As the core component of lithium batteries, the precision of the production process of lithium battery cells directly determines their performance, quality, and production efficiency. From raw material pretreatment to the production of finished battery cells, the entire production process involves multiple complex and interrelated processes, and every detail has a profound impact on the quality of the final product.
1 Polar manufacturing: Building a solid foundation for battery cell performance
(1) Mixing and Stirring: The Beginning of Material Homogenization
Mixing and stirring is the primary process in the manufacturing of polarizer, and it is also the foundation for the smooth development of subsequent processes. At this stage, it is necessary to mix the solid active materials of the positive and negative electrodes with solvents, conductive agents, binders, etc. in precise proportions, and then thoroughly stir them with a vacuum mixer to make them a uniform slurry material. Taking Honeycomb Energy as an example, it adopts a 2300L large capacity PD stirring high-speed dispersion process, and with high-speed dispersion technology, the homogenization time is shortened by 40%. To strictly control magnetic foreign objects (especially metal foreign objects), one magnetic foreign object adsorption device is set up in the powder stage, and three additional devices are added in the slurry stage. The coating machine also comes with one device, which can strictly control the amount of magnetic foreign objects within ≤ 200ppb, and the magnetic strength of the magnetic rod can reach up to 12000 Gauss (some links in the slurry system reach 17000 Gauss). This series of operations ensures the high purity and uniform mixing of raw materials, laying the foundation for the high-quality completion of subsequent coating, rolling and other processes.
(2) Coating: the core link in shaping the quality of polarizer
The coating process involves uniformly coating the stirred slurry onto a metal foil (aluminum foil for the positive electrode and copper foil for the negative electrode), and then drying it to produce positive and negative electrode sheets. This process plays a decisive role in the quality of battery cells, and factors such as uniformity, consistency, alignment, baking stability, adhesive diffusion, and surface density stability directly affect battery performance. Honeycomb Energy uses a double-layer folding extrusion coating machine, each equipped with 3 sets of beta ray surface density online detection systems, which can control the accuracy of coating surface density within ± 1.5%. At the same time, set up 2 sets of online CCD coating width detection devices for A and B surfaces to ensure that the coating width and AB surface misalignment are ≤ 0.5mm. In addition, three 8000 Gauss magnetic demagnetization devices are installed at the foil and coated electrode, and a thousand level small environment is installed at the coating head/tail to effectively control the mixing of foreign objects during coating and ensure the quality of the electrode. It is worth mentioning that its 12 section independently adjustable temperature suspension drying oven balances the transfer of polar plates through two opposing airflow streams, achieving polar plate suspension drying transfer and avoiding product contamination caused by contact during the drying process.
(3) Roll pressing, slitting, and die-cutting: refining the specifications and shapes of polarizer sheets
The rolling process aims to compact the coated electrode sheet to the design thickness, especially for high-capacity cells, which have high requirements for the compaction density of the electrode sheet. By high-pressure rolling extrusion, the active substance is tightly combined with aluminum foil and copper foil to achieve thickness and length that meet technical standards. Honeycomb Energy adopts a hot pressing process (80 degrees) in the positive electrode roller pressing stage, with a temperature control accuracy of ± 1 ° C. At the same time, it integrates foil IHA (electromagnetic pulse heating) online processing technology to effectively solve the problem of white wrinkles in the foil, and uses infrared drying equipment to quickly remove moisture from the electrode. The negative electrode roller pressing fully considers the future application of silicon-based negative electrodes, adopting a double roller continuous roller pressing process and strictly controlling the tension. Slitting is the process of continuously cutting a wide roll of pole pieces into several narrow pieces of the desired width, using AGV to automatically dock and load, and assisted by a power arm for unloading, achieving contactless production. After secondary slitting, the exposed foil is identified through online defect detection, and the pole pieces are demagnetized online using a magnetic rod. Die cutting utilizes hardware die-cutting equipment to punch the sliced electrode coil into the actual required volume of the battery. The key to this process is to strictly control burrs and ensure that the edge quality of the electrode meets the standard.
2 Cell Assembly: Building a Complete Cell Architecture
(1) Winding and laminating: forming the internal structure of the battery cell
Winding and stacking are the two main processes for processing polarizer into battery cells. The winding process has high production efficiency, and the positive and negative electrodes and separators are wound into battery cells in a specific order through equipment; The stacking process involves interlocking multiple layers of electrodes and separators to form a battery cell. Its advantages lie in uniform contact between the electrodes, stable current distribution, and outstanding performance in improving the energy density and cycle life of the battery cell. The swinging laminating technology of Honeycomb Energy can achieve a single laminating speed of up to 0.6s. The second phase plans to increase the speed to 0.45s, and the third phase plans to develop ultra high speed laminating equipment with a speed of 0.25s to enhance the cost and efficiency advantages of laminating technology in large-scale production. After the lamination is completed, HI-POT insulation testing is required (100% full inspection is carried out in three processes: lamination, pre welding, and one helium inspection), and X-RAY testing equipment is used to perform 100% alignment testing on the four corners of each pole group to ensure the accuracy and correctness of the internal structure of the battery cell.
(2) Shell insertion, welding, and liquid injection: encapsulation and activation of battery cells
In the packaging process, square shell batteries use square aluminum shells, while soft pack batteries use aluminum-plastic films. The rolled or laminated battery cells are placed inside, and then the battery cover plate is welded and packaged. Taking square shell battery cells as an example, after completing the assembly of the battery cells, ultrasonic welding and laser welding of the adapter plates need to be carried out to ensure a firm and reliable connection, and the metal welding slag generated during the welding process should be strictly cleaned. The laser welding of the top cover adopts dual light path welding technology to ensure welding strength and sealing. After welding, a helium mass spectrometer leak detector is used for 100% airtightness testing to ensure that the inside of the battery cell is in a sealed environment and prevent external impurities such as moisture and oxygen from entering. The injection process is to inject electrolyte into the interior of the battery cell to activate the electrochemical reaction of the battery cell. The injection volume and speed need to be strictly controlled, and after injection, processes such as settling, chemical transformation, and volume separation need to be carried out to achieve a stable performance state of the battery cell, ultimately completing the production and manufacturing of lithium battery cells.