An accumulator or battery pack is a rechargeable electrical energy storage on an electrochemical basis. The Latin word accumulator means " collector " (Latin cumulus " heap ", accumulare " accumulate "). An earlier name for accumulators was a collector. The colloquial term for the "Battery " is not strictly correct.
A single rechargeable storage element is called secondary element or secondary cell, as opposed to not (or only very limited) rechargeable primary cells. Secondary cells can be - like primary cells and all power sources - interconnect, either in series ( to increase the usable electrical power ) or in parallel ( to increase the usable capacity or because of the suitability for higher currents ).
Since the voltage of each accumulator battery cell is determined by the materials used, the series circuit is commonly used to increase the voltage ( see Fig starter battery). The capacity and the possible amperage on the other hand depend on the size. Therefore, a parallel connection of several cells is usually not necessary; instead use an appropriately sized battery.
- 3.1 operation
- 3.2 Energy density and efficiency
- 3.3 amount of charge (capacity)
- 3.4 charging status
- 3.5 Self -discharge - recommended storage
- 3.6 battery types
- 3.7 New Developments
- 5.1 Areas of application
- 5.2 Selection criteria
Originally accumulator with a single rechargeable storage element meant (secondary battery ). Today, the term - at least in the general language - even rechargeable memory that consist of interconnected secondary cells. When it comes down to the difference, you should use more specific names.
- Single memory element: secondary cell, secondary cell, storage cell, battery cell
- Interconnected storage elements: for example, battery pack, battery of secondary cells
A battery in a technical sense, a combination of several similar galvanic cells or elements which are connected together in series. There are batteries from primary cells ( non-rechargeable) and those from secondary cells (rechargeable). Originally, with batteries, only those of primary cells meant. Since the spread of the rechargeable storage this restrictive definition is outdated.
In everyday language, but battery is used as a generic term for a (genuine) batteries, primary cells and secondary cells. It is therefore often spoken of " batteries " when in fact only some primary cells or secondary cells ( rechargeable battery cells ) are meant.
The confusion is also supported by the fact that both cell types are interchangeable sizes on the market and both are sometimes called battery. Batteries are rechargeable batteries in English ( " rechargeable batteries ").
Electrical equipment that can be operated with both primary and secondary with cells are therefore often simply called battery operated. Only if the daily use of the device, the recharging capability plays a special role, it is preferable battery operated the label. In the technical- scientific framework is called because of the dominance of English is increasingly of " rechargeable batteries " or " secondary batteries ".
Capacitors also store electrical energy and release it again, but not in chemical form, but in an electric field between the capacitor plates. They are therefore no batteries.
The first preform a rechargeable battery, which - in contrast to the cells of Alessandro Volta - after discharge was rechargeable, was built in 1803 by Johann Wilhelm Ritter. The best-known type of battery, lead acid battery, developed in 1854, the physician and physicist Wilhelm Josef Sinsteden. At the turn of the 20th century fed consisted of wooden lead-acid batteries for electric drive automobiles. The battery technology took in a rapid phase of development. Following from Telegraph Technical Reichsamt 1924 published text shows the example of the then-recognized telegraphy and telephony still young. Accumulators are here called " collectors " and " batteries " were collections of galvanic elements:
" Were for the telegraph as for the telephone wet and dry elements the main power sources. For the telegraph batteries were used primarily zinc -copper elements; in telephone service in addition were mainly wet zinc-carbon dry cells and in use. As a more powerful power sources have been after 1900 collectors who had been used sporadically since the year 1895, companies of the microphones in the largest telephone exchanges, introduced on a larger scale. [ ... ] To charge the 12zelligen battery was adjusted to the Office dynamos, (usually light or heavy oil engines ) were equipped with its own power plant or were driven from the local power network and the required DC power supplied in adequate current capacity and voltage. It was initially worked generally in alternating charging and discharging, ie alternately fed the battery the office, while the other was loaded. Later ( 1921) went on to be to remove the power to the office immediately dynamos whose electrical properties had to be specially adapted for this purpose, and to switch them, Puffer' battery in parallel. "
In a battery during the charging electric energy is converted into chemical energy. If a load is connected, the chemical energy is converted back into electrical energy back (see: Galvanic cell). Typical of an electrochemical cell electric rated voltage, efficiency, and the energy density vary depending on the type of materials used.
Energy density and efficiency
For many applications, especially for mobile devices such as hearing aids or vehicles, the energy density is important. The higher this is, the more energy can be stored in a battery per unit mass. At identical temperature accumulators have approximately one quarter to one half of the energy density of the primary cells (secondary cells). At 30 ° C lower than conventional batteries or 200 Wh / kg, while primary cells reach values of about 400 Wh / kg, such as the zinc -air battery. An exception prototypes such as the lithium-sulfur battery dar.
Often batteries are equipped with very high energy density disproportionately expensive or have other adverse properties, particularly a limited life. For lead-acid batteries typically cost € 100 / kWh; Li -Ion batteries on the other hand currently (2012 ) is typically € 350 / kWh (200 € / kWh in 2013 ), falling. Causes are incipient mass production, which significantly reduce the unit costs through better technologies and economies of scale. However, the declining production costs not be passed on to customers, since only a small price pressure exists in this market, especially in Germany, by the few offers.
The charging and discharging of accumulators is released by the internal resistance of the cell heat whereby a portion of the energy expended to charge is lost. The ratio of the removable to be expended to load the energy is referred to as charging efficiency. Generally, the charging efficiency decreases both fast charge at very high currents as well as by rapid discharge ( Peukert effect), since the losses at the internal resistance increase. The optimal use of window is strongly dependent on the cell chemistry.
A comparison for storing electrical energy shows the advantages and disadvantages of batteries over other storage methods.
Amount of charge (capacity)
The amount of charge a battery can store, is expressed in Ampere hours (Ah ), and referred to as capacity (nominal capacity). This should not be confused with the capacitance of a capacitor, the ampere second per volt ( As / V ) is defined and in the unit farad (F) is specified. The rated capacity of the battery is always related to a particular discharge and takes particular strong at higher discharge currents from.
State of charge
An important parameter for battery-operated devices is the state of charge of batteries (English state of charge SoC). It is usually expressed in percentages, where 100% represents a fully charged battery. To determine different methods are used: chemical, voltage-dependent, flow - integrated, pressure-dependent as well as the measurement of the battery impedance. In practice, the voltage-dependent and current - accumulator inclusive and impedance method most commonly used.
Self-discharge - recommended storage
If a battery is not used, it loses over time some of its stored energy. This process is called self-discharge. The measure of self-discharge depends on the type and age of the battery and the storage temperature.
Most of the following is for the storage of batteries recommended: (Note:. Power is relatively the discharge voltage That is, if one battery has a charge level of 0%, then what is meant is that he has reached his final discharge voltage, for NiCd and NiMH batteries is this, for example, at 0.9 V and 1.0 V. )
- Li- Ion: charge level 60 %, 20 ° C; Self discharge per month <2%
- Lead-acid battery: Charging Condition 100 %, store in a cool place; Self discharge per month 5-10% (lead-acid ) and 2-5 % ( lead-gel ), a discharged battery is destroyed over time
- NiMH: 40 % charge level; Self-discharge on a monthly basis by 15-25 %, newer types than NiMH low self-discharge with only about 15% in
- NiCd: 40 % state of charge; Self discharge per month at 10 %
- Alkaline manganese RAM cells: state of charge 100%; Cell voltage should not drop below 1.2 V
Sanyo has launched 2005 ( launch in Europe August 2006) a modified called Eneloop NiMH battery on the market, subject to a self-discharge rate of only 15% per year. These are so-called LSD batteries ( Low Self Discharge), which are sold as pre -charged batteries because of their low self-discharge and, therefore, in contrast to conventional batteries before first use by the purchaser does not need to be recharged.
Any information relating to self-discharge refer to room temperature.
The accumulator types are designated according to the materials used:
- Li- Ion - Lithium Ion battery ( 3.2-3.7 V nominal voltage / cell), a generic term for secondary lithium batteries LiCoO2 - Lithium Cobaltdioxid - accumulator (3.6 V / cell), first available technology
- LiPo - Lithium - polymer battery (3.7V nominal voltage / cell), (type of polymer as the electrolyte )
- Li -Mn - lithium manganese battery ( 3.6V nominal voltage / cell)
- LiFePO4 - Lithium Iron Phosphate battery (3.3V nominal voltage / cell) LiFeYPO4 lithium iron phosphate secondary battery Yttrium ( yttria- doped to improve the properties )
Researchers at the Justus -Liebig- University of Giessen have developed together with scientists at BASF SE, a new reversible working cell based on sodium and oxygen. The reaction product in this case occurs Natriumsuperoxid. The charging and discharging to be significantly more efficient than in the case with this type of lithium-ion batteries.
Solid-state batteries are a special design, in which both electrodes and the electrolyte of various solid materials. Since no liquids are present, there is no problem with leaks, the battery should become damaged.
Also working on accumulators of organic material.
Lead-acid batteries typically cost € 100 / kWh; Li -Ion batteries on the other hand currently (1/ 2014) typically 150 USD / kWh bearish (2011: 500 € / kWh, 2012: 350 € / kWh, 2013: 200 € / kWh). Causes of the decline in prices are incipient mass production, which significantly reduce the unit costs through better technologies and economies of scale. In a lecture in October 2013, the trend researcher Lars Thomsen said at a conference for electric mobility that Tesla verbaue its batteries currently 200 USD / kWh, already by mid-2014 this price will fall below 120 USD / kWh. That was up to the introduction of nano-structures at the cathode. At the same time, the range will increase enormously.
Areas of application
Accumulators are often used when an electric or electronic device to be operated with no permanent connection to the fixed power supply or a generator. Since they are more expensive than non-rechargeable primary batteries, they are mainly used in such devices are used, which are used regularly and have a non-negligible power requirements, such as in mobile phones, laptops or cordless tools.
Even in vehicles is a battery in the form of the starter battery to provide power for light, on-board electronics and especially the starter to start the engine. If the engine runs, the battery on the machine operating as a generator light is recharged. The same applies to ships and aircraft.
When electric propulsion of motor vehicles, ships or even small aircraft whose batteries to distinguish from mere starter batteries are then called traction batteries and traction batteries connected together (see electric car, electric motorcycle, electric scooter, battery bus, electric trucks ).
Increasingly popular are pedelec, a special electric bike.
Batteries are also used to compensate for variations in the renewable generation of electricity with wind and / or sun (see solar battery ), or when a remote point of consumption can not or only at disproportionate cost to connect to the electricity grid. Often such consumption points are additionally equipped with an emergency generator that kicks in before the batteries are no longer sufficient after several days of no wind for example. Examples of such installations are not only secluded cabins, mobile phone base stations in less developed regions or space satellites, but also many parking ticket machines, in which a connection to the power grid would be more expensive than installing a solar cell and a rechargeable battery (see grid system, off-grid, off-grid system ).
Conventional submarine drives consist of diesel engines with generators ( driving and charging the batteries when not submerged drive) and with batteries powered electric motors ( dives ).
Many ships sail generally with electric drive. The required power is generated by diesel generators. Thus, the diesel engine can always operate at its optimum speed range, the energy is temporarily stored in batteries. There are also ferries that purely on electric power only battery driven and are each charged at the dock again ( sa diesel- electric drive).
Accumulators are used in systems for uninterruptible power supply (UPS) and for short-to medium-term bridge failures stationary energy supply. Key areas that need to hedge it with an emergency power supply, are, for example, data centers, alarm systems and life support systems in hospitals. If high performance is required or to bridge extended periods of time, a diesel generator is additionally installed; the batteries then take over the supply only as long as the diesel generator for starting and reaching the rated speed required. If the thus bridging time is short, other systems, this can take as accumulators, in particular on the basis of inertia or even capacitors.
Battery storage power plants are, inter alia, used to cover peak loads in the electricity grid and also to stabilize the grid in power grids.
Criteria for selection of an accumulator type for a specific application include:
- The gravimetric energy density. It tells how much electrical energy (eg kilograms ) can provide an accumulator per mass. This value is particularly interesting for electric vehicles. Conventional lead-acid batteries reach here around 30 Wh / kg, lithium -ion batteries (Li-Ion ) batteries up to 140 Wh / kg.
- The volumetric energy density. It tells us how much Wh of electrical energy can provide an accumulator per volume (for example, per liter of volume). Here, the value for conventional lead-acid batteries is about 50 Wh / l, with Li -Ion batteries about 500 Wh / l
- The maximum discharge current. It is important for all applications where a short period of very high power demand. This is, for example, when starting car engines the case, but also in power tools and auto focus cameras, especially with built-in flash devices.
- The possible dimensions (dimensions and weight) and designs of the battery cell. They are essential if the battery is to be integrated into the smallest possible space in electronic devices. A gas-tight construction such as a gel lead-acid battery allows the position-independent use without risk of leakage and or corrosive gases
- The memory effect of NiCd or NiMH battery inertia effect occurs at depends on the loading and unloading and leads to significant reductions in capacity ( NiCd) or voltage ( NiMH). In applications where the battery is not regularly fully discharge and then fully charged, so battery types should be used, which are not susceptible to these effects, such as lead-acid batteries.
The application of the above criteria are obtained for each battery type some typical application areas, where the transitions are fluid especially for NiCd, NiMH and Li -Ion batteries:
- Lead-acid battery: starter batteries for vehicles with internal combustion engines, stationary operation in emergency lighting systems and island photovoltaic systems
- NiCd battery: Power tools, drives in model, portable electronic device with briefly high current consumption (photo flash units ), traction batteries for electric cars, eg: Citroën AX electrique
- NiMH battery: portable electronic device with a constant current draw, model, electric cars, eg: GM EV1, Toyota Prius
- Li -ion battery: portable electronic devices with small dimensions and a long operating time (mobile phones, laptops, cameras )
- Li -Po battery ( Lipo, Lithium-Polymer): Drives in modeling, mobile phone, traction battery for extreme ranges, eg: Kruspan - Hotzenblitz
- Li -Mn Battery: Drives in modeling, new professional class of power tools, Pedelecs, vehicle battery for long ranges
- Li -Fe battery: Drives in modeling, new professional class of power tools, vehicle battery for long ranges
- Lithium ( Nano) -titanate battery: drive electric cars with large ranges
- No battery: but alkaline manganese cells in applications with as little energy consumption, run with it longer than a year, such as clocks, remote controls, thermometers, fire alarms, seldom used scales.
As an alternative to batteries and fuel cell systems will be discussed already used which will produce electric energy with the aid of hydrogen or of methanol from chemical energy. Fuel cells generate electrical energy without combustion and additional exothermic conversions. It should be noted that the energy output of the fuel cell can be varied little. In systems with fluctuating power demand (eg: hybrid electric vehicle), therefore, must always be used in addition also accumulators, but often remain ignored in comparisons.
In comparisons with a dedicated battery mode thus the steric bulk and weight of the fuel tank must be correctly addition to the actual fuel cell ( hydrogen bottles, methanol tank ) as well as the necessary buffer batteries are considered.
Competing energy storage are also hydraulic accumulator as well as electrochemical cells, such as the redox flow cell.