A sodium ion battery cell consistency screening method and sodium ion battery pack

Abstract

A sodium ion battery cell consistency screening method and a sodium ion battery pack belong to the technical field of sodium ion battery cell screening, and overcome the defects of long sodium ion battery cell screening process and inaccurate screening in the prior art. The sodium ion battery cell consistency screening method of the present invention comprises the following steps: S1, discharge-charge pretreatment of the battery cell after capacity division, and record the pretreated battery cell voltage as OCV1; S2, after standing for T1 time, test the voltage to obtain OCV2; S3, calculate the voltage drop K of the battery cell per unit time = (OCV1-OCV2) / T1, eliminate the battery cells of #imgabs0# and #imgabs1#, #imgabs2# is the average value of K, and α is the standard deviation of K. The present invention can improve the consistency of sodium ion battery cell screening and improve the cycle performance of sodium ion battery packs.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion battery cell screening, and in particular relates to a sodium ion battery cell consistency screening method and a sodium ion battery pack. Background Art

[0002] Sodium-ion batteries are considered to be the most promising next-generation energy storage devices because their raw materials have abundant reserves and lower costs compared to lithium-ion batteries. Currently, the industrialization process of sodium-ion batteries basically replicates the process technology of lithium batteries, especially in the selection of battery cell assembly.

[0003] However, since the discharge curve of sodium-ion batteries is significantly different from that of lithium-ion batteries, their self-discharge conditions at different SOCs are somewhat different. Therefore, the K value sorting test of sodium-ion batteries cannot completely refer to the K value sorting test process of lithium-ion batteries.

[0004] Currently, there is no screening process for the consistency of sodium-ion battery cell matching; the existing lithium-ion battery cell screening technology mainly tests the open circuit voltage of the battery cell after capacity division through aging to eliminate polarization, and tests the open circuit voltage for the second time after the second aging, and calculates the K value using the difference between the two open circuit voltages. In this process, a higher temperature (30-60°C) is usually required, which increases energy consumption and costs; the existing lithium-ion battery cell screening process takes a long time (usually 7-14 days), increases storage space, and increases battery cell manufacturing costs. When screening sodium-ion batteries, the above problems still exist when copying the lithium-ion battery cell screening technology, and there is also the problem of inaccurate screening. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the prior art that the sodium ion battery cell screening process takes a long time and the screening is inaccurate, thereby providing a sodium ion battery cell consistency screening method and a sodium ion battery pack.

[0006] To this end, the present invention provides the following technical solutions.

[0007] A method for screening consistency of sodium ion batteries comprises the following steps:

[0008] S1, perform discharge-charge pretreatment on the cell after capacity division, and record the cell voltage after pretreatment as OCV1;

[0009] S2, after standing for T1, the test voltage is obtained to obtain OCV2;

[0010] S3, calculate the voltage drop of the battery cell per unit time K = (OCV1-OCV2) / T1, eliminate and The battery cell, is the mean value of K, and α is the standard deviation of K.

[0011] Furthermore, in S1, the discharge-charge pre-processing includes:

[0012] S11, after the battery cell is left to stand for T2 time, the battery cell is discharged at a rate of C1 to 1.5V;

[0013] S12, after the discharged battery cell is left to stand for a period of time T3, it is charged at a rate C2 to 1.6-2.75V.

[0014] Furthermore, the method further includes S13, repeating steps S11 to S12 1 to 10 times.

[0015] Furthermore, the T1 is 1 to 72 hours.

[0016] Furthermore, the T2 is 1 to 60 min; and / or

[0017] The T3 is 1 to 60 min.

[0018] Furthermore, the C1 is 0.05C-2C.

[0019] Furthermore, the C2 is 0.01C-2C.

[0020] Furthermore, the S1 is performed at room temperature.

[0021] Furthermore, S2 is performed at room temperature.

[0022] A sodium-ion battery pack is made from sodium-ion cells screened using a sodium-ion cell consistency screening method.

[0023] The technical solution of the present invention has the following advantages:

[0024] 1. The sodium ion battery cell consistency screening method provided by the present invention comprises the following steps: S1, performing discharge-charge pretreatment on the battery cell after capacity division, and recording the voltage of the pretreated battery cell as OCV1; S2, after standing for T1, testing the voltage to obtain OCV2; S3, calculating the voltage drop K of the battery cell per unit time = (OCV1-OCV2) / T1, and eliminating and The battery cell, is the mean value of K, and α is the standard deviation of K.

[0025] The discharge-charge pretreatment of the present invention does not stand still after charging is completed, and is directly recorded as OCV1. The polarization characteristics after charging are used to screen abnormal K value cells, and the abnormal cells are picked out before the polarization is eliminated. When the cell is polarized, the voltage of the cell decays faster, thereby increasing the K value, making the K value difference between the abnormal cell and the normal cell larger and easier to distinguish. At the same time, the present invention does not need to stand still to eliminate polarization after charging is completed. When the polarization is not eliminated, the voltage decays quickly, which can greatly shorten the screening process time and realize the rapid screening of cell matching.

[0026] Impedance will also affect the cycle performance of the grouped battery cells, and the consistency of impedance is reflected by the consistency of polarization. The consistency of the K value in the present invention can also reflect the consistency of polarization, thereby achieving impedance consistency matching, more accurate screening of abnormal battery cells, ensuring the consistency of battery cell matching, improving module cycle consistency, and improving cycle life.

[0027] 2. In the consistency screening method provided by the present invention, in S1, the discharge-charge pretreatment includes: S11, after the battery cell is allowed to stand for a period of time T2, the battery cell is discharged to 1.5V at a rate C1; S12, after the discharged battery cell is allowed to stand for a period of time T3, it is charged to 1.6-2.75V at a rate C2.

[0028] Under low voltage conditions, the impedance of the battery cell is large and its polarization effect is more obvious, so it is easier to screen out abnormal batteries.

[0029] 3. The consistency screening method provided by the present invention further comprises S13, repeating steps S11 to S12 1 to 10 times. Repeating the discharge and charge of the battery cell multiple times can further improve the polarization.

[0030] 4. In the consistency screening method provided by the present invention, the C1 is 0.05C-2C, and the C2 is 0.01C-2C. Rapid charging and discharging can not only shorten the test time, but also further improve polarization, thereby more accurately screening out abnormal batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 The voltage / internal resistance curves of the Cu-Fe-Mn ternary layered oxide-based sodium ion battery cell under different SOCs of the present invention;

[0033] Figure 2 is a K value diagram of Example 1 of the present invention;

[0034] Figure 3 K value diagram of Example 2 of the present invention;

[0035] Figure 4 K value diagram of Example 3 of the present invention;

[0036] Figure 5 K value diagram of Example 4 of the present invention;

[0037] Figure 6 K value diagram of comparative example 1 of the present invention;

[0038] Figure 7 K value diagram of Comparative Example 2 of the present invention;

[0039] Figure 8 Schematic diagram of charge and discharge cycle diagram of battery packs of Example 5 of the present invention and Comparative Examples 3 and 4; DETAILED DESCRIPTION

[0040] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0041] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0042] For cells of different systems, their voltage curves are not consistent. The present invention is directed to a sodium ion cell based on a Cu-Fe-Mn ternary layered oxide (the preparation method refers to patents CN105185997B and CN104795552B). The voltage / internal resistance curves under different SOCs are as follows: Figure 1 As shown. According to the SOC-OCV curve and the SOC-DCIR curve, when the cell voltage is lower than 2.75V, the DCIR of the cell changes greatly, and the slope of its K value change is also greater than when the voltage is higher than 2.75V. OCV is the open circuit voltage, and DCIR is the DC resistance.

[0043] The examples and comparative examples use cells produced in the same batch.

[0044] Example 1

[0045] This embodiment provides a method for screening consistency of sodium ion batteries, which specifically adopts the following steps:

[0046] S1, perform discharge-charge pretreatment on the divided cells, and record the pretreated battery voltage as OCV1, specifically including:

[0047] S11, let the battery stand at room temperature (25°C) for 5 minutes, and discharge it to 1.5V at a rate of 0.2C;

[0048] S12, let the discharged battery stand for 5 minutes, and charge it to 2.4V at a rate of 0.02C;

[0049] S13, repeat the above steps S11-S12 twice, and read the terminal voltage OCV1 after completion.

[0050] S2. Let stand for 24 hours and test the voltage to obtain OCV2.

[0051] S3 calculates the pressure drop per unit time K = (OCV1-OCV2) / T1, and obtains Table 1 and Figure 2 , remove and The battery cell, is the mean value of K, and α is the standard deviation of K.

[0052] Table 1 K value of each battery cell in Example 1 (mV / h)

[0053] Serial number K Value Serial number K Value Serial number K Value Serial number K Value 1 0.080 9 0.075 17 0.078 25 0.077 2 0.075 10 0.135 18 0.080 26 0.079 3 0.075 11 0.074 19 0.081 27 0.082 4 0.073 12 0.077 20 0.073 28 0.079 5 0.124 13 0.071 21 0.079 29 0.082 6 0.075 14 0.080 22 0.084 30 0.077 7 0.070 15 0.079 23 0.170 31 0.080 8 0.070 16 0.085 24 0.073 32 0.089

[0054] This embodiment of is 0.084mV / h, α is 0.020mV / h, and the K values ​​of the 5th, 10th, and 23rd cells are greater than This is a battery cell with an abnormal K value.

[0055] Example 2

[0056] This embodiment provides a method for screening consistency of sodium ion batteries, which specifically adopts the following steps:

[0057] S1, perform discharge-charge pretreatment on the divided cells, and record the pretreated battery voltage as OCV1, specifically including:

[0058] S11, let the divided cells stand at room temperature (25°C) for 5 minutes, and discharge them at a rate of 0.2C to 1.5V;

[0059] S12, let the discharged battery stand for 5 minutes, and charge it to 2.4V at a rate of 0.02C;

[0060] S13, repeat the above steps S11-S12 twice, and read the terminal voltage OCV1 after completion.

[0061] S2. Let stand for 1 hour and test the voltage to obtain OCV2.

[0062] S3 calculates the pressure drop per unit time K = (OCV1-OCV2) / T1, and obtains Table 2 and Figure 3 , remove and The battery cell, is the mean value of K, and α is the standard deviation of K.

[0063] Table 2 K value of each battery cell in Example 2 (mV / h)

[0064]

[0065]

[0066] This embodiment of is 0.334mV / h, α is 0.152mV / h, and the 7th, 13th, and 20th cells have abnormal K values.

[0067] Example 3

[0068] This embodiment provides a method for screening consistency of sodium ion batteries, which specifically adopts the following steps:

[0069] S1, perform discharge-charge pretreatment on the divided cells, and record the pretreated battery voltage as OCV1, specifically including:

[0070] S11, let the divided cells stand at room temperature (25°C) for 1 min, and discharge them to 1.5V at a rate of 0.05C;

[0071] S12, let the discharged battery stand for 1 minute, and charge it to 1.6V at a rate of 0.01C; after completion, read the terminal voltage OCV1.

[0072] S2. Let stand for 1 hour and test the voltage to obtain OCV2.

[0073] S3 calculates the pressure drop per unit time K = (OCV1-OCV2) / T1, and obtains Table 3 and Figure 4 , remove and The battery cell, is the mean value of K, and α is the standard deviation of K.

[0074] Table 3 K value of each battery cell in Example 3 (mV / h)

[0075] Serial number K Value Serial number K Value Serial number K Value Serial number K Value 1 0.050 9 0.054 17 0.049 25 0.154 2 0.049 10 0.141 18 0.052 26 0.047 3 0.054 11 0.048 19 0.050 27 0.055 4 0.052 12 0.053 20 0.049 28 0.048 5 0.048 13 0.055 21 0.056 29 0.046 6 0.045 14 0.052 22 0.056 30 0.047 7 0.049 15 0.050 23 0.055 31 0.053 8 0.047 16 0.172 24 0.055 32 0.049

[0076] This embodiment of is 0.061mV / h, α is 0.031mV / h, and the 10th, 16th, and 25th cells have abnormal K values.

[0077] Example 4

[0078] This embodiment provides a method for screening consistency of sodium ion batteries, which specifically adopts the following steps:

[0079] S1, perform discharge-charge pretreatment on the divided cells, and record the pretreated battery voltage as OCV1, specifically including:

[0080] S11, let the divided cells stand at room temperature (25°C) for 60 minutes, and discharge them at a rate of 2C to 1.5V;

[0081] S12, let the discharged battery stand for 60 minutes, and charge it to 2.75V at a rate of 2C;

[0082] S13, repeat the above steps S11-S12 for 9 times, and read the terminal voltage OCV1 after completion.

[0083] S2. Let stand for 72 hours and test the voltage to obtain OCV2.

[0084] S3 calculates the pressure drop per unit time K = (OCV1-OCV2) / T1, and obtains Table 4 Figure 5 , remove and The battery cell, is the mean value of K, and α is the standard deviation of K.

[0085] Table 4 K value of each battery cell in Example 4 (mV / h)

[0086] Serial number K Value Serial number K Value Serial number K Value Serial number K Value 1 0.134 9 0.136 17 0.137 25 0.137 2 0.136 10 0.135 18 0.138 26 0.138 3 0.152 11 0.136 19 0.138 27 0.154 4 0.136 12 0.137 20 0.139 28 0.138 5 0.138 13 0.156 21 0.137 29 0.138 6 0.136 14 0.138 22 0.139 30 0.137 7 0.138 15 0.137 23 0.135 31 0.134 8 0.134 16 0.137 24 0.136 32 0.141

[0087] This embodiment of is 0.138mV / h, α is 0.005mV / h, and the 3rd, 13th, and 27th cells have abnormal K values.

[0088] Example 5

[0089] This embodiment provides a sodium ion battery pack, which is assembled using the battery cells screened in Example 1.

[0090] Comparative Example 1

[0091] This comparative example provides a method for screening consistency of sodium ion batteries, which specifically adopts the following steps:

[0092] S1, perform discharge-charge pretreatment on the cells after capacity division, let the pretreated batteries stand for a period of time, and then measure the voltage and record it as OCV1, which includes:

[0093] S11, let the divided cells stand at room temperature (25°C) for 5 minutes, and discharge them at a rate of 0.2C to 1.5V;

[0094] S12, let the discharged battery stand for 5 minutes, and charge it to 2.4V at a rate of 0.02C;

[0095] S13. Repeat the above steps S11-S12 twice, then let it stand for 72 hours and measure the voltage OCV1.

[0096] S2. Let stand for 24 hours and test the voltage to obtain OCV2.

[0097] S3 calculates the pressure drop per unit time K = (OCV1-OCV2) / T1, and obtains Table 5 and Figure 6 , remove and The battery cell, is the mean value of K, and α is the standard deviation of K.

[0098] Table 5 K value of each battery cell in comparative example 1 (mV / h)

[0099] Serial number K Value Serial number K Value Serial number K Value Serial number K Value 1 0.047 9 0.047 17 0.047 25 0.048 2 0.048 10 0.047 18 0.045 26 0.046 3 0.045 11 0.047 19 0.046 27 0.047 4 0.047 12 0.048 20 0.057 28 0.046 5 0.047 13 0.049 21 0.046 29 0.045 6 0.045 14 0.045 22 0.047 30 0.048 7 0.049 15 0.046 23 0.046 31 0.046 8 0.045 16 0.048 24 0.048 32 0.046

[0100] This comparative example It is 0.047mV / h, α is 0.002mV / h, and only one abnormal cell (the 20th) was found.

[0101] This comparative example includes two static periods. After the first static period, the polarization of the battery cell will be obviously eliminated. Testing the K value during the second static period cannot guarantee that the battery cell with abnormal K value can be accurately screened out.

[0102] Comparative Example 2

[0103] This comparative example uses the existing lithium-ion battery consistency detection method for screening, and the test steps are as follows:

[0104] Charge the divided cells to 3.0V (50% SOC);

[0105] Place the battery cell in a 45°C oven for 48 hours;

[0106] Place the battery at room temperature (25±3℃) for 48 hours and then test OCV1.

[0107] Place the battery at room temperature (25±3℃) for 72 hours and then test OCV2.

[0108] Calculate K value = (OCV1-OCV2) / 72h, and obtain Table 6 and Figure 7 .

[0109] Table 6 K value of each battery cell in comparative example 2 (mV / h)

[0110] Serial number K Value Serial number K Value Serial number K Value Serial number K Value 1 0.069 9 0.069 17 0.069 25 0.069 2 0.069 10 0.070 18 0.069 26 0.069 3 0.069 11 0.069 19 0.069 27 0.070 4 0.069 12 0.069 20 0.070 28 0.070 5 0.069 13 0.070 21 0.069 29 0.069 6 0.069 14 0.070 22 0.069 30 0.070 7 0.070 15 0.069 23 0.069 31 0.070 8 0.069 16 0.069 24 0.069 32 0.069

[0111] This comparative example is 0.069mV / h, α is 0.0003mV / h, using and No abnormal K value cells were found during the method screening; if and The method screening has the risk of over-killing a large number of battery cells, which affects the actual product qualification rate.

[0112] Comparative Example 3

[0113] This comparative example provides a sodium ion battery pack, which is assembled using the battery cells screened out in comparative example 1. Except for the different battery cell consistency screening method, the rest is the same as that of embodiment 5.

[0114] Comparative Example 4

[0115] This comparative example provides a sodium ion battery pack, which is assembled using the battery cells screened out in comparative example 2. Except for the different battery cell consistency screening method, the rest is the same as that of embodiment 5.

[0116] Test example

[0117] The sodium ion battery packs of Example 5, Comparative Example 3 and Comparative Example 4 were subjected to charge and discharge cycle tests, and the specific cycle steps were as follows:

[0118] 1) Let stand for 5 minutes;

[0119] 2) 1C constant current charging to 3.95V, constant voltage to 0.05C;

[0120] 3) Let stand for 5 minutes;

[0121] 4) 1C constant current discharge to 1.5V;

[0122] 5) Repeat steps 1) to 4) 1000 times.

[0123] The cycle results are as follows Figure 8 As shown, in the early stage of the cycle, the trends of Example 5 are basically consistent with those of Comparative Examples 3 and 4. As the number of cycles increases, the polarization of the battery pack increases and the capacity attenuation increases due to the presence of abnormal K-value cells that may not be selected in the comparative examples. When the cycle reaches 574 weeks, the retention rate of Example 5 is 93.27%, the retention rate of Comparative Example 3 is 91.65%, and the retention rate of Comparative Example 4 is 90.45%.

[0124] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A method for screening consistency of sodium ion batteries, characterized in that: The following steps are involved: S1, perform discharge-charge pretreatment on the cells after capacity division, and directly record the voltage of the cells as OCV1 without letting them stand after pretreatment; S2, after standing for T1, the test voltage is obtained to obtain OCV2; S3. Calculate the voltage drop of the battery cell per unit time K = (OCV1-OCV2) / T1, and eliminate the battery cells with K>K+α and K<K-α, where K is the average value of K and α is the standard deviation of K.

2. The method for screening consistency of sodium ion batteries according to claim 1, characterized in that: In S1, the discharge-charge pre-processing includes: S11, after the battery cell is left to stand for T2 time, the battery cell is discharged at a rate of C1 to 1.5V; S12, after the discharged battery cell is left to stand for a period of time T3, it is charged at a rate C2 to 1.6-2.75V.

3. The method for screening consistency of sodium ion batteries according to claim 2, characterized in that: The method further comprises S13, repeating steps S11 to S12 1 to 10 times.

4. The method for screening consistency of sodium ion batteries according to any one of claims 1 to 3, characterized in that: The T1 is 1 to 72 hours.

5. The method for screening consistency of sodium ion batteries according to claim 2, characterized in that: The T2 is 1 to 60 min; and / or The T3 is 1 to 60 min.

6. The method for screening consistency of sodium ion batteries according to claim 2, characterized in that: The C1 is 0.05C-2C.

7. The method for screening consistency of sodium ion batteries according to claim 2, characterized in that: The C2 is 0.01C-2C.

8. The method for screening consistency of sodium ion batteries according to any one of claims 1 to 3, characterized in that: The S1 was performed at room temperature.

9. The method for screening consistency of sodium ion batteries according to claim 8, characterized in that: The S2 is performed at room temperature.

10. A sodium ion battery pack made from sodium ion cells screened using the sodium ion cell consistency screening method according to any one of claims 1 to 9.

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