A Detection Method for Vacuum Blockage during Negative Pressure Formation of a Lithium-Ion Battery

Abstract

A method for detecting vacuum blockage in the negative-pressure formation of a lithium-ion battery proposed by the present invention. S1: First, divide the lithium-ion batteries of the same batch into M detection units, and each detection unit includes N detection groups, where N is a positive integer and N≥2; S2: Perform negative-pressure formation on the M detection units. The negative-pressure formation includes two steps: pre-formation and conventional formation. At least one of the first factors in the pre-formation process of different detection units is different, and the other processes are the same. The vacuum degrees in the pre-formation of different detection groups in the same detection unit are different, and the voltage values of the lithium-ion batteries are recorded correspondingly; S3: From the M detection units, select the detection units with relatively large differences in the voltage values of the lithium-ion batteries in different groups in the same detection unit as the screening detection units, and calculate the screening voltage for the lithium-ion batteries in the screening detection units; S4: Under the screening formation process, perform negative-pressure formation on the lithium-ion batteries to be screened, and screen out the lithium-ion batteries with voltage values exceeding the screening voltage; it can quickly determine the blockage position of the series equipment and reduce the equipment troubleshooting time.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a method for detecting vacuum blockage in negative pressure formation of lithium ion batteries. Background Art

[0002] Lithium ion batteries have the advantages of high energy density, long cycle life, small self-discharge, and no memory effect. Since their commercialization, they have received extensive attention and applications. However, safety and cost issues have also become major obstacles to the development of lithium ion batteries. In order to prevent the introduction of moisture and foreign objects into the square battery during the formation process, most current battery manufacturers adopt series negative pressure formation. However, during the formation process, there will be situations where lithium plating or swelling of the battery occurs due to insufficient negative pressure or blockage of the negative pressure port, which will result in the scrapping of lithium ion batteries and increase the risk of shipped batteries. Therefore, it is extremely important to pick out the batteries before the formation of lithium ion batteries is defective. However, there is no effective method to avoid this problem so far. Summary of the Invention

[0003] Based on the technical problems existing in the background art, the present invention proposes a method for detecting vacuum blockage in negative pressure formation of lithium ion batteries.

[0004] S1. First, divide the same batch of lithium batteries into M detection units, and each detection unit includes N detection groups, where N is a positive integer and N≥2;

[0005] S2. Perform negative pressure formation on the M detection units. The negative pressure formation includes two steps: pre-formation and conventional formation. At least one of the first factors in the pre-formation process of different detection units is different, and the other processes are the same. The vacuum degrees in the pre-formation of different detection groups in the same detection unit are different, and the voltage values of the lithium batteries are recorded correspondingly;

[0006] S3. Select the detection unit with the largest difference in voltage values of lithium batteries in different groups in the same detection unit from the M detection units as the screening detection unit, and calculate the screening voltage for the lithium batteries in the screening detection unit;

[0007] S4. Under the screening formation process, perform negative pressure formation on the lithium batteries to be screened, and screen out the lithium batteries with voltage values exceeding the screening voltage;

[0008] The first factor is the formation condition that can amplify the change trend of the voltage difference due to different vacuum degrees. The screening formation process is the negative pressure formation process in which the vacuum degree of the pre-formation is the same as that of the conventional formation and the other formation processes are exactly the same as the corresponding formation processes in the screening detection unit.

[0009] Preferably, the pre-formation step S11 includes:

[0010] S111. Place for 5 min, with a vacuum degree of 0 KPa to -60 KPa;

[0011] S112. Constant current charging, with a voltage limit of 3.2 V and a time limit of 20 min, with a vacuum degree of 0 KPa to -60 KPa;

[0012] S113. Place for 10 min, with a vacuum degree of 0 KPa to -60 KPa;

[0013] S114. Constant current charging, with a voltage limit of 3.2 V and a time limit of 30 min, with a vacuum degree of 0 KPa to -60 KPa;

[0014] S115. Shelve for a certain time, with a vacuum degree of -60 KPa.

[0015] Preferably, in the step S112, the constant charging current is 0.02C to 0.1C, and in the step S114, the shelving time is 1 to 30 min.

[0016] Preferably, in the step S1, the conventional forming step S12 includes:

[0017] S121: Constant current charging at 120 mA (0.02C), with a voltage limit of 3.2 V and a time limit of 240 min, with a vacuum degree of -60 KPa;

[0018] S122. Place for 3 min; with a vacuum degree of -60 KPa;

[0019] S123: Constant current charging at 600 mA (0.05C), with a voltage limit of 3.4 V and a time limit of 90 min; with a vacuum degree of -60 KPa;

[0020] S124. Place for 3 min, with a vacuum degree of -60 KPa;

[0021] S125: Constant current charging at 2400 mA (0.05C), with a voltage limit of 3.85 V and a time limit of 180 min, with a vacuum degree of -60 KPa;

[0022] S126. Place for 1 min, with a vacuum degree of -60 KPa.

[0023] Preferably, in the step S2, the first factor includes the constant charging current and the shelving time.

[0024] Preferably, the one detection unit includes three detection groups, and the corresponding vacuum degrees in the pre-forming are 0 / -30 / -60 KPa respectively.

[0025] Preferably, the step S4 specifically includes: S41. When the voltage of the lithium battery exceeds the screening voltage, automatically stop forming and remove the lithium battery;

[0026] After removing unqualified lithium batteries, automatically resume the low-voltage formation of lithium batteries.

[0027] Preferably, in the step S3, it includes:

[0028] S31: Each of the detection groups includes a plurality of lithium batteries. Take the median voltage of the lithium batteries in each detection group, calculate the voltage difference of each detection unit, and determine the detection unit with the largest voltage difference as the screening detection unit.

[0029] S32: Select N detection groups from the screening detection units, select the maximum voltage value V1 from the detection groups with smaller voltage values, and select the minimum voltage value V2 from the detection groups with larger voltage values;

[0030] S33: Screen the voltage V = (V1 + V2) / 2.

[0031] The beneficial effects of the present invention: It can be achieved only by setting the screening voltage V on the original formation equipment, without increasing additional costs. At the same time, the use of this method can quickly determine the blockage position of the series equipment, reduce the equipment troubleshooting time, improve the formation yield and efficiency, and is simple, efficient, and cost-saving. Description of the Drawings

[0032] Figure 1 is the formation process of the a1 / a2 / a3 group of batteries;

[0033] Figure 2 is the formation process of the b1 / b2 / b3 group of batteries;

[0034] Figure 3 is the formation process of the c1 / c2 / c3 group of batteries;

[0035] Figure 4 is the formation end voltage of the a1 / a2 / a3 group of batteries;

[0036] Figure 5 is the formation end voltage of the b1 / b2 / b3 group of batteries;

[0037] Figure 6 is the formation end voltage of the c1 / c2 / c3 group of batteries; Detailed Embodiments

[0038] Refer to Figure 1-6

[0039] The present invention provides a method for detecting vacuum blockage in the negative-pressure formation of lithium-ion batteries, including:

[0040] S1. First, divide the lithium batteries of the same batch into 3 detection units. Each of the detection units includes 3 detection groups, and N is a positive integer and N≥2;

[0041] S2. Perform negative pressure formation on three detection units. The negative pressure formation includes two steps: pre-formation first and then conventional formation. At least one of the first factors in the pre-formation process of different detection units is different, and the other processes are the same. The vacuum degrees in the pre-formation of different detection groups in the same detection unit are different, and the voltage values of the lithium batteries are recorded correspondingly. The first factors include constant charging current and soaking time.

[0042] S3. From the M detection units, select the detection units with a large difference in the voltage values of different groups of lithium batteries in the same detection unit as the screening detection units, and calculate the screening voltage for the lithium batteries in the screening detection units.

[0043] S4. Under the screening formation process, perform pre-formation and conventional formation on the other lithium batteries that have not been screened first, and screen out the lithium batteries with voltage values exceeding the screening voltage.

[0044] The screening formation process is a negative pressure formation process in which the vacuum degree of pre-formation is the same as that of conventional formation, and the other formation processes are exactly the same as the corresponding formation processes in the screening detection unit.

[0045] Combined Figure 4 It can be seen that when the constant charging current and soaking time in the pre-formation are not adjusted, the voltage values measured at different vacuum degrees in different detection groups of the same detection unit have a small difference, which leads to a large error when calculating the screening voltage and a poor screening effect.

[0046] During the small current stage of the formation of lithium-ion batteries, a large amount of gas is generated due to the formation of the SEI film. Since the adhesion between the separator and the electrode is large, the separator and the electrode of the battery will not separate under the condition of good vacuum, resulting in hindered lithium-ion migration. However, when the formation vacuum degree does not meet the standard, due to the large amount of gas generated that cannot be discharged, there will be a large number of bubbles between the electrode and the separator. As time goes by, the lithium-ion migration is hindered, resulting in an increase in the internal polarization of the battery, which is directly reflected in the increase in voltage.

[0047] That is, both the soaking time and the constant charging current will affect the voltage of the lithium battery during the formation process. Therefore, by setting multiple detection units and making the soaking time and constant charging current in the pre-formation different, it is convenient to determine the best formation process for amplifying the voltage difference change trend at different vacuum degrees by comparing the voltage differences of the lithium batteries in the detection units, and use the voltage value of this detection unit to calculate the screening voltage, thereby improving the accuracy of the screening voltage calculation and facilitating the detection of unqualified lithium batteries in series-connected lithium batteries.

[0048] In this embodiment, the pre-formation step S11 includes:

[0049] S111. Place for 5 min, with a vacuum degree of 0 KPa to -60 KPa;

[0050] S112. Constant current charging, with a voltage limit of 3.2 V, for a time limit of 20 min, with a vacuum degree of 0 KPa to -60 KPa;

[0051] S113. Place for 10 min, with a vacuum degree of 0 KPa to -60 KPa;

[0052] S114. Constant current charging, with a voltage limit of 3.2 V, for a time limit of 30 min, with a vacuum degree of 0 KPa to -60 KPa;

[0053] S115. Shelve for a certain time, with a vacuum degree of -60 KPa.

[0054] In the step S112, the constant charging current is 0.02C to 0.1C, and in the step S114, the shelving time is 1 to 30 min.

[0055] In this embodiment, in the step S1, the conventional forming step S12 includes:

[0056] S121: Constant current charging at 120 mA (0.02C), with a voltage limit of 3.2 V, for a time limit of 240 min, with a vacuum degree of -60 KPa;

[0057] S122. Place for 3 min; with a vacuum degree of -60 KPa;

[0058] S123: Constant current charging at 600 mA (0.05C), with a voltage limit of 3.4 V, for a time limit of 90 min; with a vacuum degree of -60 KPa;

[0059] S124. Place for 3 min, with a vacuum degree of -60 KPa;

[0060] S125: Constant current charging at 2400 mA (0.05C), with a voltage limit of 3.85 V, for a time limit of 180 min, with a vacuum degree of -60 KPa;

[0061] S126. Place for 1 min, with a vacuum degree of -60 KPa.

[0062] In this embodiment, the one detection unit includes three detection groups, and the corresponding vacuum degrees in the pre-forming of the three detection groups are 0 / -30 / -60 KPa respectively.

[0063] Due to the different vacuum degrees of different detection groups in the same detection unit, it can better simulate the situation of lithium metal plating or swelling of the lithium battery caused by insufficient negative pressure or blocked negative pressure port, and thus more accurately screen out unqualified lithium batteries.

[0064] In this embodiment, step S3 includes: S31: Each detection group includes multiple lithium batteries. Take the median voltage of the lithium batteries in each detection group, calculate the voltage difference of the detection unit, and determine the detection unit with the largest voltage difference as the screening detection unit.

[0065] S32: Select N detection groups from the screening detection units. Select the maximum voltage value V1 from the detection groups with smaller voltage values, and select the minimum voltage value V2 from the detection groups with larger voltage values.

[0066] S33: Screen the voltage V = (V1 + V2) / 2.

[0067] When taking the median voltage of the lithium batteries in each detection group and calculating the voltage difference of each detection unit, it can avoid the influence of the voltage values of unqualified lithium batteries on the screening detection unit.

[0068] In this embodiment, step S4 specifically includes: S41: When the voltage of the lithium battery exceeds the screening voltage, automatically stop formation and remove the lithium battery.

[0069] S42: After removing the unqualified lithium batteries, automatically resume the low-voltage formation of the lithium batteries.

[0070] That is, it realizes the positioning and screening of series-connected lithium batteries during the formation process, improving the screening efficiency of lithium batteries. Embodiment

[0071] S1: Take lithium-ion batteries produced in the same batch and divide them into three detection units, A, B, and C. The A detection unit includes three detection groups, a1, a2, and a3 respectively; the B detection unit includes three detection groups, b1, b2, and b3 respectively; the C detection unit includes three detection groups, c1, c2, and c3 respectively. Each detection group includes 3 lithium batteries.

[0072] S2: The A detection groups a1, a2, and a3 are first subjected to pre-formation respectively, and the vacuum degrees during the pre-formation are 0 / -30 / -60 KPa respectively, and the other process steps are the same.

[0073] The pre-formation S11 includes:

[0074] S111: Stand for 5 min, vacuum degree 0 / -30 / -60 KPa;

[0075] S112: Constant current charge at 120 mA (0.02C), limited voltage 3.2V, limited time 20 min, vacuum degree 0 / -30 / -60 KPa;

[0076] S113: Stand for 10 min, vacuum degree 0 / -30 / -60 KPa;

[0077] S114: Constant current charging at 120 mA (0.02C), with a voltage limit of 3.2 V, a time limit of 30 min, and a vacuum degree of 0 / -30 / -60 KPa;

[0078] S115: Standby for 1 min, with a vacuum degree of -60 KPa;

[0079] When performing normalization on the three detection groups a1, a2, and a3 uniformly, the normalization includes:

[0080] S121: Constant current charging at 120 mA (0.02C), with a voltage limit of 3.2 V, a time limit of 240 min, and a vacuum degree of -60 KPa;

[0081] S122: Standby for 3 min; with a vacuum degree of -60 KPa;

[0082] S123: Constant current charging at 600 mA (0.05C), with a voltage limit of 3.4 V, a time limit of 90 min; with a vacuum degree of -60 KPa;

[0083] S124: Standby for 3 min, with a vacuum degree of -60 KPa;

[0084] S125: Constant current charging at 2400 mA (0.05C), with a voltage limit of 3.85 V, a time limit of 180 min, and a vacuum degree of -60 KPa;

[0085] S126: Standby for 1 min, with a vacuum degree of -60 KPa.

[0086] And record the voltage data V of the three detection groups a1, a2, and a3 a1 : 2.815 v, 2.816 v, 2.82 v; V a2: : 2.805, 2.807 V, 2.81; V a3 : 2.79, 2.795, 2.797 V;

[0087] Take the middle voltage value of each group for voltage difference calculation: V a1 -V a3 = 21 Mv, that is, in the A detection unit, the maximum pressure difference between each detection group is 21 Mv.

[0088] Then, in the B detection unit, the three detection groups b1, b2, and b3 are first pre - normalized respectively, and the vacuum degrees in the pre - normalization are 0 / -30 / -60 KPa respectively, and the other process steps are the same;

[0089] The pre - normalization process steps include:

[0090] S111: Standby for 5 min, with a vacuum degree of 0 / -30 / -60 KPa:

[0091] S112: Constant current charging at 600 mA (0.1C), with a voltage limit of 3.2 V, a time limit of 20 min, and a vacuum degree of 0 / -30 / -60 KPa

[0092] S113: Stand for 10 min, with a vacuum degree of 0 / -30 / -60 KPa;

[0093] S114: Constant current charging at 600 mA (0.1C), with a voltage limit of 3.2 V, a time limit of 30 min, and a vacuum degree of 0 / -30 / -60 KPa;

[0094] S15: Stand for 1 min, with a vacuum degree of -60 KPa;

[0095] In the B detection unit, the three detection groups b1, b2, and b3 are uniformly normalized, and the normalization steps are the same as those of the B detection unit.

[0096] And record the voltage data V of the three detection groups b1, b2, and b3 b1 = 2.857 v, 2.858 v, 2.86 v; V b2 = 2.835 v, 2.840 v, 2.848; V b3 = 2.805 v, 2.810 v, 2.815 v;

[0097] Take the middle voltage value of each group for voltage difference calculation: the said V b3 -V b1 = 48 Mv, that is, in the B detection unit, the maximum pressure difference between each detection group is 48 Mv.

[0098] In the C detection unit, c1, c2, and c3 are first pre - normalized respectively, and the vacuum degrees in the pre - normalization are 0 / -30 / -60 KPa respectively, and the other steps are the same;

[0099] The said pre - normalization S1 includes:

[0100] S111: Stand for 5 min, with a vacuum degree of 0 / -30 / -60 KPa;

[0101] S112: Constant current charging at 120 mA (0.02C), with a voltage limit of 3.2 V, a time limit of 20 min, and a vacuum degree of 0 / -30 / -60 KPa; S113: Stand for 10 min, with a vacuum degree of 0 / -30 / -60 KPa;

[0102] S114: Constant current charging at 120 mA (0.02C), with a voltage limit of 3.2 V, a time limit of 30 min, and a vacuum degree of 0 / -30 / -60 KPa;

[0103] S115: Stand for 30 min, with a vacuum degree of -60 KPa;

[0104] When normalizing the three detection groups c1, c2, and c3 in the C detection unit uniformly, the normalization process steps are the same as those of the B detection unit.

[0105] And record the voltage data V of the three detection groups c1, c2, and c3 c1 = 2.855v, 2.856v, 2.861; V c2 = 2.835, 2.84, 2.848V, V c3 = 2.805v, 2.810v, 2.816;

[0106] Take the middle voltage value of each group for voltage difference calculation: V c1 -V c3 = 45Mv, that is, in the C detection unit, the pressure difference of each detection group is 45Mv.

[0107] S3. Compare the three groups of voltage values collected, calculate the magnitude of the pressure difference, and select the B detection unit with a larger pressure difference in each detection group.

[0108] Select the maximum voltage value V1 = 2.815v from the detection group b3 with a smaller voltage value, and select the minimum voltage value V2 = 2.857v from the detection group b1 with a larger voltage value; screen the voltage V = (V1 + V2) / 2 ≈ 2.836v.

[0109] S4. Under the formation process steps of the B detection unit and with a negative pressure voltage constantly at -60Kpa, perform formation on other non-detected series-connected lithium batteries. Once it is detected that the voltage exceeds the screened voltage during the formation of the lithium battery, stop the formation and screen out the unqualified lithium batteries.

[0110] The above is only the preferred specific implementation manner involved in the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. A method for detecting vacuum blockage during negative pressure formation of a lithium-ion battery, characterized in that, S1. First, divide the same batch of lithium batteries into M detection units, and each detection unit includes N detection groups, where N is a positive integer and N≥2; S2. Perform negative pressure formation on the M detection units. The negative pressure formation includes two steps: pre-formation first and then conventional formation. At least one of the first factors in the pre-formation process of different detection units is different, and the other processes are the same. The vacuum degrees in the pre-formation of different detection groups in the same detection unit are different, and the voltage values of the lithium batteries are recorded correspondingly; S3. From the M detection units, select the detection unit with the largest voltage difference between different groups of lithium batteries in the same detection unit as the screening detection unit, and calculate the screening voltage for the lithium batteries in the screening detection unit; The step S3 includes: S31: Each detection group includes multiple lithium batteries. Take the voltage median value of the lithium batteries in each detection group to calculate the voltage difference of the detection unit, and determine the detection unit with the largest voltage difference as the screening detection unit; S32: From the N detection groups in the screening detection unit, select the maximum voltage value V1 from the detection group with a smaller voltage value, and select the minimum voltage value V2 from the detection group with a larger voltage value; S33: The screening voltage is V = (V1 + V2) / 2; S4. Under the screening formation process, perform pre-formation and conventional formation on the other lithium batteries that have not been screened first, and screen out the lithium batteries with voltage values exceeding the screening voltage; The first factor is the formation condition that can amplify the voltage difference change trend due to different vacuum degrees. The screening formation process is the negative pressure formation process in which the vacuum degree of pre-formation is the same as that of conventional formation and the other formation processes are exactly the same as the corresponding formation processes in the screening detection unit; the first factors in the step S2 include constant charging current and soaking time; The step S4 specifically includes: S41. When the voltage of the lithium battery exceeds the screening voltage, automatically stop the formation and remove the lithium battery; S42. After removing the unqualified lithium batteries, automatically resume the low-voltage formation of the lithium batteries.

2. The method for detecting vacuum blockage during negative pressure formation of a lithium-ion battery according to claim 1, characterized in that, The pre-formation step S11 includes: S111. Place for 5 min, with a vacuum degree of 0 KPa to -60 KPa; S112. Constant current charging, with a voltage limit of 3.2 V and a time limit of 20 min, with a vacuum degree of 0 KPa to -60 KPa; S113. Place for 10 min, with a vacuum degree of 0 KPa to -60 KPa; S114. Constant current charging, with a voltage limit of 3.2 V and a time limit of 30 min, with a vacuum degree of 0 KPa to -60 KPa; S115. Soak for a certain time, with a vacuum degree of -60 KPa.

3. The method for detecting vacuum blockage during negative pressure formation of a lithium-ion battery according to claim 2, characterized in that, The constant charging current in the step S112 is 0.02C to 0.1C, and the soaking time in the step S114 is 1 to 30 min.

4. The method for detecting vacuum blockage during negative pressure formation of a lithium-ion battery according to claim 1, characterized in that, In the said step S1, the normalization into step S12 includes: S121: Constant current charging at 120 mA (0.02C), with a voltage limit of 3.2 V, a time limit of 240 min, and a vacuum degree of -60 KPa; S122: Place for 3 min; vacuum degree -60 KPa; S123: Constant current charging at 600 mA (0.05C), with a voltage limit of 3.4 V, a time limit of 90 min; vacuum degree -60 KPa; S124: Place for 3 min, vacuum degree -60 KPa; S125: Constant current charging at 2400 mA (0.05C), with a voltage limit of 3.85 V, a time limit of 180 min, and a vacuum degree of -60 KPa; S126: Place for 1 min, vacuum degree -60 KPa.

5. The method for detecting vacuum blockage in negative pressure formation of the lithium-ion battery according to claim 1, characterized in that the said one detection unit includes three detection groups, and the corresponding vacuum degrees during pre-formation of the three detection groups are 0 / -30 / -60 KPa respectively.

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