While the lithium-ion batteries commonly used in electric cars are capable of storing a fairly large amount of energy, they’re not able to accept or discharge that energy very quickly. That’s why electric vehicles require supercapacitors, to speedily deliver energy when accelerating, or to store it when braking. Recently, however, researchers from New York’s Rensselaer Polytechnic Institute created a new anode material, that allows Li-ion batteries to charge and discharge ten times faster than those using regular graphite anodes. It could make EV supercapacitors unnecessary, and vastly shorten the charging time required by electronic devices.
The team, led by Prof. Nikhil Koratkar, started by creating a large sheet of graphene oxide paper. About the thickness of a piece of printer paper, it was made up of layered sheets of graphene (each graphene sheet being composed of a one one-atom thick layer of linked carbon atoms).
That paper was cut into smaller pieces, which were then subjected either to a laser, or the flash from a compact camera. In either case, the resulting flash of heat caused “mini explosions” to take place throughout the thickness of the paper, as oxygen atoms were expelled from its structure. The result of this carnage was graphene sheets that were full of flaws such as cracks, pores and voids. Additionally, the pressure exerted by the escaping oxygen forced the stacked layers of graphene apart from one another, resulting in a five-fold increase in the thickness of the paper.
When samples of this paper were tested for use as anodes, however, the marked decrease in charge and discharge times was noted. This was due to the fact that the lithium ions could enter (or exit) the anode at almost any point, using its imperfections as points of entry – by contrast, on graphite anodes, the ions can only enter at the sides and then slowly work their way into the middle.
The graphene oxide paper anodes were found to still work perfectly after more than 1,000 charge/discharge cycles. According to Koratkar, the sheets can be easily and inexpensively made in just about any shape or size, and the production process should be easy to scale up. His team’s next order of business is to match the anodes up with a high-power cathode, within a full Li-ion battery.
A paper on the research was recently published in the journal ACS Nano.
Source: Rensselaer Polytechnic Institute