While relatively more eco-friendly than conventional methods, the use of such strong chemicals on an industrial scale could generate a substantial amount of secondary pollutants, posing significant safety and health risks, said Asst Prof Tay.
The NTU team found that the combination of orange peel that has been oven-dried and ground into powder, and citric acid, a weak organic acid found in citrus fruits, can achieve the same goal.
In lab experiments, the team found that their approach successfully extracted around 90 per cent of cobalt, lithium, nickel, and manganese from spent lithium-ion batteries - a comparable efficacy to the approach using hydrogen peroxide.
"The key lies in the cellulose found in orange peel, which is converted into sugars under heat during the extraction process. These sugars enhance the recovery of metals from battery waste. Naturally-occurring antioxidants found in orange peel, such as flavonoids and phenolic acids, could have contributed to this enhancement as well," said Dalton Tay, an assistant professor in the NTU School of Materials Science and Engineering and School of Biological Science.
Importantly, solid residues generated from this process were found to be non-toxic, suggesting that this method is environmentally sound, he added.
From the recovered materials, the team then assembled new lithium-ion batteries, which showed a similar charge capacity to commercial ones. Further research is underway to optimise the charge-discharge cycling performance of these new batteries made from recovered materials.
The team is now looking to further improve the performance of their batteries generated from treated battery waste. They are also optimising