Lithium ion storage between graphenes.
Bottom Line:
The number densities of lithium ions between the two graphenes are estimated from existing semi-empirical molecular orbital calculations, and the graphene sheets giving rise to the triple ion layers admit the largest storage capacity at all temperatures, followed by a marginal decrease of storage capacity for the case of double ion layers.These two configurations exceed the maximum theoretical storage capacity of graphite.Although the single ion layer provides the least charge storage, it turns out to be the most stable configuration at all temperatures.
Affiliation: Nanomechanics Group, School of Mathematical Sciences, The University of Adelaide, Adelaide, SA 5005, Australia. yue.chan@adelaide.edu.au.
ABSTRACT
In this article, we investigate the storage of lithium ions between two parallel graphene sheets using the continuous approximation and the 6-12 Lennard-Jones potential. The continuous approximation assumes that the carbon atoms can be replaced by a uniform distribution across the surface of the graphene sheets so that the total interaction potential can be approximated by performing surface integrations. The number of ion layers determines the major storage characteristics of the battery, and our results show three distinct ionic configurations, namely single, double, and triple ion forming layers between graphenes. The number densities of lithium ions between the two graphenes are estimated from existing semi-empirical molecular orbital calculations, and the graphene sheets giving rise to the triple ion layers admit the largest storage capacity at all temperatures, followed by a marginal decrease of storage capacity for the case of double ion layers. These two configurations exceed the maximum theoretical storage capacity of graphite. Further, on taking into account the charge-discharge property, the double ion layers are the most preferable choice for enhanced lithium storage. Although the single ion layer provides the least charge storage, it turns out to be the most stable configuration at all temperatures. One application of the present study is for the design of future high energy density alkali batteries using graphene sheets as anodes for which an analytical formulation might greatly facilitate rapid computational results. No MeSH data available. Related in: MedlinePlus |
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Mentions: We observe from Figure 2 that there is a single minimum for D = 5 Å, while from Figures 3 and 4, there are two minima for the cases D = 7.7 and D = 8.3 Å, respectively. The central plateau for D = 8.3 Å is flat enough to accommodate more lithium ions, which corresponds to the double ion and triple ion layers for D = 7.7 and D = 8.3 Å, respectively. As a benchmark, we also plot the total energy for D = 15 Å in Figure 5, and we observe that the central plateau widens to accommodate more ion layers than that for D = 15 Å. The numerical results agree well with similar results obtained using the semi-empirical molecular orbital calculations [8]. We also note that the total energy asymptotically approaches a certain value when the radial distance is sufficiently large, which demonstrates the rapid decay of the Lennard-Jones potential at larger distances [23]. Next, we fix r = 10 Å and vary h to investigate the minimum potential energy versus the separation D, which is shown in Figure 6. |
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Affiliation: Nanomechanics Group, School of Mathematical Sciences, The University of Adelaide, Adelaide, SA 5005, Australia. yue.chan@adelaide.edu.au.
No MeSH data available.