Silicon–air batteries are a new battery technology invented by a team led by Prof. Ein-Eli at the Grand Technion Energy Program at the

Technion – Israel Institute of Technology The Technion – Israel Institute of Technology is a public university, public research university located in Haifa, Israel. Established in 1912 by Jews under the dominion of the Ottoman Empire, the Technion is the oldest university in the coun ...

. Silicon–air battery technology is based on electrodes of

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

and

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

. 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 such as a lead-acid battery. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. Conventional curren ...

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 (chemistry), salt in the liquid state at ambient conditions. 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 wate ...

electrolyte An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble Salt (chemistry), salts, acids, and Base (chemistry), bases, dissolved in a polar solven ...

s 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 The Pennsylvania State University (Penn State or PSU) is a Public university, public Commonwealth System of Higher Education, state-related Land-grant university, land-grant research university with campuses and facilities throughout Pennsyl ...

, and Rika Hagiwara of

Kyoto University , or , is a National university, national research university in Kyoto, Japan. Founded in 1897, it is one of the former Imperial Universities and the second oldest university in Japan. The university has ten undergraduate faculties, eighteen gra ...

. Eli's reasoning for using silicon as a

fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...

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, st ...

, 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 Technology, technologically accessible, Economics, economically feasible and Culture, culturally Sustainability, sustainable and help us to satisfy our needs and want ...

(silicon being the eighth most plentiful in the

universe The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...

, the second most plentiful in

Earth's crust Earth's crust is its thick outer shell of rock, referring to less than one percent of the planet's radius and volume. It is the top component of the lithosphere, a solidified division of Earth's layers that includes the crust and the upper ...

), 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 (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...

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 Adva ...

and

the Pentagon The Pentagon is the headquarters building of the United States Department of Defense, in Arlington County, Virginia, across the Potomac River from Washington, D.C. The building was constructed on an accelerated schedule during World War II. As ...

, 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 (RTIL), and wafers containing high amounts of silicon. The wafers act as an

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

(oxidation of the fuel source) and the RTIL acts as an

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 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. 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 In physics, energy density is the quotient between the amount of energy stored in a given system or contained in a given region of space and the volume of the system or region considered. Often only the ''useful'' or extractable energy is measure ...

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 mellitus, commonly known as diabetes, is a group of common endocrine diseases characterized by sustained high blood sugar levels. Diabetes is due to either the pancreas not producing enough of the hormone insulin, or the cells of th ...

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, 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 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