Batteries could have 50% more capacity and charge far faster using phosphorene nanoribbons and sodium instead of lithium and graphene say researchers.
Phosphor is plentiful and found more widely than lithium and combined in its two-dimensional form, known as phosphorene, with sodium, it could replace lithium and graphene at the anode of batteries. Lithium ion batteries use graphene and lithium at the anode, but with phosphorene and sodium instead, researchers are expecting a 50% battery capacity boost and far faster charging times. The phosphorene nanoribbons are also expected to enable faster electronics, more efficient solar cells, improved thermoelectric devices, and have applications in nanoelectronics and quantum computing.
“There are a lot of people working on sodium ion batteries, it is fast charging, the capacity is predicted to be 50% more than lithium,” says University College London department of physics and astronomy associate professor, Chris Howard. “We’re trying to electrify vehicles and you know what the charging problems are with these cars, so if you can make it charge quicker, anything quicker is very important to investigate.”
Researchers isolated the 2D phosphorene, which is considered to be the phosphorus equivalent of graphene, in 2014. Howard pointed out that the many papers had been written predicting the wide range of potential uses for phosphorene nanoribbons. “In energy materials, for example, they are predicted to absorb infra-red light and support the excited electronic states, that are required for solar cells,” Howard added. This higher level of IR light absorption would make the solar cell more efficient.
High-speed atomic force microscopy topography of phosphorene nanoribbons with varying heights from 1 (left) to 5 layer (right) layer thicknesses. Credit: Oliver Payton
The nanoribbons were created by dissolving lithium in liquid ammonia which is at a temperature of -50 degrees Celsius and mixed with black phosphorus. The lithium would be replaced by sodium for the phosphorene, sodium anodes. After 24 hours, the ammonia is replaced with an organic solvent and it is this solvent that creates a solution of nanoribbons of mixed sizes. “We made this [phosphorene nanoribbon] material kind of by chance,” Howard explained. The nanoribbons look like they are corregated, like corregated iron.
The key to its commercial use is scaling up production to meet the quantities needed by battery and electronics manufacturers. Howard is confident that that is possible. Because a phosphorene battery can use sodium there is a potential cost saving because sodium is 100 times cheaper than lithium and far more widely available, according to Howard. The reason why a phosphorene, sodium battery can charge much faster is that the sodium ions can travel 1000 times faster within the corregations of the phosphorene than lithium ions can in the corresponding graphene material.
The team wants to investigate phosphorene’s use in applications in energy storage and work with new partners to study its possible roles in thermoelectric devices and other applications. The research involved University College London, University of Bristol, Virginia Commonwealth University and Ecole Polytechnique Federale de Lausanne. The work was funded by the United Kingdom’s Engineering and Physical Sciences Research Council and the Royal Academy of Engineering.