Computational Investigation of Li Insertion in Li₃VO₄

Parallel electrochemical reactions in low-voltage anode Li 3 VO 4 represent a fundamental barrier for fully reliable mechanistic studies even using the most advanced electrochemical and structural characterization techniques. Aiming to unravel the lithium insertion mechanism in Li 3 VO 4 anodes, we have investigated by density functional theory a total of 33 Li 3+ x VO 4 configurations ( x = 0, 0.5, 1, 1.5, 2, 2.5, 3). The key aspect of the proposed Li insertion mechanism is the structural rearrangement of the host-Li 3 VO 4 as larger amounts of Li ions are incorporated, due to ion size and electrostatic effects. We found that for 0 < x < 2 the Li 3+ x VO 4 phases are energetically stabilized by the distortion of the initial hexagonal package of the oxygen array (H1 → H2 transformation). Specifically, a very stable intermediate H2-Li 5 VO 4 phase is formed after a biphasic region at 0.7 V. The close structural relationship between H1-Li 3 VO 4 and H2-Li 5 VO 5, with a moderate volume expansion of 4%, supports an insertion reaction as the main mechanism for the reversible cycling of Li 3+ x VO 4 anodes in the range 0 < x < 2. Insertion of a third Li ion in Li 3 VO 4 would produce a reconstructive phase transformation to an antifluorite-type Li 6 VO 4 structure (H2→ C transformation). The low predicted voltage for such a process (0.14 vs Li/Li + ) and the major structural rearrangements (20% volume variation) make unlikely the reversible insertion of 3 Li ions in Li 3 VO 4 . The calculated compositional–voltage profile and X-ray diffraction patterns are in agreement with experimental observations.