On the Origin of Ion Intercalation and Conductivity Enhancement in Sn-Doped V₂O₅ Cathodes of Li-Ion Batteries: A Computational Study

Abstract

Vanadium pentoxide (V 2 O 5 ) is one of the most promising cathode materials used in metal-ion batteries due to its high theoretical capacity. But it still suffers from low electronic conductivity leading to sluggish ion transport kinetics. Although the introduction of Sn impurities in V 2 O 5 has been proposed to partially alleviate these drawbacks, the origin of the improvement is still unclear. In this work, we employed the density functional theory (DFT+U) method to study the role of Sn doping on the enhanced electronic conductivity and Li intercalation. Using a thermodynamic model based on defect formation energies and charge neutrality constraint, we find that Sn substitution at a vanadyl group (Sn VO ) is likely to occur upon Sn doping. The Sn VO defect generates one electron polaron at the nearby V center, which could escape the defect site upon thermal excitation with a barrier of 0.55 eV. Such a relatively mobile polaron could act as a charge carrier and enhance the electronic conductivity of the cathode. Upon Li intercalation, the Sn VO defect with a repulsive nature toward Li serves as a nucleation center, where Li could accumulate nearby the defect site. This could enhance the formation of a lithiated phase during the early discharge process. However, loading too much Sn could lead to inferior cathode performance since it impedes Li diffusion. Our findings provide insights into the role of Sn doping in the design of high-performance V 2 O 5 -based cathode materials for Li-ion batteries.

Enhancing V2O5 Cathode Performance through Heterostructure Engineering with the Ti3C2O2 MXene: A Computational Study

“…Computational studies also report that the polaron formation in V 3 O 5 (−0.43 eV) is less stable than that in VO 2 (−0.52 eV), leading to a smaller polaron diffusion barrier (V 3 O 5 : 0.15 eV, VO 2 : 0.56 eV) . In addition, the polaron formation strength in V 2 O 5 is increased in the presence of Sn doping, resulting in a higher polaron hopping barrier (0.55 eV) than that without doping (0.26 eV). , …”

Chalcogen Doping as a Promising Strategy to Improve the Thermochromic Properties of Vanadium Dioxide

“…Because of this, the 0 K static DFT energies for reactions involving the R phase are not expected to deliver an accurate representation of the changes in free energy under realistic conditions, while this effect is likely to be less pronounced for the M phase. Furthermore, the sum of the chemical potentials μ of oxygen and vanadium must equal the DFT energy of VO 2 (M) E VO 2 = μ V + 2 μ O while the permissible range of oxygen chemical potentials can span from oxygen-poor μ O normalO − poor = 3 E normalV O 2 − E V 3 O 5 to oxygen-rich conditions μ O normalO − rich = E V 2 O 5 − 2 E VO 2 and are limited by the stabilities of V 3 O 5 and V 2 O 5 , the closest stable vanadium oxide phases with lower and higher oxygen fractions than VO 2 , respectively. The calculated formation energies are shown in Figure over the range of permissible oxygen chemical potentials, which are expressed relative to the DFT energy of a single O 2 molecule as a reference state.…”

Metal-Ion Intercalation Mechanisms in Vanadium Pentoxide and Its New Perspectives

“…material [101]. In conclusion, the inclusion of Sn doping positively impacts electrochemical performance by providing charge carriers in the form of electron polarons and serving as nucleation sites for the formation of the lithiation phase during Li intercalation.…”

“…The polaron possesses an escape barrier of 0.55 eV, enabling it to migrate away from the defect center [100]. This escape process generates charge carriers that significantly enhance the electronic conductivity compared to that of the undoped material [101]. In conclusion, the inclusion of Sn doping positively impacts electrochemical performance by providing charge carriers in the form of electron polarons and serving as nucleation sites for the formation of the lithiation phase during Li intercalation.…”

“…DFT calculations were employed to investigate the formation of Sn-related defects and their effects. The analysis focused on point-defect formation energies and properties to determine the most probable defect and its charge compensation mechanism [101]. The study revealed that the most favorable defect is the substitution of Sn for VO, accompanied by a bound polaron at a V center serving as the charge compensation.…”