Mingshu Zhao

Co3O4–carbon nanotube heterostructures with bead-on-string architecture for enhanced lithium storage performance

In this report, alkylcarboxyl group-decorated carbon nanotubes (CNTs) with clustered functionalization patterns are achieved based on a modified Birch reduction in liquid ammonia. By using these functional CNTs (f-CNTs), a new type of Co3O4-CNT heterostructure is prepared via a simple hydrothermal method. SEM and TEM analyses reveal that the as-synthesized Co3O4-CNT heterostructures exhibit bead-on-string architecture, in which the Co3O4 spheres are threaded with CNTs. A possible growth mechanism is proposed to explain the formation of these Co3O4-CNT heterostructures. The electrochemical properties of the Co3O4-CNT heterostructures as anode materials for lithium ion batteries are investigated. The Co3O4-CNT heterostructures display high electrochemical activity, good cycle stability and improved rate performance. Such a large improvement of the electrochemical performance can be related to the robust necklace-like architectures which possess properties such as high mechanical stability, excellent electric conductivity and good strain accommodation.

Enhanced cycling stability of hierarchical NiCo2S4@Ni(OH)2@PPy core–shell nanotube arrays for aqueous asymmetric supercapacitors

In this article, a novel electrode of NiCo2S4@Ni(OH)2@polypyrrole nanotube arrays supported on nickel foam is fabricated through a facile method. Due to the superior electronic conductivity of the shell material polypyrrole (PPy) and the high pseudocapacitance of Ni(OH)2 together with the short ion transport pathway of NiCo2S4 nanotube arrays, the obtained core–shell NiCo2S4@Ni(OH)2@PPy shows an enhanced pseudocapacitive performance of about 9.1125 F cm−2 at a current density of 5 mA cm−2, which is nearly three times higher than that of the pristine NiCo2S4 sample (3.1875 F cm−2). The kinetic analysis reveals the diffusion controlled faradaic characteristic of NiCo2S4@Ni(OH)2@PPy (43.57% capacitive contribution). Moreover, an asymmetric supercapacitor is successfully assembled with NiCo2S4@Ni(OH)2@PPy as the positive electrode and active carbon (AC) as the negative electrode. The NiCo2S4@Ni(OH)2@PPy//AC device exhibits a relatively high energy density of 34.67 W h kg−1 at a power density of 120.127 W kg−1 and excellent cycling performance (about 98.87% capacitance retention over 30 000 cycles). The results show that the NiCo2S4@Ni(OH)2@PPy core–shell nanotube array is a promising electrode material for high performance supercapacitor applications.

In situ sodium chloride template synthesis of cobalt oxide hollow octahedra for lithium-ion batteries

A novel template synthesis route is developed to synthesize cobalt oxide hollow octahedra. The sodium chloride templates are formed in situ in the reaction system by controlling the supersaturation of sodium chloride in the N,N-dimethylformamide solution. Transmission electron microscopy indicates that the porous shells of hollow octahedra are composed of ultra small particles. Electrochemical tests show that the discharge capacity of the cobalt oxide hollow octahedra is about 965 mA h g−1 after 30 cycles at 0.2C.

Superior cycling stability of crystalline/amorphous Co3S4 core-shell heterostructure for aqueous asymmetric supercapacitors

In this article, a novel crystalline/amorphous Co3S4 core–shell heterostructure supported on nickel foam is fabricated through a facile method. Due to the unique structure of the crystalline Co3S4 core that provides stable mechanical support and surface-active sites and the amorphous shell that facilitates diffusion and reaction of electrolyte ions, the obtained crystalline/amorphous Co3S4 electrode shows a superior pseudocapacitive performance of 2.65 F cm−2 (2038.5 F g−1) at a current density of 5 mA cm−2 and even 1.81 F cm−2 (1392.3 F g−1) at 50 mA cm−2. In addition, the Co3S4//AC exhibits a relatively high energy density of 54.78 W h kg−1 at a power density of 400.02 W kg−1 and excellent cycling performance (about 94.8% capacitance retention over 32 500 cycles). The kinetic analysis reveals a diffusion controlled faradaic characteristic of Co3S4 (73.21% diffusion-controlled contribution). Moreover, the fabrication process presented in this work is facile, cost-effective, and environmentally benign, offering a feasible solution for fabricating next-generation high-performance energy storage devices.

Fine-Particle Lithium Iron Phosho-Olivine Synthesized by a Novel Modified Solid-State Reaction

In this paper, homogeneous and well-crystallized LiFePO4 was synthesized by a novel modified solid-state reaction method following by heat treatment at relatively low temperature of 500°C in Ar. No impurities are detected in the XRD patterns. The initial charge specific capacity and discharge specific capacity reach 157.2mAhg-1 and 152.6mAhg-1 respectively at 20°C. Voltage plateaus at around 3.45V were observed in all the curves, indicating that the charge and discharge reaction proceeds as a two-phase reaction. The initial charge specific capacity is 157.2mAhg-1 at 0.1C rate, i.e. 92% of the theoretical capacity, and specific capacity decreases slightly after 100 circles at room temperature.