Insight into the Effect of Oxygen Vacancies on Ion Intercalation and Polaron Conduction in LiV₃O₈ Cathodes of Li-Ion Batteries

Abstract

Vanadate-based compounds, in particular LiV3O8, are promising candidates for cathode materials of Li-ion batteries. Thanks to their open-layered structures and the various possible oxidation states of the V metal center, LiV3O8 can effectively accommodate Li ions and store electron potential. To further improve the transport kinetics of the cathode, in this work, we used the first-principles method to explore the effects of oxygen vacancies on Li insertion, Li diffusion, and electronic conduction in the form of polaron hopping. We find that the polaron is mobile in the [010] direction with an effective hopping barrier, E a,eff, of 0.11 eV and is sluggish in other directions with an E a,eff of 0.56 eV. Such anisotropic conduction is also observed in experiments. Interestingly, unlike other transition metal oxides, formation of a polaron negligibly affects Li insertion and diffusion, where the charge transport kinetics is solely limited by the ion movement with an E a,eff of 0.50 eV. The introduction of an oxygen vacancy, V O, creates two polarons at the two nearby V centers where at least one of them is relatively mobile (E a,eff = 0.16 eV) contributing to electronic conductivity of the materials. At low V O concentrations of up to 1%, the most stable V O exists far from the Li diffusion path and does not affect the ion transport kinetics. In contrast, if the V O concentration increases to 2–3%, the second most stable V O starts to form at the diffusion path, which greatly diminishes Li diffusion. Hence, it is suggested that controlling the low concentration of V O within 1% can enhance electronic conductivity by increasing the concentration of charge carriers while maintaining the ion diffusivity of the LiV3O8 cathode.

Synthesis, structural and electrochemical properties of V4O9 cathode for lithium batteries

“…Vanadium oxide V 4 O 9 , consists of an average oxidation state of + 4.5 thus possibly suggesting oxygen vacancies in the material. In fact, oxygen vacancies have been tied to better performance for oxygen deficient V 2 O 5 (or V-V 2 O 5 ); with ∼ 3% more oxygen deficiency than pristine V 2 O 5 (based on deconvolution of XPS spectra) ( Sun et al, 2018 ; Chotsawat et al, 2022 ). Certainly, at only 3% more O vacancies than pristine V 2 O 5 , the resultant global long-range structure V-V 2 O 5 is hardly affected.…”