The world of clean energy needs a lot of batteries to power a vast range of equipment from electric cars to mobile phones. But the battery is still a problem. There are alkaline batteries that are safe, cheap and reliable but not powerful enough to power, for example, electric cars. Then there are fire-prone lithium batteries that are more powerful and can easily be recharged. A new company funded by the founder of Sun Microsystems, Bill Joy, is presenting a critical breakthrough: A new powerful battery that is based on solid materials and doesn’t need the liquids that make the lithium battery so unreliable and sometimes dangerous.