I'm thinking I remember about several experimental "caseless" rounds the military experimented with
that used electric ignition. I want to say in the 70s or 80s. As I remember it was a triangular shaped "case", and fired flechets rather than a solid bullet. One of the gun magazines had an article about it and some field tests at Ft Benning.
Given the leaps in battery technology, I wouldn't be surprise if we might not see renewed interest.