'Radical' new aqueous aluminium batteries

Scientists from Flinders University in South Australia and Zhejiang Sci-Tech University in China have reported the first stage of developing safe and efficient non-toxic aqueous aluminium radical batteries, in an article published by the Journal of the American Chemical Society. Most batteries contain hazardous materials and can pollute the environment when disposed of in landfill or when thrown out elsewhere. Materials like lead, cadmium and mercury can poison people and animals and contaminate soils and water.

Dr Kai Zhang, from Zhejiang Sci-Tech University, and Associate Professor Zhongfan Jia’s research lab at Flinders University collaborated on the electrochemistry of stable radicals in the most-used Lewis acid electrolyte (Al(Otf)₃ and battery test. The researchers are developing aluminium radical batteries which use water-based electrolytes that are fire-retardant and air-stable, delivering a stable voltage output of 1.25 V and a capacity of 100 mAh g^-1 over 800 cycles with only 0.028% loss per cycle.

Jia hopes to use biodegradable materials to develop the soft-pack batteries of the future to make the product safe and sustainable. Multivalent metal ion batteries, including Al³⁺, Zn²⁺ or Mg²⁺, use abundant elements of the Earth’s crust and provide higher energy density than lithium-ion batteries. “In particular, aluminium-ion batteries (AIBs) attract great attention because aluminium is the third most abundant element (8.1%), which makes AIBs potentially a sustainable and low-cost energy storage system,” Jia said.

However, current AIBs have slow-moving Al³⁺ ion complexes, which can lead to AIBs with low cathode efficiency. Organic conjugated polymers are emerging cathodes for AIBs to address the ion transport issue but their battery voltage output performance remains poor. Stable radicals have been used widely in different organic battery systems, with the first of this kind commercialised by NEC in 2012.

The Jia Lab at Flinders University has previously developed radical materials for organic hybrid lithium-ion batteries, sodium-ion batteries and all-organic batteries. These radical materials have not been applied in AIBs due to a lack of understanding about their electrochemical reaction in electrolytes.

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