The lithium-ion battery assembly is a crucial and complex step in the production of energy storage devices that power many aspects of contemporary life, such as electric vehicles, renewable energy systems, and portable electronics. From the production of the electrodes to the final cell assembly, this process consists of several complex steps, all of which are essential to the overall performance, safety, and dependability of the battery. The need for effective energy storage solutions is growing along with technology, and developing novel cell assembly methods is essential to satisfying this need. This article will examine the different procedures and techniques used in lithium-ion battery cell assembly, providing insight into the complexities of this essential procedure in the field of energy storage technology.
Separating
- Separation involves cutting electrode sheets from a continuous electrode web.
- A preliminary notching process is often applied before separation.
- During notching, the dried electrode web is unwound, and electrode contours are pre-shaped.
- Post-notching, the electrode web can be rewound into a coil or fed directly to the separation process.
- Laser or shear-cutting methods can be used for both notching and separation.
- The resulting electrode sheets are collected and transported to the next processing stage.
- In single-sheet stacking, the separator foil is similarly cut into individual sheets.
Stacking
- Stacking involves creating a cell stack with alternating layers of anode, separator, cathode, and so on.
- A cell stack can comprise as many as 120 individual layers.
- Various stacking technologies are employed to assemble the cell stack, often customized and patented by manufacturers.
- Vacuum grippers are commonly used to select, transport, and position electrode sheets.
- An industry-standard stacking variant is known as Z-folding, where anodes and cathodes are inserted into the web-shaped separator from both sides, forming a Z-shaped configuration.
- Following stacking, the cell stack is enveloped with separator material, which is then cut and affixed in place using adhesive tape.
Winding and Tab Welding
- Winding is primarily utilized in the fabrication of cylindrical cells, although flat winding is occasionally employed for prismatic cells; stacking is becoming more prevalent in prismatic cell production.
- To create a cylindrical cell’s “jelly roll,” electrode and separator webs are introduced into the process.
- Before winding, an anode tab is affixed by welding.
- Winding occurs around a central pin (for cylindrical cells) or a winding mandrel (for prismatic cells), following the same web sequence as the stacking process.
- The jelly roll is secured with adhesive tape.
- The central pin can be retained within the cell housing or removed, depending on the design.
Packaging
- The uncoated sections, or flags, of the cell stack are trimmed to a specific length.
- Each of the shortened flags is welded to an anode or cathode current collector tab, with ultrasonic welding being a common method.
- An aluminum composite foil, known as pouch foil, is unrolled and drawn into shape.
- The cell stack is placed within the pouch foil in a manner that allows the tabs to extend beyond the foil’s edge.
- The top of the cell stack is enclosed with pouch foil, sealing it airtight along three sides, creating a pouch with one open side.
- Typically, the sides where tabs extend from the pouch are also sealed.
Electrolyte Filling
- Electrolyte filling is carried out after placing the electrode stack or winding within the housing or pouch foil.
- A dosing lance is precisely positioned at the packaging opening to minimize the risk of electrolyte contamination.
- During filling, the electrolyte is introduced into the cell packaging using the dosing lance, where dosing accuracy is a crucial process parameter.
- To ensure optimal electrolyte distribution, a dynamic (under-)pressure profile is applied to the cell during and after filling, activating capillary action to fill the porous cell components.
- In some cases, (partial) filling and wetting processes may be repeated multiple times.
- Following electrolyte filling, the opening of the cell packaging is sealed.
Packaging
- An insulator ring is positioned atop the jelly roll, specifically on the side where the anode tab is located.
- The cell can is then pushed over the jelly roll, with the insulator ring now situated at the bottom of the cell can. The anode tab is connected to the cell’s bottom through resistance welding.
- Another insulator ring is added to the jelly roll, on the side where the cathode tab is positioned.
- For cells with a conical opening, the opening angle may be reduced to 90 degrees via swaging, which also leaves an imprinted bead on the housing.
- The lid assembly is welded to the cathode tab.
- Following electrolyte filling, the lid assembly is crimped onto the beaded cell cup, effectively sealing the cylindrical cell.
In conclusion, the various methods used to put together the cells in lithium-ion batteries are essential to producing high-performing energy storage systems. To guarantee the dependability and performance of these batteries, the complex procedures of separating, stacking, winding, tab welding, and electrolyte filling are carefully carried out. These methods—which are frequently modified and patented by producers—have a significant impact on how battery technology will develop in the future. From pouch configurations to cylindrical cells, they enable effective energy storage solutions for a variety of uses.
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