The effect of oxygen vacancies on the structure and electrochemistry of LiTi2(PO4)3 for lithium-ion batteries: A combined experimental and theoretical study

Abstract We report that a partially oxygen deficient LiTi 2 (PO 4 ) 3 shows a much better rate capability as a cathode material for lithium-ion batteries compared to stoichiometric LiTi 2 (PO 4 ) 3 . A combination of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electrochemistry, and first-principles calculations was used to determine and rationalize the structural and electrical changes that occur with different heat treatment atmospheres. XRD and XPS experiments confirmed that some Ti 4+ transformed to Ti 3+ in oxygen deficient LiTi 2 (PO 4 ) 3 heat treated under N 2 ; Ti 3+ was detected and the lattice parameter increased compared to that of LiTi 2 (PO 4 ) 3 . Electrical conductivity measurements indicated an increase in the electronic conductivity of nearly two orders of magnitude for the oxygen deficient LiTi 2 (PO 4 ) 3 sample compared to LiTi 2 (PO 4 ) 3 . First-principles calculations suggest that the oxygen vacancies could be formed in LiTi 2 (PO 4 ) 3 under oxygen-poor conditions, and this may significantly decrease the donor levels of other possible donor defects and thus improve the electronic mobility.