Electric vehicles have the potential to drastically increase the energy efficiency of the transport industry. They are much more efficient at converting stored energy into motion than the more commonly used internal combustion engines.
A broad switch from internal combustion to electric vehicles could vastly reduce the environmental impact due to pollution from vehicles, and also reduce our dependency on oil - although currently the majority of our energy is produced from fossil fuels anyway, switching to electric power for transport would give the industry a much greater degree of flexilibity to cope with a variety of power sources.
Presently, the batteries used in electric vehicles are based on nickel metal hydride or lithium ion technology. Modern examples almost exclusively use lithium ion batteries, which offer several advantages over nickel metal hydride. However, presently no battery technology is really good enough to make electric vehicles a viable like-for-like replacement for internal combustion. The range and recharging time of electric cars limits their use to short journeys where recharging points are always nearby - perfect for city centre commutes, but not so useful for family holidays.
Nanotechnology could hold the key to making electric vehicles more widely usable by increasing battery performance. Improved electrolytes using nanoparticles and nanocomposite materials have been shown to considerably enhance specific attributes of lithium batteries, as well as other, more novel battery technologies.
Electric cars like the Tesla Model S rely on heavy, inefficient batteries to power them. Advanced engineering can overcome this barrier to some extent, but battery technology is still hampering widespread adoption of electric vehicles. Image Credits: Tesla Motors Press Centre
Current State of Electric Vehicle Technology
The main disadvantage for electric vehicles is the battery. For electric cars to gain a larger market share, it will be essential for manufacturers to bring down the cost of their battery packs, whilst enhancing the capacity and lifetime of batteries, and therefore the range and performance of the vehicles.
Many companies are betting on nanotechnology to bring about this change. The performance of the rest of the vehicle can also be improved by nano-enabled components and systems. Polymer nanocomposites, nanostructured metals and nano-enhanced sensors and power electronics can contribute to a number of vital measures to get the most out of the battery performance, such as weight reduction, energy efficiency, improved control and communications.
Nanotechnology in Batteries
Nanotechnology can play a significant role in the achievement of specific performance objectives in batteries. Conventionally, graphite powder has been used as an intercalation material on the negative electrode for lithium ion batteries. The rate of removal or insertion of lithium and the battery capacity can be improved by replacing micrometer-sized powder with carbon nanomaterials such as carbon nanotubes. Since carbon nanotubes have a high surface area, they can bind much higher concentrations of lithium. Nanowires made of titanium dioxide (TiO2), vanadium oxide (V2O5) or tin oxide (SnO) are also promising as negative electrode materials.
Commercial development of many of these materials is still in the early stages - one of the challenges in making fundamental technology changes to a giant industry like the automotive industry is that any new technology has to be ready to adapt to the huge scales of manufacturing involved. Presently available commercial oxide materials are promising candidates for electrode materials, but most of them are expensive or have safety limitations. Li(NiCoAl)O2, Li (NiMnCo)O2, LiMn2O4, Li(AlMn)2O4 or LiCo2O4 are good examples of such compounds. The nanostructuring of these materials has been shown to significantly improve their intercalation capacity.
Using nanostructured materials to improve the current density of electrodes for a number of reasons - it reduces the diffusion path for the lithium ions, increasing their mobility, and also tends to increase electrical conductivity, making the electrochemical reaction occur much more efficiently. A variety of nanostructured materials such as nanotubes, nanowire, nanopillars, nanoparticles and mesopores have been examined as candidate materials for both positive and negative electrodes. By varying the properties of the electrodes, like morphology, and surface area, researchers are aiming to find optimum compositions to squeeze as much performance as possible out of batteries which are as affordable and as light and compact as possible.
Nano-Enhanced Batteries for Electric Vehicles
The EPA’s Design for the Environment Program in the Office of Pollution Prevention and Toxics, along with National Risk Management Research Laboratory in EPA’s Office of Research and Development, performed some research comprising a screening-level lifecycle assessment (LCA) of current lithium-ion (Li-ion) battery technologies for electric vehicles, and a next-generation battery component (anode) using single-walled carbon nanotube (SWCNT) technology.
Primary data from both recyclers and battery manufacturers was used to conduct a quantitative environmental LCA as well as data related to the nano-enhanced anode being studied.
This type of study is essential to ensure that the vehicle battery industry develops in an eco-friendly and effective manner. The results obtained will mitigate present and future impacts and risks by enabling battery suppliers and manufacturers to determine which processes and materials pose an impact or potential risk to health or environment throughout the product lifecycle. The study shows how the life-cycle impacts of an evolving technology and using nanomaterials such as the SWCNT anode can be evaluated before the technology is mature, providing a benchmark for future life-cycle assessments of this technology.
Another research team at the Ulsan National Institute of Science and Technology’s Interdisciplinary School of Green Energy focused on cutting down electric car charging time from hours to minutes. This innovative technology is aimed at improving the recharging time atleast 30 times and speed 120 times compared to currently available lithium ion batteries.
Their innovative battery technology makes use of lithium manganese oxide soaked in a graphite-containing solution as a cathode material. Highly dense carbonized secondary particles are obtained from sucrose-coated nanoparticle clusters. When heat treated to 600°C, the internal sucrose graphitization helps form conductive particles inside the network, allowing all particles in the electrode to participate simultaneously in the reaction, speeding up charging and discharging. According to Professor Cho, the research group leader, a battery suitable for an electric vehicle was charged in just one minute using this technology.
Future research will be focused on bringing down cost of nanomaterials for batteries, and making sure they stand up to the requirements of large-scale commercial applications. Research on using nanotechnology for the enhancement of electric vehicle batteries is ongoing - although there are many highly promising materials available, it is not yet clear if any will be able to stand up to the commercial rigours of the automotive industry, and any substantial shift away from fossil fuel in transport is still a long way off.
Sources and Further Reading