The new battery moves electrons around in the device to deliver energy that is a flow of ions. “My intention is for ionic systems to interface with human systems,” said Prof Liangbing Hu, professor of materials science at the University of Maryland, College Park, head of the group that developed the battery where ions flow through grass fibres.
“So I came up with the reverse design of a battery,” he said. “In a typical battery, electrons flow through wires to interface electronics, and ions flow through the battery separator. In our reverse design, a traditional battery is electronically shorted so that electrons are flowing through the metal wires. Then ions have to flow through the outside ionic cables. In this case, the ions in the ionic cable – here, grass fibres — can interface with living systems.”
This would allow a more effective interface in medical systems. “Potential applications might include the development of 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,” said researcher Jianhua Zhang, PhD, a staff scientist at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health in Bethesda.
“The battery could be used to develop medical devices for the disabled, or for more efficient drug and gene delivery tools in both research and clinical settings, as a way to more precisely treat cancers and other medical diseases,” said Zhang, who performed biological experiments to test that the new battery successfully transmitted current to living cells. “Looking far ahead on the scientific horizon, one hopes also that this invention may help to establish the possibility of direct machine and human communication,” he said.
Next: Making the battery
To make the battery, the team soaked blades of Kentucky bluegrass in lithium salt solution. The channels that once moved nutrients up and down the grass blade were ideal channels to hold the solution. The demonstration battery the research team created looks like 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. At the other end of each glass tube is a metal tip through which the ionic current flows.
The researchers showed that the ionic current is flowing by touching the ends of the battery to either end of a lithium-soaked cotton string, with a dot of blue-dyed copper ions in the middle. Caught up in the ionic current, the copper moved along the string toward the negatively charged pole, just as the researchers predicted.
“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. The team plans to diversify the types of ionic current electron batteries they can produce. “We are developing multiple ionic conductors with cellulose, hydrogels and polymers,” said Wang.
The work was published in the July 24 issue of Nature Communications.