Copper surface corrosion is an important subject when considering copper busbar joints. When copper is exposed to air and moisture, it forms a thin layer of reddish-brown copper oxide and other corrosion products. These products are not as conductive as the copper, leading to increased resistance at the joint.
The increased resistance leads to local heating at the joint and faster corrosion, this is described by Staubli [2]:
Progressive film build-up increases the joint resistance Rv, heat losses and therefore the temperature of the joint, which in turn accelerates the chemical reaction producing the film build-up. This “vicious circle” of film build-up, heat loss and joint temperature can ultimately cause the busbar joint to fail totally as a result of overheating.
Staubli [2] also show the resistance growth with time in busbar joints. Although this doesn’t specify the joint as being between copper and copper they do say that the data represents tests conducted with copper-copper, aluminium-aluminium and copper-aluminium joints.
Slade [3] has shown that an increase of two times the original bolted joint’s contact resistance is a reliable measure that a bolted connection is in the initial stages of failure.
Song et al [4] shows a table of corrosion resistances of the most common used coating materials for electrically conductive surfaces and the base material copper.
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There are basically two groups of materials [4], which can be employed for corrosion protection of electrically conductive surfaces. The first group includes noble metals such as:
- gold
- silver
- palladium
The second group comprises of corrosion resistant so-called passive metals such as:
- tin
- nickel
Copper surface corrosion is an important factor to consider in the battery design and manufacturing process. It is normal to tin or nickel plate joining surfaces if they are to be bolted or to clean then before being welded.
As shown in the Staubli reference it is possible to use compounds in the joints that will inhibit corrosion and prevent increased joint resistance.
References
- Copper Corrosion Explained, Fractory
- Long-term behaviour of bare, bolted busbar joints, Staubli
- P. G. Slade, “Bus Bar Bolted Connections: Reliability and Testing,” 2021 IEEE 66th Holm Conference on Electrical Contacts (HLM), San Antonio, TX, USA, 2021, pp. 209-216
- Song, J.; Wang, L.; Zibart, A.; Koch, C. Corrosion Protection of Electrically Conductive Surfaces. Metals 2012, 2, 450-477.