Nanocomposite Li-ion battery anodes consisting of multiwalled carbon nanotubes that anchor CoO nanoparticles
Graphical abstract
Introduction
Transition metal oxides have attracted much attention in the past decade as anode materials for Li-ion batteries because of their high theoretical capacities, which are greater than that of commercial graphite (at 372 mA h g−1) [1], [2]. These transition metal oxides including Co(II)O react with lithium by a conversion reaction to form cobalt nanocrystals that are well dispersed in the Li2O matrix [2]. This process inevitably causes drastic volume variations in the matrix, resulting in severe capacity fading during the cycling process [3].
It is well recognized that electrode materials with predesigned nanostructures could accommodate the volume change, and well-incorporated active materials in nanocomposite electrodes could offer more stable cyclability [4], [5]. Among the various reports, Du et al. have demonstrated that anodes composed of carbon nanotube (CNT)–transition metal oxide composites could react with lithium effectively because of the synergistic action of the metal oxides with the unique properties of CNTs (including strong mechanical properties, excellent electronic conductivities, and large surface areas) [6]. Moreover, nanoparticles could retain their sizes, and agglomeration could be prevented because of their tight anchoring by the CNTs. Extensive efforts have been taken toward exploiting the advantages offered by metal oxide–CNT composites, and these composites have been synthesized by various methods like hydrothermal processing, chemical vapor deposition (CVD), ball-milling, and wet chemical processing [7], [8], [9], [10].
Herein, we report the fabrication of heterostructured CoO nanoparticle (NP)/multiwalled CNT (MWCNT) anodes free of binders. These nanocomposite electrodes were found to exhibit high capacity delivery with good cycle retention.
Section snippets
Experimental
The CoO NP/MWCNT composites were synthesized by a simple two-step process. First, the MWCNTs (from Hanwha Nanotech Co. Ltd.) were deposited electrophoretically on stainless steel (SS) substrates by a previously reported procedure [11]. Then, CoO NPs were decorated on the surface of the MWCNTs by a CVD process (Supplementary information). Field-emission scanning electron microscopy (FESEM, JSM-6700F, JEOL), transmission electron microscopy (TEM, JEM-2100F, JEOL), X-ray diffraction (XRD, Miniflex
Results and discussion
Fig. 1a shows the typical XRD pattern acquired from the CoO NP/MWCNT composites. The characteristic (002) reflection corresponding to the stacking of graphene layers in the MWCNTs was detected at 2θ of about 25.8°. The peaks at 36.4°, 42.4°, and 61.6° (2θ) could be indexed to reflections from (111), (200), and (220) planes of pure CoO with a cubic structure (Fm3m, JCPDS #48-1719), respectively. The considerable peak broadening and reduced intensity observed confirm the nanocrystalline nature
Conclusions
We prepared CoO NP/MWCNT nanocomposites by the direct anchoring of CoO on the surface of electrophoretically predeposited MWCNT networks via a CVD process. The CoO NP/MWCNT nanocomposite anodes that were free of binders displayed a large reversible capacity of over 550 mA h g−1 at a high rate of 715 mA g−1 even after 100 cycles. The enhancement in the electrochemical performance could be attributed to the uniform distribution of tiny CoO NPs (13 nm in diameter), the existence of highly conductive
Acknowledgment
This research was supported by the National Research Foundation of Korea Grant funded by the Korean Government (MEST) (2009-0094046, 2012M1A2A2671802 and 2012R1A2A2A01045382).
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2016, Materials LettersCitation Excerpt :To date, transitional metal oxides have been widely studied as promising candidates because of their high specific capacity, typically 2–3 times higher than that of the carbon based materials [3–5]. Among them, CoO has attracted increasing attention due to its high theoretical capacity (718 mAh g−1) [6], arising from the reversible electrochemical reaction with Li ion (CoO+2Li++2e↔Co+Li2O). However, similar to other metal oxides, the practical application of CoO as anode for LIBs is still hampered by two main issues: pulverization problem and fast capacity fading [7,8].
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2015, Journal of the Taiwan Institute of Chemical EngineersCitation Excerpt :The CoO/C polyhedra as anode of Li-ion battery exhibited an initial discharge capacity of 1025 mAh/g, and remained a reversible capacity of 510 mAh/g after 50 cycles [31]. The reversible charge capacities of CoO NPs (nanoparticles)/multiwalled carbon nanotubes fabricated by the electrophoretic deposition and chemical vapor deposition were 600 and 550 mAh/g after 50 and 100 cycles, respectively [32]. The CoO nanoparticle electrode delivered a second reversible discharge capacity of 855.47 mAh/g and exhibited about 66% of capacity retention (565.16 mAh/g) after 23 cycles [33].