Beta-alumina solid electrolyte
Encyclopedia
Beta-alumina solid electrolyte (BASE) is a fast ion conductor
material used as a membrane
in several types of molten salt electrochemical cell
. There is no known substitute. cs
β
form of aluminium oxide
(Al2O3), a hard polycrystalline ceramic
, which, when prepared as an electrolyte
, is complexed with a mobile ion
, such as Na
+, K
+ , Li
+ , Ag
+ , H
+ , Pb
2+ , Sr
2+ or Ba
2+ depending on the application. Beta-alumina is a good conductor of its mobile ion yet allows no non-ionic (i.e., electronic) conductivity.
Sodium beta alumina is a non-stoichiometric sodium aluminate
known for its rapid transport of Na+ ions. This material selectively passes sodium ions while blocking other species, including liquid sodium and liquid sulfur. It is a ceramic which can be formed and sintered by commercially available techniques and its conductivity at operating temperatures — 250 to 300 degrees Celsius — compares favorably with electrolytes used in conventional battery systems such as sulfuric acid and potassium hydroxide. The crystal structure of the Na-Al2O3 provides an essential rigid framework with channels along which the ionic species of the solid can migrate. Ion transport involves hopping from site to site along these channels.
BASE was first developed by researchers at the Ford Motor Company
, in the search for a storage device for electric vehicle
s while developing the sodium-sulfur battery
. The NaS battery consists of sulfur at the positive electrode and sodium at the negative electrode as active materials, and sodium-conducting beta alumina ceramic as the electrolyte separating both electrodes.
This hermetically sealed battery is kept at approximately 300 degrees Celsius and is operated under the condition that the active materials at both electrodes are liquid and its electrolyte is solid. At this temperature, since both active materials react smoothly, and internal resistance becomes low enough, the NaS battery shows excellent performance. As a secondary battery, which allows reversible charging and discharging, the NaS battery can be continuously used. Several commercial installations use this type of battery for load leveling.
The sodium sulfur battery was a topic of intense worldwide interest during the 1970s and 1980s, but interest in the technology for vehicle use diminished for a variety of technical and economic reasons. In contrast, its "successor", the sodium nickel chloride battery, is now entering the commercialization phase. The sodium nickel chloride battery (or ZEBRA battery, so-called for the Zeolite Battery Research Africa Project) has been under development for almost 20 years. Y.F.Y. Yao and J.T. Kummer, J. Inorg. Nucl. Chem. 29 (1967) p. 2453
When BASE is used in a sodium nickel chloride (ZEBRA) cell, several requirements must be met. It must have a low resistivity, typically 4 ohm.cm at 350 °C, and a strength in excess of 200 MPa. It must be produced in the form of a thin-walled (1.25 mm), convoluted tube by low-cost production methods, and it must maintain a stable cell resistance for up to 10 years. These requirements have mostly been met by a variation of the sol-gel process.
BASE is also used in alkali-metal thermal to electric converter
s (AMTECs). An AMTEC is a high efficiency device for directly converting heat to electricity. An AMTEC operates as a thermally regenerative electrochemical cell by expanding sodium through the pressure differential across the (BASE) membrane. BASE electrolytes have been used in some molten-carbonate fuel cell
s, as well as other liquid electrode/solid electrolyte fuel cell
designs.
Fast ion conductor
In solid-state ionics, fast ion conductors, also known as solid electrolytes and superionic conductors, are materials that act as solid state ion conductors and are used primarily in solid oxide fuel cells. As solid electrolytes they conduct due to the movement of ions through voids, or empty...
material used as a membrane
Semipermeable membrane
A semipermeable membrane, also termed a selectively permeable membrane, a partially permeable membrane or a differentially permeable membrane, is a membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally specialized "facilitated diffusion".The rate of...
in several types of molten salt electrochemical cell
Electrochemical cell
An electrochemical cell is a device capable of either deriving electrical energy from chemical reactions, or facilitating chemical reactions through the introduction of electrical energy. A common example of an electrochemical cell is a standard 1.5-volt "battery"...
. There is no known substitute. cs
β
Isomorphism (crystallography)
In crystallography crystals are described as isomorphous if they are closely similar in shape. Historically crystal shape was defined by measuring the angles between crystal faces with a goniometer...
form of aluminium oxide
Aluminium oxide
Aluminium oxide is an amphoteric oxide with the chemical formula 23. It is commonly referred to as alumina, or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry...
(Al2O3), a hard polycrystalline ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
, which, when prepared as an electrolyte
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
, is complexed with a mobile ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
, such as Na
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
+, K
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
+ , Li
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
+ , Ag
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
+ , H
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
+ , Pb
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
2+ , Sr
Strontium
Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
2+ or Ba
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
2+ depending on the application. Beta-alumina is a good conductor of its mobile ion yet allows no non-ionic (i.e., electronic) conductivity.
Sodium beta alumina is a non-stoichiometric sodium aluminate
Sodium aluminate
Sodium aluminate is an important commercial inorganic chemical. It works as an effective source of aluminium hydroxide for many industrial and technical applications. Pure sodium aluminate is a white crystalline solid having a formula variously given as NaAlO2, NaAl4 , Na2O·Al2O3, or Na2Al2O4...
known for its rapid transport of Na+ ions. This material selectively passes sodium ions while blocking other species, including liquid sodium and liquid sulfur. It is a ceramic which can be formed and sintered by commercially available techniques and its conductivity at operating temperatures — 250 to 300 degrees Celsius — compares favorably with electrolytes used in conventional battery systems such as sulfuric acid and potassium hydroxide. The crystal structure of the Na-Al2O3 provides an essential rigid framework with channels along which the ionic species of the solid can migrate. Ion transport involves hopping from site to site along these channels.
BASE was first developed by researchers at the Ford Motor Company
Ford Motor Company
Ford Motor Company is an American multinational automaker based in Dearborn, Michigan, a suburb of Detroit. The automaker was founded by Henry Ford and incorporated on June 16, 1903. In addition to the Ford and Lincoln brands, Ford also owns a small stake in Mazda in Japan and Aston Martin in the UK...
, in the search for a storage device for electric vehicle
Electric vehicle
An electric vehicle , also referred to as an electric drive vehicle, uses one or more electric motors or traction motors for propulsion...
s while developing the sodium-sulfur battery
Sodium-sulfur battery
A sodium–sulfur battery or liquid metal battery is a type of molten metal battery constructed from sodium and sulfur . This type of battery has a high energy density, high efficiency of charge/discharge and long cycle life, and is fabricated from inexpensive materials...
. The NaS battery consists of sulfur at the positive electrode and sodium at the negative electrode as active materials, and sodium-conducting beta alumina ceramic as the electrolyte separating both electrodes.
This hermetically sealed battery is kept at approximately 300 degrees Celsius and is operated under the condition that the active materials at both electrodes are liquid and its electrolyte is solid. At this temperature, since both active materials react smoothly, and internal resistance becomes low enough, the NaS battery shows excellent performance. As a secondary battery, which allows reversible charging and discharging, the NaS battery can be continuously used. Several commercial installations use this type of battery for load leveling.
The sodium sulfur battery was a topic of intense worldwide interest during the 1970s and 1980s, but interest in the technology for vehicle use diminished for a variety of technical and economic reasons. In contrast, its "successor", the sodium nickel chloride battery, is now entering the commercialization phase. The sodium nickel chloride battery (or ZEBRA battery, so-called for the Zeolite Battery Research Africa Project) has been under development for almost 20 years. Y.F.Y. Yao and J.T. Kummer, J. Inorg. Nucl. Chem. 29 (1967) p. 2453
When BASE is used in a sodium nickel chloride (ZEBRA) cell, several requirements must be met. It must have a low resistivity, typically 4 ohm.cm at 350 °C, and a strength in excess of 200 MPa. It must be produced in the form of a thin-walled (1.25 mm), convoluted tube by low-cost production methods, and it must maintain a stable cell resistance for up to 10 years. These requirements have mostly been met by a variation of the sol-gel process.
BASE is also used in alkali-metal thermal to electric converter
Alkali-metal thermal to electric converter
The alkali metal thermoelectric converter is a thermally regenerative electrochemical device for the direct conversion of heat to electrical energy...
s (AMTECs). An AMTEC is a high efficiency device for directly converting heat to electricity. An AMTEC operates as a thermally regenerative electrochemical cell by expanding sodium through the pressure differential across the (BASE) membrane. BASE electrolytes have been used in some molten-carbonate fuel cell
Molten-carbonate fuel cell
Molten-carbonate fuel cells are high-temperature fuel cells, that operate at temperatures of 600°C and above.Molten carbonate fuel cells are currently being developed for natural gas, biogas , and coal-based power plants for electrical utility, industrial, and military applications...
s, as well as other liquid electrode/solid electrolyte fuel cell
Fuel cell
A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and alcohols like methanol are sometimes used...
designs.