01Advantages of composite copper foil
Copper foil, as the negative electrode collector of lithium batteries, mainly plays the role of carrying negative electrode active materials and collecting current. Traditional copper foil uses 99% high-purity electrolytic copper as the main material, which has the advantages of strong conductivity, good heat dissipation, and low manufacturing cost. However, there are also problems such as high mass ratio and high raw material cost. There are mainly two points:
1. The traditional copper foil accounts for about 13% of the total weight of the lithium battery, but it does not provide any capacity during the charging and discharging process of the battery, so there is room for further improvement in the quality and energy density of the battery;
2. When punctured, it is easy to short-circuit internally, causing thermal runaway and even spontaneous combustion of the battery, so there are serious safety hazards.
Compared with the traditional lithium battery copper foil, the new type of composite copper foil, the most important thing is that it can solve the safety problem. In case of short circuit, the high temperature will quickly melt the outer copper plating, and the inner material can be The insulation causes the battery to be directly disconnected, which greatly reduces the spontaneous combustion of the electric car.
In addition, under the same thickness, the unit weight of the composite current collector copper foil is reduced by 55%, which is expected to increase the energy density by 5%-10%. The density of polymer film is much smaller than that of metal copper. According to our calculations, the unit area weight of mainstream 6.5μm composite copper foil products is 55% lower than that of 6μm traditional copper foil; and the weight of composite copper foil has obvious advantages. μm, its weight is lower than that of composite copper foil. According to BYD's patent test, the composite current collector can increase the energy density of the battery by 2.6%-6.1%. BYD's patent shows that the use of positive and negative electrode composite current collectors increases the energy density of the battery by 6.10%; only considering the use of composite copper foil for negative electrode current collectors, the energy density also increases by 3.30%.
Regardless of weight or energy density of the battery, composite copper foil is ahead of traditional copper foil, so it is only a matter of time before composite copper foil replaces traditional copper foil, similar to the replacement of old-fashioned TOPCON and HJT in photovoltaic cells Photovoltaic sheet, so the incremental space of composite copper foil in the future is worth looking forward to.
02 Process of composite copper foil
The composite copper foil process route is more complex and diverse. The current industry is dominated by the PET+ two-step process. The difficulty of mass production lies in equipment and yield.
(1) Material side: PET has higher tensile strength and simple process and has become the mainstream choice; PP battery side has better performance and is more favored by battery factories. It is expected to increase the volume after the process is mature.
The promotion of PET film is rapid. Currently, the industry is dominated by PET film. In the future, it is expected that PP film and PET film will run in parallel. Due to the low difficulty of the process, the current industrialization of PET film is progressing rapidly, which is the main choice of companies in the current industry. However, PP film has weak bonding force and tensile strength in magnetron sputtering, and is still being modified. It is expected that as the composite foil process matures, PP film will be selected as the composite copper foil base film due to its advantages in battery applications. proportion will increase.
(2) Production end: In practice, there are one-step, two-step and three-step methods. The one-step method is divided into all-wet method and all-dry method, with excellent product performance and high yield rate, but it is still in the stage of laboratory research; the two-step method includes magnetron sputtering + water electroplating links, with high maturity; the three-step method increases the vacuum Evaporation improves productivity and uniformity at the expense of yield. Most manufacturers currently use a two-step approach.
l From the perspective of performance: the vacuum evaporation method has larger particles, limited improvement in uniformity, and the risk of scalding the base film. Overall, the performance of the two-step method is better.
l From the point of view of yield rate: the increase in the number of steps will bring new process control and reduce the yield rate, and vacuum evaporation has the problem of high temperature scalding the PET substrate.
l From the perspective of production efficiency: the deposition efficiency of vacuum evaporation is higher, and it can be deposited to the thickness of the seed copper layer faster, so the production speed of the three-step method is faster.
l From the perspective of production cost: the three-step method adds new evaporation equipment (estimated to be 8 million yuan/set), and the cost is higher than that of the two-step method.
Companies in the industry mainly use the three-step method, mainly Chongqing Jinmei and Wanshun New Materials, while most other companies such as Baoming Technology, Shuangxing New Materials, and Fangbang choose the two-step method. With the maturity of the process, the cost is low and the quality is good. The two-step method with a high rate is expected to become the mainstream choice in the future.
(3) Battery production end: seam welding has been added, and tab welding has been changed to ultrasonic welding.
Ultrasonic welding is a solid-phase welding method. The connection between the weldments is realized through the high-frequency elastic vibration of the acoustic system and the clamping action of the static pressure between the workpieces.
Ultrasonic welding can only be used for PET copper foil tab welding. The melting points of PET and copper are different, and the wavelength of laser welding cannot meet the melting points of plastics and metals at the same time. Therefore, the physical characteristics of ultrasonic friction are used to weld the PET layer with the copper and aluminum materials. Specifically in battery production:
lAdd seam welding (ultrasonic welding pretreatment) before rolling: PET is not conductive, if only the tab is welded to one copper layer, the other copper layer is blocked by pet and cannot be conducted, so seam welding (up and down) is required first Add another layer of copper foil) to prepare for the tab welding link.
l Change the tab welding to ultrasonic final welding: the power is higher, and the welding strength and welding effect are guaranteed. In the end, the film production company led the ultrasonic welding and film production equipment into a winding machine.
03 Composite copper foil industry chain and related stocks
The industrial chain is divided into upstream materials, midstream copper foil manufacturing, and downstream battery applications.
It is currently in the initial stage of industrialization, and the layout of equipment links is relatively concentrated. Among them, Tengsheng Technology leads the front magnetron sputtering equipment, occupying half of the country; the middle water electroplating equipment is a brand-new equipment, and only Dongwei Technology has achieved mass production; Branson is on an equal footing.
The barriers to magnetron sputtering equipment are higher, and the overall equipment manufacturers may have a whole-line layout trend in the future. The layout of the entire equipment line can improve the yield rate, play a synergistic effect, and find suitable parameters to achieve maximum production capacity. At present, in addition to the layout of equipment factories with all-in-one machines, many single-equipment manufacturers have begun to consider the layout of the entire line. For example, Dongwei Technology has deployed magnetron sputtering equipment from water electroplating equipment upwards. Next layout.
At present, the PET copper foil is in the 0-1 stage and the 1-N stage. Let’s first look at the verification progress, which reflects the technical strength and the ability to take orders in the future. Jinmei has the deepest layout, the fastest downstream verification speed, and is in the first echelon. Baoming Technology has the fastest verification among the second-tier battery factories, and is in the 1.5 echelon. The progress is ahead, in the second echelon.