Exfoliated MoS 2 as Electrode for All-Solid-State Rechargeable Lithium-Ion Batteries

The electrode behavior of exfoliated MoS 2 is studied in an all-solid-state lithium-ion battery. MoS 2 nanosheets with a crystallite thickness of about 6 nm are synthesized by chemical exfoliation of bulk MoS 2 and characterized by XRD, SEM, and TEM. MoS 2 composite electrodes are obtained by uniaxial cold-pressing at 3 tons and contain 60 wt % MoS 2, 30 wt % β-Li 3 PS 4 solid electrolyte, and 10 wt % carbon black. Solid-state lithium-ion batteries are assembled using β-Li 3 PS 4 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 MoS 2 ( 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 Li 2 S) are confirmed by XRD. We also studied the behavior of bulk MoS 2 (same mass loading) and found that the performance is inferior as compared to MoS 2 nanosheets. The initial discharge capacity of bulk MoS 2 is only 259 mAh g –1, and the initial irreversible capacity is as large as 26%. Overall, the study shows that MoS 2 can be effectively cycled in all-solid-state batteries with β-Li 3 PS 4 as solid electrolyte and that the electrode performance can be significantly improved by nanostructuring.