One of the tricky conundrums with renewable energy is that the materials used to make the devices and batteries that produce clean energy are made out of unsustainable sources. That’s the main reason why researchers have been working on greener aluminum batteries that could one day replace ones made using lithium.

Lithium-ion batteries are the default choice for most personal electronics and electric cars today because they have a high energy density, but the problem is that lithium is a limited resource, and the process of mining is highly polluting for both the air and local water supplies. In a recent breakthrough, 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.

It may take some time before aluminum batteries are available outside the lab, but if they do reach parity with lithium, it could lead to a sea change where renewable energy and electric cars run on more readily available and recyclable materials.