Nanobatteries are fabricated batteries employing technology at the nanoscale, particles that measure less than 100 nanometers or 10−7 meters. These batteries may be nano in size or may use nanotechnology in a macro scale battery. Nanoscale batteries can be combined to function as a macrobattery such as within a nanopore battery.
Traditional lithium-ion battery technology uses active materials, such as cobalt-oxide or manganese oxide, with particles that range in size between 5 and 20 micrometers (5000 and 20000 nanometers – over 100 times nanoscale). It is hoped that nano-engineering will improve many of the shortcomings of present battery technology, such as volume expansion and power density.
Background
A battery converts chemical energy to electrical energy and is composed of three general parts:
Anode (positive electrode) Cathode (negative electrode) Electrolyte
The anode and cathode have two different chemical potentials, which depend on the reactions that occur at either terminus. The electrolyte can be a solid or liquid that is ionically conductive. The boundary between the electrode and electrolyte is called the solid-electrolyte interphase (SEI). Connecting a circuit across the electrodes causes the chemical energy stored in the battery to be converted to electrical energy.
Limitations of current battery technology
A battery's ability to store charge is dependent on its energy density and power density. It is important that charge can remain stored and that a maximum amount of charge can be stored within a battery. Cycling and volume expansion are also important considerations as well. While many other types of batteries exist, current battery technology is based on lithium-ion intercalation technology for its high power and energy densities, long cycle life and no memory effects. These characteristics have led lithium-ion batteries to be preferred over other battery types. To improve a battery technology, cycling ability and energy and power density must be maximized and volume expansion must be minimized.
During lithium intercalation, the volume of the electrode expands, causing mechanical strain. The mechanical strain compromises the structural integrity of the electrode, causing it to crack. Nanoparticles can decrease the amount of strain placed on a material when the battery undergoes cycling, as the volume expansion associated with nanoparticles is less than the volume expansion associated with microparticles. The little volume expansion associated with nanoparticles also improves the reversibility capability of the battery: the ability of the battery to undergo many cycles without losing charge.
In current lithium-ion battery technology, lithium diffusion rates are slow. Through nanotechnology, faster diffusion rates can be achieved. Nanoparticles require shorter distances for the transport of electrons, which leads to faster diffusion rates and a higher conductivity, which ultimately leads to a greater power density.
Advantages of nanotechnology
Using nanotechnology to manufacture of batteries offers the following benefits:
Increasing the available power from a battery and decreasing the time required to recharge a battery. These benefits are achieved by coating the surface of an electrode with nanoparticles, increasing the surface area of the electrode thereby allowing more current to flow between the electrode and the chemicals inside the battery. Nanomaterials can be used as a coating to separate the electrodes from any liquids in the battery, when the battery is not in use. In the current battery technology, the liquids and solids interact, causing a low level discharge. This decreases the shelf life of a battery.
Disadvantages of nanotechnology
Nanotechnology provides its own challenges in batteries:
Nanoparticles have low density and high surface area. The greater the surface area, the more likely reactions are to occur at the surface with the air. This serves to destabilize the materials in the battery. Owing to nanoparticle's low density, a higher interparticle resistance exists, decreasing the electrical conductivity of the material. Nanomaterials can be difficult to manufacture, increasing their cost. While nanomaterials may greatly improve the abilities of a battery, they may be cost-prohibitive to make.