ENGINEERS in the US have developed a new form of battery which works on the basis of flowing ions, rather than flowing electrons, the same kind of electrical energy used by living organisms.
The researchers, led by materials science professor Liangbing Hu at the University of Maryland say that the batteries could one day interface with human systems. In a conventional battery, ions move from one end of the battery to the other, with the current moving as a flow of electrons. In Hu’s new battery, this is reversed, with the electrons moving from one end of the battery to the other and the current moving as a flow of ions. This is the same type of signal that powers muscles, nerves and regulates the rhythm of the heart.
The electron current in a conventional battery requires ‘patching’ into the ionic current in living organisms, but this is very difficult due to the much higher voltage of an electron current. Being able to directly connect ion current battery devices into living systems could have a wide range of applications.
“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, a staff scientist at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). “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.”
Hu and the team created a prototype battery from an unusual material – blades of Kentucky bluegrass (Poa pratensis). The ion channels naturally present in the grass are ideal for holding the ions for the battery, in this case a lithium nitrate solution that the blades are soaked in. The researchers covered two blades of the soaked grass with a thermal shrink tube to prevent the solution from evaporating. The anode in the battery is made of lithium metal, while the cathode is made of vanadium oxide. Both are sealed in glass tubes with an ion exchange membrane and connected with a wire to allow the flow of electrons. The researchers connect a grass ‘cable’ to each of the membranes.
The test the batteries, the researchers connected the grass cables to either end of a lithium salt-soaked cotton string, which had a dot of blue copper ions in the middle. When the circuit was complete, the copper ions visibly moved along the string towards the negative pole, proving the ion flow.
At present, the battery is a proof-of-concept rather than something that can be used soon but the researchers say it is the first time anything like this has been achieved. They are currently developing various ionic conductors made from cellulose, hydrogels and polymers.
Nature Communications: doi.org/gbpt45
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