Although graphene is the thinnest material known, it has exceptional mechanical, optical, and electronic properties, making it extremely attractive for a wide range of applications such as sensor technology, sports equipment, and the automotive industry.

In recent years there has been much talk about the immediate incorporation of graphene into batteries and supercapacitors. Despite being an up-and-coming field, there are still some years of research to bring this reality to the market. Indeed, the incorporation of graphene in electrochemical energy storage devices could significantly improve some of their features; increasing their energy density and power, as well as their stability and safety, and making viable the development of new generation storage technologies such as lithium-sulfur (Li-S) or metal-air batteries.

CIC energiGUNE, an expert center in energy storage and participant since the beginning of the most ambitious research project at European level up to now -Graphene Flagship- has developed several strategies for the integration of graphene in different advanced electrochemical energy storage devices such as supercapacitors or batteries.

Graphene in different storage technologies

In the field of energy storage, graphene has an excellent projection. Its incorporation, mainly in the formulation of electrodes, has led to the significant improvements of specific properties in some devices such as supercapacitors or batteries. Besides, its mechanical and electronic properties will allow its integration in flexible and complex multifunctional devices. 

In the case of supercapacitors, graphene represents an alternative to activated carbons with high specific surfaces and tortuous porosity, which are generally used in the manufacture of electrodes for electrochemical capacitors. Its open, non-porous laminar structure allows the adsorption of many ions for the formation of the electric double layer quickly and reversibly. This, combined with its high electronic conductivity, makes it possible to increase the power of the devices enabling their use in applications such as AC filters, previously restricted exclusively to conventional capacitors. 

Graphene can also contribute to the improvement of hybrid supercapacitors; devices, which, in terms of energy, power, and cyclability, are in an intermediate position between lithium-ion batteries and double-layer supercapacitors. In the CIC energiGUNE research line of supercapacitors, we have recently verified that the incorporation of graphene improves the connectivity of the electrode components resulting in a significant increase in the power of these devices. 

Graphene can also be used to protect and stabilize the lithium surface in batteries that include lithium metal as the negative electrode. 

The replacement of graphite by lithium metal in lithium batteries produces a significant increase in the device´s power density. However, the limitations in terms of stability and safety make it difficult to use it widely in batteries. 

In contrast, the deposition of a few layers or even a single sheet of graphene can prevent the unwanted growth of dendrites that could lead to a short-circuit, and eventually, the explosion of the battery without this being associated with a significant increase in the weight of the device. 

Also, graphene opens the possibility of its use as a negative electrode in sodium-ion batteries (NIBs), allowing a higher gravimetric capacity of the anode, which is highly restricted in graphite anodes. The development of sodium-ion batteries would benefit from the abundance of sodium and its homogeneous geographical distribution, as well as from the possibility of using aluminum as a current collector on the anode, which would lead to a decrease in the cost of those devices compared to the current lithium-based technology.    

Finally, the integration of graphene in new innovative energy storage technologies such as lithium-sulfur or metal-air batteries improves some of their current limitations, such as cyclability or power, and will enable their development in the medium to long term.

In the case of Li-S batteries (composed exclusively of lithium, sulfur, and carbon), they are considered an alternative to conventional lithium batteries.

CIC energiGUNE´s latest developments in the use of graphene

In a recent study carried out in our laboratories, we have developed graphene oxide aerogels produced by the Basque company Graphenea, with a small amount of carbon nanotubes, which have allowed the deposition of large amounts of sulfur. 

This strategy not only leads to obtaining electrodes with greater specific surface capacities but also the processing of electrodes does not require the use of binding agents or their deposition on metal current collectors, thus reducing the weight of the final device and increasing the device´s gravimetric energy density. 

This spongy structure provides a structure that gives greater stability, reaching over 100 cycles of loading and unloading without the deterioration of the electrodes or degradation of the cell. 

On the other hand, graphene is also being evaluated as an electrode in metal-air batteries. This is a promising technology due to its high theoretical energy density. 

In fact, graphene aerogels are suitable for being used as positive electrodes in these batteries since the combination of its porosity (that favors the oxygen diffusion until the surface of the electrode and allows to accommodate a significant amount of products generated in the unloading of the battery) and its high electronic conductivity, makes it possible to improve the stability and cyclability; Achilles´ heel of this technology at the present time.

The future of graphene, very present

In short, thanks to its properties, graphene could become a fundamental component in the new generation of storage technologies, not only improving their performance in terms of energy density, power, cyclability or security, but also providing added value: the development of flexible energy storage devices or their integration into other devices, an aspect much needed in the near future based on digital interconnection (Internet of Things).