Roughly 270 years ago, Dr Johann Gottlob Leidenfrost from Germany observed a peculiar
behaviour of water droplets on heated metal surfaces. In his manuscript, “A Tract About Some
Qualities of Common Water,” he described how water skated over superheated metal surfaces as
though friction had ceased to exist. This occurs when water or any liquid forms a vapor cushion
on surfaces far above their boiling point, allowing them to glide untouched.
The phenomenon, known as the Leidenfrost effect, is why stainless-steel pans suddenly become
nonstick when heated to high temperatures. But how would a 270-year-old observation have any
bearing on the design of sustainable energy storage systems? In a study recently published in
Small, a team of researchers from the Indian Institute of Science Education and Research
(IISER) Bhopal, the Indian Institute of Technology Gandhinagar (IITGN), Swansea University,
and the University of Southern Queensland has explored how this unusual physics effect can
help create more stable, longer-lasting batteries and emerge as a practical alternative to the
lithium-ion (Li-ion) technology.
As the world pivots toward renewable energy, the demand for better batteries has never been
higher. “Lithium-ion batteries currently power everything from our smartphones to electric cars,”
said Dr Rohit Ranganathan Gaddam. He is a senior author of the study and an Assistant
Professor at IISER Bhopal, where he leads the Clean Energy Research Group and focuses on
overcoming bottlenecks in today’s energy storage systems. “However, lithium is relatively rare
and expensive to extract, making a greener, cost-effective alternative necessary.”
Sodium has long been touted as a potential replacement for lithium. A ubiquitous element found
in seawater, salt, and even your bloodstream, sodium is cheap and easy to source. This makes
sodium-ion batteries a strong candidate for large-scale energy storage, especially for renewable
energy. But the bulkiness of sodium ions poses a significant roadblock. The heavier ions end up
choking and wearing out the cathode, the positive terminal of a battery that acts as its energy
vault. For a sodium battery to work well, the material used in its cathode must allow sodium ions
to move quickly and repeatedly without damaging its structure. Many promising materials exist,
but they often lack speed, stability, or long-term durability.
“We decided to build the right cathode infrastructure, an atomic highway, so that sodium ions
could zip through!” added Subhajit Singha, first author and a PhD scholar at IISER Bhopal. The
team used Na₄Fe₃(PO₄)₂(P₂O₇), an iron-based phosphate-pyrophosphate mixture that
naturally forms a stable 3D tunnel-like structure. Knowing the conductivity and energy
drawbacks of purely iron-based cathode materials, the researchers experimented by adding a
small fraction of indium to the mixture.
It was observed that by replacing just 1% of the iron atoms with indium, the atomic spacing
within the potential cathode material increased, without alteration in its fundamental blueprint.
This allowed the sodium ions to slip through more effortlessly and improved the electronic
conductivity of the cathode material, a hallmark of high-performance batteries.
In addition to tweaks to the cathode material recipe, the team also introduced novelty in its
manufacturing process. “We tapped into the basics of the Leidenfrost effect to build cathode
materials that outlast and outpace the standards currently in the market,” said Dr Gaddam. They
sprayed the chemical mixture onto a metal surface that was hot enough to trigger the Leidenfrost
effect. As the droplets hit the blazing plate, they underwent flash evaporation, fused into porous
particles, and were baked into powder. This quick, green method skips energy-hungry furnaces,
yielding sponge-like grains that soak up electrolyte fluid for smoother sodium travel.
Advanced measurements and computational simulations provided insights into the atomic-level
restructuring. The results highlighted how indium subtly rearranges the atomic structure,
widening ion pathways, lowering energy barriers, improving conductivity, and keeping the
crystal structure of the potential cathode material intact over thousands of cycles.
“The optimised cathode material demonstrated a high energy density of ~359 Wh kg-1, and
remarkable durability with stable performance over 10,000 charge-discharge cycles,” said Dr
Raghavan Ranganathan, a co-author and an Associate Professor at IITGN’s Department of
Materials Engineering. For comparison, most phone or laptop batteries last only a few hundred
cycles. This makes the generated cathode material ideal for renewable energy storage in systems
that require long-lasting performance.
For India, aiming for 500 GW of renewables by 2030, a scaled-up, industrially tested version of
sodium-ion batteries with the novel cathode could mean affordable grid storage to harness solar
and wind without blackouts. “Our study shows that strategic atomic-level modification,
combined with a simple and scalable synthesis route, can unlock performance that was
previously out of reach for sodium-ion battery cathodes,” said Dr Gaddam.
In alignment with national energy missions and the United Nations Sustainable Development
Goals 7 (affordable clean energy) and 11 (climate action), the study is a step towards reducing
reliance on lithium, facilitating fairer supply chains, and enabling the affordable storage of green
power. “This fusion of experimental and computational expertise across institutions and
continents proves historic quirks like Leidenfrost can spark modern hubs of sustainable
innovation!” remarked Dr Ranganathan.
The authors acknowledge support from the Anusandhan National Research Foundation (ANRF),
Department of Science and Technology, University Grants Commission, the University of
Southern Queensland, and the Australian Research Council.