New energy battery connector copper aluminum circuit connection technology cable assembly
The density of copper is 8.9 × 10 3 kg / m3, the density of aluminum is 2.7 × 10 3 kg / m3, and the mass density of aluminum is less than one third of that of copper. The spot prices of copper and aluminum are shown in the following two figures. Aluminum is less than 4 / 1 of copper. In the whole industry, we are striving to reduce the weight and cost. It is the easiest and practical way for us to replace copper steel plate with aluminum in every possible link. This paper deals with the problems and solutions of copper aluminum connection.
As for the selection of replacing copper bar and copper cable with aluminum bar aluminum cable, if you look at the basic parameters, the resistivity of red copper is 0.018 Ω * m m 2 / m, the resistivity of aluminum is 0.027 Ω * mm2 / m, and the cross section of the same size, the conductivity of aluminum is 2 / 3 of copper, and the weight is 1 / 3 of copper, it is cost-effective to use aluminum. The problem is that the aluminum bar of copper bar cannot be directly overlapped, especially in humid environment. According to the conventional connection mode of copper bar, screw the joint to a piece with large screws. In a short time, it will be found that there is a large amount of oxide layer at the joint position and the resistance increases significantly. Why is that?
Electrochemical corrosion of metals
What is the corrosion of telephone between copper and aluminum? When the copper and aluminum conductors are directly connected, the contact surfaces of the two metals are easy to form electrolyte under the action of moisture, carbon dioxide and other impurities in the air, so as to form a primary battery with aluminum as the negative electrode and copper as the positive electrode (why aluminum must be the negative electrode, the loss of electrons is mainly determined by the potential of the element itself, see the table below for the element potential), which causes electrochemical corrosion of aluminum and copper The contact resistance at the aluminum connection is increased.
In addition, because the elastic modulus and thermal expansion coefficient of copper and aluminum are very different, after many cold and hot cycles (power on and power off) in operation, the contact point will have a large gap, which will affect the contact and increase the contact resistance. With the increase of contact resistance, the temperature will rise during operation. At high temperature, corrosion and oxidation will intensify, resulting in a vicious cycle, further deterioration of the connection quality, and finally lead to high contact point temperature and even smoke, burning and other accidents.
When the joint works in high temperature environment for a long time, it will be affected by mechanical vibration, which will lead to the diffusion of copper and aluminum atoms to form intermetallic compound layer and continuously thicken, which will reduce the impact toughness of the joint and increase the electrical resistance. There is a bubble air gap between the metals, which can't isolate the environment of carbon dioxide and water vapor, and the above galvanic cell reaction may occur.
In order to avoid electrochemical corrosion, it is necessary to remove the basic conditions to form the electrolyte of the primary battery, remove the water vapor or isolate the air.