The solid-state battery maker is still a speculative and divisive investment.QuantumScape (QS 18.95%), a developer of solid-state lithium batteries, hasn't commercialized any of its products or generated any revenue yet. Nevertheless, its stock rallied nearly 120% over the past 12 months and boosted its market cap to $7.2 billion.The bulls rushed to the stock in anticipation of its upcoming batteries. Is too much growth already baked into its high-flying shares, or could it skyrocket and set you up for life ...