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Tuesday, 25 August 2015

Graphene nanofluids for faster batteries

ICN2 researchers have developed a new type of fluids with graphene and other carbon nanoparticles for energy storage in flow-cells. The nanofluids can be used in applications that require high power and medium energy densities.

Improving energy storage is essential within the upcoming sustainable energy model.  The redox flow cells are one of the most promising alternatives to tackle higher-power applications at a low cost. Still, they have some drawbacks. “This type of batteries has been used for a long time. But they contain, as a electroactive material, solutions of salts such as vanadyl sulfate, which has a relatively low capacity for energy storage”, explains CSIC Prof Pedro Gómez-Romero, Group Leader at ICN2.

To increase the stored energy the electroactive material should be replaced. One of the best options are electroactrive nanofluids, which contain  nanoparticles made of an electroactive material instead of the diluted salts. The electroactive material is similar to the ones applied in conventional solid-state batteries.

The Group led by Prof Pedro Gómez-Romero has created a type of nanofluids that contain nanoparticles, made of graphene or other carbons, dispersed in an electrolytic solution. “The idea is to replace the solid-state electrode, which is limited in a small space in a conventional battery, for an electrode dispersed in the form of nanpoparticles suspended in a fluid”, he explained. “This allows us to introduce more electroactive material and therefore to increase the amount of stored energy”.

This also allows for larger batteries. For that reason, the first envisaged applications are stationary batteries, to store electricity obtained from renewable sources for and load levelling. Nevertheless, the scientists don’t exclude the possibility of applying them for future electric vehicles. In this case, it would be necessary to get a higher energy density per unit volume of nanofluid. If that is achieved, in this type of cars the tank wouldn’t be refilled with fuel but with electroactive nanofluids: the discharged nanofluids would be removed from the car and replaced with charged nanofluids.

Scientists have demonstrated in laboratory that these nanofluids allow a fast storage of energy in flow cells with high power, and a high efficiency is achieved. The energy return reaches a 90% of the stored energy, versus a 25-30% of the return/efficiency of fuel in a conventional car. The nanofluids are very stable and can be produced at low cost. The ciclability is also efficient: up to 98% of the starting charge is retained after 1.500 cycles although it could be more, as scientists says, “we keep counting”.

Information via: Knowledge Transfer, CSIC