Carbon Nanotube Anodes for Lithium Ion Batteries
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Carbon Nanotube Anodes for Lithium Ion Batteries Ryne P. Raffaelle1, Thomas Gennett1, Jeff Maranchi2, Prashant Kumta2, Aloysius F. Hepp3, Michael J. Heben4, Anne C. Dillon4 and Kim C. Jones4 1
NanoPower Research Labs, Rochester Institute of Technology, Rochester, NY 14623 Carnegie-Mellon University, 4309 Wean Hall, Pittsburgh, PA 15213 3 NASA Glenn Research Center, 12000 Brookpark Rd., Cleveland, OH 44135 4 National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401 2
ABSTRACT Highly purified single-wall carbon nanotubes (SWCNT) were investigated for use as an anode material for thin film lithium ion batteries. The high purity nanotubes were obtained through chemical refinement of soot generated by pulsed laser ablation. The purity of the nanotubes was determined via thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. The specific surface area and lithium capacity of the SWCNT’s was compared to that of other conventional anode materials (i.e., carbon black, graphite, and multi-walled carbon nanotubes). The Brunauer, Emmett, and Teller (BET) technique based on nitrogen adsorption was used to measure the specific surface area of the various anode materials. The SWCNT’s exhibited a specific surface area on the order of 915 m2/g, much higher than the other carbonaceous materials. Cyclic voltammetric behavior and the lithium-ion capacity of the materials were measured using a standard 3-electrode electrochemical cell. The cyclic voltammetry showed evidence of “staging” that was similar to other carbonaceous materials. The electrochemical discharge capacity of the purified single walled carbon nanotubes was in excess of 1300 mAh/g after 30 charge/discharge cycles when tested using a current density of 20µA/cm2. INTRODUCTION Carbon based materials have been the material of choice for lithium storage in Li-ion batteries for some time.1-2 Now, with the more recent discovery of new crystalline forms of carbon such as single and multi-walled nanotubes it appears that this trend may well continue.3-5 This is due to the fact that, in contrast to carbon black, nanotubes offer a more accessible structure for Li interaction. Carbon lamellas in carbon blacks are circumferentially oriented and block much of the particle interior, rendering much of the matrix useless as intercalation material. SWCNT’s with diameters on the order of 0.6 to 20 nm and lengths in excess of 500 nm can be grown so as to provide nearly 100% accessibility of the entire carbon structure to Li interaction. This accessibility may be mitigated somewhat by bundling effects, but should still provide a much higher accessibility than more conventional graphitic anode materials.4 This high accessibility of the structure should also confer a high mobility to ion exchange processes, a fundamental for dynamic response of batteries based on intercalation. In addition to the capacities of these materials, there are also predicted nanotube properties that make them extremely attractive for thin film polymer battery p
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