Why do lithium battery packs use copper foil for negative electrodes and aluminum foil for positive electrodes
- classification:Industry Information
- release time:2021-02-25 14:43:00
For lithium-ion batteries, the anode current collector is usually aluminum foil, and the anode current collector is copper foil. In order to ensure the stability of the current collector in 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 lithium battery pack is getting lighter and lighter. It is to reduce the thickness and weight of the current collector to reduce the volume and weight of the battery intuitively. There are three reasons why the positive electrode of the lithium battery pack uses aluminum foil and the negative electrode uses copper foil:
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 materials with good conductivity. Among the metal materials, copper foil and aluminum foil are cheap and good conductivity. 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 have problems such as brittle fracture during winding. Among the metal materials, copper aluminum foil is also a softer metal. It is to consider the cost of battery preparation. Relatively speaking, the price of copper and aluminum foil is relatively cheap, and there are abundant resources of copper and aluminum 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 the lithium battery 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 relatively common and cheaper. At the same time, a layer of oxide protective film can be formed on the surface of both.
Thickness requirements of copper and aluminum foil for lithium batteries With the rapid development of lithium batteries in recent years, the development of current collectors for lithium batteries has also been rapid. The positive aluminum foil has been reduced from 16um in the previous years to 14um and then to 12um. Now many battery manufacturers have mass-produced 10um aluminum foil, even 8um. As for the copper foil for the negative electrode, due to its better flexibility, its thickness has been reduced from 12um to 10um and then to 8um. Up to now, a large number of battery manufacturers use 6um in mass production, and some manufacturers are developing 5um/4um. It's all possible to use. Since lithium batteries have high requirements for the purity of the copper and aluminum foil used, the density of the materials is basically at the same level. As the thickness of the development decreases, the area density also decreases, and the weight of the battery is naturally getting smaller and smaller.
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