Enhanced high rate capability of Li intercalation in planar and edge defect-rich MoS₂ nanosheets

(i) Edge and planar defect-rich and (ii) defect-suppressed MoS2 nanosheets are fabricated by controlled annealing of wet-chemically processed precursors. Wrinkles, folds, bends, and tears lead to the introduction of severe defects in MoS2 nanosheets. These defects are suppressed and highly crystalline MoS2 nanosheets are obtained upon high-temperature annealing. The influence of defects on the electrochemical properties, particularly rate capability and cycling stability, in the Li intercalation regime (1 V to 3 V vs. Li/Li+) and conversion regime (10 mV to 3 V vs. Li/Li+) are investigated. In the intercalation regime, the initial Li intake (x in LixMoS2) for defect-rich nanosheets is larger (x ≈ 1.6) as compared to that in defect-suppressed MoS2 (x ≈ 1.2). Although the reversible initial capacity of all the anodes is nearly the same (x ≈ 0.9) at 0.05C rate, defect-rich MoS2 exhibits high rate capability (>40 mA h g-1 at 40C or 26.8 A g-1). When cycled at 10C (6.7 A g-1) for 1000 cycles, 75% capacity retention is observed. High rate capability can be attributed to the defect-rich nature of MoS2, providing faster access to lithium intercalation by a shortened diffusion length facilitated by Li adsorption at the defect sites. The defect-rich nanosheets exhibit a power density of ∼20% more than that of defect-suppressed nanosheets. For the first time, MoS2/Li cells with a high power density of 10-40 kW kg-1 in the intercalation regime have been realized. In the conversion regime, defect-rich and defect-suppressed MoS2 exhibit initial lithiation capacities of ∼1000 and ∼840 mA h g-1, respectively. Defect-rich MoS2 had a capacity of ∼800 mA h g-1 at 0.1C (67 mA g-1), whereas defect-suppressed MoS2 had a capacity of only ∼80 mA h g-1 at the same current rate. Capacity retention of 78% was observed for defect-rich MoS2 with a reversible capacity of 591 mA h g-1 when cycled at 0.1C (67 mA g-1) for 100 cycles. Despite having a lower energy density in the intercalation regime, the power density of defect-rich MoS2 in the intercalation regime is significantly larger (by three orders of magnitude) as compared to that of defect-suppressed MoS2 in the conversion regime. Defect-rich MoS2 nanosheets are promising for high-rate-capability applications when operated in the intercalation regime.