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Packing batteries with more punch

M Ramesh | Updated on December 20, 2020

Indian researchers are working on cells that can store more energy, last longer

The scientific world is all charged up about developing batteries that can store more energy — and India seems to be at the forefront of the exercise.

A cell, which is a unit of a battery, has four parts — anode, which supplies electrons; cathode, which receives them; electrolyte, the medium through which the anode atoms that have lost an electron (or ion) move to the cathode; and separator, a physical barrier between anode and cathode (together called electrodes).

Of these, the separator’s role is limited; intense research is on globally to make the other three better.

The favourite material for anode today — no prizes for guessing! — is lithium, for it is a very light metal with electrons to give away (though scientists are also trying out other metals such as sodium and iron). The anode is typically a compound of lithium, because pure (metallic) lithium is an uncontrollable brat. This compound is usually kept embedded in graphite.

The focus of many researchers is on developing better anodes so that a cell packs more energy and lasts longer. Scientists at the Hyderabad-based International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI) and IIT-Madras recently announced the development of a “high-performance” anode made of a composite material — an ortho-rhombic form of molybdenum trioxide and ‘single-walled carbon nanohorns’ (SWCNH).

(The SWCNHs are composed of thousands of carbon nanocones, which typically exist as spheres of 80 nanometres diameter. A nanometre is a billionth of a metre.)

This can load a lot more charge and speed up charging. “With a scalable synthesis technique and superior cell performance, the molybdenum trioxide/SWCNHs composite anode could replace the existing graphite-based anode for the next-generation lithium-ion batteries,” says Dr R Prakash, a scientist at ARCI.

ARCI has also developed a new process for making the more conventional anode — lithium titanium oxide (LTO) — which has the potential to bring down the cost of a battery. The scientists used different input materials (precursors) — TiO2 and Li2CO3, ARCI scientist Dr S Anandan says.

Solid state battery

Another significant research pertains to the development of a new type of electrolyte, a solid called ‘lithium garnet’, by Prof Ramaswamy Murugan of the University of Pondicherry. Murugan’s solid electrolyte has a crucial advantage — it enables the use of metallic lithium, which can donate more electrons, which, in turn, means more energy can be stored.

Solid state batteries are the future, Murugan tells Quantum, because of their high energy density.

“The combination of lithium garnet with metallic lithium is perfect,” he says, but notes there is still work to be done at the interface between the electrolyte and the cathode. He is trying to to solve this is by adding a polymer nano composite to the electrolyte.

Incidentally, Murugan’s project has been selected for Government of India’s financial support under an Indo-Hungarian science collaboration programme, which will cover his expenses of working with a Hungarian scientist. Hungarian help is sought to develop the polymer nano composite.

Murugan says that the technology can deliver energy density of 350 Whr/kg initially, which can easily be scaled up to 500 Whr/kg. Conventional lithium-ion batteries — of 100-260 Whr/kg capacity — are used everywhere, from cellphones and laptops to electric vehicles, but with greater storage capacity, can even power planes. His research promises to lead to cutting-edge anode-free lithium batteries, where they put a little of the metal on the cathode itself and produce the anode in-situ. This, incidentally, is the technology pursued by a US-based start-up called QuantumScape, founded by an Indian, Jagdeep Singh, and funded by Volkswagen and Bill Gates Foundation, and which went public just last year. Tellingly, the company’s tagline is “the future is solid”.

The next big breakthrough in Li-ion batteries is the commercial-scale production of a solid state battery, whose importance has been underscored by global experts such as Prof Werner Weppner of the University of Kiel, Germany. Niti Aayog has been apprised of Murugan’s invention and Hyderabad-based, NSE-listed HBL Power Systems has shown interest in a tie-up.

Scientists are also on to sodium-ion, iron-ion and zinc-ion anodes, too. While Dr AS Prakash and his team at the Central Electro-Chemical Research Institute (CECRI), Chennai, have developed a sodium-ion battery and fine-tuning its performance, Prof Ramaprabhu Sundara of IIT-Madras has come up with an iron-ion battery — the anode is a steel alloy with 0.15 per cent carbon, the cathode has vanadium pentoxide and the electrolyte is an iron perchlorate hydrate dissolved in non-inflammable ether.

His colleague, Dr Aravind Chandiran, is looking at a zinc-air battery, which will halve the cost per kWhr compared to conventional Li-ion batteries. The project has got ₹1.49 crore government funding, besides support from Ashok Leyland and Hindustan Zinc.

Battery technology is among the few technologies in which India is in the forefront of global efforts. For example, CECRI’s research in sodium-ion is on a par with work anywhere in the world, says Dr Prakash.

However, most home-grown technologies fall into what is called the ‘valley of death’ — the grey zone between lab and market. Researchers that Quantum spoke to say that industry interface is crucial for bringing lab-grown technologies to the market.

Published on December 20, 2020

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