First, the classification of copper foil:
According to the thickness, it can be divided into thick copper foil (greater than 70μm), conventional thickness copper foil (greater than 18μm and less than 70μm), thin copper foil (greater than 12μm and less than 18μm), ultra-thin copper foil (less than 12μm);
According to the surface condition, it can be divided into single-sided copper foil (single-faced wool), double-sided copper foil (double-sided rough), glossy copper foil (double-sided wool), double-sided copper foil (double light) and even Low profile copper foil (VLP copper foil) copper foil, etc.
(1) Single-sided copper foil (single-faced wool): Among the electrolytic copper foils, the largest production is single-sided surface-treated copper foil, which is not only the most used type in the manufacture of copper clad laminates and multi-layer boards. Electrolytic copper foil, and is the copper foil with the largest application range.
(2) Double-sided copper foil (double-sided rough): a multi-layer circuit board mainly used for fine wiring, the smooth surface of which has a low profile, and the copper-clad board which is made by pressing this surface with the substrate, A circuit with a high precision can be maintained after etching. The demand for such copper foil is increasing.
Divided by application:
(1) Copper clad laminate (CCL) and copper foil for printed circuit board (PCB): CCL and PCB are the most widely used fields of copper foil. PCB has become an indispensable main component of most electronic products to achieve circuit interconnection. Copper foil has become a key material for PCBs that support and interconnect components in electronic products. At present, most of the CCL and PCB industries are electrolytic copper foil.
(2) Copper foil for lithium ion secondary battery: According to the working principle and structural design of the lithium ion battery, negative electrode materials such as graphite and petroleum coke are applied to the conductive current collector. Due to its good electrical conductivity, soft texture, mature manufacturing technology and relatively low price, copper foil has become the first choice for anode current collectors for lithium-ion batteries.
(3) Copper foil for electromagnetic shielding: It is mainly used in some fields requiring electromagnetic shielding in hospitals, communications, military, etc. Since the rolled copper foil is limited by the width, the electromagnetic shielding copper foil is mostly electrolytic copper foil.
According to the production method, it can be divided into electrolytic copper foil and rolled copper foil.
Second, a method for producing a copper foil for a lithium ion battery
(1) Calendered copper foil: generally made of copper ingot as raw material, which is made by hot pressing, tempering and toughening, scaling, cold rolling, continuous toughening, pickling, calendering and degreasing and drying, etc., which is difficult to produce. The equipment has high precision and therefore high cost; the main difference of its production method lies in the selection of rolling mills, and generally adopts imported rolling mills.
Key technology: Calendered copper foil requires less thickness deviation, better flatness and residual stress, so copper foil rolling is a key process, and thickness, speed, tension and surface quality control during rolling are particularly important.
Calendered copper foil surface treatment process
(2) Electrolytic copper foil: Electrolytic copper foil is formed by depositing copper ions in the electrolyte on a circular rotating cylinder of a smooth rotating stainless steel plate (or titanium plate). The surface of the copper foil close to the surface of the cathode roller is called a smooth surface. The other side is called a matte surface.
Under the action of direct current, the divalent copper ions in the copper sulfate electrolyte in the electrolysis machine are reduced to copper atoms, and are focused and crystallized on the surface of the continuously rotating smooth cathode roll.
Pretreatment: cleaning the surface of the raw foil, removing oxidation and etching the surface, usually treated with sulfuric acid, hydrogen peroxide or a mixed solution.
Anti-oxidation treatment: In order to prevent the copper foil from encountering humid air and excessive temperature during storage, transportation and use, the surface of the copper foil is treated with acid or alkaline oxidation, and the direct current is used to produce an oxide film on the surface of the copper foil. To achieve the purpose of antioxidant
Drying: thoroughly removes moisture and does not cause damage to the surface of the copper foil.
1, the difference between electrolytic copper foil and rolled copper foil:
First, the two processes are different, electrolysis is completed by electroplating, and calendered copper is produced by coating;
Second, the performance is different. Electrolytic copper has better conductivity, and the rolled copper has better flexural properties. Generally, products with bending requirements use rolled copper foil. The unit price of rolled copper foil is more expensive than electrolytic copper foil;
Third, the electrolytic copper molecules are relatively loose and easy to break; the copper molecules are compact and flexible, and the thinner the flexibility, the better; the phosphorus-containing rolled copper molecules are fine, and the post-treatment plating table is bright, but the flexibility is worse than pure rolled copper.
Third, the inspection of copper foil:
In order to have the technical performance requirements of thickness, standard quality, appearance, tensile strength, peel strength, high temperature oxidation resistance, and quality resistance coefficient of copper foil, in addition to the above seven main performance requirements, some manufacturers have other performance requirements. Such as elongation, folding resistance, hardness, modulus of elasticity, high temperature elongation, surface roughness, etching, solderability, copper foil hue and other technical requirements, each manufacturer also has its own inspection standards and testing methods, here It is not detailed.
Fourth, the technical development trend of copper foil
With the continuous increase of energy density, power battery manufacturers have put forward higher requirements for copper foil, ultra-thin copper foil (≤6μm), high tensile strength copper foil, porous copper foil, coated copper foil, etc. .
Like the porous aluminum foil, although the negative electrode active material can be increased in load and the negative electrode forms a three-dimensional conductive network, in large-scale production, it is inevitable that it faces enormous difficulties to be solved, in coating, rolling, and There are still some technical difficulties in cutting, winding, etc., and it is necessary for the majority of colleagues to work together to solve.
Similar to coated aluminum foil, coated copper foil can also significantly reduce contact internal resistance, improve adhesion, accelerate electrolyte infiltration, improve low temperature performance, reduce burrs in the process, protect current collectors, etc. At present, the matching with the negative electrode material is not very ideal, so it has not been used in large quantities, and further research and optimization are needed.
summary:
This paper mainly introduces the classification, preparation process and development trend of copper foil. The development of any kind of technology is inseparable from a large number of repetitive experiments, verification and analysis of these seemingly boring tasks, and it is precisely because of these basic work. The continuous accumulation can promote the continuous advancement of science and technology. For the new industry of new energy, it still needs the constant repetition of the grassroots engineers, and finally completes the continuous upgrading of products and completes the dream of new energy.
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