Preparation method of lithium / sodium ion battery failure analysis symmetric battery

Abstract

The invention relates to the technical field of batteries, in particular to a preparation method of a lithium / sodium ion battery failure analysis symmetric battery. The method comprises the following steps: S1, carrying out constant-current discharge on a failed battery; s2, transferring the battery subjected to constant-current discharge into a drying room, disassembling the battery, and separating out a positive plate and a negative plate; s3, respectively immersing the separated positive plate and the separated negative plate into DMC (Dimethyl Carbonate) for water bath heating; s4, carrying out vacuum drying on the treated positive plate and negative plate; s5, preparing a positive electrode symmetrical battery and a negative electrode symmetrical battery; and S6, respectively applying certain extrusion force to the planes of the positive electrode symmetric battery and the negative electrode symmetric battery to obtain the lithium / sodium ion battery failure analysis symmetric battery. According to the method, the electrochemical alternating-current impedance spectrum of the positive plate or the negative plate can be accurately measured, and then the failure source is analyzed; the lithium / sodium ion battery failure analysis symmetric battery is simple to prepare, convenient to operate and high in reliability.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a method for preparing a symmetrical battery for failure analysis of a lithium / sodium ion battery. Background Art

[0002] As an electrochemical energy storage device, lithium / sodium ion batteries have excellent electrode stability and cycle performance, and can usually meet a variety of application scenarios such as long-term storage, high and low temperature, and long cycles. However, the electrochemical system of lithium / sodium ion batteries is a complex system, which includes positive electrode sheets, negative electrode sheets, diaphragms, electrolytes and other material components. Among them, the positive electrode provides active Li + / Na + , the negative electrode receives active Li + / Na + , which largely determines the final performance of the battery.

[0003] However, when lithium / sodium-ion batteries fail, such as due to storage flatulence, cycle attenuation, etc., it is impossible to determine whether the failure is caused by a certain material or part through full battery analysis alone.

[0004] Therefore, it is necessary to dismantle the entire battery structure and reassemble the battery to obtain the failure status of a certain independent material and then locate the source of failure. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for preparing a symmetrical battery for failure analysis of lithium / sodium ion batteries, wherein the obtained symmetrical battery has the characteristics of simple structure, convenient operation and high reliability.

[0006] In order to achieve the above invention objectives, the present invention is implemented by the following technical solutions: A method for preparing a symmetrical battery for lithium / sodium ion battery failure analysis comprises the following steps: S1: discharge the failed battery at a constant current with a certain current; S2: The battery after constant current discharge is transferred to a drying room, where the battery is disassembled to separate the positive electrode sheet and the negative electrode sheet; S3: Immerse the separated positive electrode sheet and negative electrode sheet in DMC solvent respectively, and then heat them in a water bath; S4: taking out the positive electrode sheet and the negative electrode sheet treated by S3 from the DMC solvent and then vacuum drying; S5: taking two positive and negative electrodes after vacuum drying, namely the first positive electrode sheet, the second positive electrode sheet, the first negative electrode sheet and the second negative electrode sheet; then stacking the first positive electrode sheet and the second positive electrode sheet together, separated by a separator in the middle; welding one pole ear to the first positive electrode sheet and the second positive electrode sheet respectively, and finally encapsulating and injecting liquid with an aluminum-plastic film, and finally making a positive electrode symmetrical battery; similarly, stacking the first negative electrode sheet and the second negative electrode sheet together, separated by an separator in the middle, welding one pole ear to the first negative electrode sheet and the second negative electrode sheet respectively, and then encapsulating and injecting liquid with an aluminum-plastic film, and finally making a negative electrode symmetrical battery; S6: Apply a certain extrusion force to the planes of the positive electrode symmetrical battery and the negative electrode symmetrical battery respectively to obtain a symmetrical battery for failure analysis of lithium / sodium ion batteries.

[0007] As a better implementation in the present application, in S1 of the preparation method of the symmetrical battery for failure analysis of lithium / sodium ion batteries, the current of the constant current discharge is 0.01~0.05C (specifically 0.01C, 0.02C, 0.03C, 0.04C, 0.05C, etc.), and the cut-off voltage is 0~3V (specifically 0V, 1V, 2V, 3V, etc.). If the current is too large, the battery polarization is large, and the capacity is not fully released, that is, there is still a lot of Na in the negative electrode sheet. + If the current is too small, it will take a long time and the production efficiency will be low. Similarly, if the cut-off voltage is too high, the Na + It has not completely migrated to the positive electrode, that is, it cannot represent the state of the positive electrode or the negative electrode when it is not charged.

[0008] As a better implementation mode in the present application, in S2 of the method for preparing a symmetrical battery for failure analysis of a lithium / sodium ion battery, the dew point of the drying room is ≤-45°C, otherwise the active material or electrolyte is very likely to absorb water and cause some side reactions, thereby destroying the interface state of the electrode and causing inaccurate test results.

[0009] As a better implementation in the present application, in S3 of the preparation method of the symmetrical battery for failure analysis of lithium / sodium ion batteries, the water bath temperature is 30-60°C (specifically 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, etc.), and the time is 10-60min (specifically 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, etc.). The DMC solvent can dissolve and clean the salt, additives and other substances remaining on the surface of the pole piece well. Controlling the water bath temperature at 30-60°C can greatly improve the dissolution rate and effect without causing irreversible damage to the pole piece.

[0010] As a better implementation in the present application, in S4 of the preparation method of the symmetrical battery for failure analysis of lithium / sodium ion batteries, the vacuum degree during vacuum drying is ≤-85Kpa, the temperature is 60~120℃ (specifically 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, etc.), and the time is 4~12h (specifically 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc.). The higher the vacuum degree, the lower the boiling point of the solvent or water, the better the baking effect, and the time can be saved.

[0011] As a better implementation in the present application, in S5 of the method for preparing a symmetrical battery for failure analysis of a lithium / sodium ion battery, the injection amount of the positive symmetrical battery is 20~50%M1, where M1 is the total mass of the positive electrode sheet; the injection amount of the negative symmetrical battery is 20~50%M2, where M2 is the total mass of the negative electrode sheet. When making a positive symmetrical battery or a negative symmetrical battery, it is necessary to weld one more tab on each layer of the positive electrode sheet or each layer of the negative electrode sheet, respectively, to facilitate the subsequent packaging and injection of the battery. The injection amount must meet the requirements. If the injection amount is too low, the electrode sheet and the diaphragm may not be completely infiltrated, resulting in inaccurate test results. If the injection amount is too high, on the one hand, the electrolyte is wasted, and on the other hand, it may affect the contact between the electrode sheet and the diaphragm.

[0012] As a preferred embodiment of the present application, in S6 of the method for preparing a symmetrical battery for failure analysis of a lithium / sodium ion battery, 0.2-1.2 kgf / cm2 is applied to the planes of the positive symmetrical battery and the negative symmetrical battery, respectively. 2 (Specifically 0.2kgf / cm 2 、0.4kgf / cm 2 、0.6kgf / cm 2 、0.8kgf / cm 2 、1.0kgf / cm 2 , 1.2kgf / cm 2 This is because the symmetrical battery has only two layers of pole pieces, which are easy to deform. After applying planar pressure, the flatness and good contact of the pole piece and the diaphragm can be better maintained. If the extrusion pressure is too large, the diaphragm may be damaged and cause an internal short circuit. If the extrusion pressure is too small, liquid or gas will remain between the pole piece and the diaphragm, resulting in poor internal contact.

[0013] The present application also protects a lithium / sodium ion battery failure analysis symmetrical battery prepared by any of the above methods.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (I) The present invention provides a preparation process and method for dismantling a failed battery and reassembling a symmetrical battery, which has the characteristics of simple structure, convenient operation and high reliability.

[0015] (ii) This method can be used to accurately measure the electrochemical impedance spectrum of the positive electrode or negative electrode, and then analyze the source of failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the appearance of a positive electrode symmetrical battery; Figure 2 This is a cross-sectional view of a positive electrode symmetrical battery; Figure 3 This is a schematic diagram of the appearance of a negative electrode symmetrical battery; Figure 4 This is a cross-sectional diagram of a negative electrode symmetrical battery; In the figure, it is marked as follows: 11-first positive electrode sheet ear; 12-second positive electrode sheet ear; 10-positive electrode symmetrical battery; 101-positive electrode separator; 102-first positive electrode sheet; 103-second positive electrode sheet; 21-first negative electrode sheet ear; 22-second negative electrode sheet ear; 20-negative electrode symmetrical battery; 201-negative electrode separator; 202-first negative electrode sheet; 203-second negative electrode sheet; Figure 5 This is a graph showing the AC impedance spectrum test results of the positive electrode symmetrical battery in Example 1; Figure 6 This is a graph showing the AC impedance spectrum test results of the negative electrode symmetrical battery in Example 1. DETAILED DESCRIPTION

[0017] The present invention is further described below in conjunction with embodiments, which are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by ordinary technicians in the field without creative work are all within the scope of protection of the present invention.

[0018] In the present application, % not specifically indicated indicates the mass percentage, i.e., wt%; the reagents or instruments used without indicating the manufacturer are conventional products that can be purchased commercially.

[0019] Embodiment 1: The sodium-ion batteries with cycle failure were discharged at a constant current of 0.02C to 1.5V, and then transferred to a dry room with a dew point of -50°C for disassembly to separate the positive and negative electrodes.

[0020] Prepare two 500mL portions of DMC solvent, immerse the separated positive and negative electrodes in the DMC solvent respectively, then heat them in a water bath at 40°C, keep them for 30 minutes and take them out. After the solvent on the electrode surface is naturally dripped dry, transfer them to a vacuum drying oven, set the vacuum degree of the vacuum drying oven to -90Kpa, the temperature to 80°C, and take them out after baking for 8 hours.

[0021] Take two positive electrode sheets, record them as the first positive electrode sheet and the second positive electrode sheet, set a diaphragm between the first positive electrode sheet and the second positive electrode sheet, then weld the first positive electrode sheet tab on the first positive electrode sheet, weld the second positive electrode sheet tab on the second positive electrode sheet, then inject 10g of electrolyte, and then package the battery to form a positive electrode symmetrical battery. Similarly, take two negative electrode sheets, record them as the first negative electrode sheet and the second negative electrode sheet, set a diaphragm between the first negative electrode sheet and the second negative electrode sheet, then weld the first negative electrode sheet tab on the first negative electrode sheet, weld the second negative electrode sheet tab on the second negative electrode sheet, then inject 6g of electrolyte, and then package the battery to form a negative electrode symmetrical battery.

[0022] Apply 0.5kgf / cm2 to the positive symmetrical battery and the negative symmetrical battery plane respectively. 2 The extrusion force was 100%, and the symmetrical battery for sodium ion battery failure analysis was obtained. Finally, the electrochemical workstation was used to perform AC impedance spectroscopy test.

[0023] Figure 5 It is the AC impedance spectrum test result of the positive electrode symmetrical battery of this embodiment. As can be seen from the figure, after assembling the positive electrode symmetrical battery, it is found that there is a significant difference in the AC impedance spectrum before and after the battery fails, and the AC impedance increases significantly by more than 1 times after failure.

[0024] Figure 6 It is the AC impedance spectrum test result of the negative electrode symmetrical battery of this embodiment. It can be seen from the figure that after assembling the negative electrode symmetrical battery, it is found that the AC impedance spectrum overlaps more before and after the battery fails, and there is no obvious increase phenomenon.

[0025] Combination Figure 5 and Figure 6 Analysis shows that although the whole battery suffered a cycle failure, positive and negative symmetrical batteries were assembled respectively. The AC impedance of the positive symmetrical battery increased significantly by more than 1 times before and after the cycle, while the AC impedance spectrum of the negative symmetrical battery had a high degree of overlap before and after failure, and there was no obvious increase. Therefore, it can be determined that the main failure source of the increase in battery cycle impedance comes from the positive electrode sheet.

[0026] Embodiment 2: The cycle-failed lithium-ion batteries were discharged at a constant current of 0.02C to 2.5V, and then transferred to a drying room with a dew point of -50°C for disassembly to separate the positive and negative electrodes.

[0027] Prepare two 500mL portions of DMC solvent, immerse the separated positive and negative electrodes in the DMC solvent respectively, then heat them in a water bath at 45°C, keep them for 20 minutes and take them out. After the solvent on the electrode surface is naturally dripped dry, transfer them to a vacuum drying oven, set the vacuum degree of the vacuum drying oven to -95Kpa, the temperature to 60°C, and take them out after baking for 4 hours.

[0028] Take two positive electrode sheets, record them as the first positive electrode sheet and the second positive electrode sheet, set a diaphragm between the first positive electrode sheet and the second positive electrode sheet, then weld the first positive electrode sheet tab on the first positive electrode sheet, weld the second positive electrode sheet tab on the second positive electrode sheet, then inject 15g of electrolyte, and then package the battery to form a positive electrode symmetrical battery. Similarly, take two negative electrode sheets, record them as the first negative electrode sheet and the second negative electrode sheet, set a diaphragm between the first negative electrode sheet and the second negative electrode sheet, then weld the first negative electrode sheet tab on the first negative electrode sheet, weld the second negative electrode sheet tab on the second negative electrode sheet, then inject 9g of electrolyte, and then package the battery to form a negative electrode symmetrical battery.

[0029] Apply 1.0kgf / cm2 to the positive and negative symmetrical battery planes. 2 The extrusion force was used to obtain a symmetrical battery for lithium-ion battery failure analysis. Finally, an electrochemical workstation was used to perform an AC impedance spectroscopy test.

[0030] Embodiment 3: The cycle-failed lithium-ion batteries were discharged at a constant current of 0.01C to 3V, and then transferred to a dry room with a dew point of -45°C for disassembly to separate the positive and negative electrodes.

[0031] Prepare two 500mL portions of DMC solvent, immerse the separated positive and negative electrodes in the DMC solvent respectively, then heat them in a water bath at 60°C, keep them for 10 minutes and take them out. After the solvent on the electrode surface is naturally dripped dry, transfer them to a vacuum drying oven, set the vacuum degree of the vacuum drying oven to -90Kpa, the temperature to 100°C, and take them out after baking for 4 hours.

[0032] Take two positive electrode sheets, record them as the first positive electrode sheet and the second positive electrode sheet, set a diaphragm between the first positive electrode sheet and the second positive electrode sheet, then weld the first positive electrode sheet tab on the first positive electrode sheet, weld the second positive electrode sheet tab on the second positive electrode sheet, then inject 12g of electrolyte, and then package the battery to form a positive electrode symmetrical battery. Similarly, take two negative electrode sheets, record them as the first negative electrode sheet and the second negative electrode sheet, set a diaphragm between the first negative electrode sheet and the second negative electrode sheet, then weld the first negative electrode sheet tab on the first negative electrode sheet, weld the second negative electrode sheet tab on the second negative electrode sheet, then inject 8g of electrolyte, and then package the battery to form a negative electrode symmetrical battery.

[0033] Apply 1.2kgf / cm2 to the positive and negative symmetrical battery planes. 2 The extrusion force was 100%, and the symmetrical battery for sodium ion battery failure analysis was obtained. Finally, the electrochemical workstation was used to perform AC impedance spectroscopy test.

[0034] Embodiment 4: The sodium-ion batteries with cycle failure were discharged to 0V at a constant current of 0.01C, and then transferred to a dry room with a dew point of -55°C for disassembly to separate the positive and negative electrodes.

[0035] Prepare two 500mL portions of DMC solvent, immerse the separated positive and negative electrodes in the DMC solvent respectively, then heat them in a water bath at 30°C, keep them for 60 minutes and take them out. After the solvent on the electrode surface is naturally dripped dry, transfer them to a vacuum drying oven, set the vacuum degree of the vacuum drying oven to -90Kpa, the temperature to 100°C, and take them out after baking for 4 hours.

[0036] Take two positive electrode sheets, record them as the first positive electrode sheet and the second positive electrode sheet, set a diaphragm between the first positive electrode sheet and the second positive electrode sheet, then weld the first positive electrode sheet tab on the first positive electrode sheet, weld the second positive electrode sheet tab on the second positive electrode sheet, then inject 8g of electrolyte, and then package the battery to form a positive electrode symmetrical battery. Similarly, take two negative electrode sheets, record them as the first negative electrode sheet and the second negative electrode sheet, set a diaphragm between the first negative electrode sheet and the second negative electrode sheet, then weld the first negative electrode sheet tab on the first negative electrode sheet, weld the second negative electrode sheet tab on the second negative electrode sheet, then inject 5g of electrolyte, and then package the battery to form a negative electrode symmetrical battery.

[0037] Apply 0.2kgf / cm2 to the positive symmetrical battery and the negative symmetrical battery plane respectively. 2 The extrusion force was 100%, and the symmetrical battery for sodium ion battery failure analysis was obtained. Finally, the electrochemical workstation was used to perform AC impedance spectroscopy test.

[0038] Comparative Example 1: The difference from Example 1 is that the constant current discharge current is 1C, and other operations are exactly the same.

[0039] Comparative Example 2: The difference from Example 1 is that the constant current discharge current is 0.005C.

[0040] Comparative Example 3: The difference from Example 1 is that the dew point of the drying room is -40°C.

[0041] Comparative Example 4: The difference from Example 1 is that the dew point of the drying room is -30°C.

[0042] Comparative Example 5: The difference from Example 1 is that the dew point of the drying room is -20°C.

[0043] Comparative Example 6: The difference from Example 1 is that the liquid injection amount of the positive electrode symmetrical battery is 6g, and the liquid injection amount of the negative electrode symmetrical battery is 4g, both of which are less than 20% of the total weight of the electrode.

[0044] Comparative Example 7: The difference from Example 1 is that 0.1 kgf / cm 2 of extrusion pressure.

[0045] Comparative Example 8: The difference from Example 1 is that 1.5 kgf / cm 2 of extrusion pressure.

[0046] The batteries obtained in Examples 1-4 and Comparative Examples 1-8 were tested for AC impedance spectroscopy using an electrochemical workstation. The specific results are shown in Table 1: Table 1 AC impedance spectroscopy test results for each case

[0047] As can be seen from Table 1, by comparing the embodiments and the comparative examples, it can be found that embodiments 1-4 can all significantly find that the Rct before and after the failure of the negative electrode is close, while the Rct before and after the failure of the positive electrode increases significantly, so it can be determined that the failure source occurs at the positive electrode; while comparative example 1 uses a larger current discharge, and the Rct before and after the failure of the positive and negative electrodes increases to a certain extent. Although the positive electrode increases relatively more, it is not conducive to determining the failure source. Comparative example 2 uses a smaller current discharge, and the Rct before and after the failure of the positive electrode increases significantly, and the increase in the negative electrode is relatively small. Although the failure source can be basically determined, the smaller current takes longer and the production efficiency is low. The dew point of the drying room of comparative examples 3-5 gradually increases, that is, the moisture content of the environment is getting higher and higher, resulting in a significant increase in Rct before and after the failure of the positive and negative electrodes, which is not conducive to determining the failure source. Comparative example 6 has insufficient injection volume, resulting in poor wetting of the pole piece and the diaphragm, and a large impedance, and the failure source cannot be determined. The symmetrical battery extrusion force of comparative example 7 is small, and the internal contact is poor, resulting in high impedance, and the failure source cannot be determined. The symmetrical battery extrusion force of comparative example 8 is large, resulting in the diaphragm being squeezed and the positive and negative electrodes are short-circuited, and testing cannot be performed.

[0048] Although the main inventive examples that affect the factors of this experiment have been described and listed, ordinary persons in the art can understand that various changes, explorations, modifications and combinations can be made to the embodiments without departing from the principles and purpose of the invention, and the scope of the invention is defined by the claims and their equivalents.

[0049] The above basic examples of the present invention and their further selected examples can be freely combined to form multiple embodiments, all of which are embodiments that can be adopted and claimed by the present invention. In the scheme of the present invention, each selected example can be arbitrarily combined with any other basic example and selected example. Those skilled in the art will know that there are many combinations.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a symmetrical battery for failure analysis of lithium / sodium ion batteries, characterized in that The steps include: S1: discharge the failed battery at a constant current with a certain current; S2: The battery after constant current discharge is transferred to a drying room, where the battery is disassembled to separate the positive electrode sheet and the negative electrode sheet; S3: Immerse the separated positive electrode sheet and negative electrode sheet in DMC solvent respectively, and then heat them in a water bath; S4: taking out the positive electrode sheet and the negative electrode sheet treated by S3 from the DMC solvent and then vacuum drying; S5: taking two positive and negative electrodes after vacuum drying, namely the first positive electrode sheet, the second positive electrode sheet, the first negative electrode sheet and the second negative electrode sheet; then stacking the first positive electrode sheet and the second positive electrode sheet together, separated by a separator in the middle; welding one pole ear to the first positive electrode sheet and the second positive electrode sheet respectively, and finally encapsulating and injecting liquid with an aluminum-plastic film, and finally making a positive electrode symmetrical battery; similarly, stacking the first negative electrode sheet and the second negative electrode sheet together, separated by an separator in the middle, welding one pole ear to the first negative electrode sheet and the second negative electrode sheet respectively, and then encapsulating and injecting liquid with an aluminum-plastic film, and finally making a negative electrode symmetrical battery; S6: Apply a certain extrusion force to the planes of the positive electrode symmetrical battery and the negative electrode symmetrical battery respectively to obtain a symmetrical battery for failure analysis of lithium / sodium ion batteries.

2. The method for preparing a symmetrical battery for failure analysis of a lithium / sodium ion battery according to claim 1, characterized in that: In S1, the constant current discharge current is 0.01~0.05C, and the cut-off voltage is 0~3V.

3. The method for preparing a symmetrical battery for failure analysis of a lithium / sodium ion battery according to claim 1, characterized in that: In S2, the dew point of the drying room is ≤-45°C.

4. The method for preparing a symmetrical battery for failure analysis of a lithium / sodium ion battery according to claim 1, characterized in that: In S3, the water bath temperature is 30~60℃ and the time is 10~60min.

5. The method for preparing a symmetrical battery for failure analysis of a lithium / sodium ion battery according to claim 1, characterized in that: In S4, the vacuum degree during vacuum drying is ≤-85Kpa, the temperature is 60~120℃, and the time is 4~12h.

6. The method for preparing a symmetrical battery for failure analysis of a lithium / sodium ion battery according to claim 1, characterized in that: In S5, the liquid injection amount of the positive electrode symmetrical battery is 20~50%M1, where M1 is the total mass of the positive electrode sheet; the liquid injection amount of the negative electrode symmetrical battery is 20~50%M2, where M2 is the total mass of the negative electrode sheet.

7. The method for preparing a symmetrical battery for failure analysis of a lithium / sodium ion battery according to claim 1, characterized in that: In S6, 0.2~1.2kgf / cm2 is applied to the positive symmetrical battery and the negative symmetrical battery plane respectively. 2 of extrusion pressure.

8. The method for preparing a symmetrical battery for failure analysis of a lithium / sodium ion battery according to claim 2, characterized in that: In S1, the constant current discharge current is 0.02C and the cut-off voltage is 1.5V.

9. The method for preparing a symmetrical battery for failure analysis of a lithium / sodium ion battery according to claim 7, characterized in that: In S6, 0.5 kgf / cm2 was applied to the planes of the positive symmetrical battery and the negative symmetrical battery. 2 of extrusion pressure.

10. A lithium / sodium ion battery failure analysis symmetrical battery, characterized in that: The method is prepared by any one of claims 1 to 9.

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