Rechargeable Batteries and Accumulators
Rechargeable batteries or accumulators are the oldest form of electricity storage and are widely used. Batteries store electric energy in a chemical form. Progress in battery technology is slow and the transfer of laboratory results into commercial applications is sometimes risky. Lithium ion and nickel-metal-hydride (NiMH) batteries are the only new battery technologies that have achieved significant market penetration in the last decade.
The Market For Batteries- Especially Rechargeable Ones
The market for batteries – especially rechargeable batteries – is booming. The turnover in Europe was almost €3bn in 1999, and a value of more than €4.6bn is expected for 2006 (VDI). This includes mobile applications such as mobile phones, walkmans, but also home or even village power supply in remote areas and in back up systems in case the grid goes down. In the future, the requirement for rechargeable batteries will be even more important in combination with renewable electricity production such as solar photovoltaics.
Rechargeable Batteries and Their Properties
Rechargeable batteries should be small, light, safe and eco friendly. They should deliver high voltages for more than 1000 discharge-recharge-cycles. For years, advances in rechargeable battery technology proceeded slowly from lead acid to NiCd materials. Over the past decade, however, three battery materials have significantly advanced the field: NiMH, Li-ion and Li-polymer. Nevertheless, the performance characteristics of battery materials are still insufficient for the power demands placed upon them by applications such as 3G communications. Battery materials will be the key for advances in power delivery and nanotechnology has already been identified as an enabler in this field.
Batteries High Energy Density and Design Flexibility
Because of the high energy density and design flexibility Lithium-based batteries currently outperform other systems and account for 63% of worldwide sales in portable batteries. Lithium is the most electropositive as well as the lightest metal (Tarascon 2001). Since metallic Lithium could not be used because of technical problems with shortcuts, Lithium is incorporated in Graphite.
Two Types of Rechargeable Batteries
There are basically two types of rechargeable batteries where nanostructured materials are applied and the focus of research. The first and most advanced is Lithium based, for example Li-ion batteries. The other type is based on metal hydrides, where hydrogen is the chemical energy carrier, or carbon nanotubes.
Nanocrystalline Materials and Nanotubes
Nanocrystalline materials and nanotubes have been demonstrated to greatly improve both power density, lifetime and charge/discharge rates. Nanotubes are used to replace the normal Graphite of Lithium-Graphite-Electrodes. Because of the nanostructure and the corresponding high surface area, nanotubes can incorporate more Lithium than Graphite. With open single-walled Nanotubes capacities up to 640Ah/kg have been reached in the laboratory.
Prototype Batteries Using Nanoparticles
Prototype batteries using nanoparticles have also been developed that offer 10x the charge and discharge rate (with 100x having been suggested as possible at times) of conventional rechargeable batteries. Some improvement in battery capacity per volume (energy density) has also been offered from nanostructured materials, but not a great deal.