By Tess Macallan, Journalist, Mining Magazine
The demand for lithium-ion batteries is powering a thriving lithium mining industry in Australia, which is home to some of the largest reserves of the soft, silvery-white metal. Despite its commercial success, however, current lithium-ion storage technology suffers from limitations including insufficient energy density, relatively high costs and potential safety risks. Recognising these challenges, researchers from Edith Cowan University (ECU) have been exploring an alternative solution: zinc-air batteries.
In the midst of a global transition to renewable energy, lithium is leading the energy storage landscape. Lithium- ion batteries have long been heralded as the most viable solution for powering the world’s smartphones, laptops, electric vehicles and renewable energy systems.
However, Dr Muhammad Rizwan Azhar, who led the ECU project, said this technology is far from perfect.
“There are significant concerns regarding their safety due to their flammability. Additionally, lithium-ion batteries are often criticised for their relatively low energy density.”
Over recent years, other possible alternatives have attracted interest, including aqueous metal-air batteries, which use metals like zinc, iron, magnesium or aluminium combined with oxygen from the air to generate electricity.
Zinc-air batteries (ZABs) are particularly promising due to their large theoretical energy density, meaning they can store a significant amount of energy per unit of weight (1,353 watt-hours per kilogram). They also offer a lower cost, inherent safety and are considered more environmentally friendly.
“In contrast to lithium-ion batteries, zinc-air batteries are not flammable, making them a safer alternative,” Dr Azhar said.
“Moreover, they exhibit a higher energy density compared to traditional lithium-ion batteries. This combination of safety and enhanced energy storage capacity makes zinc-air batteries a promising contender in the field of energy storage technology.”
A recent breakthrough
Until now, rechargeable zinc-air batteries have faced significant limitations, primarily concerning their short lifespan and reduced performance due to a higher voltage gap.
Dr Azhar said his team has been involved in the research of zinc-air batteries for at least the last five years and has gone through extensive iterations of designing/redesigning of cathode materials.
“Design tuning of cathode materials is important to overcome the performance and stability issues of ZABs without losing their efficiencies in terms of energy storage capability,” Dr Azhar said.
“During this process we have developed various materials that have shown promising results, with findings having been published in reputable international journals.
“Our main aim has been to design cathode materials through cost-effective and facile methods but maintain a high level of performance in ZABs.”
Dr Azhar said the research mainly focused on designing new materials for ZABs using cheap, locally available raw materials in Australia and major parts of the world.
“Metallic zinc was employed as anode for ZABs. For the development of the cathode, two types of materials are utilised, each playing a vital role in controlling oxygen evolution reaction (OER, involved in charging of battery) and oxygen reduction reaction (ORR, involved in discharging of battery).
“We employed the combination of transition metals such as cobalt, nickel, iron and carbon materials. Mostly, carbon-based materials show better ORR performance while transition metal- based compounds show better OER results.
“In this research, we created a synergy between carbon- based and transition metal-compounds through step-by-step synthesis method. The synthesised materials showed excellent performance in ZABs with ultra-long charging/discharging stability (950 hours).”
Dr Azhar said the major advantages of these batteries are their incombustibility, high energy density and environmental benignity.
“Furthermore, the structural design of our newly designed material with cages of cobalt – carbon – nitrogen (ZIF-67) and laminated nickel – iron layered double hydroxide with some extraction of cobalt from ZIF-67 provided smoother electron transfer from oxygen which improved the overall performance of the battery.”
Potential applications in Australia
Rechargeable ZABs can be used in almost every domain, just like lithium-ion batteries.
“ZABs find application across various sectors, and are particularly suited for battery energy storage systems (BESS) in both urban and regional landscapes,” Dr Azhar said.
“They are even better suited to regional areas and off-grid markets due to their high energy density and high safety.”
Furthermore, these batteries show excellent potential for low-speed vehicles such as micro mobility options and both short and long/haul trucks.
Dr Azhar said ZABs could also help decarbonise Western Australia’s mining industry.
“With the Western Australian Government’s initiative of offshore wind, the integration of ZABs with offshore wind and solar energy provide an excellent opportunity to store the harvested energy, leading to reduced load on grids and moving away from fossil fuels.”
The future with zinc
As of now, lithium-ion batteries are the dominant technology in the field of batteries and Dr Azhar said that’s not going to change anytime soon.
However, lithium is a finite resource and relying solely on lithium-based batteries poses limitations on shifting from fossil fuels to renewables.
“The energy density of lithium is around one third of zinc-air batteries,” Dr Azhar said.
“Furthermore, fire risks are high for lithium-ion batteries compared to non-flammable ZABs. Hence, robust ZABs will provide high energy density, at affordable price and in a safer manner.”
Moreover, the recycling process for ZABs is less complex and difficult in comparison to lithium. The rise of zinc-air batteries is unlikely to significantly impact demands for other critical minerals such as nickel, iron and cobalt, as these are used as cathode materials in both ZABs and lithium-ion batteries.
“On the other hand, applications of zinc have been limited to cathode protection (reducing rusting of iron and steel), personal care products, pharmaceuticals and non-rechargeable zinc batteries,” Dr Azhar said.
As a result, there is currently relatively low market demand for zinc. With increasing production of rechargeable ZABs, the production and mining of zinc are set to experience a boost in Australia and globally.
“The findings of our research provide an excellent opportunity mining companies to consider the production of battery minerals and metals,” Dr Azhar said.
“Moreover, vertical integration of zinc mining companies seems very promising in the near future, particularly as Australia is among the largest zinc producers in the world.
“All the required minerals required for ZABs are available in Australia. This eliminates the supply chain issues in unprecedented situations such as global pandemics.”
As the clean energy transition ramps up, the integration of zinc-air batteries presents a unique opportunity for Australia.
Supporting innovations in green energy technology can help combat climate change and position the nation as a global leader in batteries and electric vehicle production.