Stanford researchers recently invented a new type of rechargeable batteries employing silicon nanowire technology which can hold ten times more power than our current batteries. With the ongoing boom in smartphone and tablet markets, nanowire batteries can easily turn out to be the next game changer in an ultra-mobile world.
Need for nanowire batteries
Most of our consumer electronics (including mobile phones and cameras) run on lithium ion batteries, which were first introduced by Sony Corporation in 1991. A standard lithium ion battery consists of a Lithium metal oxide as cathode and porous carbon as anode. When the cell charges and discharges, ions shuttle between the cathode (positive electrode) and the anode (negative electrode). While lithium ions have definitely served their purpose for the last two decades, the growing demand for higher capacity smartphones and computing devices, coupled with the face-paced urban lifestyle has a put a tremendous pressure on the consumer electronics industry in terms of battery time. Contemporary smartphones have been consistently plagued by low battery times (seldom more than 5-6 hours of talktime), and research has understandably now shifted to finding alternatives to the lithium ion technology.
On such research conducted at University of Maryland showed silicon to be a better material for anode and claimed it to hold nearly 10 times as much charge as compared to carbon. Although silicon has a greater energy density compared to carbon, it does have a major drawback. Silicon placed in a battery swells as it absorbs positively charged lithium atoms during charging, and then shrinks during use as the lithium is drawn out. This expansion-compression cycle causes the silicon to pulverize, thus degrading the performance of the battery. Recent research by Dr. Yi Cui at Stanford University seemingly overcomes the drawback by using nanotechnology in the form of silicon nanowires.
Nanowires are structures with a thickness of the order 9-10 nm. As with silicon, each strand of silicon nanowire increases in volume during the charge/discharge cycle but in this case does not affect the capacity. Experiments show that the volume of the silicon nanowires increases as much as 4 times during a cycle without fracture. A silicon nanowire battery will typically undergo 250 such cycles for the charge to drop to 80% of the maximum capacity.
Targeted application areas
This new battery will have a wide range of applications, the most evident being mobile phones, music players and
digital camera which currently use lithium ion batteries.
Another big potential is for electric cars, which form the impending future for the automobile industry. Electric cars fitted with nanowire batteries will go longer distances than ever before and we will soon see the technology spill over for larger and heavier electric trucks as well. This can very well be the next big thing for delivery companies which put hundreds of trucks on the road simultaneously. The team at Stanford University currently aims to establish 3000 cycles by 2012 making it viable for use in electrical vehicles.
Further, the battery can also be used for medical equipment in the future. Hospitals that have machines running on electricity will be able to perform surgeries when there is a power failure. With the silicon nanowire battery, machines will be able to last
for hours without having to be recharged.
Who owns what?
Dr. Yi Cui, Assistant Professor of Material Science and Engineering at Stanford University invented this revolutionary development and holds a number of key patents and patent applications in various geographies:
US7816031: Nanowire battery methods and arrangements
US20110020713A1: Nanowire battery methods and arrangements,
WO2009038897A2: Nanowire battery methods and arrangements
EP2191526A4: Nanowire battery methods and arrangements
US Patent 7,816,031, in particular, claims a battery with the carbon anode substrate covered with silicon nanowires to obtain the advantages of silicon’s higher charge storage capability as well as the flexibility provided with the
nanowires for expansion-shrinking cycle in the battery.
Additionally, Enable IPC, an Intellectual Property Commercialization firm, has a patent application, US20060216603, in the nanowire technology and is creating microbattery technologies consisting of improved cathodes substrate covered with silicon nanowires.
Amprius, a startup company founded by Dr Yi Cui in 2008, is trying to commercialize the silicon nanowire technology. Amprius is funded by Google CEO Eric Schmidt, venture capital firm Kleiner Perkins Caulfield & Byers, Vantage Point Venture Partners, Stanford University, Trident
Capital and Chinese funds IPV Capital and Qian Neng Fund.
Simultaneously, researchers from Pacific Northwest and Sandia National laboratories are experimenting in creating even more efficient batteries using nanowires of titanium oxide. Researchers in Rice university lead by Dr.Pulickel Ajayan have also created a robust 3 dimensional microbattery which would charge faster and have a greater capacity compared to the lithium ion battery. The 3D batteries employ vertical arrays of nickel-tin nanowires perfectly encased in PMMA, a widely used polymer best known as Plexiglas. The team has created forests of coated nanowires; millions of them on a single fingernail sized chip, effectively increasing system proximity and thus improving the overall efficiency of chemical reactions.
The nanowire technology has its fair share of problems as well. When the negative electrode is brought to below 0.8V, the electrolyte becomes
thermodynamically reduced, forming a layer on the nanowires known as “Solid Electrolyte interface” (SEI). SEI’s are found in traditional lithium ion batteries with the deposits of the negative electrodes reaching 10µ in diameter leading to irreversible capacity loss (ICL). Fortunately SEI forming reactions are self limiting and ICL reduces with each cycle. In case of nanowires, however, the surface area per unit volume is a couple of magnitudes larger than a 10µ particle, thereby resulting in an increased formation of SEI. Contemporary research on nanowires is seemingly getting focused on combating the drastic loss in capacity due to SEI.
The nanowire technology will revolutionize the way batteries are being developed today and in the near future we should be able to lay hands on computing devices which proudly proclaim significantly north of 20 hours of battery time.
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