What is the reason why copper foil is used for negative electrode of lithium ion battery and aluminum foil is used for positive electrode

First, copper and aluminum foil has good conductivity, soft texture and low price. We all know that the working principle of a lithium ion battery is an electrochemical device that converts chemical energy into electrical energy. In this process, we need a medium to transfer the electrical energy converted from chemical energy. Conductive materials are needed here. Among ordinary materials, metal materials are the most conductive materials. Among the metal materials, copper foil and aluminum foil are cheap and conductive. At the same time, in lithium-ion batteries, we mainly have two processing methods: winding and lamination. Regarding winding, the pole pieces used to prepare the battery have a certain degree of flexibility to ensure that the pole pieces do not suffer from brittleness during winding. Among the metal materials, copper aluminum foil is also a softer metal. Finally, the cost of battery preparation is considered. Relatively speaking, the price of copper and aluminum foil is relatively cheap, and there are abundant copper and aluminum resources in the world. 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 aluminum surface layer to prevent further aluminum reaction, and this thin oxide film also has a certain protective purpose for aluminum in the electrolyte. Copper itself is relatively stable in air, and basically does not react in dry air. The third is that the positive and negative potentials of lithium-ion 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 protection for the internal aluminum. Both are used as current collectors because they have good electrical conductivity, soft texture (maybe it will also be good for bonding), and are relatively common and cheaper. At the same time, a layer of oxide protective film can be formed on the surface of both. 1. The size of the octahedral voids in the lattice of aluminum is similar to that of Li, and it is easy to form intermetallic compounds with Li. Li and Al not only form an alloy with the chemical formula LiAl, but may also form Li3Al2 or Li4Al3. Due to the high activity of the reaction between metal Al and Li, the metal Al consumes a large amount of Li, and its structure and morphology are also destroyed, so it cannot be used as the current collector of the negative electrode of the lithium ion battery; and Cu during the charging and discharging process of the battery, There is only a small lithium insertion capacity, and the structure and electrochemical performance are maintained. It can be used as the current collector of the negative electrode of the lithium ion battery; when the Cu foil is at 3.75V, the polarization current starts to increase significantly and rises linearly, causing oxidation Intensified, indicating that Cu becomes unstable at this potential; while the polarization current of the aluminum foil is small and constant throughout the polarization potential range, no obvious corrosion phenomenon is observed, and the stability of electrochemical performance is maintained. Due to the lithium-ion battery positive electrode potential range, the lithium-intercalation capacity of Al is small, and the electrochemical stability can be maintained, which is suitable for the positive electrode current collector of lithium-ion batteries. 2. The oxide layer on the copper/nickel surface is a semiconductor, and the electrons are conductive, the oxide layer is too thick, and the resistance is large; while the oxide layer on the aluminum surface, alumina is an insulator, and the oxide layer cannot conduct electricity, but because it is very thin, electrons are realized through the tunneling effect Conductivity, if the oxide layer is thick, the conductivity of the aluminum foil is poor, and even insulated. Generally, the surface of the current collector should be cleaned before use. On the one hand, it can wash off the oil stains and at the same time remove the thick oxide layer. 3. The positive electrode potential is high, and the thin aluminum oxide layer is very dense, which can prevent the current collector from oxidizing. The copper/nickel foil oxide layer is looser. In order to prevent its oxidation, the potential is better. At the same time, Li is difficult to form a lithium intercalation alloy with Cu/nickel at low potentials. However, if the copper/nickel surface is oxidized in a large amount, the voltage will be slightly higher. Under electric potential, Li will intercalate lithium with copper oxide/nickel. However, aluminum foil cannot be used as a negative electrode, and LiAl alloying will occur at low potentials. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous article: Why can't lithium-ion batteries have both high power and high energy density?