Researchers have designed a new aluminum-ion battery that could improve the safety, sustainability, and affordability of large-scale energy storage—though more research is needed to refine the technology.
The research team added an aluminum fluoride salt to the battery’s electrolyte, transforming it into a solid-state form that enhances stability and prevents leaks. Rechargeable aluminum-ion batteries (AIBs) are emerging as an alternative to lithium-ion batteries, which are widely used in electrical vehicles and energy storage systems, but can sometimes be prone to fire and are costly to produce, partly due to lithium extraction and processing costs.
AIBs use a cheaper metal and contain a non-flammable electrolyte—the component that allows ions to travel between terminals when charging or discharging. However, liquid electrolytes in AIBs are prone to water vapour absorption and corrosion, which can lead to leaks.
Introducing the aluminum fluoride salt (AlF3) into the electrolyte resolves that issue, the researchers say. Past efforts to stabilize AIB electrolytes relied on gel-polymer electrolytes or metal-organic frameworks, but those alternatives had shortcomings, including low conductivity and limited ability to maintain a stable temperature. The new design using AlF3 helps aluminum ions move more efficiently through the battery and improves its stability in “demanding electrolyte environments.”
“This new Al-ion battery design shows the potential for a long-lasting, cost-effective, and high-safety energy storage system,” said Wei Wang, one of the researchers.
The researchers also found that adding a film of fluoroethylene carbonate to coat the battery’s electrodes prevented the formation of aluminum crystals that could degrade battery health.
The resulting battery cell was able to “achieve an unprecedented long cycle life of 10,000 cycles with an average Coulombic efficiency of greater than 99%.”
Coulombic efficiency measures how efficiently a battery charges and discharges over cycles, and maintaining high efficiency over many cycles is a key indicator of long-term performance. A charge higher than 99% is normal for a lithium-ion battery, and the data from the study by Wang’s team showed the battery retaining more than 99% of its charge capacity after 10,000 cycles.
Wang’s team also tested stability in harsh conditions by subjecting the batteries to puncture tests and high temperatures. The experiments showed that a light bulb stayed lit consistently as the battery was exposed to temperatures ranging from 40°C to 200°C. The battery did not ignite even when exposed to “a high-temperature flame” of about 1000°C, and remained safe after mechanical damage; even when the battery’s internal aluminum foil tore, “the pouch cell maintains smokeless, nonexothermic, and no electrolyte leakage,” says the study.
Other findings in the research indicate that 80% of the AlF3 framework could be recycled, which would lower the overall costs of using the batteries in energy storage systems. “The ability to recover and recycle key materials makes the technology more sustainable,” Wang said. The team suggests this recycling rate could be even greater because unavoidable inefficiencies are more pronounced in small-scale laboratory experiments, and material recovery would be higher in large-scale industrial production because of improved process efficiency.
Future experiments will still be needed to improve AIBs’ energy density, cycle life, and electrolyte stability, the researchers write. Figuring out how to use the batteries in practical applications will require additional research on advanced electrodes, scaling up production, and improving cost effectiveness.
