In late July of 2008 a British solar plane set an unofficial flight-endurance record by remaining aloft for more than three days straight. Lithium-sulfur batteries emerged as one of the great technological advances that enabled the flight -powering the plane overnight with efficiency unmatched by the top batteries of the day. Ten years later, the world is still awaiting the commercial arrival of “Li-S” batteries. But a breakthrough by researchers at Drexel University has just removed a significant barrier that has been blocking their viability.