Preparation method and consistency verification method of sodium ion battery

Abstract

The present application relates to the field of sodium ion battery, especially to a preparation method and consistency verification method of sodium ion battery; in the process of cell formation, the first screening is carried out, and the cell with large delta V1 is removed, so that the cell with problems such as uneven SEI film formation and high moisture content can be removed; the direct current resistance is used for matching in the present application, the direct current resistance can directly reflect the electrochemical reaction process and ion diffusion process, which includes ohmic resistance and polarization resistance, and can be more close to the actual use process of the battery, so that the consistency of the battery pack can be more effectively improved; the more similar the polarization performance of each single battery in the battery pack is, the better the consistency of the battery pack is, and the cycle stability of the battery pack is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, and more particularly to a method for preparing a sodium-ion battery and a method for verifying its consistency. Background Technology

[0002] Sodium-ion batteries, as an emerging energy storage battery product, have become a research hotspot due to their similar working principle and manufacturing process to lithium-ion batteries, as well as the high compatibility of production equipment, which can effectively reduce investment costs. However, because there are still differences in their mechanisms, the process parameters of sodium-ion batteries still differ significantly from those of lithium-ion batteries, requiring the development of processes tailored to the technical characteristics of sodium-ion batteries.

[0003] Sodium-ion battery packs consist of multiple individual cells. To ensure the cycle stability of the battery pack, the consistency of each individual cell must be guaranteed. Verification, referencing the manufacturing process of lithium-ion batteries, showed no abnormalities in the initial stages of sodium-ion battery pack production. However, during actual applications, problems arose such as individual cells lagging behind, resulting in a severe shortage of overall battery capacity. Therefore, developing a suitable manufacturing process for sodium-ion batteries has become a crucial aspect of battery application.

[0004] In current battery manufacturing processes, AC internal resistance is typically used to screen for consistency in individual cells. However, AC internal resistance primarily reflects ohmic resistance, excluding polarization resistance, and therefore cannot fully reflect the internal characteristics of the cell. Consequently, after cells are assembled into a battery pack, the variation trends of individual cells differ, leading to decreased consistency among individual cells during battery pack use and affecting the battery pack's lifespan. Currently, methods exist for consistency assessment using DC internal resistance. DC internal resistance reflects both ohmic and polarization resistance, providing a more direct indication of cell performance. However, current testing methods for DC internal resistance in sodium-ion batteries have low compatibility with the characteristics of sodium-ion batteries. Therefore, a DC internal resistance testing method specifically designed for sodium-ion batteries is needed. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing sodium-ion batteries and a method for verifying their consistency.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of this invention is to provide a method for preparing a sodium-ion battery, comprising the steps of:

[0008] S1. The sodium iron pyrophosphate positive electrode, hard carbon negative electrode and separator are assembled into a bare cell. After welding, casing, full welding, cell baking and one liquid injection, a semi-finished cell is obtained.

[0009] S2. After the semi-finished battery cell obtained in step S1 is subjected to a first static treatment, it is then subjected to high-temperature negative pressure formation.

[0010] S3. After the cells in step S2 have undergone high temperature negative pressure formation, let them stand at room temperature for 30 minutes and test the voltage V1. Then, let them stand at high temperature for 6-12 hours and at room temperature for 1 hour, test the voltage V2 and record the voltage change ΔV1=V1-V2. Then, perform the DCR1 test and record R1. Based on the values ​​of ΔV1 and R1, perform preliminary screening of the cells.

[0011] S4. After the cells that pass the initial screening are injected with electrolyte a second time, let them stand for 6-12 hours, and then perform capacity testing. Record the first discharge capacity C1 and the first coulombic efficiency CE. If the cell's first discharge capacity C1 value is ≥ nominal capacity, the range within the group is ≤0.5%, and the range within the group of the first coulombic efficiency CE is ≤1%, then proceed to the next step.

[0012] S5. Perform DCR2 test on the cells after capacity grading, record R2, charge with 10-60% of the rated capacity, and perform DCR3 test, record R3, and calculate the internal resistance change ΔR=|R3-R2|; if the values ​​of R2, R3, and ΔR meet the standard, they can be used for group matching.

[0013] S6. After the cell from step S5 is left to stand at room temperature for 6-8 hours, it is subjected to high-temperature aging treatment. Then the voltage V4 is tested and the voltage change ΔV2=V3-V4 is recorded. If the values ​​of V4 and ΔV2 are qualified, the sodium-ion battery is obtained.

[0014] Preferably, in step S2, the first settling process includes: settling at room temperature for 8-12 hours, and then settling at high temperature for 24-48 hours.

[0015] Preferably, in step S2, the high-temperature negative pressure formation includes: charging with 20-60% of the rated capacity of electricity.

[0016] Preferably, in step S3, the initial screening qualification conditions are: △V1<80mV, and the range of R1 values ​​of cells within the group is ≤10%.

[0017] Preferably, in step S4, the capacity grading process includes: 0.5C constant current discharge to the cutoff voltage and 0.1C discharge to the cutoff voltage, and the discharge capacity of the two steps is summed to obtain the initial discharge capacity of the cell.

[0018] Preferably, in step S5, the criteria for grouping are: the range of R2, R3, and ΔR values ​​within a group is ≤10%, and the ratio of ΔR value to R3 value is <5%.

[0019] Preferably, in step S6, the high-temperature aging treatment includes: first, standing at high temperature for 24-72 hours, and then standing at room temperature for 24-72 hours.

[0020] Preferably, in step S6, the qualification standard is △V2≤5mV and the range within group V4≤5mV.

[0021] Preferably, the test method for DCR1, DCR2 and DCR3 is: 2C constant current discharge for 5s.

[0022] A second aspect of the present invention is to provide a consistency verification method for a sodium-ion battery, wherein the sodium-ion battery is a sodium-ion battery prepared by the above-described preparation method, and the steps include:

[0023] A1. Perform capacity calibration on the sodium-ion battery pack, and record the voltage difference ΔV_discharge of each cell when the battery pack is discharged; after fully charging, record the voltage difference ΔV_charge of each cell when the battery pack is fully charged; store the battery pack in a 60℃ environment for 7 days, and record the voltage difference of each cell in the battery pack every 4 hours.

[0024] A2. After 7 days, remove the battery pack and let it stand at room temperature for 4 hours. Record the voltage difference of each cell in the battery pack.

[0025] A3. Discharge the battery pack to the cutoff voltage to obtain the retention capacity, calculate the capacity retention rate, and record the voltage difference ΔV_discharge of each cell when the battery pack is discharged; after fully charging the battery pack, record the voltage difference ΔV_charge of each cell when the battery pack is fully charged.

[0026] A4. Calculate the difference between ΔV_discharge0 and ΔV_discharge1, and the difference between ΔV_charge0 and ΔV_charge1. If any difference is greater than 20%, the battery consistency is considered poor, and the battery formation, aging, and capacity testing processes need to be adjusted.

[0027] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0028] (1) In the cell formation process, the present invention performs a first screening to remove cells with larger ΔV1, which can remove cells with problems such as uneven SEI film formation and high moisture content.

[0029] (2) The present invention uses DC internal resistance for grouping. DC internal resistance can intuitively reflect the electrochemical reaction process and ion diffusion process. It includes ohmic resistance and polarization resistance. At the same time, it can be closer to the actual use process of the battery and can more effectively improve the consistency of the battery pack. The more similar the polarization performance of each cell in the battery pack, the better the consistency of the battery pack, which greatly improves the cycle stability of the battery pack.

[0030] (3) In this invention, ΔR is used to determine consistency. Since DC internal resistance is strongly correlated with SOC, ΔR can be used to compare the DC internal resistance of the cell in the discharged state and the specified SOC state, thereby effectively screening cells with good consistency and thus effectively improving the cycle stability of the battery pack.

[0031] (4) In this invention, for the DC internal resistance test, based on the characteristics of sodium-ion batteries, the first DC internal resistance test (DCR1) is performed during the cell formation stage to remove problematic cells with uneven SEI film formation or high moisture content, thus preventing problematic cells from being transferred to subsequent grouping steps; DCR2 is performed on cells after capacity grading and discharge (0% SOC), and DCR3 is performed on cells after charging to a specified amount of power (10%-60% SOC). The consistency is determined by using the DC internal resistance of cells with different SOC states together, which can more accurately determine the consistency of cells under different states. This can simulate the consistency of individual cells in the battery pack at different SOC states during actual use and charging and discharging. For sodium-ion cells with a SOC state of 10%-60%, based on the layered oxide material system and the polyanionic material system, this SOC state range is where the cell self-discharge is most obvious, which can effectively screen for cell consistency. By using this method for consistency determination, we can produce battery packs with superior performance and effectively improve the cycle stability of the battery packs. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0034] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0035] Example 1

[0036] This embodiment provides a method for preparing a sodium-ion battery, the steps of which include:

[0037] S1. The sodium iron pyrophosphate positive electrode, hard carbon negative electrode and separator are assembled into a bare cell. After welding, casing, full welding, cell baking and one liquid injection, a semi-finished cell is obtained.

[0038] S2. After the semi-finished battery cell obtained in step S1 is left to stand at room temperature for 8-12 hours, and then left to stand at high temperature for 24-48 hours, it is charged with 20-60% of the rated capacity and subjected to high temperature negative pressure formation.

[0039] S3. After the cells in step S2 have undergone high-temperature negative pressure formation, let them stand at room temperature for 30 minutes. The test voltage V1 is 2.975V. Then, let them stand at high temperature for 6-12 hours and then at room temperature for 1 hour. The test voltage V2 is 2.955V. Record the voltage change ΔV1 = V1 - V2 = 20mV. Then, perform a DCR1 test by 2C constant current discharge for 5 seconds. Record R1 as 2.667mΩ. Based on the values ​​of ΔV1 and R1, perform preliminary screening of the cells. If ΔV1 < 80mV and the range of R1 values ​​within the group is ≤ 10%, it meets the preliminary screening standard.

[0040] S4. After the cells that pass the initial screening are injected with electrolyte a second time, they are allowed to stand for 6-12 hours, and then capacity testing is performed. The cells are discharged at a constant current of 0.5C to the cutoff voltage and at 0.1C to the cutoff voltage. The initial discharge capacity C1 is recorded as 42.5Ah, the initial coulombic efficiency CE is 85.2%, the initial discharge capacity C1 of the cell is ≥ the nominal capacity of 40Ah, the range within the group is ≤0.5%, and the range within the group of the initial coulombic efficiency CE is ≤1%. Proceed to the next step.

[0041] S5. After capacity grading, the cells are subjected to a 2C constant current discharge for 5 seconds and a DCR2 test is performed. The R2 value is recorded as 3.064mΩ. The cells are then charged with 30% of their rated capacity and subjected to a 2C constant current discharge for 5 seconds and a DCR3 test is performed. The R3 value is recorded as 2.941mΩ. The internal resistance change ΔR = |R3 - R2| = 0.123mΩ is calculated. The range of R2, R3, and ΔR values ​​within the group is ≤10%, and the ratio of ΔR to R3 is <5%. The cells are then used for grouping.

[0042] S6. After the cell from step S5 is left to stand at room temperature for 6-8 hours, then at high temperature for 24-72 hours, and then at room temperature for 24-72 hours, the voltage V4 is tested and found to be 2.831V. The voltage change ΔV2 = V3 - V4 = 3mV is recorded. ΔV2 ≤ 5mV and the range within group V4 ≤ 5mV, thus obtaining a sodium-ion battery.

[0043] Example 2

[0044] This embodiment provides another method for preparing a sodium-ion battery, the steps of which include:

[0045] S1. The sodium iron pyrophosphate positive electrode, hard carbon negative electrode and separator are assembled into a bare cell. After welding, casing, full welding, cell baking and one liquid injection, a semi-finished cell is obtained.

[0046] S2. After the semi-finished battery cell obtained in step S1 is left to stand at room temperature for 8 hours, and then left to stand at high temperature for 24 hours, it is charged with 50% of the rated capacity and subjected to high temperature negative pressure formation.

[0047] S3. After the cells in step S2 have undergone high-temperature negative pressure formation, let them stand at room temperature for 30 minutes. The test voltage V1 is 2.822V. Then, let them stand at high temperature for 12 hours and then at room temperature for 1 hour. The test voltage V2 is 2.804V. Record the voltage change ΔV1 = V1 - V2 = 18mV. Then, perform a DCR1 test by constant current discharge at 2C for 5 seconds. Record R1 as 2.471mΩ. Based on the values ​​of ΔV1 and R1, perform preliminary screening of the cells. ΔV1 < 80mV, and the range of R1 values ​​of cells in the group is ≤ 10%, which meets the preliminary screening standard.

[0048] S4. After the cells that passed the initial screening are injected with electrolyte a second time, they are left to stand for 12 hours and then subjected to capacity testing. They are discharged at a constant current of 0.5C to the cutoff voltage and at 0.1C to the cutoff voltage. The initial discharge capacity C1 is recorded as 53.1Ah and the initial coulombic efficiency CE is recorded as 84.9%. The initial discharge capacity C1 of the cell is ≥ the nominal capacity of 50Ah, the range within the group is ≤0.5%, and the range within the group of the initial coulombic efficiency CE is ≤1%. Proceed to the next step.

[0049] S5. After capacity grading, the cells are subjected to a 2C constant current discharge for 5 seconds and a DCR2 test is performed. The R2 value is recorded as 2.961mΩ. The cells are then charged with 30% of their rated capacity and subjected to a 2C constant current discharge for 5 seconds and a DCR3 test is performed. The R3 value is recorded as 2.865mΩ. The internal resistance change ΔR = |R3 - R2| = 0.096mΩ is calculated. The range of R2, R3, and ΔR values ​​within the group is ≤10%, and the ratio of ΔR to R3 is <5%. The cells are then used for grouping.

[0050] S6. After the cell from step S5 is left to stand at room temperature for 6 hours, then at high temperature for 24 hours, and then at room temperature for 48 hours, the voltage V4 is tested and found to be 2.860V. The voltage change ΔV2 = V3 - V4 = 4mV is recorded. ΔV2 ≤ 5mV and the range within group V4 ≤ 5mV, thus obtaining a sodium-ion battery.

[0051] Example 3

[0052] This embodiment provides another method for preparing a sodium-ion battery, the steps of which include:

[0053] S1. The sodium iron pyrophosphate positive electrode, hard carbon negative electrode and separator are assembled into a bare cell. After welding, casing, full welding, cell baking and one liquid injection, a semi-finished cell is obtained.

[0054] S2. After the semi-finished battery cell obtained in step S1 is left to stand at room temperature for 12 hours and then left to stand at high temperature for 24 hours, it is charged with 60% of the rated capacity and subjected to high temperature negative pressure formation.

[0055] S3. After the cells in step S2 have undergone high-temperature negative pressure formation, let them stand at room temperature for 30 minutes. The test voltage V1 is 2.982V. Then, let them stand at high temperature for 12 hours and then at room temperature for 1 hour. The test voltage V2 is 2.957V. Record the voltage change ΔV1 = V1 - V2 = 25mV. Then, perform a DCR1 test by constant current discharge at 2C for 5 seconds. Record R1 as 2.895mΩ. Perform preliminary screening of the cells based on the values ​​of ΔV1 and R1. If ΔV1 < 80mV and the range of R1 values ​​of cells in the group is ≤ 10%, it meets the preliminary screening standard.

[0056] S4. After the cells that passed the initial screening are injected with electrolyte a second time, they are allowed to stand for 2 hours and then subjected to capacity testing. They are discharged at a constant current of 0.5C to the cutoff voltage and at 0.1C to the cutoff voltage. The initial discharge capacity C1 is recorded as 33.6Ah, the initial coulombic efficiency CE is 85.8%, the initial discharge capacity C1 of the cell is ≥ the nominal capacity of 30Ah, the range within the group is ≤0.5%, and the range within the group of the initial coulombic efficiency CE is ≤1%. Proceed to the next step.

[0057] S5. After capacity grading, the cells are subjected to a 2C constant current discharge for 5 seconds and a DCR2 test is performed. The R2 value is recorded as 3.297mΩ. The cells are then charged with 30% of their rated capacity and subjected to a 2C constant current discharge for 5 seconds and a DCR3 test is performed. The R3 value is recorded as 3.150mΩ. The internal resistance change ΔR = |R3 - R2| = 0.147mΩ is calculated. The range of R2, R3, and ΔR values ​​within the group is ≤10%, and the ratio of ΔR to R3 is <5%. The cells are then used for grouping.

[0058] S6. After the cell from step S5 is left to stand at room temperature for 8 hours, then at high temperature for 24 hours, and then at room temperature for 48 hours, the voltage V4 is tested and found to be 2.840V. The voltage change ΔV2 = V3 - V4 = 4mV is recorded. ΔV2 ≤ 5mV and the range within group V4 ≤ 5mV, thus obtaining a sodium-ion battery.

[0059] Comparative Example 1

[0060] In Comparative Example 1, the battery cell underwent AC internal resistance testing, while the remaining manufacturing steps were the same as in Example 1. Voltage, internal resistance, capacity, and first-time efficiency all met the requirements of this invention.

[0061] Comparative Example 2

[0062] In Comparative Example 2, the battery cell underwent a DC internal resistance test. DCR1 and DCR2 tests were not performed; only DCR3 was tested. The remaining manufacturing steps were the same as in Example 2. Voltage, internal resistance, capacity, and first-time efficiency all met the requirements of this invention.

[0063] Comparative Example 3

[0064] In Comparative Example 3, the battery cell underwent a DC internal resistance test, and in step S5, it was charged to 70% of its rated capacity. The remaining manufacturing steps were the same as in Example 3. Voltage, internal resistance, capacity, and first-time efficiency all met the requirements of this invention.

[0065] Detection Examples

[0066] Cyclic tests were conducted on the batteries of Examples 1-3 and Comparative Examples 1-3, respectively.

[0067]

[0068] According to the test data, the battery packs of Examples 1-3 showed good consistency and good cycle stability at both room temperature and high temperature. Although the battery packs of Comparative Examples 1-3 had better matching results, the lack of AC and DC internal resistance testing and the fact that the charging amount in step S5 did not meet the scope of this invention resulted in an incomplete assessment of battery consistency and lower cycle stability compared to the Examples.

[0069] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for preparing a sodium-ion battery, characterized in that the steps include... include: S1. The sodium iron pyrophosphate positive electrode, hard carbon negative electrode and separator are assembled into a bare cell. After welding, casing, full welding, cell baking and one liquid injection, a semi-finished cell is obtained. S2. After the semi-finished battery cell obtained in step S1 is subjected to a first static treatment, it is then subjected to high-temperature negative pressure formation. S3. After the cells in step S2 have undergone high temperature negative pressure formation, let them stand at room temperature for 30 minutes and test the voltage V1. Then, let them stand at high temperature for 6-12 hours and at room temperature for 1 hour, test the voltage V2 and record the voltage change ΔV1=V1-V2. Then, perform the DCR1 test and record R1. Based on the values ​​of ΔV1 and R1, perform preliminary screening of the cells. S4. After the cells that pass the initial screening are injected with electrolyte a second time, let them stand for 6-12 hours, and then perform capacity testing. Record the first discharge capacity C1 and the first coulombic efficiency CE. If the cell's first discharge capacity C1 value is ≥ nominal capacity, the range within the group is ≤0.5%, and the range within the group of the first coulombic efficiency CE is ≤1%, then proceed to the next step. S5. Perform DCR2 test on the cells after capacity grading, record R2, charge with 10-60% of the rated capacity, and perform DCR3 test, record R3, and calculate the internal resistance change ΔR=|R3-R2|; if the values ​​of R2, R3, and ΔR meet the standard, they can be used for group matching. S6. After the battery cell from step S5 is left to stand at room temperature for 6-8 hours, it is subjected to high-temperature aging treatment, and then the voltage V4 is tested and the voltage change ΔV2=V3-V4 is recorded. If the values ​​of V4 and ΔV2 are qualified, a sodium-ion battery can be produced.

2. The preparation method according to claim 1, characterized in that, In step S2, the first settling process includes: settling at room temperature for 8-12 hours, and then settling at high temperature for 24-48 hours.

3. The preparation method according to claim 1, characterized in that, In step S2, the high-temperature negative pressure formation includes: charging with 20-60% of the rated capacity.

4. The preparation method according to claim 1, characterized in that, In step S3, the initial screening qualification conditions are: △V1<80mV, and the range of R1 values ​​of cells within the group is ≤10%.

5. The preparation method according to claim 1, characterized in that, In step S4, the capacity grading process includes: 0.5C constant current discharge to the cutoff voltage and 0.1C discharge to the cutoff voltage. The discharge capacity of the two steps is summed to obtain the initial discharge capacity of the cell.

6. The preparation method according to claim 1, characterized in that, In step S5, the criteria for grouping are: the range of R2, R3, and ΔR values ​​within a group are all ≤10%, and the ratio of ΔR value to R3 value is <5%.

7. The preparation method according to claim 1, characterized in that, In step S6, the high-temperature aging treatment includes: first, standing at high temperature for 24-72 hours, and then standing at room temperature for 24-72 hours.

8. The preparation method according to claim 1, characterized in that, In step S6, the qualification criteria are △V2≤5mV and the range within group V4≤5mV.

9. The preparation method according to claim 1, characterized in that, The test method for DCR1, DCR2 and DCR3 is the same: 2C constant current discharge for 5s.

10. A consistency verification method for sodium-ion batteries, characterized in that, The sodium-ion battery is a sodium-ion battery prepared by the method according to any one of claims 1-9, the steps of which include: A1. Perform capacity calibration on the sodium-ion battery pack and record the voltage difference ΔV between each cell under the condition of the battery pack being discharged. 放0 After fully charging, record the voltage difference ΔV between each cell when the battery pack is fully charged. 充0 Store the battery pack in a 60°C environment for 7 days, and record the voltage difference of each cell in the battery pack every 4 hours. A2. After 7 days, remove the battery pack and let it stand at room temperature for 4 hours. Record the voltage difference of each cell in the battery pack. A3. Discharge the battery pack to the cutoff voltage, obtain the retention capacity, calculate the capacity retention rate, and record the voltage difference ΔV between each cell under the battery pack discharge condition. 放1 After fully charging the battery pack, record the voltage difference ΔV between each cell when the battery pack is fully charged. 充1 ; A4. Calculate △V 放0 With △V 放1 The difference between them and ΔV 充0 With △V 充1 If any difference between the values ​​is greater than 20%, the battery consistency is considered poor, and the battery formation, aging, and capacity testing processes need to be adjusted.

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