Short communicationNovel carbon nanofiber-cobalt oxide composites for lithium storage with large capacity and high reversibility
Introduction
Among the various sorts of transition metal oxides, spinel Co3O4 is an important magnetic p-type semiconductor, which has been widely used in many fields, such as solid-state sensors, supercapacitors, heterogeneous catalysts, and electrochromic devices [1], [2], [3]. Such a broad perspective of utilization makes the preparation of nanostructural Co3O4 much more attractive [4], [5]. So far, Co3O4 and some other transition metal oxides have been reported to have high capacity for advanced lithium batteries [6], [7], [8], [9]. But the Co3O4 active material, in general, undergoes a large irreversible capacity loss (ca. 32%) in the 1st cycle and relatively fast capacity fading rate during electrochemical cycling. On the other hand, carbon nanofibers and carbon nanotubes have been used as a promising supporting material in both heterogeneous catalysis and electrocatalysis because of their unique properties, such as high external surface, good electronic conductivity, and high mechanical stability [10], [11], [12]. Due to high specific capacity, low electrode potential, high columbic efficiency, long cycle life and a high level of safety, several types of carbon nanofibers have been successfully used in lithium battery applications [13], [14].
In this work, a new CNF-supported cobalt oxide composite anode material was prepared by the precipitation of Co(OH)2 on the surface-activated CNF and subsequent calcination in argon flow. In rechargeable lithium batteries, this new composite material shows very high reversible Li-storage capacity and excellent electrochemical cycling stability. It could be a promising anode material for advanced Li-ion batteries.
Section snippets
Experimental
The commercial carbon nanofiber with average diameter of 200 nm was pretreated in concentrated HNO3–H2SO4 (4:1, v/v) solution at 85 °C for 5 h, intensively washed with deionized water and dried in vacuum. A given amount of Co(NO3)2·6H2O was dissolved into 100 ml of isopropyl alcohol–water (1:1, v/v) solution in a three-necked round-bottom. 0.2 g of acid-treated CNF was dispersed in the above solution by ultrasonication for 0.5 h and then stirred for several hours under an argon flow. Then appropriate
Results and discussion
The phase purity and crystallinity of Co3O4 samples and CNF-Co3O4 nanocomposite were characterized using XRD. Fig. 1 shows XRD patterns of the home-made Co3O4 powder and CNF-Co3O4 composite powder, in comparison with commercial Co3O4 product. The clear diffraction peaks of all the samples represent a typical character of the crystalline face-centered cubic (fcc) Co3O4 phase [space group: Fdm (2 2 7)]. The (3 1 1) reflection of Co3O4 of the synthesized samples was used to calculate the average
Conclusions
In conclusion, novel CNF-supported Co3O4 nanocomposite materials can be prepared by developing CNF-Co(OH)2 composite precursors in aqueous solution without any surfactants and calcining the precursor under Ar flow. The reticular and morphology-stable composite texture with fine dispersion of Co3O4 nanoparticles on the mixed conductive CNF provides an excellent electronic and ionic conduction pathway for the electrochemical processes, which ensures high reversible capacity and excellent
Acknowledgment
This work was supported by National Basic Research Program of China (973 Program, No. 2007CB209705).
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