Battery consistency evaluation method

Abstract

The invention discloses a battery consistency evaluation method, which comprises the following steps of S1, correspondingly extracting a plurality of batteries from different batches of batteries, dividing the batteries into groups according to the corresponding batches, and carrying out battery capacity grading; s2, extracting part of the batteries after capacity grading, and carrying out instant pressure intensity test to obtain pressure intensity P1; s3, part of batteries are extracted from the remaining batteries of the corresponding groups for high-temperature circulation, part of batteries are selected from the batteries subjected to high-temperature circulation for gas production pressure testing, and the testing numerical value is P2; s4, in the step S3, the remaining batteries subjected to high-temperature circulation treatment in the corresponding groups are selected to be subjected to gas production rate testing, the gas production rate is V2, and then a preset value P0 meeting circulation consistency is set; and S5, if P2 is greater than or equal to a preset value P0, judging that the batch of batteries meet the cyclic consistency requirement. According to the battery consistency evaluation method provided by the invention, the relationship model between the generated gas pressure and the battery consistency is established by testing the change of the internal pressure of the battery in a certain state.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly to a method for evaluating battery consistency. Background Art

[0002] With the rapid development of electric vehicles, energy storage systems, and portable electronic devices, the battery pack, as the core energy storage unit, its performance and lifespan directly affect the reliability and safety of the overall system. A battery pack is usually composed of multiple single cells connected in series or parallel. However, due to factors such as manufacturing processes, material differences, and usage environments, there are often inconsistencies among single cells. This inconsistency can lead to a decline in the performance of the battery pack, a shortening of its lifespan, and even cause safety problems.

[0003] Currently, the methods for evaluating battery consistency mainly include the measurement and analysis of parameters such as voltage, capacity, internal resistance, and temperature. However, these methods have the following limitations. The voltage consistency evaluation method is affected by factors such as temperature and SOC, making it difficult to comprehensively reflect the true state of the battery. And the capacity consistency evaluation has a long test duration, and it is difficult to accurately evaluate when the capacity attenuation is inconsistent, etc.

[0004] Therefore, it is necessary to provide a better method for evaluating the consistency of lithium-ion batteries to ensure battery consistency. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for evaluating battery consistency, by testing the change in internal pressure of the battery in a certain state, and establishing a relationship model between the generated gas pressure and battery consistency.

[0006] The technical solution adopted by a method for evaluating battery consistency disclosed by the present invention is as follows:

[0007] A method for evaluating battery consistency includes the following steps:

[0008] S1. Corresponding to several batteries are extracted from different batches of batteries, and the corresponding batches are divided into groups for battery grading.

[0009] S2. From the corresponding groups, a part of the graded batteries are taken out for instantaneous pressure testing, and the obtained pressure is P1.

[0010] S3. From the remaining batteries in the corresponding groups, a part of the batteries are taken out for high-temperature cycling, and then from the batteries after high-temperature cycling, a part is selected for generated gas pressure testing, and the measured value is P2.

[0011] S4. From step S3, the remaining batteries in the corresponding groups after high-temperature cycling treatment are selected for generated gas volume testing, the generated gas volume is V2, the generated gas volume V2 and the generated gas pressure satisfy a positive correlation, and a cyclic consistency preset value P0 is further set.

[0012] S5. If P2 is greater than or equal to the preset value P0, it is determined that the batch of batteries meets the cycle consistency requirement.

[0013] As a preferred solution, the average value of P1 is X - , the absolute value of the difference between P1 and the average value X - is denoted as ΔP, and ΔP = |P1 - X - |.

[0014] As a preferred solution, the batteries are divided into the following three grades according to the magnitude of the air pressure difference ΔP;

[0015] 0MP < ΔP ≤ 0.01Mpa, the battery is divided into Grade 1;

[0016] 0.01MP < ΔP ≤ 0.02Mpa, the battery is divided into Grade 2;

[0017] 0.02MP < ΔP ≤ 0.03Mpa, the battery is divided into Grade 3;

[0018] According to the above three gradients, the consistency of the batteries can be divided into three grades

[0019] As a preferred solution, 6 - 10 batteries are selected from the remaining batteries in the group corresponding to step S2 for high-temperature cycle testing. The test temperature range is 45 - 60 degrees, the cycle voltage range is 2.75 - 4.2V, the charging current range is 0.5 - 1C, the discharge current range is 1 - 2C, and the cycle number range is 50 - 200 cycles. 3 - 6 test batteries are selected from the 6 - 10 batteries after high-temperature cycling to measure the instantaneous gas production pressure.

[0020] As a preferred solution, in the pressure testing process: cut the cylindrical battery column to expose the upper aluminum foil of the CID, then pad an insulating film with a slightly smaller diameter, and apply a sealing glue around the insulating film to seal it. Pierce the insulating film with a needle and pierce the upper aluminum foil of the CID. The other end of the needle is connected to a pressure sensor and can read the test data, that is, the gas pressure.

[0021] As a preferred solution, the relationship between the gas production volume and the gas production pressure: According to PV = nRT, the gas production pressure P, the gas production volume n, P = (RT / V) * n, is in a direct proportional relationship.

[0022] As a preferred solution, the gas production value is V2, and the gas production volume test method is one of the drainage method, the syringe method, and the gas injection method.

[0023] As a preferred solution, the preset value P0 is the critical gas production pressure. When P1 ≥ P0, the high-temperature cycle meets the test requirements; when P1 < P0, the cycle does not meet the requirements.

[0024] As a preferred solution, the range of P0 is between 0.14 - 0.145 MPa.

[0025] As a preferred solution, in step S4, the high-temperature test cycle satisfies that the retention rate after 800 cycles is ≥ 80%.

[0026] The beneficial effect of a battery consistency evaluation method disclosed by the present invention is as follows: by using the battery production air pressure data before and after cycling, to evaluate the consistency of the battery high-temperature cycle, and then according to the relationship between P1, P2 and V2, to establish a relationship model between the production air pressure and the battery consistency, so as to judge whether the high-temperature cycle performance of different batches of batteries meets the requirements, providing technical support for the consistency evaluation and high-temperature cycle performance evaluation of lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flow chart of a battery consistency evaluation method of the present invention.

[0028] Figure 2 is an instantaneous gas pressure diagram of the battery before high-temperature cycling of a battery consistency evaluation method of the present invention.

[0029] Figure 3 is an instantaneous gas pressure diagram of the battery after cycling of a battery consistency evaluation method of the present invention.

[0030] Figure 4 is a diagram of the instantaneous gas pressure and gas production of the battery after cycling of a battery consistency evaluation method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] The following further elaborates and explains the present invention in combination with specific embodiments and the accompanying drawings of the specification:

[0032] Please refer to Figure 1 , a battery consistency evaluation method, including the following steps:

[0033] S1. Corresponding extract a number of batteries from different batches of batteries, divide the corresponding batches into groups, and perform battery grading. For example, from five different batches of batteries, select 15 - 20 batteries each, and label them as groups A, B, C, D, and E, and perform battery grading correspondingly.

[0034] S2. From the corresponding groups, extract 5 graded batteries each for instantaneous pressure testing, and test the instantaneous pressure when the battery SOC is 0%. For example, the average production air pressure of 5 batteries tested in group A is P1-1# - 5#, as Figure 2 shown.

[0035] The high-temperature cycle consistency of the battery can be judged according to P1-1 - 5#, and the average value of P1-1 - 5# is X -, the absolute values of the differences between different groups of P1-1-5# and the average value X - are denoted as ΔP-1# - ΔP-5# respectively, where ΔP = |P1 - X - |. As shown in the table, ΔP-1# - ΔP-5# are 0.1767 Ma, 0.1612 MPa, 0.1497 MPa, 0.1431 MPa, and 0.1401 MPa respectively.

[0036] Furthermore, the batteries are divided into the following three grades according to the magnitude of the air pressure difference ΔP.

[0037] (1) 0 MPa < ΔP ≤ 0.01 Mpa, the battery is classified as Grade 1;

[0038] (2) 0.01 MPa < ΔP ≤ 0.02 Mpa, the battery is classified as Grade 2;

[0039] (3) 0.02 MPa < ΔP ≤ 0.03 Mpa, the battery is classified as Grade 3;

[0040] According to the above three gradients, the consistency of the batteries can be divided into three grades. It can be concluded that 1# is from Batch A, that is, the third grade; 2# and 3# are from Batches B and C, that is, the first grade; 4# and 5# are from Batches D and E, that is, the second grade; 1# is from Batch A, that is, the third grade.

[0041] S3. From the remaining batteries in the corresponding group, 6 - 10 batteries are randomly selected for high-temperature cycling tests. The test temperature range is 45 - 60 degrees, the cycling voltage range is 2.75 - 4.2 V, the charging current range is 0.5 - 1 C, the discharging current range is 1 - 2 C, and the cycling number range is 50 - 200 cycles. From the 6 - 10 batteries after high-temperature cycling, 3 - 6 test batteries are selected to measure the instantaneous gas production pressure, and the measured value is P2.

[0042] In this embodiment, specifically, the test temperature is 45 degrees, the cycling voltage range is 2.75 - 4.2 V, the charging current range is 0.5 C, the discharging current range is 1 C, and the cycling number range is 100 cycles. From the batteries after high-temperature cycling, 3 test batteries are selected to measure the instantaneous gas production pressure. The average value of the gas production pressure measured for the three batteries in each group is denoted as P2-1# - 5#, as Figure 3 shown.

[0043] The instantaneous gas production pressure test is a kind of battery gas production pressure acquisition equipment obtained commercially. The specific pressure test process: Cut the cylindrical battery column to expose the aluminum foil at the upper end of the CID, then pad an insulating film with a slightly smaller diameter, and apply a sealing glue around the insulating film to seal it. Pierce the insulating film with a needle and pierce the aluminum foil at the upper end of the CID. The other end of the needle is connected to a pressure sensor and can read the test data, that is, the gas pressure.

[0044] Among them, exposing the battery aluminum foil is for the convenience of the needle piercing, and padding with soft silica gel is for the convenience of the gas injection process without gas leakage, ensuring airtightness, and thus ensuring the accuracy of the test.

[0045] S4. From step S3, select the remaining batteries after high-temperature cycling in the corresponding group for gas production measurement. The gas production is V2, and the preset value P0 is the critical gas production pressure. Through data processing, it is found that there is a negative correlation between the gas production P1 of the battery after formation and the gas production P2 after cycling, and there is a positive correlation between the gas production V2 after cycling and the gas production pressure P2 after cycling. Accordingly, the critical gas production pressure P0 can be set. When P1≥P0, the high-temperature cycling meets the test requirements; when P1<P0, the cycling does not meet the requirements. The range of P0 is between 0.14 - 0.145 MPa.

[0046] In this embodiment, select 5 remaining batteries after high-temperature cycling from different groups to measure the gas production. The average value of the gas production values of the 5 batteries is recorded as V2-1-5#, such as Figure 4 . V2-1-5# are 0.2805, 0.3025, 0.3235, 0.3285, and 0.3375 respectively.

[0047] The relational expression between gas production and gas production pressure: According to PV = nRT, for gas production pressure P and gas production n, P=(RT / V)*n, which is in a direct proportional relationship. The gas production value is V2. The gas production measurement method is one of the drainage method, syringe method, and gas injection method with a needle.

[0048] S5. If P2 is greater than or equal to the preset value P0, it is determined that the batch of batteries meets the cycling consistency requirements.

[0049] Accordingly, in this embodiment, the critical gas production pressure P0 can be set. When P1≥P0, P0 is 0.145 Mpa. The high-temperature cycling meets the test requirements; when P1<P0, the cycling does not meet the requirements. It can be concluded that 1# - 3# meet the high-temperature cycling requirements with a capacity retention rate of not less than 80% after 800 cycles, and 4# and 5# batteries do not meet this requirement.

[0050] Furthermore, the high-temperature test cycle meets a cycle retention rate of ≥80% after 800 cycles.

[0051] The present invention provides a battery consistency evaluation method, which uses the gas production pressure data of the battery before and after cycling to evaluate the consistency of the battery high-temperature cycling. Then, according to the relationships among P1, P2, and V2, a relationship model between gas production pressure and battery consistency is established to determine whether the high-temperature cycling performance of different batches of batteries meets the requirements, providing technical support for the consistency evaluation and high-temperature cycling performance evaluation of lithium batteries, etc.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for evaluating battery consistency, characterized in that, It includes the following steps: S1. Corresponding several batteries are extracted from batteries of different batches, the corresponding batches are divided into groups, and the batteries are subjected to formation. S2. From the corresponding groups, some of the formed batteries are taken out for instantaneous pressure test, and the pressure P1 is obtained through the test. S3. From the remaining batteries in the corresponding groups, some more batteries are taken out for high-temperature cycling. Then, from the batteries after high-temperature cycling, some are selected for gas production pressure test, and the test value is P2. S4. From step S3, for the remaining batteries in the corresponding groups after high-temperature cycling treatment, gas production test is carried out, and the gas production is V2. The gas production V2 and the gas production pressure are positively correlated, and a preset value P0 for cycle consistency is set again. S5. If P2 is greater than or equal to the preset value P0, it is determined that the batteries of this batch meet the cycle consistency requirements.

2. The battery consistency evaluation method according to claim 1, wherein The average value of P1 is X - , the absolute value of the difference between P1 and the average value X - is denoted as ΔP, and ΔP = |P1 - X - |.

3. The battery consistency evaluation method according to claim 2, characterized in that The batteries are divided into the following 3 grades according to the magnitude of the pressure difference ΔP; 0MP<ΔP≤0.01Mpa, the batteries are divided into grade 1; 0.01MP<ΔP≤0.02Mpa, the batteries are divided into grade 2; 0.02MP<ΔP≤0.03Mpa, the batteries are divided into grade 3; According to the above three gradients, the consistency of the batteries can be divided into three grades.

4. The battery consistency evaluation method according to claim 1, wherein From the remaining batteries in the corresponding groups in step S2, 6 - 10 batteries are taken out for high-temperature cycling test. The test temperature range is 45 - 60 degrees, the cycle voltage range is 2.75 - 4.2V, the charging current range is 0.5 - 1C, the discharging current range is 1 - 2C, and the cycle number range is 50 - 200 cycles. From 6 - 10 batteries after high-temperature cycling, 3 - 6 batteries are selected to test the instantaneous gas production pressure of the batteries.

5. The battery consistency evaluation method according to claim 4, wherein The process of the pressure test: Cut the column of the cylindrical battery to expose the upper aluminum foil of the CID, then pad an insulating film with a slightly smaller diameter, and apply a sealing glue around the insulating film to seal it. The needle penetrates the insulating film and pierces the upper aluminum foil of the CID. The other end of the needle is connected with a pressure sensor and can read the test data, that is, the gas pressure.

6. The battery consistency evaluation method according to claim 1, characterized in that The relational formula between the gas production and the gas production pressure: According to PV=nRT, the gas production pressure P, the gas production n, P=(RT / V)*n, is in a direct proportional relationship.

7. The battery consistency evaluation method according to claim 1, wherein The gas production value is V2, and the gas production test method is one of the drainage method, the syringe method, and the gas injection method with a needle.

8. The battery consistency evaluation method according to claim 1, wherein The preset value P0 is the critical gas production pressure. When P1≥P0, the high-temperature cycling meets the test requirements; when P1<P0, the cycling does not meet the requirements.

9. The battery consistency evaluation method according to claim 8, wherein The range of P0 is between 0.14 - 0.145MPa.

10. A method for evaluating the consistency of batteries according to claim 1, characterized in that, In step S4, the high-temperature test cycle meets that the cycle retention rate of 800 cycles is ≥80%.

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