Sample preparation method for testing gram capacity of circularly aged lithium battery pole piece

Abstract

The invention discloses a sample preparation method for testing gram capacity of a lithium battery pole piece after cycle aging. The manufacturing method of the test sample comprises the following steps: carrying out multi-stage discharge on an aged lithium battery, so that the internal voltage of the lithium battery is reduced to a preset voltage; disassembling the lithium battery to obtain a pole piece of the lithium battery; and cleaning and drying the pole piece by using an electrolyte solvent of the lithium battery to obtain a test sample. According to the technical scheme, the electrochemical activity of a pole piece material is inhibited through multi-stage discharge of the pole piece of the lithium battery, the possibility that the disassembled pole piece is subjected to a redox reaction with oxygen and other substances in air in a natural environment is reduced, impurities on the surface of an electrode are effectively removed through sufficient washing of an electrolyte solvent, and the service life of the lithium battery is prolonged. And the electrode material can be relatively completely protected, and the damage of the electrode plate material is prevented, so that the gram capacity value of the electrode plate obtained by adopting the technical scheme can be relatively completely measured.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a sample preparation method for testing the gram capacity of lithium battery pole pieces after cycle aging. Background Art

[0002] After lithium battery cycle aging, the gram capacity of its positive or negative electrode materials will decrease, resulting in battery cycle capacity failure. In order to find the cause of battery failure, it is necessary to disassemble the battery and take out the electrode pieces as test samples to test the gram capacity to determine the degree of loss of its positive or negative active materials. However, due to the high reactivity of the electrode active materials, due to improper operation during the disassembly process, the electrode active materials may be destroyed and no effective gram capacity data can be measured. Summary of the invention

[0003] The main purpose of the present invention is to propose a sample preparation method for testing the gram capacity of carp battery electrodes after cycle aging, aiming to solve the problem that the electrode active materials have high reactivity and the disassembly process is improper, resulting in the destruction of the electrode active materials and the inability to measure effective gram capacity data.

[0004] To achieve the above object, the present invention proposes a sample preparation method for testing the gram capacity of a lithium battery electrode after cycle aging, comprising:

[0005] Perform multi-stage discharge on aged lithium batteries to reduce their internal voltage to a preset voltage;

[0006] Disassemble the lithium battery and obtain the pole piece of the lithium battery;

[0007] The electrode is cleaned and dried using the electrolyte solvent of the lithium battery to obtain a test sample.

[0008] In some embodiments, performing multi-stage discharge on an aged lithium battery includes:

[0009] The lithium battery is discharged step by step at a current rate that decreases step by step from 0.01C to 0.5C.

[0010] In some embodiments, the multi-stage discharge method includes:

[0011] S1. Control the lithium battery to perform primary discharge at a preset current rate through a charge and discharge tester until the voltage of the lithium battery reaches a preset voltage;

[0012] S2, detect whether the voltage of the lithium battery rises;

[0013] S3. If the voltage of the lithium battery rises back up, the lithium battery is controlled again to perform secondary discharge at a preset current rate less than S1 until the voltage of the lithium battery is maintained at the preset voltage.

[0014] In some embodiments, the preset voltage is 2.0V to 3.0V, and the number of multi-stage discharges is ≤ 10 times.

[0015] In some embodiments, before detecting whether the voltage of the lithium battery rises, the method further includes:

[0016] The lithium battery is left to stand for a first preset time period, where the first preset time period is 1 minute to 100 minutes.

[0017] In some embodiments, the first preset duration is 5 minutes to 10 minutes.

[0018] In some embodiments, cleaning includes: soaking the electrode in an electrolyte solvent for a second preset time period, wherein the second preset time period is 3 minutes to 30 minutes.

[0019] In some embodiments, the second preset duration is 5 minutes to 10 minutes.

[0020] In some embodiments, the electrolyte solvent is at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0021] In some embodiments, obtaining a pole piece of a lithium battery includes:

[0022] The pole pieces of the lithium battery are cut to obtain pole pieces of a preset size.

[0023] The beneficial effects of the technical solution of the present invention are:

[0024] The pole piece of the lithium battery suppresses the electrochemical activity of the pole piece material through multi-stage discharge, reducing the possibility of the pole piece obtained by disassembly to undergo redox reaction with oxygen and other substances in the air when in a natural environment. The disassembly process does not need to be carried out in a glove box with an inert atmosphere, which improves the convenience and efficiency of the disassembly and sample preparation operation. Moreover, the present invention uses sufficient electrolyte solvent to soak and clean the electrode pole piece, which can effectively remove the interference of electrode impurities on the measurement results, thereby improving the accuracy of the test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A flow chart of a method for preparing a lithium battery gram capacity test sample according to an embodiment of the present invention;

[0026] Figure 2 A flow chart of a method for preparing a lithium battery gram capacity test sample according to another embodiment of the present invention;

[0027] Figure 3 The present invention is a flowchart of a method for preparing a lithium battery gram capacity test sample according to another embodiment of the present invention.

[0028] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0029] The scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] It should be noted that the descriptions involving "first", "second", etc. in the present invention are only used for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features.

[0031] In view of the technical defects existing in the related art, this embodiment provides a method for preparing a lithium battery gram capacity test sample. Figure 1 As shown, Figure 1 The process of the test sample preparation method of this embodiment is shown, and the test sample preparation method includes:

[0032] Step S100, multi-stage discharge is performed on the aged lithium battery to reduce its internal voltage to a preset voltage; the fully charged electrode has a high reaction activity, and the present application adopts multi-stage discharge to ensure that the lithium battery after cycle aging can be discharged as much as possible, so as to effectively inhibit the redox activity of the positive and negative electrodes. In the embodiment of the present application, the multi-stage can be a method of gradually decreasing the discharge current, or it can be a method of multiple discharges at a preset current. It can be understood that in the aged lithium battery, the concept of "aging" refers to the state in which the battery performance of the lithium battery is reduced after multiple charge and discharge, resulting in the inability to provide the rated voltage to the electronic device, that is, the voltage output by the aged lithium battery is significantly lower than the voltage output by the normal lithium battery.

[0033] Step S200, dismantle the lithium battery to obtain the pole piece of the lithium battery. Since the lithium battery has been fully discharged after the multi-stage discharge treatment in step S100, the electrochemical activity of the pole piece material is suppressed, so that it can be dismantled in a natural environment, which facilitates the pole piece dismantling process.

[0034] Step S300, use the electrolyte solvent of the lithium battery to clean the pole piece, dry it, and obtain a test sample. It should be noted that the electrolyte solvent used to clean the pole piece in this embodiment is the solvent part used to dissolve the electrolyte in the lithium battery electrolyte. Since the pole piece is stained with electrolyte after disassembly, the pole piece is cleaned with a solvent that can dissolve the electrolyte; after cleaning the pole piece, the electrolyte solvent on the surface of the pole piece is dried to obtain a sample for lithium battery gram capacity test.

[0035] Compared with the related art, in this embodiment, the pole piece of the lithium battery suppresses the electrochemical activity of the pole piece material through multiple discharges. Therefore, even if the pole piece obtained by disassembly is in a natural environment, the possibility of undergoing redox reaction with oxidizing substances such as oxygen in the air is low, thereby preventing the pole piece material from deteriorating. Therefore, by using the test sample produced by the production method of this embodiment, the gram capacity test of the lithium battery can be carried out in a natural environment, thereby eliminating the need for a testing environment such as a glove box with limited operating environment and inconvenient operation. Moreover, the pole piece is effectively washed to remove impurities on the surface of the electrode, which can better protect the electrode material and prevent damage to the pole piece material. Therefore, the pole piece obtained by the technical solution of the present invention can more completely measure the gram capacity value of the pole piece.

[0036] like Figure 2 As shown, in some embodiments, step S200 is performed after step S100. In this embodiment, the pole piece of the lithium battery can be obtained by cutting. Since the pole piece of the finished lithium battery is in a wound state, it can be cut into a predetermined size to obtain the desired pole piece, such as a square of 5 cm × 5 cm. Of course, according to actual needs, the cut pieces of the pole piece are not necessarily square in shape, but can also be strips, triangles, rectangles or circles. The size of the cut pieces can also be determined according to actual needs, for example: 3 cm × 5 cm, 2 cm × 3 cm, 3.5 cm × 4.3 cm, 2.3 cm × 5.6 cm, etc. Since the size of the cut pole piece is smaller than the original pole piece, the amount of cleaning liquid can be saved in the subsequent cleaning process, and in the drying process, the drying time is saved due to the small drying area, which improves the production efficiency of the test sample.

[0037] Due to the characteristics of lithium batteries, the voltage of lithium batteries may rise after the lithium batteries are discharged. In order to stabilize the voltage of the lithium batteries after discharge at a preset voltage, in some embodiments, such as Figure 3 As shown, step S100 specifically includes:

[0038] Step S110, control the lithium battery to perform primary discharge at a preset current rate through the charge and discharge tester until the voltage of the lithium battery reaches the preset voltage. For example, in this embodiment, the preset voltage is set to 2.5V. During the first discharge process, the lithium battery is discharged at a current discharge rate of 0.2C through the charge and discharge tester until the voltage of the lithium battery reaches the preset voltage. In the embodiment of the present application, 0.2C is only a choice in the preferred embodiment, and the lithium battery after cycle aging can also be discharged multiple times using a current rate that decreases step by step from 0.5C, 0.1C, 0.05C, 0.02C, and 0.01C.

[0039] Step S120, detecting whether the voltage of the lithium battery has recovered. Exemplarily, before detecting whether the voltage of the lithium battery has recovered, the lithium battery undergoing discharge treatment is left to stand for a first preset time, which may be 5 minutes, 10 minutes, or an intermediate value of 7 minutes.

[0040] If the voltage of the lithium battery does not rise after the first preset time, it means that the number of charge and discharge cycles of the lithium battery is relatively large, and the electrode material basically loses its electrochemical activity through only one discharge process, so step S200 can be performed directly. If the voltage of the lithium battery rises, a second discharge treatment is required. Exemplarily, after the first discharge treatment, the voltage of the lithium battery rises from 2.5V to 3V, and the lithium battery needs to be discharged again. During the second discharge, the voltage after the rise is significantly lower than the initial voltage, so it can be discharged with a smaller current. Exemplarily, during the second discharge, a secondary discharge can be performed at a current rate of 0.02C until the voltage of the lithium battery reaches the preset voltage. Of course, if the voltage recovery rate is high, the discharge current can be appropriately increased. For example: after the first discharge treatment, the voltage of the lithium battery rises from 2.5V to 3.5V, then during the second discharge, it can be discharged at a current of 0.1C until the voltage of the lithium battery reaches the preset voltage.

[0041] After the second discharge, the lithium battery is left to stand for the first preset time again. If the voltage of the lithium battery does not rise after the first preset time, step S200 can be performed directly. If the voltage of the lithium battery rises again, the lithium battery is discharged again, that is, the third discharge is performed. Since the rise in the voltage of the lithium battery is significantly reduced after the second discharge and may rise to 2.8V, a smaller current is used for discharge during the third discharge, such as a three-stage discharge at a current rate of 0.01C, until the voltage of the lithium battery reaches the preset voltage. By analogy, the discharge and voltage recovery detection of the lithium battery are repeated until the voltage of the lithium battery maintains the preset voltage. If the voltage of the lithium battery maintains the preset voltage, it is considered that the discharge is complete. At this time, step S200 can be executed to disassemble the lithium battery.

[0042] Since sufficient discharge suppresses the electrochemical activity of the electrode material, the possibility of the lithium battery electrode undergoing redox reaction with oxygen or other substances in the air is significantly reduced, further improving the integrity of the electrode material and the accuracy of the gram capacity measurement results. Furthermore, since sufficient discharge suppresses the electrochemical activity of the electrode material, in the embodiment of the present application, there is no need to prepare the lithium battery gram capacity test sample in the glove box, which improves the convenience of the lithium battery gram capacity test.

[0043] In some embodiments, in order to fully wash the electrolyte on the surface of the electrode, when executing step S300, the electrode is immersed in the electrolyte solvent for a second preset time. Exemplarily, the second preset time is 5 minutes to 10 minutes. In one embodiment, the electrode can be immersed in the electrolyte solvent for 5 minutes. In another embodiment, in order to fully dissolve the electrolyte, the electrode can be immersed in the electrolyte solvent for 10 minutes; from the perspective of dissolution efficiency, in a preferred embodiment, the electrode is immersed in the electrolyte solvent. The intermediate value can be 7 minutes. In the embodiment of the present application, the aforementioned electrolyte solvent can be at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethyl acrylate, and methyl acrylate.

[0044] For example, in order to increase the dissolution rate of the electrolyte, the electrolyte solvent may be a mixture of diethyl carbonate and dimethyl carbonate. The mixture of ethylene carbonate and dimethyl carbonate has a high dissolution rate for the electrolyte lithium salt, so the time for the pole piece to be immersed in the electrolyte solvent can be relatively shortened. For example, the electrolyte on the surface of the pole piece, that is, the lithium salt, can be fully washed by immersing the pole piece in the electrolyte solvent for 5 minutes.

[0045] In another example, the electrolyte solvent may be a mixture of diethyl carbonate and ethylene carbonate. The mixture of diethyl carbonate and ethylene carbonate also has a high dissolution rate for lithium salt, thereby improving the washing efficiency of the electrode.

[0046] After the electrolyte on the surface of the electrode is fully dissolved, the electrode is taken out, and then the electrolyte solvent on the surface of the electrode is dried to finally obtain a sample for lithium battery gram capacity test.

[0047] In some embodiments, the present application also provides a sample for testing gram capacity of a lithium battery and a method for testing gram capacity of a lithium battery. The sample for testing gram capacity of a lithium battery is manufactured by the manufacturing method provided in the above embodiment. In the process of executing the method for testing gram capacity of a lithium battery, the gram capacity of the lithium battery can be measured more accurately due to the use of the sample for testing gram capacity of a lithium battery.

[0048] The implementation process of the present invention will be described in detail below by way of examples and comparative examples.

[0049] Example 1

[0050] Step 1: Discharge the aged lithium battery to 2.5V at a current rate of 0.2C (equivalent to primary discharge).

[0051] Step 2: Leave the lithium battery in a natural environment for 10 minutes.

[0052] Step 3: If the voltage of the lithium battery is detected to have risen, it will be discharged again to 2.5V at a current rate of 0.02C (equivalent to secondary discharge).

[0053] Step 4: Leave the lithium battery in the natural environment for 10 minutes again.

[0054] Step 5: Check again whether the voltage of the lithium battery rises. If the voltage rises, repeat the discharge process and the static process. The minimum current rate of the discharge process is 0.01C (equivalent to three-stage discharge).

[0055] Step 6: If the voltage of the lithium battery does not recover, disassemble the lithium battery, cut out the required positive electrode sheet, and immerse it in dimethyl carbonate.

[0056] Step 7: After soaking for 5 minutes, the dimethyl carbonate on the surface of the electrode is dried to complete the lithium battery gram capacity test sample.

[0057] The test procedure of the test sample in this example is: charge the test sample to 4.45V at 0.1C constant current and constant voltage, and the cut-off current is 0.01C; then discharge to 3.0V at 0.1C. The test results show that the gram capacity of the positive electrode of the aged lithium battery is 173.96mAh / g, which fully utilizes the gram capacity level of the electrode itself (the gram capacity of the fresh uncycled electrode is 180mAh / g).

[0058] Example 2

[0059] Step 10: Discharge the aged lithium battery to 2.8V (equivalent to primary discharge) at a current rate of 0.2C.

[0060] Step 20: Leave the lithium battery in a natural environment for 10 minutes.

[0061] Step 30: If it is detected that the voltage of the lithium battery has risen, it will be discharged again to 2.8V at a current rate of 0.02C (equivalent to secondary discharge).

[0062] Step 40: Leave the lithium battery in a natural environment for 10 minutes again.

[0063] Step 50, check again whether the voltage of the lithium battery rises. If the voltage rises, the discharge process and the static process are repeated, and the current rate of the discharge process is as low as 0.01C (equivalent to three-stage discharge).

[0064] Step 60: If the voltage of the lithium battery does not recover, the lithium battery is disassembled and the required positive electrode sheet is cut out and then immersed in dimethyl carbonate.

[0065] Step 70: After soaking for 5 minutes, the dimethyl carbonate on the surface of the electrode is dried to complete the lithium battery gram capacity test sample.

[0066] The test procedure of the test sample in this example is: charge the test sample to 4.45V at 0.1C constant current and constant voltage, and discharge it to 3.0V at 0.1C. The test results show that the gram capacity of the positive electrode of the aged lithium battery is 171.34mAh / g, which fully demonstrates the gram capacity level of the electrode itself.

[0067] Comparative Example 1

[0068] Compared with the above two examples, in this comparative example, the aged battery is not subjected to multi-stage discharge operation, but maintained at a charge state of 4.45V. Then, the disassembly and washing process as in the above example is performed to obtain a test sample. When the test sample is used to perform a gram capacity test, the test results show that the gram capacity of the electrode piece without discharge can only be measured to be 135.32mAh / g, which is significantly different from the test results of the above examples.

[0069] Comparative Example 2

[0070] Compared with Example 1, in this comparative example, the disassembled electrode was not washed, and the other operation steps were the same to prepare a test sample. When the test sample was used for gram capacity test, the test results showed that the gram capacity of the electrode without washing could only measure 8.2 mAh / g, which was significantly different from the test results of the above example.

[0071] Comparing the results of Comparative Example 1 and Examples 1 and 2, it can be seen that if the aged lithium battery is not subjected to multi-stage discharge treatment, the activity of the pole piece material is still relatively active even for the aged lithium battery. Therefore, if the multi-stage discharge treatment is not carried out, disassembly and washing in a natural environment may cause the pole piece material to undergo redox reaction with the oxidizing components in the air, thereby affecting the integrity of the pole piece material. Comparing the results of Comparative Example 2 and Examples 1 and 2, it can be seen that if the pole piece after disassembly is not fully cleaned, the deposited impurities in the electrolyte in the aged battery will affect the test accuracy of the pole piece gram capacity, and the measured gram capacity value is seriously low.

[0072] Based on the test results of Example 1 and Example 2, after the aged lithium battery is subjected to multi-stage discharge treatment, even if it is disassembled and tested for gram capacity in a natural environment, the measured gram capacity value of the electrode piece is significantly higher than the test result of the comparison ratio. Moreover, the difference between the test results of Example 1 and Example 2 is small, which is sufficient to show that the above-mentioned method for making samples for lithium battery gram capacity test effectively suppresses the electrochemical activity of the electrode material, reduces the possibility of the electrode piece obtained by disassembly undergoing redox reaction with oxygen and other substances in the air when in a natural environment, so that the electrode piece obtained by the technical solution can more completely measure the gram capacity value of the electrode piece.

[0073] The above description is only a partial or preferred embodiment of the present invention. Neither the text nor the drawings can limit the scope of protection of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the overall concept of the present invention, or direct / indirect application in other related technical fields are included in the scope of protection of the present invention.

Claims

1. A sample preparation method for testing the gram capacity of lithium battery pole pieces after cycle aging, characterized in that: include: Perform multi-stage discharge on aged lithium batteries to reduce their internal voltage to a preset voltage; Disassembling the lithium battery to obtain the electrode of the lithium battery; The electrode piece is cleaned with a lithium battery electrolyte solvent and dried to obtain a test sample.

2. The sample preparation method for testing the gram capacity of lithium battery pole pieces after cycle aging according to claim 1, characterized in that: The multi-stage discharge of the aged lithium battery comprises: The lithium battery is discharged step by step at a current rate that decreases step by step from 0.01C to 0.5C.

3. The sample preparation method for testing the gram capacity of lithium battery pole pieces after cycle aging according to claim 2, characterized in that: The multi-stage discharge method comprises: S1. Controlling the lithium battery to perform primary discharge at a preset current rate through a charge and discharge tester until the voltage of the lithium battery reaches the preset voltage; S2, detecting whether the voltage of the lithium battery rises; S3. If the voltage of the lithium battery rises again, the lithium battery is controlled to perform secondary discharge at a preset current rate less than S1 until the voltage of the lithium battery is maintained at the preset voltage.

4. The sample preparation method for testing the gram capacity of lithium battery pole pieces after cycle aging according to claim 3, characterized in that: The preset voltage is 2.0V to 3.0V, and the number of multi-stage discharges is ≤10 times.

5. The sample preparation method for testing the gram capacity of lithium battery pole pieces after cycle aging according to claim 1, characterized in that: Before detecting whether the voltage of the lithium battery rises, the method further includes: The lithium battery is left to stand for a first preset time period, where the first preset time period is 1 minute to 100 minutes.

6. The sample preparation method for testing the gram capacity of lithium battery pole pieces after cycle aging according to claim 5, characterized in that: The first preset time length is 5 minutes to 10 minutes.

7. The sample preparation method for testing the gram capacity of lithium battery pole pieces after cycle aging according to claim 1, characterized in that: The cleaning comprises: soaking the electrode in an electrolyte solvent for a second preset time period, wherein the second preset time period is 3 minutes to 30 minutes.

8. The sample preparation method for testing the gram capacity of lithium battery pole pieces after cycle aging according to claim 7, characterized in that: The second preset time length is 5 minutes to 10 minutes.

9. The method for preparing samples for testing the gram capacity of lithium battery pole pieces after cycle aging according to claim 1, characterized in that: The electrolyte solvent is at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

10. The sample preparation method for testing the gram capacity of lithium battery pole pieces after cycle aging according to claim 1, characterized in that: The step of obtaining a lithium battery electrode comprises: The pole pieces of the lithium battery are cut to obtain pole pieces of a preset size.

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