Synthesis, characterization, and lithium battery applications of molybdenum oxysulfides

Molybdenum oxysulfides, MoO[sub x]S[sub y], obtained by thermal decomposition of (NH[sub 4])[sub 2]MoO[sub 2]S[sub 2], have been identified as Li insertion positive electrodes for rechargeable Li batteries. The compositions of the oxysulfides and their discharge capacity and rechargeability in Li cells were influenced by the temperature at which they were formed from (NH[sub 4])[sub 2]MoO[sub 2]S[sub 2]. Thermolysis of the latter in the 200-380[degrees]C range appeared to occur by a solid-state polymerization reaction, wherein the MoO[sub x]S[sub y] formed at different temperatures can be viewed as polymers with different chain lengths. MoO[sub x]S[sub y] prepared at 200, 300, and 380[degrees]C and in a two-step 200/380[degrees]C thermolysis, respectively, exhibited first discharge capacity, in Li cells, equivalent to the incorporation of 2.70, 2.80, 1.90, and 1.30 Li per molybdenum. These capacities 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 discharge of Li/MoO[sub x]S[sub y] cells was irreversible, and it is largely attributed to a phase change accompanying Li insertion into the material. MoO[sub x]S[sub y] obtained by the decomposition of an intimate 1:1 mixture of (NH[sub 4])[sub 2]MoO[sub 4] and (NH[sub 4])[sub 2]MoS[sub 4] at 380[degrees]C exhibited electrochemical behavior reminiscent of the Mo-oxysulfide obtained by decomposition of (NH[sub 4])[sub 2]MoO[sub 2]S[sub 2] at the same temperature. 21 refs., 14 figs., 5 tabs.