A nanowire battery is a form of chemical storage battery based on the lithium-ion battery model, first developed in 2007 at Stanford University in the US. It is still undergoing refinement as of 2011, with sales to the public scheduled for 2012. The technology utilizes an array of many connected silicon nanowires at a billionth-of-a-meter scale, situated at the negative voltage end of the battery. This advancement in materials science has increased storage density from 8 to 10 times over that of conventional lithium-ion batteries, which would make something like a rechargeable camera, cell phone, or laptop battery last 8 to 10 times longer before it was depleted and had to be plugged in. The nanowire battery is also seen as a key development for electric cars, as it has much faster charge rates both because of the increased surface area of the nanowires themselves and due to the use of silicon in its chemical structure.
The principles behind the nanowire battery have facilitated similar research at Sandia National Laboratories in the US as of 2010, where a silicon nanowire anode formed by just one nanowire is used. This nanowire is 100 nanometers wide, or about the width of an average human red blood cell, and about 10,000 nanometers long, or 0.01 millimeters. The purpose of this battery, which is made with a transmission electron microscope (TEM), is to further research the capabilities of the technology. There are also plans for it to serve as an extremely small power source for medical implants as well as power other microelectronics devices.
The development of the nanowire battery is seen as revolutionary, though it has some limited drawbacks. Since the surface area of the combined nanowires is much greater than the area that a graphite anode in a typical battery has, after a period of several recharging phases, the nanowires begin to acquire a solid electrolyte interphase (SEI). This is a type of chemical coating that restricts the current carrying capacity of the silicon nanowire anode. Such a limitation could result in a rapid drop off in power for the nanowire battery as it ages, though research has shown that they can be practically recharged to 80% of full levels at least 250 times, and the goal is to reach a recharge level of 3,000 times in commercial sector products.
Research into silicon-based storage batteries has been going on for over thirty years. Practical problems with the silicon swelling have limited the usefulness of the idea until nanowires were invented. The lead researcher on the project at Stanford University, Dr. Yi Cui, has been refining the nanowire battery since at least 2007. It is now seen as being capable of scaling up to practical mass production levels by the use of carbon-silicon nanowires, which don't require high temperatures to grow like pure silicon does.