Lithium-Ion Battery Soaks Up The Sun For Recharge

Credit: Michael De Volder/Nano Lett.
A cathode made of vanadium pentoxide nanofibers (shown) both harvests light and stores lithium ions in a new lithium-ion battery that charges itself in the sun.

Hooking up solar panels to batteries is the norm for storing extra energy produced when the sun is shining. To streamline this process, researchers have developed a lithium-ion battery that can be directly charged in sunlight, with no solar cells needed 

“The idea is to simplify how solar energy is harvested and stored,” says Michael De Volder, a mechanical engineer at the University of Cambridge who led the work. If the team can improve the efficiency and lifetime of the hybrid device, its cost will likely be lower than that of combining solar cells and batteries. “For the price of a battery, you get both functionalities,” he says.

This low cost could make it suitable for use when there’s no electrical outlet nearby, and for regions of the world that lack access to affordable energy.

The key of the new light-rechargeable battery is a cathode made of vanadium pentoxide nanofibers. The material stores lithium ions and also harvests light to generate paired electrons and positive charges, or holes. The researchers mixed the nanofibers with poly(3-hexylthiophene-2,5-diyl) (P3HT), which blocks the movement of holes, and graphene oxide, which aids electron transport.

To make the battery, they drilled an opening on the cathode side of a coin cell and placed a glass window in it to let light through. When the device is illuminated, electrons generated at the cathode move through an external circuit to the lithium anode. Meanwhile, the holes trigger the vanadium cathode to release lithium ions, which migrate through the electrolyte and combine with the electrons at the anode to form lithium, charging the battery.

At 2.6%, the device’s efficiency is still too low for practical use. But it is early days for the research, De Volder says. He and his team are starting to explore materials other than vanadium pentoxide for the photocathode and are thinking carefully about cathode design to increase the efficiency.

More research on other parts of the battery, such as the electrolytes and the interfaces between the electrodes and electrolytes, would also help, says Karim Zaghib, a materials engineer at McGill University. With improvements in efficiency, he says, he can see a device like this becoming a sustainable power source for small sensors and consumer electronic devices