MOF-Derived ZnS Nanodots/Ti3C2Tx MXene Hybrids Boosting Superior Lithium Storage Performance

Abstract

ZnS has great potentials as an anode for lithium storage because of its high theoretical capacity and resource abundance; however, the large volume expansion accompanied with structural collapse and low conductivity of ZnS cause severe capacity fading and inferior rate capability during lithium storage. Herein, 0D-2D ZnS nanodots/Ti₃C₂T_x MXene hybrids are prepared by anchoring ZnS nanodots on Ti₃C₂T_x MXene nanosheets through coordination modulation between MXene and MOF precursor (ZIF-8) followed with sulfidation. The MXene substrate coupled with the ZnS nanodots can synergistically accommodate volume variation of ZnS over charge-discharge to realize stable cyclability. As revealed by XPS characterizations and DFT calculations, the strong interfacial interaction between ZnS nanodots and MXene nanosheets can boost fast electron/lithium-ion transfer to achieve excellent electrochemical activity and kinetics for lithium storage. Thereby, the as-prepared ZnS nanodots/MXene hybrid exhibits a high capacity of 726.8 mAh g^-1 at 30 mA g^-1, superior cyclic stability (462.8 mAh g^-1 after 1000 cycles at 0.5 A g^-1), and excellent rate performance. The present results provide new insights into the understanding of the lithium storage mechanism of ZnS and the revealing of the effects of interfacial interaction on lithium storage performance enhancement.

Keywords: Heterointerface; Interfacial interaction; Lithium-ion batteries; MOF; Ti3C2Tx MXene; ZnS.

Fig. 1

Schematic illustration for the synthesis of ZnS/MXene hybrids

Fig. 2

Morphology characterizations. SEM images of a ZIF-8 and b ZIF-8/MXene-0.9, and c TEM image of ZIF-8/MXene-0.9. d SEM image of ZnS/MX64 and e EDS elemental mapping of Ti, S, Zn and C of the corresponding SEM image of the ZnS/MX64. f, g HRTEM images of ZnS/MX64 and h the corresponding SAED pattern

Fig. 3

Structural characterizations of the ZnS nanodots/MXene hybrids. a XRD patterns, b Raman spectra, and c, d high-resolution Ti 2p, e O 1s, f Zn 2p, j S 2p XPS spectra

Fig. 4

In situ XRD characterization of commercial ZnS anodes during lithium storage. a Contour plot of in situ XRD characterization with corresponding voltage profile and b diffraction patterns for CZnS anode in the first cycle. c Schematic illustration of the phase evolution of the CZnS in the first lithiation–delithiation cycle

Fig. 5

Lithium storage performance. CV curves of as-prepared a ZnS and b ZnSMX64 at a scan rate of 0.1 mV s⁻¹. c Galvanostatic charge/discharge profiles of ZnSMX64 at 100 mA g⁻¹. d Cyclability at 100 mA g⁻¹, e long-term cycling performance of ZnSMX64 at 0.5 A g⁻¹ with ex situ HRTEM images in the insets, f rate capabilities at different currents, and g Nyquist plots for ZnS and ZnS/MXene hybrids

Fig. 6

Electrochemical kinetics for the ZnS/MXene hybrids. CV curves of a ZnSMX64 and b ZnSMX80 at different sweep rates from 0.1 to 2.0 m V⁻¹, and c the plots of log i versus log υ. d CV curve of ZnSMX64 with the surface dominating capacity contribution for cathodic process at 0.5 mV s⁻¹, and e the proportion of capacity contributions at different scan rates. f In situ EIS characterization of ZnSMX64 at different lithiation states between 2.0 and 0.01 V. g GITT potential profile of the ZnSMX64 and h the Li⁺ diffusion coefficients in lithiation process

Fig. 7

Theoretical simulation for lithium adsorption/migration at ZnS-Ti₃C₂T_x MXene heterointerface. a Lithium adsorption and the corresponding adsorption energy at Ti top, C top, Ti-C top and hollow site at ZnS (111)/Ti₃C₂T_x MXene heterointerface and b charge density differences of ZnS (111)/Ti₃C₂T_x MXene heterointerface. DOS plots (fermi levels are set as zero and indicated with dashed lines) of c Ti₃C₂T_x, d ZnS, and e ZnS/Ti₃C₂T_x MXene. f Planar average potential charge density along the z axis (vertical direction) of ZnS (111)/Ti₃C₂T_x MXene heterointerface. g Lithium diffusion pathway and h the corresponding relative diffusion energy variation at ZnS (111)/Ti₃C₂T_x MXene heterointerface

Fig. 8

Schematic illustration for interfacial interaction at ZnS-MXene heterointerface boosting electron transfer and lithium diffusion