For lithium-ion batteries, the commonly used positive current collector is aluminum foil, and the negative current collector is copper foil. In order to ensure the stability of the current collector inside the battery, the purity of both is required to be above 98%. With the continuous development of lithium battery technology, whether it is lithium batteries used in digital products or batteries for electric vehicles, we all hope that the energy density of the battery is as high as possible, and the weight of the battery is getting lighter and lighter, and the most important thing in the current collector is Reduce the thickness and weight of the current collector to reduce the volume and weight of the battery intuitively. There are three reasons why lithium-ion batteries use aluminum foil for the positive electrode and copper foil for the negative electrode:

First, copper and aluminum foil has good conductivity, soft texture and low price. We all know that the working principle of a lithium 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 batteries, we mainly have two processing methods: winding and lamination. Compared with winding, the pole pieces used to prepare the battery need to 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 effect on 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 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. 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.

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