In-depth analysis of square lithium battery aluminum casing industry knowledge

The square lithium battery aluminum casing refers to the metal shell component that is made of high-quality aluminum alloy materials through precision stamping, stretching or deep drawing and other forming processes, and is used to package square lithium-ion batteries. As one of the three core structural components of lithium batteries (positive electrode, negative electrode, casing and separator), the aluminum casing assumes multiple functions such as mechanical support, environmental sealing, heat conduction and safety protection in the battery cell. Compared with the Aluminum Laminate Pouch for Li-ion Batteries used in soft-pack lithium batteries, the square aluminum casing has higher mechanical strength, better dimensional stability and better thermal management capabilities; compared with the cylindrical steel casing, the aluminum casing has obvious advantages in lightweight and space utilization.

 

The aluminum casing of a square lithium battery is usually composed of the main body of the casing and the cover assembly (including positive and negative poles, explosion-proof valves, injection holes, etc.). The cover and casing are sealed by laser welding. As the requirements for energy density and safety of electric vehicles, energy storage systems and portable electronic devices continue to increase, the square aluminum shell solution widely adopted by mainstream car companies such as Prismatic Cell for BYD brand has become one of the leading packaging forms in the power battery field. The selection of aluminum shell materials, molding accuracy and welding sealing quality directly determine the cycle life, safety performance and production yield of the battery. Therefore, this component is classified as a high-value-added and high-tech threshold link in the power battery industry chain.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The aluminum alloy material selected for the aluminum casing of the square lithium battery, its grade selection and microstructure control directly determine the molding performance, welding quality and corrosion resistance of the casing. Currently, the most commonly used materials in the industry are 3003 aluminum alloy (aluminum-manganese alloy) and 6061 aluminum alloy (aluminum-magnesium-silicon alloy). Among them, 3003 alloy has become the mainstream choice for square aluminum shells due to its excellent deep drawing performance, good corrosion resistance and moderate strength. The main alloying element of 3003 aluminum alloy is manganese (about 1.0-1.5%), which improves the tensile strength and work hardening properties of the material without significantly reducing the electrical and thermal conductivity. The thickness of the material is usually controlled between 0.3 mm and 1.2 mm, and the specific value depends on the capacity and size of the battery core - large-capacity power batteries (such as 100Ah and above) tend to use thicker shells (0.8- 1.2 mm) to ensure structural strength; consumer batteries use thinner shells (0.3- 0.6 mm) to pursue higher energy density. In terms of structure control, aluminum shell materials usually require a grain size finer than level 5 to avoid orange peel defects or cracking during the deep drawing process.

 

In terms of surface condition, the inner wall of the aluminum shell usually needs to be chemically passivated or anodized to improve chemical compatibility with the electrolyte and prevent aluminum from reacting with lithium hexafluorophosphate (LiPF₆) to generate hydrofluoric acid that corrodes the shell. For the same type of materials used in the EV Battery Pouch Cell Aluminum Case, additional consideration needs to be given to the insulation cooperation with the positive and negative tabs. Usually, an insulating layer is coated on the inner wall of the case, or an insulating film is inserted during assembly. It is worth noting that although the basic material system of Aluminum shell for Prismatic and cylindrical battery cases is similar, the requirements for the anisotropy index (r value) and work hardening index (n value) of the material are different due to differences in the molding process (deep drawing for square and multiple variable diameter drawing for cylinder).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The manufacturing of aluminum casings for square lithium batteries involves multiple precision forming processes, among which the deep drawing process is the most technically difficult and core link that has the greatest impact on product quality. The process flow starts with the uncoiling and blanking of aluminum alloy coils: the aluminum strip is fed into a high-speed punch, and a rounded rectangular or approximately square blank piece (called a blank) is punched out through a blanking die. The shape and size of the blank are accurately calculated to achieve a reasonable distribution of the material in subsequent multi-pass drawing. The subsequent core process is multi-pass deep drawing: the piece of material is passed through several sets of punch and concave dies in sequence, gradually deforming the flat piece of material into a square shell with a predetermined depth and bottom rounded corners. The number of drawing passes depends on the ratio of the depth of the shell to the opening size (i.e., the drawing ratio). A typical square aluminum shell for a power battery requires 4-7 drawing processes.

 

After each drawing pass, an intermediate annealing treatment may be interspersed to eliminate work hardening and restore the plasticity of the material. During the drawing process, it is necessary to strictly control the gap between the punch and the die (usually 1.05-1.15 times the material thickness), the type and coating amount of lubricant, and the drawing speed to prevent wrinkles, cracks, or serious uneven thickness on the side walls of the shell. The semi-finished products after deep drawing are trimmed (trimmed) to remove irregular edges and then cleaned to remove drawing oil and aluminum chips. The wall thickness reduction rate is a key indicator to measure the level of the deep drawing process - excellent process design can control the maximum wall thickness reduction rate within 15%, and the bottom corner of the shell is the area with the thinnest wall thickness, and the local thinning there should not be less than 75% of the design wall thickness.

 

For the highly demanding EV Battery Pouch Cell Aluminum Case or Aluminum shell for single cell lithium ion battery, side wall correction (size finishing) and bottom surface leveling will also be performed after deep drawing to ensure that the straightness, verticality and bottom surface flatness of the shell meet the positioning requirements of the automated assembly line. Laser welding between the cover assembly (including pole, explosion-proof valve, liquid injection hole) and the shell is another key process. Continuous fiber laser or pulse laser is usually used for peripheral sealing welding. The welding speed, laser power and defocus need to be accurately matched to obtain a weld with no pores, no spatter, and sufficient penetration depth. The welded shell needs to undergo air tightness testing (helium mass spectrometry leak detection or pressure drop method) and weld appearance inspection.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

With the rapid development of new energy vehicles, distributed energy storage, and portable new energy equipment, the application scenarios of lithium batteries continue to expand, and the market's requirements for the adaptability, safety, and customization capabilities of battery casings continue to increase, which has given rise to various segmented customized aluminum casing products. In response to the special needs of the vehicle power battery field, the EV Battery Pouch Cell Aluminum Case power battery pouch and square cell aluminum case have been specially optimized for vehicle operating conditions and have stronger resistance to vibration, high temperature, and deformation, and are suitable for complex vehicle driving conditions. At the same time, the industry is highly adapted to the needs of brand customization. Special square battery cell aluminum casings such as Prismatic Cell for BYD brand are customized and developed according to the exclusive size, packaging process and performance standards of the brand's battery cells to achieve precise adaptation of the casing and battery cells. In addition, the popularity of small single cell lithium battery equipment has also made Aluminum shell for single cell lithium ion battery widely used, fully covering various large, medium and small lithium battery application scenarios.

Looking at the development trends of the industry, the aluminum casing of square lithium batteries is continuously iteratively upgraded in the direction of lightweight, high strength, high safety, high precision, and green environmental protection. At the material level, the industry continues to optimize the aluminum alloy ratio. Through new alloy modification technology, while maintaining the advantage of lightweight, the tensile strength, impact resistance and high temperature resistance of the material are further improved to meet the development needs of high-power, high-rate charge and discharge lithium battery products. At the process level, technologies such as automated precision stamping, surface strengthening treatment, and micron-level precision control have gradually become popular, allowing the sealing, flatness, and corrosion resistance of the casing to continue to improve, meeting the stringent standards of high-end energy storage and vehicle-mounted power batteries. In terms of product form, in addition to traditional hard aluminum shells, flexible packaging supporting structures continue to innovate. The Aluminum Laminate Pouch for Li-ion Batteries lithium battery aluminum-plastic film composite packaging structure further enriches the product form of lithium battery shells and adapts to the research and development needs of thin, lightweight and flexible lithium battery equipment. In the future, as the smart energy storage and new energy vehicle industries continue to upgrade, the technology iteration and scene adaptability of lithium battery aluminum casings will continue to improve.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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