Lithium ion battery pole piece foil leakage area safety risk assessment method

Abstract

The invention discloses a safety risk assessment method for a foil leakage area of a lithium ion battery pole piece. The method comprises the following steps: S1, obtaining a pole piece qualified by a certain battery system; s2, treating the qualified pole piece to obtain a foil-exposed pole piece; s3, manufacturing a foil leakage battery roll core with short circuit of positive and negative electrodes; s4, manufacturing a battery sample by using the positive and negative electrode short-circuited foil leakage battery roll core according to a normal production process; and S5, performing formation test on the manufactured battery sample, obtaining a charge-discharge curve and a battery temperature rise curve of the battery sample after the test is finished, and performing empty electricity disassembly on the battery sample to confirm the conditions of a diaphragm and a pole piece in a short-circuit region in the leaked foil so as to obtain a test result related to the area of the leaked foil. And determining the safety risk corresponding to the foil leakage area of the pole piece according to a test result. The method has universality, can perform foil leakage area safety risk assessment on different battery systems, and can obtain safety risks of different battery systems under different foil leakage areas for each battery system according to the steps of the method, so that corresponding management and control standards are formulated according to the risk range; therefore, safety risks such as fire and explosion caused by internal short circuit of the battery product are controlled.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium-ion batteries, and in particular relates to a safety risk assessment method for a lithium-ion battery pole piece leakage foil area. Background Art

[0002] With the increasing requirements for lithium-ion battery performance in new energy vehicles, consumer electronics, energy storage and other fields, high energy density has become one of the core directions of lithium battery development. Positive and negative electrode materials represented by high-voltage lithium cobalt oxide (LCO), high-nickel ternary materials (NCA, NCM811 and Ni90, etc.) and silicon negative electrodes are developing rapidly. Lithium-ion batteries with a volume energy density greater than 800Wh / L and a weight energy density greater than 300Wh / kg have been mass-produced. However, the increase in the energy density of lithium-ion batteries is inevitably accompanied by an increase in safety risks. Internal short circuit is the main safety failure mode during the manufacturing and use of lithium batteries.

[0003] There are four types of internal short circuit models for batteries, namely 1) positive electrode-negative electrode short circuit; 2) aluminum foil-negative electrode short circuit; 3) positive electrode-copper foil short circuit; 4) aluminum foil-copper foil short circuit. The equivalent circuit of the internal short circuit is as follows: Figure 1 As shown, from the internal short-circuit equivalent circuit, it can be seen that the short-circuit safety risk between the positive and negative poles is the highest and needs to be evaluated first.

[0004] Therefore, in the manufacturing process of lithium-ion batteries, it is necessary to strictly control the abnormal leakage of the electrode foil to prevent the battery from safety failure due to leakage.

[0005] At present, the control of leakage foil by various lithium-ion battery manufacturers in the electrode manufacturing process is generally divided into two aspects: quantity and area. The quantity and area of ​​leakage foil are measured by CCD visual inspection and optical microscope respectively, and the measurement method is relatively accurate. However, according to statistics, the industry standard for the leakage foil area of ​​positive and negative electrodes is 0-10 mm 2 , each manufacturer’s process control standards for pole piece leakage foil are mostly formulated based on their own experience, lacking objective experimental data as support, which can easily lead to the outflow of safety risk products caused by overly broad standards. At present, the research of various research institutions on the direction of pole piece leakage foil process control standards is mostly focused on the correspondence between the short-circuit area and heat generation in the battery, and there is no research or record on the correlation between the pole piece leakage foil area and the safety risk of batteries with different energy densities. However, the research of various research institutions is not very referenceable for the formulation of specific process standards for battery leakage foil. Therefore, in order to provide a reference for the formulation of process standards for pole piece leakage foil, it is necessary to develop a method for assessing the safety risk of the pole piece leakage foil area of ​​lithium-ion batteries. Summary of the invention

[0006] In view of the shortcomings described in the above-mentioned prior art, the present invention provides a method for assessing the safety risk of the leakage foil area of ​​a lithium-ion battery pole piece. The present invention can test and assess different battery systems to obtain the safety risks associated with the leakage foil area, and provide a reference for the production standard of the pole piece leakage foil process.

[0007] The technical solution adopted by the present invention is: A safety risk assessment method for a lithium-ion battery electrode leakage area, comprising the following steps: S1, obtaining a qualified electrode of a battery system; the electrode may be a positive electrode or a negative electrode, or both a positive electrode and a negative electrode; S2, processing the qualified electrode to obtain a leaky foil electrode; A leakage foil area is formed on the electrode, and the position of the leakage foil area is located outside the winding core when the electrode is wound into a winding core; the leakage foil area is formed by removing the active material on the electrode body to expose the electrode body, but without damaging the electrode body; When the electrode is a negative electrode, the preparation of the leakage foil electrode is to lay the negative electrode flat on a horizontal sample table to ensure that the horizontal sample table is smooth and free of impurities; use a ceramic knife to scrape off the negative electrode active material according to the required leakage foil area; and the leakage foil area of ​​the negative electrode is 1-10mm 2 ; The number of leakage foil areas on a negative electrode sheet is 3-5, and the leakage foil area (length*width) can be selected as 1mm*1mm, 1mm*2mm, 1mm*3mm, 2mm*2mm, 2mm*3mm or 2mm*4mm.

[0008] When the electrode is a positive electrode, the production of the leaking foil electrode is to lay the positive electrode flat on a horizontal sample table, ensure that the horizontal sample table is smooth and free of impurities, and gently wipe the positive electrode surface with alcohol cotton dipped in NMP solution according to the required leaking foil area to remove the positive electrode active material. The leaking foil area of ​​the positive electrode is 1-10mm 2 ; The number of leakage foil areas on a positive electrode sheet is 3-5, and the leakage foil area (length*width) can be selected as 1mm*1mm, 1mm*2mm, 1mm*3mm, 2mm*2mm, 2mm*3mm, 2mm*4mm or 2mm*5mm.

[0009] S3, making a leaky foil battery roll core with short circuit between positive and negative electrodes; S31, using the leaky foil electrode sheet to manufacture the battery core according to the normal electrode sheet winding battery core process; S32, after the battery roll core is manufactured, the outer layer of the roll core is first disassembled, the leaking foil area is found, and the diaphragm corresponding to the leaking foil area is punctured to obtain a leaking foil battery roll core with positive and negative electrodes short-circuited; the punctured diaphragm area is larger than 1 / 2 of the leaking foil area; and the punctured diaphragm area is smaller than the leaking foil area; S4, using the leaky foil battery core with short-circuited positive and negative electrodes to perform shell filling, liquid filling, and packaging according to the normal production process to make battery samples; S5, performing formation test on the manufactured battery samples, obtaining the charge and discharge curve and battery temperature rise curve of the battery samples after the test, and disassembling the battery samples to confirm the diaphragm and electrode conditions in the leakage foil short-circuit area to obtain the test results related to the leakage foil area, and determining the safety risk corresponding to the electrode leakage foil area based on the test results.

[0010] As a preferred embodiment of the present invention, the formation test is to use a charge and discharge tester to perform a charge and discharge test on a battery sample in an explosion-proof cabinet; during the charge and discharge process, the battery voltage, capacity and surface temperature of the battery sample are recorded.

[0011] As a preferred embodiment of the present invention, the formation test process is as follows: sleep for 5 minutes; 0.5C constant current and constant voltage charging to the first charging voltage; sleep for 5 minutes; 0.5C discharge to the first discharge voltage; sleep for 5 minutes; 0.5C constant current and constant voltage charging to the second charging voltage; sleep for 5 minutes; 0.5C discharge to the second discharge voltage; 1C constant current and constant voltage charging to the third charging voltage; sleep for 5 minutes; 1C discharge to the third discharge voltage; 1C constant current and constant voltage charging to the fourth charging voltage; sleep for 5 minutes; 1C discharge to the fourth discharge voltage. According to different battery systems, the first charging voltage, the second charging voltage, the third charging voltage, the fourth charging voltage, the first discharge voltage, the second discharge voltage, the third discharge voltage, and the fourth discharge voltage corresponding to the formation test are not the same, which is related to the battery system.

[0012] As a preferred embodiment of the present invention, when manufacturing a leaky foil battery roll core with short circuit between positive and negative electrodes, one electrode piece used is a leaky foil electrode piece and the other is a qualified electrode piece.

[0013] As a preferred embodiment of the present invention, the test results include no abnormality, battery temperature exceeding the standard and severe diaphragm melting, and battery fire and explosion; the safety risks include low risk, medium risk and high risk.

[0014] The present invention is universal and can evaluate the safety risk of the leakage foil area for different battery systems. The safety risks of different battery systems under different leakage foil areas can be obtained by following the method steps of the present invention for each battery system, so as to formulate corresponding management and control standards according to the risk range, so as to control the safety risks of fire, explosion and the like caused by internal short circuit of battery products. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 It is a schematic diagram of the structure of the leakage foil electrode of the present invention.

[0017] Figure 2 It is a schematic diagram of the structure of the outer ring of the positive electrode foil roll core of the present invention. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0019] At present, commercial lithium-ion batteries can be divided into lithium cobalt oxide system, ternary system and lithium iron phosphate system according to the positive electrode system. Among them, the lithium cobalt oxide system is mainly used in digital electronics and other fields, with an energy density of 700Wh / L-800Wh / L; the ternary system and lithium iron phosphate system are mainly used in power batteries and energy storage fields, with energy densities of 260Wh / kg-330Wh / kg and 160Wh / kg-210Wh / kg respectively. Safety performance lithium iron phosphate system>ternary system≈lithium cobalt oxide system. The positive and negative electrode system and capacity design of the battery determine the level of safety risks.

[0020] Therefore, the present invention provides an embodiment of a method for assessing the safety risk of a lithium-ion battery electrode foil leakage area, and the steps are as follows: S1, obtaining a qualified electrode of a battery system; the battery system is an existing battery system, and the electrode may be a positive electrode or a negative electrode, or both a positive electrode and a negative electrode; the selection is based on the evaluation needs.

[0021] S2, processing the qualified electrode to obtain a leaky foil electrode; A leakage foil area 2 is made on the electrode 1, and the position of the leakage foil area 2 is located at the position outside the winding core when the electrode 1 is wound into a winding core; the leakage foil area is made by removing the active material on the electrode body to expose the electrode body, but without damaging the electrode body. Figure 1 As shown; When the electrode is a negative electrode, the preparation of the leakage foil electrode is to lay the negative electrode flat on a horizontal sample table to ensure that the horizontal sample table is smooth and free of impurities; use a ceramic knife to scrape off the negative electrode active material according to the required leakage foil area; and the leakage foil area of ​​the negative electrode is 1-10mm 2 ; The number of leakage foil areas on a negative electrode sheet is 3-5, and the leakage foil area (length*width) can be selected as 1mm*1mm, 1mm*2mm, 1mm*3mm, 2mm*2mm, 2mm*3mm or 2mm*4mm.

[0022] When the electrode is a positive electrode, the production of the leaking foil electrode is to lay the positive electrode flat on a horizontal sample table, ensure that the horizontal sample table is smooth and free of impurities, and gently wipe the positive electrode surface with alcohol cotton dipped in NMP solution according to the required leaking foil area to remove the positive electrode active material. The leaking foil area of ​​the positive electrode is 1-10mm 2 ; The number of leakage foil areas on a positive electrode sheet is 3-5, and the leakage foil area (length*width) can be selected as 1mm*1mm, 1mm*2mm, 1mm*3mm, 2mm*2mm, 2mm*3mm, 2mm*4mm or 2mm*5mm.

[0023] S3, making a leaky foil battery roll core with short circuit between positive and negative electrodes; S31, using the leaky foil electrode sheet to manufacture the battery core according to the normal electrode sheet winding battery core process; And the electrode used before winding is one leaky foil electrode and one qualified electrode. It can be positive electrode leaky foil or negative electrode leaky foil; S32, after the battery core is manufactured, the outer layer of the core is first disassembled, the leaking foil area 2 is found, and the diaphragm 3 corresponding to the leaking foil area is punctured with a ceramic knife to obtain a leaking foil battery core with a positive and negative short circuit; the area of ​​the punctured diaphragm is larger than 1 / 2 of the area of ​​the leaking foil area; and the area of ​​the punctured diaphragm is smaller than the area of ​​the leaking foil area; taking the positive electrode leaking foil battery core as an example, Figure 2 As shown, a schematic diagram showing the short circuit of positive and negative poles is shown.

[0024] S4, using the leaky foil battery core with short-circuited positive and negative electrodes to perform shell filling, liquid filling, and packaging according to the normal production process to make battery samples; S5, conduct formation test on the manufactured battery samples, The battery samples were charged and discharged in an explosion-proof cabinet using a charge and discharge tester; and the battery voltage, capacity and surface temperature of the battery samples were recorded during the charge and discharge process.

[0025] The formation test process is: sleep for 5 minutes; 0.5C constant current and constant voltage charging to the first charging voltage; sleep for 5 minutes; 0.5C discharge to the first discharge voltage; sleep for 5 minutes; 0.5C constant current and constant voltage charging to the second charging voltage; sleep for 5 minutes; 0.5C discharge to the second discharge voltage; 1C constant current and constant voltage charging to the third charging voltage; sleep for 5 minutes; 1C discharge to the third discharge voltage; 1C constant current and constant voltage charging to the fourth charging voltage; sleep for 5 minutes; 1C discharge to the fourth discharge voltage. According to different battery systems, the first charging voltage, second charging voltage, third charging voltage, fourth charging voltage, first discharge voltage, second discharge voltage, third discharge voltage, and fourth discharge voltage corresponding to the formation test are not the same, which is related to the battery system. The charging and discharging voltages corresponding to different battery systems are shown in the following table: Table: Battery system and charge and discharge voltage correspondence table After the test, the charge and discharge curves and battery temperature rise curves of each battery sample are statistically analyzed, abnormal cells are confirmed and analyzed, and then all battery samples are disassembled without electricity to confirm the diaphragm and pole piece conditions in the short-circuit area of ​​the leakage foil, and the test results related to the leakage foil area are obtained. The test results include no abnormality, rapid temperature rise of the battery and severe diaphragm melting, severe diaphragm melting due to excessive battery temperature, and battery fire and explosion; the safety risk corresponding to the pole piece leakage foil area is determined based on the test results. The safety risks include low risk, medium risk, and high risk. That is to say, the safety risk level is obtained based on the temperature rise rate after the short circuit, the battery temperature, and the diaphragm melting; When there is no abnormality, the safety risk corresponding to the current foil leakage area is low risk; When the battery temperature rises quickly and the diaphragm melts, the safety risk corresponding to the current leakage foil area is medium risk; When the battery temperature exceeds the standard, the separator melts severely, or the battery catches fire or explodes, the safety risk corresponding to the current foil leakage area is high risk; According to this correspondence, different leakage foil areas of batteries of different systems can be tested to obtain the safety risks of different leakage foil areas, providing a reference for the process standard of electrode leakage foil area.

[0026] Battery samples with different leakage foil areas can be prepared at the same time, and multiple formation tests can be performed at one time. The principle of the present invention is explained below with a specific experimental example.

[0027] Taking 18650 cylindrical batteries as an example, for the NCM523 system with the positive electrode material being NCM523 and the negative electrode being natural graphite, the safety risks of different leakage foil areas of the positive and negative electrodes were tested respectively. The test scheme is shown in the following table: Conclusion of safety risk assessment on leakage area of ​​NCM523 system Similarly, taking the 18650 cylindrical battery as an example, for the NCA system with the positive electrode material being NCA and the negative electrode being artificial graphite + silicon oxide negative electrode, the safety risks of different leakage foil areas of the positive and negative electrodes were tested respectively. The test plan and results are shown in the following table: Taking the 21700 cylindrical battery as an example, the safety risks of different leakage foil areas of the positive and negative electrodes were tested for the NCM system with the positive electrode material being NCM (Ni content > 90%) and the negative electrode being artificial graphite + silicon oxide negative electrode. The test plan and results are shown in the following table: It can be seen from the above experimental examples that according to the method of the present invention, different battery systems with different leakage foil areas can be tested to associate the electrode leakage foil area with the safety risk, providing guidance for the standard of the electrode leakage foil process.

[0028] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0029] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for safety risk assessment of the leakage foil area of ​​a lithium-ion battery electrode, characterized in that: S1, obtain the pole piece that has passed the inspection of a battery system; S2, processing the qualified electrode to obtain a leaky foil electrode; A leakage foil area is formed on the electrode, and the position of the leakage foil area is located outside the winding core when the electrode is wound into a winding core; the leakage foil area is formed by removing the active material on the electrode body to expose the electrode body, but without damaging the electrode body; S3, making a leaky foil battery roll core with short circuit between positive and negative electrodes; S31, using the leaky foil electrode to make a battery roll core; S32, after the battery roll core is manufactured, the outer layer of the roll core is first disassembled, the leaking foil area is found, and the diaphragm corresponding to the leaking foil area is punctured to obtain a leaking foil battery roll core with positive and negative electrodes short-circuited; the punctured diaphragm area is larger than 1 / 2 of the leaking foil area; and the punctured diaphragm area is smaller than the leaking foil area; S4, using the leaky foil battery roll core with short-circuited positive and negative electrodes to make battery samples according to the normal production process; S5, performing formation test on the manufactured battery samples, obtaining the charge and discharge curve and battery temperature rise curve of the battery samples after the test, and disassembling the battery samples to confirm the conditions of the diaphragm and the electrode in the short-circuit area of ​​the leakage foil to obtain the test results related to the leakage foil area, and determining the safety risk corresponding to the electrode leakage foil area according to the test results.

2. The lithium-ion battery pole piece leakage area safety risk assessment method according to claim 1, characterized in that: When the electrode sheet is a negative electrode sheet, the preparation of the drain foil electrode sheet is to lay the negative electrode sheet flat on a horizontal sample table to ensure that the horizontal sample table is smooth and free of impurities; and use a ceramic knife to scrape off the negative electrode active material according to the required drain foil area; When the electrode is a positive electrode, the leaky foil electrode is made by laying the positive electrode flat on a horizontal sample table, ensuring that the horizontal sample table is smooth and free of impurities, and gently wiping the surface of the positive electrode with NMP solution according to the required leaky foil area to remove the positive electrode active material.

3. The lithium-ion battery pole piece leakage area safety risk assessment method according to claim 2, characterized in that: The leakage area of ​​the negative electrode sheet is 1-10 mm 2 ; The number of leakage foil areas on a negative electrode sheet is 3-5.

4. The lithium-ion battery pole piece leakage area safety risk assessment method according to claim 3, characterized in that: The area of ​​the leakage foil area is 1mm*1mm, 1mm*2mm, 1mm*3mm, 2mm*2mm, 2mm*3mm or 2mm*4mm.

5. The method for safety risk assessment of the leakage foil area of ​​a lithium-ion battery electrode according to claim 2, characterized in that: The leakage area of ​​the positive electrode sheet is 1-10mm 2 ; The number of leakage foil areas on a positive electrode sheet is 3-5.

6. The method for safety risk assessment of the leakage foil area of ​​a lithium-ion battery pole piece according to claim 5, characterized in that: The area of ​​the leakage foil area is 1mm*1mm, 1mm*2mm, 1mm*3mm, 2mm*2mm, 2mm*3mm, 2mm*4mm or 2mm*5mm.

7. The method for safety risk assessment of the leakage foil area of ​​a lithium-ion battery pole piece according to any one of claims 1 to 6, characterized in that: The formation test is to use a charge and discharge tester to perform a charge and discharge test on a battery sample in an explosion-proof cabinet; during the charge and discharge process, the battery voltage, capacity and surface temperature of the battery sample are recorded.

8. The lithium-ion battery pole piece leakage area safety risk assessment method according to claim 7, characterized in that: The formation test process is as follows: sleep for 5 minutes; charge to the first charging voltage at 0.5C constant current and constant voltage; sleep for 5 minutes; discharge to the first discharging voltage at 0.5C; sleep for 5 minutes; 0.5C constant current and constant voltage charging to the second charging voltage; sleep for 5 minutes; 0.5C discharge to the second discharge voltage; 1C constant current and constant voltage charging to the third charging voltage; sleep for 5 minutes; 1C discharge to the third discharge voltage; 1C constant current and constant voltage charging to the fourth charging voltage; sleep for 5 minutes; 1C discharge to the fourth discharge voltage.

9. The method for safety risk assessment of the leakage foil area of ​​a lithium-ion battery electrode according to claim 7, characterized in that: When making a leaky foil battery roll core with a short circuit between the positive and negative electrodes, the electrodes used are a leaky foil electrode and a qualified electrode.

10. The lithium-ion battery pole piece leakage area safety risk assessment method according to claim 9, characterized in that: The test results include no abnormalities, battery temperature exceeding the standard and severe diaphragm melting, and battery fire and explosion; the safety risks include low risk, medium risk, and high risk.

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