The composite current collector is a composite material in which copper/aluminum molecules are stacked on both sides of the raw material film such as PET as the base film through vacuum coating and other processes.
1. The concept of composite current collectors
Compared with the traditional current collector, the composite current collector adopts the "metal-polymer material-metal" three-layer composite structure, and forms nano-scale metal on the surface of the polymer PET/PP film by vacuum evaporation, magnetron sputtering, etc. The metal layer deposition is thickened to more than 1 μm by electroplating with water.
Under the trend of lightening and thinning, PET composite copper/aluminum foil can achieve a composite current collector with a thickness of less than 8 μm, which plays an important role in the lightweight of power batteries. Power battery has large market demand and there are so many excellent power battery companies. You can get into our website and read the article of top 15 power battery companies.
Composite current collector has the advantages of high safety, high energy density, and low cost. The middle layer is made of polymer insulating material. The polymer is not easy to break and has strong puncture resistance, which can effectively avoid short circuit in the battery and the resulting heat runaway and battery spontaneous combustion. The composite current collector has both flame retardant function, which can greatly improve the safety of the battery.
PET/PP polyester material is lighter in weight. Due to the difference in material density, 6.5-micron PET composite copper foil has a significant weight reduction effect compared to 4.5-micron pure copper foil, and has a significant effect on improving battery energy density. The production process of polyester materials is mature, and the unit cost is lower than that of copper/aluminum metals.
After large-scale mass production, it will have cost advantages. Taking copper foil as an example, a 1GWh battery uses 650 tons of 6μm ordinary copper foil, the density of copper is 8900kg/m3, and the corresponding area is about 12 million square meters. If 470 tons of 4.5μm copper foil is used, the corresponding area is 11.74 million square meters Meter.
If 12 million square meters of 6μm composite copper foil (4μm pet base film + 2μm copper layer) is used, the material cost is 39 million/GWh and 24.82 million RMB/GWh. Problems with composite current collector include low production efficiency and impact on battery output power. Due to the complex magnetron sputtering and evaporation technology, the production efficiency and yield of composite metal foils are not as good as those of traditional foils.
For example, magnetron sputtering has the problem of low target utilization rate, which affects the uniformity of the film. In addition, new processes such as transfer welding need to be added, which increases the manufacturing cost of the battery. The PET and metal of the composite foil have a large contact resistance. At the same time, due to the introduction of media such as flame retardants, the resistance of the battery will increase, and the battery power will decrease slightly.
2. Existing status of composite current collector industry
Chinese enterprises have successively deployed, and the entire industry chain has developed in concert. With the improvement of the production process, many Chinese enterprises have begun to set foot in the field of composite current collector, and the equipment, base film materials and manufacturing links have a good momentum of development.
- On the product side, new material manufacturers extend the composite current collector business, and traditional copper foil companies follow. Chongqing Jinmeiji fluid products MA and MC have entered the stage of mass production; Baoming Technology plans to invest in the construction of a lithium battery composite copper foil production base in Ganzhou Economic and Technological Development Zone, with a planned total investment of 6 billion RMB. The PET copper foil samples developed by Wanshun New Materials in 2021 have been sent to downstream battery companies for verification and are in the stage of optimizing the production process.
- On the equipment side, composite current collector equipment includes magnetron sputtering equipment and PET electroplating equipment. Chinese manufacturers are developing rapidly in the field of electroplating equipment. With its technical advantages in the field of electroplating equipment, KSDW has overcome the high technical index requirements of ultra-thin, ultra-light, non-deformed and non-perforated coating materials, and has formed its own proprietary technology. It has achieved mass production of two generations of PET coating equipment. At present, it is the only company in China that can realize mass production of PET copper plating equipment. After the introduction of vacuum plating technology, KSDW started research and development, and is expected to manufacture magnetron sputtering equipment.
- On the material side, the optical-grade base film has high technical barriers and is highly dependent on Japanese and Korean manufacturers (Toray, Mitsubishi, SKC, etc.). As the world's leading BOPET manufacturer, Shuangxing New Materials is used in the PET base film of composite current collector, and the cost has obvious advantages over foreign manufacturers, and it is expected to replace foreign production capacity. At the same time, the company has gradually formed an integrated production capacity of PET copper foil on the basis of 4.5-micron substrates, which has a strong cost advantage. At present, the terminal products have been sent to many manufacturers for inspection and are in the testing and verification stage.
3. Composite current collector production process
Traditional aluminum foil and copper foil are mainly produced by rolling or electrolysis process, while composite aluminum/copper foil is produced by magnetron sputtering and vacuum evaporation on the surface of plastic film with a thickness of 2μm to make a layer of 50-80nm metal. Then, the metal layer is thickened to 1 μm by water electroplating to make a composite metal foil with a total thickness of about 6-8 μm to replace the traditional current collector of 4-13 μm.
① Composite aluminum foil processThe preparation process of composite aluminum foil is more difficult than the traditional aluminum foil process. Its main production process is specifically primary evaporation, secondary evaporation, slitting and so on. Taking Chongqing Jinmei as an example, the composite aluminum foil products are deposited with aluminum on both sides of the PET base film. Vacuum evaporation coating. It is one of the process of making composite current collector.
② Traditional copper foil craftsmanship
The traditional copper foil manufacturing process can be divided into two methods: electrolysis and calendering. The current mainstream is the electrolysis method, which has simple equipment and lower cost. The main production processes of the electrolytic method are copper melting, raw foil, post-processing, and slitting. It's very different from the composite current collector.
The copper-dissolving process is to use sulfuric acid and deionized water to make the copper material into a copper sulfate solution to provide an electrolyte that meets the technological standards for the raw foil process. The raw foil process is that in the electrolytic cell of the raw foil machine, the copper sulfate electrolyte is deposited by the copper ions under the action of direct current to make the original foil.
③ Composite copper foil process
The production process of composite copper foil is similar to that of composite aluminum foil. However, the physical vapor deposition method (PVD) is mainly used to sputter a layer of tens of nanometers of metal on the PET surface with a thickness of 4.5 μm. The copper thickness is about 900nm. After that, the copper foil goes through water washing, anti-oxidation treatment, drying and slitting. For acid ion replacement, copper balls are generally placed in an anode bag made of titanium blue, and then the entire anode bag is immersed in the acid agent.
The membrane surface is used as the cathode, and the metal layer on the membrane surface is used as the cathode. Running between the rollers, the film surface is immersed in the agent, reacts and performs ion migration and replacement. After electrons are obtained on the film surface, a copper layer is formed on the film surface, and the thickness of the copper accumulation layer formed on the film surface is 900nm.
4. Composite current collector industry chain
Sputtering refers to the phenomenon in which charged particles bombard a solid surface (target), causing solid atoms or molecules to be ejected from the surface. The technology of depositing thin films by sputtering is sputtering coating. Specifically, the inert gas (usually argon) generates glow discharge to generate charged ions.
The charged ions are accelerated by an electric field and then hit the surface of the target, causing the target to The atoms are bombarded and fly out, and at the same time, secondary electrons are generated, and then hit the gas atoms to form more charged ions. The target atoms carry enough kinetic energy to reach the surface of the material to be plated (substrate) for deposition.
① Vacuum depositionVacuum evaporation refers to a process in which the coating material (or film material) is evaporated and vaporized by a certain heating evaporation method under vacuum conditions, and the particles fly to the surface of the substrate to condense and form a film. Evaporation is an early and widely used vapor deposition technology, which has the advantages of simple film formation method, fast speed, easy operation, high film purity and density, and unique film structure and performance.
② Water electroplatingWater electroplating refers to the process of plating one or more metals (non-metals) on a metal surface under the action of an external current in an electrolyte solution. Specifically, the parts are immersed in a solution of metal salts as the cathode, and the metal plate is used as the anode. After connecting the DC power supply, the desired coating is deposited on the parts. Water electroplating is widely used and suitable for specific application scenarios. The technology of water electroplating has been relatively mature and stable, and because the process is relatively simple, the requirements from equipment to environment are not as harsh as vacuum plating, and it is widely used.
③ Basement membraneIn the composite copper/aluminum foil, the metal foil needs to be directly attached to the base film, which is a typical technology-intensive industry. The importance of the base film involves technical indicators such as molecular structure, strength, flatness, uniform thickness, and ductility.
5. Analysis of major copper foil companies
- KSDW: KSDW is a major supplier of PET electroplating equipment in China and has a first-mover advantage. By expanding the application of the existing roll-to-roll vertical continuous electroplating technology system in the film material industry, the company conducts independent research and development and innovation, and produces equipment that can produce high-quality PET copper foil. At present, only one company in China, KSDW, has achieved mass production of PET copper plating equipment.
- Wanshun New Materials: Wanshun New Materials is a national high-tech enterprise integrating the three major businesses of environmental protection packaging materials, high-precision aluminum foil and functional films. The company has been deeply involved in the packaging material industry and has gradually developed into a leading enterprise with leading advantages in China.
- Baoming Technology: The company's main business focuses on flat panel display devices, and the layout of composite copper foil business. You can read our top 10 lithium battery copper foil companies article to find if Baoming is on the list. Baoming Technology's main products are LED backlight and capacitive touch screen, which are key supporting components of flat panel displays and are widely used in smart phones, tablet computers, automotive displays and other fields.
- Double star new material: The company is the world's leading BOPET manufacturer and has entered the field of composite copper foil manufacturing. The main product of Shuangxing New Materials is polyester film materials. It has formed an influential industrial cluster of polyester functional film materials, optical film production and deep processing in China. The product line covers more than 60 series. market. Through years of technical accumulation, the company has realized the integration of the industrial chain of "PET chips - base film - application film", and is one of the few enterprises in China that has the ability to produce large-scale base films.