Exfoliated MoS2 as Electrode for All-Solid-State Rechargeable Lithium-Ion Batteries

The electrode behavior of exfoliated MoS2 is studied in an all-solid-state lithium-ion battery. MoS2 nanosheets with a crystallite thickness of about 6 nm are synthesized by chemical exfoliation of bulk MoS2 and characterized by XRD, SEM, and TEM. MoS2 composite electrodes are obtained by uniaxial cold-pressing at 3 tons and contain 60 wt % MoS2, 30 wt % beta-Li3PS4 solid electrolyte, and 10 wt % carbon black. Solid-state lithium-ion batteries are assembled using beta-Li3PS4 as the solid electrolyte and a Li-In alloy as the counter electrode. The electrode performance is well above state-of-the-art with an initial specific capacity of about 439 mAh g(-1) when discharged at 67 mA g(-1) (C/10) in the potential range of 0.01-3.0 V. The initial irreversible capacity is only 9%. The specific capacity retention is excellent with 312 mAh g(-1) obtained after 500 cycles. In view of the theoretical capacity of MoS2 (q(th) = 670 mAh g(-1)), the solid-state reaction in the cell is incomplete; yet the end phases of the conversion reaction after discharge (Mo and Li2S) are confirmed by XRD. We also studied the behavior of bulk MoS2 (same mass loading) and found that the performance is inferior as compared to MoS2 nanosheets. The initial discharge capacity of bulk MoS2 is only 259 mAh g(-1), and the initial irreversible capacity is as large as 26%. Overall, the study shows that MoS2 can be effectively cycled in all-solid-state batteries with beta-Li3PS4 as solid electrolyte and that the electrode performance can be significantly improved by nanostructuring.