3. Laser cutting: laser cutting replacement of pole pieces accelerates as high rate cells drive up lug/sheet cutting volumes
3.1 Advantages: higher accuracy and lower operating costs than die-cutting tools, helping to improve efficiency and reduce costs in battery production
Laser cutting technology can be used in the manufacturing process of lithium batteries for lug cutting, slitting and diaphragm slitting. Compared to die-cutting, laser cutting offers advantages such as higher accuracy and lower operating costs, helping to reduce costs and efficiency in battery production. Conventional die-cutting inevitably causes wear, dust and burrs, which can lead to dangerous problems such as overheating, short circuits and even explosions. To avoid the dangers caused by poor quality processing of lithium batteries, cutting with a laser is more suitable. Compared to traditional mechanical cutting, laser cutting offers the advantages of no physical wear and tear, flexible cutting shapes, edge quality control, greater accuracy and lower operating costs, contributing to lower manufacturing costs, higher production efficiency and significantly shorter die-cutting cycles for new products.
3.2 Lug cutting: laser cutting is the dominant technology, unwinding speed and tension control are the main points of competition
Laser lug forming is now a mainstream technology where the process parameters, control system and cutting station design determine the speed and quality of the cut. Traditionally, mechanical die-cutting has been used to form the lugs. Mechanical die-cutting process has the limitations of fast die loss, long die change time, poor flexibility and low production efficiency, which has been increasingly unable to meet the development requirements of lithium battery manufacturing. Due to the many advantages of laser cutting technology, with the maturity of high power, high beam quality nanosecond lasers and single mode continuous fibre technology, laser lug cutting is now gradually becoming the mainstream of lug forming technology. Stable unwinding speed, tension and position control in the width direction of the pole piece. Precise and stable unwinding speed, tension and deflection control are the basis for high quality and speed pole ear forming.
3.3 Pole cutting: traditional die-cutting efficiency is the bottleneck for production line efficiency, MOPA technology has both cost and performance advantages.
The quality of disc slit and die-cut products is unstable; laser energy and cutting movement speed are the two main process parameters. There are three ways of cutting poles: disc slitting, die-cutting and laser cutting. Both disc slitting and die-cutting suffer from tool wear, which can lead to unstable processes, resulting in poor cut quality and reduced battery performance. Laser energy and cutting movement speed have a huge impact on the quality of the cut. When the laser power is too low or the movement speed is too fast, the pole piece cannot be cut completely, while when the power is too high or the movement speed is too low, the laser area of action on the material becomes larger and the size of the cut is bigger.
MOPA is a laser modulation technique that combines high peak power and high beam quality in an optimal way. The current special customised pulsed fibre laser for pole cutting can achieve a line cutting efficiency of 120m/min, a cutting burr of less than 7μm, a heat affected zone of less than 50μm and a variable frequency, variable power response time of <10μs, which effectively reduces the quality problems caused by parameter changes at the corner joints. The MOPA technology is a high power amplification of the seed light source by coupling the seed signal light and pump light with high beam quality into a double-clad fiber in a certain way.
Picosecond is the best long-term option and MOPA is currently the most cost-effective option. According to the "Analysis of laser cutting of lithium-ion power cell poles", in addition to pulse width, repetition frequency, beam pattern and laser wavelength also have an impact on cut quality. The narrow pulse width, high repetition frequency picosecond laser is therefore the ideal laser for cutting aluminium and copper foil. However, because picosecond technology is not fully mature, the price is still high and it is difficult to promote it industrially. The MOPA laser with a relatively "narrow" pulse width is the most cost-effective laser for cutting positive electrodes, and as its pulse width decreases and frequency increases, its applications will become more and more promising.
3.4 Diaphragm cutting: diaphragm laser cutting is still in the layout stage and thermal impact control is a difficult issue
Diaphragm cutting is currently based on tool cutting and there are currently two patents for laser cutting technology. Patent 1: According to the patent "A diaphragm laser cutting machine", the diaphragm is usually cut with a steel diaphragm cutter. The diaphragm cutter is less stable, the cutter needs to be replaced regularly, the diaphragm cutter is not effective, it is easy to burr or curl, the structure is complex and it is not easy to debug and maintain. These problems can be solved by laser cutting. Patent 2: According to the patent "Laser Cutting Equipment for Lithium Battery Diaphragm Production", the diaphragm wound by the two diaphragm winding units is alternately switched by the laser cutting unit, which achieves the function of automatic and uniform cutting of the diaphragm, avoiding the phenomenon of de-powdering, picking, shredding and unbroken cutting during the cutting process, and facilitating the practical use in batch production lines.
Thermal impact control is still a difficult issue, and UV lasers exist as a possible alternative to traditional die-cutting. The melting points of PP and PE films for lithium-ion battery separators are different, with PE diaphragms at around 130°C and PP diaphragms at around 160°C. In areas such as thin film processing of non-metallic materials, high energy UV photons directly break molecular bonds on the surface of non-metallic materials, causing the molecules to break away from the object, without generating a high heat reaction, and therefore often referred to as "cold processing". In the diaphragm cutting process, which is still dominated by die-cutting, the lower melting point of the diaphragm makes it difficult to control the thermal impact of laser cutting, and the UV laser has the advantage of "cold processing" as an alternative to traditional die-cutting.
3.5 Stacking process technology: expected to lead to increased demand for laser cutting.
Demand for laser pole lug and pole piece cutting in the square stack process is expected to increase. In the square stack method, because the positive and negative electrodes are isolated from each other, each electrode is fitted with an ear, which is then welded together to form the final positive and negative electrodes, but in the winding method, in order to reduce the number of layers, only one ear is fitted at a time, usually half the total. Based on the above, we judge that the laminating process doubles the number of lugs compared to the winding process and the demand for lug cutting in the laminating process is expected to rise, while the laminating process requires multiple cutting of the positive and negative laminations (thermal lamination process) and the demand for lug cutting will also increase.
4. Other applications: laser cleaning, laser marking
4.1 Laser cleaning: avoiding problems such as cleaning damage and improving battery manufacturing processes
Laser cleaning of the poles before coating can effectively avoid the damage caused by the original wet ethanol cleaning. Cell welding before the laser cleaning using pulsed laser substrate heat vibration expansion to overcome the surface adsorption of contaminants from the substrate to achieve the effect of decontaminatio. Laser cleaning of insulating plates and end plates can be carried out during the battery assembly process to clean the dirty surface of the cells, roughen the surface of the cells and improve the adhesion of the paste or glue coating. Before electrode coating: The positive and negative electrodes of Li-ion batteries are coated with Li-ion battery positive and negative materials on a thin metal strip, which needs to be cleaned when coating electrode materials. Laser cleaning machine can effectively solve the above problems.
The thermal expansion causes the contaminant or the substrate to vibrate, thus causing the contaminant to overcome the surface adsorption force and to break away from the substrate surface, thus removing the stain from the surface of the object. This method effectively removes dirt, dust, etc. from the end surfaces of the electrodes and prepares the battery for soldering, thus reducing defective soldering. Battery assembly process: In order to prevent safety accidents in lithium batteries, it is generally necessary to apply adhesive treatment to the lithium battery cells in order to play the role of insulation, to prevent short circuits and to protect the wiring and prevent scratches. Laser cleaning of insulation boards and end plates cleans the surface of the core, roughens the surface of the core and improves the adhesion of the adhesive or glue coating, and does not produce harmful pollutants after cleaning, which is an environmentally friendly green cleaning method, which is becoming more and more important in the global high concern for environmental protection.
4.2 Laser laser marking: more efficient and secure information tracking possibilities for power cells
The disadvantages of traditional marking technology are obvious. There are several traditional marking techniques, namely inkjet marking, steel needle engraving marking, sticker marking, etc., but all these methods have corresponding process defects. For example, inkjet marking requires consumables, after spraying the ink is not dry for other processes will have the possibility of colour loss, etc.; steel needle engraving speed is slow processing efficiency is low, etc., thus the emergence of new technology is laser marking technology.
Secondly, safety has been improved in varying degrees. In order to better control product quality and trace the entire production information of lithium batteries, including raw material information, production process and technology, product batches, manufacturers and dates, key information needs to be stored in the QR code and marked on the battery. Traditional inkjet coding technology is prone to friction and loss of information over time, while laser marking is permanent, anti-counterfeiting, highly accurate, wear-resistant, safe and reliable, and can provide the best solution for product quality tracking.
