Sn(II)-treated MoO₃ as cathode material for rechargeable lithium batteries

We report on the synthesis and structural, thermal and electrochemical characterisation of reduced molybdenum oxides with layered α-MoO ₃ type structure. The samples have been prepared by reactions of various amounts of water-free tin dichloride with fine-particulated orthorhombic molybdenum trioxide in n-hexane (non-aqueous media) or in aqueous media, which yielded materials with different Sn:Mo ratio. XRD investigations of these materials proved that the crystal structure of the layered α-MoO ₃ has been maintained after the reduction process. No crystalline impurity phases (e.g. tin oxides) could be detected by XRD. The tin-reduced samples exhibited a drastically improved cycling stability and capacity retention on cycling in 1 M LiC10₄/propylene carbonate, i.e. the discharge capacities were well above 100 mAh g^-1 after 20 cycles whereas the non-treated MoO₃ (reference sample) has retained only about 45 mAh g^-1. At higher cycle numbers (approx. cycle 100) the discharge capacity of the reduced molybdenum oxides stabilises at a level of approx. 100 mAh g^-1. This significant improvement of the rechargeability may be related to improved electronic conductivity and/or higher structural stabilisation of the layered MoO₃ structure either due to (i) a coating of the MoO₃ particles with a protective thin layer of a tin containing compounds, and/or (ii) an amorphisation of the structure after reductive treatment. Further efforts of this study were devoted to a variation of the conductive carbon content in the electrode composition and to changes of cut-0ff voltages and current densities.