Standing next to the Ping-Pong table in the offices of the battery startup Ambri, chief technology officer David Bradwell needs both hands to pick up what he hopes will be a build- ing block for a new type of electricity grid. Made of thick steel, it's a container shaped like a large round cake pan, 16 inches in diameter. Inside it are two metal pucks and some salt powder; a round plate has been welded to the top to make a 100-pound battery cell.
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