include cells with good health states, that is, good thermal stability, and cells whose thermal stability can be accepted in actual use and have deteriorated to a certain extent. In this way, a threshold group with a certain gradient can be obtained for more comprehensive comparison and evaluation. In short, the reference cell is not at the end of its life cycle, and its SOH value is higher than the SOH value of the cell to be evaluated, especially more than 70%. In addition, the explosion-proof valves of the reference cells are all in an unopened state. In addition, the reference cell is also charged to a predetermined SOC and then left for a predetermined time before performing a predetermined mode of heating, and the arrangement of the mounting fixture and thermocouples, etc. is also the same as described above, such as Figure 2 and Figure 3 As shown, in order to obtain relevant measurement data under the same conditions.

[0044] Tables 1 and 2 below respectively show exemplary examples of partial measurement data during the heating process of an evaluated battery cell with an open explosion-proof valve at 64% SOH and a reference battery cell with an open explosion-proof valve at 70% SOH.

[0045] Table 1

[0046] t / min T-1 / ℃ T-2 / ℃ T-3 / ℃ T-4 / ℃ T-5 / ℃ U / V 164.10833 196.1 195.3 187.5 202.2 215.2 4.046 164.11000 196.0 195.1 187.5 202.2 215.2 4.045 164.11167 196.1 195.1 187.5 202.2 215.1 2.449 164.11333 195.9 195.0 187.5 202.1 214.9 0.414

[0047] Table 2

[0048] t / min T-1 / ℃ T-2 / ℃ T-3 / ℃ T-4 / ℃ T-5 / ℃ U / V 153.74166 169.7 174.5 169.5 165.2 173.7 4.112 152.74333 169.7 174.5 169.5 165.2 173.7 4.112 153.74500 169.7 174.5 169.6 165.1 173.7 4.112 153.74666 169.7 174.5 169.6 165.0 173.7 0.354

[0049] In this example, as shown in Table 1, the cell voltage U of the cell to be evaluated with an open explosion-proof valve at 64% SOH suddenly drops when heated to 164 minutes, indicating that thermal runaway occurs. At this time, the ambient temperature T-5 around the cell is about 215°C.

[0050] In contrast, as shown in Table 2, the cell voltage U of the reference cell with 70% SOH and the explosion-proof valve not opened suddenly dropped when heated to nearly 154 minutes, that is, thermal runaway occurred. At this time, the ambient temperature T-5 around the cell was lower than 174°C.

[0051] It can be seen that in this evaluation example, the battery cell to be evaluated experienced thermal runaway at a higher ambient temperature (215°C) after being heated for a longer time (164 minutes). Therefore, it can be considered that the thermal stability of the battery cell to be evaluated has not decreased, that is, the thermal runaway risk of the battery cell with open explosion-proof valves at the end of its life cycle has not increased, and these relevant measurement data can be used for subsequent theoretical analysis.

[0052] In addition, after the battery cell experiences thermal runaway and stops heating, the measurement data may continue to be collected until the temperature returns to room temperature, so as to obtain more data for related theoretical analysis.

[0053] The method for evaluating the thermal stability of a battery cell of the present invention is not limited to evaluating a battery cell with 100% SOC at the end of its life cycle with an explosion-proof valve open, but can be used to evaluate batteries with various degrees of degradation, explosion-proof valve opening states, and various SOCs. In addition, in addition to different degrees of degradation, the reference battery cell may also include batteries with different explosion-proof valve states and batteries with different SOCs. In summary, various reference batteries can be used as needed to obtain corresponding threshold data, and various batteries to be evaluated can be evaluated by comparison with the threshold.

[0054] Although specific embodiments of the present invention are described in detail herein, they are provided for the purpose of explanation only and should not be considered to limit the scope of the present invention. Various substitutions, changes and modifications may be conceived without departing from the spirit and scope of the present invention.

Claims

1. A method for evaluating thermal stability of a battery cell, comprising: Preparing a battery cell with a predetermined SOH and a predetermined SOC and an open explosion-proof valve as a battery cell to be evaluated; Heating the battery cell to be evaluated in a predetermined mode until thermal runaway occurs and collecting corresponding measurement data; and Compare the relevant measurement data of the battery cell to be evaluated when thermal runaway occurs with the corresponding threshold value to evaluate the thermal stability of the battery cell to be evaluated.

2. The method for evaluating thermal stability of a battery cell according to claim 1, wherein: The predetermined SOH value corresponds to the SOH value at the end of the life cycle of the battery cell to be evaluated, in particular 64%; and / or The predetermined SOC value is 100%.

3. The method for evaluating thermal stability of a battery cell according to claim 1 or 2, wherein: The predetermined mode of heating is performed on the reference cell until thermal runaway occurs and corresponding reference measurement data is collected, and the relevant reference measurement data when thermal runaway occurs in the reference cell is used as the corresponding threshold value.

4. The method for evaluating thermal stability of a battery cell according to claim 3, wherein: The reference cell has a SOH higher than the predetermined SOH value, in particular, greater than 70%; The explosion-proof valve of the reference battery cell is in an unopened state; and / or The reference cell also has the predetermined SOC.

5. The method for evaluating thermal stability of a battery cell according to any one of claims 1 to 4, wherein: After charging the battery cell to the predetermined SOC, leaving it for a predetermined time, in particular for 6 hours, and then performing the heating in the predetermined mode; and / or The heating in the predetermined mode is heating at a predetermined temperature increase rate starting from room temperature.

6. The method for evaluating thermal stability of a battery cell according to claim 5, wherein: The predetermined heating rate is selected from the range of 0.01 to 2°C / min, preferably 1°C / min; and / or The predetermined pattern of heating includes synchronous heating of the surroundings of the battery cell.

7. The method for evaluating thermal stability of a battery cell according to any one of claims 1 to 6, wherein: The collected measurement data includes time data, temperature data and cell voltage data collected at a predetermined sampling frequency.

8. The method for evaluating thermal stability of a battery cell according to claim 7, wherein: The temperature data includes the positive pole temperature, the negative pole temperature, the bottom center temperature, the explosion-proof valve temperature and the ambient temperature of the battery cell; and / or The predetermined sampling frequency is 10 Hz.

9. The method for evaluating thermal stability of a battery cell according to claim 7 or 8, wherein: The sudden drop of cell voltage is used as a sign of thermal runaway of the cell; The relevant measurement data includes the cumulative heating time when the battery cell experiences thermal runaway; and / or The relevant measurement data includes the ambient temperature of the battery cell when thermal runaway occurs in the battery cell.

10. The method for evaluating thermal stability of a battery cell according to any one of claims 1 to 9, further comprising: The measurement data is continuously collected after thermal runaway occurs until the temperature drops to normal temperature.

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