Ultrathin high-strength seamless battery housing and manufacturing method therefor, and secondary battery

Abstract

An ultrathin high-strength seamless battery housing and a manufacturing method therefor, and a secondary battery. The manufacturing method comprises: forming a metal material into a housing blank of a cylindrical structure by means of an extrusion process; sleeving a core rod of a cold drawing die with the housing blank; extending the front end of the housing blank into a cold drawing cavity of an outer die of the cold drawing die, and clamping the front end of the housing blank; pulling the housing blank in a drawing direction, moving the core rod in the same direction as the housing blank in the drawing direction, so that the housing blank as a whole passes through the cold drawing cavity to form the battery housing; and demolding the battery housing from the core rod. According to the method, the battery housing is formed by means of a cold drawing after extrusion, the battery housing has high strength, and the formed battery housing has no welding seam; the core rod moves synchronously during drawing, so that the force of friction between the inner wall of the housing blank and the outer wall of the core rod during drawing can be greatly reduced, thus, the pulling force during drawing can be reduced, and the battery housing is prevented from being broken due to too small wall thickness.

Description

Ultra-thin high-strength seamless battery shell and manufacturing method thereof, secondary battery TECHNICAL FIELD

[0001] The present application belongs to the field of secondary battery shell, in particular to an ultra-thin high-strength seamless battery shell and manufacturing method thereof, secondary battery. BACKGROUND

[0002] In the prior art, the wall thickness of the four sides of the battery shell is generally equal, and the manufacturing method is generally to first stamp a side assembly in an unfolded state, then bend the side assembly into a rectangular tube shape and then weld it to form four sides, and form a weld on one of the sides. In the previous secondary battery (such as a blade battery), the explosion-proof valve is generally made on the top cover, and the wall thickness of the four sides will not be affected; however, with the development of secondary battery technology and the continuous expansion of its application range, the method of making an explosion-proof valve on the side of the secondary battery shell instead of the top cover has been widely adopted. Since the wall thickness of the battery shell cannot be too thin to meet the requirements of making an explosion-proof valve, the wall thickness of the battery shell is limited, which prevents the battery shell from being made too thin.

[0003] SUMMARY

[0004] In view of the above shortcomings of the prior art, the technical problem to be solved by the present application is to provide an ultra-thin high-strength seamless battery shell and a manufacturing method thereof, as well as a secondary battery.

[0005] To solve the above technical problems, the present application provides the following technical solutions:

[0006] A manufacturing method of an ultra-thin high-strength seamless battery shell for manufacturing an ultra-thin high-strength seamless battery shell, comprising the following steps:

[0007] S1, forming a shell blank with a cylindrical structure by an extrusion process; the length of the shell blank is less than the length of the battery shell, the cross-sectional dimension of the shell blank is greater than the cross-sectional dimension of the battery shell, and the wall thickness of the shell blank is greater than the wall thickness of the battery shell;

[0008] S2, sleeving the shell blank on the core rod of the cold drawing die;

[0009] S3, extending the front end of the shell blank into the cold drawing cavity of the outer mold of the cold drawing die and clamping the front end of the shell blank; the size of the core rod is adapted to the size of the internal cavity of the battery shell;

[0010] S4, pulling the shell blank in the drawing direction and moving the core rod in the drawing direction in the same direction as the shell blank, so that the shell blank as a whole passes out of the cold drawing cavity to form a battery shell;

[0011] S5, demolding the battery shell from the core rod.

[0012] An ultra-thin high-strength seamless battery shell is formed by an ultra-thin high-strength seamless battery shell manufacturing method, the battery shell comprises a thick side and three thin sides, the thick side and the three thin sides enclose a rectangular cylindrical structure with openings at two ends; an explosion-proof valve is arranged on the thick side, and the wall thickness of the thick side is greater than the wall thickness of the three thin sides.

[0013] In the present application, the battery shell is formed by cold drawing after extrusion molding. The battery shell is always hard during the drawing process and will not become soft without heating, so the strength is high. The formed battery shell has no weld, and there is no risk of leakage after long-term use. The core rod moves synchronously during the drawing process, which can greatly reduce the friction between the inner wall of the shell blank and the outer wall of the core rod during the drawing process, thereby reducing the drawing force and avoiding the battery shell from being pulled apart due to the excessively thin wall thickness. Before drawing, the shell blank is first formed into an oil film by oil immersion, which can facilitate subsequent battery shell demolding and further reduce the friction between the inner wall of the shell blank and the outer wall of the core rod during drawing. The core rod vibrates during the drawing process, which not only facilitates the demolding of the battery shell, but also improves the forming effect of the battery shell. BRIEF DESCRIPTION OF DRAWINGS

[0014] The drawings described herein are used to provide further understanding of the present application, and form a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0015] Fig. 1 is a structural schematic view of a battery shell formed by bending and then welding in the prior art.

[0016] Fig. 2 is a schematic view of a prior cold drawing process.

[0017] Fig. 3 is a flowchart of an embodiment of the ultra-thin high-strength seamless battery shell manufacturing method of the present application.

[0018] Fig. 4 is a structural schematic view of a shell blank.

[0019] Fig. 5 is a structural schematic view of a cold drawing die of the present embodiment.

[0020] Fig. 6 is a schematic view of the shell blank during drawing.

[0021] Fig. 7 is a schematic view of the battery shell sleeved on the core rod after drawing is completed.

[0022] Fig. 8 is a top view of a prior battery shell.

[0023] Fig. 9 is a top view of the battery shell of the present embodiment.

[0024] Figure 10 is a schematic diagram of the internal cavity of the battery shell of the present embodiment compared with the prior art battery shell.

[0025] Figure 11 is a schematic diagram of the structure of an embodiment of the ultra-thin high-strength seamless battery shell of the present application.

[0026] Figure 12 is a schematic diagram of the structure when directly etching the anti-explosion notch on the side to form the anti-explosion valve.

[0027] The reference signs in the description are as follows:

[0028] Shell blank - 100; first side wall - 111; second side wall - 112; third side wall - 113; fourth side wall - 114; necked portion - 120; battery shell - 200; side - 210; first side - 211; second side - 212; third side - 213; fourth side - 214; anti-explosion valve - 220; anti-explosion disc - 221; reinforcing boss - 222; first anti-explosion notch - 223; second anti-explosion notch - 230; outer die - 310, 810; cold-drawing cavity - 320, 820; feed section - 321; outer orifice - 321a; inner orifice - 321b; forming section - 322; mandrel - 330, 830; vibration waveform - 331; metal blank - 700; side assembly - 910; weld - 920. DETAILED DESCRIPTION

[0029] The embodiments of the present application are described below through specific examples, and the figures provided in the following examples only schematically illustrate the basic concept of the present application, and the following examples and features in the examples can be combined with each other without conflict.

[0030] Referring to Figure 1, the manufacturing method of the existing secondary battery shell (such as the shell of a blade battery) is generally to first stamp a side assembly 910 in an unfolded state, then bend the side assembly 910 into a cylindrical shape and weld the joint to form a weld 920. When the battery is used for a long time, there is a certain risk of leakage at the weld.

[0031] Referring to Figure 2, the outer die 810 and the mandrel 830 are generally stationary during the cold-drawing process. If a metal blank 700 is used to form a battery shell through a cold-drawing process, the outer wall of the metal blank 700 and the inner wall of the cold-drawing cavity 820 of the outer die 810 will generate a friction force f1 opposite to the drawing direction on the metal blank 700, and the inner wall of the metal blank 700 and the outer wall of the mandrel 830 will generate a friction force f2 opposite to the drawing direction on the metal blank 700. The directions of the friction forces f1 and f2 are opposite to the direction of the pulling force F1 during drawing, and therefore the pulling force F1 cannot be less than the reverse pulling force formed by the combination of the friction forces f1 and f2.

[0032] In order to increase the internal volume of the battery shell, the wall thickness of the battery shell is generally thin, so the tensile force that the battery shell can withstand is limited; if the battery shell is made by cold drawing process, when the battery shell is thin, the positive pulling force formed by the tensile force F1 and the reverse pulling force formed by the combination of the friction force f1 and the friction force f2 will easily cause the part formed by drawing to break and other conditions; in addition, the battery shell made by cold drawing process will also inevitably form drawing marks on the battery shell, and there are problems such as inconsistency in forming.

[0033] Please refer to FIG. 3, which is a flow chart of an embodiment of the method for manufacturing the ultra-thin high-strength seamless battery shell. The method for manufacturing the ultra-thin high-strength seamless battery shell in this embodiment includes the following steps:

[0034] S1, please refer to FIG. 4, the metal material is formed into a shell blank 100 with a cylindrical structure by an extrusion process. The metal material can be an aluminum alloy material, and in this embodiment, a rectangular cylindrical battery shell 200 is taken as an example for illustration, which includes a first side surface 211, a second side surface 212, a third side surface 213 and a fourth side surface 214; therefore, the shell blank 100 in this embodiment is a rectangular cylindrical structure, including a first side wall 111, a second side wall 112, a third side wall 113 and a fourth side wall 114; the wall thickness of the first side wall 111, the second side wall 112, the third side wall 113 and the fourth side wall 114 can be equal or not equal. Of course, the battery shell 200 can also be a cylindrical shape or other shapes, at this time, the shell blank 100 is also a cylindrical structure or other structures corresponding to the shape of the battery shell 200.

[0035] The length of the shell blank 100 is less than the length of the battery shell 200, and the length of the battery shell 200 and the length of the shell blank 100 satisfy the following formula: L k = L p *(1+δ)

[0036] Wherein, L k represents the length required by the battery shell 200 (i.e. the length of the battery shell 200 after cold drawing); L p represents the length of the shell blank 100; δ represents the elongation rate of cold drawing, i.e. the ratio of the length of the battery shell 200 obtained after cold drawing to the length of the shell blank 100 before cold drawing. Knowing the elongation rate of cold drawing, the corresponding length of the shell blank 100 can be calculated according to the length required by the battery shell 200.

[0037] For example, the length of the shell blank 100 before cold drawing is 200mm, and the length of the battery shell 200 obtained after cold drawing is 280mm, then: elongation rate δ = (280-200) / 200 = 0.4

[0038] When the shell with a length of 700mm is needed, the formula above can be used to get: L p *(1+0.4)=700mm L p =500mm

[0039] The cross-sectional dimension of the shell blank 100 is larger than that of the battery shell 200, so that the cross-sectional dimension of the shell is shrunk during cold drawing, thereby increasing the strength of the battery shell 200. The wall thickness of the shell blank 100 is larger than that of the battery shell 200. In this embodiment, the ratio of the wall thickness of the shell blank 100 to that of the battery shell 200 after cold drawing is in the range of 1.1-1.5, preferably 1.2-1.25.

[0040] S2, the shell blank 100 is sleeved on the core rod 330 of the cold drawing die. In this embodiment, the length of the die core is larger than that of the battery shell 200 after cold drawing, so that the die core and the shell blank 100 move in the same direction. The size of the core rod 330 is matched with the size of the internal cavity of the battery shell 200 after drawing. Since the cross-sectional dimension of the shell blank 100 is larger than that of the battery shell 200, the size of the core rod 330 must be smaller than the size of the internal cavity of the shell blank 100.

[0041] In order to facilitate demolding after cold drawing, the shell blank 100 can be immersed in oil before cold drawing (for example, before performing S2 step), and then the shell blank 100 is taken out of the oil and placed obliquely to drain the oil drops. After the oil film is formed on the inner wall of the shell blank 100, the shell blank 100 is sleeved on the core rod 330 of the cold drawing die for cold drawing. The oil film can reduce the friction between the inner wall of the battery shell 200 obtained after cold drawing and the core rod 330, and reduce the difficulty of demolding of the battery shell 200.

[0042] S3, the front end of the shell blank 100 is inserted into the cold drawing cavity 320 of the outer die 310 of the cold drawing die, and the front end of the shell blank 100 is clamped by a clamp (not shown in the figure). Referring to FIG. 5, the cold drawing cavity 320 includes a feeding section 321 and a forming section 322. The feeding section 321 is a trumpet hole that gradually decreases from the outer orifice 321a to the inner orifice 321b. The forming section 322 is a horizontally arranged cylindrical hole. The forming section 322 is connected with the inner orifice 321b of the feeding section 321, and the cross-sectional dimension of the forming section 322 is the same as that of the inner orifice 321b of the feeding section 321. The distance between the outer wall of the core rod 330 and the inner wall of the forming section 322 is matched with the wall thickness of the battery shell 200.

[0043] In this step S1, a necking portion 120 is generally formed at the front end of the shell blank 100, the necking portion 120 has a cross-sectional dimension smaller than the internal dimension of the forming section 322, so that the necking portion 120 can extend into the forming section 322, and the shell blank 100 can be pulled by the clamp. The length of the necking portion 120 is generally 25mm-30mm.

[0044] In step S4, the shell blank 100 is pulled by the clamp in the drawing direction, and the mandrel 330 moves in the drawing direction together with the shell blank 100, so that the shell blank 100 is drawn out of the cold drawing cavity 320 as a whole to form the battery shell 200. After the drawing, the four side walls of the shell blank 100 form the four side surfaces 210 of the battery shell 200, specifically, the first side wall 111 of the shell blank 100 forms the first side surface 211 of the battery shell 200, the second side wall 112 of the shell blank 100 forms the second side surface 212 of the battery shell 200, the third side wall 113 of the shell blank 100 forms the third side surface 213 of the battery shell 200, and the fourth side wall 114 of the shell blank 100 forms the fourth side surface 214 of the battery shell 200.

[0045] Please refer to FIG. 6, during the drawing, the outer wall of the shell blank 100 and the inner wall of the cold drawing cavity 320 will generate a friction force f1 opposite to the drawing direction; however, since the mandrel 330 moves in the drawing direction together with the shell blank 100, the friction force f2 between the inner wall of the shell blank 100 and the outer wall of the mandrel 330 opposite to the drawing direction can be greatly reduced. The moving speed V3 of the mandrel 330 is generally selected between the moving speed V1 of the clamp pulling the shell blank 100 (i.e. the moving speed of the front end of the shell blank 100) and the feeding speed V2 of the shell blank 100 (i.e. the moving speed of the rear end of the shell blank 100), i.e. V1≥V3≥V2. By reasonably selecting V3, the friction force f2 between the inner wall of the shell blank 100 and the outer wall of the mandrel 330 can be minimized, so that the counteracting pulling force formed by the combination of the friction force f1 and the friction force f2 can be reduced, and the pulling force F1 applied during the drawing can be reduced, so that the battery shell 200 can be prevented from being broken during the drawing. In addition, the oil film formed by the shell blank 100 before the drawing can also reduce the friction force f1 and the friction force f2, so that the pulling force F1 can be further reduced.

[0046] In order to further reduce the size of the pulling force F1 and facilitate the subsequent demolding of the battery shell 200, the core rod 330 is vibrated along the drawing direction during the drawing process in the S4 step. For example, the core rod 330 can be ultrasonically vibrated. The sine waveform in FIG. 6 is a schematic of the vibration waveform 331 when ultrasonic vibration is used. By vibrating, the contact between the outer wall of the shell blank 100 and the inner wall of the cold drawing cavity 320 can be changed from continuous contact to intermittent contact and disengagement. Thus, the friction f1 between the outer wall of the shell blank 100 and the inner wall of the cold drawing cavity 320 can be greatly reduced, thereby further reducing the combined friction force f1 and f2 and the resulting reverse pulling force. By vibrating, the oil film on the shell blank 100 can be homogenized, and the friction f1 and f2 can be reduced.

[0047] In addition, by vibrating the core rod 330, the drawing marks on the battery shell 200 can be avoided, the forming effect of the battery shell 200 can be improved, the stress between the inner wall of the battery shell 200 and the core rod 330 can be significantly reduced, thereby greatly reducing the frictional resistance during the subsequent demolding of the battery shell 200 and reducing the difficulty of demolding the battery shell 200. In order to ensure the effect of vibration, the vibration amplitude of the core rod 330 is generally not less than 5 μm. Of course, in order to avoid the vibration of the core rod 330 having a significant impact on the size of the pulling force F1 required during cold drawing, the vibration amplitude of the core rod 330 should not be too large, and is generally less than 30 μm. For example, the vibration amplitude of the core rod 330 can be 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 21 μm, 25 μm, 28 μm, etc. In the present embodiment, the vibration amplitude of the core rod 330 is generally in the range of 12 μm to 18 μm. In addition, the vibration frequency of the core rod 330 also has a certain influence on the cold drawing process. The vibration frequency of the core rod 330 is generally in the range of 10 KHz to 25 KHz, and is preferably 20 KHz to 22 KHz. Please refer to FIG. 7. In the present embodiment, since the core rod 330 is not fixed but moves synchronously with the shell blank 100, after the drawing is completed, the battery shell 200 is still sleeved on the core rod 330, which requires an additional demolding step to remove the battery shell 200 from the core rod 330.

[0048] Referring to Fig. 8, in the prior art, the wall thickness of the four sides 210 of the rectangular cylindrical battery case 200 is generally uniform, and the wall thickness of the side 210 of the battery case 200 made of aluminum alloy is generally above 0.8 mm, for example, the wall thickness of the side 210 is generally 1.2 mm. However, with the development of secondary battery technology and the continuous expansion of the application range, the method of making a pressure relief valve on the side wall of the secondary battery case 200 has been widely used. Since the wall thickness of the side 210 is too thin to meet the requirements of making a pressure relief valve, the wall thickness of the side 210 is limited, which results in that the battery case 200 cannot be made too thin.

[0049] Referring to Fig. 9, in order to further thin the wall thickness of the battery case 200, the wall thickness of the three sides 210 which do not need to be provided with a pressure relief valve is thinned in the embodiment, so that the wall thickness of one side 210 of the battery case 200 which is not thinned is greater than the wall thickness of the other three sides 210. For example, in the embodiment, in the S1 step, the wall thickness of the second side wall 112, the third side wall 113 and the fourth side wall 114 of the case blank 100 formed by extrusion is also less than the conventional thickness, so that the wall thickness of the first side wall 111 of the case blank 100 is also greater than the wall thickness of the second side wall 112, the third side wall 113 and the fourth side wall 114, and further, the wall thickness of the first side 211 of the battery case 200 formed by cold drawing is also greater than the wall thickness of the second side 212, the third side 213 and the fourth side 214.

[0050] When the battery case 200 is made of aluminum alloy, the wall thickness of the first side 211 is in the range of 0.8 mm to 1.2 mm. In the embodiment, the wall thickness of the first side 211 is 0.8 mm. The wall thickness of the second side 212, the third side 213 and the fourth side 214 is in the range of 0.3 mm to 0.7 mm. In the embodiment, the wall thickness of the second side 212, the third side 213 and the fourth side 214 is 0.3 mm.

[0051] By making the wall thickness of the four sides 210 (i.e. the first side 211, the second side 212, the third side 213 and the fourth side 214) of the battery case 200 not uniform, and by thinning the wall thickness of the three sides 210 (i.e. the second side 212, the third side 213 and the fourth side 214) which do not need to be provided with a pressure relief valve, the volume inside the battery case 200 can be increased without changing the external size, so that more battery material can be loaded to increase the capacity of the battery. Referring to Fig. 10, the dashed line part is the boundary of the internal cavity when the wall thickness of the four sides 210 of the battery case 200 is equal and the external size is the same. By comparison, it can be seen that the size of the internal cavity of the battery case 200 is increased, i.e. the internal accommodating space of the battery case 200 is increased, after the structure of the embodiment is adopted.

[0052] S5, the battery shell 200 is demolded from the mandrel 330. During demolding, the mandrel 330 can be moved in the direction opposite to the drawing direction until the mandrel 330 is demolded from the battery shell 200, the clamp is loosened, and the battery shell 200 is removed. During demolding, although the oil film formed by oil immersion before drawing of the shell blank 100 can reduce the friction between the inner wall of the battery shell 200 and the mandrel 330, to a certain extent, facilitate demolding; but due to the thin wall thickness of the battery shell 200, the difficulty of demolding is still great.

[0053] In this step, the mandrel 330 can also vibrate along its axial direction when the battery shell 200 is demolded from the mandrel 330, so that the difficulty of demolding the battery shell 200 can be further reduced. The vibration amplitude and frequency of the mandrel 330 can be the same as in step S4.

[0054] In this embodiment, the battery shell 200 is formed by cold drawing after extrusion molding. The battery shell 200 is always hard during drawing and will not become soft without heating, so the strength is high; and the formed battery shell 200 has no weld, and there is no risk of leakage after long-term use. The mandrel 330 moves synchronously during drawing, which can greatly reduce the friction between the inner wall of the shell blank 100 and the outer wall of the mandrel 330 during drawing, thereby reducing the drawing force and avoiding the battery shell 200 being pulled apart due to the thin wall thickness. The shell blank 100 is formed into an oil film by oil immersion before drawing, which can facilitate the subsequent demolding of the battery shell 200 and further reduce the friction between the inner wall of the shell blank 100 and the outer wall of the mandrel 330 during drawing. The mandrel 330 vibrates during drawing, which not only facilitates the demolding of the battery shell 200, but also improves the forming effect of the battery shell 200.

[0055] Please refer to Fig. 11, which is a structural schematic diagram of an embodiment of the ultra-thin high-strength seamless battery shell. The ultra-thin high-strength seamless battery shell of the embodiment is formed by the method for manufacturing the ultra-thin high-strength seamless battery shell, and includes a first side surface 211, a second side surface 212, a third side surface 213, and a fourth side surface 214. The battery shell is a seamless structure formed integrally, i.e., the first side surface 211, the second side surface 212, the third side surface 213, and the fourth side surface 214 are all free of welding seams 920. Among them, the first side surface 211 is a thick side surface, and the second side surface 212, the third side surface 213, and the fourth side surface 214 are three thin side surfaces respectively. The thick side surface and the thin side surface refer to the thickness of the four side surfaces of the battery shell when compared with each other, i.e., the thick side surface is the side surface with the largest thickness among the four side surfaces, and the thin side surface is the side surface with a thickness smaller than that of the thick side surface. The wall thickness range of the thick side surface and the thin side surface will be described in detail later. The first side surface 211, the second side surface 212, the third side surface 213, and the fourth side surface 214 form a rectangular cylindrical structure with openings at both ends. Among them, the first side surface 211 and the third side surface 213 are oppositely arranged, and the second side surface 212 and the fourth side surface 214 are oppositely arranged. The width of the first side surface 211 and the third side surface 213 is generally equal; and the width of the second side surface 212 and the fourth side surface 214 is generally equal.

[0056] The prior art adopts the mode of bending the side surface assembly into a rectangular cylindrical structure and then welding it, which can ensure the sealing performance at the welding seam 920 in a short period of time. However, the wall thickness at the welding seam 920 is necessarily uneven, and after long-term use, the position with a thinner wall thickness at the welding seam may leak due to oxidation, corrosion, and other reasons of the material. In the embodiment, the battery shell adopts a seamless structure formed integrally, which can effectively avoid this situation. Moreover, since welding is not required, the thickness of the side surface can be made thinner, for example, the wall thickness of the second side surface 212, the third side surface 213, and the fourth side surface 214 in the embodiment is reduced to 0.3 mm. Of course, with the progress of technology, the wall thickness of the second side surface 212, the third side surface 213, and the fourth side surface 214 can be made thinner, which is not limited by the welding process of the welding seam 920.

[0057] The first side surface 211 is provided with an explosion-proof valve 220. Specifically, an explosion-proof hole (not shown in the figure) is formed on the first side surface 211, the explosion-proof valve 220 is an explosion-proof piece 221 for sealing the explosion-proof hole, a reinforcing boss 222 is arranged on the outer edge of the explosion-proof piece 221, and a first explosion-proof notch 223 is formed on the explosion-proof piece 221. Of course, as shown in Fig. 12, the explosion-proof hole can also not be formed on the first side surface 211, but the explosion-proof valve 220 can be formed by directly etching a second explosion-proof notch 230 on the first side surface 211.

[0058] In the embodiment, the first side 211 has a smaller width than the second side 212. When multiple batteries are assembled into a battery pack, the battery shells with wider sides are usually bonded together to reduce the size of the battery pack. Therefore, the wider sides are not suitable for mounting the explosion-proof valve 220. Thus, the explosion-proof valve 220 is usually mounted on the narrower side. Of course, the explosion-proof valve 220 can also be mounted on the wider side if necessary. Therefore, the first side 211 can also have a larger width than the second side 212.

[0059] As shown in FIG. 9, the first side 211 has a larger wall thickness than the second side 212, the third side 213, and the fourth side 214. The wall thicknesses of the second side 212, the third side 213, and the fourth side 214 are usually equal. Of course, the wall thicknesses of the second side 212, the third side 213, and the fourth side 214 can also be different, but the wall thicknesses of the second side 212, the third side 213, and the fourth side 214 are all smaller than the wall thickness of the first side 211.

[0060] In the embodiment, the battery shell is made of an aluminum alloy material. The wall thickness of the first side 211 is usually in the range of 0.8 mm to 1.2 mm. The wall thicknesses of the second side 212, the third side 213, and the fourth side 214 are usually in the range of 0.3 mm to 0.7 mm.

[0061] In the embodiment, the wall thicknesses of the four sides of the battery shell are not uniform, forming an asymmetric structure with different wall thicknesses. The three sides without the explosion-proof valve 220 can be thinned, so that the volume of the battery shell can be increased without changing the external size, thereby allowing more battery material to be accommodated to increase the capacity of the battery. In combination with the cold-drawing process, a super-thin high-strength battery shell can be obtained.

[0062] In addition, by thinning the three sides without the explosion-proof valve 220 to form three thin sides, the material cost of the battery shell can also be reduced. Although the increased capacity of each battery and the reduced material cost are limited, for products such as new energy vehicles that require a large number of batteries, the accumulated increased capacity of the batteries and the reduced material cost are still very obvious.

[0063] The application also discloses a secondary battery. The secondary battery can be a power battery or an energy storage battery. For example, the secondary battery can be a blade battery. The shell of the secondary battery adopts the super-thin high-strength seamless battery shell of any of the above embodiments. Of course, the secondary battery also includes a battery core accommodated in the battery shell and other structures necessary for conventional secondary batteries. These are all prior art and will not be described here.

[0064] The above examples only express the preferred embodiments of the present application, which are described in a more specific and detailed manner, but should not be understood as a limitation to the scope of the patent. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, which are all within the scope of protection of the present application. Therefore, the scope of protection of the present application patent should be subject to the appended claims.

Claims

1. A method for manufacturing an ultra-thin, high-strength, seamless battery housing, characterized in that: The following steps are involved: S1. Extruding a metal material into a cylindrical shell blank; the length of the shell blank is shorter than the length of the battery shell, the cross-sectional dimension of the shell blank is larger than the cross-sectional dimension of the battery shell, and the wall thickness of the shell blank is larger than the wall thickness of the battery shell; S2, putting the shell blank on the core rod of the cold drawing die; S3, extending the front end of the shell blank into the cold drawing cavity of the cold drawing die outer die and clamping the front end of the shell blank; the size of the mandrel is adapted to the size of the internal cavity of the battery shell; S4, pulling the shell blank along the drawing direction, and moving the mandrel in the same direction as the shell blank along the drawing direction, so that the shell blank as a whole passes through the cold drawing cavity to form a battery shell; S5. Demolding the battery shell from the core rod.

2. The method for manufacturing an ultra-thin, high-strength, seamless battery casing according to claim 1, wherein: In the step S1, the length of the battery case and the length of the case blank satisfy the following formula: L k =L p *(1+δ) Among them, L k Indicates the length of the battery shell; L p Indicates the length of the shell blank; δ indicates the elongation of cold drawing.

3. The method for manufacturing an ultra-thin, high-strength, seamless battery casing according to claim 2, wherein: The ratio of the wall thickness of the shell blank to the wall thickness of the battery shell is in the range of 1.1 to 1.

5.

4. The method for manufacturing an ultra-thin, high-strength, seamless battery casing according to claim 3, wherein: The ratio of the wall thickness of the shell blank to the wall thickness of the battery shell is in the range of 1.2 to 1.

25.

5. The method for manufacturing an ultra-thin, high-strength, seamless battery casing according to claim 1, wherein: Before cold drawing, the shell blank is immersed in oil, then taken out of the oil and placed at an angle to drain the oil droplets. Cold drawing is carried out after an oil film is formed on the inner wall of the shell blank.

6. The method for manufacturing an ultra-thin, high-strength, seamless battery casing according to claim 1, wherein: The length of the core rod is greater than the length of the battery shell.

7. The method for manufacturing an ultra-thin, high-strength, seamless battery casing according to claim 1, wherein: The cold drawing cavity includes a feeding section and a forming section. The feeding section is a trumpet hole that gradually becomes smaller from the outer opening to the inner opening, and the forming section is a horizontal cylindrical hole. The forming section is smoothly connected to the inner opening of the feeding section.

8. The method for manufacturing an ultra-thin, high-strength, seamless battery casing according to claim 7, wherein: In the step S1, a necking portion is formed at the front end of the shell blank. The cross-sectional dimension of the necking portion is smaller than the inner dimension of the forming section, and the length of the necking portion is greater than the length of the forming section.

9. The method for manufacturing an ultra-thin, high-strength, seamless battery casing according to claim 1, wherein: In the step S1, the shell blank is a rectangular cylindrical structure having four side walls, and the thickness of one side wall of the rectangular cylindrical structure is greater than the thickness of the other three side walls; In the S4 step, the shell blank is formed into a rectangular cylindrical battery shell after cold drawing, and the four side walls of the shell blank respectively form the four side surfaces of the battery shell after cold drawing, and the wall thickness of one side surface of the battery shell is greater than the wall thickness of the other three side surfaces.

10. The method for manufacturing an ultra-thin, high-strength, seamless battery casing according to claim 1, wherein: In the step S4, the moving speed of the core rod is less than or equal to the moving speed of the clamp during drawing, and is greater than or equal to the feeding speed of the shell blank.

11. The method for manufacturing an ultra-thin, high-strength, seamless battery casing according to any one of claims 1 to 10, characterized in that: In the step S4, the core rod is vibrated along the drawing direction while moving; in the step S5, the core rod is vibrated along its axial direction during the demolding process.

12. The method for manufacturing an ultra-thin, high-strength, seamless battery casing according to claim 11, wherein: The vibration amplitude of the core rod is 5 μm to 30 μm; the vibration frequency of the core rod is 10 KHz to 25 KHz.

13. The method for manufacturing an ultra-thin, high-strength, seamless battery casing according to claim 12, wherein: The vibration amplitude of the core rod is 12 μm to 18 μm; the vibration frequency of the core rod is 20 KHz to 22 KHz.

14. An ultra-thin, high-strength, seamless battery casing, characterized by: The battery shell is manufactured using the ultra-thin, high-strength, seamless battery shell manufacturing method as described in any one of claims 1 to 13, and the battery shell includes a thick side and three thin side surfaces, and the thick side surface and the three thin side surfaces together form a rectangular cylindrical structure with openings at both ends; an explosion-proof valve is provided on the thick side surface, and the wall thickness of the thick side surface is greater than the wall thickness of the three thin side surfaces.

15. The ultra-thin, high-strength, seamless battery case according to claim 14, wherein: The thick side surface is the first side surface, and the three thin side surfaces are the second side surface, the third side surface and the fourth side surface; the widths of the first side surface and the third side surface are equal, the widths of the second side surface and the fourth side surface are equal, and the width of the first side surface is smaller than the width of the second side surface; the wall thicknesses of the second side surface, the third side surface and the fourth side surface are all equal.

16. The ultra-thin, high-strength, seamless battery case according to claim 14, wherein: The battery shell is made of aluminum alloy material, the wall thickness of the thick side is 0.8mm-1.2mm, and the wall thickness of the thin side is 0.3mm-0.7mm.

17. The ultra-thin, high-strength, seamless battery case according to claim 16, wherein: The wall thickness of the thick side surface is 0.8 mm, and the wall thickness of the thin side surface is 0.3 mm.

18. The ultra-thin, high-strength, seamless battery case according to claim 14, wherein: An explosion-proof hole is opened on the thick side surface, and the explosion-proof valve is an explosion-proof plate welded to close the explosion-proof hole. A reinforcing boss is provided on the outer edge of the explosion-proof plate, and a first explosion-proof notch is formed on the explosion-proof plate.

19. A secondary battery, characterized in that: The invention comprises an ultra-thin high-strength seamless battery shell as described in any one of claims 14 to 18.

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