Glossary
This is the place to find explanations of many terms from charging technology. See also the explanations from the Fraunhofer Institute for Systems and Innovation Research.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Accumulator
A battery which can store or accumulate electric current. See Secondary system.
Alkaline zinc-manganese dioxide cell, alkaline-manganese battery
Primary system, 1.5 V, Zn/KOH/MnO2. The most commonly used primary battery for small consumers, high resilience and good shelf life, good value. For use in portable and stationary devices with a low power requirement.
Anode
Electrode where electrochemical oxidation occurs. The oxidation is related to the anode giving up electrons: current flows outwards. To balance the charge, there is a simultaneous flow of anions to the anode in the electrolyte.
Attention! In secondary systems, the same electrode functions as a cathode and an anode, depending on whether the system is being charged or discharged!
Battery
The word battery is normally used as a global term for an electrochemical energy store. Strictly speaking, the term battery designates an array of similar objects - so in the case of electrochemical stores, an array of several cells used to maintain a certain operating voltage and/or capacity.
BattV, Battery Ordinance
On 27/03/1998, the German Federal Government passed an ordinance on the return and disposal of used batteries and accumulators. It is called BattV. This ordinance states, for example, that distributors are obliged to accept the return of used batteries from end users free of charge. The end user is obliged to return batteries containing harmful substances to a distributor or to the collection points which have been installed for this purpose by the public waste management organisations. The battery manufacturers and the Central Association of the Electrical Engineering and Electronics Industries (ZVEI) have founded the Common Battery Return System Foundation (GRS Batterien) for this purpose.
Capacity
Amountof current [Ah] which can be drawn from an electrochemical energy source at nominal load. Nominal load [A] x time until the discharge cut-off voltage [h] is reached.
Cathode
Electrode where electrochemical reduction occurs. The reduction is related to the anode gaining electrons: current flows into the electrode from outside. To balance the charge, there is a simultaneous flow of cations to the cathode in the electrolyte.
Attention! In secondary systems,the same electrode functions as a cathode and an anode, depending on whether the system is being charged or discharged!
Cell, electrochemical
Every electrochemical energy store consists of at least one cell, i.e. a container containing two electrodes which are in intimate contact with an electrolyte and at which the electrochemical reactions take place.The electrodes are separated from one another electrically by a separator. Cells are manufactured in closed, gas-tight and open designs. Two electrode connections which are electrically insulated from one another - the positive and negative poles - are fed out of the casing. When the two poles are connected with an electric conductor (consumer, light bulb) an electrical current flows through this.
Charge cut-off voltage
The voltage [V] which may not be exceeded when a battery is being charged,e.g. 2.35 V/cell for a closed lead battery. If the charge cut-off voltage is exceeded, undesirable reactions take place in the cells,e.g. with an open lead-acid battery an unnecessary amount of water is decomposed and the battery becomes too warm (maintenance, service life,build-up of hydrogen gas). With other secondary systems, irreversible reactions can occur whereby the electrolyte is decomposed. With closed lead batteries, bubbles are formed in the gel-like electrolyte which greatly increase the internal resistance and also lead to an impermissible increase in pressure in the cell. With lithium batteries there is a danger that finely distributed metallic lithium isdeposited. This lithium reacts very easily with the electrolyte and maybe pyrophoric. Exceeding the charging voltage may also lead to 'thermal runaway'.
Charging methods
Depending on the electrochemical system and the design, various methods are used when recharging batteries for temporal control and to manage the course of the charging current and the charging voltage. The abbreviations for the most common methods for charging lead-acid batteries are: IU, IUW,IUIa, IoIa and W (see the relevant entries for explanations). Steca's processor-controlled chargers automatically adjust to the electrochemical systems and battery sizes. Some chargers also allow a deep discharge before the actual charging process in order to avoid the memory effect in NiCd cells.
Current collector
The active masses in electrodes often have relatively poor conductivity. To keep the voltage drop in an electrode low, the mass of electrodes is connected to a current collector with good conductivity. This may consist, for example, of a thin sheet or net of metal which is good at conducting electricity.
Discharge cut-off voltage
When this voltage value [V] is reached, the electrochemically active substances of an electrochemical energy source which are supplying energy have almost been completely converted - the battery is "empty". Primary systems have to be replaced at this point, secondary systems recharged. In some secondary systems, the voltage must not fall below this value, as this could lead to harmful processes taking place in the cells.
Dissociation
Dissociation is the ability of certain chemicals (acids, bases, salts) to split into charged particles in a solvent. In this way, common salt (NaCl) dissociates in an aqueous solution to sodium and chloride ions:
NaCl Na+ + Cl- ions are generally contained in a solvate shell, which means that solution molecules are more or less tightly bonded to the ion byvan der Waals and electrostatic forces.
Electrochemical cell
A system of two electrodes of different chemical compositions which are immersed in an electrolyte. As long as the element is not discharged, a voltage difference between the electrodes can be measured. If the electrodes are linked by an electron conductor (e.g. copper wire), an electrical current flows through this conductor. A half cell consists of just one electrode.
Each cell of a battery is an electrochemical cell. However, there are also so-called standard cells which used to serve as a voltage standard, such as the Weston or cadmium standard cell, with a voltage of 1.01830 volts at 20°C.
Electrochemical energy source/store
A system which converts chemical energy into electrical energy through electrochemical reactions or can store electrical energy in electrochemically active substances and release it again: batteries, accumulators, electrolytic capacitors, double layer capacitors, fuelcells.
Electrochemical reactions
Heterogeneous chemical reactions which take place at the boundary between electrode and electrolyte and are linked to a transfer of electrons between atoms -also called RedOx reactions. Oxidation is when electrons are given up by an atom (or an atom in a molecule), and reduction is where they are gained. When a zinc-manganese dioxide cell (alkaline-manganese battery) is discharged, the metallic zinc (Zn°) of the negative electrode oxidises to a divalent zinc compound by giving up 2 electrons:
Zn0 Zn2+ + 2 e-
Electrochemical series
A table of the voltage difference values of electrochemical half cells (electrodes) compared with the reference potential of the standardhydrogen electrode. Electrochemically active substances develop anequilibrium potential when they come into contact with an electrolyte which contains ions from the substance in solution. This means, for example, that per unit of time, the same number of ions dissolve by giving up electrons as are deposited by gaining electrons. If an electrode is immersed in a solution with a concentration of 1 mol/l of the associated ions, this is called standard electrode potential. The position of a metal within the electrochemical series shows the metal's tendency to dissolve by giving up electrons. For instance, the base metals, which are strongly negative in relation to the standard hydrogen electrode, react violently with water by accumulating bases and reducing the water to hydrogen gas. In other words, base metals give up electrons very easily, whereas the precious metal gold remains in the earth's crust over millions of years without reacting.
Theelectrochemical series can be used to easily ascertain the voltage (EMF) of a combination of half cells by adding their numeric values.
Electrochemistry
A branch of physical chemistry that studies the phenomena which occur when electrons are transferred between electrodes and electrolytes.
Electrode
Positive or negative electrode = the part of an electrochemical cell at or in which electrochemical reactions occur through the loss or gain of electrons. An electrode can consist of a pure chemical element which conducts electricity (e.g. zinc sheet) or of a specially manufactured active mass with several constituents [e.g. the electrochemically active mass lithium cobalt dioxide together with current collector, graphite powder (to improve the electrical conductivity), polyvinylidene fluoride (as a mechanical binding agent), etc.].
Electrolyte
In electrochemical reactions, ions are always being lost or gained by the active masses. This means that a transfer of ions from one electrode to the other is required in an electrochemical cell under load (flow of current through an external consumer, e.g. light bulb). This transfer takes place through a medium which contains the free ions in a sufficiently high concentration. An electrolyte can be a ceramic solid,a polymer with ionogenic groups, or a liquid with a dissolved, dissociated conducting salt. The charge transfer through ions within the cell is part of the flow of current outside the cell through the consumer.
EMF
Electromotive force = voltage produced by an electrochemical cell without a load.
Internal resistance
Sum of the resistances which the components of an electrochemical cell offer against the flow of electrical current. During charging/discharging a considerable voltage drop can occur on the internal resistance => reduction/increase in the terminal voltage, warming. Components: polarisation resistance of the electrochemical reactions, the ion flow resistance in the electrolyte and at the separator; ohmic resistances in the electrode connections, the current collector and in the active mass etc.. In batteries, the resistances of the cell connections and attachments are added to this.
IoIa charging
Initial charging with increased constant current up to the point where the gassing voltage of open lead-acid batteries is reached (Io). Charging then continues with a lower constant current, and is automatically switched off once the charge cut-off voltage is reached (Ia).
Ion activity
The effective concentration of the free ions of a substance in solution.The ion activity is only equal to the concentration of the substance in the case of very diluted solutions and the salts of strong acids or bases. At higher concentrations, the degree of dissociation must be taken into account, as a certain amount of the undissociated substances may also be present in the solution.
Ions
Electrically charged atoms or molecules. The electrical surplus charge comes about through a change in the valence of an atom (as part of a molecule) which is linked to the loss or gain of electrons. Cations are positively charged ions, and anions negatively charged. It is through ions that charge is transferred within an electrochemical cell. In an electrolyte, the charge of the ions is constantly compensated for by the corresponding amount of opposite ions, which makes the electrolyte electrically neutral.
Anions: SO42- (sulphate), Cl- (chloride). Cations: H3O+ (hydrogen), Ca2+ (calcium), Zn2+ (zinc), Li+ (lithium).
IU charging
Method of charging open lead-acid batteries whereby they are charged with a constant current (I) until the gassing voltage is reached, or with a decreasing current. From approx. 2.4 V/cell, this voltage is kept constant (U) and the battery continues to be charged with a decreasing current. A comparable charging method is used for modern Li-Ionbatteries, whereby the charging current is limited and the battery temperature is measured and taken into account as well, for safety reasons. Because no reversible overcharge reaction exists in these systems, the system-dependent charge cut-off voltage must be precisely adhered to, and must not be exceeded under any circumstances. Exceeding the charge cut-off voltage can lead to the batteries being destroyed. Because of these strict operating conditions, manufacturers only supply these batteries complete with supervisory circuits integrated into the case.
IUIa charging
Method of charging open lead-acid batteries whereby a constant current is used until the gassing voltage is reached (I). This voltage is then kept constant as the current decreases until a specified current strength is reached (U). This is kept constant whilst the voltage increases again until the cut-off voltage is reached (Ia).
IUW charging
Method of charging open lead-acidbatteries whereby the voltage is increased to more than the gassing voltage towards the end of the charging process. The purpose of this method is to accelerate the balancing processes in the battery.
Lead-acid battery, lead battery, starter battery (car)
Secondary system, 2.0 V, Pb/H2SO4/PbO2. Open and closed (gas-tight) designs. Good value, capable of overcharge (open design), good performance data. Used as a starter battery in cars, as storage for electric traction systems and for stationary stores in emergency power generators. The lead-acid battery is the most commonly used secondary system.
Leclanché cell, Zn-manganese dioxide battery, dry battery
Primary system, 1.5 V, Zn/NH4Cl/MnO2(C). The standard Leclanché element, introduced in 1866, is hardly used today due to the high mercury content in the zinc electrode - it has been displaced by alkaline-manganese cells. Use as cost-effective primary cell where a small power supply is required for intermittent operation. When it is discharged, the electrolyte is used up and turns solid => dry battery.
Lithium-carbon monofluoride cell
Primary System, 3.0 V, Li/organic solvent, LiBF4/CFx. Lithium cell with solid cathode made of carbon monofluoride. Electrolyte solutions with the conducting salts lithium tetrafluoroborate (LiBF4) or lithium arsenicfluoride (LiAsF4) dissolved in organic solvents such as butyrol actone,(THF), propylene carbonate (PC), dimethyl sulphide (DMSI) and dimethoxyethane (DME). High energy content, low self-discharge. Used primarily for devices with a low electricity requirement and long periods of use.
Lithium ion battery, Li ion battery
Secondary system, 3.6 V, Li(C)/organic solvent, Li-Salt/LiCoO2.
Since its introduction in 1992 by Sony, this has been a common lithium system for portable devices (mobile phones, laptops etc.). It was developed further to make large batteries of up to 40 Ah for electric traction.It is the rechargeable battery system with the best performance data on the market in terms of the ratio of stored energy to weight.
Lithium/lithium cobalt oxide battery with inorganic electrolyte solution
Secondary system, 3.9 V, Li/LiAlCl4×SO2/LiCoO2. Lithium/lithium cobalt oxidebattery with inorganic electrolyte solution (solvate complex made of lithium tetrachloroaluminate dissolved in liquid sulphur dioxide). At the development stage for heavy-duty applications (Fraunhofer Institute of Chemical Technology, ICT, Pfinztal). Capable of overcharge.
Lithium-manganese dioxide cell, Li/MnO2 cell
Primary system, 2.8 V, Li/organic solvent, LiClO4/MnO2. Lithium cell with high energy content and good low temperature behaviour. Cost-effective. Contains no heavy metals. Used for portable devices and buffer batteries.
Lithium polymer battery
Secondary system, 3.7 V, Li(C)/polym. Electrolyte/LiCoO2. Lithium battery with solid to gel-like polymer electrolyte layer which has good conductivity whilst also ensuring the electrical separation of the electrodes and the bond of the cell components. This cell structure allows thin film batteries to be manufactured, and is thus a favourable design for integration into portable devices.
Lithium-sulphur dioxide cell
Primary system,2.8 V, Li/Acetonitrile,LiBr/SO2(C). Lithium cell with high energy content, high resilience and good low temperature behaviour. Is used almost exclusively in the military sector due to the potential risks (inflammable, sulphur dioxide, metallic lithium).
Lithium-thionyl chloride cell
Primary system, 3.4 V, Li/LiAlCl4 in SOCl2 /SOCl2(C). Lithium cell with liquid cathode, very high energy content, low self-discharge and good low temperature behaviour. Mostly used in the military sector due to the aggressive ingredients.
Memory effect
The memory effect is a phenomenon which is observed above all in NiCd batteries which constantly remain connected to a charger. However, italso occurs to a lesser extent in Ni-metal hydride and other secondary systems. With this reversible effect a battery appears to remember that it was discharged by, for example, just 10% of its capacity. If the full nominal capacity is withdrawn, the terminal voltage falls significantly and control units assert that the battery is empty. This effect can be avoided by carrying out an occasional deep discharge -modern chargers therefore offer the option of fully discharging the cells before beginning to charge them.
Cause: two processes cause this behaviour in NiCd batteries. Firstly, when the cell is constantly being charged, the cadmium crystallites in the negative electrode constantly get bigger, which reduces the electrochemically active surface. With an electrode with a smaller active surface, greater polarisation (voltage drop) occurs under a current load. Secondly, the higher temperatures of a constantly charged cell result in the formation of the intermetallic compound Ni5Cd21, which can only be discharged at a 100 - 120 mV lower potential. Both processes can be reversed through deep discharge.
Negative pole
The cell connection from which electrons flow in the external circuit to the positive pole when a battery is being discharged. On some batteries, this pole is marked with a - sign and/or a blue or black colour.
Nickel-cadmium battery, NiCd battery
Secondary system, 1.2V, Cd/KOH/NiOOH. Robust, alkaline secondary system. Capable of deep discharge, high durability in discharged state, open and closed (gas-tight) design, good service life, good performance data. Used for portable devices and stationary emergency power systems.
Nickel-metal hydride battery, NiMH battery
Secondary system, 1.2 V, MH/KOH/NiOOH. Robust, alkaline secondary system. System and voltage compatible with NiCd battery. Capable of deep discharge,high durability in discharged state, closed (gas-tight) design, good service life, good performance data, high specific energy. Used in portable devices and electric traction.
Nominal load
The continuous current [A] for which the battery is technically designed. Batteries of the same size can be adjusted to various load cases through their design. The nominal capacity specifies a current at which the operating conditions are favourable and, for instance, the cells do not get too warm and the service life and the dischargeable capacity correspond with the expected values.
Output volume
Output per unit of volume = [W/l] nominal load [A] x mean discharge voltage [V] / volume [l]
Overcharge reaction
Electrochemical reaction which may take place towards the completion of a battery's charging process. The electrochemical reactions which are intended to allow the battery to store energy are largely complete at this point, and another power supply causes the overcharge reaction, e.g. the electrochemical decomposition of the sulphuric acids in open lead-acid batteries into hydrogen and oxygen (hydrogen gas, danger of explosion!).
Caution: not all batteries are capable of overcharge.
Although the overcharge reaction decreases the overall efficiency of the energy storage, this is accepted in the case of open lead-acid batteries. The batteries are operated with this gassing reaction over a limited period of time during charging so that the conversion is complete and the battery acid is well mixed.
Polymer electrolyte
Polymer electrolytes consist of a three-dimensional network of organic macromolecules which have dissociated functional groups chemically bonded to their thread-shaped matrix. The material is therefore made up of so-called fixed ions, e.g. sulphonic acid groups on the polymer matrix, and free lithium ions. Lithium ions are able to flow through such a plastic film in a lithium battery. The film does not conduct electrons, however, and so it insulates the positive electrode from the negative one as a separator. Polymer networks which contain an additional liquid organic phase in their molecular pore structure in which conducting salts are dissolved are also often called polymer electrolytes.
Positive pole
The cell connection to which electrons flow in the external circuit from the negative pole when a battery is being discharged. On most batteries, this pole is marked with a + sign and/or the colour red.
Potential, electrochemical
Electrochemically active substances develop an electrochemical potential when they come into contact with an electrolyte. The potential is a measure of the substance's electron affinity. In other words, the more negative the potential, the greater the substance's tendency to give up electrons and form cations. Thus the base metals, for instance, dissolve when they come into contact with water to form hydrogen (water is reduced), whilst the precious metals gold or silver show no reaction. Individual potentials cannot be measured. An electrochemical potential is always determined in relation to a reference electrode. The point of reference of the entire electrochemical series is the standard hydrogen electrode.
Primary system
An electrochemical energy store which converts chemical energy into electrical energy through electrochemical reactions. With a primary system, the reactions which take place are irreversible, which means that a primary cell can only be used once.
Rated voltage
Battery or cell voltage in volts [V] under nominal load (rated current). Thisis in contrast to the open circuit voltage or EMF: the values are normally fairly arbitrary. They normally refer to the typical voltage under the most common conditions of use.
Secondary system
Rechargeable battery / accumulator. An electrochemical energy store which converts chemical energy into electrical energy through electrochemical reactions. Because the reactions are reversible, the opposite process is also possible. The electrochemical reactions which have taken place during discharge can be reversed by applying an external voltage - the battery can be recharged. For some examples, see NiCd battery, lead-acid battery.
Separator
The separator divides two electrodes of an electrochemical cell in order to avoid an electrical short circuit between the electrodes. The separator must therefore consist of a material which does not conduct electricity but is nevertheless permeable to ions. Normally porous films made of plastics such as polypropylene or polyvinyl chloride are the most common separators, but glass fibre mats are also used. The material must be chemically inert in the extracellular environment and feature sufficient mechanical stability. Polymer or solid electrolytes such as ß-aluminium oxide are a special case. With these, the electrolyte also assumes the function of the separator.
Silver-zinc battery
Secondary System, 1.5 V, Zn/KOH/Ag2O. Rechargeable alkaline high-performance cell. The service life/number of cycles when fully discharged is relatively low (20 to 150). High costs (silver electrodes). Used in heavy-duty applications and in the military sector as a primary battery which can be activated (torpedo propulsion).
Size designations of round cells
There are international standards for designating cell sizes. These are not binding, however, and so manufacturers also use their own nomenclatures. Basically, there are three systems in use: ANSI, IEC and consumer nomenclature (the latter consists of terms such as 'micro' and 'mono'). Japanese manufacturers have introduced a simple nomenclature, particularly for Li-Ion cells, which uses the dimensions in mm directly as type labels. According to this system, the common cell type 18650 has the dimensions: Ø 18 mm, height 65 mm. The prismatic type 344814 has the dimensions: length 34 mm, width 48 mm, height 14 mm.
Solid electrolyte
Solid body which conducts ions. In high-temperature batteries of the sodium-sulphur type, pipes or cups made of ß-aluminium oxide are used as the electrolyte and separator. The ß-aluminium oxide conducts sodium ions sufficiently at temperatures of >300°C. Another example is rubidium silver iodide (RbAg4J5), which conducts silver ions even at room temperature and is used in the very long-life silver-iodine primary cells as a solid electrolyte.
Specific energy
Energy per unit of mass = [Wh/kg], mean discharge voltage [V] x current [A] x time [h] / weight [kg]
Specific output
Output per unit of mass = [W/kg], mean discharge voltage [V] x current [A] x time [h] / weight [kg]
Specific volume, energy density
Energyper unit of volume = [Wh/l], mean discharge voltage [V] x current [A] x time until discharge cut-off voltage is reached [h] / volume [l]
Standard hydrogen electrode
Point of reference on the electrochemical potential scale and the electrochemical series.
Definition: half cell consisting of a single platinum electrode. This is immersed in an aqueous solution which has an H+ ion activity of 1 and is purged with pure hydrogen gas at a pressure of 1013.24 mbar. This reference point is declared to be zero by definition and serves to determine the potentials of other electrodes.
Thermal runaway
This term designates the overheating and destruction of primary and secondary cells which can occur in extreme situations. A thermal runaway occurs due to excessive and self-reinforcing heat production in the cells and/or insufficient heat dissipation into the surroundings, and can lead to fire and explosions.
Causes: if, for instance, NiCd cells are charged with a constant voltage source without a current limit, they heat up towards the completion of charging. As they heat up, the electrolyte resistance decreases - this raises the current and the heating effect increases. At the same time, the EMF of the cells decreases at a higher temperature, which in turn causes an increase in the current. These processes are therefore self-reinforcing and can lead to the cells being destroyed. Chargers therefore put a limit on the current and/or the charging time. For larger charging stations, the cell temperature can also be taken into account for regulating the charging process. Primary and secondary lithium cells have a high energy content. They contain substances (organic solvents, metal oxides etc.) which can chemically react with one another, and which are only prevented from doing so by kinetic inhibition (low reaction rate) and a low temperature. When the cell temperature increases, however, (120 °C) these internal reactions begin taking place on a considerable scale and may supply so much heat that this can no longer be dissipated into the surroundings. As a result, the cell heats up, even without an electrical load, the temperature rises and the reaction rate increases. With this greater reaction rate, heat which cannot be dissipated is produced even more quickly, and the self-reinforcing process culminates in the failure of the battery.
W-charging
During the charging process, the charging current falls to the charge cut-off current as the battery voltage increases, and is then switched off automatically (Wa) or by hand (W). Chargers with W characteristic curves are not available from Steca, as these are only suitable for non-professional applications. Steca only offers processor-controlled chargers.
Zinc-manganese dioxide battery, zinc-manganese dioxide cell, dry battery
Primary system, 1.5 V, Zn/ZnCl2/MnO2(C). Further development of the Leclanché cell for higher resilience - the ammonium chloride in the electrolyte has in most cases been replaced with zinc chloride. The resulting increased Zn corrosion is prevented by inhibitors (previously mercury chloride and cadmium, now more often organic chemicals). For a low current load, but suitable for continuous operation. Like the Leclanché cell, the system is now being displaced by the alkaline-manganese system (better resilience and lower self-discharge).