SYNTHESIS, CHARACTERIZATION, AND LITHIUM BATTERY APPLICATIONS OF MOLYBDENUM OXYSULFIDES

Molybdenum oxysulfides, MoO(x)S(y), obtained by thermal decomposition of (NH4)2MoO2S2, have been identified as Li insertion positive electro des for rechargeable Li batteries. The compositions of the oxysulfides and their discharge capacity and rechargeability in Li cells were inf luenced by the temperature at which they were formed from (NH4)2MoO2S2 . Thermolysis of the latter in the 200-380-degrees-C range appeared to occur by a solid-state polymerization reaction, wherein the MoO(x)S(y ) formed at different temperatures can be viewed as polymers with diff erent chain lengths. MoO(x)S(y) prepared at 200, 300, and 380-degrees- C and in a two-step 200/380-degrees-C thermolysis, respectively, exhib ited first discharge capacity, in Li cells, equivalent to the incorpor ation of 2.70, 2.80, 1.90, and 1.30 Li per molybdenum. These capacitie s translated into quasi-theoretical specific energies from 290 to 685 W h/kg for the Li cells. A fraction of the capacity in the first disch arge of Li/MoO(x)S(y) cells was irreversible, and it is largely attrib uted to a phase change accompanying Li insertion into the material. Mo O(x)S(y) obtained by the decomposition of an intimate 1:1 mixture of ( NH4)2MoO4 and (NH4)2MoS4 at 380-degrees-C exhibited electrochemical be havior reminiscent of the Mo-oxysulfide obtained by decomposition of ( NH4)2MoO2S2 at the same temperature.