A dash of iodide unlocks tin's full four-electron power for grid batteries

Water-based flow batteries are safe and cheap for storing grid electricity, but they've always been too weak to compete with lithium-ion — until now. A team led by China's Dalian Institute of Chemical Physics found that adding iodide to a tin solution smooths the tin atoms' electron handoffs, cutting wasted energy tenfold and packing four electrons into every tin atom instead of two. Their tin-bromine battery, reported in the peer-reviewed journal Nature Chemistry, stores 205 watt-hours per litre at 89 percent efficiency, and a kilowatt-scale prototype ran steadily for more than 1,000 hours. Cheap, abundant tin — bottling sunshine for the grid.