Molten-salt batteries are a class of
battery that uses
molten salt
Molten salt is salt which is solid at standard temperature and pressure but liquified due to elevated temperature. A salt that is liquid even at standard temperature and pressure is usually called a room-temperature ionic liquid, and molten salts ...
s as an
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 ...
and offers both a high
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 ...
and a high
power density
Power density, defined as the amount of power (the time rate of energy transfer) per unit volume, is a critical parameter used across a spectrum of scientific and engineering disciplines. This metric, typically denoted in watts per cubic meter ...
. Traditional non-rechargeable thermal batteries can be stored in their solid state at room temperature for long periods of time before being activated by heating. Rechargeable liquid-metal batteries are used for industrial power backup, special
electric vehicle
An electric vehicle (EV) is a motor vehicle whose propulsion is powered fully or mostly by electricity. EVs encompass a wide range of transportation modes, including road vehicle, road and rail vehicles, electric boats and Submersible, submer ...
sand for
grid energy storage
Grid energy storage, also known as large-scale energy storage, are technologies connected to the electrical power grid that store energy for later use. These systems help balance supply and demand by storing excess electricity from variabl ...
, to balance out intermittent
renewable power sources such as
solar panels
A solar panel is a device that converts sunlight into electricity by using photovoltaic (PV) cells. PV cells are made of materials that produce excited electrons when exposed to light. These electrons flow through a circuit and produce direct ...
and
wind turbines
A wind turbine is a device that converts the kinetic energy of wind into electrical energy. , hundreds of thousands of large turbines, in installations known as wind farms, were generating over 650 gigawatts of power, with 60 GW added each y ...
.
In 2023, the use of molten salts as electrolytes for high-energy rechargeable lithium metal batteries was demonstrated.
History
Thermal batteries originated during
World War II
World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
when German scientist Georg Otto Erb developed the first practical cells using a salt mixture as an electrolyte. Erb developed batteries for military applications, including the
V-1 flying bomb
The V-1 flying bomb ( "Vengeance Weapon 1") was an early cruise missile. Its official Reich Aviation Ministry () name was Fieseler Fi 103 and its suggestive name was (hellhound). It was also known to the Allies as the buzz bomb or doodlebug a ...
and the
V-2 rocket, and artillery fuzing systems. None of these batteries entered field use during the war. Afterwards, Erb was interrogated by British intelligence. His work was reported in "The Theory and Practice of Thermal Cells". This information was subsequently passed on to the United States Ordnance Development Division of the
National Bureau of Standards
The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical sc ...
. When the technology reached the
United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
in 1946, it was immediately applied to replacing the troublesome liquid-based systems that had previously been used to power artillery
proximity fuzes. They were used for
ordnance applications (e.g., proximity fuzes) since WWII and later in
nuclear weapons
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either nuclear fission, fission (fission or atomic bomb) or a combination of fission and nuclear fusion, fusion reactions (thermonuclear weap ...
. The same technology was studied by
Argonne National Laboratories and other researchers in the 1980s for use in
electric vehicle
An electric vehicle (EV) is a motor vehicle whose propulsion is powered fully or mostly by electricity. EVs encompass a wide range of transportation modes, including road vehicle, road and rail vehicles, electric boats and Submersible, submer ...
s.
Rechargeable configurations
Since the mid-1960s much development work has been undertaken on
rechargeable batteries
A rechargeable battery, storage battery, or secondary cell (formally a type of energy accumulator), is a type of electrical battery which can be charged, discharged into a load, and recharged many times, as opposed to a disposable or prima ...
using
sodium
Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...
(Na) for the negative electrodes. Sodium is attractive because of its high
reduction potential
Redox potential (also known as oxidation / reduction potential, ''ORP'', ''pe'', ''E_'', or E_) is a measure of the tendency of a chemical species to acquire electrons from or lose electrons to an electrode and thereby be reduced or oxidised respe ...
of −2.71 volts, low weight, relative abundance, and low cost. In order to construct practical batteries, the sodium must be in liquid form. The
melting point
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilib ...
of sodium is . This means that sodium-based batteries operate at temperatures between . Research has investigated metal combinations with operating temperatures at and room temperature.
Sodium–sulfur
The
sodium–sulfur battery
A sodium–sulfur (NaS) battery is a type of molten-salt battery, molten-salt battery (electricity), battery that uses liquid sodium and liquid sulfur electrodes. This type of battery has a similar energy density to lithium-ion battery, lithium-i ...
(NaS battery), along with the related
lithium–sulfur battery
The lithium–sulfur battery (Li–S battery) is a type of rechargeable battery. It is notable for its high specific energy. The low atomic weight of lithium and moderate atomic weight of sulfur means that Li–S batteries are relatively light (a ...
employs cheap and abundant electrode materials. It was the first
alkali-metal commercial battery. It used liquid
sulfur
Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
for the positive electrode and a
ceramic
A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...
tube of
beta-alumina solid electrolyte (BASE). Insulator corrosion was a problem because they gradually became conductive, and the self-discharge rate increased.
Because of their high specific power, NaS batteries have been proposed for space applications. An NaS battery for space use was successfully tested on the
Space Shuttle
The Space Shuttle is a retired, partially reusable launch system, reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. ...
mission
STS-87
STS-87 was a Space Shuttle mission launched from Launch Complex 39B of the Kennedy Space Center on 19 November 1997. It was the 88th flight of the Space Shuttle and the 24th flight of '' Columbia''. The mission goals were to conduct experiments ...
in 1997,
but the batteries have not been used operationally in space. NaS batteries have been proposed for use in the high-temperature environment of
Venus
Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...
.
A consortium formed by
Tokyo Electric Power Co. (TEPCO) and NGK Insulators Ltd. declared their interest in researching the NaS battery in 1983, and became the primary drivers behind the development of this type ever since. TEPCO chose the NaS battery because its component elements (sodium, sulfur and ceramics) are abundant in Japan. The first large-scale field testing took place at TEPCO's Tsunashima substation between 1993 and 1996, using 32 MW, 6.6 kV battery banks. Based on the findings from this trial, improved battery modules were developed and were made commercially available in 2000. The commercial NaS battery bank offers:
*Capacity : 25–250 kWh per bank
*Efficiency of 87%
*Lifetime of 2,500 cycles at 100% depth of discharge (DOD), or 4,500 cycles at 80% DOD
Sodium–nickel chloride (Zebra) battery
A lower-temperature variant of molten-salt batteries was the development of the ZEBRA (originally, "Zeolite Battery Research Africa"; later, the "Zero Emissions Batteries Research Activity") battery in 1985, originally developed for electric vehicle applications. The battery uses with Na
+-beta-alumina ceramic electrolyte.
The battery operates at and uses molten
sodium tetrachloroaluminate (), which has a melting point of , as the electrolyte. The negative electrode is molten sodium. The positive electrode is
nickel
Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...
in the discharged state and
nickel chloride in the charged state. Because nickel and nickel chloride are nearly insoluble in neutral and
basic
Basic or BASIC may refer to:
Science and technology
* BASIC, a computer programming language
* Basic (chemistry), having the properties of a base
* Basic access authentication, in HTTP
Entertainment
* Basic (film), ''Basic'' (film), a 2003 film
...
melts, contact is allowed, providing little resistance to charge transfer. Since both and Na are liquid at the operating temperature, a sodium-conducting
β-alumina ceramic is used to separate the liquid sodium from the molten . The primary elements used in the manufacture of these batteries have much higher worldwide reserves and annual production than lithium.
It was invented in 1985 by the Zeolite Battery Research Africa Project (ZEBRA) group at the
Council for Scientific and Industrial Research (CSIR) in
Pretoria, South Africa
Pretoria ( ; ) is the administrative capital of South Africa, serving as the seat of the executive branch of government, and as the host to all foreign embassies to the country.
Pretoria straddles the Apies River and extends eastward into ...
. It can be assembled in the discharged state, using NaCl, Al, nickel and iron powder. The positive electrode is composed mostly of materials in the solid state, which reduces the likelihood of corrosion, improving safety.
Its
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 ...
is 100 Wh/kg; specific power is 150 W/kg. The β-alumina solid ceramic is unreactive to sodium metal and sodium aluminum chloride. Lifetimes of over 2,000 cycles and twenty years have been demonstrated with full-sized batteries, and over 4,500 cycles and fifteen years with 10- and 20-cell modules. For comparison,
LiFePO4 lithium iron phosphate batteries
The lithium iron phosphate battery ( battery) or LFP battery (''lithium ferrophosphate'') is a type of lithium-ion battery using lithium iron phosphate () as the cathode material, and a graphitic carbon electrode with a metallic backing as th ...
store 90–110 Wh/kg, and the more common
LiCoO2 lithium-ion batteries store 150–200 Wh/kg. A nano
lithium-titanate battery
The lithium-titanate or lithium-titanium-oxide (LTO) battery is a type of rechargeable battery which has the advantage of being faster to charge than other Lithium-ion battery, lithium-ion batteries but the disadvantage is a much lower energy den ...
stores 72 Wh/kg and can provide power of 760 W/kg.
The ZEBRA's liquid electrolyte freezes at , and the normal operating temperature range is . Adding iron to the cell increases its power response.
ZEBRA batteries are currently manufactured by FZSoNick and used as a power backup in the telecommunication industries, Oil&Gas and Railways. It is also used in special electric vehicles used in mining. In the past it was adopted in the
Modec Electric Van, the
Iveco Daily
The Iveco Daily is a large light commercial vehicle, light commercial van produced by the Italy, Italian automaker Iveco since 1978; it was also sold as the Fiat Daily by Fiat Automobiles, Fiat until 1983. Unlike the more car-like unibody Fiat D ...
3.5-ton delivery vehicle, the prototype
Smart ED, and the
Th!nk City. In 2011 the US Postal Service began testing all-electric delivery vans, one powered by a ZEBRA battery.
In 2010
General Electric
General Electric Company (GE) was an American Multinational corporation, multinational Conglomerate (company), conglomerate founded in 1892, incorporated in the New York (state), state of New York and headquartered in Boston.
Over the year ...
announced a battery that it called a sodium–metal halide battery, with a 20-year lifetime. Its cathode structure consists of a conductive nickel network, molten salt electrolyte, metal current collector, carbon felt electrolyte reservoir and the active sodium–metal halide salts. In 2015, as a result of a global restructuring, the company abandoned the project. In 2017 Chinese battery maker Chilwee Group (also known as Chaowei) created a new company with General Electric (GE) to bring to market a Na-NiCl battery for industrial and energy storage applications.
When not in use, batteries are typically kept molten and ready for use because if allowed to solidify they typically take twelve hours to reheat and charge. This reheating time varies depending on the battery-pack temperature, and power available for reheating. After shutdown a fully charged battery pack loses enough energy to cool and solidify in five-to-seven days depending on the amount of insulation.
Sodium metal chloride batteries are very safe; a
thermal runaway
Thermal runaway describes a process that is accelerated by increased temperature, in turn releasing Thermal energy, energy that further increases temperature. Thermal runaway occurs in situations where an increase in temperature changes the cond ...
can be activated only by piercing the battery and also, in this unlikely event, no fire or explosion will be generated. For this reason and also for the possibility to be installed outdoor without cooling systems, make the sodium metal chloride batteries very suitable for the industrial and commercial energy storage installations.
Sumitomo studied a battery using a salt that is molten at , far lower than sodium based batteries, and operational at . It offers energy densities as high as 290 Wh/L and 224 Wh/kg and charge/discharge rates of 1C with a lifetime of 100–1000 charge cycles. The battery employs only nonflammable materials and neither ignites on contact with air nor risks thermal runaway. This eliminates waste-heat storage or fire- and explosion-proof equipment, and allows closer cell packing. The company claimed that the battery required half the volume of lithium-ion batteries and one quarter that of sodium–sulfur batteries. The cell used a nickel cathode and a glassy carbon anode.
In 2014 researchers identified a liquid sodium–cesium alloy that operates at and produced 420 milliampere-hours per gram. The new material was able to fully coat, or "wet," the electrolyte. After 100 charge/discharge cycles, a test battery maintained about 97% of its initial storage capacity. The lower operating temperature allowed the use of a less-expensive polymer external casing instead of steel, offsetting some of the increased cost of cesium.
Innovenergy in
Meiringen
Meiringen () is a municipality in the Interlaken-Oberhasli administrative district in the canton of Bern in Switzerland. Besides the village of Meiringen, the municipality includes the settlements of Balm, Brünigen, Eisenbolgen, Hausen, Prasti, ...
,
Switzerland
Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...
has further optimised this technology with the use of domestically sourced raw materials, except for the nickel powder component. Despite the reduced capacity compared with
lithium-ion batteries
A lithium-ion or Li-ion battery is a type of rechargeable battery that uses the reversible intercalation of Li+ ions into electronically conducting solids to store energy. Li-ion batteries are characterized by higher specific energy, energy ...
, the ZEBRA technology is applicable for
stationary energy storage from
solar power
Solar power, also known as solar electricity, is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Solar panels use the photovoltaic effect to c ...
. In 2022, the company operated a 540 kWh storage facility for solar cells on the roof of a shopping center, and currently produces over a million battery units per year from sustainable, non-toxic materials (
table salt
In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as ro ...
).
Liquid-metal batteries
Professor
Donald Sadoway at the Massachusetts Institute of Technology has pioneered the research of liquid-metal rechargeable batteries, using both magnesium–antimony and more recently
lead–antimony. The electrode and electrolyte layers are heated until they are liquid and self-segregate due to density and
immiscibility. Such batteries may have longer lifetimes than conventional batteries, as the electrodes go through a cycle of creation and destruction during the charge–discharge cycle, which makes them immune to the degradation that afflicts conventional battery electrodes.
[ ()]
The technology was proposed in 2009 based on
magnesium
Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
and
antimony
Antimony is a chemical element; it has chemical symbol, symbol Sb () and atomic number 51. A lustrous grey metal or metalloid, it is found in nature mainly as the sulfide mineral stibnite (). Antimony compounds have been known since ancient t ...
separated by a molten salt.
[Staff (2012]
Ambri Technology
Ambri company web page, Retrieved 6 December 2012. Magnesium was chosen as the negative electrode for its low cost and low solubility in the molten-salt electrolyte. Antimony was selected as the positive electrode due to its low cost and higher anticipated discharge voltage.
In 2011, the researchers demonstrated a cell with a lithium anode and a lead–antimony cathode, which had higher ionic conductivity and lower melting points (350–430 °C).
The drawback of the Li chemistry is higher cost. A Li/LiF + LiCl + LiI/Pb-Sb cell with about 0.9 V open-circuit potential operating at 450 °C had electroactive material costs of US$100/kWh and US$100/kW and a projected 25-year lifetime. Its discharge power at 1.1 A/cm
2 is only 44% (and 88% at 0.14 A/cm
2).
Experimental data shows 69% storage efficiency, with good storage capacity (over 1000 mAh/cm
2), low leakage (< 1 mA/cm
2) and high maximal discharge capacity (over 200 mA/cm
2). By October 2014 the MIT team achieved an operational efficiency of approximately 70% at high charge/discharge rates (275 mA/cm
2), similar to that of
pumped-storage hydroelectricity
Pumped-storage hydroelectricity (PSH), or pumped hydroelectric energy storage (PHES), is a type of hydroelectric energy storage used by electric power systems for load balancing (electrical power), load balancing.
A PSH system stores energy i ...
and higher efficiencies at lower currents. Tests showed that after 10 years of regular use, the system would retain about 85% of its initial capacity.
In September 2014, a study described an arrangement using a molten alloy of lead and antimony for the positive electrode, liquid lithium for the negative electrode; and a molten mixture of lithium salts as the electrolyte.
A recent innovation is the PbBi alloy which enables lower melting point lithium-based battery. It uses a molten salt electrolyte based on LiCl-LiI and operates at 410 °C.
Ionic liquids
An ionic liquid (IL) is a 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 water and gasoline are ...
have been shown to have prowess for use in rechargeable batteries. The electrolyte is pure molten salt with no added solvent, which is accomplished by using a salt having a room temperature liquid phase. This causes a highly viscous solution, and is typically made with structurally large salts with malleable lattice structures.
Thermal batteries (non-rechargeable)
Technologies
Thermal batteries use an electrolyte that is solid and inactive at ambient temperatures. They can be stored indefinitely (over 50 years) yet provide full power in an instant when required. Once activated, they provide a burst of high power for a short period (a few tens of seconds to 60 minutes or more), with output ranging from
watt
The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), quantify the rate of Work ...
s to
kilowatt
The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), quantify the rate of Work ...
s. The high power is due to the high
ionic conductivity of the molten salt (resulting in a low internal resistance), which is three orders of magnitude (or more) greater than that of the
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
in a
lead–acid car battery.
One design uses a fuze strip (containing
barium chromate and powdered
zirconium
Zirconium is a chemical element; it has Symbol (chemistry), symbol Zr and atomic number 40. First identified in 1789, isolated in impure form in 1824, and manufactured at scale by 1925, pure zirconium is a lustrous transition metal with a greyis ...
metal in a ceramic paper) along the edge of the heat pellets to initiate the electrochemical reaction. The fuze strip is typically fired by an
electrical igniter or
squib which is activated with an electric current.
Another design uses a central hole in the middle of the battery stack, into which the high-energy electrical igniter fires a mixture of hot gases and
incandescent
Thermal radiation is electromagnetic radiation emitted by the thermal motion of particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation. The emission of energy arises from a combination of electro ...
particles. This allows much shorter activation times (tens of milliseconds) vs. hundreds of milliseconds for the edge-strip design. Battery activation can be accomplished by a
percussion primer, similar to a
shotgun shell
A shotgun cartridge, shotshell, or shell is a type of rimmed, cylindrical (straight-walled) ammunition used specifically in shotguns. It is typically loaded with numerous small, spherical sub-projectiles called shot. Shotguns typically use a ...
. The heat source should be gasless. The standard heat source typically consists of mixtures of
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
powder and
potassium perchlorate
Potassium perchlorate is the inorganic salt with the chemical formula K Cl O4. Like other perchlorates, this salt is a strong oxidizer when the solid is heated at high temperature, although it usually reacts very slowly in solution with reducin ...
in weight ratios of 88/12, 86/14, or 84/16. The higher the potassium perchlorate level, the higher the heat output (nominally 200, 259, and 297
cal Cal or CAL may refer to:
Arts and entertainment
* ''Cal'' (novel), a 1983 novel by Bernard MacLaverty
* "Cal" (short story), a science fiction short story by Isaac Asimov
* ''Cal'' (1984 film), an Irish drama starring John Lynch and Helen Mir ...
/
g respectively). This property of unactivated storage has the double benefit of avoiding deterioration of the active materials during storage and eliminating capacity loss due to
self-discharge until the battery is activated.
In the 1980s
lithium
Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...
-alloy anodes replaced
calcium
Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
or
magnesium
Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
anodes, with cathodes of
calcium chromate,
vanadium
Vanadium is a chemical element; it has Symbol (chemistry), symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an ...
or
tungsten oxides. Lithium–
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 ...
alloys are favored over the earlier lithium–aluminium alloys. The corresponding cathode for use with the lithium-alloy anodes is mainly
iron disulfide (pyrite) replaced by cobalt disulfide for high-power applications. The electrolyte is normally a
eutectic mixture
A eutectic system or eutectic mixture ( ) is a type of a homogeneous mixture that has a melting point lower than those of the constituents. The lowest possible melting point over all of the mixing ratios of the constituents is called the ''eutec ...
of
lithium chloride
Lithium chloride is a chemical compound with the formula Li Cl. The salt is a typical ionic compound (with certain covalent characteristics), although the small size of the Li+ ion gives rise to properties not seen for other alkali metal chlorid ...
and
potassium chloride
Potassium chloride (KCl, or potassium salt) is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water, and its solutions have a sa ...
.
More recently, other lower-melting, eutectic electrolytes based on
lithium bromide
Lithium bromide (LiBr) is a chemical compound of lithium and bromine. Its extreme hygroscopic character makes LiBr useful as a desiccant in certain air conditioning systems.Wietelmann, Ulrich and Bauer, Richard J. (2005) "Lithium and Lithium Compo ...
,
potassium bromide
Potassium bromide ( K Br) is a salt, widely used as an anticonvulsant and a sedative in the late 19th and early 20th centuries, with over-the-counter use extending to 1975 in the US. Its action is due to the bromide ion ( sodium bromide is equa ...
, and lithium chloride or
lithium fluoride
Lithium fluoride is an inorganic compound with the chemical formula LiF. It is a colorless solid that transitions to white with decreasing crystal size.
Its structure is analogous to that of sodium chloride, but it is much less soluble in water. ...
have also been used to provide longer operational lifetimes; they are also better conductors. The so-called "all-lithium" electrolyte based on
lithium chloride
Lithium chloride is a chemical compound with the formula Li Cl. The salt is a typical ionic compound (with certain covalent characteristics), although the small size of the Li+ ion gives rise to properties not seen for other alkali metal chlorid ...
,
lithium bromide
Lithium bromide (LiBr) is a chemical compound of lithium and bromine. Its extreme hygroscopic character makes LiBr useful as a desiccant in certain air conditioning systems.Wietelmann, Ulrich and Bauer, Richard J. (2005) "Lithium and Lithium Compo ...
, and
lithium fluoride
Lithium fluoride is an inorganic compound with the chemical formula LiF. It is a colorless solid that transitions to white with decreasing crystal size.
Its structure is analogous to that of sodium chloride, but it is much less soluble in water. ...
(no potassium salts) is also used for high-power applications, because of its high ionic conductivity. A
radioisotope thermal generator
A radioisotope thermoelectric generator (RTG, RITEG), or radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the Decay heat, heat released by the decay of a suitable radioactive material i ...
, such as in the form of pellets of
90SrTiO
4, can be used for long-term delivery of heat for the battery after activation, keeping it in a molten state.
Uses
Thermal batteries are used almost exclusively for military applications, notably for nuclear weapons and
guided missiles
A missile is an airborne ranged weapon capable of self-propelled flight aided usually by a propellant, jet engine or rocket motor.
Historically, 'missile' referred to any projectile that is thrown, shot or propelled towards a target; this u ...
.
They are the primary power source for many missiles such as the
AIM-9 Sidewinder
The AIM-9 Sidewinder is a short-range air-to-air missile. Entering service with the United States Navy in 1956 and the Air Force in 1964, the AIM-9 is one of the oldest, cheapest, and most successful air-to-air missiles. Its latest variants rema ...
,
AIM-54 Phoenix,
MIM-104 Patriot
The MIM-104 Patriot is a mobile interceptor missile surface-to-air missile (SAM) system, the primary such system used by the United States Army and several allied states. It is manufactured by the U.S. defense contractor Raytheon and derives it ...
,
BGM-71 TOW
The BGM-71 TOW ("Tube-launched, Optically tracked, wire-guided missile, Wire-guided", pronounced ) is an American anti-tank missile. TOW replaced much smaller missiles like the SS.10 and ENTAC, offering roughly twice the effective range, a more ...
,
BGM-109 Tomahawk
The BGM-109 Tomahawk () Land Attack Missile (TLAM) is an American long-range, all-weather, jet-powered, Subsonic flight, subsonic cruise missile that is primarily used by the United States Navy and Royal Navy in ship and submarine-based land-att ...
and others. In these batteries the electrolyte is immobilized when molten by a special grade of
magnesium oxide
Magnesium oxide (MgO), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions ...
that holds it in place by
capillary action
Capillary action (sometimes called capillarity, capillary motion, capillary rise, capillary effect, or wicking) is the process of a liquid flowing in a narrow space without the assistance of external forces like Gravitation, gravity.
The effe ...
. This powdered mixture is pressed into
pellets to form a separator between the
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 ...
and
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 ...
of each cell in the battery stack. As long as the electrolyte (salt) is solid, the battery is inert and remains inactive. Each cell also contains a
pyrotechnic heat source, which is used to heat the cell to the typical operating temperature of 400–550 °C.
See also
*
Primary cell
A primary battery or primary cell is a battery (a galvanic cell) that is designed to be used once and discarded, and it is not rechargeable unlike a secondary cell ( rechargeable battery). In general, the electrochemical reaction occurring in ...
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Secondary cell
A rechargeable battery, storage battery, or secondary cell (formally a type of Accumulator (energy), energy accumulator), is a type of electrical battery which can be charged, discharged into a load, and recharged many times, as opposed to a ...
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Smart grid
The smart grid is an enhancement of the 20th century electrical grid, using two-way communications and distributed so-called intelligent devices. Two-way flows of electricity and information could improve the delivery network. Research is main ...
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Flow battery
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Carnot battery
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List of battery types
This list is a summary of notable electric battery types composed of one or more electrochemical cells. Three lists are provided in the table. The primary (non-rechargeable) and secondary (rechargeable) cell lists are lists of battery chemistry. ...
References
External links
Sadoway Group - Liquid Metal Batteries
{{emerging technologies, energy=yes
Rechargeable batteries
Battery types
Energy storage
Grid energy storage