A Lifetime Durability Testing Method for Lithium-ion Batteries Based on Stepped Charging

Abstract

This invention discloses a lithium-ion battery lifespan durability testing method based on stepped charging, belonging to the field of lithium-ion battery lifespan durability testing technology. The method includes: selecting multiple identical lithium-ion batteries as parallel test samples; conducting operating condition tests on the parallel test samples; performing data analysis based on the operating condition test results to obtain multiple battery lifespan durability testing methods based on different stepped charging methods; testing each parallel test sample using multiple methods to obtain lifespan durability test results, and simultaneously obtaining EIS test data for each parallel test sample before and after the lifespan durability test; determining the optimal lifespan durability testing method based on the operating condition test results, lifespan durability test results, and EIS test data, and using this optimal lifespan durability testing method to conduct lifespan durability tests on other identical lithium-ion batteries. The method described in this invention can more accurately determine the lifespan durability of lithium-ion batteries while meeting the requirements of fast charging.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery life durability testing technology, and in particular to a lithium-ion battery life durability testing method based on stepped charging. Background Technology

[0002] Lithium-ion batteries, as a new generation of green, high-energy rechargeable batteries, possess advantages such as high energy density, high voltage stability, long cycle life, no memory effect, wide operating temperature range, light weight, and no environmental harm. They meet current requirements for energy efficiency and cleanliness and are widely used in portable electronic devices, electric vehicles, aerospace, and other fields. Like other types of battery systems, lithium-ion batteries also have a lifespan issue. Testing and obtaining the cycle life of lithium-ion batteries will effectively improve battery quality and greatly contribute to their development.

[0003] Traditional lithium-ion battery lifespan testing methods involve charging and discharging batteries from the same batch. The lifespan of the batch is determined by the number of cycles required for the discharge capacity to decrease to 80% of the initial discharge capacity (or other specified value). Currently, the primary charging method used in lithium-ion battery applications and testing is constant current-constant voltage (CC-CV) charging, which is simple, easy to implement, and convenient. However, with the increasing demand for fast charging of lithium-ion batteries, the limitations of this method are becoming more apparent. In particular, high-current constant current-constant voltage charging directly affects battery lifespan, and the potential risks of high-current constant current-constant voltage charging increase significantly after a certain period of use. Therefore, other charging methods can be used for lithium-ion battery lifespan testing, such as stepped charging (MSCC) and pulse charging (PC). Among them, stepped charging involves multiple CC-CV segments. The selection of segments needs to be determined based on the basic charging properties of the battery. However, the charging process of lithium-ion batteries involves complex phase transitions of positive and negative electrode materials, interfacial electrochemical reactions, polarization, and irreversible reactions, making the selection of segments difficult and making it impossible to obtain optimal test conditions. The pulse charging mode is mainly characterized by periodic changes in the magnitude and direction of the charging current. This charging mode is relatively more complex to operate and requires high response accuracy from the equipment.

[0004] In other words, the above-mentioned method for testing the lifespan of lithium-ion batteries using existing charging systems still has certain drawbacks. On the one hand, the existing testing method cannot meet the current demand for fast charging of lithium-ion batteries, resulting in low battery charging efficiency. On the other hand, considering that the capacity retention rate of batteries varies under different charging conditions, the existing method cannot guarantee the optimal lifespan of the battery during the test, which leads to a certain deviation between the final test results and the actual situation. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a lithium-ion battery lifespan durability testing method based on stepped charging. This method acquires various test data through operating condition testing, lifespan durability testing, and EIS (Electrochemical Impedance Spectroscopy) testing. Based on data analysis from different dimensions, it explores the differences in capacity retention under different stepped charging conditions, thereby determining the optimal testing method. This optimal method is then used to conduct lithium-ion battery lifespan durability testing. This method can improve the battery's capacity retention during stepped charging while meeting the requirements of fast charging, ensuring optimal lithium-ion battery lifespan and enabling more accurate assessment of lithium-ion battery lifespan durability.

[0006] This invention provides a method for testing the lifespan and durability of lithium-ion batteries based on stepped charging, comprising:

[0007] Multiple identical lithium-ion batteries were selected as parallel test samples.

[0008] Operating condition tests were conducted on the parallel test samples;

[0009] Based on the test results, data analysis was conducted to obtain various battery life and durability testing methods based on different step charging methods.

[0010] Based on multiple battery life and durability testing methods, each parallel test sample is tested to obtain life and durability test results. At the same time, EIS test is conducted to obtain EIS test data for each parallel test sample before and after the life and durability test.

[0011] Based on the results of operating condition tests, lifespan and durability tests, and EIS test data, the optimal lifespan and durability test method is determined, and this optimal lifespan and durability test method is used to conduct lifespan and durability tests on other identical lithium-ion batteries.

[0012] A further technical solution is that the operating condition test includes a capacity calibration test, a rate charging test, and a DC internal resistance test performed sequentially.

[0013] Further technical solutions include conducting operational condition tests on parallel test samples, including:

[0014] The calibrated capacity of each parallel test sample is obtained through capacity calibration testing.

[0015] At room temperature, rate charging tests were performed on all parallel test samples to obtain the electrical performance data and dV / dQ curves of each cell at different charging rates, thereby determining the charging rate selected for different dV / dQ stages.

[0016] At room temperature, DC internal resistance tests were performed on each parallel test sample at different charging rates to obtain DCIR data for each cell during charging, thereby determining the selected charging rate for different SOCs.

[0017] Further technical solutions employ multiple battery life durability testing methods based on different step charging methods and a battery life durability testing method based on 1C constant current room temperature charging to test each parallel test sample.

[0018] Among them, the test methods for various room temperature stepped charging and 1C constant current room temperature charging all include a sequential process of rest-constant current discharge-rest-constant current charging-rest-constant current discharge, as well as a repeated process of rest-characteristic charging-rest-constant current discharge multiple times.

[0019] Further technical solutions involve different characteristic charging processes for different testing methods: in the 1C constant current room temperature charging test method, the characteristic charging adopts constant current and constant voltage charging; in the different room temperature stepped charging test methods, the characteristic charging adopts stepped constant current and constant voltage charging with different charging rate sequences and different charging time.

[0020] In a further technical solution, during the characteristic charging process of the optimal lifespan durability test method, a small-rate constant current charging is first used, followed by a large-rate constant current charging, and the charging rate of the constant current charging is gradually reduced in a stepwise manner over time.

[0021] The above one or more technical solutions have the following beneficial effects:

[0022] 1. This invention provides a lithium-ion battery lifespan durability testing method based on stepped charging. By conducting operating condition tests and lifespan durability tests on the lithium-ion battery, electrical performance test results are obtained. Before and after the lifespan durability test, an electrochemical workstation is used to scan the EIS (Electrochemical Indication Sequence) to obtain EIS test results. Through data analysis from different dimensions, the differences in capacity retention rate of lithium-ion batteries under different stepped charging conditions are explored, thereby determining and verifying the optimal testing method. Using this optimal testing method for lithium-ion battery lifespan durability testing can improve the capacity retention rate of the battery during stepped charging while meeting the requirements of fast charging, ensuring that the lithium-ion battery lifespan reaches its optimal level. This allows for a more accurate assessment of the lifespan durability of lithium-ion batteries and provides guidance for optimizing battery testing methods and extending battery lifespan durability.

[0023] 2. Compared with existing testing methods, this invention provides a lithium-ion battery life durability testing method based on stepped charging. By combining operating condition testing, long-term life durability testing, and EIS testing, the battery life durability testing method is optimized, which can better and more accurately determine the life of lithium-ion batteries. This stepped charging-based testing method is simple, fast, and accurate to operate. It can not only ensure the life durability performance of lithium-ion batteries, but also improve the charging efficiency of batteries in a targeted manner, and can achieve fast charging in about 20 minutes. It has high practical application value in the fast charging of lithium-ion batteries. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0025] Figure 1 This is a flowchart of the lithium-ion battery life durability testing method based on stepped charging as described in an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the dV / dQ curves of the battery cell at different charging rates in an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the DCIR curves of the battery cell at different charging rates in an embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram comparing the results of battery life durability tests using different charging methods in an embodiment of the present invention.

[0029] Figure 5 This is a schematic diagram comparing EIS data before and after battery life durability testing using different charging methods in an embodiment of the present invention. Detailed Implementation

[0030] It should be noted that the following detailed descriptions are exemplary and are intended only to describe specific embodiments and to provide further explanation of the invention, and are not intended to limit the scope of exemplary embodiments of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0031] Example 1

[0032] Considering the complex phase transitions of positive and negative electrode materials, interfacial electrochemical reactions, polarization, and irreversible reactions involved in lithium-ion battery charging, and based on the battery's CC-CV charging voltage-capacity curve, it is evident that during the constant current charging stage, the battery capacity does not increase linearly with the charging voltage. Instead, it exhibits different charging voltage variations at different states of charge (SOC). This characteristic is determined by the positive and negative electrode materials and the battery design. Based on the above analysis, this embodiment, according to the charging properties of lithium-ion batteries and the phase transition characteristics of battery materials, formulates a stepped charging regime to improve battery charging efficiency while ensuring battery lifespan. Specifically, this embodiment provides a lithium-ion battery lifespan durability testing method based on stepped charging, such as... Figure 1 As shown, the method includes:

[0033] Multiple identical lithium-ion batteries were selected as parallel test samples.

[0034] Operating condition tests were conducted on the parallel test samples;

[0035] Based on the test results, data analysis was conducted to obtain various battery life and durability testing methods based on different step charging methods.

[0036] Based on multiple battery life and durability testing methods, each parallel test sample is tested to obtain life and durability test results. At the same time, EIS test is conducted to obtain EIS test data for each parallel test sample before and after the life and durability test.

[0037] Based on the results of operating condition tests, lifespan and durability tests, and EIS test data, the optimal lifespan and durability test method is determined, and this optimal lifespan and durability test method is used to conduct lifespan and durability tests on other identical lithium-ion batteries.

[0038] The following content provides a more detailed description of the lithium-ion battery life durability testing method based on stepped charging proposed in this embodiment.

[0039] Step S1: Select multiple identical lithium-ion batteries as parallel test samples. In this embodiment, eight 3Ah soft-pack lithium iron phosphate battery parallel samples were selected, and their basic performance before storage was measured. They were named 1-8# sequentially.

[0040] Step S2: Perform operating condition tests on the parallel test samples, which include capacity calibration test, rate charging test and DC internal resistance (DCIR) test performed sequentially.

[0041] Step S2.1, Capacity Calibration Test. The capacity calibration test is performed on each battery cell used as a parallel test sample to obtain the calibrated capacity of each cell. This calibrated capacity is then used to conduct other operating condition tests.

[0042] Step S2.2, Rate Charging Test. At room temperature (25℃), rate charging tests are performed on all parallel test samples to obtain the electrical performance data and dV / dQ curves of each cell at different charging rates, thereby determining the charging rate selected for different dV / dQ stages.

[0043] Specifically, all battery cells were tested at 25°C to obtain electrical performance data at different rates (including 0.2C, 0.4C, 0.6C, 0.8C, 1C, 1.2C, 1.4C, 1.6C, 1.8C, and 2.0C). This electrical performance data includes total charging time, total charging capacity, constant current time, constant voltage time, 80% SOC capacity, 80% SOC time, 80% SOC voltage, 80% SOC current, constant current capacity, constant voltage capacity, and constant current capacity ratio. The constant current capacity ratio refers to the ratio of constant current charging capacity to the total battery capacity. This parameter is a key value for measuring the charging efficiency of a group of batteries. Generally, the higher the percentage, the higher the amount of electricity charged during the constant current stage, which proves that the battery has higher charging efficiency. SOC (State of Charge) refers to the battery's state of charge, indicating the current state of charge or remaining capacity of the battery. It reflects the proportion of electrical energy stored in the battery to its maximum storable electrical energy. For example, a 3Ah battery cell has a 100% SOC when its current capacity is 3Ah, and similarly, a 3Ah battery cell has a 50% SOC when its current capacity is 1.5Ah.

[0044] The obtained cell rate charging performance data are shown in Table 1 below. The constant current capacity ratio of the cell reaches 79.97%, 80.57%, and 79.93% at 1.6C, 1.8C, and 2.0C, respectively. The cell rate charging performance is excellent at these times. In addition, considering that the instantaneous voltage of 80% SOC at 1.8C is 3.515V, which is very close to the cell's charging cutoff voltage, the 1.8C constant current and constant voltage charging mode can be used to achieve the fast charging target of 80% SOC in 30 minutes.

[0045] Table 1. Electrical performance data of battery cells at different charging rates.

[0046]

[0047] Furthermore, the phase transitions of the positive and negative electrodes of a lithium-ion battery during charging and discharging can be analyzed based on the dV / dQ curves of the full cell. Specifically, by selecting one cell and processing its electrical performance data at different charging rates using a differential method, the following can be obtained: Figure 2The diagram shows the dV / dQ curves of the battery cell at different charging rates. The dV / dQ curve is crucial data for analyzing the overall performance and suitability of a battery. This graph plots the differential potential dQ relative to the differential voltage dV, providing insight into the electrochemical processes occurring within the battery cell during charge and discharge cycles. The dV / dQ curve chart is generated by separating capacity from voltage, as the battery undergoes charge and discharge cycles. Here, dQ represents a small adjustment in the rate potential, and dV represents a small change in voltage.

[0048] Combination Figure 2 Analysis shows that the characteristic peaks in the dV / dQ curve mainly reflect the phase transitions of the positive and negative electrode active materials during lithium delithiation and lithium insertion. Taking the dV / dQ curve at 0.4C charging as an example, characteristic peak 1 (around 0 Ah) mainly reflects the initial phase transition of the overall positive and negative electrode materials, while characteristic peak 2 (around 2.8 Ah) is determined by both positive and negative electrode materials. As the charging rate increases, the phase transitions of the positive and negative electrode materials occur earlier, resulting in a multiphase coexistence phenomenon, manifested as some phase transition peaks shifting to the left or even disappearing. First, assuming that the positive electrode experiences uniform loss of active material during the battery's lifespan, meaning that the active material mass of the positive electrode becomes less after decay, the positive electrode potential will rise to a higher voltage when charging with the same amount of charge. This leads to a steeper slope in the positive electrode charging curve, causing the battery to reach the charging cutoff voltage at a lower capacity, indirectly affecting the lifespan of the battery cell.

[0049] In summary, to achieve the fast charging target of 80% SOC in 30 minutes while avoiding potential lithium plating risks, the initial charging step determines the SOC with a significant phase transition peak. In this step, considering that changes in the phase transition peak can reflect the usage of the positive and negative electrode materials, the presence of lithium plating can be distinguished by the phase transition peak. Therefore, this embodiment determines the changes in the phase transition peak at different rates based on the relationship between the phase transition peak and SOC, thereby selecting the SOC with a significant phase transition peak. This phase transition peak is also one of the factors considered in determining the step charging method; simultaneously, combined with... Figure 2 As shown in the dV / dQ curve, the dV / dQ curve changes with the SOC at different SOC states. This dV / dQ curve is also one of the factors considered in determining the stepped charging method. In this embodiment, different charging rates are selected for different dV / dQ stages, including: using the absolute value of dV / dQ as the basis for the stepped charging rate; selecting a high charging rate for the range where the absolute value of dV / dQ is relatively small, and selecting a low charging rate for the range where the absolute value of dV / dQ is relatively large; wherein the high rates include 1.6C, 1.8C, and 2.0C, and the low rates include 0.4C, 0.6C, and 0.8C. Through the above method, the stepped charging method is determined based on the phase transition peak and the dV / dQ curve.

[0050] Step S2.3, DCIR Test. At room temperature (25℃), the DC internal resistance of each parallel test sample is tested at different charging rates to obtain the DCIR data for each cell, thereby determining the selected charging rate for different states of charge (SOC). The DCIR data includes DCIR values ​​at different charging rates and different SOCs.

[0051] Specifically, based on the test results of step S2.2 above, the data from the rate charging shows that the constant current capacity of the battery cells is relatively high at 1.6C, 1.8C, and 2.0C. DCIR tests were performed on all battery cells at different rates, and the test data are shown in Table 2 below. For simplicity, this embodiment selects the DCIR data of cells #2, #3, and #5 to plot a line graph, as shown below. Figure 3 As shown.

[0052] Based on Table 2 below, combined with Figure 3 The shown DCIR curves for the battery cells indicate that cells (#2,#3,#5) exhibit higher DCIR at low SOC states, especially exceeding 40mΩ at 0% SOC, and ≥23mΩ between 0% and 5% SOC. As the SOC increases, the DCIR gradually decreases. From the perspective of DCIR, using a lower charging rate in the 0-5% SOC range effectively reduces energy loss. Furthermore, the DCIR gradually increases between 70% and 90% SOC; similarly, gradually reducing the charging rate during this range effectively minimizes energy loss.

[0053] Table 2 DCIR test results of battery cells at different charging rates

[0054]

[0055] In summary, different charging rates should be selected for different SOCs, including: using SOC as the basis for step-by-step charging rates, selecting a relatively smaller charging rate when the SOC is 0-5%, and selecting a relatively larger charging rate when the SOC is 70%-90%, and gradually decreasing the test rate; among them, the large rates include 1.6C, 1.8C, and 2.0C, and the small rates include 0.4C, 0.6C, and 0.8C.

[0056] Step S3: Analyze the data based on the working condition test results to obtain various battery life durability test methods based on different step charging methods.

[0057] Step S4: Based on multiple battery life durability testing methods, each parallel test sample is tested simultaneously at room temperature of 25°C to obtain life durability test results. At the same time, EIS test is conducted to obtain the EIS test data and EIS changes of each parallel test sample before and after the life durability test.

[0058] Specifically, this embodiment sets up three battery life durability testing methods, namely, multiple battery life durability testing methods based on different stepped charging methods, including the first, second, and third room temperature stepped charging battery life durability testing methods. The first, second, and third room temperature stepped charging battery life durability testing methods and the 1C constant current room temperature charging battery life durability testing method are used to test each parallel test sample.

[0059] Furthermore, various test methods for room temperature stepped charging and 1C constant current room temperature charging all include a sequential process of rest-constant current discharge-rest-constant current charging-rest-constant current discharge, followed by multiple cycles of rest-characteristic charging-rest-constant current discharge. Different test methods employ different characteristic charging processes: in the 1C constant current room temperature charging test method, characteristic charging uses constant current and constant voltage charging; in different room temperature stepped charging test methods, characteristic charging uses stepped constant current and constant voltage charging with different charging rate sequences and different charging times.

[0060] Specifically, the characteristic charging processes of the above-mentioned different test methods are as follows:

[0061] For the life durability test method of 1C constant current room temperature rechargeable battery, 1C constant current charging to 3.65V, constant voltage charging to 0.05C;

[0062] For the first-stage rechargeable battery life durability test method at room temperature, the following steps were performed: 1C constant current discharge to 2.5V; rest for 30 minutes; 0.8C constant current charging to 3.65V, charging time 5.25 minutes; 1.8C constant current charging to 3.65V, charging time 19.33 minutes; 1.6C constant current charging to 3.65V, charging time 5.63 minutes; 0.6C constant current charging to 3.65V, charging time 15 minutes; 0.4C constant current charging to 3.65V; and constant voltage charging to 0.05C.

[0063] For the second-stage rechargeable battery life durability test method at room temperature, the following steps were performed: 1C constant current discharge to 2.5V; rest for 30 minutes; 0.8C constant current charging to 3.65V, charging time 5.25 minutes; 2.0C constant current charging to 3.65V, charging time 6.9 minutes; 1.8C constant current charging to 3.65V, charging time 13.33 minutes; 1.6C constant current charging to 3.65V, charging time 3.75 minutes; 0.6C constant current charging to 3.65V, charging time 15 minutes; 0.4C constant current charging to 3.65V; and constant voltage charging to 0.05C.

[0064] For the third-stage rechargeable battery life durability test method at room temperature, the following steps were performed: 1C constant current discharge to 2.5V; rest for 30 minutes; 0.8C constant current charging to 3.65V, charging time 5.25 minutes; 2.0C constant current charging to 3.65V, charging time 11.4 minutes; 1.8C constant current charging to 3.65V, charging time 8.33 minutes; 1.6C constant current charging to 3.65V, charging time 3.75 minutes; 0.6C constant current charging to 3.65V, charging time 15 minutes; 0.4C constant current charging to 3.65V; and constant voltage charging to 0.05C.

[0065] In this embodiment, the following lifespan durability test procedure is used for specific testing:

[0066] (1) 1C constant current room temperature rechargeable battery life durability test, i.e., room temperature life durability 1C / 1C

[0067] 1. Take two 3.Ah soft-pack lithium iron phosphate batteries, #1 and #2;

[0068] 2. Let stand at room temperature for 2 hours;

[0069] 3. Discharge at a constant current of 0.05C to 2.5V;

[0070] 4. Let stand for 5 minutes;

[0071] 5. Charge at 1C constant current to 3.65V for 30 minutes;

[0072] 6. Let stand for 1 hour;

[0073] 7. Discharge at 1C constant current to 2.5V for 10 seconds;

[0074] 8. Let stand for 30 minutes;

[0075] 9. Charge at 1C constant current to 3.65V, then charge at 0.05C constant voltage:

[0076] 10. Let stand for 30 minutes;

[0077] 11. Discharge at a constant current of 1C to 2.5V;

[0078] 12. Let stand for 30 minutes;

[0079] 13. Perform steps 9-12 for a lifespan of 2000 cycles.

[0080] (2) First-stage rechargeable battery life durability test at room temperature, i.e., room temperature staged life durability 1: 25℃ staged charging 1

[0081] 1. Take two 3.Ah soft-pack lithium iron phosphate batteries, one #3 and one #4;

[0082] 2. Let stand at room temperature for 2 hours;

[0083] 3. Discharge at a constant current of 0.05C to 2.5V;

[0084] 4. Let stand for 5 minutes;

[0085] 5. Charge at 1C constant current to 3.65V for 30 minutes;

[0086] 6. Let stand for 1 hour;

[0087] 7. Discharge at 1C constant current to 2.5V for 10 seconds;

[0088] 8. Let stand for 30 minutes;

[0089] 9. Discharge at a constant current of 1C to 2.5V;

[0090] 10. Let stand for 30 minutes;

[0091] 11. 0.8C constant current charging at 3.65V for 5.25 minutes;

[0092] 12. 1.8C constant current charging at 3.65V for 19.33 minutes;

[0093] 13. 1.6C constant current charging at 3.65V for 5.63 minutes;

[0094] 14. 0.6C constant current charging at 3.65V for 15 minutes;

[0095] 15. Charge at a constant current of 0.4C to 3.65V, and charge at a constant voltage of 0.05C.

[0096] 16. Let stand for 30 minutes;

[0097] 17. Discharge at a constant current of 1C to 2.5V;

[0098] 18. Let stand for 30 minutes;

[0099] 19. Perform steps 11-18 for a lifespan of 2000 cycles.

[0100] (3) Second ambient temperature stepped charging battery life durability test, i.e., ambient temperature stepped life durability 2: 25℃ stepped charging 2

[0101] 1. Take two 3.Ah soft-pack lithium iron phosphate batteries, one #5 and one #6;

[0102] 2. Let stand at room temperature for 2 hours;

[0103] 3. Discharge at a constant current of 0.05C to 2.5V;

[0104] 4. Let stand for 5 minutes;

[0105] 5. Charge at 1C constant current to 3.65V for 30 minutes;

[0106] 6. Let stand for 1 hour;

[0107] 7. Discharge at 1C constant current to 2.5V for 10 seconds;

[0108] 8. Let stand for 30 minutes;

[0109] 9. Discharge at a constant current of 1C to 2.5V;

[0110] 10. Let stand for 30 minutes;

[0111] 11. 0.8C constant current charging at 3.65V for 5.25 minutes;

[0112] 12. 2.0C constant current charging at 3.65V for 6.9 minutes;

[0113] 13. 1.8C constant current charging at 3.65V for 13.33 minutes;

[0114] 14. 1.6C constant current charging at 3.65V for 3.75 minutes;

[0115] 15. 0.6C constant current charging at 3.65V for 15 minutes;

[0116] 16. Charge at a constant current of 0.4C to 3.65V, and charge at a constant voltage of 0.05C.

[0117] 17. Let stand for 30 minutes;

[0118] 18. Discharge at a constant current of 1C to 2.5V;

[0119] 19. Let stand for 30 minutes;

[0120] 20. Perform steps 11-19 for a lifespan of 2000 cycles.

[0121] (4) Third ambient temperature stepped charging battery life durability test, namely ambient temperature stepped life durability 3: 25℃ stepped charging 3

[0122] 1. Take two 3.Ah soft-pack lithium iron phosphate batteries, one #7 and one #8;

[0123] 2. Let stand at room temperature for 2 hours;

[0124] 3. Discharge at a constant current of 0.05C to 2.5V;

[0125] 4. Let stand for 5 minutes;

[0126] 5. Charge at 1C constant current to 3.65V for 30 minutes;

[0127] 6. Let stand for 1 hour;

[0128] 7. Discharge at 1C constant current to 2.5V for 10 seconds;

[0129] 8. Let stand for 30 minutes;

[0130] 9. Discharge at a constant current of 1C to 2.5V;

[0131] 10. Let stand for 30 minutes;

[0132] 11. 0.8C constant current charging at 3.65V for 5.25 minutes;

[0133] 12. 2.0C constant current charging at 3.65V for 11.4 minutes;

[0134] 13. 1.8C constant current charging at 3.65V for 8.33 minutes;

[0135] 14. 1.6C constant current charging at 3.65V for 3.75 minutes;

[0136] 15. 0.6C constant current charging at 3.65V for 15 minutes;

[0137] 16. Charge at a constant current of 0.4C to 3.65V, and charge at a constant voltage of 0.05C.

[0138] 17. Let stand for 30 minutes;

[0139] 18. Discharge at a constant current of 1C to 2.5V;

[0140] 19. Let stand for 30 minutes;

[0141] 20. Perform steps 11-19 for a lifespan of 2000 cycles.

[0142] Based on the above testing methods, after approximately four months of testing, the lifespan durability data processing yielded the lifespan durability test results, including lifespan durability cycles and capacity retention rate, as detailed in Table 3 below. Figure 4 As shown. Based on the table data and Figure 4It can be seen that under the 25℃ stepped charging method 2, the average capacity retention rate of the two cells is 96.69%, which is 1.69% higher than the average capacity retention rate of 95% for cells under conventional 1C / 1C charging and discharging. Under the 25℃ stepped charging method 2, fast charging from 7% SOC to 80% SOC can be achieved in 20.27 minutes, indicating that stepped charging method 2 can ensure both high lifespan and fast charging in about 20 minutes.

[0143] Table 3 Current Lifetime Durability and Capacity Retention Rate

[0144] Charging method Current lifespan and durability cycles Current capacity retention rate 1C Lifespan Durability 1# 843 94.77％ 1C Lifespan Durability_2# 843 95.24％ 25℃ stepped charging 1_3# 888 94.62％ 25℃ stepped charging 1_4# 890 94.65％ 25℃ stepped charging 2_5# 877 96.57％ 25℃ stepped charging 2_6# 871 96.81％ 25℃ stepped charging 3_7# 894 94.88％ 25℃ stepped charging 3_8# 883 95.88％

[0145] During the above testing process, the EIS was scanned once before and once after the lifespan durability test using an electrochemical workstation to obtain the EIS test data, as follows: Figure 5 As shown, the intersection with the horizontal axis represents the AC impedance of the battery cell. The data on the horizontal axis at the beginning and end of charging shows that the AC internal resistance of the 25°C stepped charging test method is the smallest compared to the initial EIS data, followed by stepped charging 3. The AC impedance increases the most in the normal lifespan endurance test (i.e., 1C charging).

[0146] Step S5: Based on the operating condition test results, lifespan durability test results, and EIS test data, determine the optimal lifespan durability test method. Specifically, according to the capacity retention rate and EIS chart of the lifespan durability data, it can be seen that the stepped charging 2 performs optimally in both lifespan durability capacity retention rate and AC impedance growth. Therefore, the optimal lifespan durability test method is determined to be the second room temperature stepped charging battery lifespan durability test method. In this method, a low-rate constant current charging is first used: 0.8C constant current charging; then a high-rate constant current charging is used, with the charging rate gradually decreasing stepwise over time: first 2.0C constant current charging, then 1.8C, 1.6C, 0.6C, and 0.4C constant current charging sequentially, and the charging time of 2.0C constant current charging is less than the charging time of 1.8C constant current charging.

[0147] By using this optimal testing method to conduct lifespan and durability tests on other identical lithium-ion batteries, it is possible to achieve fast charging to 80% SOC in about 20 minutes while maintaining the optimal lifespan and capacity retention rate. This method greatly improves the lifespan and fast charging performance of lithium batteries.

[0148] The above description is only a preferred embodiment of the present invention. Although the specific implementation of the present invention has been described in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that, based on the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative effort are still within the scope of protection of the present invention.

Claims

1. A method for testing the lifespan and durability of lithium-ion batteries based on stepped charging, characterized in that, include: Multiple identical lithium-ion batteries were selected as parallel test samples. Perform operating condition tests on parallel test samples; Based on the test results, data analysis was conducted to obtain various battery life and durability testing methods based on different step charging methods. Based on multiple battery life and durability testing methods, each parallel test sample is tested to obtain life and durability test results. At the same time, EIS test is conducted to obtain EIS test data for each parallel test sample before and after the life and durability test. Based on the results of operating condition tests, life durability tests, and EIS test data, the optimal life durability test method is determined, and this optimal life durability test method is used to conduct life durability tests on other identical lithium-ion batteries. The operating condition test includes a capacity calibration test, a rate charging test, and a DC internal resistance test performed sequentially. Operating condition tests were performed on the parallel test samples, including: The calibrated capacity of each parallel test sample is obtained through capacity calibration testing. At room temperature, rate charging tests were performed on all parallel test samples to obtain the electrical performance data and dV / dQ curves of each cell at different charging rates, thereby determining the charging rate selected for different dV / dQ stages. At room temperature, DC internal resistance tests were performed on each parallel test sample at different charging rates to obtain DCIR data of each cell during charging, thereby determining the selected charging rate for different SOCs. The use of different charging rates for different dV / dQ stages means that the absolute value of dV / dQ is used as the basis for the stepped charging rate. For the range where the absolute value of dV / dQ is relatively small, a higher charging rate is selected, and for the range where the absolute value of dV / dQ is relatively large, a lower charging rate is selected. Using different charging rates at different SOCs means using SOC as the basis for step-by-step charging rates: when the SOC is 0-5%, choose a low charging rate, and when the SOC is 70-90%, choose a high charging rate. The high magnification rates include 1.6C, 1.8C, and 2.0C, and the low magnification rates include 0.4C, 0.6C, and 0.8C.

2. The lithium-ion battery lifespan and durability testing method based on stepped charging as described in claim 1, characterized in that, The electrical performance data includes total charging time, total charging capacity, constant current time, constant voltage time, 80% SOC capacity, 80% SOC time, 80% SOC voltage, 80% SOC current, constant current capacity, constant voltage capacity, and constant current capacity ratio. The DCIR data includes DCIR values ​​at different charging rates and different SOCs.

3. The lithium-ion battery lifespan and durability testing method based on stepped charging as described in claim 1, characterized in that, Multiple battery life durability testing methods based on different step charging methods and a battery life durability testing method based on 1C constant current room temperature charging were used to test each parallel test sample. Among them, the test methods for various room temperature stepped charging and 1C constant current room temperature charging all include a sequential process of rest-constant current discharge-rest-constant current charging-rest-constant current discharge, as well as a repeated process of rest-characteristic charging-rest-constant current discharge multiple times.

4. The lithium-ion battery lifespan and durability testing method based on stepped charging as described in claim 3, characterized in that, Different test methods employ different characteristic charging processes: in the 1C constant current room temperature charging test method, the characteristic charging adopts constant current and constant voltage charging; in the different room temperature stepped charging test methods, the characteristic charging adopts stepped constant current and constant voltage charging with different charging rate sequences and different charging time.

5. The lithium-ion battery life durability testing method based on stepped charging as described in claim 1, characterized in that, The lifespan durability test results include lifespan cycles and capacity retention.

6. The lithium-ion battery life durability testing method based on stepped charging as described in claim 1, characterized in that, In the characteristic charging process of the optimal lifespan durability test method, a small-rate constant current charging is first used, followed by a large-rate constant current charging, and the charging rate of the constant current charging is gradually reduced in a stepwise manner over time.

7. The lithium-ion battery lifespan and durability testing method based on stepped charging as described in claim 6, characterized in that, The first step is to use a low-rate constant current charging, specifically 0.8C constant current charging. The charging rate of the constant current charging, which is then gradually reduced in a stepwise manner over time, is as follows: first, a constant current of 2.0C is used, followed by constant currents of 1.8C, 1.6C, 0.6C, and 0.4C in sequence, and the charging time of the constant current of 2.0C is less than the charging time of the constant current of 1.8C.

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