Why use copper foil instead of aluminum foil for the negative electrode of lithium ion battery? The way to increase the specific energy of lithium-ion batteries is to use higher-capacity positive and negative materials, thinner separator paper, thinner copper foil and aluminum foil, and reduce other auxiliary additives as much as possible. The main material of the current collector of lithium-ion batteries is metal foil (such as copper foil, aluminum foil), and its function is to gather the current generated by the battery's active material to form a larger current output.
Why use copper foil instead of aluminum foil for the negative electrode of lithium ion battery?
According to the working principle and structural design of lithium-ion batteries, the positive and negative materials need to be coated on the conductive current collector, so the current collector should be in full contact with the active material, and the internal resistance should be as small as possible. Copper foil and aluminum foil have the advantages of good electrical conductivity, formed oxide protective film, soft texture, which is good for bonding, mature manufacturing technology, and relatively low price. Therefore, they are selected as the main materials of lithium-ion battery current collectors.
The positive electrode potential of lithium ion batteries is high, and the oxide layer of aluminum foil is relatively dense, which can prevent the current collector from oxidizing, while copper will undergo lithium intercalation reaction at high potential. It is not suitable for positive electrode current collectors. The positive electrode current collector generally uses aluminum foil; and the negative electrode potential Low, aluminum foil is easy to form aluminum-lithium alloy at low potential. Copper foil is generally used as the negative electrode current collector, and there is no interchangeability between copper foil and aluminum foil.
First, copper and aluminum foil has good conductivity, soft texture and low price.
Second, copper and aluminum foil is relatively stable in the air. Aluminum is easy to chemically react with oxygen in the air, forming a dense oxide film on the surface of aluminum to prevent further aluminum reaction, and this thin oxide film also has a certain protective effect on aluminum in the electrolyte.
The third is that the positive and negative potentials of lithium batteries determine the aluminum foil for the positive electrode and the copper foil for the negative electrode, not the other way around. The positive electrode potential is high, the copper foil is easily oxidized under high potential, and the oxidation potential of aluminum is high, and the surface of the aluminum foil has a dense oxide film, which also has a better protective effect on the internal aluminum.
The impact of lithium battery copper foil performance indicators on lithium batteries
As the current collector of the lithium battery, the thickness of the lithium battery copper foil is usually between 7-20 μm. At present, the thickness of the copper foil equipped with new energy vehicles is 8-12μm, and the quality of the copper foil of the whole vehicle reaches more than 10kg. The smaller the thickness of the lithium copper foil, the lighter the weight of the battery.
At the same time, thinner lithium copper foil also means smaller resistance, and the performance of the battery will also be improved. Therefore, reducing the quality of copper foil on the battery, reducing the cost of copper foil raw materials, while providing higher energy density, has become the key to copper foil for power lithium batteries. We believe that the use of thinner and lighter lithium copper foil is a general trend in the future.
What are the advantages of microporous foil in the application of lithium-ion batteries?
1. Directly and effectively improve the specific energy of lithium batteries
The same specifications of foil, the microporous foil with a porosity of 17%, the weight is reduced by 17%; the same areal density, the positive and negative electrode compaction is improved.
2. Effectively improve the rate performance of lithium batteries
In conventional foil lithium batteries, the migration of lithium ions is diffused through the two-dimensional direction of the foil to the tab end. After the foil passes through the holes, the diffusion path of lithium ions can be transformed into three-dimensional and omni-directional penetration, and can pass into the pores. The contact surface between the positive and negative electrode materials and the foil is increased, which reduces the lithium ion migration radius and improves the conduction efficiency.
3. Effectively reduce the internal resistance of lithium batteries
The comparison of the same foil material shows that the use of punched copper foil and aluminum foil at the same time can effectively reduce the internal resistance by 8% to 20%.
4. Lithium battery electrolyte ensures the consistency of infiltration
In conventional foil lithium batteries, the electrolyte diffuses and infiltrates from the longitudinal sides to the center, and after perforation, it becomes three-dimensional infiltration and diffusion, which completely eliminates the problem of infiltration in the center of some battery pole pieces. In the industry, it has been reported that one of the reasons for the insufficient consistency of single cells is caused by the consistency of infiltration.
Copper foil is not only the carrier of the negative electrode active material in the lithium ion battery, but also the collector and conductor of the negative electrode electrons. Therefore, it has special technical requirements, that is, it must have good conductivity and the surface can be uniformly coated with the negative electrode material. Does not fall off, and has good corrosion resistance.
