The increasing demand for portable electronic devices has driven the technological improvements in rechargeable solid-state batteries. A battery consists of several electrochemical cells that are connected to provide the required voltage and capacity. Each cell is composed of a positive and a negative electrode separated by an electrolyte solution containing dissociated salts. [1]
Lithium Ion battery (LIB) is a kind of rechargeable battery in which lithium ions move from the positive electrode to the negative electrode during charging and back during discharging. Lithium Ion battery is a big family including many types whose chemistry, cost and safety characteristics vary across different types. Lithium Primary batteries are disposable and use metallic lithium as the electrode material while Lithium Ion batteries use an intercalated lithium compound as the electrode material. Compared to other batteries, Lithium Ion batteries have the characteristics of high-energy density, flexible and lightweight design, and longer lifespan. Due to their high energy density and design flexibility, around 2000, Li-based batteries account for 63% of worldwide sales values in portable batteries. [1]
Whatever the considered battery technology, measures of its performance (for instance, cell potential, capacity or energy density) are related to the intrinsic property of the materials that form the positive and negative electrodes. Due to a lot of chemical or physical modifications, carbon negative electrodes display improving electrochemical performances. Reversible capacities up to 450 mAh/g have been reached, compared with a practical value of 350 mAh/g for graphite (372 mAh/g for the end compound LiC6). [1] Also, because of its capability for reversible lithium ion intercalation in the layered crystals, graphite is a practical anode material used for LIB. Graphene nanosheet (GNS) materials have similar structures to graphite and therefore may provide another type of intercalation anode compound. The lithium storage properties of graphene nanosheet materials as high capacity anode materials for rechargeable lithium ion batteries were investigated by Yoo et al. [2]
Graphene is a single layer of carbon atoms which are tightly packed into a two-dimensional honeycomb carbon lattice. Recently, grapheme has attracted a great deal of attention from both perspectives of fundamental science and technology, because they are nontoxic, chemically and thermally tolerant, electrical conductive and mechanically hard. [3] In particular, grapheme nanosheets have superior electrical conductivities than graphitic carbon, high surface areas of over 2600 m2/g, chemical tolerance, and a broad electrochemical window that would be advantageous for application in energy technologies. [4]
Through investigation grapheme sheets turn out to have very high specific capacity, which is up to 540 mAh/g, much larger than that of graphites. [2] And the capacity could even reach 730 mAh/g and 784 mAh/g, respectively, by the incorporation and macromolecules of carbon nanotubes and fullerenes to the graphene sheets. All of these render graphene as an attractive electrode material for lithium ion batteries.
The current electrode materials employed in Lithium Ion batteries are lithium intercalation compounds such as graphite, because they can be reversibly charged and discharged under intercalation potentials with sufficient specific capacity. However, the demand for much higher density electrodes is still increasing. And through investigation, graphene nanosheets turn out to be very attractive electrode materials for its high specific capacity.
© Yao Li. 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.
[1] J. M. Tarascon and M. Armand, "Issues and Challenges Facing Rechargeable Lithium Batteries," Nature 414, 359 (2001).
[2] E. Yoo, et al., "Large Reversible Li Storage of Graphene Nanosheet Families for Use in Rechargeable Lithium Ion Batteries," Nano Letters 8, 2277 (2008).
[3] A. K. Geim and K. S. Novoselov, "The Rise of Graphene," Nature Materials 6, 183 (2007).
[4] A. V. Murugan, T.Muraliganth and A. Manthiram, "Rapid, Facile Microwave-Solvothermal Synthesis of Graphene Nanosheets and Their Polyaniline Nanocomposites for Energy Storage," Chem. Mater. 21, 5004 (2009).