A DFT study of VO43- polyanion substitution into the Li-ion battery cathode material Li2FeSiO4
2010 (English)In: Computational materials science, ISSN 0927-0256, Vol. 50, no 1, 191-197 p.Article in journal (Refereed) Published
Density Functional Theory (DFT) has here been used to study the substitution of SiO44- for VO43- polyanions in the orthosilicate Li-ion battery cathode material Li2FeSiO4, in order to enhance electron transfer between the TM-ions and thereby achieve a capacity increase from the potential redox activity of the orthovanadate polyanion. Comparison of results for five different model structures for LiFeXO4, X = Si, P and V, reveals that VO43- substitution destabilizes the tetrahedral structures towards olivine- or spinel-type structures. Our modelling of lithiation of the hypothetical 100% substituted system LiFeVO4 to Li2FeVO4 predicts the reduction of V5+ in the VO43- anion to V4+ at a potential of 2.1 V. While complete delithiation of LiFeVO4 to FeVO4 is accompanied by Fe2+/Fe3+ oxidation at similar to 3.1 V. These lithiation and delithiation processes trigger changes in the unit-cell volume: -6% and +10%, respectively. Notably, only minor structural distortions were observed in both VO43- and the more exotic VO44- tetrahedra. Thermodynamically feasible VO43- substitution levels are also shown to be <30%. This is exemplified for a 12.5% VO4-substituted system which exhibits similar to 50% smaller band-gap and increased capacity at an average deintercalation potential of similar to 3.2 V compared to the un-substituted system.
Place, publisher, year, edition, pages
2010. Vol. 50, no 1, 191-197 p.
Li-ion battery, Positive electrode material, Silicates, DFT calculations, Polyanion, Crystal structure, Redox activity
Research subject Chemistry with specialization in Inorganic Chemistry
IdentifiersURN: urn:nbn:se:uu:diva-135362DOI: 10.1016/j.commatsci.2010.07.025ISI: 000284250700026OAI: oai:DiVA.org:uu-135362DiVA: diva2:375253