Not long ago, there was a qualitative breakthrough in the cathode cutting process that had plagued the industry for so long.
Stacking and winding processes：
In recent years, as the new energy market has become hot, the installed capacity of power batteries has increased year by year, and their design concept and processing technology have been continuously improved, among which the discussion on the winding process and laminating process of electric cells has never stopped. At present, the mainstream in the market is the more efficient, lower cost and more mature application of the winding process, but this process is difficult to control the thermal isolation between the cells, which can easily lead to local overheating of the cells and the risk of thermal runaway spread.
In contrast, the lamination process can better play the advantages of large battery cells, its safety, energy density, process control are more advantageous than winding. In addition, the lamination process can better control the cell yield, in the user of new energy vehicle range is increasingly high trend, the lamination process high energy density advantages more promising. At present, the head of the power battery manufacturers are research and production of laminated sheet process.
For potential owners of new energy vehicles, mileage anxiety is undoubtedly one of the key factors influencing their choice of vehicle. Especially in cities where charging facilities are not perfect, there is a more urgent need for long range electric vehicles. At present, the official range of pure electric new energy vehicles is generally announced at 300-500km, with the real range often discounted from the official range depending on the climate and road conditions. The ability to increase the real range is closely related to the energy density of the power cell, and the lamination process is therefore more competitive.
However, the complexity of the lamination process and the many technical difficulties that need to be solved have limited the popularity of this process to some extent. One of the key difficulties is that the burrs and dust generated during the die-cutting and laminating process can easily cause short circuits in the battery, which is a huge safety hazard. In addition, the cathode material is the most costly part of the cell (LiFePO4 cathodes account for 40%-50% of the cost of the cell, and ternary lithium cathodes account for an even higher cost), so if an efficient and stable cathode processing method cannot be found, it will cause great cost wastage for battery manufacturers and limit the further development of the lamination process.
Hardware die-cutting status quo - high consumables and low ceiling
At present, in the die-cutting process before the laminating process, it is common in the market to use hardware die punching to cut the pole piece using the extremely small gap between the punch and the lower tool die. This mechanical process has a long history of development and is relatively mature in its application, but the stresses brought about by the mechanical bite often leave the processed material with some undesirable characteristics, such as collapsed corners and burrs.
In order to avoid burrs, hardware die punching has to find the most suitable lateral pressure and tool overlap according to the nature and thickness of the electrode, and after several rounds of testing before starting batch processing. What's more, hardware die punching can cause tool wear and material sticking after long hours of work, leading to process instability, resulting in poor cut-off quality, which can ultimately lead to lower battery yields and even safety hazards. Power battery manufacturers often change the knives every 3-5 days to avoid hidden problems. Although the tool life announced by the manufacturer may be 7-10 days, or can cut 1 million pieces, but the battery factory to avoid batches of defective products (bad need to be scrapped in batches), often will change the knife in advance, and this will bring huge consumables costs.
In addition, as mentioned above, in order to improve the range of vehicles, battery factories have been working hard to improve the energy density of batteries. According to industry sources, in order to improve the energy density of a single cell, under the existing chemical system, the chemical means to improve the energy density of a single cell has basically touched the ceiling, only through the compaction density and the thickness of the pole piece of the two to do articles. The increase in compaction density and pole thickness will undoubtedly hurt the tool more, which means that the time to replace the tool will be shortened again.
As the cell size increases, the tools used to perform die-cutting also have to be made larger, but larger tools will undoubtedly reduce the speed of mechanical operation and reduce cutting efficiency. It can be said that the three main factors of long-term stable quality, high energy density trend, and large size pole cutting efficiency determine the upper limit of the hardware die-cutting process, and this traditional process will be difficult to adapt to future development.
Picosecond laser solutions to overcome positive die-cutting challenges
The rapid development of laser technology has shown its potential in industrial processing, and the 3C industry in particular has fully demonstrated the reliability of lasers in precision processing. However, early attempts were made to use nanosecond lasers for pole cutting, but this process was not promoted on a large scale because of the large heat-affected zone and burrs after nanosecond laser processing, which did not meet the needs of battery manufacturers. However, according to the author's research, a new solution has been proposed by companies and certain results have been achieved.
In terms of technical principle, the picosecond laser is able to rely on its extremely high peak power to instantly vaporise the material due to its extremely narrow pulse width. Unlike thermal processing with nanosecond lasers, picosecond lasers are vapour ablation or reformulation processes with minimal thermal effects, no melting beads and neat processing edges, which break the trap of large heat affected zones and burrs with nanosecond lasers.
The picosecond laser die-cutting process has solved many of the pain points of the current hardware die-cutting, allowing for a qualitative improvement in the cutting process of the positive electrode, which accounts for the largest proportion of the cost of the battery cell.
1. Quality and yield
Hardware die-cutting is the use of the principle of mechanical nibbling, cutting corners are prone to defects and require repeated debugging. The mechanical cutters will wear out over time, resulting in burrs on the pole pieces, which affects the yield of the entire batch of cells. At the same time, the increased compaction density and thickness of the pole piece to improve the energy density of the monomer will also increase the wear and tear of the cutting knife.The 300W high power picosecond laser processing is of stable quality and can work steadily for a long time, even if the material is thickened without causing equipment loss.
2. Overall efficiency
In terms of direct production efficiency, the 300W high power picosecond laser positive electrode production machine is at the same level of production per hour as the hardware die-cutting production machine, but considering that hardware machinery needs to change knives once every three to five days, which will inevitably lead to a production line shutdown and a re-commissioning after the knife change, each knife change means several hours of downtime. The all-laser high-speed production saves the time of tool change and the overall efficiency is better.
3. Flexibility
For power cell factories, a laminating line will often carry different cell types. Each changeover will take a few more days for the hardware die-cutting equipment, and given that some cells have corner punching requirements, this will further extend the changeover time.
The laser process, on the other hand, does not have the hassle of changeovers. Whether it is a shape change or a size change, the laser can "do it all". It should be added that in the cutting process, if a 590 product is replaced by a 960 or even a 1200 product, the hardware die-cutting requires a large knife, while the laser process only requires 1-2 additional optical systems and the cutting efficiency is not affected. It can be said that, whether it is a change of mass production, or small-scale trial samples, the flexibility of the laser advantages have broken through the upper limit of the hardware die-cutting, for battery manufacturers to save a lot of time.
4. Low overall cost
Although the hardware die cutting process is currently the mainstream process for slitting poles and the initial purchase cost is low, it requires frequent die repairs and die changes, and these maintenance actions lead to production line downtime and cost more man-hours. In contrast, the picosecond laser solution has no other consumables and minimal follow-up maintenance costs.
In the long run, the picosecond laser solution is expected to completely replace the current hardware die-cutting process in the field of lithium battery positive electrode cutting, and become one of the key points to promote the popularity of the laminating process, just like "one small step for the electrode die-cutting, one big step for the laminating process". Of course, the new product is still subject to industrial verification, whether the picosecond laser's positive die-cutting solution can be recognized by the major battery manufacturers, and whether the picosecond laser can really solve the problems brought to the users by the traditional process, let us wait and see.
Post time: Sep-14-2022