Imaging: M. Iqbal Shaikh

It’s unlikely that anyone in Calcutta would know Parag Banerjee. But soon, we all will be benefited by the work being carried out by this young Bengali researcher, born and raised in Chandigarh, at the University of Maryland in the US.

The university’s NanoCenter, of which Banerjee is a part, is designing a new type of energy storage device which will benefit a wide range of devices in use today — from electric cars to laptops to renewable energy systems.

Batteries that are currently used in electric or hybrid cars don’t hold enough energy for driving long distances. Besides, they take excruciatingly long hours to recharge and can’t give enough power for acceleration. For instance, electric cars manufactured by Indian carmaker Reva can clock just 40 kilometres before a recharge is due. But, once fully developed, the energy storage device, envisaged by the Maryland team, will be able to make electric cars run for 500km.

Furthermore, this device — which combines the best features of conventional devices to store a large quantity of charge and release it rapidly — will be useful for storing electrical energy produced by alternative energy sources. Renewable energy sources like the sun and wind provide time-varying, unpredictable energy supply, and hence they must be captured and stored as electrical energy. “Conventional devices to store and deliver electrical energy (batteries and capacitors) cannot achieve the desired combination of high energy density, high power and fast recharge,” says Gary Rubloff, Banerjee’s supervisor.

At the heart of the new energy storage device, is a novel class of nanostructures that Banerjee helped design and build. These nanostructures are basically tiny holes created on a thin film — as thin as an atomic layer. The scientists created such nanopores on a very thin film using a process called Atomic Layer Deposition that Banerjee had used during his six-year-long stint at a semiconductor firm prior to signing up for a doctoral programme under the guidance of Rubloff about three years ago. “My background as an R&D engineer at Micron Technology Inc. came in very handy throughout the project and led to its ultimate success,” Banerjee told KnowHow.

Parag Banerjee, one of the brains behind the technology

These nanopores store energy just as a conventional capacitor stores energy, by storing charge in an insulator sandwiched between two metal plates. The scientists have successfully created capacitors inside the nanopores. “We could accommodate as many as one million tiny capacitors on one square centimetre area,” says Banerjee, who is the first author of the study, which was recently published in the journal Nature Nanotechnology.

Once these nanopores were created, the scientists deposited a metal, then an insulator, and then again a metal in them. These tiny metal-insulator-metal structures work exactly like electrostatic capacitors, says Banerjee.

Electrical storage devices fall into three categories. Batteries, particularly lithium ion ones, store large amounts of energy but cannot provide high power or recharge fast. Electrochemical capacitors, such as those used in a household inverter, offer higher power but can store very little energy. Electrostatic capacitors, on which the current research is focused, operate purely by physical means, storing charge on the surfaces of two conductors. This makes them suitable for high-burst power applications. But they have very low energy density.

Keeping these in mind, the Maryland researchers have developed a prototype of a super battery. “These super batteries target a particular problem in the energy requirements of modern society. That is, they help store large amounts of charge and help deliver very high bursts of energy when called upon. It is indeed a big step towards realisation of cheap electric cars someday,” says Banerjee.

“This one looks like an interesting development. But its value will depend whether they can take what they have achieved in the lab to the market,” says N.G. Renganathan, who leads research into lithium batteries at the Central Electrochemical Research Institute in Karaikudi in Tamil Nadu. The challenge actually lies in producing such nanocapacitors on an industrial scale, that too at competitive prices, he says.

Banerjee hopes that in future it might be possible to roll out large foil-like sheets containing these nanopores, into which capacitors can be built. Banerjee, as part of his Ph.D., plans to integrate this super energy storage device with photovoltaic (PV) panels that produce electricity using solar energy. “I will not venture to guess whether it can be possible or not, without attempting it first,” he says. But, he hopes, this will make PVs compact and commercially viable.