Different materials for cathode and annode in the same DC supply?

Question

I have just seen a diagram of the 787 Dreamliner's battery system. In it, the negative terminal is copper and the positive is aluminium.

In a DC system I understood that the current at the supply was equal to the current at the 'sink', i.e. the same amount of current must be passing through both terminals. Why, then are they made from different materials? The only reason I can think of is that it means they could make the copper terminal smaller due to it having less resistance, but I'm just guessing.

Answer 1

The Lithium Ion battery cathode is Aluminum coated with LiMn2O4, the anode is Copper coated with graphite. Here is a link to a mfgr's anodes.

The aluminum and copper are brought outside of the cell for connection. The dissimilar metals can be managed by cladding the aluminum. From the pics of the dreamliner cells, it looks like a triangular intermediate link is connected by rivets to two posts going into the cell.

I am gonna guess that the diagram is not exactly correct, and guess that those triangular links are copper, so the interconnect is not across dissimilar metals.