Scientists at Chalmers Technical University (Sweden) have used graphene to create a new type of anode for sodium-ion batteries, making their capacity comparable to lithium-ion batteries.
Sodium-ion batteries are not used very often in mobile devices, since traditional lithium-ion batteries offer 2 times higher energy density – 285 kWh / kg. Scientists at Chalmers Technical University have found that with a new type of graphene electrode, a sodium ion battery can demonstrate similar performance: this material is able to hold the same number of sodium ions. Sodium-ion batteries are more stable and cost-effective – in electric vehicles and electronics, they will prove useful, while lithium-ion batteries can be dangerous if they overheat.
For fast charging and a large battery capacity, ions must easily enter the anode material. The cathode of a sodium ion battery is made from sodium oxides, and a carbon-based material is used as the anode. It may be activated carbon, but it is expensive and difficult to produce. Its inexpensive analogue is graphite; however, sodium ions cannot efficiently move between graphene layers. To overcome this problem, scientists have created a new material that consists of alternating layers of graphene and benzene. The benzene layer increases the distance between the graphene layers, allowing sodium ions to move freely. In addition, benzene can form a strong bond with sodium ions.
According to the calculations of the authors of the project, the capacity of such a battery is comparable to that of a lithium-ion: with pure graphite, the energy density is 30 mA h / g, and with a new material it rises to more than 330 mA h / g.