Screening method of metal lithium batteries

Abstract

The invention discloses a method for screening metal lithium batteries, which comprises the following steps of: after fully charging the metal lithium batteries, obtaining the battery capacity through a discharge test; clamping by using a clamping plate at a set pressure, and charging to a specified electric quantity; shelving for a first set time length, measuring a first open-circuit voltage, shelving for a second set time length, measuring a second open-circuit voltage, and calculating a voltage drop rate; removing the clamping plate, putting the battery into a low-pressure box, measuring the first thickness of the maximum plane center of the battery by using a laser measuring instrument under the conditions of normal temperature and normal pressure, controlling the air pressure value of the low-pressure box to a specified air pressure value, measuring the second thickness of the maximum plane center of the metal lithium battery, and calculating the center thickness increment of the low-pressure battery; and rejecting unqualified batteries by judging whether the battery capacity, the voltage drop rate and the center thickness increment of the low-pressure battery meet a specified range or not. According to the method, the gas production condition of the metal lithium battery can be indirectly evaluated without interference, so that a large number of single metal lithium batteries with gas production are removed, and effective screening of the metal lithium batteries is realized.

Description

Technical Field

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

[0002] With the development of science and technology, metal lithium batteries are gradually maturing. Soft-pack monomers are a common structural form of metal lithium batteries. Metal lithium monomer batteries of this structural form have higher specific energy and larger expansion and contraction variable energy. However, the polar materials involved in the reaction inside the metal lithium battery monomer may have the potential risk of increased gas production. The ordinary storage and shelving test method cannot detect this defect in the early stage before the single battery is installed. After the single battery is installed, after long-term storage or occasional use, the metal lithium battery may occasionally produce gas internally.

[0003] At present, the test method for gas production inside metal lithium batteries is mainly achieved through the water displacement method, that is, immersing the battery in a liquid of a certain depth and calculating the volume of gas generated inside the battery by measuring the change in the liquid level. However, the water displacement method is not suitable for the screening of large-scale products, and it is easy to cause the battery to be stained with water, causing quality problems. Summary of the invention

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

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

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

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

[0008] S3, after charging to a specified power, placing the metal lithium battery on hold for a first set time, measuring a first open circuit voltage of the metal lithium battery, placing the metal lithium battery on hold for a second set time, and measuring a second open circuit voltage of the metal lithium battery again, and calculating a voltage drop rate based on the first open circuit voltage, the second open circuit voltage, and the second set time;

[0009] S4, remove the splint, put the metal lithium battery into the 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 measure the second thickness of the center of the largest plane of the metal lithium battery with a laser measuring instrument again, and 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] 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 decreases to a second set current;

[0013] A discharge test is performed on the fully charged lithium metal battery with 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 clamp to the metal lithium battery is in the range of 0.05Mpa to 0.5Mpa.

[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 specified capacity range is 10Ah to 10.5Ah.

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

[0024] Optionally, in step S5, the specified 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 expanded 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 is placed for 36h to 72h, 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 characteristics and advantages, which will be apparent from the drawings incorporated herein and the following detailed description, or will be described in detail in the drawings incorporated herein and the following detailed description, which together serve to explain the specific principles of the present 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 in conjunction with the accompanying drawings, in which like reference numerals generally represent like components.

[0029] Figure 1 A flow chart showing the steps of a method for screening a metal lithium battery 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, that is, 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-power storage without interference, thereby eliminating metal lithium battery cells that produce a large amount of gas due to excessive side reactions, thereby achieving effective screening of metal lithium batteries.

[0031] The present invention will be described in more detail below with reference to the accompanying drawings. Although preferred embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, 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 method for screening a metal lithium battery according to the present invention comprises:

[0033] S1. After fully charging the metal lithium battery, the capacity of the metal lithium 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 decreases to a second set current, indicating that the battery is fully charged.

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

[0036] Among them, the range of the first setting current is 0.1C~1C; the range of the second setting current is 0.02C; the range of the third setting current is 0.1C~2C; the range of the maximum voltage is 4.2V~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 this voltage until the current drops to 0.02C, and then discharged at 0.1C to 2C. The test capacity is C x .

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

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

[0040] In one example, the battery is clamped with a clamp at a pressure of 0.05Mpa to 0.5Mpa, charged at 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, placing the metal lithium battery on hold for a first set time, measuring a first open circuit voltage of the metal lithium battery, placing the metal lithium battery on hold for a second set time, and measuring a second open circuit voltage of the metal lithium battery again, and calculating a voltage drop rate 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 ranges from 36 hours to 72 hours, and the second set time ranges from 240 hours to 720 hours.

[0043] In one example, the voltage drop rate K after the large current pulse test under continuous extrusion is calculated. x =(U1-U2) / t2.

[0044] S4, remove the splint, put the metal lithium battery into the 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, measure the second thickness of the center of the largest plane of the metal lithium battery with a laser measuring instrument again, and 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 as 0 to 50000 Pa, and the preferred range is 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 of the center of the largest plane of the battery is measured with 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 of the center of the largest plane of the battery is measured with 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 be no more than 0.1mV / h; unqualified metal lithium batteries should be eliminated according to the rules.

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

[0051] (1) A screening method for metal lithium batteries that are 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 alone for 36 to 72 hours, eliminating the influence of the previous charging step on the open circuit voltage. The test results are more accurate and reliable than those of existing methods.

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

[0056] Example:

[0057] This embodiment provides a method for screening lithium metal batteries. The following steps are performed in order 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 at 4.4V constant voltage until the current drops to 0.2A (corresponding to 0.02C), then discharge at 5A (corresponding to 0.5C) constant current, and the test capacity is C x ;

[0059] Step 2: The metal lithium battery is clamped with a clamping plate at a pressure of 0.05Mpa to 0.5Mpa, and charged at a current of 2A until the battery reaches 4.4V, and then charged at a constant voltage of 4.4V until the current decreases to 0.2A, so that the single battery undergoes a certain degree of deformation;

[0060] Step 3: After the charged single battery is left for 60 hours, the open circuit voltage U1 is measured; after the single battery is left for 680 hours, the open circuit voltage U2 is measured; the voltage drop rate K after the high current pulse test x =(U1-U2) / 680;

[0061] Step 4, remove the clamping plate, put the metal lithium battery into the low pressure box, measure the thickness h1 of the center of the largest plane of the 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, the absolute pressure of the air pressure value specified in this embodiment is 5000Pa-6000Pa, measure the thickness h2 of the center of the largest plane of the battery with a laser measuring instrument, and calculate △h=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 is not greater than 10% of the initial thickness of the single battery, the voltage drop rate K x Not more than 0.1mV / h, unqualified metal lithium batteries are eliminated.

[0063] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes 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 metal lithium battery, the capacity of the metal lithium battery is obtained through a discharge test; S2, clamping the discharged lithium metal battery with a clamping plate at a set pressure, and charging the lithium metal battery to a specified power; S3, after charging to a specified power, placing the metal lithium battery on hold for a first set time, measuring a first open circuit voltage of the metal lithium battery, placing the metal lithium battery on hold for a second set time, and measuring a second open circuit voltage of the metal lithium battery again, and calculating a voltage drop rate based on the first open circuit voltage, the second open circuit voltage, and the second set time; S4, remove the splint, put the metal lithium battery into the 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 measure the second thickness of the center of the largest plane of the metal lithium battery with a laser measuring instrument again, and 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: 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 decreases to a second set current; A discharge test is performed on the fully charged lithium metal battery with 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, characterized in that: In step S2, the set pressure applied by the clamp to the metal lithium battery is in the range of 0.05Mpa to 0.5Mpa.

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

6. The method for screening metal lithium batteries according to claim 1, characterized in that: 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 specified air pressure value is 0 to 50000 Pa.

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

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

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