Screening methods for lithium metal batteries

Abstract

The present invention discloses a method for screening lithium metal batteries, comprising: after fully charging the lithium metal battery, obtaining the battery capacity through a discharge test; clamping the battery with a set pressure using a clamping plate and charging it to a specified power level; shelving the battery for a first set time, measuring a first open-circuit voltage, shelving the battery for a second set time, measuring a second open-circuit voltage, and calculating the voltage drop rate; removing the clamping plate, placing the battery in a low-pressure box, measuring the first thickness of the center of the largest plane of the battery using a laser measuring instrument under normal temperature and pressure conditions, controlling the air pressure of the low-pressure box to a specified air pressure value, measuring the second thickness of the center of the largest plane of the lithium metal battery, and calculating the thickness increment at the center of the low-pressure battery; and eliminating unqualified batteries by judging whether the battery capacity, voltage drop rate, and thickness increment at the center of the low-pressure battery meet the specified range. The present invention can indirectly evaluate the gas production of lithium metal batteries without interference, thereby eliminating lithium metal battery cells that produce a large amount of gas, and achieving effective screening of lithium metal batteries.

Description

Technical Field

[0001] The present invention relates to the field of metal lithium batteries, and more particularly, to a screening method for metal lithium batteries. Background Art

[0002] With the advancement of science and technology, lithium metal batteries are gradually maturing. Soft-pack cells are a common structural form of lithium metal batteries, which offer higher specific energy and greater expansion and contraction capacity. However, the polar materials involved in the reaction within lithium metal battery cells may pose a potential risk of increased gassing. Conventional storage and shelving testing methods cannot detect this defect in the initial stages before the cell is installed. However, after installation, lithium metal batteries may occasionally experience internal gassing after prolonged storage or occasional single use.

[0003] Currently, the main method for testing internal gas production in lithium metal batteries is through the water displacement method. This involves immersing the battery in liquid to a certain depth and measuring the change in the liquid level to calculate the volume of gas generated within the battery. However, the water displacement method is not suitable for screening large quantities of products and can easily cause the battery to become wet, leading to quality issues. Summary of the Invention

[0004] The purpose of the present invention is to propose a screening method for lithium metal batteries, which can achieve non-interference and indirect evaluation of the gas production of lithium metal batteries during long-term slow-discharge state storage, thereby eliminating lithium metal battery cells that produce a large amount of gas due to excessive side reactions, and completing the effective screening of lithium metal batteries.

[0005] To achieve the above objectives, the present invention proposes a method for screening metal lithium batteries, comprising:

[0006] S1. After fully charging the metal lithium battery, obtain the capacity of the metal lithium battery through a discharge test;

[0007] S2. Clamp the discharged lithium metal battery with a clamping plate at a set pressure, and charge the lithium metal battery to a specified power;

[0008] S3. After charging to a specified power level, the lithium metal battery is placed on hold for a first set time, and then a first open circuit voltage of the lithium metal battery is measured. The lithium metal battery is placed on hold for a second set time, and then a second open circuit voltage of the lithium metal battery is measured again. A voltage drop rate is calculated based on the first open circuit voltage, the second open circuit voltage, and the second set time.

[0009] S4. Remove the splint, place the metal lithium battery in a low-pressure box, measure the first thickness of the center of the largest plane of the metal lithium battery with a laser measuring instrument under normal temperature and pressure conditions, control the air pressure of the low-pressure box to a specified air pressure value, and measure the second thickness of the center of the largest plane of the metal lithium battery with the laser measuring instrument again. Calculate the center thickness increment of the low-pressure battery based on the first thickness and the second thickness;

[0010] S5. Eliminate unqualified lithium metal batteries by judging whether the capacity of the lithium metal battery meets the specified battery capacity range, whether the voltage drop rate meets the specified voltage drop rate range, and whether the low-pressure battery center thickness increment meets the specified low-pressure battery center thickness increment range.

[0011] Optionally, step S1 specifically includes:

[0012] Charging the metal lithium battery at a first set current to a maximum voltage, and then performing constant voltage charging at the maximum voltage until the current decreases to a second set current;

[0013] A discharge test is performed on the fully charged lithium metal battery at a third set current to obtain the capacity of the lithium metal battery.

[0014] Optionally, the first set current ranges from 0.1C to 1C;

[0015] The second set current is 0.02C;

[0016] The range of the third setting circuit is 0.1C to 2C;

[0017] The maximum voltage ranges from 4.2V to 4.4V.

[0018] Optionally, in step S2, the set pressure applied by the clamping plate to the metal lithium battery is in the range of 0.05 MPa to 0.5 MPa.

[0019] Optionally, in step S2, the prescribed power range is 90% to 100%.

[0020] Optionally, in step S3, the first set time length ranges from 36 hours to 72 hours, and the second set time length ranges from 240 hours to 720 hours.

[0021] Optionally, in step S4, the specified air pressure value has an absolute pressure range of 0 to 50,000 Pa.

[0022] Optionally, in step S5, the prescribed capacity range is 10Ah to 10.5Ah.

[0023] Optionally, in step S5, the prescribed voltage drop rate range is no more than 0.1 mV / h.

[0024] Optionally, in step S5, the prescribed range of the low-pressure battery center thickness increment is: no more than 10% of the initial thickness of the single battery.

[0025] The beneficial effects of the present invention are:

[0026] The present invention proposes a screening method for metal lithium batteries that are prone to gas production. The method utilizes full-charge acceleration and combines the principle that the volume difference between single cells with large gas production at low pressure and normal temperature and pressure is large. That is, a small amount of gas is allowed to expand under low-pressure conditions, and the thickness at the center of the largest surface of the battery is measured after expansion. The gas production inside the battery can be detected more sensitively. At the same time, the method of measuring the thickness at the center of the largest surface of the battery with a laser measuring instrument can indirectly evaluate the gas production and side reactions of the metal battery during long-term storage without interference, thereby achieving high-efficiency screening of metal lithium batteries and solving the technical problem that the gas production is difficult to measure during the screening process. In addition, after the metal lithium battery is charged, the method can be shelved for 36 hours to 72 hours, so that the open circuit voltage of the slow-charging metal lithium battery can be fully stable, and the influence of the previous charging step on the open circuit voltage can be eliminated. Compared with the test results of existing means, it is more accurate and reliable.

[0027] The system of the present invention has other features and advantages that will be apparent from or will be described in detail in the accompanying drawings and subsequent detailed description incorporated herein, which together serve to explain the specific principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings, in which like reference numerals generally represent like components.

[0029] Figure 1 A flowchart of the steps of a screening method for metal lithium batteries according to the present invention is shown. DETAILED DESCRIPTION

[0030] In order to solve the problems existing in the prior art, the present invention proposes a screening method for the gas production of large-scale batteries, namely, using low-pressure conditions to allow a small amount of gas to expand, and measuring the thickness of the battery through a laser rangefinder, so as to indirectly evaluate the gas production of metal lithium batteries during long-term slow-charge state storage without interference, thereby eliminating metal lithium battery cells that produce a large amount of gas due to excessive side reactions, and realizing effective screening of metal lithium batteries.

[0031] The present invention will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention may be implemented in various forms and is not limited to the embodiments set forth herein. Rather, these embodiments are provided to make the present invention more thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0032] like Figure 1 As shown, a screening method for metal lithium batteries according to the present invention includes:

[0033] S1. After fully charging the lithium metal battery, the capacity of the lithium metal battery is obtained through a discharge test;

[0034] In this step, the metal lithium battery is charged to a maximum voltage at a first set current, and then constant voltage charging is performed at the maximum voltage until the current drops to a second set current, indicating that the battery is fully charged.

[0035] Then, a discharge test is performed on the fully charged lithium metal battery at a third set current to obtain the capacity of the lithium metal battery.

[0036] The first setting current ranges from 0.1C to 1C; the second setting current ranges from 0.02C; the third setting current ranges from 0.1C to 2C; and the maximum voltage ranges from 4.2V to 4.4V.

[0037] In one example, the metal lithium battery is charged at a current of 0.1C to 1C to a maximum voltage of 4.4V, then charged at the same voltage until the current drops to 0.02C, and then discharged at 0.1C to 2C. The test capacity is C x .

[0038] S2. Clamp the discharged lithium metal battery with a clamping plate at a set pressure, and charge the lithium metal battery to a specified power;

[0039] In this step, the set pressure range of the clamping plate on the metal lithium battery is 0.05Mpa to 0.5Mpa; the specified power range is 90% to 100%.

[0040] In one example, the battery is clamped with a pressure of 0.05 MPa to 0.5 MPa, and charged with a current of 0.1C to 1C to a voltage corresponding to 90% to 100% of the charge, and then charged at a constant voltage at this voltage until the current drops to 0.02C.

[0041] S3. After charging to a specified power level, the lithium metal battery is placed on hold for a first set time, and then a first open circuit voltage of the lithium metal battery is measured. The lithium metal battery is placed on hold for a second set time, and then a second open circuit voltage of the lithium metal battery is measured again. The voltage drop rate is calculated based on the first open circuit voltage, the second open circuit voltage, and the second set time.

[0042] In this step, the first set time range is 36 hours to 72 hours, and the second set time range is 240 hours to 720 hours.

[0043] In one example, the test is performed after t1 hour of suspension (the suspension time t1 is 36h~72h), and the open circuit voltage U1 is measured. The test is then performed after t2 hours of suspension (the suspension time t2 is 240h~720h), and the open circuit voltage U2 is measured. The voltage drop rate K after the high current pulse test under continuous extrusion is calculated. x =(U1-U2) / t2.

[0044] S4. Remove the splint, place the metal lithium battery in a low-pressure box, measure the first thickness of the center of the largest plane of the metal lithium battery with a laser measuring instrument under normal temperature and pressure conditions, control the air pressure value of the low-pressure box to a specified air pressure value, and again measure the second thickness of the center of the largest plane of the metal lithium battery with the laser measuring instrument. Calculate the center thickness increment of the low-pressure battery based on the first thickness and the second thickness;

[0045] In this step, the absolute pressure range of the specified air pressure value can be selected from 0 to 50000 Pa, preferably from 5000 Pa to 6000 Pa.

[0046] In one example, the splint is removed and the metal lithium battery is placed in a low-pressure box. The thickness h1 at the center of the largest plane of the battery is measured using a laser measuring instrument under normal temperature and pressure conditions. The air pressure of the low-pressure box is controlled to a specified air pressure value (between 0 and 50,000 Pa). The thickness h2 at the center of the largest plane of the battery is measured using a laser measuring instrument, and △h = h2 - h1 is calculated.

[0047] S5. Eliminate unqualified lithium metal batteries by judging whether the capacity of the lithium metal battery meets the specified battery capacity range, whether the voltage drop rate meets the specified voltage drop rate range, and whether the low-pressure battery center thickness increment meets the specified low-pressure battery center thickness increment range.

[0048] In this step, the specified capacity range is 10Ah to 10.5Ah, the specified voltage drop rate range is no more than 0.1mV / h, and the specified low-pressure battery center thickness increment range is no more than 10% of the initial thickness of the single cell.

[0049] In one example, according to C x Meet the specified capacity range; the low-pressure battery center thickness increment △h meets the specified size range, and the low-pressure battery center thickness increment △h is not greater than 10% of the initial thickness of the single battery; the voltage drop rate K x To meet the specified range, the voltage drop rate should not be greater than 0.1mV / h; unqualified metal lithium batteries should be eliminated according to the rules.

[0050] The advantages of the screening method for metal lithium batteries of the present invention are as follows:

[0051] (1) A screening method for metal lithium batteries prone to gas production is proposed, which can effectively solve the problem of abnormal gas production of metal lithium batteries;

[0052] (2) Using low pressure conditions to allow a small amount of gas to expand, and measuring the thickness of the battery after expansion, the gas production of each part of the battery can be detected more sensitively;

[0053] (3) The gas production of metal lithium batteries can be evaluated indirectly without interference by using a laser rangefinder to characterize the gas production.

[0054] (4) After charging, the open circuit voltage of the slow-charging lithium metal battery can be fully stabilized by leaving it for 36 to 72 hours, eliminating the influence of the previous charging step on the open circuit voltage. Compared with the test results of existing methods, it is more accurate and reliable.

[0055] The method of the present invention is further explained below through a specific embodiment.

[0056] Example:

[0057] This embodiment provides a method for screening lithium metal batteries. The following steps are performed in sequence at room temperature and pressure:

[0058] Step 1: Charge the high-power 10Ah lithium metal battery to 4.4V at 2A (corresponding to 0.2C), then charge it at 4.4V constant voltage until the current drops to 0.2A (corresponding to 0.02C), and then discharge it at 5A (corresponding to 0.5C) constant current. The test capacity is C x ;

[0059] Step 2: The lithium metal battery is clamped with a clamping plate at a pressure of 0.05 MPa to 0.5 MPa, and charged at a current of 2 A until the battery reaches 4.4 V. Then, the battery is charged at a constant voltage of 4.4 V until the current drops to 0.2 A, causing the single battery to deform to a certain extent.

[0060] Step 3: After charging, place the single battery for 60 hours and measure the open circuit voltage U1. After placing it for 680 hours, measure the open circuit voltage U2. The voltage drop rate K after the high current pulse test x =(U1-U2) / 680;

[0061] Step 4: Remove the splint and place the metal lithium battery in a low-pressure box. Use a laser measuring instrument to measure the thickness h1 at the center of the largest plane of the battery under normal temperature and pressure conditions. Control the air pressure value of the low-pressure box to a specified air pressure value. In this embodiment, the specified air pressure value is an absolute pressure of 5000 Pa to 6000 Pa. Use a laser measuring instrument to measure the thickness h2 at the center of the largest plane of the battery, and calculate Δh = h2 - h1.

[0062] Step 5: Follow C x Meet the specified capacity range of 10Ah ~ 10.5Ah, the low-pressure battery center thickness increment △h meets the specified size not greater than 10% of the initial thickness of the single battery, the voltage drop rate K x Not more than 0.1mV / h, reject unqualified metal lithium batteries.

[0063] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for screening metal lithium batteries, characterized in that: include: S1. After fully charging the lithium metal battery, the capacity of the lithium metal battery is obtained through a discharge test; S2. Clamp the discharged lithium metal battery with a clamping plate at a set pressure, and charge the lithium metal battery to a specified power; S3. After charging to a specified power level, the lithium metal battery is placed on hold for a first set time, and then a first open circuit voltage of the lithium metal battery is measured. The lithium metal battery is placed on hold for a second set time, and then a second open circuit voltage of the lithium metal battery is measured again. A voltage drop rate is calculated based on the first open circuit voltage, the second open circuit voltage, and the second set time. S4. Remove the splint, place the metal lithium battery in a low-pressure box, measure the first thickness of the center of the largest plane of the metal lithium battery with a laser measuring instrument under normal temperature and pressure conditions, control the air pressure of the low-pressure box to a specified air pressure value, and measure the second thickness of the center of the largest plane of the metal lithium battery with the laser measuring instrument again. Calculate the center thickness increment of the low-pressure battery based on the first thickness and the second thickness; S5. Eliminate unqualified lithium metal batteries by judging whether the capacity of the lithium metal battery meets the specified battery capacity range, whether the voltage drop rate meets the specified voltage drop rate range, and whether the low-pressure battery center thickness increment meets the specified low-pressure battery center thickness increment range.

2. The method for screening metal lithium batteries according to claim 1, characterized in that: Step S1 specifically includes: Charging the metal lithium battery at a first set current to a maximum voltage, and then performing constant voltage charging at the maximum voltage until the current decreases to a second set current; A discharge test is performed on the fully charged lithium metal battery at a third set current to obtain the capacity of the lithium metal battery.

3. The method for screening metal lithium batteries according to claim 2, characterized in that: The first set current ranges from 0.1C to 1C; The second set current is 0.02C; The range of the third setting circuit is 0.1C to 2C; The maximum voltage ranges from 4.2V to 4.4V.

4. The method for screening metal lithium batteries according to claim 1, wherein: In step S2, the set pressure applied by the clamping plate to the metal lithium battery is in the range of 0.05 MPa to 0.5 MPa.

5. The method for screening metal lithium batteries according to claim 1, wherein: In step S2, the prescribed power range is 90% to 100%.

6. The method for screening metal lithium batteries according to claim 1, wherein: In step S3, the first set time period ranges from 36 hours to 72 hours, and the second set time period ranges from 240 hours to 720 hours.

7. The method for screening metal lithium batteries according to claim 1, characterized in that: In step S4, the absolute pressure range of the prescribed air pressure value is 0 to 50,000 Pa.

8. The method for screening metal lithium batteries according to claim 1, wherein: In step S5, the prescribed capacity range is 10 Ah to 10.5 Ah.

9. The method for screening metal lithium batteries according to claim 1, wherein: In step S5, the prescribed voltage drop rate range is no more than 0.1 mV / h.

10. The method for screening metal lithium batteries according to claim 1, characterized in that: In step S5, the prescribed range of the center thickness increment of the low-pressure battery is: no more than 10% of the initial thickness of the single battery.

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