A look at how nanotechnology is driving innovation in battery technology.
Requirements for future battery technologies are higher storage capacities (gravimetric and volumetric energy densities); longer cycle life; improved safety; and reduced costs (key to widespread adoption). The market is driven, as are other future energy technologies, by the need to reduce greenhouse gas emissions and dependence on foreign oil and fossil fuels. Battery power is also a crucial element for enabling today’s mobile device applications and large scale energy harvesting.
In no small part due to the impact of nanomaterials, lithium ion battery technology has progressed greatly in the past few years and now provides impressive levels of power, energy, safety and life for deployment in large-scale systems. Lithium ion batteries have received considerable attention in applications ranging from portable electronics to automobiles, due to their superior energy density over other rechargeable battery technologies. Market demand for lighter, thinner and higher capacity lithium ion batteries necessitate ongoing research for new materials with improved properties over that of state-of-the-art.
Nanostructured materials are allowing companies to develop the next generation of battery devices with high power density, high energy density and high safety for application in sectors such as hybrid electric vehicles (HEV), plug in hybrid electric vehicles (PHEV) and pure electric vehicles (PEV). Automotive companies such as Chrysler utilize nanomaterials in their electric vehicles to improve battery capacity, cycle life, and charge-discharge rates with a high degree of safety. Other large multinational companies developing nanomaterial based battery products include GE, Panasonic Sanyo, Matsushita Industrial Co., Ltd., NEC, Toshiba, LG Chem, Samsung and Sony for application in areas such as cell phones and PCs, medical devices, military applications and cordless power tools. Innovative product developers and materials producers include A123 Systems, mPhase Technologies and Altair Nanotechnologies.
Advantages of nanomaterials include:
• Nano-size shortens lithium-ion diffusion length.
• Nano-size combined with conductive coatings improves electronic transport.
• Decreased mechanical stresses due to volume change lead to increased cyclability and lifetime.
• Nano-size enhances the electrode capability of Li storage.
• Ordered mesoporous structure favours both Li storage and fast electrode kinetics. The resulting higher surface area, smaller nanocrystal size, and better diffusion pathway leads to enhancement of the electrode capacity, power performance and cycle life.
• Nanostructure enhances cycle stability.
Nanomaterials utilized in lithium-ion batteries include:
• Carbon nanotubes: Nanotubes have the intrinsic characteristics desired in material used as electrodes in batteries and capacitors-high surface area and good electrical conductivity.
• Fullerenes: Anode materials based on modified fullerene materials have been developed for lithium-ion rechargeable batteries as thin films and electrodes.
• Graphene: Graphene sheets coated with a thin layer of ion-storage material allow electrons and lithium ions to combine much more quickly in the electrode, which allows for fast battery recharge times.
• Metal oxide nanomaterials: Recent advances in nanostructured tin (Sn), silicon (Si), nickel (Ni), cobalt (Co), and intermetallic alloys (Cu6Sn5, InSb, Cu2Sb) as replacements for carbon-based anodes have resulted in batteries with higher specific capacity and enhanced cycle life.
• Nanosilver: ZPower claims that silver-zinc batteries deliver 40% more energy than lithium-ion and 2-3 times the energy of nickel metal-hydride
• Nanofibers: Nanofiber-based polymeric battery separators boost the performance and safety of lithium ion batteries. Nanofiber battery separators can increase power by 15 to 30%, increase battery life by up to 20% and improve battery safety by providing stability at high temperatures.
• Nanoporous materials: Nanoporous materials have a much higher surface area than non-porous materials and are used to coat electrodes in batteries and the increase in surface area leads to key benefits. Nanoporous materials typically improve the charge and discharge rates (power density) of electrodes and low temperature performance.
The market suffered a blow recently when it was announced that the leading nanomaterials enabled Li-Ion battery supplier, A123 Systems, will need to replace batteries by clients such as electric sports car maker Fisher Karma. The cost of this recall to A123 Systems has been estimated at $55 million. However, this problem was a result of manufacturing problems not relevant to the technology itself; a result of wrongly calibrated machinery that resulted in a misalignment of battery components. Of greater concern is that the overall EV market has not grown as anticipated with a number of manufacturers reporting significant losses in this segment.
