Lithium ion batteries existed in the 90s and were being explored for BEV use by Nissan in 1996. They were already fairly ubiquitous in consumer electronics, at least high end ones, at the time the EV-1 was killed.

GM just tapped out too early because despite the cars being incredibly popular, they didn't want the short-term hit to the books that a niche product full of brand new technology represents.