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

Abstract

Vanadium pentoxide (V2O5) 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 V2O5 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 (SnVO) is likely to occur upon Sn doping. The SnVO 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 SnVO 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 V2O5-based cathode materials for Li-ion batteries.