Accelerated test method for storage life of lithium ion battery

Abstract

The invention relates to a lithium ion battery storage life acceleration test method, which comprises the following steps: S1, carrying out capacity calibration on batteries in the same batch, and recording the initial capacity; s2, charging to a target SOC, storing for 30 days at a set temperature, and measuring the voltage and internal resistance before storage; s3, standing for 5 hours after storage, measuring voltage and internal resistance after storage, and testing retention capacity and recovery capacity; and S4, circularly executing the steps S2-S3 until the recovery capacity is less than or equal to 80% of the initial capacity. Through the multi-SOC / temperature cycle storage test, the voltage drop, the internal resistance growth rate and the capacity recovery rate are quantified, and the test period is greatly shortened.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery performance testing, and in particular to a method for accelerating the storage life of a lithium-ion battery. Background Art

[0002] In actual production and use, the storage of lithium-ion batteries is very common. The battery sales cycle may be placed in inventory for a long time, and sometimes it is in a long-term storage state during actual use. During the long-term storage of lithium-ion batteries, especially in harsh environments, the battery is in an unstable state at SOC100% charge state and will continue to transition to an equilibrium state. When accumulated to a certain extent, it will not only cause changes in the voltage and internal resistance of the lithium-ion battery, but also affect the performance and safety characteristics, thereby reducing the storage life of the battery. Lithium-ion batteries will undergo irreversible capacity decay and performance degradation during long-term storage, mainly due to the following mechanisms: (1) SEI film continues to grow: consumes active lithium ions, resulting in capacity loss; (2) Electrolyte decomposition: Side reactions intensify at high temperatures, generating gas and increasing impedance; (3) Electrode material structural collapse: Lithium ion deintercalation stress at high state of charge (SOC) triggers material failure.

[0003] The existing methods for testing the storage life of lithium-ion batteries have the following defects: (1) Existing test schemes usually only test the capacity retention rate at a single temperature, without considering the cumulative effect of multiple SOC states and cycle storage; (2) Traditional methods only focus on capacity decay and ignore key safety parameters such as voltage drop and internal resistance growth rate; (3) There is a lack of quantitative assessment of capacity recoverability after storage, such as the amount of dead lithium generated. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned shortcomings and provide a lithium-ion battery storage life accelerated testing method, which evaluates the battery storage life through multi-parameter comparison and quantitatively evaluates: self-discharge rate, irreversible capacity loss, and safety margin changes under different operating conditions.

[0005] The object of the present invention is achieved like this: A method for accelerating the storage life of a lithium-ion battery, comprising the following: S1. Select a batch of lithium batteries from the same batch, calibrate the capacity of the lithium batteries at room temperature, and record the discharge capacity C 初始 ; S2. Charge the lithium battery to a specified SOC state, then store it at a specified temperature for 30 days, and measure the battery voltage V before storage. 存储前、Internal resistance R 存储前 ; S3. After the storage time is over, take out the lithium battery and place it at room temperature for 5 hours, then measure the battery voltage V 存储后 、Internal resistance R 存储后 , then discharge and record the holding capacity as C 保持 , recalibrate the capacity and record the restored capacity C 恢复 ; S4. Repeat steps S2 and S3 in a loop until the storage life ends.

[0006] Furthermore, in step S1, the capacity is calibrated by performing multiple 1C charge and discharge cycles on the batteries of the same batch at room temperature, and taking the average discharge capacity as the initial capacity of the batteries before storage.

[0007] Furthermore, the storage life is terminated in step S4 when the restored capacity is less than or equal to 80% of the initial capacity.

[0008] Furthermore, the voltage, internal resistance, and discharge capacity of the lithium battery before and after storage in step S2 and step S3 are compared to provide a reference for the actual use of the lithium-ion battery: Voltage change rate = (V 存储前 -V 存储后 ) / V 存储前 ; Internal resistance change rate = (R 存储后 -R 存储前 ) / R 存储前 ; Capacity retention rate = C 保持 / C 初始 ; Capacity recovery rate = C 恢复 / C 初始 .

[0009] Furthermore, in steps S2 and S3, the battery parameters (V 存储后 、Internal resistance R 存储后 、C 保持 、C 恢复 ) before storing the parameters (V 存储前 、Internal resistance R 存储前 、C 初始 ) changes, including: Voltage drop change: The voltage drop does not change significantly when the battery is stored at 5°C, 25°C, and 45°C in this state of charge; Internal resistance change: When the battery is stored at 5°C, 25°C, and 45°C in this state of charge, the polarization change of the ohmic internal resistance is smaller when stored at 5°C, and the internal resistance growth rate is smaller; Capacity change: When the battery is stored at 5°C, 25°C, and 45°C in this state of charge, the loss of uncyclable lithium is smaller when stored at 5°C, and the capacity recovery rate is higher.

[0010] Furthermore, in steps S2 and S3, the battery parameters (V 存储后 、Internal resistance R 存储后 、C 保持 、C 恢复 ) before storing the parameters (V 存储前 、Internal resistance R 存储前 、C 初始 ) changes, including: Voltage drop change: When the battery is stored at 5°C, 25°C, and 45°C at this state of charge, the voltage drop is greater when stored at 45°C, indicating that the battery has a higher self-discharge rate at this state of charge and when stored at high temperature; Internal resistance change: When the battery is stored at 5°C, 25°C, and 45°C in this state of charge, lithium ions are lost when stored at 45°C, and the impedance of the two poles continues to increase, resulting in an increase in internal resistance; Capacity change: When the battery is stored at 5°C, 25°C, and 45°C in this state of charge, some of the lithium embedded in the negative electrode graphite loses its activity when stored at 45°C, turning into dead lithium that cannot return to the positive electrode through discharge, resulting in a low capacity recovery rate.

[0011] Furthermore, the battery voltage and internal resistance were measured before and after each storage using a battery internal resistance tester, with an AC internal resistance test frequency of 1 kHz ± 30 Hz.

[0012] Furthermore, the battery internal resistance tester measures the voltage and internal resistance of the battery before and after storage in the following manner: select the voltage and internal resistance gears, select the appropriate range, calibrate to zero, let the positive test lead touch the positive pole of the battery, the negative test lead touch the negative pole of the battery, and record the voltage value and internal resistance value displayed on the instrument panel.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for accelerating the storage life of lithium-ion batteries, which compares the battery parameters (V 存储后 、Internal resistance R 存储后 、C 保持 、C 恢复 ) and the parameters before storage (V 存储前 、Internal resistance R 存储前 、C 初始 ) comparison, to understand the self-discharge performance and capacity attenuation characteristics of lithium batteries during storage, and provide a reference for the actual storage process of lithium-ion batteries; it has the following advantages: (1) Multidimensional parameter correlation analysis: By comparing the voltage drop > 5% and the internal resistance growth rate > 20% at SOC 100% + high temperature (45°C), the risk of electrolyte decomposition is warned; Combined with the capacity recovery rate (e.g., SOC100% battery recovery rate ≤85% at 45°C), the amount of dead lithium generated is quantified; (2) Accelerated life end determination: Cyclic storage until capacity recovery rate ≤ 80%, greatly shortening the test cycle compared to traditional static testing; (3) Simulate actual complex storage scenarios: Through SOC / temperature orthogonal experimental design, data support is provided for battery storage temperature control strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the method of the present invention.

[0015] Figure 2 Graph showing the voltage and internal resistance test data of samples 1#, 2# and 3# before and after storage in Example 1 of the present invention.

[0016] Figure 3 This is a graph showing the voltage and internal resistance test data of samples 4#, 5# and 6# before and after storage in Example 1 of the present invention.

[0017] Figure 4 This is a graph showing the initial capacity and recovery capacity test data of samples 1#, 2# and 3# before and after storage in Example 1 of the present invention.

[0018] Figure 5 This is a graph showing the initial capacity and recovery capacity test data of samples 4#, 5# and 6# before and after storage in Example 1 of the present invention. DETAILED DESCRIPTION

[0019] To better understand the technical solution of the present invention, the following detailed description is provided with reference to the relevant illustrations. It should be understood that the following specific embodiments are not intended to limit the specific implementation of the technical solution of the present invention; they are merely examples of possible implementations of the technical solution of the present invention. It should be noted that references herein to the positional relationships of various components, such as component A being located above component B, are based on the relative positions of the components in the illustrations and are not intended to limit the actual positional relationships of the components. Example 1

[0020] See also Figure 1-Figure 5 , Figure 1 Draw a schematic flow chart of the method of the present invention. As shown in the figure, the present invention provides an accelerated test method for the storage life of a lithium-ion battery, including the following contents: S1. Select a batch of lithium batteries from the same batch, calibrate the capacity of the lithium batteries at room temperature, and record the discharge capacity C 初始 ; In this Example 1, at room temperature, the lithium battery was discharged at a constant current of 1C to a voltage of 2.5V, allowed to stand for 30 minutes, then charged at a constant current of 1C to 3.65V and then switched to constant voltage charging. Charging was stopped when the current dropped to 0.05C. After charging, the battery was allowed to stand for 30 minutes, and then discharged at 1C to a voltage of 2.5V. The discharge capacity was recorded. The battery was charged and discharged three times, and the average of the three discharge capacities was used as the initial capacity of the battery before storage, as shown in Table 1 below:

[0021] S2. Charge the lithium battery to a specified SOC state, then store it at a specified temperature for 30 days, and measure the battery voltage V before storage. 存储前 、Internal resistance R 存储前 ; In this embodiment 1, samples 1#, 2# and 3# are charged to SOC40%, and samples 4#, 5# and 6# are charged to SOC100%. Then, samples 1# and 4# are stored at 5°C for 30 days, samples 2# and 5# are stored at 25°C for 30 days, and samples 3# and 6# are stored at 45°C for 30 days. The battery voltage V is measured before storage. 存储前 、Internal resistance R 存储前 ; See Figure 2 and Figure 3 Data charts; S3. After the storage time is over, take out the lithium battery and place it at room temperature for 5 hours, then measure the battery voltage V 存储后 、Internal resistance R 存储后 , then discharge and record the holding capacity as C 保持 , recalibrate the capacity and record the restored capacity C 恢复 ; In this embodiment 1, after the storage time is over, the lithium battery is taken out and placed at room temperature for 5 hours and then the battery voltage V is measured. 存储后 、Internal resistance R 存储后 ,like Figure 2 、 Figure 3 Then, discharge the capacitor at 1C constant current until the voltage reaches 2.5V, and record the capacity as C. 保持 Then charge at a constant current of 1C until the voltage reaches 3.65V and then switch to constant voltage charging. Stop charging when the current drops to 0.05C. After charging, let it stand for 30 minutes, and then discharge at 1C until the voltage reaches 2.5V. Record the recovered capacity C. 恢复 ;like Figure 4 、 Figure 5 As shown; S4. Repeat steps S2 and S3 in a loop until the storage life ends. When the restored capacity is ≤ 80% of the initial capacity, the storage life ends.

[0022] Specifically, at SOC 40%, the battery parameters (V 存储后 、Internal resistance R 存储后 、C 保持 、C 恢复 ) before storing the parameters (V 存储前 、Internal resistance R 存储前 、C 初始 ) changes, including: Voltage drop change: The voltage drop does not change significantly when the battery is stored at 5°C, 25°C, and 45°C in this state of charge; Internal resistance change: When the battery is stored at 5°C, 25°C, and 45°C in this state of charge, the polarization change of the ohmic internal resistance is smaller when stored at 5°C, and the internal resistance growth rate is smaller; Capacity change: When the battery is stored at 5°C, 25°C, and 45°C in this state of charge, the loss of uncyclable lithium is smaller when stored at 5°C, and the capacity recovery rate is higher.

[0023] Specifically, at SOC 100%, the battery parameters (V 存储后 、Internal resistance R 存储后 、C 保持 、C 恢复 ) before storing the parameters (V 存储前 、Internal resistance R 存储前 、C 初始 ) changes, including: Voltage drop change: When the battery is stored at 5°C, 25°C, and 45°C at this state of charge, the voltage drop is greater when stored at 45°C, indicating that the battery has a higher self-discharge rate at this state of charge and when stored at high temperature; Internal resistance change: When the battery is stored at 5°C, 25°C, and 45°C in this state of charge, lithium ions are lost when stored at 45°C, and the impedance of the two poles continues to increase, resulting in an increase in internal resistance; Capacity change: When the battery is stored at 5°C, 25°C, and 45°C in this state of charge, some of the lithium embedded in the negative electrode graphite loses its activity when stored at 45°C, turning into dead lithium that cannot return to the positive electrode through discharge, resulting in a low capacity recovery rate.

[0024] Specifically, the voltage, internal resistance, and discharge capacity of the lithium battery before and after storage in step S2 and step S3 are compared to provide a reference for the actual use of the lithium-ion battery: Voltage change rate = (V 存储前 -V 存储后 ) / V 存储前 ; Internal resistance change rate = (R 存储后 -R 存储前 ) / R 存储前 ; Capacity retention rate = C 保持 / C 初始 ; Capacity recovery rate = C 恢复 / C 初始 .

[0025] Specifically, the instrument used to measure the battery voltage and internal resistance before and after each storage is a battery internal resistance tester. The frequency of testing AC internal resistance is: 1kHz±30Hz. The measurement method is: select the voltage and internal resistance gear, select the appropriate range, calibrate to zero, let the positive test lead touch the positive pole of the battery, and the negative test lead touch the negative pole of the battery, and record the voltage and internal resistance values ​​displayed on the instrument panel, accurate to three decimal places.

[0026] Working principle: The present invention provides a method for accelerating the storage life of lithium-ion batteries, which compares the battery parameters (V 存储后 、Internal resistance R 存储后 、C 保持 、C 恢复 ) and the parameters before storage (V 存储前 、Internal resistance R 存储前 、C 初始 ) comparison to understand the self-discharge performance and capacity attenuation characteristics of lithium batteries during storage, and provide a reference for the actual storage process of lithium-ion batteries.

[0027] The test method of the present invention combines the cycle storage test with the multi-parameter attenuation correlation analysis for the first time, breaking through the limitation of single capacity evaluation; through the SOC / temperature orthogonal experimental design (see Figure 2-Figure 5 ), providing data support for battery storage temperature control strategies; stipulating that the battery should be stored for 5 hours to eliminate polarization, and the internal resistance measurement frequency should be 1kHz±30Hz (matching the characteristic frequency band of SEI film impedance); guiding actual storage strategies: data shows that the internal resistance increases by less than 3% when stored at SOC40%+5℃, and a low-temperature and low-SOC storage solution is recommended.

[0028] The above are only specific application examples of the present invention and do not constitute any limitation on the scope of protection of the present invention. Any technical solutions formed by equivalent transformation or equivalent replacement shall fall within the scope of protection of the present invention.

Claims

1. A method for accelerating the storage life of a lithium-ion battery, characterized in that: Includes the following: S1. Select a batch of lithium batteries from the same batch, calibrate the capacity of the lithium batteries at room temperature, and record the discharge capacity C 初始 ; S2. Charge the lithium battery to a specified SOC state, then store it at a specified temperature for 30 days, and measure the battery voltage V before storage. 存储前 、Internal resistance R 存储前 ; S3. After the storage time is over, take out the lithium battery and place it at room temperature for 5 hours, then measure the battery voltage V 存储后 、Internal resistance R 存储后 , then discharge and record the holding capacity as C 保持 , recalibrate the capacity and record the restored capacity C 恢复 ; S4. Repeat steps S2 and S3 in a loop until the storage life ends.

2. The method for accelerating the storage life of a lithium-ion battery according to claim 1, wherein: Capacity calibration in step S1: Perform multiple 1C charge and discharge cycles on batteries of the same batch at room temperature, and take the average discharge capacity as the initial capacity of the battery before storage.

3. The method for accelerating the storage life of a lithium-ion battery according to claim 1, wherein: In step S4, the storage life ends when the restored capacity is less than or equal to 80% of the initial capacity.

4. The method for accelerating the storage life of a lithium-ion battery according to claim 1, wherein: Comparing the voltage, internal resistance, and discharge capacity of the lithium battery before and after storage in step S2 and step S3 provides a reference for the actual use of lithium-ion batteries: Voltage change rate = (V 存储前 -V 存储后 ) / V 存储前 ; Internal resistance change rate = (R 存储后 -R 存储前 ) / R 存储前 ; Capacity retention rate = C 保持 / C 初始 ; Capacity recovery rate = C 恢复 / C 初始 .

5. The method for accelerating the storage life of a lithium-ion battery according to claim 4, wherein: In steps S2 and S3, at SOC 40%, the battery parameters (V 存储后 、Internal resistance R 存储后 、C 保持 、C 恢复 ) before storing the parameters (V 存储前 、Internal resistance R 存储前 、C 初始 ) changes, including: Voltage drop change: The voltage drop does not change significantly when the battery is stored at 5°C, 25°C, and 45°C in this state of charge; Internal resistance change: When the battery is stored at 5°C, 25°C, and 45°C in this state of charge, the polarization change of the ohmic internal resistance is smaller when stored at 5°C, and the internal resistance growth rate is smaller; Capacity change: When the battery is stored at 5°C, 25°C, and 45°C in this state of charge, the loss of uncyclable lithium is smaller when stored at 5°C, and the capacity recovery rate is higher.

6. The method for accelerating the storage life of a lithium-ion battery according to claim 4, wherein: In steps S2 and S3, the battery parameters (V 存储后 、Internal resistance R 存储后 、C 保持 、C 恢复 ) before storing the parameters (V 存储前 、Internal resistance R 存储前 、C 初始 ) changes, including: Voltage drop change: When the battery is stored at 5°C, 25°C, and 45°C at this state of charge, the voltage drop is greater when stored at 45°C, indicating that the battery has a higher self-discharge rate at this state of charge and when stored at high temperature; Internal resistance change: When the battery is stored at 5°C, 25°C, and 45°C in this state of charge, lithium ions are lost when stored at 45°C, and the impedance of the two poles continues to increase, resulting in an increase in internal resistance; Capacity change: When the battery is stored at 5°C, 25°C, and 45°C in this state of charge, some of the lithium embedded in the negative electrode graphite loses its activity when stored at 45°C, turning into dead lithium that cannot return to the positive electrode through discharge, resulting in a low capacity recovery rate.

7. The method for accelerating the storage life of a lithium-ion battery according to claim 1, wherein: The battery voltage and internal resistance are measured before and after each storage using a battery internal resistance tester. The frequency of the AC internal resistance test is 1kHz±30Hz.

8. The method for accelerating the storage life of a lithium-ion battery according to claim 7, wherein: The battery internal resistance tester measures the voltage and internal resistance of the battery before and after storage in the following way: select the voltage and internal resistance gear, select the appropriate range, calibrate to zero, let the positive test lead touch the positive terminal of the battery, the negative test lead touch the negative terminal of the battery, and record the voltage and internal resistance values ​​displayed on the instrument panel.

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