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Graphene is a material that has been touted for many applications, both low-tech and high-tech. While it may take some time to make it into many electronic devices as a conductive medium/printable circuitry, it has started to gain a lot of attention and commercial viability in the small-scale energy storage systems, such as batteries and capacitors, which are used in many electronics. In this article, we’re going to look at where graphene can be used in energy storage components.
Graphene is a material that shouldn’t need much introduction if you’re here reading this article. For those who are unaware, graphene is a 2D material composed of all carbon atoms arranged in a hexagonal lattice (much like chicken wire or honeycomb). Many people tout it as a single atomic layer—which it technically is—but in the real-world, it can come in many forms from single-layer to multilayer and even in thinner ribbon-like forms (which are known as nanoribbons). Most graphene forms exhibit a very high electrical conductivity and charge carrier mobility, as well as a high stability to temperature, chemicals, and other stimuli, so it is these properties that have enabled it to gain a lot of interest across various energy storage devices.
Batteries
Graphene-based batteries are the most widely developed energy storage device that uses graphene and have not only been extensively tested in the academic laboratory (in various forms) but are now being produced commercially by some companies within the industry. So, even though the adoption from the end-user markets has taken some time (as it does with any new material that is to be trialed in batteries due to long-term safety requirements), the ability to make them commercially is starting to produce graphene-based batteries in the real-world through the likes of Samsung (who are the biggest company to use graphene) and other smaller battery manufacturers.
Graphene, like graphite, is used in the electrodes. However, it’s not often that an electrode is purely made of graphene (there are some exceptions in the academic world), as it is often used in conjunction with graphite to form hybrid electrodes. In some cases, the graphene can be coated on to the surface of graphite electrodes, with one well-known example being the use of Samsung trialing ‘graphene balls’ in electrode coatings. If the original developments from the academic lab are anything to go by, graphene has the potential to be used across many different battery types—and not just Li-ion batteries—to improve the efficiencies, stability, and cycle/discharge cycle rates of the batteries.
Capacitors/Supercapacitors
Capacitors, and supercapacitors (sometimes referred to as ultracapacitors) is another area where graphene is making its way into. The main reason for using graphene is that it has a high surface area, stability, and conductivity (as well as charge carrier mobility) can be utilized to accumulate and store charge—which is the fundamental mechanism of energy storage in capacitors. Of all the capacitor types, graphene has shown the most potential in supercapacitors as they can be used in the carbon coatings on the capacitor plates (instead of activated carbon) to form an efficient electric double layer coating. These supercapacitors can then be used to store large amounts of energy.
While supercapacitors are not utilized as widely as batteries and other capacitors (due to a higher cost compared to conventional capacitors), there is the possibility of supercapacitors experiencing a significant growth increase over other energy storage systems in the next few years, as they could become the more-preferred option in electric vehicles over batteries. As it stands, many different companies graphene-based supercapacitors commercially, so the supply will be there if this demand increase does materialize.
Battery-Capacitor Hybrids
While it is not as common as the two areas mentioned above, another area has emerged which combines both batteries and capacitors into a single hybrid device. As mentioned above, one of the reasons why supercapacitors have not been widely used compared to conventional capacitors and other energy storage mediums is down to cost. One way of reducing the cost has been to create hybrid storage devices which utilize the strength of Li-ion batteries with the rapid charging ability of supercapacitors.
This has been achieved so far by integrating graphene-based supercapacitors into Li-ion modules to increase the lightweightness, energy density, charge, and discharge cycle rates, and stability against the appropriate individual constituents. It’s an area which is relatively new compared to the other energy storage areas, but the benefits achievable could see it grow in the future—especially in areas such as electric vehicles which could benefit from the properties of both batteries and supercapacitors, all while utilizing the properties of graphene.
Sources and Further Reading
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