title: Evaluating bulk Nb2O2F3 for Li-battery electrode applications.
abstract: This investigation has the primary objective of elucidating the lithium intercalation process in the crystal structure of a new niobium oxyfluoride compound Nb2O2F3. The framework of the density functional theory was applied in a generalized gradient approximation together with the hybrid functional method. It is revealed that lithium atoms intercalate in this material in a maximum concentration of one Li atom per formula unit forming LiNb2O2F3. Moreover, octahedral positions in between the layers of Nb-O-F appear as the Li preferred occupancy resulting in a structural volume expansion of only 5%. Electronic structure evolution with the insertion of lithium displays a transformation from semi-conductor to metal when half of the lithium atoms are added. This transformation occurs due to a symmetry break induced by the transition from the +8 to +7 oxidation state of half of the Nb2 dimers. Then, after full lithiation the symmetry is recovered and the material becomes a semiconductor again with a band gap amounting to 1 eV. The evaluated average deintercalation potential reaches 1.29 V vs. Li/Li(+) with activation energy for lithium ion migration of 0.79 eV. The computed low potential of the redox reaction Nb2(8+) to Nb2(7+) includes niobium oxyfluoride in the map of possible materials for the anode application of Li-ion batteries.
authors.affiliation: Condensed Matter Theory Group, Department of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden. rafaelbna@gmail.com.
authors.forename: Rafael B
authors.initials: RB
authors.lastname: Araujo
authors.affiliation: Condensed Matter Theory Group, Department of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden. rafaelbna@gmail.com and Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), S-100 44 Stockholm, Sweden.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Ahuja