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Theoretical Prediction of Two-Dimensional SnP3 as a Promising Anode Material for Na-Ion Batteries
journal contribution
posted on 2018-07-10, 00:00 authored by Chun-Sheng Liu, Xiao-Le Yang, Jin Liu, Xiao-Juan YeTin
(Sn) as a cheaper and more environment-friendly alternative
to lead (Pb) has been widely used in the field of green energy. Especially,
Sn-based nanomaterials have attracted tremendous attention in Na-ion
batteries. Interestingly, the layered bulk structure of SnP3 has been experimentally synthesized, and it is metallic and stable
at room temperature. On the basis of first-principles calculations,
we demonstrate that the production of monolayer SnP3 by
exfoliation of bulk crystal could be feasible due to the moderate
cleavage energy (∼1.10 J/m2). Because of the weak
π–π interaction and Jahn–Teller effect,
the single-layer SnP3 has a high buckling height with an
indirect band gap (0.68 eV) responding to ultraviolet–visible–near-infrared
wavelength lights. The hole mobility is up to 103 cm2 V–1 s–1, which is comparable
to that of black phosphorene. More importantly, monolayer SnP3 experiences indirect–direct band gap and semiconductor–metal
transitions under biaxial strain. Furthermore, we explore SnP3 as an anode for Na-ion batteries. Upon Na adsorption, the
semiconducting SnP3 transforms to a metallic state, ensuring
good electrical conductivity. Specially, the ultralow energy barrier
(0.03 eV) of Na diffusion on monolayer SnP3 indicates a
fast diffusivity. During the Na adsorption process, the slight volume
variations (<1.0%) suggest a good cycling reversibility. The theoretical
specific capacity (253.31 mA h g–1) and moderate
average electron potential (1.29 V) are in between those of commercial
anodes, graphite and TiO2. Moreover, bilayer SnP3 greatly improves the Na binding strength. Meanwhile, the diffusion
of Na on the outside surface of bilayer SnP3 is extremely
anisotropic. The diffusion along the armchair direction (0.38 eV)
is energetically favorable. However, the high energy barrier (1.83
eV) along the zigzag direction leads to a nearly forbidden diffusion.
These results are helpful to deepen the understanding of SnP3 as a potential anode for Na-ion batteries.