Unusual Conversion-type Lithiation in LiVO3 Electrode for Lithium Ion Batteries

Abstract

This work finds that LiVO3 is lithiated by a conversion reaction at 25 C, which is unusual for the family of vanadium oxides. The spectroscopic studies and first-principle calculations performed on the lithiation mechanism of LiVO3 consistently propose that a two-phase insertion-type lithiation proceeds in the early stage of lithiation; LiVO3 transforms into a rock-salt structured Li2VO3. The continuing single-phase Li+ insertion into the tetrahedral sites in the rock-salt Li2VO3 produces a more Li-rich phase (Li2.5VO3), which is highly distorted because of the unfavorable Li+ insertion into the tetrahedral sites such as to be vulnerable to lattice breakdown. Hence, a two-phase (nucleation/growth type) conversion reaction is followed along with a structural disintegration; the Li2.5VO3 phase decomposes into metallic vanadium and Li2O. To determine the factors facilitating the conversion reaction of LiVO3, galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) are performed on LiVO3, the results of which are then compared to those observed with V2O5, which is not lithiated by the conversion reaction at 25 degrees C. The results show that the quasi-equilibrium potential for the conversion reaction is more positive for LiVO3 (thermodynamically more feasible). Also, the conversion reaction is kinetically more facilitated for LiVO3 due to faster solid-state diffusion of mobile ionic species during the two-phase growth stage of metallic vanadium and lithium oxide (Li2O) in the conversion process.