One of the oddest electrical technologies of the past is the sodium cable. As the name indicates, it's an insulated power cable with metallic sodium as a conductor, in place of the usual copper or aluminum. Apparently it was "the next big thing" for a while in the 1960s, but as far as I know, it never caught on - though it probably "caught fire" a few times!
How would you make a reliable electrical connection to a sodium conductor? Sodium is so soft that it makes the "cold flow" problems of aluminum look like nothing. I can't see how any kind of crimp or mechanical lug is going to stay tight.
Then there's the whole "reacts explosively with water" thing...
Yes, terminations must have been a major problem. The only thing I've seen in that regard is a reference to threaded connectors; I suppose they used some kind of lug that was screwed onto the exposed conductor. But it must have been difficult to come up with a design that could be screwed on tightly enough to make a good connection while not breaking the conductor.
It's really incredible that such a technology could actually have been approved and deployed by utilities. Apparently its only advantage was cost savings; surprisingly (to me) sodium was cheaper than copper and aluminum.
When I first heard of sodium cables, I thought they would be used for some exotic super-duper extra-high-voltage cryogenic superconducting transmission system, but in fact the application was ordinary secondary-voltage underground residential distribution.
When I brought up the topic on another list, a former lineman said one of the problems was that when water got into the cable due to jacket damage, the conductor would corrode for a long distance from the point of entry. His crew ended up replacing a lot of the stuff.