Method for judging battery life consistency through DC internal resistance DCR

Abstract

The invention discloses a method for judging battery life consistency through direct current internal resistance DCR, and belongs to the technical field of batteries, direct current internal resistance DCR data of the same group of batteries in different temperature environments and different SOC states are tested, and the method is characterized by comprising the following specific steps: 1) testing normal temperature direct current internal resistance DCR; 2) testing low-temperature direct-current internal resistance DCR; and 3) comparing the DCR data of different electric quantities at different temperatures to perform advantage and disadvantage screening and pre-judgment on the cycle performance of the battery cell, the lower the temperature is, the more obvious the difference of the DC internal resistance of the battery is, and the longer the cycle life of the battery is, the larger the DCR data change at the low temperature is. And related problems of service life, pressure difference, temperature difference and the like generated after the battery pack is packaged in the truck are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a method for determining the consistency of battery life by using a direct current internal resistance (DCR). Background Art

[0002] Since its advent, lithium batteries have been widely used in electronic products, aerospace, electric vehicles and other equipment due to their excellent electrochemical properties. In modern electric vehicles and energy storage systems, lithium batteries are important components for energy storage and release, and their consistency has a vital impact on the performance and life of the entire system. However, due to many reasons, there will be some differences in the production process of lithium batteries, such as differences in chemical composition, electrochemical properties, mechanical structure, etc., resulting in inconsistent parameters such as capacity, internal resistance, and voltage within the same batch of batteries or even within the same battery pack. Battery life consistency refers to the consistency of performance degradation of each single cell in the battery pack during charging and discharging. Battery life consistency is crucial to improving the overall performance and reliability of the battery pack. Inconsistent battery life will cause some batteries to fail prematurely, affecting the performance and life of the entire battery pack. Lithium battery life consistency determination is mainly used in electric vehicles, energy storage systems and other fields, and plays an important role in ensuring system performance, safe use and improving battery life. By evaluating and optimizing the internal consistency of the battery pack, the battery life can be extended, the efficiency and stability of the entire system can be improved, and maintenance costs and risks can be reduced. It has broad market prospects and application value. Summary of the invention

[0003] In view of the shortcomings of the prior art, the present invention provides a method for determining the consistency of battery life by using the DC internal resistance DCR. The method has the advantages of better screening the consistency of the life of single cells and reducing the problems related to the service life, pressure difference, temperature difference, etc. generated after the battery pack is packaged in the vehicle. The specific steps are as follows: 1) Test the DC internal resistance DCR at room temperature; 2) Test low temperature DC internal resistance DCR; 3) Compare the DCR data of different capacities at different temperatures to screen and predict the cycling performance of the battery cells. The lower the temperature, the more obvious the difference in the DC internal resistance of the battery. The greater the change in DCR data at low temperatures, the worse the cycle life of the battery.

[0004] Preferably, the low temperature is -20°C.

[0005] Preferably, the method for testing the room temperature DC internal resistance DCR in step 1) is: a The battery is charged and discharged in a standard way at room temperature to adjust the SOC state according to the capacity; b. Perform a 3C pulse discharge test on the battery at room temperature, collect the voltage and current changes during the 3C pulse discharge from the full-charge state to the empty state, and calculate the battery's room-temperature DCR by testing the voltage and current generated by the high-current discharge.

[0006] Preferably, the method for testing the low temperature DC internal resistance DCR in step 2) is: a The same group of batteries are fully charged in a conventional manner at room temperature, and then discharged after being placed in a low temperature environment of -20°C for ≥24 hours. The low temperature discharge capacity is collected, and the low temperature SOC state is adjusted at low temperature according to this capacity; b. Perform a 3C pulse discharge test on the battery in a low temperature environment, collect the voltage and current changes of the battery during the 3C pulse discharge from a fully charged state to an empty state, and calculate the low temperature DCR of the battery by testing the voltage and current generated by the large current discharge.

[0007] Preferably, the 3C pulse discharge test conditions are: test time 30S, test interval 10%SOC, and data interval 1s.

[0008] Compared with the prior art, the present invention has the following advantages: The method of the present invention is suitable for determining the consistency of battery life, providing data guarantee for the consistency of battery packs in a whole vehicle, which is beneficial to the overall design and application of battery packs in a whole vehicle, improving the battery utilization efficiency and pack production efficiency, and greatly reducing the failure frequency of battery packs in a whole vehicle. The method of the present invention can better screen the consistency of the life of single cells, and reduce the service life, pressure difference, temperature difference and other related problems generated after the battery pack is packaged in the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a DCR test curve diagram generated by the high current discharge of the battery in Example 1 at room temperature 25°C; Figure 2 The DCR curve of the battery in Example 1 at room temperature 25°C; Figure 3 The DCR curve of the battery in Example 1 at low temperature of -20°C; Figure 4 It is the cycle life curve of the battery in Example 1 at room temperature 25°C. DETAILED DESCRIPTION

[0010] The technical solution of the present invention is clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example

[0011] A method for determining battery life consistency by DC internal resistance DCR, the specific steps are as follows: 1) Test the DC internal resistance DCR at room temperature: a The battery is charged and discharged in a standard way at room temperature to adjust the SOC state according to the capacity; b. The battery is subjected to a 3C pulse discharge test for 30 seconds at room temperature, with a test interval of 10% SOC and a data interval of 1 second. The voltage and current changes of the battery during the 3C pulse discharge from full to empty state are collected. The voltage generated by the high current discharge is tested. Figure 1 The battery DCR at room temperature is calculated by the current. Figure 2 ; 2) Test the DC internal resistance DCR at -20℃: a The same group of batteries are fully charged in a conventional manner at room temperature, and then discharged after being placed in a low temperature environment of -20°C for ≥24 hours. The low temperature discharge capacity is collected, and the low temperature SOC state is adjusted at low temperature according to this capacity; b. Perform a 3C pulse discharge test on the battery for 30 seconds in a low temperature environment. The test interval is 10% SOC and the data interval is 1 second. The voltage and current changes of the battery during the 3C pulse discharge from full power to empty power are collected. The battery low temperature DCR is calculated by testing the voltage and current generated by high current discharge. Figure 3 ; 3) Compare the DCR data of different capacities at different temperatures to screen and predict the cycling performance of the battery cells. The lower the temperature, the more obvious the difference in the DC internal resistance of the battery. The greater the change in DCR data at low temperature of -20°C, the worse the cycle life of the battery.

[0012] Cycle Verification The four batteries tested in the above embodiment were subjected to cycle testing in the same manner; Cycle verification method: 0.5C / 1C cycle at room temperature 25℃; Cyclic charging mode: 0.5C CCCV 4.2V, cut-off current 0.1C; Cyclic discharge mode: 1C DC 2.75CV; Charge and discharge interval time: 15min; Cycle life curve Figure 4 .

[0013] Conclusion: Combining the DCR data at room temperature and low temperature -20℃ with the cycle data, the DCR of the four batteries at room temperature is basically the same, but the DCR at low temperature -20℃ is quite different, mainly in two aspects: 1. The DCR value at low temperature of -20℃ reflects the battery life.

[0014] Batteries with small 3C discharge DCR values ​​at low temperature of -20℃ have longer cycle life. For example, the low temperature DCR of 2# and 3# batteries is smaller than that of the other two batteries as a whole, and their life is also the longest among the four batteries. The second is 1# battery, whose DCR value at low temperature of -20℃ is in the middle, and its life is also in the middle; the worst cycle is 4# battery, which has the largest DCR at low temperature of -20℃.

[0015] 2. The difference in DCR data at low temperature of -20°C reflects the difference in battery cycle life trends.

[0016] From above Figure 3 It can be observed that the DCR values ​​of 2# and 3# batteries at room temperature and at low temperature of -20℃ are the closest among the four batteries, so the consistency of their cycle life is also the best. There are differences in DCR at low temperature of -20℃ between 1# battery, 2# battery and 3# battery, so the cycle life is slightly worse. The DCR difference of 4# battery at low temperature of -20℃ is the largest, so its cycle life is also the worst.

[0017] The above descriptions are merely embodiments of the present invention. It should be pointed out that, for those skilled in the art, various changes, modifications, substitutions and variations can be made to these embodiments without departing from the technical principles of the present invention. These changes, modifications, substitutions and variations should also be regarded as the scope of protection of the present invention.

Claims

1. A method for determining battery life consistency by DC internal resistance DCR, by testing DC internal resistance DCR data of the same group of batteries in different SOC states under different temperature environments, characterized in that: The specific steps are as follows: 1) Test the DC internal resistance DCR at room temperature; 2) Test low temperature DC internal resistance DCR; 3) Compare the DCR data of different capacities at different temperatures to screen and predict the cycling performance of the battery cells. The lower the temperature, the more obvious the difference in the DC internal resistance of the battery. The greater the change in DCR data at low temperatures, the worse the cycle life of the battery.

2. The method for determining battery life consistency by direct current internal resistance DCR according to claim 1, characterized in that: The low temperature is -20°C.

3. The method for determining battery life consistency by direct current internal resistance DCR according to claim 1, characterized in that: The method for testing the DC internal resistance DCR at room temperature in step 1) is as follows: a The battery is charged and discharged in a standard way at room temperature to adjust the SOC state according to the capacity; b. Perform a 3C pulse discharge test on the battery at room temperature, collect the voltage and current changes during the 3C pulse discharge from the full-charge state to the empty state, and calculate the battery's room-temperature DCR by testing the voltage and current generated by the high-current discharge.

4. The method for determining battery life consistency by direct current internal resistance DCR according to claim 1, characterized in that: The method for testing the low temperature DC internal resistance DCR in step 2) is: a The same group of batteries are fully charged in a conventional manner at room temperature, and then discharged after being placed in a low temperature environment of -20°C for ≥24 hours. The low temperature discharge capacity is collected, and the low temperature SOC state is adjusted at low temperature according to this capacity; b. Perform a 3C pulse discharge test on the battery in a low temperature environment, collect the voltage and current changes of the battery during the 3C pulse discharge from a fully charged state to an empty state, and calculate the low temperature DCR of the battery by testing the voltage and current generated by the large current discharge.

5. A method for determining battery life consistency by direct current internal resistance DCR according to claim 3 or 4, characterized in that: The 3C pulse discharge test conditions are as follows: a test time of 30 seconds, a test interval of 10% SOC, and a data interval of 1 second.

Images