Topotactic Transformation of the Cationic Conductor Li4Mo5O17 into a Rock Salt Type Oxide Li12Mo5O17

Abstract

Intercalation of lithium in the ribbon structure Li4Mo5O17 has been achieved, using both electrochemistry and soft chemistry. The ab initio structure determination of the “Mo−O” framework of Li12Mo5O17 shows that the [Mo5O17]∞ ribbons keep the same arrangement of edge sharing MoO6 octahedra and the same orientation as in the parent structure but that a topotactic antidistortion of the ribbons appears, as a result of the larger size of Mo4+ in “Li12” compared to Mo6+ in “Li4”. On the basis of bond valence calculations, it is observed that 12 octahedral sites are available for Li+ in the new structure so that an ordered hypothetical rock salt type structure can be proposed for Li12Mo5O17. After the first Li insertion, a stable reversible capacity of 100 mA·h/g is maintained after 20 cycles. A complete structural reversibility leading back to the ribbon type Li4Mo5O17 structure is obtained using a very low rate of C/100. The exploration of the Li mobility in those oxides shows that Li4Mo5O17 is a cationic conductor with σ = 10−3.5 S/cm at 500 °C and Ea = 0.35 eV.