Method for manufacturing a battery case

Abstract

The application discloses a preparation method of a battery shell, which comprises the following steps: S1, melting and casting an aluminum alloy to obtain an aluminum alloy rod, wherein the composition of the aluminum alloy is as follows: Mn 1%-1.3%, Si 0.1%-0.3%, Fe 0.3%-0.5%, Cu 0.1%-0.3%, Mg <=0.02%, Zn <=0.02%, and the balance is Al and inevitable impurities; S2, uniformly treating the aluminum alloy rod; S3, extruding the aluminum alloy rod by using an extrusion die to obtain an extruded blank; and S4, performing an extruding treatment on the extruded blank by using an extruding die to obtain a square battery shell body with unequal walls; the method can reduce the occupied external space of the battery shell body or increase the internal space of the battery shell body, and can reduce the material cost.

Description

Technical Field

[0001] This invention relates to the field of battery casing manufacturing, and in particular to a method for preparing a battery casing. Background Technology

[0002] Aluminum alloy square battery casings using end-welded caps typically have four equal-walled sides, except for the end caps. This is primarily because the manufacturing process imposes certain requirements on the product's forming. Currently popular unibody molding technologies, whether "aluminum sheet + cold stamping and extrusion" or "hot extrusion profile + cold drawing," are generally only suitable for products with four or two equal-walled sides. However, typically only one of these four sides of the square casing is functional, used to install explosion-proof valves or electrode posts. The other three sides usually only serve a sealing and protective function. Therefore, using the other three sides may result in material waste and lead to an excessively large battery size or reduced capacity. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a method for preparing a battery casing.

[0004] A method for preparing a battery casing according to a first aspect of the present invention includes the following steps:

[0005] S1. Melt and cast the aluminum alloy to obtain an aluminum alloy rod;

[0006] S2. Homogenize the aluminum alloy rod.

[0007] S3. Use an extrusion die to extrude the aluminum alloy rod to obtain a drawn billet;

[0008] S4. Use a drawing mold to draw the blank to obtain a square battery casing with unequal walls.

[0009] The unequal-walled square battery casing has a thick side, a thin side, and two equal-walled sides, with the thick side and the thin side being distributed opposite to each other, and the two equal-walled sides being distributed opposite to each other.

[0010] The aluminum alloy comprises, by mass percentage: Mn 1%-1.3%, Si 0.1%-0.3%, Fe 0.3%-0.5%, Cu 0.1%-0.3%, Mg ≤0.02%, Zn ≤0.02%, with the balance being Al and unavoidable impurities.

[0011] The battery casing preparation method according to the present invention has at least the following beneficial effects: by using the aluminum alloy with the above composition and in conjunction with homogenization, extrusion and drawing processes, a square battery casing with unequal walls can be obtained, which reduces the external space occupied by the battery casing or increases the internal space of the battery casing and reduces material costs.

[0012] According to some embodiments of the present invention, the average grain size of the aluminum alloy rod is ≤100μm.

[0013] According to some embodiments of the present invention, the homogenization treatment employs a segmented heat preservation process, including the following steps:

[0014] Step 1: Keep warm at 580℃±10℃ for 3±0.5h;

[0015] Step 2: Keep warm at 600℃±10℃ for 6±0.5h;

[0016] Step 3: Keep warm at 610℃±10℃ for 3±0.5h;

[0017] Step 4: Cool the furnace to 560℃±10℃;

[0018] Step 5: Perform spray cooling.

[0019] According to some embodiments of the present invention, the drawn blank includes a blank thick wall corresponding to the thick edge, a blank thin wall corresponding to the thin edge, and a blank equal wall corresponding to the equal wall edge;

[0020] Wherein, the drawing deformation amount of the blank with equal wall is X%, X = 10-25, and the drawing deformation amount of the blank with thick wall is (XY)%, Y = 0.5-5;

[0021] The drawing deformation of the thin-walled billet is (XZ)%, where Z = 0-3.

[0022] According to some embodiments of the present invention, the wall thickness of the thick side is d1, the wall thickness of the thin side is d2, the wall thickness of the equal-walled side is d3, Y = d1 / d2, and Z = d1 / d3.

[0023] According to some embodiments of the present invention, the drawing deformation of the billet thick wall, the billet thin wall, and the billet equal wall has a correction verification value of ±1%.

[0024] According to some embodiments of the present invention, the extrusion die includes four diversion holes corresponding to the four sides of the drawn blank, and at least one diversion bridge extending along the extrusion direction is provided in each diversion hole.

[0025] According to some embodiments of the present invention, the drawing mold includes an inner mold and an outer mold. The outer mold is provided with a drawing cavity extending along the drawing direction. The inner mold is capable of being placed into the drawing cavity. A drawing gap corresponding to the unequal-walled square battery casing is formed between the outer edge of the inner mold and the inner wall of the drawing cavity. The drawing gap includes a wide slit and a narrow slit corresponding to the thick side and the thin side of the unequal-walled square battery casing, respectively. The drawing blank is set to pass through the drawing mold from front to back. The front part of the inner mold is deflected toward one side of the narrow slit relative to the drawing direction of the drawing mold.

[0026] According to some embodiments of the present invention, the inclination angle of the inner mold relative to the drawing direction of the drawing mold is greater than 0° and less than 10°.

[0027] According to some embodiments of the present invention, the wall thickness of the thick side is d1, the wall thickness of the thin side is d2, and the inclination angle of the inner mold relative to the drawing direction of the drawing mold is 2°*d1 / d2. Attached Figure Description

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0029] Figure 1 This is a cross-sectional schematic diagram of a rectangular battery casing with unequal walls according to an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the microstructure of the aluminum rod according to an embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of an extrusion die according to an embodiment of the present invention;

[0032] Figure 4 This is a front structural diagram of an extrusion die according to an embodiment of the present invention;

[0033] Figure 5 This is a schematic diagram of the wall thickness of the blank in an embodiment of the present invention;

[0034] Figure 6 This is a schematic diagram of the extraction device according to an embodiment of the present invention.

[0035] Figure label:

[0036] Inner mold 100, flow divider hole 101, flow divider bridge 110, outer mold 200, drawing gap 201, billet thick wall 801, billet thin wall 802, billet equal wall 803, chuck 910, thick edge 901, thin edge 902, equal wall edge 903. Detailed Implementation

[0037] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0038] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0039] In the description of this invention, the use of "first" and "second" is for the purpose of distinguishing technical features only, and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated or the order of the technical features indicated.

[0040] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0041] The method for preparing a battery casing according to an embodiment of the present invention includes the following steps:

[0042] S1. Melt and cast the aluminum alloy to obtain an aluminum alloy rod;

[0043] S2. Homogenize the aluminum alloy rod.

[0044] S3. Use an extrusion die to extrude the aluminum alloy rod to obtain a drawn billet;

[0045] S4. Use a drawing mold to draw the blank to obtain a square battery casing with unequal walls.

[0046] The unequal-wall square battery casing has a thick side 901, a thin side 902 and two equal-wall sides 903. The wall thickness of the thick side 901 is greater than the wall thickness of the thin side 902. The thick side 901 and the thin side 902 are relatively distributed, and the two equal-wall sides 903 are relatively distributed.

[0047] The composition of aluminum alloy by mass percentage is: Mn 1%-1.3%, Si 0.1%-0.3%, Fe 0.3%-0.5%, Cu 0.1%-0.3%, Mg≤0.02%, Zn≤0.02%, with the balance being Al and unavoidable impurities.

[0048] Using the aluminum alloy with the above composition, and in conjunction with homogenization, extrusion, and drawing processes, unequal-walled square battery casings can be produced, reducing the external space occupied by the battery casing or increasing the internal space of the battery casing, and reducing material costs.

[0049] like Figure 2 As shown, in some embodiments of the present invention, the average grain size of the aluminum alloy rod is ≤100μm.

[0050] In some embodiments of the present invention, the homogenization process employs a segmented heat preservation process, including the following steps:

[0051] Step 1: Keep warm at 580℃±10℃ for 3±0.5h;

[0052] Step 2: Keep warm at 600℃±10℃ for 6±0.5h;

[0053] Step 3: Keep warm at 610℃±10℃ for 3±0.5h;

[0054] Step 4: Cool the furnace to 560℃±10℃;

[0055] Step 5: Perform spray cooling.

[0056] By using a segmented heat preservation process for homogenization, the billet is prevented from becoming coarse during extrusion, thus reducing defects such as rough surface during the drawing process.

[0057] In some embodiments of the present invention, the drawn billet in the F state has the following properties: tensile strength higher than 105 MPa, elongation after fracture greater than 30%, and average grain size less than or equal to 75 μm.

[0058] In some embodiments of the present invention, the blank drawing includes a blank thick wall 801 corresponding to the thick edge 901, a blank thin wall 802 corresponding to the thin edge 902, and a blank equal wall 803 corresponding to the equal wall edge 903; wherein, the drawing deformation of the blank equal wall 803 is X%, X = 10-25, the drawing deformation of the blank thick wall 801 is (XY)%, Y = 0.5-5, and the drawing deformation of the blank thin wall 802 is (XZ)%, Z = 0-3.

[0059] Correction coefficients Y and Z are introduced to correct the wall thickness of the thick wall 801 and thin wall 802 of the billet being drawn, so as to eliminate the influence of unequal walls on the drawing process and make the drawing deformation of the unequal wall shell more coordinated.

[0060] Specifically, such as Figure 1 , Figure 5As shown, the wall thickness of the thick side 901 is d1, the wall thickness of the thin side 902 is d2, and the wall thickness of the equal side 903 is d3. The wall thickness of the thick side 801 of the billet is D1 = (100% + (XY)%) * d; the wall thickness of the thin side 802 of the billet is D2 = (100% + (XZ)%) * d2; and the wall thickness of the equal side 803 of the billet is D3 = (100% + X%) * d3.

[0061] In some embodiments of the present invention, the wall thickness of the thick side 901 is d1, the wall thickness of the thin side 902 is d2, the wall thickness of the equal side 903 is d3, Y = d1 / d2, when d1 / d2 > 5, Y is 5, Z = d1 / d3, when d1 / d3 > 3, Z is 3, so as to quantify the correction coefficients Y and Z.

[0062] In some embodiments of the present invention, the drawing deformation of the billet thick wall 801, the billet thin wall 802 and the billet equal wall 803 has a correction verification value of ±1% to eliminate the influence of other external factors such as room temperature and humidity.

[0063] Specifically, D1 = (100% + (XY)%) * d1 * (100% ± 1%); D2 = (100% + (XZ)%) * d2 * (100% ± 1%); D3 = (100% + X) * d3 * (100% ± 1%).

[0064] like Figure 3 , Figure 4 As shown, in some embodiments of the present invention, the extrusion die includes four diversion holes 101 corresponding to the four sides of the drawn blank, and at least one diversion bridge 110 extending along the extrusion direction is provided in the diversion hole 101. By configuring the diversion bridge 110, the material flow can be guided, turbulence and pressure imbalance can be reduced, and the extrusion stability and the quality of the extruded product can be improved.

[0065] Specifically, when the aluminum alloy rod is extruded through the flow divider bridge 110, the flow divider bridge 110 extending along the extrusion direction can guide the material, reduce the occurrence of the material flow direction deviating from the extrusion direction, balance the extrusion pressure, and make the material distribution uniform, so that incomplete welding, substandard thickness and other problems are less likely to occur, thus improving the product qualification rate.

[0066] In some embodiments of the present invention, the diversion bridge 110 has a flat structure to achieve a better flow guiding effect.

[0067] Specifically, the aluminum alloy conveying direction is from front to back, and the diversion bridge 110 has a teardrop-shaped structure that is wider at the front and narrower at the back.

[0068] In some embodiments of the present invention, each diversion hole 101 is provided with a diversion bridge 110. The diversion bridge 110 is disposed in the middle of the diversion hole 101 and extends along the extrusion direction. By diverting and guiding the flow in the middle through a single diversion bridge 110, the material flow can be guided better, and the impact on the material flow rate and pressure can be reduced.

[0069] Of course, in the specific implementation process, if the diversion hole 101 is large, two or more diversion bridges 110 can be configured as needed, which will not be described in detail here.

[0070] According to some embodiments of the present invention, in step S3, the temperature of the extrusion die is 420℃-440℃, and the temperature of the aluminum alloy rod is 470℃-510℃. This temperature setting allows the aluminum alloy rod to have certain deformation properties and is beneficial for controlling the coarse grain layer of this type of product, resulting in good mechanical properties.

[0071] like Figure 6 As shown, in some embodiments of the present invention, the drawing mold includes an inner mold 100 and an outer mold 200. The outer mold 200 is provided with a drawing cavity extending along the drawing direction. The inner mold 100 can be placed into the drawing cavity. A drawing gap 201 corresponding to the unequal wall square battery shell is formed between the outer edge of the inner mold 100 and the inner wall of the drawing cavity. The drawing gap 201 includes a wide slit and a narrow slit corresponding to the thick side 901 and thin side 902 of the unequal wall square battery shell, respectively. The drawing blank is set to pass through the drawing mold from front to back. The front part of the inner mold 100 is deflected towards the narrow slit side relative to the drawing direction of the drawing mold, so as to reduce the force difference generated on the drawing mold when the material passes through the wide slit and the narrow slit. This can better balance the force, meet the drawing requirements of the unequal wall thickness shell, and improve product quality.

[0072] Specifically, after the inner mold 100 tilts towards the narrow slit side, the outer edge of the inner mold 100 at the wide slit will tilt at a small angle and form an angle of attack corresponding to the material input direction, increasing the force at the wide slit when the material is input. Similarly, the force at the narrow slit is reduced, thereby reducing the difference in drawing force and ensuring the quality of the drawn product.

[0073] In some embodiments of the present invention, the inclination angle of the inner mold 100 relative to the drawing direction of the drawing mold is selected according to the actual wall thickness difference.

[0074] Specifically, the inclination angle of the inner mold 100 relative to the drawing direction of the drawing mold is greater than 0° and less than 10°, which can achieve a good balance effect and meet the current drawing requirements of battery cases with different wall thicknesses.

[0075] Specifically, the tilt angle of the inner mold 100 relative to the drawing direction of the drawing mold can also be determined by the calculation formula: tilt angle = 2°*d1 / d2, which can achieve a better balance effect.

[0076] like Figure 6 As shown, the blank is drawn from front to back through the drawing mold and connected to the chuck 910. The chuck 910 is connected to the traction trolley. The inner mold 100 and the outer mold 200 are connected and fixed or pulled. When the traction trolley moves backward, it can pull the blank through the drawing mold to form an elongated box.

[0077] Example 1

[0078] The method for preparing the battery casing includes the following steps:

[0079] S1. Melt and cast the aluminum alloy to obtain an aluminum alloy rod;

[0080] S2. A segmented heat preservation process is used to homogenize the aluminum alloy rod.

[0081] S3. Use an extrusion die to extrude the aluminum alloy rod to obtain a drawn billet;

[0082] S4. Use a drawing mold to draw the blank to obtain a square battery casing with unequal walls.

[0083] The aluminum alloy is composed of the following by mass percentage: Mn 1.2%, Si 0.2%, Fe 0.4%, Cu 0.2%, Mg 0.02%, Zn 0.02%, with the balance being Al and unavoidable impurities.

[0084] The drawing deformation of billet with equal wall 803 is 25%, the drawing deformation of billet with thick wall 801 is 23.5%, Y = 0.5-5; the drawing deformation of billet with thin wall 802 is 24%, Z = 0-3.

[0085] The inclination angle of the inner mold 100 relative to the drawing direction of the drawing mold is 2°.

[0086] Unequal wall square battery casings were produced without any breakage. The wall thickness fluctuation was about 0.015 mm (the wall deviation problem was not obvious). The welding performance was good, and the success rate of the drawing process was greater than 96%.

[0087] Example 2

[0088] The method for preparing the battery casing includes the following steps:

[0089] S1. Melt and cast the aluminum alloy to obtain an aluminum alloy rod;

[0090] S2. A segmented heat preservation process is used to homogenize the aluminum alloy rod.

[0091] S3. Use an extrusion die to extrude the aluminum alloy rod to obtain a drawn billet;

[0092] S4. Use a drawing mold to draw the blank to obtain a square battery casing with unequal walls.

[0093] The aluminum alloy is composed of the following by mass percentage: Mn 1.2%, Si 0.2%, Fe 0.4%, Cu 0.2%, Mg 0.02%, Zn 0.02%, with the balance being Al and unavoidable impurities.

[0094] The drawing deformation of the equal-walled billet 803 is 20%, the drawing deformation of the thick-walled billet 801 is 18%, and the drawing deformation of the thin-walled billet 802 is 18.5%.

[0095] The inclination angle of the inner mold 100 relative to the drawing direction of the drawing mold is 5°.

[0096] Unequal wall square battery casings were produced without any breakage. The wall thickness fluctuation was about 0.02 mm (the wall deviation problem was not obvious). The welding performance was good, and the success rate of the drawing process was greater than 95%.

[0097] Example 3

[0098] The method for preparing the battery casing includes the following steps:

[0099] S1. Melt and cast the aluminum alloy to obtain an aluminum alloy rod;

[0100] S2. A segmented heat preservation process is used to homogenize the aluminum alloy rod.

[0101] S3. Use an extrusion die to extrude the aluminum alloy rod to obtain a drawn billet;

[0102] S4. Use a drawing mold to draw the blank to obtain a square battery casing with unequal walls.

[0103] The aluminum alloy is composed of the following components by mass percentage: Mn 1.3%, Si 0.2%, Fe 0.3%, Cu 0.3%, Mg 0.02%, Zn 0.02%, with the balance being Al and unavoidable impurities.

[0104] The drawing deformation of billet with equal wall 803 is 20%, the drawing deformation of billet with thick wall 801 is 19.5%, Y = 0.5-5; the drawing deformation of billet with thin wall 802 is 20%.

[0105] The inclination angle of the inner mold 100 relative to the drawing direction of the drawing mold is 0.5°.

[0106] Unequal wall square battery casings were produced without any breakage. The wall thickness fluctuation was approximately 0.025 mm (the wall thickness deviation was not significant). The welding performance was good, and the success rate of the drawing process was greater than 94%.

[0107] Comparative Example 1

[0108] The method for preparing the battery casing includes the following steps:

[0109] S1. Melt and cast the aluminum alloy to obtain an aluminum alloy rod;

[0110] S2. A segmented heat preservation process is used to homogenize the aluminum alloy rod.

[0111] S3. Use an extrusion die to extrude the aluminum alloy rod to obtain a drawn billet;

[0112] S4. Use a drawing mold to draw the blank to obtain a square battery casing with unequal walls.

[0113] The aluminum alloy composition by mass percentage is: Mn 1.2%, Si 0.4%, Fe 0.3%, Cu 0.05%, Mg 0.01%, Zn 0.03%, with the balance being Al and unavoidable impurities.

[0114] The drawing deformation of the equal-walled billet 803 is 25%, the drawing deformation of the thick-walled billet 801 is 25%, and the drawing deformation of the thin-walled billet 802 is 25%.

[0115] The inclination angle of the inner mold 100 relative to the drawing direction of the drawing mold is 2°.

[0116] Unequal wall square battery casings were produced without breakage, but the wall thickness fluctuated significantly, with the thickness of the thick edge 901 fluctuating more than 0.1 mm at both ends.

[0117] Comparative Example 2

[0118] The method for preparing the battery casing includes the following steps:

[0119] S1. Melt and cast the aluminum alloy to obtain an aluminum alloy rod;

[0120] S2. A segmented heat preservation process is used to homogenize the aluminum alloy rod.

[0121] S3. Use an extrusion die to extrude the aluminum alloy rod to obtain a drawn billet;

[0122] S4. Use a drawing mold to draw the blank to obtain a square battery casing with unequal walls.

[0123] The aluminum alloy composition by mass percentage is: Mn 1.2%, Si 0.4%, Fe 0.3%, Cu 0.05%, Mg 0.03%, Zn 0.01%, with the balance being Al and unavoidable impurities.

[0124] The drawing deformation of the equal-walled billet 803 is 20%, the drawing deformation of the thick-walled billet 801 is 20%, and the drawing deformation of the thin-walled billet 802 is 20%.

[0125] The inclination angle of the inner mold 100 relative to the drawing direction of the drawing mold is 0°.

[0126] Unequal wall square battery casings were produced. 31% of the finished products had broken or surface defects on the thin edge 902, and the wall thickness fluctuated greatly. Among them, the wall thickness fluctuation at the beginning and end of the thick edge 901 and the thin edge 902 was greater than 0.1 mm.

[0127] Of course, the present invention is not limited to the above-described embodiments. Those skilled in the art can make equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A method of producing a battery case, characterized by, Includes the following steps: S1. Melt and cast the aluminum alloy to obtain an aluminum alloy rod; S2. Homogenize the aluminum alloy rod. S3. Use an extrusion die to extrude the aluminum alloy rod to obtain a drawn billet; S4. Use a drawing mold to draw the blank to obtain a square battery casing with unequal walls. The unequal-walled square battery casing has a thick side (901), a thin side (902), and two equal-walled sides (903). The thick side (901) and the thin side (902) are distributed opposite to each other, and the two equal-walled sides (903) are distributed opposite to each other. The aluminum alloy comprises, by mass percentage: Mn 1%-1.3%, Si 0.1%-0.3%, Fe 0.3%-0.5%, Cu 0.1%-0.3%, Mg ≤ 0.02%, Zn ≤ 0.02%, with the balance being Al and unavoidable impurities; The drawing mold includes an inner mold (100) and an outer mold (200). The outer mold (200) is provided with a drawing cavity extending along the drawing direction. The inner mold (100) can be inserted into the drawing cavity. A drawing gap (201) corresponding to the unequal wall square battery housing is formed between the outer edge of the inner mold (100) and the inner wall of the drawing cavity. The drawing gap (201) includes a wide slit and a narrow slit corresponding to the thick side (901) and the thin side (902) of the unequal wall square battery housing, respectively. The drawing blank is set to pass through the drawing mold from front to back. The front part of the inner mold (100) is deflected toward the side of the narrow slit relative to the drawing direction of the drawing mold. The wall thickness of the thick side (901) is d1, the wall thickness of the thin side (902) is d2, and the inclination angle of the inner mold (100) relative to the drawing direction of the drawing mold is 2°*d1 / d2.

2. The method for preparing the battery casing according to claim 1, characterized in that, The average grain size of the aluminum alloy rod is ≤100μm.

3. The method for preparing the battery casing according to claim 1, characterized in that, The homogenization process employs a segmented heat preservation technique, including the following steps: Step 1: Keep warm at 580℃±10℃ for 3±0.5h; Step 2: Keep warm at 600℃±10℃ for 6±0.5h; Step 3: Keep warm at 610℃±10℃ for 3±0.5h; Step 4: Cool the furnace to 560℃±10℃; Step 5: Perform spray cooling.

4. The method for preparing the battery casing according to claim 1, characterized in that, The drawn blank includes a blank thick wall (801) corresponding to the thick edge (901), a blank thin wall (802) corresponding to the thin edge (902), and a blank equal wall (803) corresponding to the equal wall edge (903). Wherein, the drawing deformation of the equal wall (803) billet is X%, X=10-25, and the drawing deformation of the thick wall (801) billet is (XY)%, Y=0.5-5; The drawing deformation of the thin-walled billet (802) is (XZ)%, Z=0-3.

5. The method for preparing the battery casing according to claim 4, characterized in that, The wall thickness of the thick side (901) is d1, the wall thickness of the thin side (902) is d2, the wall thickness of the equal side (903) is d3, Y = d1 / d2, Z = d1 / d3.

6. The method for preparing the battery casing according to claim 4, characterized in that, The drawing deformation of the billet thick wall (801), the billet thin wall (802) and the billet equal wall (803) has a correction verification value of ±1%.

7. The method for preparing the battery casing according to claim 1, characterized in that, The extrusion die includes four diversion holes (101) corresponding to the four sides of the extruded blank, and at least one diversion bridge (110) extending along the extrusion direction is provided in each diversion hole (101).

8. The method for preparing the battery casing according to claim 1, characterized in that, The inclination angle of the inner mold (100) relative to the drawing direction of the drawing mold is greater than 0° and less than 10°.

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