Transforming large-scale industrially produced carbon nanotubes to high-performance electrode materials for lithium-ion
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Large-scale industrial production of carbon nanotubes (CNTs) has recently become available, but there are relatively few reports of the investigation of these industrially produced bulk CNTs as potential electrode materials for electrochemical energy storage such as lithium-ion batteries (LIBs). Here, we report our evaluation of the electrochemical performance of the industrially produced CNTs from one manufacturer and our utilization of a kinetically controlled, vapor diffusion synthesis method combined with in-situ carbothermal reduction to homogeneously grow nanocrystalline tin (Sn) particles (;200 nm) in the matrix of the CNTs, yielding a Sn@CNTs composite. After surface coating with a layer of carbon coating (3–4 nm), this composite was transformed to a surface-modified Sn@CNTs composite that exhibited much higher reversible capacity, initial Coulombic efficiency, and rate capacity than the pristine CNTs as anode materials for LIB.
I. INTRODUCTION
Carbon nanotubes (CNTs) have been regarded as promising functional materials for nearly 20 years due to their excellent thermal, electrical, and mechanical properties.1 Recently, large-scale industrial production of multiwalled CNTs became available at relatively low cost, significantly accelerating interest in potential applications of these CNTs. Thus far, most practical applications of these bulkmanufactured CNTs have been for mechanical strengthening and antistatic coating.2 Although there have been many investigations of CNTs as electrode materials for electrochemical energy storage such as lithium-ion batteries (LIBs) and supercapacitors in the past decades,3–10 those CNTs were all synthesized at the laboratory scale of multiple grams, permitting high levels of quality control of crystal structure, diameter, purity, and dispersibility and facilitating optimization of performance. Because these synthesis conditions differ markedly from those industrially to produce CNTs in quantities of tens of tons, it is necessary to reinvestigate industrially produced CNTs to determine their potential usefulness as electrode materials for electrochemical energy storage. Alloying anode materials such as metallic tin (Sn) are very attractive for next-generation LIB in comparison with present commercial graphite anodes because of their high theoretical capacities (e.g., 991 mAh/g for Sn versus 372 mAh/g for graphite).11 However, the large volume change of Sn during its reversible alloying/dealloying with Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2011.397 410
J. Mater. Res., Vol. 27, No. 2, Jan 28, 2012
Li causes Sn to pulverize and finally lose mechanical and electrical contact with the bulk electrode.12–14 As a result, the cyclability of Sn anodes alone is very poor. Numerous strategies have been proposed to address the problem, including the fabrication of composites in which Sn is incorporated within a resilient matrix to buffer
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