Third electrode for assisting in testing positive / negative electrode potential, soft package lithium battery and application

Abstract

The present application relates to the technical field of soft package battery performance detection, and discloses a third electrode for assisting in testing positive / negative electrode potential, which comprises a copper metal long sheet and a lithium metal long sheet connected in the length direction, the width of the copper metal long sheet is greater than or equal to the lithium metal long sheet, the thickness of the copper metal long sheet is greater than the lithium metal long sheet, one end of the copper metal long sheet is welded to one end of the lithium metal long sheet after being overlapped and coincided, and an adhesive sheet is further arranged on the copper metal long sheet, the adhesive sheet is located at a non-overlapping position of the copper metal long sheet, and both ends of the adhesive sheet extend out of both side edges of the copper metal long sheet. The third electrode is packaged into a soft package lithium battery, the battery core does not need to be disassembled when the performance of the soft package lithium battery is tested, the performance detection of the whole life cycle and online detection can be realized, the detection result is stable and reliable, and the cost is low.

Description

Technical Field

[0001] This invention relates to the field of performance testing technology for pouch batteries, specifically to a third electrode for auxiliary testing of positive / negative electrode potentials, a pouch lithium battery equipped with the third electrode, and a method for testing the positive / negative electrode potentials of the pouch battery using the third electrode. Background Technology

[0002] With the rapid development of lithium battery technology, increasing emphasis is being placed on the study of lithium battery mechanisms. Normal lithium batteries can only be used to study the overall electrochemical performance of the battery, and cannot be used to study the positive / negative polarity separately. When the performance of a lithium battery fails to meet a certain expected technical target, it is often necessary to disassemble and analyze the cell to perform positive and negative electrode analysis.

[0003] Currently, the industry's methods for analyzing the positive and negative electrodes of full-cell batteries involve disassembling the battery in a glove box or a low-humidity room (dew point ≤ -45℃), collecting the positive and negative electrode sheets, and assembling the positive electrode sheet, separator, negative electrode sheet, and third electrode to form a three-electrode battery for testing and analysis. Common third electrodes include lithium sheets, copper wire, stainless steel sheets, or platinum. Using lithium batteries as the third electrode is not only complex, but also raises concerns about measurement accuracy and the stability and reliability of the results due to the easy oxidation of lithium metal in air. Using copper or stainless steel as the third electrode is problematic because lithium battery research typically focuses on the lithium-to-metal potential. Copper or stainless steel as the third electrode yields data representing the potential of graphite / lithium iron phosphate relative to copper or stainless steel, requiring conversion, and the accuracy and stability of the test data are generally low. Using platinum as the third electrode results in relatively high costs.

[0004] Furthermore, for the batteries to be tested, testing can only be conducted by disassembling them and assembling the positive / negative electrodes and the third electrode separately, making it impossible to monitor the battery's entire lifecycle. Moreover, analyzing used lithium batteries often requires comparing them with the initial data of fresh batteries. The manufacturing cost of a single battery cell is very high; based on an estimate of a 3.2V / 30Ah LFP, the overall cost of a single cell is nearly 100 yuan, making it prohibitively expensive.

[0005] Therefore, there is currently a lack of effective methods for lithium battery performance research that can achieve low-cost, high-precision, and full-lifecycle testing. Summary of the Invention

[0006] To address the issue of low stability in measurement results using the third electrode currently employed for testing the positive / negative electrode potentials of lithium batteries, the present invention aims to provide a third electrode for assisting in testing the positive / negative electrode potentials. This third electrode offers higher testing accuracy and better result stability compared to lithium or copper as the third electrode, while also being less expensive than platinum electrodes.

[0007] Another objective of this invention is to provide a pouch lithium battery equipped with the third electrode, which allows for performance testing of the pouch lithium battery at any time without disassembly, thus enabling performance testing throughout its entire life cycle.

[0008] Another object of the present invention is to provide a method for testing the positive / negative electrode potentials of a pouch lithium battery using the third electrode.

[0009] This invention provides the following technical solution:

[0010] A third electrode includes a long thin sheet of copper metal and a long thin sheet of lithium metal connected in the longitudinal direction. The width of the long thin sheet of copper metal is greater than or equal to that of the long thin sheet of lithium metal, and the thickness of the long thin sheet of copper metal is greater than that of the long thin sheet of lithium metal. One end of the long thin sheet of copper metal and one end of the long thin sheet of lithium metal are stacked and welded together. An adhesive sheet is also provided on the long thin sheet of copper metal, located in the non-stacked part of the long thin sheet of copper metal, and the two ends of the adhesive sheet extend out of the two sides of the long thin sheet of copper metal.

[0011] The third electrode provided by this invention is assembled by welding long thin sheets of copper and lithium metal. The width of the long thin sheet of copper is greater than or equal to that of the long thin sheet of lithium metal, and the thickness of the long thin sheet of copper is greater than that of the long thin sheet of lithium metal. In use, the long thin sheet of copper is exposed to form the third electrode tab, while the long thin sheet of lithium metal is encapsulated inside the battery to avoid oxidation. Lithium potential data for either the positive or negative electrode can be obtained directly without conversion, and lithium oxidation is avoided. The test stability and accuracy are high. The electrode cost is between that of pure copper and pure lithium electrodes, which is perfectly acceptable.

[0012] As a preferred embodiment of the present invention, the width of the copper metal elongated sheet is 3-5 mm; the thickness of the copper metal elongated sheet is 0.1-0.3 mm. Preferably, the thickness of the copper metal elongated sheet is 0.2 mm.

[0013] As a preferred embodiment of the present invention, the width of the lithium metal elongated sheet is 3-4 mm; the thickness of the lithium metal elongated sheet is 0.08-0.12 mm. Preferably, the thickness of the lithium metal elongated sheet is 0.1 mm.

[0014] As a preferred embodiment of the present invention, the solder mark at the welding end of the lithium metal sheet is smaller in the width direction of the lithium metal sheet than the width of the lithium metal sheet, preferably 2.5 to 3.5 mm.

[0015] As a preferred embodiment of the present invention, a gap is provided at the welding ends of the adhesive sheet and the long thin lithium metal sheet. This ensures that the long thin lithium metal sheet is completely encapsulated in the airbag and away from the encapsulation portion.

[0016] Preferably, the adhesive sheet comprises two pieces, arranged on both sides of the long thin copper sheet, and the corresponding portions of the two adhesive sheets extending beyond the sides of the long thin copper sheet are bonded together. Preferably, the dimension of the adhesive sheet in the length direction of the long thin copper sheet is 3-5 mm; the dimension of the adhesive sheet in the width direction of the long thin copper sheet is 8-10 mm; and the thickness of the adhesive sheet is 0.08-0.12 mm, more preferably 0.1 mm.

[0017] As a preferred embodiment of the present invention.

[0018] The vertical misalignment between the two adhesive sheets is ≤0.1mm;

[0019] The misalignment between the two adhesive sheets is ≤0.1mm.

[0020] A pouch lithium battery equipped with the aforementioned third electrode is disclosed. The third electrode is encapsulated in the center of the pouch lithium battery's air bladder, with the non-welded end of a long, thin copper metal sheet extending out of the air bladder to the adhesive sheet portion. The third electrode is unaffected by lithium sheet oxidation or assembly precision issues, and its single encapsulation ensures long-term use. This allows the pouch lithium battery to be analyzed without disassembly, enabling performance monitoring throughout its entire lifecycle.

[0021] A method for testing the positive / negative electrode potential using the aforementioned third electrode includes the following steps:

[0022] (1) The third electrode is encapsulated in the middle of the air bag of the soft-pack lithium battery, and the non-welded end of the copper metal long thin sheet extends out of the air bag to the adhesive sheet.

[0023] (2) Before the first charging of the soft-pack lithium battery, the potential data of the positive electrode tab, negative electrode tab, and third electrode were collected respectively, and recorded as V. 正 V 负 V 三 The positive electrode potential V0 = V before the first charge is obtained. 正 -V 三 The negative electrode potential to lithium is V1 = V 负 -V 三 ;

[0024] (3) Repeatedly charge and discharge the soft-pack lithium battery, collect the potential data of each electrode again, and calculate V0' and V1'.

[0025] (4) Compare and analyze the data obtained initially with the data after repeated charging and discharging to determine the reasons for the decline in cell performance during battery charging and discharging.

[0026] Compared with directly using pure lithium or copper sheets as the third electrode, the test method of this invention overcomes the test stability problem caused by lithium sheet oxidation, as well as the low test accuracy and data conversion problems of copper sheets, and the test method has high result stability.

[0027] As a preferred method of the present invention, the determination method is as follows:

[0028] If the initial V0 differs significantly from the V0' after cycling, the positive electrode will cause a decrease in battery performance.

[0029] If the initial V1 differs significantly from the V1' after cycling, the negative electrode will cause a decrease in battery performance.

[0030] Taking the LFP system as an example, the average voltage of LFP to the lithium sheet is 3.25V, and the average voltage after cycling is 3.23V. However, the average voltage of the negative electrode to the lithium potential V1 is 1.0V before and after cycling, with no difference. Therefore, it can be determined that the battery performance is reduced due to the positive electrode.

[0031] The beneficial effects of this invention are as follows:

[0032] (1) Compared with the existing third electrode, the third electrode provided by the present invention avoids the oxidation of lithium by combining copper metal long thin sheet and lithium metal long thin sheet, and directly obtains the lithium potential, the detection result is stable and reliable, and the cost is low.

[0033] (2) The soft-pack lithium battery of the present invention allows for long-term use after the third electrode is encapsulated once, and is not affected by lithium oxidation or assembly precision each time. It does not require disassembling the cell and can achieve full life cycle performance testing and online testing.

[0034] (3) The test method of the present invention has high detection accuracy for positive / negative electrode potential, good stability of results, and easy interpretation of results. Attached Figure Description

[0035] Figure 1 This is a front view of the third electrode.

[0036] Figure 2 This is a side view of the third electrolysis.

[0037] Figure 3 This is a structural view of a pouch lithium battery with the third electrode vertically mounted on the main tab.

[0038] Figure 4 This is a structural view of a pouch lithium battery with the third electrode parallel to the main tab.

[0039] Figure 5 This is the discharge curve of Example 2.

[0040] Figure 6 This is the discharge curve of Comparative Example 1.

[0041] 1. Third electrode; 1.1. Copper metal long thin sheet; 1.2. Lithium metal long thin sheet; 1.3. Adhesive sheet; 1.4. Solder mark; 1.5. Third tab; 2. Soft-pack lithium battery; 2.1. Cell body; 2.2. Positive tab; 2.3. Negative tab; 2.4. Airbag. Detailed Implementation

[0042] The specific embodiments of the present invention will be further described below.

[0043] Unless otherwise specified, all raw materials used in this invention are commercially available or commonly used in the field. Unless otherwise specified, the methods in the following embodiments are conventional methods in the field.

[0044] To maintain consistency, the positive and negative electrode sheets used in the following examples and comparative examples are all from the same batch of qualified products. The positive electrode material is lithium iron phosphate and the negative electrode material is graphene.

[0045] Example 1

[0046] A third electrode for assisting in testing the potential of positive / negative electrodes, such as Figure 1 and 2 As shown, the third electrode 1 includes a copper metal long thin sheet 1.1 and a lithium metal long thin sheet 1.2. The width of the copper metal long thin sheet is 3-5 mm, and the width of the lithium metal long thin sheet is 3-4 mm, with the width of the lithium metal long thin sheet not exceeding that of the copper metal long thin sheet. The thickness of the copper metal long thin sheet is 0.1-0.3 mm, and the thickness of the lithium metal long thin sheet is 0.08-0.12 mm, with the thickness of the lithium metal long thin sheet being less than that of the copper metal long thin sheet. The lower end of the copper metal long thin sheet and the upper end of the lithium metal long thin sheet are stacked and welded together, so that the lithium metal long thin sheet is centered on the copper metal long thin sheet. Considering that lithium metal is easily oxidized when exposed to air, the welding and storage temperature of the lithium metal long thin sheet is ≤-40℃. The weld mark 1.4 formed by the welding has a dimension of 2.5-3.5 mm in the width direction of the lithium metal long thin sheet, which is smaller than the width of the lithium metal long thin sheet. An adhesive sheet, made of PP material, is also provided on the long thin copper sheet. Two adhesive sheets are provided and symmetrically arranged on both sides of the long thin copper sheet. The two ends of the two adhesive sheets extend beyond the two sides of the long thin copper sheet, and the corresponding parts are bonded together by heating at 150°C. The vertical misalignment of the two adhesive sheets is ≤0.1mm, the horizontal misalignment of the two adhesive sheets is ≤0.1mm, and there is a gap between the adhesive sheets and the welding ends of the long thin lithium sheet.

[0047] Example 2

[0048] A method for testing the positive / negative electrode potential of a pouch lithium battery, using the third electrode provided in Example 1, wherein:

[0049] The width of the copper metal sheet is 5 mm, and the width of the lithium metal sheet is 3 mm.

[0050] The thickness of the copper metal sheet is 0.2 mm, and the thickness of the lithium metal sheet is 0.1 mm.

[0051] The weld mark 1.4 formed by welding has a dimension of 2.5 mm in the width direction of the lithium metal sheet;

[0052] The specific steps are as follows:

[0053] (1) Packaging as Figure 3 The process of the soft-pack lithium battery 2 shown is as follows: the positive electrode, separator and negative electrode are stacked in sequence and wound to form a core. The core is sealed in an aluminum-plastic film to form the main body of the cell 2.1. The positive electrode and negative electrode protruding from the aluminum-plastic film naturally form the positive electrode tab 2.2 and the negative electrode tab 2.3, which constitute the main electrode tab of the soft-pack lithium battery. Then, 12g / Ah of electrolyte is injected into the main body of the cell to fill the battery with electrolyte and obtain the soft-pack lithium battery. After the electrolyte is injected, the above-mentioned third electrode tab is sealed in the center of the air bag 2.4 of the soft-pack lithium battery. The third electrode is perpendicular to the main electrode tab. The part of the long thin copper metal sheet from the non-welded end to the adhesive sheet protrudes from the air bag to form the third electrode tab 1.5. The adhesive sheet is bonded and heat-sealed to the air bag seal.

[0054] (2) Before the first charging of the packaged pouch lithium battery, a three-electrode testing device was used to collect the potential data at the positive electrode tab, negative electrode tab, and third electrode tab of the pouch lithium battery, respectively, and recorded as V. 正 V 负 V 三 The positive electrode potential V0 = V before the first charge is obtained. 正 -V 三 The negative electrode potential to lithium is V1 = V 负 -V 三 ;

[0055] (3) Perform cyclic charging and discharging at a rate of 2.5 to 3.65V@0.04C, collect the potential data at each tab after each cycle of charging and discharging, and calculate V0' and V1'. Then compare and analyze the data with the data obtained in the first cycle.

[0056] (4) When the performance of the soft-pack lithium battery deteriorates, the reasons for the decline in cell performance during charging and discharging are determined based on the changes in lithium potential data of the positive and negative electrodes. The determination criteria are as follows:

[0057] If the initial V0 differs significantly from the V0' after cycling, the positive electrode will cause a decrease in battery performance.

[0058] If the initial V1 differs significantly from the V1' after cycling, the negative electrode will cause a decrease in battery performance.

[0059] It should be noted that the packaging of pouch lithium batteries can also adopt the method shown in 4, with the third electrode parallel to the main tab, relative to... Figure 3 This method eliminates the need to extend the width of the airbag, resulting in a smaller airbag and requiring less electrolyte.

[0060] Example 3

[0061] A method for testing the positive / negative electrode potential of a soft-pack lithium battery, which differs from Example 2 in that...

[0062] In the third electrode, the weld mark 1.4 formed by welding has a size of 3 mm in the width direction of the lithium metal sheet, which basically coincides with the width of the lithium metal sheet.

[0063] Comparative Example 1

[0064] The difference from Example 2 is that, in the method for testing the positive / negative electrode potential of the soft-pack lithium battery, a pure lithium metal sheet is used instead of the third electrode in Example 2. The length of the pure lithium metal sheet is the same as the total length of the third electrode in Example 2, and the width and thickness are the same as the long thin sheet of lithium metal in Example 2.

[0065] Comparative Example 2

[0066] The difference from Example 2 is that in the method for testing the positive / negative electrode potential of a soft-pack lithium battery, the width of the copper metal sheet in the third electrode is 3 mm and the width of the lithium metal sheet is 4 mm, with the width of the copper metal sheet being smaller than that of the lithium metal sheet.

[0067] Comparative Example 3

[0068] The difference from Example 2 is that in the method for testing the positive / negative electrode potential of the soft-pack lithium battery, the thickness of the copper metal sheet in the third electrode is 0.1 mm and the thickness of the lithium metal sheet is 0.12 mm, with the copper metal sheet being thinner than the lithium metal sheet.

[0069] Comparative Example 4

[0070] The difference from Example 2 is that in the method for testing the positive / negative electrode potential of the soft-pack lithium battery, the adhesive sheet on the copper metal long thin sheet in the third electrode is the same width as the copper metal long thin sheet, that is, the adhesive sheet does not extend beyond the two sides of the copper metal long thin sheet.

[0071] The changes in the positive electrode-to-lithium potential (three charge-discharge cycles) obtained by the test methods of Examples 2-3 and Comparative Examples 1-4 were analyzed. The discharge curves of Example 2 and Comparative Example 1 are shown in the figure. Figure 5 and Figure 6 As shown, the positive electrode potential data for each embodiment and comparative example are shown in Table 1.

[0072] Table 1. Data on the change of lithium potential at the cathode.

[0073]

[0074] From Example 2 Figure 5 Corresponding to Comparative Example 1 Figure 6 A comparison shows that in Example 2, the discharge curves basically overlapped during the three charge-discharge cycles, while in Comparative Example 1, the first discharge curve deviated significantly from the second and third. This discrepancy in the data indicates that Comparative Example 1 exhibits greater dispersion than Example 2, suggesting that using the third electrode provided by this invention, compared to pure lithium metal sheets, yields more stable and reliable results. Furthermore, a comparison between Example 3 and Example 2 shows that when the width of the solder mark is the same as the width of the long thin lithium metal sheet, the detection stability decreases slightly, but remains higher than that of Comparative Example 1.

[0075] Comparative Examples 2 and 3 show that, compared to Example 2, when the width of the copper metal sheet is smaller than that of the lithium metal sheet, the stability of the detection decreases; when the thickness of the copper metal sheet is smaller than that of the lithium metal sheet, the stability of the detection also decreases. Comparative Example 4 shows that, compared to Example 2, when the adhesive sheet only covers the copper metal sheet without any extension, the stability of the detection results decreases.

Claims

1. A soft-pack lithium battery equipped with a third electrode, characterized by, The copper metal long sheet and the lithium metal long sheet are connected in the length direction, the width of the copper metal long sheet is greater than or equal to the lithium metal long sheet, the thickness of the copper metal long sheet is greater than the lithium metal long sheet, one end of the copper metal long sheet is overlapped with one end of the lithium metal long sheet and then welded, and an adhesive sheet is arranged on the copper metal long sheet, the adhesive sheet is located at a non-overlapping position of the copper metal long sheet, and both ends of the adhesive sheet extend out of both side edges of the copper metal long sheet. The third electrode is packaged in the middle of the air bag of the soft package lithium battery, and the non-welded end of the copper metal long sheet extends out of the air bag bag together with the adhesive sheet.

2. The soft package lithium battery with a third electrode according to claim 1, wherein the width of the copper metal long sheet is 3-5 mm, and the thickness of the copper metal long sheet is 0.1-0.3 mm.

3. The soft package lithium battery with a third electrode according to claim 1 or 2, wherein the width of the lithium metal long sheet is 3-4 mm, and the thickness of the lithium metal long sheet is 0.08-0.12 mm. The size of the welding mark of the welded end of the lithium metal long sheet in the width direction of the lithium metal long sheet is smaller than the width of the lithium metal long sheet. The welding end of the lithium metal long sheet is provided with a spacing from the adhesive sheet. 4.The soft-pack lithium battery with a third electrode of claim 1, wherein, The adhesive sheet is provided with two sheets and arranged on both side surfaces of the copper metal long sheet, and the corresponding parts of the two adhesive sheets extending out of both side edges of the copper metal long sheet are bonded.

5. The soft-pack lithium battery equipped with a third electrode according to claim 1, characterized in that, 7. The soft package lithium battery with a third electrode according to claim 6, wherein the up-down misalignment size of the two adhesive sheets is ≤0.1 mm, and the left-right misalignment size of the two adhesive sheets is ≤0.1 mm.

6. The soft-pack lithium battery equipped with a third electrode according to claim 1 or 5, characterized in that, 7. The soft package lithium battery with a third electrode according to claim 6, wherein the up-down misalignment size of the two adhesive sheets is ≤0.1 mm, and the left-right misalignment size of the two adhesive sheets is ≤0.1 mm. The method comprises the following steps: (1) The third electrode is packaged in the middle of the air bag of the soft package lithium battery, and the non-welded end of the copper metal long sheet extends out of the air bag bag together with the adhesive sheet. (3) The soft package lithium battery is repeatedly charged and discharged, the potential data of each electrode is collected again, and V0' and V1' are calculated.

8. A method for testing the positive / negative electrode potential using the soft-pack lithium battery equipped with a third electrode according to any one of claims 1 to 7, characterized by, (4) The data obtained for the first time is compared and analyzed with the data after the cyclic charging and discharging, and the reason for the performance decline of the battery during charging and discharging is determined. The determination method is as follows: (2) Collect the potential data of the positive electrode, negative electrode and third electrode before the first charging of the soft package lithium battery, denoted as V 正 , V 负 , V 三 , respectively, to obtain the positive electrode potential against lithium V0=V 正 -V 三 and the negative electrode potential against lithium V1=V 负 -V 三 before the first charging; If the initial V0 and the V0' after the cycle are greatly different, the positive electrode causes the performance decline of the battery. If the initial V1 and the V1' after the cycle are greatly different, the negative electrode causes the performance decline of the battery.

9. The positive / negative electrode potential test method according to claim 8, characterized by, ​ ​ ​

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