Greener ‘water batteries’ a step closer thanks to breakthrough by Melbourne researchers

<span>A water battery developed by researchers at RMIT in Melbourne.</span><span>Photograph: Carelle Mulawa-Richards/RMIT University</span>
A water battery developed by researchers at RMIT in Melbourne.Photograph: Carelle Mulawa-Richards/RMIT University

An RMIT-led research team has come up with an innovative way to make greener, safer, recyclable “water batteries” that could replace common lead-acid batteries.

There are three key components that make up a battery: a cathode, an anode and an electrolyte. In common lithium-ion or lead-acid batteries, the electrolyte is a liquid chemical solution that, once inserted, cannot be easily recovered.

The lead researcher, Prof Tianyi Ma, said his team’s water battery – known as an “aqueous metal-ion battery” – addresses the issue by swapping out the hazardous chemical electrolyte for water.

“It’s pure water. It’s the daily water we drink, but we do add additives to the water like inorganic salts,” Ma said.

Ma said his battery operates comparably to current lead-acid batteries but can be easily recycled without the risk of chemical pollution or the need for specialist equipment and disposal facilities.

“There are several advantages of using water as an electrolyte, the first being that we can assemble and dissemble it on the bench,” Ma said. “We can recycle it right here – we can do it in open air, we don’t need to avoid water, avoid moisture in the atmosphere as with lithium-ion batteries.”

Another advantage is that water batteries eliminate the risk of fires commonly associated with lithium-ion batteries. According to the Australian Council of Recycling, lithium-ion batteries cause at least three fires in recycling streams every day.

Water batteries are also cheaper. Because they do not require complex manufacturing processes and the materials cost less, they can be produced for a third of the price of lithium-ion batteries, Ma said.

So far the team has prototyped water batteries in coin-cell-type devices commonly found in small clocks, battery packs once used in old Nokia-style mobile phones and AA-style cylinder batteries.

These have achieved 500 or more charge cycles but maintain 80% of their capacity after 700 cycles.

Ma said if commercialised, the technology offers a “greener, safer” replacement for lead-acid batteries in household appliances or could be used in larger applications such as rooftop solar power storage or on a solar farm.

But as the technology improves over the next decade or longer, he believes they could eventually challenge lithium-ion batteries.

The RMIT-led team’s breakthrough is published in Advanced Materials, outlining a process by which zinc anode is coated with a nano material composed of bismuth metal, which is allowed to oxidise.

This rust creates a protective layer that stops dendrites from forming. Dendrites are tiny spurs that form on the metal anode over the course of a charging cycle, a common problem in battery development.

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This layer also provides protection from corrosion caused by the water electrolyte.

The managing director of Deakin University’s Battery Research and Innovation Hub, Dr Timothy Khoo, who was not involved in the research, said he was sceptical about any claims water batteries may one day replace lithium-ion, but said the protective layer developed by the RMIT-led team represents a “novel and quite unique” approach that solves “a key stability issue” with battery technology.

“You could describe it as they’ve ‘grown it’,” he said. “They’ve been able to put this bismuth oxide layer on the zinc anode that stops all the side reactions occurring and it helps the zinc, when it plates back on, to plate back on quite favourably,” Khoo said.

“Their solution solves a number of issues within aqueous batteries. How stable it cycles, whether it forms dendrites on the surface – it looks like it inhibits a lot of the site reactions that you don’t want.

“It’s very comprehensive work.”