|Fig. 1: Crystalline structure of graphene. (Source: Wikimedia Commons)|
With the increasing prominence of renewable energies, energy storage has become a major topic of interests for researchers and scientists. Since energy generation from renewable energy sources such as solar, wind, and hydro, does not always coincide with the energy demand, an advanced method of energy storage is in high demand.  With the rise of electric vehicles, many companies are also developing new ways of cheap, high energy, reliable battery storage technology. The ideal storage system has high energy and high-power density. Lithium ion batteries, a common battery used in electronics today, have very high energy density but are not suitable for large-scale applications. 
Since the early 2000s, graphene has been a material widely-researched because of its high potential as the future of batteries. (See Fig. 1 for graphene's crystalline structure). Graphene-based materials have many highly appealing properties. First, its high surface area of up to 2600 m2 g-1 and high porosity makes it ideal for gas absorption and electrostatic charge storage.  Second, it is extremely lightweight and strong which allows it to be easily transported. Third, it is a potent conductor of electrical and thermal energy, which makes it a great material to store energy.  In addition, it has other properties that are ideal for new battery features, such as its flexibility and high-charging capability. 
Graphene-based batteries have many applications. One application is in rechargeable batteries, as its high energy capacity and charge rate makes it very desirable. Another application is in supercapacitors because it has high conductivity, is electrochemically stable, has open porosity, and higher surface area than activated carbon, the material used in supercapacitors today.  Because it is extremely thin and lightweight, it can be made into a paper- like material and be used to create flexible or rollable batteries. Graphene can also be used to make solar panels because of its high conductivity. 
Despite its many encouraging properties, the largest limitation for graphene-based batteries is that there are no mass production techniques of high-quality batteries at this time. The cost of production ranges from tens to thousands of dollars per kilogram, which is significantly higher than the cost of producing activated carbon at $15 per kilogram.  Moreover, the thickness of graphene-based materials is generally limited to micrometers, which limits the overall battery capacity significantly. Last but not least, they generally show very high first cycle loss at 50%-60%, low cycling efficiencies at 95%-98%, and poor capacity retention at high current densities. 
While many believe graphene has remarkable properties and strong properties, further research is necessary to determine the practical capabilities of this material. As mentioned above, mass production techniques remain a high priority of research if graphene can ever be considered for commercial applications. In the near term, composite materials are probably the most practical application prospect for graphene.  Researchers have demonstrated that combining small amounts of graphene with polymers can yield tough, lightweight materials that conduct electricity. Graphene will likely be a crucial material in the future of electronics and large-scale energy storage.
© Allen Yu. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 K.C. Divya and J. Østergaard, "Battery Energy Storage Technology For Power Systems - An Overview," Electr. Pow. Syst. Res. 70, 511 (2009).
 H. Kim et al., "All-Graphene-Battery: Bridging the Gap between Supercapacitors and Lithium Ion Batteries," Sci. Rep. 4, 5278 (2014).
 U. K, Sur, "Graphene: A Rising Star on the Horizon of Materials Science," Int. J. Electrochem. 2012, 237698 (2012).
 D. Lamuel et al., "Silicon Oxycarbide Glass-Graphene Composite Paper Electrode For Long-Cycle Lithium-Ion Batteries," Nat. Commun. 7, 10998 (2016).