While some green energy stocks are charging higher, one lithium stock is the subject of considerable skepticism. While the S&P 500 is on course to end the week lower than where it began, shares of battery stock EnerSys (ENS -0.94%) and energy-efficiency leader Ameresco (AMRC 5.17%) have soared. But not all clean energy stocks are headed for gains. Lithium Americas (LAC 1.45%), a company developing lithium production assets, plummeted this week in response to a critical report from a short seller. From the e ...