The solid-state battery maker still has a lot to prove. QuantumScape (QS 1.41%) was one of the market's hottest investments during the meme stock rally in late 2020 and 2021. The developer of solid-state batteries went public by merging with a special purpose acquisition company (SPAC) in November 2020, and its stock opened at $24.80 before soaring to a record high of$131.67 less than a month later. At its peak, QuantumScape's market cap reached $48 billion. However, the company hadn't commercialized any o ...