World's first non-toxic aluminum-ion batteries developed – Interesting Engineering

by | Jul 10, 2023 | Engineer

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While batteries have become an essential part of our daily lives, traditional disposable batteries heavily pollute the environment, containing hazardous materials like lead, cadmium, and mercury that are incredibly challenging to recycle. 
Scientists emphasize that the toxic material can poison people and animals as well as contaminate soil and water when they are exposed to the environment over time.
However, in a recent development, scientists from China and Australia have come a long way towards producing the world’s first safe and efficient non-toxic battery. 
The researchers say that they have successfully completed the first stage of developing the new batteries, and have set a new standard for battery safety and performance.
The study was conducted by a team of researchers from Flinders University in South Australia and Zhejiang Sci-Tech University in China.
The new batteries are made using special materials known as stable organic radicals which contain a crucial element 2,2,6,6-tetramethylpiperidyl-1-oxy – also known as TEMPO.
Instead of using harmful chemicals, they use water-based liquids. These water-based electrolytes helped evolved the first design of aluminum radical batteries that are both fire-retardant and air-stable, according to the researchers. 
They said, “the element delivers a stable voltage output of 1.25 V and a capacity of 110 mAh g–1 over 800 cycles with only 0.028% loss per cycle.”
The composition allows the batteries to store energy efficiently and equips them with the ability to not catch fire easily. It increases their potential to be cost-effective and delivers a safe way to store energy for various uses.
The statement says that Professor Zhongfan Jia, from Flinders University, hopes to use biodegradable materials for development of the soft-pack batteries in the future to make the product safe and sustainable.
Additionally, the batteries made of multivalent metal ions particularly – Al3+, Zn2+, or Mg2+, employ abundant elements of the Earth’s crust and provide much higher energy density than commonly used lithium-ion batteries (LIBs).
“In particular, aluminum-ion batteries (AIBs) attract great attention because aluminum is the third most abundant element (8.1%), which makes AIBs potentially a sustainable and low-cost energy storage system,” Jia said.
One of the significant challenges scientists face is the slow movement of AI3+ ion complexes, which can cause the batteries to lower their cathode efficiency. 
The researchers say that the organic conjugated polymers are emerging cathodes for AIBs to address the ion transport issue, but their battery voltage output performance remains poor.
“These radical materials have never been applied in AIBs due to lacking understanding of their (electro) chemical reaction in electrolytes,” state the researchers. 
The journal was published on 23 June in the Journal of the American Chemical Society.
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.

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