Renewable energy might soon have storage batteries that are more environmentally friendly in their own right. Researchers have developed a new form of aluminum battery with twice the energy density of previous designs, making the technology more practical for large-scale projects like solar and wind farms while using more sustainable materials. The trick was to replace the usual graphite cathode (the positive electrode) with anthraquinone, an organic carbon-based molecule that ups the density by storing positive charge carriers coming from the electrolyte.