Lithium ion copper foilAt present, as the negative current collector of lithium batteries, due to the high amount of copper used in lithium battery copper foil, the material cost is greatly affected by copper prices, and there are bottlenecks in battery safety and energy density. Power battery manufacturers have the motivation and demand to seek new alternative materials for cost, safety, and energy density considerations. Based on the characteristics of saving about 2/3 of raw material costs, higher safety and energy density, PET copper foil is in line with downstream development laws and is expected to replace traditional copper foil to a certain extent, achieving a process from 0 to 1.
1. What is composite copper foil? Composite copper foil is a battery current collector material with a sandwich like shape, in which the middle layer is a 4.5 μ m thick PET and PP base film, and the outer layer is coated with 1 μ m thick copper. Therefore, from a structural perspective, compared to the current traditional 6 μ m lithium copper foil, PET copper foil replaces metal copper with a lower cost PET base film, thereby reducing copper usage by 2/3 and achieving the goal of reducing raw material costs.
2. Why is composite copper foil attracting market attention? Composite copper foil has four major advantages and is expected to replace traditional copper foil.
1) High safety: Battery spontaneous combustion is caused by internal short circuit due to uncontrolled heating. Traditional copper foil is prone to breakage under pressure and can easily puncture the diaphragm, causing internal short circuits and leading to uncontrolled heating. And PET material has a flame retardant effect due to the presence of a membrane in the middle, which makes the polymer less prone to breakage. Even if a fracture occurs, 1 μ m copper plating cannot meet the strength standard for piercing the separator, thereby avoiding the risk of internal short circuit and improving battery safety.
2) Improving energy density: PET material is lighter than metallic copper, so the overall weight of composite copper foil is smaller, which can effectively reduce battery weight and improve battery energy density.
3) Long lifespan: During battery charging and discharging, compared to metals, polymer materials have a lower expansion rate, a more uniform surface, and a lifespan that is 5% longer than traditional copper foils.
3. What are the current barriers to PET copper foil? We will start with the production process of PET copper foil and explore the difficulties and barriers currently encountered in the industry. According to the environmental impact assessment report of Chongqing Jinmei, we can categorize the manufacturing process into the following three steps. Let's take the two-step method as an example:
1) Raw material and equipment procurement: PET copper foil mainly purchases PET base film with a thickness of 4.5 μ m, copper target material, auxiliary materials and other raw materials. At present, the main equipment for producing PET copper foil in the industry are magnetron sputtering equipment/electron beam evaporation equipment, water and electricity plating, etc. The equipment for magnetron sputtering is mostly imported, and the equipment for water plating is mostly imported.
2) PVD coating method: Currently, metalization on the base film is mainly achieved through magnetron sputtering and evaporation coating. In a vacuum environment, a copper film of about 50nm is first deposited on the base film using magnetron sputtering equipment. The specific principle is that electrons collide with argon atoms during the leap process under vacuum conditions (during which pure argon gas is introduced), ionizing and producing Ar and new electrons; Constrained by the magnetic field on the back of the magnetron sputtering target material, most electrons are confined around the magnetic field, while Ar accelerates towards the Cu target under the action of the electric field and bombards the surface of the Cu alloy target with high energy, causing sputtering of the target material. In the sputtered particles, neutral target atoms or some ions deposit on the base film to form a thin film with a thickness of about 50nm. During this process, the utilization rate of copper target material is relatively low, at 32.12%.
3) Ion exchange process/water electroplating: Metal exchange is performed through an ion exchange machine to thicken the metal layer. The metal layer on the membrane surface is used as the cathode, and the membrane surface passes through the lower rollers of the reagent tank. The membrane surface undergoes ion migration and displacement reaction in the reagent, and after obtaining electrons on the membrane surface, a copper layer is formed on the membrane surface. The thickness of the copper layer is about 1 μ m.
During this process, the utilization rate of copper balls and oxygen free copper corners is around 80%.
In summary, we believe that the current barriers to PET copper foil mainly lie in the process and equipment aspects.
1) Process barrier: Magnetron sputtering method is a difficult step in the process, that is, how to evenly and tightly coat copper on an extremely thin base film. This requires continuous trial and error of the sputtering path and sputtering force, otherwise problems such as uneven sputtering, breakdown of the base film/powder loss may occur. The subsequent thickening copper plating process actually comes from the PCB electroplating process. Unlike the PCB electroplating process, after the base film is metalized, the copper attached to the base film is thinner (PET copper film thickness is around 50nm, PCB copper film thickness is in the μ m level), so higher requirements are placed on tension control and uniformity.
2) Equipment barriers: The equipment for vacuum magnetron sputtering mainly adopts overseas equipment, while equipment manufacturers such as Dongwei Technology mainly use water plating thickening equipment. Due to PET copper foil being an emerging product, equipment may require new research and development as well as renovation. The main difficulty lies in how the equipment can meet the requirements of good uniformity, no deformation, and no perforation of PET copper foil substrate or film material after the film is thin.
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