A flow battery is a form of rechargable battery in which electrolyte containing one or more dissolved electroactive species flows through a power cell / reactor that converts chemical energy to electricity. See also Rechargeable electricity storage system A rechargeable battery, also known as a storage battery, is a group of two or more secondary An electrolyte is any substance containing free Ions that behaves as an electrically conductive medium An electrochemical cell is a device used for generating an Electromotive force ( Voltage) and current from chemical reactions. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Additional electrolyte is stored externally, generally in tanks, and is usually pumped through the cell (or cells) of the reactor, although gravity feed systems are also known. Flow batteries can be rapidly "recharged" by replacing the electrolyte liquid (in a similar way to refilling fuel tanks for internal combustion engines) while simultaneously recovering the spent material for re-energization. The internal combustion engine is an engine in which the Combustion of Fuel and an Oxidizer (typically air occurs in a confined space called a
Fuel cells are generally defined as electrochemical devices for converting chemical energy to electricity in which the reactants are flowed through a power cell / reactor from an external source (tank, cylinder or surrounding environment). A fuel cell is an electrochemical conversion device It produces electricity from Fuel (on the Anode side and an oxidant (on the
Under these definitions it may be concluded that the flow battery is a special type of fuel cell. However, what is rarely explicitly stated is that the electrolyte in a fuel cell remains at all times within the reactor (in the form of an ion-exchange membrane, for example). ion-exchange resin is an insoluble matrix (or support structure normally in the form of small (1-2 mm diameter beads usually white or yellowish fabricated from an organic Polymer What flows into the reactor are only the electroactive chemicals, which are non-conducting (e. g. hydrogen, methanol, oxygen, etc. ) This is in contrast to a flow battery in which at least some of the electrolyte (generally the majority in weight and volume terms) flows through the reactor.
Flow batteries are also distinguished from fuel cells by the fact that the chemical reaction involved is often reversible, i. A fuel cell is an electrochemical conversion device It produces electricity from Fuel (on the Anode side and an oxidant (on the e. they are generally of the secondary battery type and so they can be recharged without replacing the electroactive material. See also Rechargeable electricity storage system A rechargeable battery, also known as a storage battery, is a group of two or more secondary
To add to the confusion the European Patent Organisation classes redox flow cells (H01M8/18C4) as a sub-class of regenerative fuel cells (H01M8/18). The European Patent Organisation ( EPO or EPOrg) is a public international organisation created in 1977 to grant Patents in Europe under
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Classes of flow batteries
Various classes of flow batteries exist including the redox (reduction-oxidation) flow battery, in which all electroactive components are dissolved in the electrolyte. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state If one or more electroactive component is deposited as a solid layer the system is known as a hybrid flow battery. The main difference between these two types of flow battery is that the energy of the redox flow battery can be determined fully independently of the battery power, because the energy is related to the electrolyte volume (tank size) and the power to the reactor size. In Physics, power (symbol P) is the rate at which work is performed or energy is transmitted or the amount of energy required or expended for The hybrid flow battery, similarly to a conventional battery, is limited in energy to the amount of solid material that can be accommodated within the reactor. In practical terms this means that the discharge time of a redox flow battery at full power can be varied, as required, from several minutes to many days, whereas a hybrid flow battery may be typically varied from several minutes to a few hours.
Another type of flow battery is the redox fuel cell. This has a conventional flow battery reactor, which only operates to produce electricity (i. e. it is not electrically recharged). Recharge occurs by reduction of the negative electrolyte using a fuel (e. Fuel is any material that is burned or altered in order to obtain energy g. hydrogen) and oxidation of the positive electrolyte using an oxidant (typically oxygen or air). Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the
Examples of redox flow batteries are the vanadium redox flow battery, polysulfide bromide battery (Regenesys), and uranium redox flow battery. The vanadium redox (and redox flow battery in its present form (with sulfuric acid electrolytes was patented by the University of New South Wales in Australia in 1986. The PolySulfide Bromide battery (PSB is a regenerative fuel cell involving a reversible electrochemical reaction between two salt-solution electrolytes sodium bromide and sodium polysulfide Hybrid flow batteries include the zinc-bromine, cerium-zinc and all-lead flow batteries. The zinc-bromine flow battery is a type of hybrid flow battery Redox fuel cells are less common commercially although many systems have been proposed.
Advantages and disadvantages
Redox flow batteries, and to a lesser extent hybrid flow batteries, have the advantages of flexible layout (due to separation of the power and energy components), long cycle life (because there are no solid-solid phase changes), quick response times (in common with nearly all batteries), no need for "equalisation" charging and no harmful emissions (in common with nearly all batteries). In Thermodynamics, phase transition or phase change is the transformation of a thermodynamic system from one phase to another Some types also offer easy state-of-charge determination (through voltage dependence on charge), low maintenance and tolerance to overcharge/ overdischarge.
On the negative side, flow batteries are rather complicated in comparison with standard batteries as they may require pumps, sensors, control units and secondary containment vessels. The energy densities vary considerably but are, in general, rather low compared to portable batteries, such as the Li-ion. Energy density is the amount of Energy stored in a given system or region of space per unit Volume, or per unit Mass, depending on the context although Lithium-ion batteries (sometimes abbreviated Li-ion batteries) are a type of Rechargeable battery in which a Lithium ion moves between the Anode
Applications
Taking the above considerations together it should be apparent that flow batteries are normally considered for relatively large (1 kW - many MW) stationary applications. These are for load levelling, where the battery is used to store cheap night-time electricity and provide electricity when it is more costly, as well as storing energy from renewable sources such as wind or solar for discharge during periods of peak demand; peak shaving, where spikes of demand are met by the battery; and UPS, where the battery is used if the main power fails to provide an uninterrupted supply. An uninterruptible power supply ( UPS) also known as a continuous power supply ( CPS) or a battery backup is a device which maintains a continuous
Because flow batteries can be rapidly "recharged" by replacing the electrolyte, they have been proposed for electric vehicles, and the use of vanadium redox flow batteries for load levelling in wind farm applications is already showing promise. The Electric Vehicle was an American Automobile manufactured only in 1899 The vanadium redox (and redox flow battery in its present form (with sulfuric acid electrolytes was patented by the University of New South Wales in Australia in 1986. A wind farm is a group of Wind turbines in the same location used for production of electric power
A further potential application for redox flow batteries lies in the fact that all cells share the same electrolyte/s. Therefore, the electrolyte/s may be charged using a given number of cells and discharged with a different number. Because the voltage of the battery is proportional to the number of cells used the battery can therefore act as a very powerful dc-dc converter. Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical In Electronic engineering, a DC to DC converter is a circuit which converts a source of Direct current (DC from one Voltage level to another In addition, if the number of cells is continuously changed (on the input and/ or output side) power conversion can also be ac-dc, ac-ac or dc-ac, with the frequency limited by that of the switching gear. In Electrical engineering, power conversion has a more specific meaning namely converting Electric power from one form to another
See also
References
- ^ T. See also Timeline of hydrogen technologies Hydrogen technologies are technologies that relate to the production and use of hydrogen Load balancing (electrical power (daily peak demand reserve refers to the use of various techniques by electrical Power stations to store excess electrical power during low A redox electrode is an Electrode made from electron-conductive material and characterized by high Chemical stability in the solution under test Fujii, T. Hirose, and N. Kondou, in JP Patent 55096569 (1979), to Meidensha Electric Mfg. Co. Ltd.
- ^ M. Bartolozzi, "Development of redox flow batteries. A historical Bibliography," J. Power Sources, vol. 27, pp. 219-234, 1989.
- ^ L. H. Cutler, in US Patent 3607420 (1969), to E. I. du Pont de Nemours and Co.
- ^ Y. Shiokawa, H. Yamana, and H. Moriyama, "An application of actinide elements for a redox flow battery," J. Nucl. Sci. Tech. , vol. 37, pp. 253-256, 2000.
- ^ W. Borchers, in US Patent 567959 (1894)
- ^ W. Nernst, in DE Patent 264026 (1912)
- ^ R. M. Keefer, in US Patent 3682704 (1970), to Electrocell Ltd.
- ^ J. T. Kummer and D. -G. Oei, "A chemically regenerative redox fuel cell," J. Appl. Electrochem. , vol. 12, pp. 87-100, 1982
- ^ P. M. Spaziante, K. Kampanatsanyakorn, and A. Zocchi, in WO Patent 03043170 (2001), to Squirrel Holdings Ltd.
External links
Dictionary
flow battery
-noun
- (physics) A form of electrochemical storage cell in which electrolyte flows between connected tanks; the direction of flow being opposite when the cell is charging and discharging; used to store electricity from intermittent suppliers such as wind farms.
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