Electrochemical lithium insertion in two polymorphs of a reduced molybdenum oxide (gamma and gamma '- Mo4O11)

A study of the electrochemical lithium insertion in two polymorphs of a red uced molybdenum oxide. Mo4O11. is presented in this work. When used as acti ve materials in cells discharged down to 1 V vs. Li+/ Li, both forms. the o rthorhombic gamma-Mo4O11 and the monoclinic gamma'-Mo4O11, incorporated a s imilar number of lithium atoms per metal atom (Li/Mo = 2.12 and 2.25, respe ctively). Step potential electrochemical spectroscopy experiments proved th at the insertion reaction proceeds in both casts through different mechanis ms. In situ X-ray diffraction studies showed an almost complete loss of cry stallinity of both compounds after the first discharge, leading to amorphou s materials with different electrochemical behaviour on cycling. When disch arged to low potentials (0.5 V vs. Li+/Li), the gamma'-MO4O11 polymorph sho wed very good cycling behaviour for at least five lithium atoms per formula unit. corresponding to a specific capacity of 230 Ah/kg after seven comple te charge-discharge cycles.