Na uptake at TiO2 anatase surfaces under electric field control: A first-principles study

Abstract

Na-ion batteries (NIBs) are promising devices for large-scale energy-storage facilities. Nanostructured TiO2 is an efficient NIB negative electrode, showing good cycling performance and rate capability, but its activity depends on the crystalline facets exposed by anatase nanoparticles. Hence, we propose here a DFT+U study of Na+ adsorption and insertion at (101), (100) and (001)-TiO2 surfaces under the influence of external electric fields, which are simulated by adding a sawtooth-like electrostatic potential to the bare ionic potential. We find that field polarization affects Na+ uptake as well as titania electronic features, promoting redox processes within Ti sublattice, as in battery charge/discharge cycling. Our results highlight the high-energy (001) surface to be the most active, for both directions of external fields, proving its activity to be exerted reversibly. Besides further insights, these outcomes pave the route for further exploration and design of electrode materials by simulation of battery in operando conditions. Graphical Abstract

The ENEA′s 2019–2021 Three‐Year Research Project on Electrochemical Energy Storage

“…It was also found that field polarization affects Na + uptake as well as titania electronic features, promoting redox processes within Ti sublattice. These results highlight the high‐energy (001) surface is the most active, for both directions of external fields, proving its activity to be exerted reversibly [44] …”

“…Ab-initio computational simulations of the geometric and electronic properties of cathodes for SIBs were performed [42] and the atomic interaction between the surface of the ionic polymers and the sodium metal electrode was investigated. [43][44][45] Using a new surface slab model, the interaction between the layered Na 0.85 Li 0.17 Ni 0.21 Mn 0.64 O 2 (001) surface and the Na + ions was examined to identify the most favourable adsorption sites and the possible paths for the migration of the Na + ions on the electrode surface. The analysis of atomic partial charges and atomic magnetic moments revealed that Li has a purely structural role, while Ni and Mn actively participate in both redox processes and electronic conduction.…”

“…These results highlight the high-energy (001) surface is the most active, for both directions of external fields, proving its activity to be exerted reversibly. [44] To address the structural and electronic properties of heterointerfaces between the MoS 2 monolayers and graphene, a potential anode material for Na-ion batteries, two MoS 2 polymorphs were considered. It was showed that the best Na host site is found at the MoS 2 side of the interface, and the evaluation of the band structure revealed a proper n-type character of the graphene moiety, which is responsible for electric conduction.…”

“…The factors that directly affect the sodiation/de‐sodiation processes have been identified at the electrode/electrolyte interface. Ab‐initio computational simulations of the geometric and electronic properties of cathodes for SIBs were performed [42] and the atomic interaction between the surface of the ionic polymers and the sodium metal electrode was investigated [43–45] . Using a new surface slab model, the interaction between the layered Na 0.85 Li 0.17 Ni 0.21 Mn 0.64 O 2 (001) surface and the Na + ions was examined to identify the most favourable adsorption sites and the possible paths for the migration of the Na + ions on the electrode surface.…”

Advances and challenges in multiscale characterizations and analyses for battery materials

“…By accessing the electronic structure of materials, QM methods enable both the prediction of materials' properties and the fundamental understanding of their complex mechanisms of functioning. Indeed, the latest example is represented by the DFT work of Fasulo et al [17], published in this focus issue, where electric field polarization effects on TiO 2 nanoparticles are shown to favor reversible Na uptake at the (001) surface.…”