Lithium-ion batteries are at the forefront of technology and used in hardware and solar battery systems, including grid-scale energy storage systems.

The batteries contain a liquid electrolyte solution such as ethylene carbonate to create lithium ions, which allows the battery to store large amounts of energy.

That liquid electrolyte is extremely volatile and highly flammable, with the heat from a lithium-ion battery failure soaring to 400C in a matter of seconds.

A lithium-ion battery fire is self-sustaining and hard to contain.

RMIT lead researcher professor Tianyi Ma said the recyclable water batteries were at the forefront of an emerging field of aqueous energy storage devices.

He said replacing the volatile electrolytes with water meant the batteries could not start a fire or explode, unlike their lithium-ion counterparts.

"Addressing end-of-life disposal challenges that consumers, industry and governments globally face with current energy storage technology, our batteries can be safely disassembled and the materials can be reused or recycled," Ma said. 

"We use materials such as magnesium and zinc that are abundant in nature, inexpensive and less toxic than alternatives used in other kinds of batteries, which helps to lower manufacturing costs and reduces risks to human health and the environment."

Ma said researchers overcame some technological challenges such as boosting energy storage capacity and lifespan by testing a series of small-scale trial batteries.

They also found a way to prevent the growth of disruptive dendrites, which are spiky metallic formations that can cause short circuits and other serious faults, by coating affected battery parts with bismuth.

The oxide from bismuth forms a rust that acts as a protective layer to prevent dendrite formation.

Ma said that meant the batteries lasted significantly longer compared to commercial lithium-ion batteries on the market.

"With impressive capacity and extended lifespan, we've not only advanced battery technology but also successfully integrated our design with solar panels, showcasing efficient and stable renewable energy storage," he said.

"We recently made a magnesium-ion water battery that has an energy density of 75 watt-hours per kilogram and the next step is to increase the energy density of our water batteries by developing new nano materials as the electrode materials."

Ma said magnesium would be the material of choice for future water batteries. 

"Magnesium-ion water batteries have the potential to replace lead-acid batteries in the short term and replace lithium-ion batteries in the long term," he said.

"Magnesium is lighter than the alternative metals, including zinc and nickel, has a greater potential energy density, and will enable batteries with faster charging times and better capability to support power-hungry devices and applications."