Functionalized Two-Dimensional Nanoporous Graphene as Efficient Global Anode Materials for Li-, Na-, K-, Mg-, and Ca-Ion Batteries

Abstract

Two-dimensional nanoporous graphene (NPG) with uniformly distributed nanopores has been synthesized recently and shown remarkable electronic, mechanical, thermal, and optical properties with potential applications in several fields [Science 360, 199 (2018)]. Here, we explore the potential application of NPG as an anode material for Li, Na, K, Mg and Ca ion batteries. We use density functional theory calculations to study structural properties, defect formation energies, metal binding energies, charge analysis, and electronic structures of NPG monolayers. Pristine NPG can bind effectively K + cations, but cannot bind the other metal cations sufficiently strongly, which is a prerequisite of an efficient anode material. However, upon substitution with oxygen-rich functional groups (e.g., O, OH, COOH) and doping with heteroatoms (B, N, P, S), the metal binding ability of NPG is significantly enhanced. Of the considered systems, S-doped NPG (S-NPG) binds the metal cations most strongly with binding energies of -3.87 (Li), -3.28 (Na), -3.37 (K), -3.68 (Mg), and -4.97 (Ca) eV, followed by P-NPG, O-NPG, B-NPG, and N-NPG. Of the substituted NPG systems, O substituted NPG exhibits the strongest metal binding with binding energies of -3.30 (Li), -2.62 (Na), -2.89 (K), -1.67 (Mg) and -3.40 eV (Ca). Bader charge analysis and Roby-Gould bond indices show that a significant amount of charge is transferred from the metal cations to the functionalized NPG monolayers. Electronic properties were studied by density of states plots and all the systems were found to be metallic upon the introduction of metal cations. These results suggest that functionalized NPG could be used as a global anode material for Li, Na, K, Mg, and Ca ion batteries.

Optical excitations and thermoelectric properties of two-dimensional holey graphene

“…The pores are made of two benzene rings and they became terminated with hydrogen atoms. Also, the bond lengths between C-C and C-H are 1.38-1.43 and 1.09 Å, respectively, and they are consistent with previous works [48,49].…”

“…It is evident that it has a direct band gap of 0.65 eV at the point. The computed band gap is in good agreement with previously investigated works [38,[48][49][50]. This band of the HG structure depends on the thickness of the interconnects, which is clearly governed by the nanoribbon width.…”

Optical excitations and thermoelectric properties of 2D holey graphene

“…Figure 1 shows the top and side view of HG structure which shows the planar structure. Also, we have calculated the bond length between C-C and C-H are 1.38 to 1.43 Å and 1.09 Å which is good consistent with previous work [46,47].…”

“…There is no contribution from the hydrogen S-orbitals also appears in VBM and CBM region. The computed band gap is good consistent with previously investigated work [32,[46][47][48]. As per we know PBE generally underestimates the band gap of materials hence to find the more accurate electronic band structure, we use hybrid functional HSE06, which involves 25% of Fock exchange (clearify this).…”

Defects in Hard Carbon: Where Are They Located and How Does the Location Affect Alkaline Metal Storage?

“…Previously, we have studied defects on the basal plane (using graphene as a model for this structural motif), cylindrical pores (using carbon nanotubes as a model for curved motifs), and planar graphitic pores (using bilayer graphite as a model for the graphitic stacks with varying interlayer distances). [7,21,[32][33][34][35] In this paper, we consider more complex HC models, to include the effect of edges, curvature, and strain on the defect formation. These models are based on the reconstructed graphite (10)(11) surface, which we have employed previously to study metal binding at the transition from curved to planar carbon morphologies.…”