A new battery tech that is safe, efficient, and non-toxic

Dr. Kai Zhang of Zhejiang Sci-Tech University teamed up with Associate Professor Zhongfan Jia's research lab at Flinders University to explore the electrochemistry of stable radicals. Their collaborative work focused on the most commonly utilized Lewis acid electrolyte, Al(Otf)3, and included battery testing.

Stable radicals are organic molecules that have been widely used in different organic battery systems. They have never been applied in aluminium-ion batteries (AIBs) before, due to a lack of understanding of their (electro)chemical reaction in electrolytes.

The researchers discovered that a stable radical called TEMPO can undergo reversible disproportionation in the presence of a Lewis acid, which enables the formation of aluminum radical batteries.

Professor Jia said that most batteries contained hazardous materials and could pollute the environment when disposed of in landfills or when thrown out elsewhere. He said that materials like lead, cadmium, and mercury could poison people and animals and contaminate soils and water, and they stayed in the environment for a long time.

Water-based electrolytes

He said that their battery used water-based electrolytes that were fire-retardant and air-stable, making it safe and sustainable. He also said that they used biodegradable materials for the soft-pack batteries to reduce the environmental impact.

Professor Jia said that aluminum-ion batteries had great potential as an alternative to lithium-ion batteries, which were widely used in consumer electronics, electric vehicles, and renewable energy storage systems.

He said that aluminum-ion batteries used abundant elements of the Earth’s crust and provided much higher energy density than lithium-ion batteries. However, he said that one of the major challenges for current AIBs was the slow movement of Al3+ ion complexes, which led to AIBs with low cathode efficiency. He said that organic conjugated polymers were emerging cathodes for AIBs to address the ion transport issue but their battery voltage output performance remained poor.

He said that their novel design of aluminum radical batteries solved this problem by using stable radicals as cathodes, which could achieve a high voltage output and a high capacity with excellent cycling stability.

The researchers hoped to further optimize the battery performance and scale up the production for commercialization in the future.

The study was published in the Journal of American Chemistry.

Study abstract:

Nitroxide radicals, such as 2,2,6,6-tetramethylpiperidyl-1-oxy (TEMPO), are typical organic electrode materials featuring high redox potentials and fast electrochemical kinetics and have been widely used as cathode materials in multivalent metal-ion batteries. However, TEMPO and its derivatives have not been used in emerging rechargeable aluminum-ion batteries (AIBs) due to the known disproportionation and possible degradation of nitroxide radicals in acidic conditions. In this study, the (electro)chemical behavior of TEMPO is examined in organic and aqueous Lewis acid electrolytes. Through in situ (electro)chemical characterizations and theoretical computation, we reveal for the first time an irreversible disproportionation of TEMPO in organic Al(OTf)3 electrolytes that can be steered to a reversible process when switching to an aqueous media. In the latter case, a fast hydrolysis and ligand exchange between [Al(OTf)3TEMPO]− anion and water enable the overall reversible electrochemical redox reaction of TEMPO. These findings lead to the first design of radical polymer aqueous AIBs that are fire-retardant and air-stable, delivering a stable voltage output of 1.25 V and a capacity of 110 mAh g–1 over 800 cycles with 0.028% loss per cycle. This work demonstrates the promise of using nonconjugated organic electroactive materials for cost-effective and safe AIBs that currently rely on conjugated organic molecules.