Enhanced high rate capability of Li intercalation in planar and edge defect-rich MoS2 nanosheetsElectronic supplementary information (ESI) available: Structural characterization (XRD, SEM & EDS, DSC/TGA) of filtered chocolate brown precipitate, HRTEM of MoS2-800-5 h and MoS2-900-1 h nanosheets, BET graphs of MoS2 nanosheets, cyclic voltammetry plots, EIS of MoS2 nanosheets, schematic showing structural changes during charge/discharge (10 mV to 3 V), tables of electrochemical properties of differ

• Main Authors: Budumuru, Akshay Kumar, Rakesh, Benadict, Sudakar, Chandran
• Format: Journal Article
• Language: English
• Published: 09.05.2019
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/c9nr02043h

(i) Edge and planar defect-rich and (ii) defect-suppressed MoS 2 nanosheets are fabricated by controlled annealing of wet-chemically processed precursors. Wrinkles, folds, bends, and tears lead to the introduction of severe defects in MoS 2 nanosheets. These defects are suppressed and highly crystalline MoS 2 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 Li x MoS 2 ) for defect-rich nanosheets is larger ( x 1.6) as compared to that in defect-suppressed MoS 2 ( 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 MoS 2 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 MoS 2 , 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, MoS 2 /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 MoS 2 exhibit initial lithiation capacities of ∼1000 and ∼840 mA h g −1 , respectively. Defect-rich MoS 2 had a capacity of ∼800 mA h g −1 at 0.1C (67 mA g −1 ), whereas defect-suppressed MoS 2 had a capacity of only ∼80 mA h g −1 at the same current rate. Capacity retention of 78% was observed for defect-rich MoS 2 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 MoS 2 in the intercalation regime is significantly larger (by three orders of magnitude) as compared to that of defect-suppressed MoS 2 in the conversion regime. Defect-rich MoS 2 nanosheets are promising for high-rate-capability applications when operated in the intercalation regime. Defects in MoS 2 nanosheets improve the rate capability and cycling stability in the intercalation regime. Li adsorbed at defect sites facilitates a high power density.