Method for rapidly testing cycle life of lithium ion battery

Abstract

The invention relates to the technical field of battery testing methods, in particular to a method for quickly testing the cycle life of a lithium ion battery, which comprises the following steps: S1, calibrating the initial discharge capacity of the lithium ion battery to be tested; s2, (a) carrying out constant-current charging to 70%-100% SOC (State of Charge); (b) standing; (c) carrying out constant-current discharge to 60%-90% of SOC (State of Charge); (d) standing; (e) carrying out constant-current charging to 70%-100% SOC; (f) standing; (g) after the steps (c)-(f) are circulated for multiple times, calibrating the current discharge capacity of the lithium ion battery to be detected; and S3, when the current discharge capacity reaches a threshold value, stopping the cyclic acceleration test and recording the cycle time of the battery, or when the cycle time reaches a threshold value, stopping the cyclic acceleration test and recording the capacity retention ratio of the battery. The method provided by the invention not only ensures that the battery capacity attenuation mechanism is consistent with the conventional circulation, but also can shorten the test time.

Description

Technical Field

[0001] The invention relates to the technical field of battery testing methods, and in particular to a method for quickly testing the cycle life of a lithium-ion battery. Background Art

[0002] Lithium-ion batteries have the advantages of high specific capacity, good cycle stability, and no memory effect, and are used in various fields. However, different application fields have different requirements for the cycle life of lithium-ion batteries. In addition, the cycle life test of lithium-ion batteries takes a long time, and the performance under different system combinations is also different. There are many tests, which leads to long evaluation cycles and large investment resources. The commonly used method is: at 25°C, charge at a constant current and constant voltage at a rate of 1C to the known upper limit voltage of charging (for lithium iron phosphate batteries, the known upper limit voltage of charging is 3.65V) and the cut-off current (for lithium iron phosphate batteries, the cut-off current is 0.05C), leave it for 10 minutes, and then discharge at a constant current at a rate of 1C to the known lower limit voltage of discharge (for lithium iron phosphate batteries, the known lower limit voltage of discharge is 2.5V), leave it for 10 minutes. For lithium iron phosphate batteries, one cycle takes at least 2.3 hours. When the battery capacity retention rate decays to 80%, assuming that the number of cycles is 4000, it takes about 383 days to test. Therefore, it is very important to develop a test method that can shorten the time used for lithium-ion battery cycle testing. The invention patent with patent number CN112946506A reduces the SOC range of each charge and discharge of the battery, allowing it to cycle between low SOC and high SOC intervals, while increasing the cycle temperature and changing the static step to constant voltage charging. Although this type of cycle acceleration method greatly reduces the time required for testing, it cannot guarantee that its high-temperature cycle attenuation is consistent with the normal temperature cycle attenuation mechanism. In addition, during the cycle test, overcharging to 110% SOC is used to accelerate the cycle attenuation, which is quite different from the actual situation.

[0003] Therefore, developing a testing method that can ensure that the battery capacity attenuation mechanism is consistent with conventional cycles and shorten the time used for lithium-ion battery cycle testing is a technical problem that needs to be urgently solved in this field. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for quickly testing the cycle life of a lithium-ion battery. The method for testing the cycle life of a lithium-ion battery provided by the present invention not only ensures that the battery capacity attenuation mechanism is consistent with conventional cycles, but also can shorten the time used for lithium-ion battery cycle testing. It can be used to compare the cycle performance of different materials and shorten the time required for product development.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for quickly testing the cycle life of a lithium-ion battery, and the method includes the following steps:

[0007] S1. Constant-volume test: Calibrate the initial discharge capacity of the lithium-ion battery to be tested.

[0008] S2. Cycle acceleration test: (a) First, charge the lithium-ion battery to be tested at a constant current to 70%-100% SOC; (b) Let it stand; (c) Discharge the lithium-ion battery after standing at a constant current to 60%-90% SOC; (d) Let it stand; (e) Charge the lithium-ion battery after standing at a constant current to 70%-100% SOC; (f) Let it stand; (g) After repeating steps (c) to (f) multiple times, calibrate the current discharge capacity of the lithium-ion battery to be tested.

[0009] S3. Take one cycle acceleration test from step (a) to step (g). When the current discharge capacity of the lithium-ion battery to be tested reaches the threshold, stop the cycle acceleration test and record the battery cycle time, or when the cycle time of the lithium-ion battery to be tested reaches the threshold, stop the cycle acceleration test and record the battery capacity retention rate.

[0010] The method for testing the cycle life of a lithium-ion battery provided by the present invention not only ensures that the battery capacity attenuation mechanism is consistent with the conventional cycle, but also can shorten the time required for the lithium-ion battery cycle test, can be used to compare the cycle performance of different materials, and shorten the time required for product development.

[0011] Further, the calibration of the initial discharge capacity of the lithium-ion battery to be tested includes: Constant-volume for multiple circles at a 1C rate, and take the average discharge capacity of multiple circles or the discharge capacity of the last circle as the initial discharge capacity of the lithium-ion battery to be tested.

[0012] Further, in step (a), the current for the constant-current charging is 0.33C - 3C.

[0013] Further, in step (b), the standing time is 1 - 10 minutes.

[0014] Further, in step (c), the current for the constant-current discharge is 1C to 2C.

[0015] Further, in step (d), the standing time is 1 - 5 minutes.

[0016] Further, in step (e), the current for the constant-current charging is 0.33C - 3C.

[0017] Further, in step (f), the standing time is 1 - 5 minutes.

[0018] Further, in step (g), after repeating steps (c) to (f) 30 - 200 times, the current discharge capacity of the lithium-ion battery to be tested is calibrated.

[0019] Further, in step S2, the calibration of the current discharge capacity of the lithium-ion battery to be tested includes: charging at a constant current of 1C to a known upper charging voltage, then charging at a constant voltage of the known upper charging voltage until the cut-off current, after standing, discharging at a constant current of 1C to a known lower discharge voltage, performing charge and discharge at 0 - 100% SOC multiple times, and taking the average discharge capacity of multiple times or the last discharge capacity as the current discharge capacity of the lithium-ion battery to be tested;

[0020] And / or, in step S3, when the current discharge capacity of the lithium-ion battery to be tested does not reach the threshold, or when the cycle time of the lithium-ion battery to be tested does not reach the threshold, perform another cycle acceleration test according to steps (a) to (g);

[0021] And / or, the test temperature for the cycle life of the lithium-ion battery is 23 - 27°C;

[0022] And / or, the capacity of the lithium-ion battery to be tested includes but is not limited to 1000 - 7000 mAh;

[0023] And / or, the positive active material of the lithium-ion battery to be tested includes lithium iron phosphate, and the negative active material includes artificial graphite.

[0024] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0025] (1) The method for testing the cycle life of a lithium-ion battery provided by the present invention not only ensures that the battery capacity attenuation mechanism is consistent with the conventional cycle, but also can shorten the time required for the lithium-ion battery cycle test, can be used to compare the cycle performance of different materials, and shorten the time required for product development.

[0026] (2) The method for testing the cycle life of a lithium-ion battery provided by the present invention can accelerate the battery cycle attenuation and can be used for battery failure analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1 It is the dQ / dV spectrum of Embodiments 1 - 9 and Comparative Example 1 of the present invention;

[0029] Figure 2 This is the EIS diagram of Examples 1-9 and Comparative Examples 1 and 3 of the present invention. Detailed implementation manners

[0030] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. For the process parameters without specific conditions noted in the following embodiments, they are usually in accordance with conventional conditions.

[0031] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0032] The present invention provides a method for quickly testing the cycle life of a lithium-ion battery, and the method includes the following steps:

[0033] S1. Constant volume test: Calibrate the initial discharge capacity of the lithium-ion battery to be tested.

[0034] S2. Cycle acceleration test: (a) First, charge the lithium-ion battery to be tested at a constant current to 70%-100% SOC (for example, it can be 70% SOC, 80% SOC, 90% SOC or 100% SOC, preferably 100% SOC); (b) Let it stand; (c) Discharge the lithium-ion battery after standing at a constant current to 60%-90% SOC (for example, it can be 60% SOC, 80% SOC or 90% SOC, preferably 80% SOC); (d) Let it stand; (e) Charge the lithium-ion battery after standing at a constant current to 70%-100% SOC (for example, it can be 70% SOC, 80% SOC, 90% SOC or 100% SOC, preferably 100% SOC); (f) Let it stand; (g) After repeating steps (c) to (f) multiple times, calibrate the current discharge capacity of the lithium-ion battery to be tested.

[0035] S3. Conduct a cycle acceleration test from step (a) to step (g). When the current discharge capacity of the lithium-ion battery under test reaches the threshold, stop the cycle acceleration test and record the battery cycle time. Or, when the cycle time of the lithium-ion battery under test reaches the threshold, stop the cycle acceleration test and record the battery capacity retention rate.

[0036] Cycling in the high SOC range will increase the amount of dead lithium in the negative electrode interlayer, resulting in an increase in capacity loss. Cycling in the high SOC range promotes the formation of the SEI film on the negative electrode surface and side reactions such as redox reactions between the electrode material and the electrolyte, accelerating the consumption of lithium-ion reactions, the decline of the electrode material structure, and the decomposition of the electrolyte, thus realizing the rapid test of the battery cycle life.

[0037] The present invention provides a method for shortening the cycle life test time without changing the attenuation mechanism of the lithium-ion battery, effectively solving problems such as long test time and much resource occupation. It can be seen from the test results that compared with the battery cells cycled in the 0-100% SOC range, for the battery cells cycled in the high SOC range, when the capacity retention rate is the same, the cycle time is shortened, indicating that this method has an accelerating effect on the cycle life test of the battery cells. Example 8 shows that in the 80%-100% SOC range, superimposing a 1.8C discharge rate has the best accelerating effect on the cycle life of the battery cells.

[0038] The method for testing the cycle life of the lithium-ion battery provided by the present invention not only ensures that the battery capacity attenuation mechanism is consistent with the conventional cycle, but also can shorten the time required for the lithium-ion battery cycle test, and can be used to compare the cycle performance of different materials, shortening the time required for product development.

[0039] In the above method for rapidly testing the cycle life of a lithium-ion battery, as an optional implementation manner, the calibration of the initial discharge capacity of the lithium-ion battery under test includes: performing constant volume for multiple circles at a 1C rate, and taking the average discharge capacity of multiple circles or the discharge capacity of the last circle as the initial discharge capacity of the lithium-ion battery under test.

[0040] In the above method for rapidly testing the cycle life of a lithium-ion battery, as an optional implementation manner, the 1C rate constant volume includes constant current charging at a 1C current to a known charging upper limit voltage, then constant voltage charging at the known charging upper limit voltage to the cut-off current, standing for 10 minutes, and then constant current discharging at a 1C current to a known discharging lower limit voltage.

[0041] Specifically, for a lithium iron phosphate battery, the known charging upper limit voltage is 3.65V, the cut-off current is 0.05C, and the known discharging lower limit voltage is 2.5V.

[0042] In the above method for quickly testing the cycle life of a lithium-ion battery, as an alternative embodiment, in step (a), the current for constant current charging is 0.33C - 3C, for example, it can be 0.33C, 0.5C, 1C, 2C or 3C.

[0043] In the above method for quickly testing the cycle life of a lithium-ion battery, as an alternative embodiment, in step (b), the standing time is 1 - 10 minutes, for example, it can be 1 minute, 3 minutes, 5 minutes, 7 minutes or 10 minutes, preferably 5 - 10 minutes. The standing time of 5 - 10 minutes in step b is the full charge depolarization elimination time at 0 - 100% SOC, and the standing time of 1 - 5 minutes in other steps is the cycle depolarization elimination within different SOC segments, and it is also to shorten the test time.

[0044] In the above method for quickly testing the cycle life of a lithium-ion battery, as an alternative embodiment, in step (c), the current for constant current discharging is 1C - 2C, preferably 1.5C - 2C. Due to different material characteristics, when the charging rate is too high, lithium plating is likely to occur on the surface of the negative electrode. Therefore, superimposing a discharge rate between 1C - 2C can shorten the time required for the cycle test of the lithium-ion battery.

[0045] In the above method for quickly testing the cycle life of a lithium-ion battery, as an alternative embodiment, in step (d), the standing time is 1 - 5 minutes.

[0046] In the above method for quickly testing the cycle life of a lithium-ion battery, as an alternative embodiment, in step (e), the current for constant current charging is 0.33C - 3C, for example, it can be 0.33C, 0.5C, 1C, 2C or 3C.

[0047] In the above method for quickly testing the cycle life of a lithium-ion battery, as an alternative embodiment, in step (f), the standing time is 1 - 5 minutes.

[0048] In the above method for quickly testing the cycle life of a lithium-ion battery, as an alternative embodiment, in step (g), after cycling steps (c) - (f) 30 - 200 times (for example, it can be 30 times, 50 times, 100 times, 150 times or 200 times), the current discharge capacity of the lithium-ion battery to be tested is calibrated.

[0049] In the above method for quickly testing the cycle life of a lithium-ion battery, as an alternative embodiment, in step S2, the calibration of the current discharge capacity of the lithium-ion battery to be tested includes: charging at a constant current of 1C to a known upper charging voltage, then charging at a constant voltage of the known upper charging voltage until the cut-off current, after standing, discharging at a constant current of 1C to a known lower discharge voltage, performing 0-100% SOC charge and discharge multiple times, and taking the average discharge capacity of multiple times or the last discharge capacity as the current discharge capacity of the lithium-ion battery to be tested.

[0050] In the above method for quickly testing the cycle life of a lithium-ion battery, as an alternative embodiment, in step S3, when the current discharge capacity of the lithium-ion battery to be tested does not reach the threshold, or when the cycle time of the lithium-ion battery to be tested does not reach the threshold, perform a cycle acceleration test again according to steps (a) to (g).

[0051] In the above method for quickly testing the cycle life of a lithium-ion battery, as an alternative embodiment, the test temperature for the cycle life of the lithium-ion battery is 23-27°C.

[0052] In the above method for quickly testing the cycle life of a lithium-ion battery, as an alternative embodiment, the capacity of the lithium-ion battery to be tested includes but is not limited to 1000-7000 mAh, for example, it can be 1000 mAh, 3000 mAh, 5000 mAh or 7000 mAh.

[0053] In the above method for quickly testing the cycle life of a lithium-ion battery, as an alternative embodiment, the positive active material of the lithium-ion battery to be tested includes lithium iron phosphate, and the negative active material includes artificial graphite.

[0054] The present invention will be further described in detail below with reference to specific examples and comparative examples.

[0055] Comparative Example 1

[0056] The cycle life of a lithium-ion battery was tested by a conventional method, which specifically included the following steps:

[0057] S1. Constant volume test: A soft-pack battery was made with lithium iron phosphate as the positive electrode and artificial graphite as the negative electrode. The battery capacity was designed to be 3000 mAh, and the charge and discharge voltage range of the battery was 2.5V-3.65V. The constant volume test was carried out at room temperature. Under the condition of 25°C, the battery was constant-volume cycled 3 times at a rate of 1.0C, and ended with empty power. The capacity of the third cycle was taken as the initial capacity of the battery. Among them, the constant-volume cycling 3 times at a rate of 1.0C included charging at a constant current of 1C to 3.65V, then charging at a constant voltage of 3.65V until 0.05C, standing for 10 minutes, and then discharging at a constant current of 1C to 2.5V.

[0058] S2. Cycling test: Select three batteries with capacities close to each other (the difference in battery capacity is within 0.01 Ah) as a group and perform the same test items; cycle at a rate of 1.0C in the 0%-100% SOC region at 25°C. When the battery capacity retention rate decays to 80%, record the number of battery cycles and the number of cycling days. Among them, the number of cycles and the number of cycling days are the average values of the three batteries.

[0059] Example 1

[0060] The batteries used are the same as those in Comparative Example 1, but the test conditions are different. At 25°C, the battery is fixed-capacity cycled 3 times at a rate of 1.0C, charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to 0.05C, allowed to stand for 10 minutes, and then discharged at a constant current of 1C to 2.5V to end with no charge. Take the capacity of the third cycle as the initial capacity of the battery. Select three batteries with capacities close to each other (the difference in battery capacity is within 0.01 Ah) as a group and perform the same test items. Cycle 50 times at a rate of 1.0C in the 90%-100% SOC region, then charge at a constant current and constant voltage of 1C to 3.65V and cut off at 0.05C. After standing for 10 minutes, discharge at a constant current of 1C to 2.5V, and perform charge and discharge from 0 to 100% SOC three times to calibrate the capacity of the current state of the battery. Repeat the above cycle. When the current discharge capacity retention rate of the lithium-ion battery to be tested reaches 80%, record the number of battery cycles and the number of cycling days. The results are shown in Table 1. Among them, the number of cycles and the number of cycling days are the average values of the three batteries.

[0061] Specifically, the method for quickly testing the cycle life of a lithium-ion battery provided in this example includes the following steps:

[0062] S1. Fixed-capacity test: At 25°C, charge the lithium-ion battery to be tested at a constant current of 1C to 3.65V, then charge at a constant voltage of 3.65V to 0.05C, allow it to stand for 10 minutes, and then discharge at a constant current of 1C to 2.5V. Perform fixed-capacity cycling 3 times to end with no charge. Take the discharge capacity of the third cycle as the initial discharge capacity of the lithium-ion battery to be tested;

[0063] S2. Cyclic acceleration test: At 25°C, (a) first, charge the lithium-ion battery under test at a constant current of 1.0C to 100% SOC; (b) let it stand for 5 minutes to eliminate polarization; (c) discharge the lithium-ion battery after standing at a constant current of 1.0C to 90% SOC; (d) let it stand for 2 minutes; (e) charge the lithium-ion battery after standing at a constant current of 1.0C to 100% SOC; (f) let it stand for 2 minutes; (g) after cycling steps (c) to (f) 50 times, charge at a constant current of 1C to 3.65V, then charge at a constant voltage of 3.65V until cutoff at 0.05C, then let it stand for 10 minutes, and then discharge at a constant current of 1C to 2.5V. Perform 0-100% SOC charge and discharge three times, and take the last discharge capacity as the current discharge capacity of the lithium-ion battery under test;

[0064] S3. One cycle of the cyclic acceleration test is from step (a) to step (g). Conduct multiple cyclic acceleration tests. When the retention rate of the current discharge capacity of the lithium-ion battery under test reaches 80%, stop the cyclic acceleration test, and record the number of battery cycles and the number of cycle days.

[0065] Example 2

[0066] The battery used is the same as that in Comparative Example 1, but the test conditions are different. At 25°C, the battery is fixed-capacity cycled 3 times at a rate of 1.0C, charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V until cutoff at 0.05C. After standing for 10 minutes, discharge at a constant current of 1C to 2.5V until the battery is empty, and take the capacity of the third cycle as the initial capacity of the battery. Select 3 batteries with capacities close to each other (the difference in battery capacity is within 0.01Ah) as a group to perform the same test items. At 25°C, cycle 50 times at a rate of 1.0C in the 80%-90% SOC region, then charge at a constant current and constant voltage of 1C to 3.65V until cutoff at 0.05C. After standing for 10 minutes, discharge at a constant current of 1C to 2.5V, and perform 0-100% SOC charge and discharge three times to calibrate the capacity of the current state of the battery. Repeat the above cycle. When the retention rate of the current discharge capacity of the lithium-ion battery under test reaches 80%, record the number of battery cycles and the number of cycle days. The results are shown in Table 1, where the number of cycles and the number of cycle days are the average values of the 3 batteries.

[0067] Specifically, the method for quickly testing the cycle life of a lithium-ion battery provided in this example is basically the same as that in Example 1, except that in step S2, in step (a), it is charged to 90%, in step (c), it is discharged to 80% SOC, and in step (e), it is charged to 90%.

[0068] Example 3

[0069] The battery used is the same as that in Comparative Example 1, but the test conditions are different. At 25°C, the battery is fixed in capacity for 3 cycles at a rate of 1.0C, charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to 0.05C. After standing for 10 minutes, it is discharged at a constant current of 1C to 2.5V until the battery is discharged completely. The capacity of the third cycle is taken as the initial capacity of the battery. Three batteries with similar capacities (the difference in battery capacity is within 0.01Ah) are selected as a group to perform the same test items. At 25°C, they are cycled 50 times at a rate of 1.0C in the 80%-100% SOC region, then charged at a constant current and constant voltage of 1C to 3.65V and cut off at 0.05C. After standing for 10 minutes, they are discharged at a constant current of 1C to 2.5V, and charged and discharged from 0 to 100% SOC three times to calibrate the capacity of the current state of the battery. The above cycle is repeated. When the current discharge capacity retention rate of the lithium-ion battery to be tested reaches 80%, the number of battery cycles and the number of cycle days are recorded. The results are shown in Table 1, where the number of cycles and the number of cycle days are the average values of the three batteries.

[0070] Specifically, the method for rapidly testing the cycle life of a lithium-ion battery provided in this embodiment is basically the same as that in Embodiment 1, except that in step S2, in step (c), it is discharged to 80% SOC.

[0071] Embodiment 4

[0072] The battery used is the same as that in Comparative Example 1, but the test conditions are different. At 25°C, the battery is fixed in capacity for 3 cycles at a rate of 1.0C, charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to 0.05C. After standing for 10 minutes, it is discharged at a constant current of 1C to 2.5V until the battery is discharged completely. The capacity of the third cycle is taken as the initial capacity of the battery. Three batteries with similar capacities (the difference in battery capacity is within 0.01Ah) are selected as a group to perform the same test items. At 25°C, it is charged at a rate of 1.0C and discharged at a rate of 1.5C and cycled 50 times in the 90%-100% SOC region, then charged at a constant current and constant voltage of 1C to 3.65V and cut off at 0.05C. After standing for 10 minutes, it is discharged at a constant current of 1C to 2.5V, and charged and discharged from 0 to 100% SOC three times to calibrate the capacity of the current state of the battery. The above cycle is repeated. When the current discharge capacity retention rate of the lithium-ion battery to be tested reaches 80%, the number of battery cycles and the number of cycle days are recorded. The results are shown in Table 1, where the number of cycles and the number of cycle days are the average values of the three batteries.

[0073] Specifically, the method for rapidly testing the cycle life of a lithium-ion battery provided in this embodiment is basically the same as that in Embodiment 1, except that in step S2, in step (c), it is discharged at a constant current of 1.5C to 90% SOC.

[0074] Embodiment 5

[0075] The battery used is the same as that in Comparative Example 1, but the test conditions are different. At 25°C, the battery is fixed in capacity for 3 cycles at a rate of 1.0C, charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to 0.05C. After standing for 10 minutes, it is discharged at a constant current of 1C to 2.5V until the battery is completely discharged. The capacity of the third cycle is taken as the initial capacity of the battery. Three batteries with similar capacities (the difference in battery capacity is within 0.01Ah) are selected as a group to perform the same test items. At 25°C, they are charged at a rate of 1.0C and discharged at a rate of 1.8C in the 90%-100% SOC region for 50 cycles. Then, they are charged at a constant current and constant voltage of 1C to 3.65V and cut off at 0.05C. After standing for 10 minutes, they are discharged at a constant current of 1C to 2.5V, and charged and discharged from 0 to 100% SOC three times to calibrate the capacity of the current state of the battery. Repeat the above cycle. When the current discharge capacity retention rate of the lithium-ion battery to be tested reaches 80%, record the number of battery cycles and the number of cycle days. The results are shown in Table 1, where the number of cycles and the number of cycle days are the average values of the three batteries.

[0076] Specifically, the method for rapidly testing the cycle life of a lithium-ion battery provided in this embodiment is basically the same as that in Embodiment 1, except that in step S2, in step (c), it is discharged at a constant current of 1.8C to 90% SOC.

[0077] Example 6

[0078] The battery used is the same as that in Comparative Example 1, but the test conditions are different. At 25°C, the battery is fixed in capacity for 3 cycles at a rate of 1.0C, charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to 0.05C. After standing for 10 minutes, it is discharged at a constant current of 1C to 2.5V until the battery is completely discharged. The capacity of the third cycle is taken as the initial capacity of the battery. Three batteries with similar capacities (the difference in battery capacity is within 0.01Ah) are selected as a group to perform the same test items. At 25°C, they are charged at a rate of 1.0C and discharged at a rate of 2.0C in the 90%-100% SOC region for 50 cycles. Then, they are charged at a constant current and constant voltage of 1C to 3.65V and cut off at 0.05C. After standing for 10 minutes, they are discharged at a constant current of 1C to 2.5V, and charged and discharged from 0 to 100% SOC three times to calibrate the capacity of the current state of the battery. Repeat the above cycle. When the current discharge capacity retention rate of the lithium-ion battery to be tested reaches 80%, record the number of battery cycles and the number of cycle days. The results are shown in Table 1, where the number of cycles and the number of cycle days are the average values of the three batteries.

[0079] Specifically, the method for rapidly testing the cycle life of a lithium-ion battery provided in this embodiment is basically the same as that in Embodiment 1, except that in step S2, in step (c), it is discharged at a constant current of 2.0C to 90% SOC.

[0080] Example 7

[0081] The battery used is the same as that in Comparative Example 1, but the test conditions are different. At 25 °C, the battery is constant-volume cycled 3 times at a rate of 1.0C, charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to 0.05C. After standing for 10 minutes, it is discharged at a constant current of 1C to 2.5V until the battery is empty. The capacity of the third cycle is taken as the initial capacity of the battery. Three batteries with similar capacities (the difference in battery capacity is within 0.01 Ah) are selected as a group to perform the same test items. At 25 °C, they are charged at a rate of 1.0C and discharged at a rate of 1.5C in the 80%-100% SOC region for 50 cycles. Then, they are charged at a constant current and constant voltage of 1C to 3.65V and cut off at 0.05C. After standing for 10 minutes, they are discharged at a constant current of 1C to 2.5V, and charged and discharged from 0 to 100% SOC three times to calibrate the capacity of the current state of the battery. Repeat the above cycle. When the current discharge capacity retention rate of the lithium-ion battery to be tested reaches 80%, record the number of battery cycles and the number of cycle days. The results are shown in Table 1, where the number of cycles and the number of cycle days are the average values of the three batteries.

[0082] Specifically, the method for quickly testing the cycle life of a lithium-ion battery provided in this embodiment is basically the same as that in Embodiment 1, except that in step S2, in step (c), it is discharged at a constant current of 1.5C to 80% SOC.

[0083] Example 8

[0084] The battery used is the same as that in Comparative Example 1, but the test conditions are different. At 25 °C, the battery is constant-volume cycled 3 times at a rate of 1.0C, charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to 0.05C. After standing for 10 minutes, it is discharged at a constant current of 1C to 2.5V until the battery is empty. The capacity of the third cycle is taken as the initial capacity of the battery. Three batteries with similar capacities (the difference in battery capacity is within 0.01 Ah) are selected as a group to perform the same test items. At 25 °C, they are charged at a rate of 1.0C and discharged at a rate of 1.8C in the 80%-100% SOC region for 50 cycles. Then, they are charged at a constant current and constant voltage of 1C to 3.65V and cut off at 0.05C. After standing for 10 minutes, they are discharged at a constant current of 1C to 2.5V, and charged and discharged from 0 to 100% SOC three times to calibrate the capacity of the current state of the battery. Repeat the above cycle. When the current discharge capacity retention rate of the lithium-ion battery to be tested reaches 80%, record the number of battery cycles and the number of cycle days. The results are shown in Table 1, where the number of cycles and the number of cycle days are the average values of the three batteries.

[0085] Specifically, the method for quickly testing the cycle life of a lithium-ion battery provided in this embodiment is basically the same as that in Embodiment 1. The difference is that in step S2, in step (c), constant current discharge is performed at a rate of 1.8C until 80% SOC.

[0086] Embodiment 9

[0087] The battery used is the same as that in Comparative Example 1, but the test conditions are different. At 25°C, the battery is fixed-capacity cycled 3 times at a rate of 1.0C, charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to 0.05C. After standing for 10 minutes, it is discharged at a constant current of 1C to 2.5V to end with no power. The capacity of the third cycle is taken as the initial capacity of the battery. Three batteries with capacities close (the difference in battery capacity is within 0.01 Ah) are selected as a group for the same test items. At 25°C, they are charged at a rate of 1.0C and discharged at a rate of 2.0C in the 80%-100% SOC region for 50 cycles. Then, they are charged at a constant current and constant voltage of 1C to 3.65V and cut off at 0.05C. After standing for 10 minutes, they are discharged at a constant current of 1C to 2.5V, and charged and discharged from 0 to 100% SOC three times to calibrate the capacity of the current state of the battery. The above cycle is repeated. When the current discharge capacity retention rate of the lithium-ion battery to be tested reaches 80%, the number of battery cycles and the number of cycle days are recorded. The results are shown in Table 1, where the number of cycles and the number of cycle days are the averages of the three batteries.

[0088] Specifically, the method for quickly testing the cycle life of a lithium-ion battery provided in this embodiment is basically the same as that in Embodiment 1. The difference is that in step S2, in step (c), constant current discharge is performed at a rate of 2.0C until 80% SOC.

[0089] Comparative Example 2 (compared with Embodiment 8)

[0090] The battery used is the same as that in Comparative Example 1, but the test conditions are different. At 25 °C, the battery is fixed in volume at a rate of 1.0C for 3 cycles, charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to 0.05C. After standing for 10 minutes, it is discharged at a constant current of 1C to 2.5V until the battery is empty. The capacity of the third cycle is taken as the initial capacity of the battery. Three batteries with similar capacities (the difference in battery capacity is within 0.01Ah) are selected as a group to perform the same test items. At 25 °C, they are charged at a rate of 1.0C and discharged at a rate of 1.8C in the 30%-50% SOC region for 50 cycles. Then, they are charged at a constant current and constant voltage of 1C to 3.65V and cut off at 0.05C. After standing for 10 minutes, they are discharged at a constant current of 1C to 2.5V, and charged and discharged from 0 to 100% SOC three times to calibrate the capacity of the current state of the battery. The above cycle is repeated. When the current discharge capacity retention rate of the lithium-ion battery to be tested reaches 80%, the number of battery cycles and the number of cycle days are recorded. The results are shown in Table 1, where the number of cycles and the number of cycle days are the average values of the three batteries.

[0091] Specifically, the method for quickly testing the cycle life of a lithium-ion battery provided in this comparative example is basically the same as that in Example 1, except that in step S2, in step (a), it is charged to 50% SOC, in step (c), it is discharged at a constant current of 1.8C to 30% SOC, and in step (e), it is charged to 50% SOC.

[0092] Comparative Example 3 (compared with Example 8)

[0093] The battery used is the same as that in Comparative Example 1, but the test conditions are different. At 25 °C, the battery is fixed in volume at a rate of 1.0C for 3 cycles, charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to 0.05C. After standing for 10 minutes, it is discharged at a constant current of 1C to 2.5V until the battery is empty. The capacity of the third cycle is taken as the initial capacity of the battery. Three batteries with similar capacities (the difference in battery capacity is within 0.01Ah) are selected as a group to perform the same test items. At 25 °C, they are charged at a rate of 1.0C and discharged at a rate of 3C in the 80%-100% SOC region for 50 cycles. Then, they are charged at a constant current and constant voltage of 1C to 3.65V and cut off at 0.05C. After standing for 10 minutes, they are discharged at a constant current of 1C to 2.5V, and charged and discharged from 0 to 100% SOC three times to calibrate the capacity of the current state of the battery. The above cycle is repeated. When the current discharge capacity retention rate of the lithium-ion battery to be tested reaches 80%, the number of battery cycles and the number of cycle days are recorded. The results are shown in Table 1, where the number of cycles and the number of cycle days are the average values of the three batteries.

[0094] Specifically, the method for quickly testing the cycle life of a lithium-ion battery provided in this comparative example is substantially the same as that of Example 1, except that in step S2, in step (c), the battery is discharged at a constant current rate of 3.0 C to 80% SOC.

[0095] Table 1

[0096]

[0097] Figure 1 is the dQ / dV spectrum of Examples 1-9 and Comparative Example 1, Figure 2 The EIS graphs (Electrochemical Impedance Spectroscopy) of Examples 1-9 and Comparative Examples 1 and 3 are shown.

[0098] From Table 1, Figure 1 and Figure 2 At least the following points can be seen:

[0099] (1) It can be seen from Comparative Example 1 and Examples 1-9 in Table 1 that the method for testing the cycle life of a lithium-ion battery provided by the present invention can shorten the time used for the lithium-ion battery cycle test, and can be used to compare the cycle performance of different materials and shorten the time required for product development; Figure 1 and Figure 2 It can be seen that the dQ / dV capacity differential curve and EIS test show that the redox peak position and peak intensity of the dQ / dV capacity differential curve of Comparative Example 1 and Examples 1-9 are consistent, and the EIS impedance is not much different, indicating that the by-products and battery capacity attenuation mechanisms are the same.

[0100] (2) It can be seen from Examples 1-3 and Examples 4-9 that when the discharge rate is 1.5C-2C, the time taken for the lithium-ion battery cycle test can be further shortened.

[0101] (3) It can be seen from Example 8 and Comparative Example 2 that the test time increases significantly when cycling in the low SOC range.

[0102] (4) It can be seen from Example 8 and Comparative Example 3 in Table 1 that when the discharge current is too large, the test time increases instead; Figure 2 It can be seen that when the discharge current is 3C, the internal resistance of the battery deviates abnormally, and the battery capacity attenuation mechanism is inconsistent with the conventional cycle.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for quickly testing the cycle life of a lithium-ion battery, characterized in that: The method comprises the following steps: S1. Constant capacity test: calibrate the initial discharge capacity of the lithium-ion battery to be tested; S2, cycle acceleration test: (a) firstly charge the lithium ion battery to be tested with constant current to 70%-100% SOC; (b) stand still; (c) discharge the lithium ion battery after standing still with constant current to 60%-90% SOC; (d) stand still; (e) charge the lithium ion battery after standing still with constant current to 70%-100% SOC; (f) stand still; (g) after multiple cycles of steps (c) to (f), calibrate the current discharge capacity of the lithium ion battery to be tested; S3. Perform a cycle acceleration test according to steps (a) to (g). When the current discharge capacity of the lithium-ion battery to be tested reaches a threshold value, stop the cycle acceleration test and record the battery cycle time. Alternatively, when the cycle time of the lithium-ion battery to be tested reaches a threshold value, stop the cycle acceleration test and record the battery capacity retention rate.

2. The method for rapidly testing the cycle life of a lithium-ion battery according to claim 1, characterized in that: The calibrating of the initial discharge capacity of the lithium-ion battery to be tested includes: performing constant capacity calibration for multiple cycles at a 1C rate, and taking the average discharge capacity of the multiple cycles or the discharge capacity of the last cycle as the initial discharge capacity of the lithium-ion battery to be tested.

3. The method for rapidly testing the cycle life of a lithium-ion battery according to claim 1, characterized in that: In step (a), the constant current charging current is 0.33C-3C.

4. The method for rapidly testing the cycle life of a lithium-ion battery according to claim 1, characterized in that: In step (b), the standing time is 1-10 minutes.

5. The method for rapidly testing the cycle life of a lithium-ion battery according to claim 1, characterized in that: In step (c), the constant current discharge current is 1C to 2C.

6. The method for rapidly testing the cycle life of a lithium-ion battery according to claim 1, characterized in that: In step (d), the standing time is 1-5 minutes.

7. The method for rapidly testing the cycle life of a lithium-ion battery according to claim 1, characterized in that: In step (e), the constant current charging current is 0.33C-3C.

8. The method for rapidly testing the cycle life of a lithium-ion battery according to claim 1, characterized in that: In step (f), the standing time is 1-5 minutes.

9. The method for rapidly testing the cycle life of a lithium-ion battery according to claim 1, characterized in that: In step (g), after steps (c) to (f) are cycled 30-200 times, the current discharge capacity of the lithium-ion battery to be tested is calibrated.

10. The method for rapidly testing the cycle life of a lithium-ion battery according to claim 1, characterized in that: In step S2, the calibration of the current discharge capacity of the lithium-ion battery to be tested includes: charging with a 1C constant current to a known upper limit voltage of charging, then charging with a known upper limit voltage of charging to a cut-off current, and after standing, discharging with a 1C constant current to a known lower limit voltage of discharge, performing 0-100% SOC charging and discharging multiple times, and taking the average discharge capacity of multiple times or the last discharge capacity as the current discharge capacity of the lithium-ion battery to be tested; And / or, in step S3, when the current discharge capacity of the lithium ion battery to be tested does not reach the threshold value, or, when the cycle time of the lithium ion battery to be tested does not reach the threshold value, performing another cycle acceleration test according to steps (a) to (g); and / or, the test temperature for the cycle life of lithium-ion batteries is 23-27°C; And / or, the capacity of the lithium-ion battery to be tested includes but is not limited to 1000-7000 mAh; And / or, the positive electrode active material of the lithium ion battery to be tested includes lithium iron phosphate, and the negative electrode active material includes artificial graphite.

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