Square, Cylindrical, Soft Pack: Analysis of Manufacturing Processes for Different Lithium Battery Packaging Form

In the new energy era, lithium batteries, as the core power and storage units, are of undeniable importance. Among the many characteristics of lithium batteries, the packaging shape, though an external manifestation, actually contains complex technological considerations and technical logic. The three mainstream packaging shapes—square, cylindrical, and soft pack—each correspond to unique manufacturing processes, akin to three keys that open the doors to different application scenarios. This article delves into the technical routes and manufacturing mysteries behind these three lithium battery packaging shapes.

1. Square Lithium Battery: Craftsmanship Behind Solidity

(1) Structural and Design Advantages

The square lithium battery is known for its regular shape, which offers significant advantages in space utilization. Its flat structure can be tightly arranged, making it suitable for scenarios with high space layout requirements, such as battery modules for electric vehicles. Structurally, the square casing provides stable support for internal components like electrodes and separators, helping improve the battery’s overall strength and stability.

(2) Manufacturing Process

Shell Manufacturing: The outer casing of square lithium batteries is typically made from metal materials, such as aluminum alloys or stainless steel. The manufacturing process involves stamping and stretching operations, where metal sheets are processed into casings of specific shapes and sizes through molds. The precision of molds is critical to ensure the consistency and surface smoothness of the casing, which is essential for assembling internal battery components. The stretching process further shapes the shell’s depth and form, allowing it to house the battery core.

Cell Assembly: The core of square lithium batteries is meticulously complex in its assembly. Positively and negatively charged layers and separators are stacked or wound into the cell and then carefully placed into the formed casing. The stacking process can enhance the battery’s energy density and charge/discharge performance because it minimizes the internal resistance and mechanical stress within the cell. The winding process is more suited for large-scale production, providing high efficiency. After cell assembly, electrolyte injection takes place, where the injection quantity and uniformity directly affect the battery’s performance and lifespan.

Sealing and Welding: To ensure the battery’s tightness and safety, processes like laser welding or resistance welding are used to seal the shell and top cover. Laser welding has the advantages of high energy density, fast welding speed, and narrow and attractive weld seams, effectively preventing electrolyte leakage and external air ingress. Parameter control during welding is crucial, such as laser power, welding speed, and pulse frequency; any deviation could lead to welding quality issues affecting the battery’s overall performance.

(3) Application Scenarios and Challenges

Square lithium batteries find extensive applications in electric vehicles and energy storage systems. In electric vehicles, their compact structure can better fit the vehicle’s chassis space, enhancing vehicle range and handling performance. However, the manufacturing process for square lithium batteries is relatively complex, with higher costs and stringent requirements for production equipment and process control. Additionally, square batteries face certain challenges in heat dissipation, requiring efficient thermal management systems to ensure stable performance under different operating conditions.

2. Cylindrical Lithium Battery: Efficiency Under a Round Form

(1) Unique Structural Features

Cylindrical lithium batteries stand out with their rounded shape. Common cylindrical battery types, such as 18650 and 21700, have standardized dimensions. This standardized design facilitates large-scale production and interchangeability, offering innate advantages in consumer electronics. The cylindrical structure leads to more uniform internal heat dissipation paths, promoting battery safety and stability during charge and discharge.

(2) Manufacturing Process Analysis

Shell Forming: The cylindrical battery case is usually made from metallic materials, often utilizing seamless steel tube stretching techniques. By stretching metal tubes in specific molds, a shell with defined wall thickness and length is formed. During stretching, careful control over material properties, stretching speed, and mold lubrication conditions is necessary to ensure shell dimensional accuracy and surface quality. Compared to square battery casings, cylindrical casing manufacturing is relatively straightforward, with higher production efficiency.

Cell Winding: Cylindrical battery cells commonly adopt winding techniques. Positive and negative layers and separators are alternately stacked and wound into a cylindrical cell. Controlling winding tension is critical because tension that is too high or too low will impact the cell’s internal structure and performance. Additionally, winding speed and precision directly relate to battery consistency and yield.

Sealing and Assembly: After cell winding, sealing and assembly processes follow. In sealing, resistance welding is typically used to connect the top cover and casing tightly. Resistance welding applies high current momentarily, causing high temperatures at the welding site to achieve metal fusion. The assembly process includes installing components like cell, electrolyte, and protection circuits into the casing, forming a complete battery.

(3) Application Scenarios and Limitations

Cylindrical lithium batteries dominate consumer electronics like laptops and portable power supplies. Their standardized dimensions and excellent heat dissipation make product design and manufacturing more convenient. However, in electric vehicle applications, cylindrical lithium batteries face challenges. Due to the relatively small capacity of a single cylindrical cell, meeting electric vehicle’s high energy demands requires many cells to be connected in series and parallel, increasing the complexity and cost of battery management systems. Moreover, space utilization efficiency is relatively low within battery modules, somewhat affecting the energy density of the entire battery system.

3. Soft Pack Lithium Battery: Innovation and Breakthrough of a Flexible Form

(1) The Charm of Flexible Structure

Soft pack lithium batteries differentiate themselves from square and cylindrical batteries with their unique soft packaging structure. Their casing uses aluminum-plastic composite film, a material that combines the barrier properties of metal with the flexibility of plastic. The soft package structure allows the battery to be custom-designed for different application needs, such as ultra-thin or irregular shapes, meeting stringent requirements for battery shape in some specialized scenarios. Additionally, soft pack batteries have intrinsic safety advantages; when the internal pressure is excessively high, the aluminum-plastic composite film will bulge and rupture to release pressure, avoiding serious accidents like explosions.

(2) Detailed Manufacturing Process

Aluminum-Plastic Composite Film Preparation: The aluminum-plastic composite film is a critical material for soft pack lithium batteries, with a complex preparation process. Typically, aluminum foil and plastic film are laminated with adhesives, followed by surface coating to enhance film barrier properties, heat sealability, and resistance to electrolyte corrosion. The coating material formulation and coating process significantly affect the composite film’s performance, directly related to battery lifespan and safety.

Cell Stacking: Soft pack lithium batteries often use stacking techniques to prepare cells. Unlike the winding process of cylindrical cells, stacking involves placing positive and negative sheets and separators in sequence to form the cell. This technique can increase battery energy density because the stacked structure minimizes internal voids, leading to more adequate contact between electrode materials and electrolyte. Also, the stacking process aids in improving battery charge/discharge performance and cycle life.

Heat-Sealing and Packaging: Upon completing cell stacking, cells are placed into aluminum-plastic composite films and sealed using heat sealing techniques. Heat sealing temperature, pressure, and duration are key parameters, requiring precise control to ensure good sealing effects, preventing electrolyte leakage. After packaging, post-processes such as electrolyte injection and forming are conducted to achieve stable electrochemical properties for the battery.

(3) Application Scenarios and Development Bottlenecks

Soft pack lithium batteries have widespread applications in consumer electronics, wearable devices, and some high-end electric vehicles. In wearable devices, their lightweight, flexible characteristics allow them to better conform to the human body, providing a comfortable wearing experience. In electric vehicles, the high energy density and custom design capability of soft pack batteries offer possibilities for vehicle lightweight design and space optimization. However, manufacturing processes for soft pack batteries demand high environmental humidity and cleanliness, making production quality control difficult. Moreover, the cost of aluminum-plastic composite film is relatively high, limiting the cost advantages of soft pack batteries in large-scale applications.

4. Comparison of Technical Routes and Future Prospects of Three Packaging Shapes

(1) Technical Route Comparison

From a manufacturing complexity standpoint, square lithium batteries, with their structural design and sealing process requirements, have the most complex manufacturing processes and relatively high costs; cylindrical lithium batteries have simpler manufacturing processes and high standardization, suitable for large-scale production; soft pack lithium batteries, although cell stacking is relatively simple, demands stringent requirements for aluminum-plastic composite film preparation and heat-sealing techniques, posing considerable overall process difficulty.

In terms of energy density, soft pack lithium batteries, due to their stacking process and relatively compact structure, have higher energy density under equal conditions; optimized stacking processes and structural designs allow square lithium batteries to reach high energy density; cylindrical lithium batteries, given their internal structural characteristics, have relatively lower energy density but continuously improve it through electrode material and process advances.

Regarding safety, soft pack lithium batteries have inherent advantages in pressure release; square lithium batteries ensure high safety with perfect thermal management systems and fail-proof safety designs; cylindrical lithium batteries benefit from heat dissipation advantages to improve safety, yet require enhanced protection in extreme scenarios like overcharge and short circuit.

(2) Future Prospects

With the continuous development of new energy technologies, all three lithium battery packaging shapes will keep innovating in their respective advantage fields. Square lithium batteries will further optimize their processes in electric and energy storage fields, aiming to enhance energy density and safety while reducing costs; cylindrical batteries are expected to expand their application in electric vehicles with technological advancements while consolidating their position in consumer electronics; soft pack lithium batteries, benefiting from their flexible and customizable strengths, will achieve greater breakthroughs in wearable devices and high-end electronics, along with parts of niche electric vehicle segments.

In the future, technical development routes for lithium battery packaging shapes will closely revolve around enhancing energy density, security, reducing costs, and adapting to varied application scenarios. Different lithium battery packaging shapes will compete and complement each other, jointly driving the new energy industry to new heights. In this game of shape and technology, the ultimate beneficiaries will be the whole new energy ecosystem and the vast consumer base.

 

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