­ Seaweed-based Separator Halts Dendrite Formation

Dendrites are a block to progress in several new battery types. These branch-like structures grow between the anode and cathode and can be detrimental to the performance of the battery, or even cause short circuits. Either way, there is a sharp decrease in the number of charge-discharge cycles available to the user. Both solid-state lithium batteries and sodium metal batteries are badly affected by dendrites. Both of these chemistries would be advancements on the lithium-ion batteries that we mainly use today. Solid-state batteries are smaller than their Li-ion counterparts, charge faster and are much safer. Sodium-metal batteries also offer high energy capacity and have the potential to be much cheaper than Li-ion batteries. If dendrites could be eliminated, designers and consumers would be offered a much greater choice. Sodium-metal batteries also have a further advantage in that they are manufactured from cheap and abundant materials, whereas there is predicted to be a shortage of lithium, at least in the short to medium term, and the extraction of lithium often damages the environment. The realization of the potential of sodium-metal batteries would fulfil some of the shortfall, leaving lithium available for high priority applications.

There are many teams of researchers working on how to solve the dendrite problem, and one of them has come up with a unique solution. The researchers from the University of Bristol in collaboration with Imperial College and University College London have built on previous work and made a separator from cellulose nanomaterials derived from brown seaweed. Separators are porous barriers that are situated between the anode and cathodes of the battery. The new research describes manufacturing the fibres from the seaweed-derived nanomaterials and also how they stop the crystals from the sodium electrodes penetrating the separator, and improve the performance of the batteries.

“The aim of a separator is to separate the functioning parts of a battery and allow free transport of the charge. We have shown that seaweed-based materials can make the separator very strong and prevent it being punctured by metal structures made from sodium. It also allows for greater storage capacity and efficiency, increasing the lifetime of the batteries - something which is key to powering devices such as mobile phones for much longer,” said Jing Wang, first author and PhD student in the Bristol Composites Institute (BCI).

Dr Amaka Onyianta, also from the BCI, who created the cellulose nanomaterials and co-authored the research, said: “The nanomaterials strengthen the separator materials and enhance our capability to move towards sodium-based batteries.”

The next challenge is to upscale production of the new materials.

The paper detailing the research has been published in advanced Materials and is entitled ‘Stable Sodium Metal Batteries in Carbonate Electrolytes Achieved by Bifunctional, Sustainable Separators with Tailored Alignment’ by Stephen Eichhorn, Amaka Onyianta and Jing Wang et al.

https://www.bristol.ac.uk/