Grain boundary and curvature enhanced lithium adsorption on carbon

Abstract

a b s t r a c tWhile the speculation that graphene may owe double or even higher capacity of lithium adsorption than graphite does remains speculative, there is growing evidence that defects and edges may promote lithium adsorption on graphene and other nanostructured carbon. Here we report a first-principles study on how grain boundary defects in graphene may influence the adsorption of lithium. The adsorption energy for Li atoms trapping in 5-, 7-, and 8-rings is much lower than the counter-part of Li atoms and pristine graphene. Such defective graphene could adsorb more Li atoms, and may reach the speculated ratio of 1:1 for C-Li adsorption. In a contrast study of lithium on fullerenes of different size, we find that the adsorption energy decreases with increasing size of fullerenes, but does not approach the energy when Li atoms adsorb on flat graphene. The energy in carbon nanotubes, however, converges to the adsorption energy between Li atoms and flat graphene if the radius of carbon nanotubes is sufficiently large. It hence indicates that while curvature plays a role in the enhanced adsorption in fullerenes, the twelve 5 rings in a fullerene ball is the primary factor accounting for the enhanced lithium adsorption.

Absorption of calcium ions on oxidized graphene sheets and study its dynamic behavior by kinetic and isothermal models

“…We found that, adsorption kinetic parameters of calcium ion on our oxidized graphene sheets agree with the adsorption nature of the other graphene oxide. Which is produced by another process with increasing adsorption capacity of our graphene oxidized sheets toward calcium ions respecting to other ions in the same rank, so a pseudosecond demand model can be considered (Pang et al 2016, Liu et al 2016aTan et al 2016). The latter is shown that the rate determining step may be chemical adsorption one through the exchange of electrons amidst adsorbent and adsorbate.…”

sp2/sp3 Hybridized Carbon as an Anode with Extra Li-Ion Storage Capacity: Construction and Origin

“…As expected, the adsorption energies on different curvature models are gradually reduced as the number of adsorbed Li atoms increases ( Figure 5 d), which mainly originates from the Li–Li Coulombic repulsion. 11 The values of the adsorption energies are still negative, indicating an exothermic and stable reaction. 33 Importantly, even though the Li–Li distance (LiC 2 ) on NEGS is shorter relative to that (LiC 6 ) in the graphene, the adsorption energies of NEGS for LiC 2 remain stronger than that of graphene for LiC 6 with the increase of Li atoms.…”

“…In particular, theoretical calculations suggested that the positive and negative curvature structures of the carbon materials not only show a positive effect on Li + adsorption but also lead to three-dimensional Li-ion diffusion paths with relatively low energy barriers. 10 , 11 In fact, the geometric architecture is essentially derived from the transformation of the hybridized orbital types of carbon atoms to generate the response of chemical bonds to bending deformations, 12 thereby resulting in the regulation of the geometric and electronic structures within the atomic-scale scope. 8 , 13 − 16 However, the underlying reasons for extra capacity have not been uncovered deeply, especially the level of the electronic structure, much less to construct the relationship between non-coplanar sp 2 /sp 3 hybridized orbital and their corresponding Li-ion storage properties.…”

Topological Design of Graphene

“…First-principle calculations [158] based on density functional theory (DFT) revealed that the lithium adsorption on graphene could be enhanced by topological defects including divacancy (5-8-5 rings) and Stone-Wales defect (5-7-5-7 rings) due to the increased charge transfer between the adatom and defected sites in graphene. Later theoretical studies found that not only topological defects like 5-, 7-and 8-rings (Fig 14a-c), but curvatures (Fig 14d) of the graphene sheet could also enhance lithium adsorption resulting in better lithium storage property [159].…”