PPy-Coated Mo3S4/CoMo2S4 Nanotube-like Heterostructure for High-Performance Lithium Storage

Abstract

Heterostructured materials show great potential to enhance the specific capacity, rate performance and cycling lifespan of lithium-ion batteries owing to their unique interfaces, robust architectures, and synergistic effects. Herein, a polypyrrole (PPy)-coated nanotube-like Mo₃S₄/CoMo₂S₄ heterostructure is prepared by the hydrothermal and subsequent in situ polymerization methods. The well-designed nanotube-like structure is beneficial to relieve the serious volume changes and facilitate the infiltration of electrolytes during the charge/discharge process. The Mo₃S₄/CoMo₂S₄ heterostructure could effectively enhance the electrical conductivity and Li⁺ transport kinetics owing to the refined energy band structure and the internal electric field at the heterostructure interface. Moreover, the conductive PPy-coated layer could inhibit the obvious volume expansion like a firm armor and further avoid the pulverization of the active material and aggregation of generated products. Benefiting from the synergistic effects of the well-designed heterostructure and PPy-coated nanotube-like architecture, the prepared Mo₃S₄/CoMo₂S₄ heterostructure delivers high reversible capacity (1251.3 mAh g^-1 at 300 mA g^-1), superior rate performance (340.3 mAh g^-1 at 5.0 A g^-1) and excellent cycling lifespan (744.1 mAh g^-1 after 600 cycles at a current density of 2.0 A g^-1). Such a design concept provides a promising strategy towards heterostructure materials to enhance their lithium storage performances and boost their practical applications.

Keywords: CoMo2S4; Mo3S4; heterostructure; lithium-ion batteries; nanostructure design.

Scheme 1

Preparation scheme of PPy-coated Mo₃S₄/CoMo₂S₄ heterostructure.

Figure 1

(a) XRD patterns of Mo₃S₄/CoMo₂S₄ and Mo₃S₄/CoMo₂S₄-30PPy; XPS spectra of Mo₃S₄/CoMo₂S₄-30PPy: (b) survey spectrum; (c) S 2p; (d) Co 2p; (e) Mo 3d.

Figure 2

SEM images of samples: (a) Co-Fe PBA, (b) Co-Mo sulfide intermediate, (c) Mo₃S_4/CoMo₂S₄, (d) Mo₃S₄/CoMo₂S₄-30PPy; (e,f) HRTEM images and (g) element mapping of Mo₃S₄/CoMo₂S₄-30PPy.

Figure 3

(a) N₂ adsorption–desorption isotherm and (b) aperture distribution of Mo₃S₄/CoMo₂S₄ and Mo₃S₄/CoMo₂S₄-30PPy samples.

Figure 4

(a,b) CV curves at 0.1 mV s⁻¹; (c) rate performances at different current densities; (d,e) cycling performances at 300 mA g⁻¹ and 2.0 A g⁻¹ of Mo₃S₄/CoMo₂S₄ and Mo₃S₄/CoMo₂S₄-30PPy.

Figure 5

(a,b) Nyquist plots and the relationships between Z’ and ω^−1/2 in low-frequency region of Mo₃S₄/CoMo₂S₄, Mo₃S₄/CoMo₂S₄-30PPy; (c,e) CV curves at scan rates from 0.2 to 1.0 mV s⁻¹ and (d,f) the relationships between log v and log i plots for cathodic and anodic peaks of Mo₃S₄/CoMo₂S₄-30PPy and Mo₃S₄/CoMo₂S₄; (g) ratio of the capacitive-controlled charge contribution (shaded area) to the total current at a scan rate of 8 mV s⁻¹; and (h) pseudo-capacitance contribution under different scan rates of Mo₃S₄/CoMo₂S₄-30PPy.