Tesla’s “Battery Day” in Fremont, California, this past September felt like Lollapalooza for energy nerds. As record-breaking wildfires burned just six miles away, underscoring Tesla’s mission to rid the world of climate change-causing fossil fuels, the electric vehicle company organized an hour-long celebration of lithium-ion batteries — one of a handful of technological breakthroughs that have made low carbon policies possible.  On a giant outdoor stage, Elon Musk, Tesla’s co-founder and chief executive and Drew Baglino, a senior vice president, wore black t-shirts with a close-up image of Tesla’s new battery structure as they waxed poetic about the chemistry of lithium ion batteries. With energy-dense, durable and versatile cells, the nearly 50-year-old lithium ion battery now powers everything from laptops and smartphones to electric vehicles. The battery’s inventors — John B. Goodenough, M. Stanley Whittingham and Akira Yoshino — even won the Nobel Pri