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Rechargeable batteries or accumulators are the earliest forms of storing electricity and are extensively used. Electric energy is stored in batteries in a chemical form. Advancement in battery technology is slow and the transfer of laboratory results into commercial applications is at times uncertain.
Among the new battery technologies, only lithium-ion (Li-ion) and nickel-metal-hydride (NiMH) batteries have realized noteworthy market penetration in the last 10 years.
The Market for Batteries—Especially Rechargeable Ones
The market for batteries—particularly rechargeable batteries—is thriving. In Europe, the revenue was nearly €3 billion in 1999, and a value of over €4.6 billion is anticipated for 2006 (VDI). This includes mobile applications like mobile phones and Walkmans, as well as home or even village power supply in remote areas, and in backup systems in the event of grid failure.
Sooner or later, the necessity for rechargeable batteries will be even more important along with the production of renewable electricity using products like solar photovoltaics.
Rechargeable Batteries and their Properties
Rechargeable batteries should be small, safe, light, and environment-friendly. They should supply high voltages for over 1000 discharge-recharge-cycles. For years, developments in rechargeable battery technology advanced sluggishly from lead acid to NiCd materials. Over the last 10 years, however, three battery materials such as NiMH, Li-ion, and Li-polymer have considerably advanced the field.
However, the performance features of the battery materials are still inadequate for the power demands laid upon them by applications like 3G communications. Battery materials will be a significant factor for advances in power delivery, and nanotechnology has already been recognized as an enabler in this area.
Batteries’ High Energy Density and Design Flexibility
Due to the high energy density and design versatility, lithium-based batteries presently outpace other systems and make up for 63% of international sales in portable batteries. In addition, lithium is the most electropositive and lightest metal (Tarascon 2001). As metallic lithium could not be employed because of technical issues with shortcuts, lithium is combined with graphite.
Two Types of Rechargeable Batteries
There are mainly two types of rechargeable batteries where nanostructured materials are applied and are the focus of researchers. The first and most progressive type is lithium-based, for instance, Li-ion batteries. The other type is based on carbon nanotubes or metal hydrides, where hydrogen is the chemical energy carrier.
Nanocrystalline Materials and Nanotubes
Nanocrystalline materials and nanotubes have been shown to significantly enhance power density, charge/discharge rates, and lifetime. Nanotubes are used to substitute the standard graphite of lithium-graphite-electrodes.
Owing to the nanostructure and the corresponding high-surface area, nanotubes can include more lithium than graphite. With open single-walled nanotubes, it was possible to achieve capacities up to 640 Ah/kg in the lab.
Prototype Batteries Using Nanoparticles
Prototype batteries based on nanoparticles have also been created, that deliver 10x the charge and discharge rate (with 100x having been proposed as possible sometimes) of traditional rechargeable batteries. Some upgrade in battery capacity per volume (energy density) has also been provided using nanostructured materials, but not to a large extent.