First-Principles Study of Na Intercalation and Diffusion Mechanisms at 2D MoS₂/Graphene Interfaces

Abstract

Na-ion batteries (NIBs) are emerging as promising energy storage devices for large-scale applications. Great research efforts are devoted to design new effective NIB electrode materials, especially for the anode side. A hybrid 2D heterojunction with graphene and MoS2 has been recently proposed for this purpose: while MoS2 has shown good reversible capacity as a NIB anode, graphene is expected to improve conductivity and resistance to mechanical stress upon cycling. The most relevant processes for the anode are the intercalation and diffusion of the large Na ion, whose complex mechanisms are determined by the structural and electronic features of the MoS2/graphene interface. Understanding these processes and mechanisms is crucial for developing new nanoscale anodes for NIBs with high performances. To this end, here we report a state-of-the-art DFT study to address (a) the structural and electronic properties of heterointerfaces between the MoS2 monolayers and graphene, (b) the most convenient insertion sites for Na, and (c) the possible diffusion paths along the interface and the corresponding energy barrier heights. We considered two MoS2 polymorphs: 1T and 3R. Our results show that 1T-MoS2 interacts more strongly with graphene than 3R-MoS2. In both cases, the best Na host site is found at the MoS2 side of the interface, and the band structure reveals a proper n-type character of the graphene moiety, which is responsible for electronic conduction. Minimum-energy paths for Na diffusion show very low barrier heights for the 3R-MoS2/graphene interface (<0.25 eV) and much higher values for its 1T counterpart (∼0.7 eV). Analysis of structural features along the diffusion transition states allows us to identify the strong coordination of Na with the exposed S atoms as the main feature hindering an effective diffusion in the 1T case. These results provide new hints on the physicochemical details of Na intercalation and diffusion mechanisms at complex 2D heterointerfaces and will help further development of advanced electrode materials for efficient NIBs.

Ru-Doping of P2-NaxMn0.75Ni0.25O2-Layered Oxides for High-Energy Na-Ion Battery Cathodes: First-Principles Insights on Activation and Control of Reversible Oxide Redox Chemistry

“…The on-site correction is applied to the d electrons of Ru, Ni, and Mn atoms with a unified average effective U-J parameter, U eff , equal to 4 eV, as already successfully applied to TM oxides. ,− This choice is based on previous experience on mixed TM oxides where having the same average U eff value for different TM oxides allowed us to obtain qualitatively reliable results. − The proposed approach has also been validated against hybrid HF-DFT calculations for the undoped parent material Na 0.75 Ni 1/4 Mn 3/4 O 2 . The D3 dispersion correction with the Becke–Johnson (BJ) damping function is included to account for van der Waals (vdW) forces that represent dominant interactions in interfaces and layered materials. − A kinetic energy of 750 eV and a Γ-centered 4 × 4 × 4 k -point sampling mesh are used to ensure converged energies within 3 meV/f.u. with respect to the PW basis set size and Brillouin zone sampling, respectively.…”

Solid‐State Post Li Metal Ion Batteries: A Sustainable Forthcoming Reality?

“…On the anode side, several studies have addressed the capability of TiO 2 polymorphs to reversibly intercalate the Na + ; [ 152 ] recent studies were also able to dissect the most convenient facets of titania anatase for effective use as NIB anode. [ 153 ] Intercalation and diffusion of Na in composite materials with Graphene such as prototypical anodes TiO 2 /G [ 154 ] and MoS 2 /G [ 155 ] have been addressed as well with first principles calculations. Decomposition of polymer electrolytes at the metallic anode surface such EC [ 156 ] and FEC/DFEC [ 157 ] has been object of few studies using molecular‐type non periodic DFT models.…”

A Review: Ion Transport of Two-Dimensional Materials in Novel Technologies from Macro to Nanoscopic Perspectives

“…To enhance the effects of ion transport, the structural designs of 2D materials can be used to reengineer the ways in which ions propagate, with a significant jump in the super-diffusive regime [134,138]. When restricted by a 2D planar surface, the diffusion in normal and anomalous diffusion (the sub-diffusive and super-diffusive processes) is a quintessential property.…”