While lithium-ion batteries are currently our most effective batteries, they’re still not powerful enough to full displace gasoline-powered cars or cheap enough to solve the big energy-storage problem of solar and wind power. A Massachusetts-based startup believes they have the solution: a reliable rechargeable lithium-metal battery. The battery can pack nearly double the energy of a conventional lithium-ion battery and has the potential to power a Tesla car for 800 km (500 miles) on a single charge, rather than today’s upper limits of 400 km.