Uptake of lithium by layered molybdenum oxide and its tin exchanged derivatives: high volumetric capacity materials

The materials A0.25MoO3 (A=Na, Li, Sn), prepared by a ‘chimie douce’ route, are a promising alternative as anode materials in Li ion batteries. These materials present large reversible charge capacities, greater than 900 mAh/g, with a good capacity retention on cycling. At least 65% of the charge capacity (600 mAh/g) is maintained under 1.5 V vs. Li. The gravimetric capacities, on the order of 4000 mAh/cm3, are three to four times greater than for high capacity carbon materials and twice that of Sn oxide-based glasses. A mild heat treatment and an appropriate discharge cut-off potential stabilizes the cycling behavior. A discharge cut-off of 5 mV is associated with a large polarization, and fading charge retention, probably related to the oxygen diffusion process into the highly sub-stoichiometric oxide during the charge sweep. Conversely, raising the charge potential to 200 mV may conserve the oxygen environment surrounding the Mo centre to some degree, thus facilitating oxygen migration during charge. The irreversible capacity and the high average potential in charge are the major drawbacks in these systems. By utilizing the exchange capability of the interlayers ions, Sn can be incorporated into the material, thus lowering the average charge potential but at the expense of capacity fading. Finally, a catalytic effect of the carbon black in these composite electrodes via an interface effect is present, which must be accounted for by methods other than simple subtraction of the carbon contribution to the total capacity by mass fraction.