Research in Japan has been able to create a new, highly porous carbon-based material that replaces graphite, and can be used as an aodo in sodium-ion batteries, increasing its energy density above lithium ones.
A team of researchers from the University of Tokyo has managed to increase the energy density of sodium batteries. It is an energy efficient method to produce a new carbon-based material with a very high capacity to store sodium. The procedure is based on taking advantage of the highly porous nanostructure of this charcoal to use as a negative electrode of batteries (apod).
Sodium vs. Lithium
Lithium-ion batteries are used today in virtually all mobile applications, such as phones, laptops or electric vehicles. Its advantage is in the energy density they offer, which translates into more autonomy, above the longevity or stability of their components. Its biggest drawback is that the materials of which they are composed, such as cobalt andlithium, are scarce and expensive. As demand for electric vehicles and stationary electricity storage facilities increases, these materials will become more difficult to obtain and possibly raise their price.
Sodium is a material obtained from the oceans or the Earth’s crust and is therefore cheap, abundant and sustainable, making it a great candidate for large-scale energy storage. James Quinn, CEO of Faradion Ltd, a British sodium ion battery developer, told Bloomberg last September that “sodium is the sixth most abundant element on earth: it is unlimited and sustainable since it is harvested, not extracted.”
Unfortunately, these batteries don’t have as much energy as lithium batteries and also give degradation problems when charging and unloading. The key drawback for some of the most promising cathode materials is that a layer of inactive sodium crystals accumulates on the cathode surface, stopping the flow of sodium ions and consequently destroying the battery.
A new material raises the energy density of sodium batteries
The University of Tokyo study published by the Angewandte Chemie International Edition details an energy-efficient method for producing a new carbon-based material that raises the storage capacity of sodium batteries. It is based on the synthesis of hard carbon (charcoal), which is a solid form of carbon that cannot be converted into graphite by heat treatment.
The goal was to achieve a different battery negative electrode material than graphite currently used in lithium batteries as it does not work with sodium batteries. By using magnesium oxide (MgO) it is possible to adjust the nanostrucure of this highly porous material. After multiple experimental and theoretical analyses, the optimal manufacturing conditions and ingredients necessary for its production were established, so that it is possible to reach a capacity of 478 mAh/g,the highest of those that have been reported for graphite, which is 372 mAh/g.
A sodium-ion battery with this negative electrode would theoretically work with a potential difference of 0.3 volts lower than that of a standard lithium-ion battery. The higher capacity of the former would lead to a much higher energy density per kilogram of weight, 1,600 Wh/kg versus 1,430 Wh/kg, i.e.19% increase in energy density.
The study will continue to analyze other key parameters of these sodium ion batteries, such as input and output power, service life or low temperature operating capacity.
