Lithium Insertion into Li₂MoO₄: Reversible Formation of (Li₃Mo)O₄ with a Disordered Rock-Salt Structure

Abstract

During Li-insertion in some complex transition metal molybdates with a NASICON structure, which serve as cathodes in Li-ion rechargeable cells, a formation of a cubic rock-salt-type phase was often detected between 1 and 2 V vs. Li + /Li. Detailed information about elemental composition and stability of this compound was missing and suggestions were made toward a solid solution composed of lithium oxide and two-valence transition metal oxide MO with M a 3d element. In the present work, we showed that Li 2 MoO 4 with a phenacite-type structure without any additional transition metal can reversibly accommodate Li-ions at room temperature with the formation of the NaCl-type compound. Reversible Li-incorporation into the Li 2 MoO 4 structure is accompanied by a reduction of Mo ions and changes in their oxygen coordination. Li-ions are shifted from a tetrahedral to an octahedral site, resulting in the formation of a cubic (Li 3 Mo)O 4 framework with a random distribution of Li and Mo on one site. This mixed occupancy is remarkable because of significant charge and size differences between Li + and Mo 5+ . The novel compound shows Li-deficiency at least up to x Li = 0.2, which can be deduced from charge flow in the galvanostatic cycling of the electrochemical cells with a (Li 3 Mo)O 4 cathode between 1.5 and 2.75 V vs. Li + /Li. An increase in the cell potential above 3 V leads to the oxidation of (Li 3 Mo)O 4 back to Li 2 MoO 4 with phenacite-type structure. The reaction of (Li 3 Mo)O 4 to Li 2 MoO 4 also occurs upon a short exposure to air.

Lithiation-driven structural transition of VO2F into disordered rock-salt LixVO2F

“…Intercalation of the third lithium into V2O5 occurs at a voltage below 1.9 V, which leads to an irreversible phase transition into disordered rock-salt (ω-LixV2O5, Fm3,¯ m). 11 Lithiation induced structural transition to disordered rock-salt has been observed for other materials, such as Li2MoO4, 12 LiVO3 13 and Li1.211Mo 0.467Cr 0.3O2. 14 Disordered rock-salt was also found as intermediate phase during the lithiation reactions of FeOF, 15 Li-and Mn-rich layered materials 16 and spinels.…”

A disordered rock salt anode for fast-charging lithium-ion batteries

“…Butyl-lithium was used as the lithiation reagent 12,14 . Stoichiometric amounts of V2O5 powders were added into the 1.6 M butyl-lithium hexane solution (10% excess of butyl-lithium) with magnetic stirring for 60 min under argon atmosphere.…”

“…Lithium-rich disordered rock salt (DRS) oxides are known to be promising cathode materials, with fast lithium (Li) diffusion that is due to a perco-lating network of octahedrontetrahedron-octahedron pathways 4,10 . However, although the formation of DRS such as Li3MoO4 and Li5W2O7 oxides during electrochemical reactions is known 11,12 , there have been no investigations of further insertion of Li into DRS oxides to form potential anode materials. Delmas showed that three Li ions could intercalate into V2O5 to form Li3V2O5 when the discharge cut-off voltage is extended to 1.9 V, with the proposed structure to be a rock salt phase with crystallo-graphic formula Li0.6V0.4O (refs.…”

Hetero-Element-Doped Molybdenum Oxide Materials for Energy Storage Systems

“…Therefore, Li 2 MoO 3 can carry out a two-electron electrochemical reaction per unit molecule, so it has a huge potential for energy storage (theoretical capacity is about 339 mA h g −1 ) [27,28]. The crystal of Li 2 MoO 4 (Figure 2a) shows a tunnel structure, consisting of a three-dimensional network of corner-linked, slightly distorted LiO 4 and MoO 4 tetrahedra along crystallographic caxis [29,30]. As is well-known, materials with NASICON-type structure are also promising candidates for energy storage systems.…”