Lithium ion battery life endurance test method based on stepped charging

Abstract

The invention discloses a lithium ion battery life endurance test method based on stepped charging, and relates to the technical field of lithium ion battery life endurance test, and the method comprises the steps: selecting a plurality of same lithium ion batteries as parallel test samples; working condition testing is carried out on the parallel test sample; data analysis is carried out according to a working condition test result, and various battery life durability test methods based on different stepped charging modes are obtained; testing each parallel test sample based on a plurality of methods to obtain a life durability test result, and meanwhile, obtaining EIS test data of each parallel test sample before and after the life durability test; and based on the working condition test result, the service life durability test result and the EIS test data, determining an optimal service life durability test method, and performing service life durability test on other identical lithium ion batteries by using the optimal service life durability test method. According to the method, the service life and durability of the lithium ion battery can be more accurately judged under the condition that the requirement of quick charging is met.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery life durability testing, and in particular to a lithium ion battery life durability testing method based on step charging. Background Art

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

[0003] The traditional lithium-ion battery life durability test method is to perform charge and discharge cycles on the batteries of the same batch, and the number of cycles when the discharge capacity decays to 80% (or other specified values) of the initial discharge capacity after the cycle is used as the life durability value of the same batch of lithium batteries. Among them, the charging system currently used in the application and testing of lithium-ion batteries is mainly the constant current constant voltage (CC-CV) charging method, which is simple and easy to operate. However, with the increasing demand for the application of lithium-ion battery fast charging, the limitations of this method are becoming more and more obvious, especially high-current constant current constant voltage charging will directly affect the service life of the battery, and even after the battery has been used for a certain period of time, the potential risk of high-current constant current constant voltage charging will become greater and greater. For this reason, other charging systems can also be used to test the life of lithium-ion batteries, such as the step charging system (MSCC) and the pulse charging system (PC). Among them, step charging is to carry out multiple CC-CV segments. The selection of segments needs to be determined based on the basic charging properties of the battery. The charging process of lithium-ion batteries involves complex phase changes in positive and negative electrode materials, interfacial electrochemical reactions, polarization and irreversible reactions. The segment selection is relatively difficult and it is impossible to obtain the optimal test conditions. The pulse charging system is mainly characterized by periodic changes in the size and direction of the charging current. This charging system is relatively more complicated to operate and has high requirements on the response accuracy of the equipment.

[0004] That is, the above-mentioned method of using the existing charging system to test the life durability of lithium-ion batteries still has certain drawbacks. On the one hand, the existing testing method cannot meet the current demand for fast charging of lithium-ion batteries, and the battery charging efficiency is low. On the other hand, considering that the capacity retention rate of the battery during the charging process is different under different step charging conditions, the existing method cannot guarantee the optimal life durability 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 deficiencies of the above-mentioned prior art, the present invention provides a lithium-ion battery life durability testing method based on step charging, and obtains a variety of test data through operating condition testing, life durability testing and EIS testing (Electrochemical Impedance Spectroscopy). According to data analysis in different dimensions, the difference in capacity retention rate of lithium-ion batteries under different step charging conditions is explored to determine the optimal testing method, and the lithium-ion battery life durability test is performed using the optimal testing method. The capacity retention rate of the battery in the step charging process can be improved while meeting the demand for fast charging, thereby ensuring that the service life of the lithium-ion battery reaches the optimal level, and the life durability of the lithium-ion battery can be judged more accurately.

[0006] The present invention provides a lithium ion battery life durability testing method based on step charging, comprising:

[0007] Select multiple identical lithium-ion batteries as parallel test samples;

[0008] Conduct working condition tests on parallel test samples;

[0009] Data analysis is performed based on the working condition test results to obtain a variety of battery life durability test methods based on different step charging methods;

[0010] Based on a variety of battery life durability test methods, each parallel test sample is tested to obtain the life durability test results. At the same time, through EIS test, the EIS test data of each parallel test sample before and after the life durability test is obtained;

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

[0012] According to a further technical solution, the operating condition test includes a capacity calibration test, a rate charging test and a DC internal resistance test which are performed in sequence.

[0013] A further technical solution is to conduct working condition tests on parallel test samples, including:

[0014] Through the capacity calibration test, the cell calibration capacity of each parallel test sample is obtained;

[0015] At room temperature, perform rate charging tests on all parallel test samples to obtain the electrical performance data and dV / dQ curves of each battery cell at different charging rates, so as to determine the charging rate selected at different dV / dQ stages;

[0016] At room temperature, each parallel test sample is tested for DC internal resistance at different charging rates to obtain the DCIR data of each battery cell, so as to determine the charging rate selected at different SOCs.

[0017] As a further technical solution, a variety of battery life endurance test methods based on different step charging methods and a battery life endurance test method based on 1C constant current and room temperature charging are used to test each parallel test sample;

[0018] Among them, the various test methods for normal temperature step charging and 1C constant current normal temperature charging all include the process of static-constant current discharge-static-constant current charging-static-constant current discharge in sequence, and then repeated static-characteristic charging-static-constant current discharge process for multiple cycles.

[0019] A further technical solution is that different test methods adopt different characteristic charging processes, namely: in the test method of 1C constant current and room temperature charging, the characteristic charging adopts constant current and constant voltage charging; in the test methods of different room temperature step charging, the characteristic charging adopts stepwise constant current and constant voltage charging with different charging rate sequences and different rate charging times.

[0020] A further technical solution is that in the characteristic charging process of the optimal life durability test method, a small rate constant current charging is first adopted, and then a large rate constant current charging is adopted, and the charging rate of the constant current charging is gradually reduced in steps over time.

[0021] One or more of the above technical solutions have the following beneficial effects:

[0022] 1. The present invention provides a lithium-ion battery life durability test method based on step charging. The method performs operating condition tests and life durability tests on lithium-ion batteries to obtain electrical performance test results. The method uses an electrochemical workstation to scan EIS before and after the life durability test to obtain EIS test results. The method analyzes data from different dimensions to explore the difference in capacity retention rates of lithium-ion batteries under different step charging conditions, thereby determining and verifying an optimal test method. The lithium-ion battery life durability test is performed using the optimal test method, which can improve the capacity retention rate of the battery during step charging while meeting the demand for fast charging, and ensure that the service life of the lithium-ion battery reaches the optimal level. The life durability of the lithium-ion battery can be judged more accurately, and has guiding significance for optimizing the battery test method and extending the battery life durability.

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

[0024] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0025] Figure 1 This is a flow chart of a lithium-ion battery life durability testing method based on step charging according to an embodiment of the present invention;

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

[0027] Figure 3 Schematic diagram of DCIR curve of the battery cell at different charging rates in an embodiment of the present invention;

[0028] Figure 4 A schematic diagram showing comparison of results of battery life endurance tests using different charging methods in an embodiment of the present invention;

[0029] Figure 5 Schematic diagram of EIS data comparison before and after battery life endurance test using different charging methods in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] It should be noted that the following detailed descriptions are exemplary only, are intended to describe specific embodiments, are intended to provide further explanation of the present invention, and are not intended to limit exemplary embodiments according to the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those of ordinary skill in the art to which the present invention belongs. In addition, it should also be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0031] Embodiment 1

[0032] Considering that the charging process of lithium-ion batteries involves complex phase changes in positive and negative electrode materials, interfacial electrochemical reactions, polarization effects, and irreversible reactions, combined with the battery CC-CV charging voltage-capacity curve, it can be seen that in the constant current charging stage, the battery capacity does not increase linearly with the battery charging voltage, but has different charging voltage changes under different states of charge (SOC). This feature is determined by the positive and negative electrode materials and battery design. Based on the above analysis, this embodiment is based on the charging properties of lithium-ion batteries, combined with the phase change characteristics of battery materials, and on the premise of ensuring the battery life, a step charging system is formulated to improve the battery charging efficiency. Specifically, this embodiment provides a lithium-ion battery life durability test method based on step charging, such as Figure 1 As shown, the method includes:

[0033] Select multiple identical lithium-ion batteries as parallel test samples;

[0034] Conduct working condition tests on parallel test samples;

[0035] Data analysis is performed based on the working condition test results to obtain a variety of battery life durability test methods based on different step charging methods;

[0036] Based on a variety of battery life durability test methods, each parallel test sample is tested to obtain the life durability test results. At the same time, through EIS test, the EIS test data of each parallel test sample before and after the life durability test is obtained;

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

[0038] The following content introduces the lithium-ion battery life durability testing method based on step charging proposed in this embodiment in more detail.

[0039] Step S1, select multiple identical lithium-ion batteries as parallel test samples. In this embodiment, 8 3Ah soft-pack lithium iron phosphate battery parallel samples are selected to measure their basic performance before storage, and are named 1-8# in sequence.

[0040] Step S2, performing an operating condition test on the parallel test samples, wherein the operating condition test includes a capacity calibration test, a rate charging test, and a direct current internal resistance (DCIR) test performed in sequence.

[0041] Step S2.1, capacity calibration test: Perform capacity calibration test on each battery cell used as a parallel test sample to obtain the cell calibration capacity of each parallel test sample, and perform other working condition tests based on the calibration capacity.

[0042] Step S2.2, rate charging test. At room temperature of 25°C, rate charging test is performed on all parallel test samples to obtain the electrical performance data and dV / dQ curve of each battery cell at different charging rates, so as to determine the charging rate selected at different dV / dQ stages.

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

[0044] The obtained cell rate charging performance data are shown in Table 1 below, where the constant current capacity ratios of the cells at 1.6C, 1.8C and 2.0C are 79.97%, 80.57% and 79.93% respectively. At this time, the rate charging performance of the cells is relatively excellent. In addition, considering that the instantaneous voltage of 80% SOC charging at 1.8C is 3.515V, which is very close to the charging cut-off voltage of the cell, the 1.8C constant current and constant voltage charging system can be used to achieve the fast charging goal of charging 80% SOC in 30 minutes.

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

[0046]

[0047] Furthermore, the phase change of the positive and negative electrodes of the lithium-ion battery during the charging and discharging process can be analyzed based on the dV / dQ curve of the whole battery. Specifically, one of the cells is selected, and the electrical performance data of its rate charging is processed using the differential method to obtain the following: Figure 2The dV / dQ curves of the cells shown are for different charging rates. The dV / dQ curve of a battery is an important data for analyzing the overall performance and applicability of the battery. The graph plots the differential potential dQ relative to the differential voltage dV, which provides insight into the electrochemical processes occurring within the battery cell during the charge and discharge cycles. The dV / dQ curve chart is generated by separating the capacity from the voltage as the battery undergoes charge and discharge cycles. Among them, 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 change of the positive and negative active materials during the process of lithium removal and lithium insertion. Taking the 0.4C charging dV / dQ curve as an example, characteristic peak 1 (about 0Ah) mainly reflects the initial phase change of the positive and negative electrode materials as a whole, and characteristic peak 2 (about 2.8Ah) is determined by the positive and negative electrode materials. When the charging rate increases, the phase change of the positive and negative electrode materials will occur in advance, thus forming a multi-phase coexistence phenomenon, showing that some phase change peaks shift to the left or even disappear. First, it is assumed that the positive electrode loses active materials uniformly during the life durability process, that is, the amount of active materials in the positive electrode becomes less after decay. Therefore, when the same amount of electricity is charged during the charging process, the positive electrode potential will rise to a higher voltage, resulting in a larger slope of the positive electrode charging curve, causing the battery to reach the charging cut-off voltage at a lower capacity, which will indirectly affect the life durability of the battery cell.

[0049] In summary, in order to achieve the fast charging target of charging 80% SOC in 30 minutes while avoiding the potential risk of lithium plating, the charging ladder preliminarily determines the SOC with obvious phase change peaks. In this step, considering that the change of the phase change peak can reflect the use of the positive and negative electrode materials, the phase change peak can be used to distinguish whether there is lithium plating. Furthermore, this embodiment determines the change of the phase change peak at different rates based on the relationship between the phase change peak and the SOC, so as to select the SOC with obvious phase change peaks. The phase change peak is also one of the considerations for determining the step charging method. At the same time, combined with Figure 2 As shown in the dV / dQ curve in , under different SOC states, the dV / dQ curve changes with the change of SOC. The dV / dQ curve is also one of the considerations for determining the step charging method. In this embodiment, different charging rates are selected for different dV / dQ stages, including: taking the absolute value of dV / dQ as the basis for the step charging rate, for the interval with a relatively small absolute value of dV / dQ, a large rate is selected for charging, and for the interval with a relatively large absolute value of dV / dQ, a small rate is selected for charging; wherein the large rate includes 1.6C, 1.8C, and 2.0C, and the small rate includes 0.4C, 0.6C, and 0.8C. In the above manner, the step charging method is jointly determined based on the phase change peak and the dV / dQ curve.

[0050] Step S2.3, DCIR test. At room temperature of 25°C, conduct DC internal resistance tests at different charging rates on each parallel test sample to obtain DCIR data for each battery cell, so as to determine the charging rate selected at different SOCs. The DCIR data includes DCIR values ​​at different charging rates and different SOCs.

[0051] Specifically, according to the test results of step S2.2 above, it can be seen from the rate charging data that the constant current capacity of the battery cell at 1.6C, 1.8C and 2.0C is relatively high. All the batteries are subjected to DCIR tests at different rates, and the test data are shown in Table 2 below. For simplicity, this embodiment selects the DCIR data of 2#, 3#, and 5# batteries to draw a line graph, as shown in Table 2. Figure 3 shown.

[0052] Based on the following Table 2, combined Figure 3 From the cell charging DCIR curve shown, it can be seen that the charging DCIR of the cells (2#, 3#, 5#) is high at low SOC, especially when the SOC is 0, the charging DCIR exceeds 40mΩ, and when the SOC is 0-5%, the charging DCIR is ≥23mΩ; as the SOC of the cell increases, its charging DCIR gradually decreases. From the perspective of charging DCIR, in the 0-5% SOC range, charging with a smaller charging rate can effectively reduce energy loss; from the perspective of charging DCIR, charging DCIR is gradually increasing at 70%-90% SOC. Similarly, in the 70%-90% SOC stage, the charging rate needs to be gradually reduced to effectively reduce energy loss.

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

[0054]

[0055] In summary, different charging rates are selected under different SOCs, including: using SOC as the basis for the step charging rate, selecting a relatively small charging rate when the SOC is 0-5%, selecting a relatively large charging rate when the SOC is 70%-90%, and gradually reducing 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: Perform data analysis based on the working condition test results to obtain a variety of battery life endurance test methods based on different step charging methods.

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

[0058] Specifically, three battery life endurance test methods are set up in this embodiment, namely, multiple battery life endurance test methods based on different step charging methods include the first, second, and third normal temperature step charging battery life endurance test methods, and the first, second, and third normal temperature step charging battery life endurance test methods and the 1C constant current normal temperature charging battery life endurance test method are used to test each parallel test sample.

[0059] Furthermore, the various test methods for normal temperature step charging and 1C constant current normal temperature charging all include a sequence of static-constant current discharge-static-constant current charging-static-constant current discharge processes, and then multiple cycles of static-characteristic charging-static-constant current discharge processes; wherein different test methods use different characteristic charging processes, namely: in the test method of 1C constant current normal temperature charging, the characteristic charging uses constant current and constant voltage charging; in different normal temperature step charging test methods, the characteristic charging uses step-by-step constant current and constant voltage charging with different charging rate sequences and different charging times.

[0060] Specifically, in the above-mentioned various test methods, the characteristic charging processes are respectively:

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

[0062] For the first normal temperature step charging battery life endurance test method, 1C constant current discharge to 2.5V; stand for 30 minutes; 0.8C constant current charge to 3.65V, charging time 5.25min; 1.8C constant current charge to 3.65V, charging time 19.33min; 1.6C constant current charge to 3.65V, charging time 5.63min; 0.6C constant current charge to 3.65V, charging time 15min; 0.4C constant current charge to 3.65V, constant voltage charge to 0.05C;

[0063] For the second normal temperature step charging battery life endurance test method, 1C constant current discharge to 2.5V; stand for 30 minutes; 0.8C constant current charge to 3.65V, charging time 5.25min; 2.0C constant current charge to 3.65V, charging time 6.9min; 1.8C constant current charge to 3.65V, charging time 13.33min; 1.6C constant current charge to 3.65V, charging time 3.75min; 0.6C constant current charge to 3.65V, charging time 15min; 0.4C constant current charge to 3.65V, constant voltage charge to 0.05C;

[0064] For the third normal temperature step charging battery life endurance test method, 1C constant current discharge to 2.5V; stand for 30 minutes; 0.8C constant current charge to 3.65V, charging time 5.25 minutes; 2.0C constant current charge to 3.65V, charging time 11.4 minutes; 1.8C constant current charge to 3.65V, charging time 8.33 minutes; 1.6C constant current charge to 3.65V, charging time 3.75 minutes; 0.6C constant current charge to 3.65V, charging time 15 minutes; 0.4C constant current charge to 3.65V, constant voltage charge to 0.05C.

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

[0066] (1) 1C constant current room temperature charging battery life durability test, that is, room temperature life durability 1C / 1C

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

[0068] 2. Leave it at room temperature for 2 hours;

[0069] 3. 0.05C constant current discharge to 2.5V;

[0070] 4. Let stand for 5 minutes;

[0071] 5. 1C constant current charge to 3.65V for 30min;

[0072] 6. Let stand for 1 hour;

[0073] 7. 1C constant current discharge to 2.5V 10s;

[0074] 8. Let stand for 30 minutes;

[0075] 9. 1C constant current charging to 3.65V, constant voltage charging to 0.05C:

[0076] 10. Let stand for 30 minutes;

[0077] 11. 1C constant current discharge to 2.5V;

[0078] 12. Let stand for 30 minutes;

[0079] 13. Execute steps 9 to 12 and the lifespan will be 2000 times.

[0080] (2) The first normal temperature step charging battery life durability test, i.e. normal temperature step life durability 1: 25℃ step charging 1

[0081] 1. Take 2 3.Ah soft-pack lithium iron phosphate batteries, No. 3 and No. 4;

[0082] 2. Leave it at room temperature for 2 hours;

[0083] 3. 0.05C constant current discharge to 2.5V;

[0084] 4. Let stand for 5 minutes;

[0085] 5. 1C constant current charge to 3.65V for 30min;

[0086] 6. Let stand for 1 hour;

[0087] 7. 1C constant current discharge to 2.5V 10s;

[0088] 8. Let stand for 30 minutes;

[0089] 9. 1C constant current discharge to 2.5V;

[0090] 10. Let stand for 30 minutes;

[0091] 11. 0.8C constant current charging 3.65V 5.25min;

[0092] 12. 1.8C constant current charging 3.65V 19.33min;

[0093] 13. 1.6C constant current charging 3.65V 5.63min;

[0094] 14. 0.6C constant current charging 3.65V 15min;

[0095] 15. 0.4C constant current charge to 3.65V, constant voltage charge to 0.05C;

[0096] 16. Let stand for 30 minutes;

[0097] 17. 1C constant current discharge to 2.5V;

[0098] 18. Let stand for 30 minutes;

[0099] 19. Execute steps 11 to 18 and the lifespan will be 2000 times.

[0100] (3) The second normal temperature step charging battery life endurance test, i.e. normal temperature step life endurance 2: 25℃ step charging 2

[0101] 1. Take 2 3.Ah soft-pack lithium iron phosphate batteries of 5# and 6#;

[0102] 2. Leave it at room temperature for 2 hours;

[0103] 3. 0.05C constant current discharge to 2.5V;

[0104] 4. Let stand for 5 minutes;

[0105] 5. 1C constant current charge to 3.65V for 30min;

[0106] 6. Let stand for 1 hour;

[0107] 7. 1C constant current discharge to 2.5V 10s;

[0108] 8. Let stand for 30 minutes;

[0109] 9. 1C constant current discharge to 2.5V;

[0110] 10. Let stand for 30 minutes;

[0111] 11. 0.8C constant current charging 3.65V 5.25min;

[0112] 12. 2.0C constant current charging 3.65V 6.9min;

[0113] 13. 1.8C constant current charging 3.65V 13.33min;

[0114] 14. 1.6C constant current charging 3.65V 3.75min;

[0115] 15. 0.6C constant current charging 3.65V 15min;

[0116] 16. 0.4C constant current charge to 3.65V, constant voltage charge to 0.05C;

[0117] 17. Let stand for 30 minutes;

[0118] 18. 1C constant current discharge to 2.5V;

[0119] 19. Let stand for 30 minutes;

[0120] 20. Execute steps 11 to 19 and the service life will be 2000 times.

[0121] (4) The third normal temperature step charging battery life endurance test, i.e. normal temperature step life endurance 3: 25℃ step charging 3

[0122] 1. Take 2 3.Ah soft-pack lithium iron phosphate batteries of No. 7 and No. 8;

[0123] 2. Leave it at room temperature for 2 hours;

[0124] 3. 0.05C constant current discharge to 2.5V;

[0125] 4. Let stand for 5 minutes;

[0126] 5. 1C constant current charge to 3.65V for 30min;

[0127] 6. Let stand for 1 hour;

[0128] 7. 1C constant current discharge to 2.5V 10s;

[0129] 8. Let stand for 30 minutes;

[0130] 9. 1C constant current discharge to 2.5V;

[0131] 10. Let stand for 30 minutes;

[0132] 11. 0.8C constant current charging 3.65V 5.25min;

[0133] 12. 2.0C constant current charging 3.65V 11.4min;

[0134] 13. 1.8C constant current charging 3.65V 8.33min;

[0135] 14. 1.6C constant current charging 3.65V 3.75min;

[0136] 15. 0.6C constant current charging 3.65V 15min;

[0137] 16. 0.4C constant current charge to 3.65V, constant voltage charge to 0.05C;

[0138] 17. Let stand for 30 minutes;

[0139] 18. 1C constant current discharge to 2.5V;

[0140] 19. Let stand for 30 minutes;

[0141] 20. Execute steps 11 to 19 and the service life will be 2000 times.

[0142] Based on the above test method, after about 4 months of testing, the life durability data was processed to obtain the life durability test results, which include the life durability cycles and capacity retention rate, as shown in Table 3 and Figure 4 According to the table data and Figure 4It can be seen that under 25℃ step charging 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 the conventional 1C / 1C charging and discharging cells of 95%. Under 25℃ step charging 2, fast charging from 7% SOC to 80% SOC can be achieved in 20.27 minutes, indicating that under step charging 2, a higher lifespan can be guaranteed and fast charging of about 20 minutes can be achieved.

[0143] Table 3 Current life durability and capacity retention rate

[0144] Charging method Current lifespan durability cycles Current capacity retention rate 1C lifespan durability 1# 843 94.77％ 1C life durability_2# 843 95.24％ 25℃ Step Charging 1_3# 888 94.62％ 25℃ Step Charge 1_4# 890 94.65％ 25℃ Step Charging 2_5# 877 96.57％ 25℃ Step Charging 2_6# 871 96.81％ 25℃ Step Charging 3_7# 894 94.88％ 25℃ Step Charging 3_8# 883 95.88％

[0145] In the above test process, before and after the life durability test, the electrochemical workstation is used to scan EIS once to obtain EIS test data such as Figure 5 As shown, the intersection with the horizontal axis is the AC impedance of the battery cell. It can be seen from the horizontal axis data at the start and end of charging that compared with the initial EIS data, the AC internal resistance of the 25℃ step charging 2 test method has the smallest increase, followed by step charging 3. The largest increase in AC impedance is in normal life endurance (i.e. 1C charging).

[0146] Step S5, based on the working condition test results, life durability test results, and EIS test data, determine the optimal life durability test method. Specifically, according to the life durability data capacity retention rate and EIS graph, it can be seen that the step charging 2 performs best in both life durability capacity retention rate and AC impedance growth, that is, the optimal life durability test method is determined to be the second normal temperature step charging battery life durability test method, in which a small rate constant current charging is first used, that is, 0.8C constant current charging is used; then a large rate constant current charging is used and the charging rate of the constant current charging is gradually reduced stepwise over time, that is, 2.0C constant current charging is first used, and then 1.8C, 1.6C, 0.6C, and 0.4C constant current charging are used in sequence, 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 life 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 life durability capacity retention rate. This method greatly improves the life durability of lithium batteries and their fast charging performance.

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

Claims

1. A lithium-ion battery life durability test method based on step charging, characterized in that: include: Select multiple identical lithium-ion batteries as parallel test samples; Conduct working condition tests on parallel test samples; Data analysis is performed based on the working condition test results to obtain a variety of battery life durability test methods based on different step charging methods; Based on a variety of battery life durability test methods, each parallel test sample is tested to obtain the life durability test results. At the same time, through EIS test, the EIS test data of each parallel test sample before and after the life durability test is obtained; Based on the operating condition test results, life durability test results, and EIS test data, the optimal life durability test method is determined, and the optimal life durability test method is used to perform life durability tests on other identical lithium-ion batteries.

2. A lithium-ion battery life durability test method based on step charging as claimed in claim 1, characterized in that: The operating condition test includes a capacity calibration test, a rate charging test and a DC internal resistance test which are performed in sequence.

3. A lithium-ion battery life durability test method based on step charging as claimed in claim 2, characterized in that: Perform operating tests on parallel test samples, including: Through the capacity calibration test, the cell calibration capacity of each parallel test sample is obtained; At room temperature, perform rate charging tests on all parallel test samples to obtain the electrical performance data and dV / dQ curves of each battery cell at different charging rates, so as to determine the charging rate selected at different dV / dQ stages; At room temperature, each parallel test sample is tested for DC internal resistance at different charging rates to obtain the DCIR data of each battery cell, so as to determine the charging rate selected at different SOCs.

4. A lithium-ion battery life durability test method based on step charging as claimed in claim 3, characterized in that: The electrical performance data include total charging time, total charging capacity, constant current time, constant voltage time, charging 80% SOC capacity, charging 80% SOC time, charging 80% SOC voltage, charging 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.

5. A lithium-ion battery life durability test method based on step charging as claimed in claim 3, characterized in that: Different charging rates are selected at different dV / dQ stages, which means that the absolute value of dV / dQ is used as the basis for the step charging rate. For the interval with a relatively small absolute value of dV / dQ, a high charging rate is selected, and for the interval with a relatively large absolute value of dV / dQ, a low charging rate is selected. Selecting different charging rates at different SOCs means: using SOC as the basis for the step-by-step charging rate, when the SOC is 0-5%, choose a low charging rate, and when the SOC is 70%-90%, choose a high charging rate; The large ratio includes 1.6C, 1.8C, and 2.0C, and the small ratio includes 0.4C, 0.6C, and 0.8C.

6. A lithium-ion battery life durability test method based on step charging as claimed in claim 1, characterized in that: A variety of battery life endurance test methods based on different step charging methods and a battery life endurance test method based on 1C constant current room temperature charging are used to test each parallel test sample; Among them, the various test methods for normal temperature step charging and 1C constant current normal temperature charging all include the process of static-constant current discharge-static-constant current charging-static-constant current discharge in sequence, and then repeated static-characteristic charging-static-constant current discharge process for multiple cycles.

7. A lithium-ion battery life durability test method based on step charging as claimed in claim 6, characterized in that: Different test methods use different characteristic charging processes, namely: in the 1C constant current and room temperature charging test method, the characteristic charging adopts constant current and constant voltage charging; in the different room temperature step charging test methods, the characteristic charging adopts stepwise constant current and constant voltage charging with different charging rate sequences and different rate charging times.

8. A lithium-ion battery life durability test method based on step charging as claimed in claim 1, characterized in that: The life durability test results include life durability cycles and capacity retention rate.

9. A lithium-ion battery life durability test method based on step charging as claimed in claim 1, characterized in that: In the characteristic charging process of the optimal life durability test method, a small rate constant current charging is first adopted, and then a large rate constant current charging is adopted, and the charging rate of the constant current charging is gradually reduced step by step over time.

10. A lithium-ion battery life durability test method based on step charging as claimed in claim 9, characterized in that: The first step is to use a small rate constant current charging, which is: using a 0.8C constant current charging; The high-rate constant-current charging is then adopted and the charging rate of the constant-current charging is gradually reduced over time, that is: 2.0C constant-current charging is first adopted, and then 1.8C, 1.6C, 0.6C, and 0.4C constant-current charging are adopted in sequence, and the charging time of 2.0C constant-current charging is shorter than the charging time of 1.8C constant-current charging.

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