Silicon–air batteries are a new

battery Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...

technology invented by a team led by Prof. Ein-Eli at the

Grand Technion Energy Program The Nancy and Stephen Grand Technion Energy Program (GTEP) or Grand Technion Energy Program was established in 2007 at Technion - Israel Institute of Technology, which is Israel, Israel's first university, founded in 1912. Overview GTEP's state ...

at the

Technion – Israel Institute of Technology The Technion – Israel Institute of Technology ( he, הטכניון – מכון טכנולוגי לישראל) is a public research university located in Haifa, Israel. Established in 1912 under the dominion of the Ottoman Empire, the Technion ...

. Silicon–air battery technology is based on electrodes of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

and

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ta ...

. Such batteries can be lightweight, with a high tolerance for both extremely dry conditions and high humidity. Like other anode-air batteries, in particular metal-air batteries, silicon–air batteries rely on atmospheric

for their

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in wh ...

s; they accordingly do not include any cathode materials in their structures, and this permits economies in cost and weight. Experimental cells using a room-temperature

ionic liquid An ionic liquid (IL) is a salt in the liquid state. In some contexts, the term has been restricted to salts whose melting point is below a specific temperature, such as . While ordinary liquids such as water and gasoline are predominantly made of ...

electrolytes have produced between 1 and 1.2 volts at a current density of 0.3 milliamperes per square centimeter of silicon.

History

The only research report available to the public was done by its creator, Yair-Ein-Eli. Eli began research in Technion – Israel Institute of Technology with David Starosvetsky, graduate student Gil Cohen of Technion, Digby Macdonald of Pennsylvania State University, and Rika Hagiwara of Kyoto University. Eli's reasoning for using silicon as a fuel cell is because of its high

specific energy Specific energy or massic energy is energy per unit mass. It is also sometimes called gravimetric energy density, which is not to be confused with energy density, which is defined as energy per unit volume. It is used to quantify, for example, sto ...

, its large

availability In reliability engineering, the term availability has the following meanings: * The degree to which a system, subsystem or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at ...

as a

resource Resource refers to all the materials available in our environment which are technologically accessible, economically feasible and culturally sustainable and help us to satisfy our needs and wants. Resources can broadly be classified upon their ...

(silicon being the eighth most plentiful in the

universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. ...

, the second most plentiful in Earth's crust), tolerance of places with high humidity, and non-toxic properties. In their experiments, they tested for different potential energies and

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...

s, using different liquid oxygen solutions. The experimental results and theories on the battery were published online in 2009 in the journal ''Electrochemistry Communications''. This got the attention of organizations such as

DARPA The Defense Advanced Research Projects Agency (DARPA) is a research and development agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Originally known as the Ad ...

and

the Pentagon The Pentagon is the headquarters building of the United States Department of Defense. It was constructed on an accelerated schedule during World War II. As a symbol of the U.S. military, the phrase ''The Pentagon'' is often used as a meton ...

, where they are currently working on military usage of this battery. The battery is still under research by these organizations and not available for commercial use.

Design

The battery's energy source is made using an

known as 1-ethyl-3-methylimidazolium oligofluorohydrogenate (EMI·2.3HF·F), classified in the article as a

room temperature ionic liquid An ionic liquid (IL) is a salt in the liquid state. In some contexts, the term has been restricted to salts whose melting point is below a specific temperature, such as . While ordinary liquids such as water and gasoline are predominantly made of ...

(RTIL), and

wafers A wafer is a crisp, often sweet, very thin, flat, light and dry biscuit, often used to decorate ice cream, and also used as a garnish on some sweet dishes. Wafers can also be made into cookies with cream flavoring sandwiched between them. They ...

containing high amounts of silicon. The wafers act as an

anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic ...

(oxidation of the fuel source) and the RTIL acts as an electrolyte which turns the wafers into usable energy. In its idle state, the RTIL dissolves the wafers at a slow rate because there is no

semi-conductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

to speed up the reaction. When put into use, the RTIL will then react faster to dissolve the silicon wafers, which will produce energy for use in any electronics. The battery lacks a built-in cathode that most batteries use to balance the anode's charge. Instead, the membrane of the battery allows oxygen from the atmosphere to flow through it and acts as the cathode.

SPECTRE

The ''Stressed Pillar-Engineered CMOS Technology Readied for Evanescence'' (SPECTRE) is under research by

and

SRI Shri (; , ) is a Sanskrit term denoting resplendence, wealth and prosperity, primarily used as an honorific. The word is widely used in South and Southeast Asian languages such as Marathi, Malay (including Indonesian and Malaysian), Javanes ...

. It is based on a silicon-air batteries with an added feature: in equipment where the enemy is to be denied the ability to profit from captured devices or from information to be gained from such devices, a SPECTRE battery can respond to a ''kill'' signal by self-destructing along with the device it powers. This is of potential interest in military applications.

Storage capacity

The storage capacity of the battery is very comparable to that of aluminum-air battery. The

of the silicon-air battery is estimated to be 8470 Wh/kg and the energy density is about 2109.0 Wh/L. The battery voltage is 1 – 1.2 V. By the use of a dedicated electrolyte flow system, discharge times of more than 1000 hours can be achieved for aqueous electrolytes, which allows for 100% usage of the silicon anode.

Applications

One particularly promising field of application for silicon–air batteries is powering small-scale medical devices such as

diabetic Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...

pumps and

hearing aid A hearing aid is a device designed to improve hearing by making sound audible to a person with hearing loss. Hearing aids are classified as medical devices in most countries, and regulated by the respective regulations. Small audio amplifiers s ...

s, in which tedious charging would be a disadvantage. The nature of the silicon-air battery also renders it particularly suitable for humid climates such as in

tropical regions The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

of Asia, America or Africa. Research is under way to develop silicon-air batteries for everyday applications. Examples include power for consumer electronics such as laptops and phones. Efforts to develop deployable and scalable systems based on the silicon-air technology are underway.

References