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Sodium ions are chemistry that is receiving increasing attention in the battery research community, due to the fact that it offers a more sustainable alternative to those based on the tried and true lithium which is relatively rare and expensive to mine. In contrast, sodium is abundant and offers high theoretical capacity, and research is beginning to find that they could play a useful and low-cost role in our future energy storage needs.

One problem scientists continue to encounter with sodium-based batteries, however, is the uncontrolled growth of tentacle-like structures called dendrites. These form as the battery cycles, and they can puncture the separating membrane located between its two electrodes and trigger problems with shorting out the device.

Researchers at the University of Bristol have come up with a new solution to this problem. Working with scientists from Imperial College and University College London, the team has extracted cellulose material from brown seaweed and used it to form a new fiber-based sodium battery separator material. These fibers prevent the formation of dendrites, but also happen to enhance the performance of the battery.

The purpose of the separator is to separate the functional part of the cell (positive and negative) and allow free charge transfer,” said Jing Wang, the first author of the paper on the study. We have found that the algae-based material makes the separator very strong and prevents it from being punctured by a metal structure made of sodium. In addition, it allows for greater storage capacity and efficiency, and increases the life of the battery – the key to providing longer power for devices such as cell phones.”

In tests, the team found that the battery design could maintain unprecedented long-term stability, which could be achieved by maintaining high energy density even after 1,000 cycles. The team said this approach could also be applied to other battery types to make them more efficient, and they are now turning their attention to scaling up the production of the material.

“I’m excited to see how these nanomaterials can strengthen separator materials and enhance our ability to move toward sodium-based batteries,” said Dr. Amaka Onyianta, “which means we won’t have to rely on scarce materials like lithium, which is often mined unethically and uses large amounts of natural resources like water to extract it.”

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