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Why is the lithium battery negative electrode plated with nickel on copper tabs instead of copper?

2021-05-14

Lithium ion is mostly usedNickel-plated copper lug materialOr copper plating materials, so why not use copper directly? The advantages of using copper are as follows. Nickel is more expensive than copper. The potential difference between Ni / Ni2 + and Cu / Cu2 + is close to 0.8V, and slight corrosion may occur at the welding part. The melting point of copper is 1083°C, which is lower than the 1453°C of nickel. In hot melt welding (such as ultrasonic welding), copper and copper should stick together more easily. The electrical and thermal conductivity of copper is much higher than that of nickel. Some people say this is a welding problem, so why is copper/nickel easier to weld?

The specific reasons are as follows:

The collectors are made because they have good electrical conductivity, a soft texture (which may help bonding), are relatively common and inexpensive, and have a protective oxide film formed on both surfaces.

The oxide layer on the nickel surface is a semiconductor, which is electronically conductive. The oxide layer is too thick and has high impedance. Generally, the liquid is collected before use. It is best to clean the surface first. On the one hand, the oil must be washed away, and the thicker oxide layer can be removed at the same time.

Nickel lugs are also used in soft bags. Electrolyte ears must pass the electrolyte immersion, bending test, high and low temperature thermal shock test, and coating corrosion resistance test. Therefore, copper is generally not used on the basis of these tests (copper has poor bending resistance and corrosion resistance) .

Because this is a welding problem. For example, for packaging, nickel lugs can be electro-welded, while copper lugs must be laser-welded. In addition, nickel lugs are also cheaper, but they are not as conductive as copper. In some cases, if pure nickel lugs are used, it will fail certain safety tests of the battery (for example, a short circuit occurs when the glue burns). At this time, we will use copper-plated nickel lugs as the next best choice.

The welding reliability and stability of nickel-plated electrode tabs are much better than pure copper electrode tabs.


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