Electronic and structural properties of Li_n@Be₂B₈ (n = 1–14) and Li_n@Be₂B₃₆ (n = 1–21) nanoflakes shed light on possible anode materials for Li‐based batteries

Abstract

Systematic addition of Li atoms to the Be B and Be B backbones has been studied by density functional theory-based calculations with the aim to investigate properties of interest on possible anode materials for Li-based batteries. For the Be B Li (n = 1-8) and the Be B Li (n = 1-20) systems, lithium salts are dominant whereas a clear electride feature shows up for Be B Li (n = 9-14) and Be B Li . Addition of hydrogen radicals to these systems shows that the Be B Li electride becomes a Be B Li H hydride electride whereas Be B Li leads to a Be B Li H salt. Moreover, for the addition of Li atoms to Be B and the Be B backbones, large values of the interaction and of the adsorption energy per Li atom, high specific capacity of Be B Li and of Be B Li (1860 and 1017 mAh g , respectively) and low and flat voltage associated with lithiation have been found. Likewise, the considerable thermodynamic driving force (ΔG° = -29.66 kcal/mol) and the small energy barrier ( ΔG# = 0.26 kcal/mol) associated with electron transfer in Be B Li and Be B species confirm that boron rich species have potential abilities to be used in the Li-based battery. © 2018 Wiley Periodicals, Inc.

Theoretical Descriptors of Electrides

“…The molecular electrides (sometimes called superalkalies) are a class of compounds that have been proposed and subsequently explored using theoretical models. − The first comparison of a molecular species to an electride was made by Chen et al, in 2004, while investigating the water trimer anion . Specifically, the observation was made that certain trimer configurations would form a strong dipole and the excess electron would occupy an extremely diffuse molecular orbital, localized at one end of the cluster.…”

Spatial and Electronic Structures of BeB8 and MgB8: How far Does the Analogy Go?

“…It should be noted that the BeÀ B clusters and analogous MgÀ B clusters usually don't have the same geometry shapes. [59,60,86] The GM structures of neutral BeB 2À and MgB 8 2À . [86] The most stable triplet state structures of BeB 8 and MgB 8 do not have the same geometry features as in the case of the GM structures (Figure 1).…”

“…As can be seen from Figure 1, the most stable structures of BeB 8 and MgB 8 exhibit the same geometry, and that is the singlet state umbrella‐like structure. It should be noted that the Be−B clusters and analogous Mg−B clusters usually don't have the same geometry shapes [59,60,86] . The GM structures of neutral BeB 8 and MgB 8 adopt the C 7v geometry in which the metal atom is hypercoordinated to the concave B 8 fragment.…”

“…[57] Furthermore, Mg 2 B 8 exhibits a compass like structure with a very characteristic dynamical behaviour, [59] while Be 2 B 8 adopts the sandwich-like structure. [60] It is also well known that Mg and Be have very different roles in biosystems. Mg is a cofactor in more than 300 enzymes that regulate diverse chemical reactions in our body, [61] while overexposure to Be can cause several diseases, such as beryllium sensitization, chronic beryllium disease, and even lung cancer.…”

“…For instance, BeB 8 2− has a planar wheel D 8h structure, whilst MgB 8 2− takes the pyramidal C 8v form [57] . Furthermore, Mg 2 B 8 exhibits a compass like structure with a very characteristic dynamical behaviour, [59] while Be 2 B 8 adopts the sandwich‐like structure [60] . It is also well known that Mg and Be have very different roles in biosystems.…”