Lithium ion batteries are receiving considerable attention in applications, ranging from portable electronics to electric vehicles, due to their superior energy density over other rechargeable battery technologies. However, the societal demands for lighter, thinner, and higher capacity lithium ion batteries necessitate ongoing research for novel materials with improved properties over that of stateof-the-art. Such an effort requires a concerted development of both electrodes and electrolyte to improve battery capacity, cycle life, and charge-discharge rates while maintaining the highest degree of safety available. Carbon nanotubes (CNTs) are a candidate material for use in lithium ion batteries due to their unique set of electrochemical and mechanical properties. The incorporation of CNTs as a conductive additive at a lower weight loading than conventional carbons, like carbon black and graphite, presents a more effective strategy to establish an electrical percolation network. In addition, CNTs have the capability to be assembled into free-standing electrodes (absent of any binder or current collector) as an active lithium ion storage material or as a physical support for ultra high capacity anode materials like silicon or germanium. The measured reversible lithium ion capacities for CNT-based anodes can exceed 1000 mAh g À1 depending on experimental factors, which is a 3Â improvement over conventional graphite anodes. The major advantage from utilizing free-standing CNT anodes is the removal of the copper current collectors which can translate into an increase in specific energy density by more than 50% for the overall battery design. However, a developmental effort needs to overcome current research challenges including the first cycle charge loss and paper crystallinity for free-standing CNT electrodes. Efforts to utilize pre-lithiation methods and modification of the single wall carbon nanotube bundling are expected to increase the energy density of future CNT batteries. Other progress may be achieved using open-ended structures and enriched chiral fractions of semiconducting or metallic chiralities that are potentially able to improve capacity and electrical transport in CNT-based lithium ion batteries. Lithium ion batteriesThe need to have better energy storage for technological applications like consumer electronics, hybrid-electric-vehicles, and remote sensing applications is propelling electrochemical devices to the forefront of research goals. 1,2 In particular, battery

A method of purity assessment for multi-walled carbon nanotubes (MWNTs) using Raman spectroscopy has been developed. Reference sample sets were constructed using MWNTs, synthesized by injection chemical vapor deposition (CVD), and carbon impurities (i.e. carbon soot and nanostructured carbon). Raman spectroscopy was performed and ratios of the characteristic peaks were measured (i.e. I D /I G , I G' /I G , and I G' /I D). Different vibrational modes in the various carbon species give rise to these peaks and result in characteristic Raman spectra for MWNTs and carbon impurities. Calibration curves were constructed from the reference sample sets. These calibration curves were used to evaluate MWNTs synthesized under varying experimental conditions (i.e. temperature of 650-950 o C, gas flow rate of 0.5-1.75 L/min, precursor injection rate of 1.5-4 .5 mL/hr, and precursor concentration of 0.04-0.1 M) to determine their 'purity'. The limits associated with this method are discussed in relation to other qualitative and potentially quantitative methods of determining MWNT purity.

Germanium nanoparticles (Ge-NPs) were synthesized through a one-step chemical vapor deposition process and were included in a hybrid free-standing single-wall carbon nanotube (SWCNT) electrode. The Ge-NPs were characterized through scanning electron microscopy and Raman spectroscopy to confirm the presence of crystalline nanoparticles with average diameters of 60 nm. Electrochemical testing of the Ge-NPs shows high reversible lithium ion capacity up to 900 mAh g–1 and a Coulombic efficiency of 96% on the first cycle, with capacities realizing 1000 mAh g–1 and a Coulombic efficiency of 98% on the second cycle. The use of SWCNTs to provide a stable nanoscale electrical network to support Ge-NPs resulted in a hybrid three-dimensional free-standing electrode, which is an attractive alternative to the conventional composite-current collector approach. The Ge-NP:SWCNT hybrid electrode with thin film titanium contacts produced electrode capacities of 983 mAh g–1 versus Li/Li+ up to 3 V. The higher anode capacity for the hybrid is maintained at modest cycling rates up to 1C. The pairing of the hybrid electrode with a commerical LiFePO4 cathode showed excellent performance with anode capacities of 800 mAh g–1 over a 1 V discharge range. Even at higher discharge rates, up to 1C, the anode energy density changes by only 8.5%. Thus, this demonstrates the first full battery comprising a free-standing Ge-based anode with a high power cathode exhibiting improved energy and power density.

Carbon nanotubes are being considered for adoption in lithium ion batteries as both a current collector support for high-capacity active materials (replacing traditional metal foils) and as free-standing electrodes where they simultaneously store lithium ions. The necessity to establish good electrical contact to these novel electrode designs is critical for success. In this work, application of nickel and titanium as both separable and thin film electrical contacts to free-standing single-wall carbon nanotube (SWCNT) electrodes is shown to dramatically enhance both the reversible lithium ion capacity and rate capability in comparison with stainless steel. Scanning electron microscopy showed that evaporation of Ni and Ti can effectively coat the SWCNT bundles in a bulk electrode which is capable of providing an improved electrical contact. A thin film of titanium emerged as the preferred electrical contact promoting the highest capacity ever measured for a SWCNT free-standing electrode of 1250 mAh/g. In addition, the titanium contacting approach demonstrated a 5-fold improvement in lithium ion capacity at extraction rates greater than 1C for a high-energy density Ge-SWCNT electrode. The overall performance improvement with Ti contacts is attributed to a lower contact resistance, nanoscale "wetting" of SWCNT bundles to improve contact uniformity, and effective electron coupling between Ti and SWCNTs due to work function-energy level alignment. The experimental results provide the basis for a Ragone analysis (power vs energy parameters), whereby Ge-SWCNT-Ti anodes paired with a LiFePO(4) cathode can lead to a 60% improvement over conventional graphite anodes in both power and energy density for a complete battery.