A precision strip for a lithium battery explosion-proof sheet and a processing technology thereof

Abstract

The present application relates to a kind of lithium battery explosion-proof sheet precision strip and its processing technology, comprising the following steps: S1, raw material initial rolling;S2, middle blank recrystallization annealing;S3, finished product finish rolling;S4, finished product recrystallization annealing.The raw material steel strip of the present application adopts stainless steel, so that the explosion-proof sheet prepared subsequently itself has excellent corrosion resistance and high temperature resistance.In the finished product finish rolling, the last two passes are rolled using special point-shaped work rolls with a surface roughness of Ra1.0-1.5 μm, so that the surface roughness of the steel strip reaches Ra0.5-0.7 μm, which can significantly improve the scratch resistance of the explosion-proof sheet.After the finished product recrystallization annealing is completed, the finished product steel strip obtains low hardness and ultra-large grains, with an average grain size ≤6 levels, which can ensure the explosion-proof sheet to meet the requirements of explosion-proof scribing residual thickness, with a stable residual thickness >0.05 mm, ensuring the safety performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of precision strip manufacturing technology, and in particular relates to a precision strip for lithium battery explosion-proof sheets and its processing technology. Background Technology

[0002] The high energy density, fast charging, high safety, and long lifespan of new lithium batteries such as cylindrical, prismatic, and blade batteries make them a good fit for the long range and ultra-fast charging requirements of mid-to-high-end passenger vehicles. In the electric vehicle market, Tesla was the first to introduce large cylindrical lithium batteries, followed quickly by BMW, NIO, and others. Battery companies such as Tesla, Panasonic, EVE Energy, CATL, and BYD are also actively developing new lithium batteries such as cylindrical, prismatic, and blade batteries to meet customer demand. The main structural components of a lithium battery include the casing and top cover. The top cover includes explosion-proof diaphragms, sealing rings, connecting pieces, and steel caps, primarily serving to transmit energy, carry the electrolyte, protect safety, and fix and support the battery.

[0003] With the development of lithium battery technology, the requirements for explosion-proof sheets on the top cover are becoming increasingly stringent. Traditional explosion-proof sheets made of pre-nickel-plated SPCC carbon steel / aluminum sheets have gradually revealed the following shortcomings: 1. Insufficient corrosion resistance of SPCC carbon steel; 2. Lower melting point of aluminum sheets compared to stainless steel, making them unsuitable for high temperatures; 3. Low surface roughness of pre-nickel-plated SPCC carbon steel / aluminum sheets, making them susceptible to scratches. Therefore, it is necessary to develop a precision strip material and its processing technology for lithium battery explosion-proof sheets that possess excellent corrosion resistance, high temperature resistance, and scratch resistance. Summary of the Invention

[0004] The main objective of this invention is to propose a precision strip for explosion-proof lithium batteries and its processing technology, which can effectively solve the problems in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A processing technology for precision strips used in lithium battery explosion-proof sheets includes the following steps:

[0007] S1. Raw material initial rolling: Stainless steel raw material strip with a thickness of 1.5-1.7mm is rolled in 4-6 passes. The deformation amount in each of the last three passes does not exceed 10%, and the rolling speed in each pass does not exceed 150m / min, to obtain a medium billet steel strip with a thickness of 0.9-1.2mm and a surface roughness Ra of 0.7-0.9μm.

[0008] S2. Recrystallization Annealing of Billet: The billet steel strip is recrystallized and annealed in a continuous annealing furnace at a temperature of 950-1050℃ and a speed of 20-30m / min. High-concentration, high-flow-rate hydrogen gas is used for protection throughout the process.

[0009] S3, finished product finish rolling: after the middle blank recrystallization annealing is completed, the middle blank steel strip is rolled through 4-6 passes, the deformation of the last two passes is not more than 10% per pass, the rolling speed of each pass is not more than 150 m / min, and the last two passes are rolled by changing the point-shaped work roll with a surface roughness Ra of 1.0-1.5 mu m each pass, so that the finished product steel strip with a thickness of 0.5-0.7 mm and a surface roughness Ra of 0.5-0.7 mu m is obtained;

[0010] S4, finished product recrystallization annealing: the finished product steel strip is treated by recrystallization annealing in a continuous annealing furnace, the annealing temperature is 1100-1150 DEG C, the annealing speed is 10-20 m / min, and high-concentration high-flow hydrogen is used for protection in the whole process.

[0011] Preferably, in step S1, the stainless steel raw material strip specifically adopts a stainless steel with Nb element Nb >= 0.4%.

[0012] Preferably, in step S3, the width of the point-shaped work roll is 700-1400 mm, the diameter is 45-55 mm, and the surface is subjected to superfine matte sand blasting treatment.

[0013] Preferably, in step S4, the holding temperature during the recrystallization annealing process is > 1100 DEG C, and the holding time is > 3 minutes.

[0014] A precision strip for lithium battery explosion-proof sheet is produced by the above processing technology.

[0015] The application provides a precision strip for lithium battery explosion-proof sheet and a processing technology thereof, and has the following beneficial effects:

[0016] 1. The raw material steel strip of the application adopts stainless steel, so that the explosion-proof sheet prepared subsequently has excellent corrosion resistance and high temperature resistance. In the application, the stainless steel raw material strip specifically adopts a stainless steel with Nb element Nb >= 0.4%, which improves the pitting resistance of the steel strip and further improves the corrosion resistance of the explosion-proof sheet and prolongs the service life.

[0017] 2. In the finished product finish rolling, in order to obtain higher surface roughness precision, the last two passes are rolled by special point-shaped work rolls with a surface roughness Ra of 1.0-1.5 mu m, so that the surface roughness of the steel strip reaches Ra 0.5-0.7 mu m, which can significantly improve the scratch resistance of the explosion-proof sheet, and at the same time improve the welding bonding force between the explosion-proof sheet and the external connecting piece, and ensure the safety performance of the battery.

[0018] 3、The finished steel strip obtains low hardness and super-large grains after the finished product recrystallization annealing is completed, the average grain size is less than or equal to 6, the residual thickness of the anti-explosion piece can meet the requirement of anti-explosion line marking, the residual thickness is stable and greater than 0.05 mm, so that the anti-explosion piece still has sufficient thickness to withstand internal pressure after line marking processing, prevents premature rupture, and also ensures reliable rupture at the designed pressure threshold to release pressure, thereby ensuring the safety performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The flow chart of the processing technology of the present application is shown in the figure.

[0020] Figure 2 The surface roughness Ra test result graph of example 1 of the present application is shown in the figure.

[0021] Figure 3 The average grain size test result graph of example 1 of the present application is shown in the figure. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the present application will be described clearly and completely below in combination with the drawings of the present application.

[0023] The technical scheme in the present application will be described clearly and completely below in combination with examples, obviously, the described examples are part of the examples of the present application, rather than all the examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor belong to the protection scope of the present application.

[0024] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0025] In addition, the terms "first", "second", "third", etc. are used only for descriptive purposes and are not to be construed as indicating or implying relative importance or an ordered ranking of the indicated technical features. Thus, features defined with "first", "second" or "third" can include one or more of the features implicitly or explicitly. In the description of the application, the meaning of "a plurality of" is two or more, unless otherwise expressly and specifically defined. In addition, the terms "mounting", "connecting", "connection" should be interpreted broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be direct connection, or indirect connection through an intermediate medium, or internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0026] Reference Figure 1 A processing technology of a precision strip for lithium battery explosion-proof sheet, comprising the following steps:

[0027] S1, raw material rough rolling: the stainless steel raw material strip with a thickness of 1.5-1.7 mm is rolled through 4-6 passes, the deformation of the last three passes is not more than 10% per pass, and the rolling speed is not more than 150 m / min per pass, to obtain a medium billet strip with a thickness of 0.9-1.2 mm and a surface roughness Ra of 0.7-0.9 μm.

[0028] The raw material strip is made of stainless steel, so that the explosion-proof sheet made subsequently has excellent corrosion resistance and high temperature resistance. In the present application, the stainless steel raw material strip specifically uses stainless steel with Nb element added, Nb≥0.4%. Niobium is a strong carbide forming element, which can combine with carbon to form stable carbides, thereby reducing the precipitation of carbides at the grain boundary and improving the pitting resistance of the strip. The improvement of pitting resistance means that the performance of the material in a local corrosion environment is enhanced, which can further improve the corrosion resistance of the explosion-proof sheet and prolong the service life.

[0029] The thickness of the medium billet strip is 0.9-1.2 mm, which is realized by multi-pass rolling, and the surface roughness Ra is 0.7-0.9 μm, which is obtained by the last three passes of rolling. Therefore, the deformation of the last three passes is controlled to be not more than 10% per pass, and the rolling speed is not more than 150 m / min per pass, to ensure the surface roughness accuracy of the medium billet strip.

[0030] S2, medium billet recrystallization annealing: the medium billet strip is subjected to recrystallization annealing treatment in a continuous annealing furnace, the annealing temperature is 950-1050℃, the annealing speed is 20-30 m / min, and high concentration and high flow hydrogen is used for protection throughout the process;

[0031] Through high temperature annealing treatment, the alloy elements in the steel strip are fully dissolved, the internal stress generated in the rolling process is eliminated, the microstructure of the material is improved, the plasticity and toughness of the steel strip are improved, at the same time, the use of hydrogen protection can prevent the oxidation of the steel strip and maintain the purity of the material.

[0032] S3, finished product finish rolling: after the middle blank recrystallization annealing is completed, the middle blank steel strip is rolled by 4-6 passes, the deformation of the last two passes is not more than 10% per pass, the rolling speed is not more than 150 m / min per pass, and the last two passes are rolled by changing the point-shaped work roll with surface roughness Ra1.0-1.5μm per pass, to obtain the finished product steel strip with thickness 0.5-0.7mm and surface roughness Ra0.5-0.7μm.

[0033] Preferably, the width of the point-shaped work roll is 700-1400mm, the diameter is 45-55mm, and the surface is treated by superfine matte sandblasting.

[0034] After multi-pass rolling, the thickness of the steel strip is further reduced to 0.5-0.7mm, and in order to obtain higher precision of surface roughness, the last two passes are rolled by special point-shaped work roll with surface roughness Ra1.0-1.5μm, so that the surface roughness of the steel strip reaches Ra0.5-0.7μm, which can significantly improve the scratch resistance of the anti-explosion sheet, and at the same time improve the welding bonding force between the anti-explosion sheet and the external connecting piece, to ensure the safety performance of the battery.

[0035] S4, finished product recrystallization annealing: the finished product steel strip is treated by recrystallization annealing in a continuous annealing furnace, the annealing temperature is 1050-1100℃, the annealing speed is 10-20m / min, and high concentration and large flow hydrogen protection is used throughout the process.

[0036] Preferably, the holding temperature during recrystallization annealing is >1100℃, and the holding time is >3 minutes.

[0037] After the finished product recrystallization annealing is completed, the hardness of the finished product steel strip will decrease, which is helpful for the subsequent anti-explosion sheet stamping production, at the same time, the recrystallization annealing promotes the growth of the grains, forming a super large grain structure, under the above precise finished product recrystallization annealing parameters, the finished product steel strip can reach an average grain size ≤6 grade (the smaller the grade, the coarser the grain), which helps to improve the plasticity and toughness of the anti-explosion sheet.

[0038] In the application of lithium battery anti-explosion sheet, anti-explosion line is a structure designed to break and release pressure when the internal pressure of the battery is too high, and the residual thickness of the anti-explosion line is an important parameter in the design of lithium battery anti-explosion sheet, which directly affects the safety performance of the battery.

[0039] When the hardness of the rupture disc is higher, more force is needed to achieve the same depth during the scoring process, which can result in a smaller residual thickness. Conversely, materials with lower hardness are more likely to plastically deform during scoring, which can leave a larger residual thickness. Plasticity refers to the ability of a material to deform plastically without breaking when subjected to external forces. Rupture discs with good plasticity can better absorb impact forces during the scoring process, reducing the generation of cracks and maintaining a larger residual thickness.

[0040] After the finished product recrystallization annealing is completed, the finished steel strip has low hardness and ultra-large grains, with an average grain size of ≤6, which can ensure the requirements of the rupture disc for the residual thickness after scoring, and the residual thickness is stable >0.05mm, thereby ensuring that the rupture disc still has sufficient thickness to withstand internal pressure after scoring, preventing premature rupture, and also ensuring that it can reliably rupture at the designed pressure threshold to release pressure, thereby ensuring the safety performance of the battery.

[0041] Example 1

[0042] S1, raw material rough rolling: a stainless steel raw material steel strip with a thickness of 1.5mm is rolled through 4 passes, with a deformation of no more than 20% in the last three passes and a rolling speed of no more than 150m / min in each pass, to obtain a medium billet steel strip with a thickness of 0.9mm and a surface roughness Ra of 0.78μm.

[0043] S2, medium billet recrystallization annealing: the medium billet steel strip is subjected to recrystallization annealing treatment in a continuous annealing furnace at an annealing temperature of 950℃ and an annealing speed of 30m / min, with high-concentration high-flow hydrogen protection used throughout, and the concentration of the hydrogen protection gas can reach 99.99%.

[0044] S3, finished product finish rolling: after the medium billet recrystallization annealing is completed, the medium billet steel strip is rolled through 4 passes, with a deformation of no more than 10% in the last two passes and a rolling speed of no more than 150m / min in each pass, and the last two passes are rolled with point-shaped work rolls with a surface roughness Ra of 1.0, to obtain a finished steel strip with a thickness of 0.5mm and a surface roughness Ra of 0.587μm.

[0045] S4, finished product recrystallization annealing: the finished steel strip is subjected to recrystallization annealing treatment in a continuous annealing furnace at an annealing temperature of 1100℃ and an annealing speed of 20m / min, with high-concentration high-flow hydrogen protection used throughout, and the concentration of the hydrogen protection gas can reach 99.99%.

[0046] Reference Figure 2 , Figure 3 The finished steel strip obtained by the above processing technology has a surface roughness Ra of 0.587μm (tested using a bench-type roughness tester), and an average grain size of 5.5.

[0047] The above examples are only used to illustrate the technical solutions of the present application, but not to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those ordinarily skilled in the art should understand: the technical solutions recorded in the foregoing examples can still be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A process for processing a precision strip for a lithium battery rupture disc, characterized by, The method comprises the following steps: S1, raw material rough rolling: a stainless steel raw material strip with a thickness of 1.5-1.7 mm is rolled through 4-6 passes, the deformation of the last three passes is not more than 10% per pass, and the rolling speed of each pass is not more than 150 m / min, to obtain a medium billet strip with a thickness of 0.9-1.2 mm and a surface roughness Ra of 0.7-0.9 μm; S2, medium billet recrystallization annealing: the medium billet strip is subjected to recrystallization annealing treatment in a continuous annealing furnace at an annealing temperature of 950-1050 ℃ and an annealing speed of 20-30 m / min, and high-concentration and high-flow hydrogen is used for protection throughout the process; S3, finished product finishing rolling: after the recrystallization annealing of the medium billet is completed, the medium billet strip is rolled through 4-6 passes, the deformation of the last two passes is not more than 10% per pass, the rolling speed of each pass is not more than 150 m / min, and the last two passes are rolled by changing the point-shaped work roll with a surface roughness Ra of 1.0-1.5 μm, to obtain a finished product strip with a thickness of 0.5-0.7 mm and a surface roughness Ra of 0.5-0.7 μm; S4, finished product recrystallization annealing: the finished product strip is subjected to recrystallization annealing treatment in a continuous annealing furnace at an annealing temperature of 1100-1150 ℃ and an annealing speed of 10-20 m / min, and high-concentration and high-flow hydrogen is used for protection throughout the process; In step S1, the stainless steel raw material strip specifically adopts a stainless steel with Nb≥0.4% added.

2. The process for processing the precision strip for the explosion-proof sheet of lithium battery according to claim 1, characterized in that: In step S3, the point-shaped work roll has a width of 700-1400 mm, a diameter of 45-55 mm, and a surface subjected to superfine matte sandblasting treatment.

3. The process for processing the precision strip for the explosion-proof sheet of lithium battery according to claim 1, characterized in that: In step S4, the holding temperature during the recrystallization annealing is >1100 ℃, and the holding time is >3 minutes.

4. A precision strip for a lithium battery rupture disc, characterized by: The precision strip for the explosion-proof sheet of the lithium battery is produced by the processing technology according to any one of claims 1-3.

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