There are varied opportunities for carbon nanotubes in the automotive sector, but some pitfalls must be overcome to release their undoubted potential.
According to Future Markets, the CNT market is projected to grow to $2.3 billion by 2020. “Many traditional materials used in automobiles, inside and out, can be enhanced using carbon nanotubes,” says Dave Arthur, Chief Executive of SouthWest NanoTechnologies (SWeNT). The company manufactures three types – single-wall, multi-wall and an intermediate type, which it classifies as few-wall.
There are three automotive market sectors that are currently the focus of SWeNT’s commercialization efforts:
- Energy storage applications – batteries and supercapacitors
- Printable, thermoformable, capacitive touch sensors for replacing membrane switches in automotive interiors (as well as in white goods and medical equipment and devices).
- Polymer composites with enhanced electrical conductivity, thermal conductivity and mechanical properties.
SWeNT’s patented technology is scalable, using a low-cost manufacturing method based on fluidized-bed catalytic chemical vapor deposition (CCVD), widely recognized as the most scalable means for commercial production of CNTs. As such, the manufacturing can be set up anywhere, and the company has established a volume manufacturing facility in Azerbaijan. The CoMoCAT catalyst is the “secret sauce” of the growth process – it contains cobalt (Co) and molybdenum (Mo), the origin of the CoMoCAT brand name, but the compositions are kept under wraps. “By carefully tuning the catalyst, we can generate single-wall, few-wall, and multi-wall CNTs, with precise control over wall number, diameter, metal/semiconductor ratio, and chiral composition. In turn, this provides careful control of electronic, optical, and structural properties,” says Arthur.
Energy Storage – Conservative Cathodes, Advanced Anodes
Arthur hopes that CNTs may significantly impact the development of lithium-ion batteries for electric and hybrid vehicles. Replacing carbon black cathodes with CNTs would provide an increase in energy density by preventing electrode degradation, and also offer lower impedance, higher discharge capacity and improved charging cycling. The improvement in low temperature performance is also important in the automotive sector.
Arthur is frustrated by the lack of willingness of manufacturers to embrace the potential of nanotubes; instead, the company is having to opt for incremental development projects using small loadings of nanotubes in existing compositions. Sprinkling a small amount of CNT makes it possible to get 20% of the potential benefit but with no process changes.
Anodes however, are a different story. Battery makers are already interested in using silicon anodes, because they have much higher capacity than carbon anodes. But the big volumetric contraction and expansion during charging and discharging cycles limits life. Using nanotubes with silicon changes this dramatically, with dramatic improvements in the cycle life.
Supercapacitors are another exciting area. These meet the high power-density demands of electric vehicles, supplied by combustion engines on traditional vehicles. As with Li-ion batteries, the key materials requirements are high conductivity, high purity, and high surface area.
The traditional material used is activated carbon which has a high specific surface area, providing high capacitance per gram. To match activated carbon, the cheaper multi-wall nanotubes (as used in the batteries) would need a fourfold improvement. Single wall CNTs can beat activated carbon, but at a financial cost – it would also be hard to meet a demand which would rapidly escalate to many tons.
Few walled carbon nanotubes (FWCNTs) are positioned in-between and these can form electrodes that work as well as single wall. FWCNTs fall within the acceptable range of power density and can run at higher voltage than activated carbon, leading to better performance than activated carbon but at a price premium. However, the price penalty is not thought to be a major barrier because very little is used on each device.
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