Scottish and Chinese scientists used a red bread mould to transform a mixture of manganese chloride and urea into an electrochemical mineral composite – manganese oxide.
And when they popped it in a lithium-ion battery, senior author and University of Dundee microbiologist Geoffrey Gadd was "surprised" with its performance.
A rechargable battery needs materials to act as an electrode to attract positive ions (such as lithium ions) as the battery charges.
Manganese oxides are suitable candidates. Their atomic structure forms holes and tunnels through which lithium ions can freely travel when the battery is charging or in use.
But while cheap and less toxic than other materials, manganese oxides aren't very stable. So scientists must come up with new ways to make them. And what better way than getting nature to do it?
Previous research into the bread mould Neurospora crassa showed it could precipitate 90% of calcium from calcium carbonate into calcite. Gadd and colleagues suspected it might do the same for manganese.
So they added N. crassa to a mix of urea and manganese chloride for 12 days, after which time they found the fungi's branching filaments completely mineralised or covered by a mineral sheath.
After heating the fungi to 300°C for four hours (and killing it), they were left with carbonised biomass, including manganese oxides. Incredibly, the mineralised filements retained their hollow branched shapes, although they were more fragile after being burnt.
When they used the biomass on an electrode in a lithium-ion battery, the researchers found it retained 92% of its initial capacity after 200 charging cycles.
The study, published in Current Biology, was the first to produce active electrode materials using fungi. Gadd says the team intends to expand N. crassa's metal carbonate-precipitation repertoire, and see how well it can scavenge scarce metal elements.