Sodium-metal batteries (SMBs) are among the most promising high-energy and low-cost energy storage systems for the next-generation of large-scale applications. However, one of the major impediments to the development of SMBs is uncontrolled growth of dendrites, which penetrate the battery's separator and result in short-circuiting.
Building on previous work at the University of Bristol, and in collaboration with Imperial College and University College London, the Bristol-led team succeeded in making a separator from cellulose nanomaterials derived from brown seaweed.
Their research paper describes how fibres containing these seaweed-derived nanomaterials not only stop crystals from the sodium electrodes penetrating the separator, they also improve the performance of the batteries.
"The aim of a separator is to separate the functioning parts of a battery (the plus and the minus ends) and allow free transport of the charge," said Jing Wang, first author and PhD student in the Bristol Composites Institute (BCI).
"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".
Professor Steve Eichhorn, who led the research at the BCI, said: "I was delighted to see that these nanomaterials are able to strengthen the separator materials and enhance our capability to move towards sodium-based batteries. This means we wouldn't have to rely on scarce materials such as lithium, which is often mined unethically and uses a great deal of natural resources, such as water, to extract it.
"This work really demonstrates that greener forms of energy storage are possible, without being destructive to the environment in their production".
The next challenge is to upscale production of these materials and to supplant current lithium-based technology.
Dr Amaka Onyianta, also from the BCI, who created the cellulose nanomaterials, co-authored the research.
The research paper - 'Stable Sodium Metal Batteries in Carbonate Electrolytes Achieved by Bifunctional, Sustainable Separators with Tailored Alignment' - has been published in the journal Advanced Materials.
Last month, the world's largest flow battery energy storage station was connected to the grid in Dalian, China, with the intention of reducing the pressure on the power supply during peak energy usage periods.
Battery energy storage systems have also been suggested as one possible answer to the UK energy crisis, as a way of optimising the flow of energy to and from the grid and minimising the loss of wasted energy.
