Nanobatteries

Nanobatteries are fabricated batteries employing technology at the nanoscale, a scale of minuscule particles that measure less than 100 nanometers or 100x10⁻⁹ meters. In comparison, traditional Li-Ion 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 failings of present battery technology, such as recharging time and battery 'memory'.

Several companies are researching and developing these technologies. In March 2005, Toshiba announced^[1] that they had a new Lithium-Ion battery with a nanostructured lattice at the cathode and anode that allowed the battery to recharge a surprising eighty times faster than previously. Prototype models were able to charge to eighty percent capacity in one minute, and were one hundred percent recharged after 10 minutes.

When a traditional lithium-ion battery is charged too quickly, it creates a bottleneck in which the lithium moving through electrolyte liquid from the negative electrode to the positive backs up on the surface of the liquid. Under slower charging conditions, the lithium "hides" in void space and does not cause a problem.

"Liquid electrolyte is unstable in the presence of metallic lithium and will cause all sorts of problems. That is why it is imperative to observe the slow-charging rate rule with lithium-ion batteries," Donald Sadoway, MIT professor of materials chemistry and an electrochemistry researcher, explained to TechNewsWorld. Sadoway said the consequences could be as severe as the battery exploding.

Background

Nanobatteries are generally described by three sections

• Anode
• Cathode
• Electrolyte

In Li-ion batteries the anode is almost always graphite, so most research is being done on the cathode and electrolyte materials. By reducing the size of the materials used in a nanobattery, higher conductivity can be reached, leading to an increase in power, in both charge and discharge.

Advantages

Using nanotechnology in the manufacture of batteries offers the following benefits:^[2]

• 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. This increases the surface area of the electrode thereby allowing more current to flow between the electrode and the chemicals inside the battery. This technique could increase the efficiency of hybrid vehicles by significantly reducing the weight of the batteries needed to provide adequate power.
• Increasing the shelf life of a battery by using nanomaterials to separate liquids in the battery from the solid electrodes when there is no draw on the battery. This separation prevents the low level discharge that occurs in a conventional battery, which increases the shelf life of the battery dramatically.
• Reducing the possibility of batteries catching fire by providing less flammable electrode material.

Unique Fabrication

A gel is created by the chosen design and is used to impregnate the anodic pores. This impregnated gel is placed between membrane walls and on top of the electrolyte. The anodic film is placed below the electrolyte, with the width of the cathode being much smaller than the height of the cathode. The separation of the cathodes by the membrane walls creates in essence a series of nanobatteries. This is helpful in research because it allows each set of cathode to be tested separately, or all at once.

Academic Research

In 2007, the first cross-sectional observation of an all solid state Li-ion nanobattery was taken by TEM. By looking at a nanobattery in TEM, the deterioration on the battery interface due to cycling is able to be observed with an attempt to not only understand by finding the underlying causes behind battery deterioration. The next step in the process is to cycle the battery while in TEM so that the live deterioration can be observed. Three layers of the battery were looked at in TEM, with two nanobatteries observed. The first nanobattery was pristine and uncycled, while the second nanobattery was run through ten cycles so that the deterioration might be characterized. A large irreversible capacity between the first charge and discharge was seen in the cycled nanobattery. The capacity of the battery was also seen to disappear rapidly during cycling.

Printable batteries

Researchers at the University of California, Los Angeles have successfully developed a "nanotube ink" for manufacturing flexible batteries using printed electronics techniques. Using nanotube ink, the carbon cathode and manganese oxide electrolyte components of a zinc-carbon battery can be printed as different layers on a surface, over which an anode layer of zinc foil can be printed. The resultant battery is less than a millimeter thick. Although discharge currents of the batteries are at present below the level of practical use, the nanotubes in the ink allow the charge to conduct more efficiently than in a conventional battery, such that the nanotube technology could lead to improvements in battery performance.^[3]

Various companies, listed below, are working at making nanobatteries into a viable commercial technology.

Toshiba

By using nanomaterial, Toshiba has increased the surface area of the lithium and widened the bottleneck, allowing the particles to pass through the liquid and recharge the battery more quickly. Toshiba states that it tested a new battery by discharging and fully recharging one thousand times at 77 degrees and found that it lost only one percent of its capacity, an indication of a long battery life.

Toshiba's battery is 3.8 mm thick, 62 mm high and 35 mm deep.

A123Systems

A123Systems has also developed a commercial nano Li-Ion battery. A123 Systems claims their battery has the widest temperature range at -30C to 70C. Much like Toshiba's nanobattery, A123 Li-Ion batteries charge to "high capacity" in five minutes. Safety is a key feature touted by the A123 technology, with a video on their website of a nail drive test, in which a nail is driven through a traditional Li-Ion battery and an A123 Li-Ion battery, where the traditional battery flames up and bubbles at one end, the A123 battery simply emits a wisp of smoke at the penetration site. Thermal conductivity is another selling point for the A123 battery, with the claim that the A123 battery offers 4 times higher thermal conductivity than conventional Lithium-Ion cylindrical cells. The nanotechnology they employ is a patented nanophosphate technology.

Valence

Also in the market is Valence Technology, Inc. The technology they are marketing is Saphion Li-Ion Technology. Like A123, they are using a nanophosphate technology, and different active materials than traditional Li-Ion batteries.

Altair

AltairNano has also developed a nanobattery with a one-minute recharge. The advance that Altair claims to have made is in the optimization of nano-structured lithium titanate spinel oxide (LTO).

U.S. Photonics

U.S. Photonics is in the process of developing a nanobattery utilizing "environmentally friendly" nanomaterials for both the anode and cathode as well as arrays of individual nano-sized cell containers for the solid polymer electrolite. U.S. Photonics has recently received a National Science Foundation SBIR phase I grant for development of nanobattery technology.

Next Alternative Inc.

Next Alternative has a new Carbon Nanotube (CNT) battery that is a modification of existing car battery types that will allow for the battery to recharge in less than 10 minutes and has a Reserve Capacity of at least 8 times the original unmodified battery. The major difference comes from a typical lead acid battery providing 12-15 kW-hours of electricity or a range of 50–100 miles, where the CNT lead/lead-acid battery will deliver 380 miles distance between charges. This battery could also be recharged in under 10 minutes. The typical lead-acid battery has a recharge time between 4 and 10 hours. The recharge life of the battery (200 cycles for lead-acid) can be extended by at a minimum of 4 times with the new CNT lead/lead-acid battery.

Sony

Produced the first cobalt-based lithium-ion battery in 1991. Since the inception of this first Li-ion battery, the research of nanobatteries has been underway with Sony continuing their strides into the nanobattery field.

See also

• Supercapacitor

References

1. ^ http://www.toshiba.co.jp/about/press/2005_03/pr2901.htm
2. ^ How can nanotechnology improve batteries?
3. ^ Nanotube tangles power printable batteries

External links

• http://www.accelerating.org/articles/phevfuture.html
• http://accelerating.org/newsletter/2005/31may05.html
• http://www.technewsworld.com/story/hardware/41889.html
• http://www.a123systems.com
• http://www.valence.com/
• http://www.altairnano.com/markets_amps.html
• Overview of Nanobatteries at UnderstandingNano Website