A rendition of a possible grass battery. Image credit: University of MarylandResearchers at the University of Maryland have invented a biocompatible battery that produces the same kind of ion-based electrical energy used by humans and other living things.

In traditional batteries, electrical energy — otherwise known as current — flows in the form of moving electrons. The current of electrons out of the battery generates within the battery by moving positive ions from one end of the battery to the other.

The UMD battery does the opposite — it moves electrons around in the device to deliver energy consisting of a flow of ions. Researchers claim this is the first time an ionic current generating battery has been invented.

"My intention is for ionic systems to interface with human systems," said Liangbing Hu, professor of materials science at the University of Maryland. "So I came up with the reverse design of a battery. In this case, the ions in the ionic cable — here, grass fibers — can interface with living systems."

The battery might be useful in the next generation of devices to micro-manipulate neuronal activities and interactions that can prevent and/or treat such medical problems, as Alzheimer’s disease and depression. It could also be used to develop medical devices for the disabled, or more efficient drug and gene delivery tools for both research and clinical settings.

How They Did It

The UMD battery uses grass to store its energy. The team soaked blades of Kentucky bluegrass in a lithium salt solution, and used the channels that once moved nutrients up and down the grass blade as conduits to hold the solution.

The battery has two glass tubes with a blade of grass inside, each connected by a thin metal wire at the top. The wire is where the electrons flow through to move from one end of the battery to the other as the stored energy slowly discharges. In the other glass tube resides a metal tip where the ionic current flows.

The ionic current was proved by touching the ends of the battery to either end of the lithium-soaked cotton string, with a dot of blue-dyed copper ions in the middle. The copper moved along the string toward the negatively charged pole.

"The microchannels in the grass can hold the salt solution, making them a stable ionic conductor," said Chengwei Wang, a graduate student in the Materials Science and Engineering department at the University of Maryland.

The full research can be found in the journal Nature Communications.