Effect of Oxygen Vacancies and F-Doping on TiO₂(B) as Anode for Mg-Ion Batteries

Abstract

To find alternatives to lithium-ion batteries, much effort is being devoted to finding electrode materials that allow reversible Mg2+ disinsertion/insertion. Due to the strong Coulomb force between Mg2+ and electrode materials, certain modification methods are often needed to reduce the energy barrier of Mg jumping in materials. The bronze-phase TiO2(B) has attracted considerable attention as a promising anode for lithium-ion batteries, but it has proven to be difficult for Mg to insert therein. The PBE+U calculations show that the low capacity of perfect TiO2 as the anode of magnesium-ion batteries (MIB) is mainly due to the high diffusion energy barrier of the Mg ion (at least 1.27 eV). Both the defects of oxygen vacancies and F-doping can significantly reduce the band gap value and the Mg-ion migration barriers. The results of CM5 charges and charge density differences prove that the local lattice distortion caused by oxygen vacancies can cause the distribution of Ti3+ away from Mg, resulting in a significant decrease in the Mg–O binding energy, which is beneficial to the reduction of the migration barrier. F-doping can make the binding energy of Mg at each site tend to be the same, so that the energy barrier of Mg jumping along the way is lower. In addition, the coexistence of oxygen vacancy and F doping in TiO2(B) has synergistic effects in improving Mg-ion diffusion.

First-Principles Dynamics Investigation of Germanium as an Anode Material in Multivalent-Ion Batteries

“…However, using metal anodes presents several unfavorable issues, including sluggish ion diffusion kinetics in both the electrolyte and electrodes, instability of the electrodes, formation of a complicated solid electrolyte interface, and self-corrosion of the anodes [17][18][19]. Certain anode materials, such as titanium oxides and vanadium oxides were investigated based on their intercalation reactions [20,21]; however, research on anodes for MIBs remains challenging compared to that on cathodes. Despite the promise of emerging materials, such as organic electrodes [22] and structure-engineered composites [23], which have advantages that include flexibility in design and a wide range of property tunabilities, the practical implementation of MIBs was hindered by inherent challenges, including relatively low redox potentials, and insufficient electronic and ionic conductivities.…”