Innovative methods to recover energy from batteries

Researchers from NCKU have developed a new approach to recover energy from used batteries.

In many self-powered devices, alkaline and zinc-carbon batteries are frequently present. Once these batteries have been used, they are discarded, as it is estimated that from the 15 billion batteries that are annually produced and sold worldwide, the majority end up in landfills. However, this does not have to be the case. It is thought that although these batteries are not usable, there is a small amount of energy left in them. Approximately half of the batteries discarded often contain as much as 50% energy. There is therefore a potential to recover this energy from the batteries.

Recently, a group of researchers from Taiwan investigated the feasibility of recovering this energy from single-use discarded batteries. Led by Professor Chien-Hsing Lee from NCKU, Taiwan, the group focused its research efforts on this front to promote a circular economy for discarded batteries.

The study was published in Volume 69, Issue 6 of the journal IEEE Transactions on Industrial Electronics.

Combining methods to recover energy from batteries

In their study, the researchers proposed a new method called ‘self-adaptive pulse discharge’ (SAPD), which can be used to determine the optimal values of two key parameters – pulse frequency and duty cycle. These determine the discharge current from the discarded batteries. Simply put, a high discharge current amounts to a high amount of recovered energy.

“Draining small remaining energy from household batteries is a starting point for waste reduction, and the proposed energy recovery method serves as an effective tool to reutilise a large number of discarded primary batteries,” said Professor Lee, explaining his motivation behind the study.

The researchers also built a hardware prototype for their proposed approach. This was used to recover the remaining capacity of a battery bank, capable of holding – at least six and at most ten – batteries of different brands. They managed to recover between 798 and 1,455 J of energy from these batteries, with a recovery efficiency of 33% to 46%.

© iStock/SergeyKlopotov

The researchers found that for a discarded primary cell, the short-circuit discharge (SCD) method had the highest discharge rate at the beginning of the discharge cycle. The SAPD method, however, showed a higher discharge rate at the end of the discharge cycle. By using the SCD and SAPD methods, the energy recovered was 32% and 50%, respectively. However, by combing these methods, researchers recovered 54% of the energy.

To validate the feasibility of combing the methods, a few discarded AA and AAA batteries were chosen for energy recovery. This resulted in 35% to 41% of the energy being successfully recovered.

“While there seems to be no advantage in draining a small amount of energy from a single discarded battery, the recovered energy significantly increases if a large number of waste batteries are exploited,” highlighted Professor Lee.

It was suggested that there could be a direct link between the recovery efficiency and the remaining capacity of discarded batteries.

Utilising this method for the future

As for the future implications of their work, Professor Lee stated: “The model and the prototype developed can be applied to battery types other than AA and AAA. In addition to different types of single-use batteries, rechargeable batteries, such as lithium-ion batteries, can also be examined to provide more information about the variability among different batteries.”

The findings of this study have the potential to impact the energy industry, subsequently paving the way for the world’s transition to a sustainable future.

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