Lead accumulator

Lead accumulator for automobiles

A lead accumulator (short lead accumulator ) is an accumulator in which the electrodes consist of lead or lead dioxide and the electrolyte consists of dilute sulfuric acid . Lead and lead compounds are poisonous. Sulfuric acid is corrosive and destroys skin, bones and all organic tissue, but it is not toxic.

Lead-acid batteries are reliable and inexpensive for a service life of a few years. Compared to other types of accumulators, they have a large mass in relation to their volume and a low energy density of 0.11 MJ / kg. In terms of volume, the energy density is similar to that of other accumulators. The best-known application is the starter battery for motor vehicles. They are also used as energy storage for electric vehicles. Because of their large mass and their temperature dependence, however, they can only be used to a limited extent. The high weight can also be used to advantage, for example in forklifts , in which the lead-acid battery also serves as a counterweight on the rear axle.

history

By discovering the muscle contractions in dead frogs through contact with iron and copper, Luigi Galvani laid the foundation for the development of the galvanic cell by Alessandro Volta in 1792. Volta recognized that the twitching frog legs in Galvani's experiment had a physical basis, and he then examined it Contact voltage of different metals and developed the electrochemical series . In 1802 Johann Wilhelm Ritter developed a similar system, but Ritter's cells - in contrast to Volta's cells - were rechargeable after discharge. This rechargeable secondary system was a pre-form for the accumulators known today.

In 1854, the German physician and physicist Wilhelm Josef Sinsteden developed the first lead-acid battery. Sinsteden placed two large lead plates, which did not touch one another, in a vessel filled with dilute sulfuric acid. By connecting a voltage source and frequent discharging and charging (forming), it reached a measurable capacity after a certain time . Lead dioxide ( lead (IV) oxide ) formed on one of the plates and pure lead on the other. In 1859, Sinsteden's lead accumulator was further developed by Gaston Planté with a spiral arrangement of the lead plates. Accumulators have also recently been built according to this principle.

In industry there was initially hardly any use for electricity-storing cells, but this only changed twenty years later. In 1866 Werner von Siemens developed the electrical generator and the demand for ways to store electrical energy increased rapidly. In 1880, the lead-acid battery was decisively further developed by the French engineer Camille Alphonse Faure ; thanks to a coating of lead powder and sulfur, the lead-acid battery achieved a high capacity after just a few charging cycles (forming).

Henri Tudor's first major economic success was with his lead-acid batteries. As early as 1882, he is said to have succeeded in designing a direct current system using a waterfall, which could continuously recharge various lead-acid batteries. He used the water wheel of the mill on his parents' country estate, the so-called Irminenhof. He used this system to implement the electrical lighting in the Irminenhof. The Irminenhof was thus one of the first private buildings in Europe to have electric light throughout. The first big order for Tudor was the electric lighting in the city of Echternach in 1886.

In 1887 Adolph Müller founded the first battery factory in Germany, from which the VARTA Group later developed .

In 1910, 70,000 tons of lead were used for lead-acid batteries. They were used as stationary and transportable direct current sources for low-voltage technology.

construction

Schematic representation of the structure of the lead accumulator

Scheme of a cell of a lead-acid battery. In a 12 V accumulator, 6 cells are connected in series.

A lead accumulator consists of an acid-proof housing and two lead plates or groups of plates, one of which serves as a positive electrode and the other as a negative electrode, as well as a filling of 37 percent ( mass fraction ) sulfuric acid (H ₂ SO ₄ ) as the electrolyte . In the commercially available version, the electrode plates are nested tightly one inside the other, with separators in between, for example made of perforated, corrugated polyvinyl chloride (PVC), which prevent direct contact ( short circuit ). The connections and connecting straps for starter batteries are made of metallic lead.

In the discharged (neutral) state, a layer of lead (II) sulfate (PbSO ₄ ) is deposited on both electrode groups . When charged, the positive electrodes have a layer of lead (IV) oxide (PbO ₂ ), the negatively polarized electrodes consist of more or less porous lead (lead sponge).

The state of charge can be determined with a hydrometer ("acid siphon"). This works via the acid density of the battery acid : 1.28 g / cm³, corresponding to 100% charge, up to 1.10 g / cm³, corresponding to 0% charge.

The acid density is also a measure of the state of charge . With a charged battery it is approx. 1.28 g / cm³ (100% charge) and with a discharged battery 1.10 g / cm³ (discharge 100%, deep discharge). The charge or discharge state is linearly linked to the electrolyte density and changes per unit 0.01 g / cm³ by approx. 5.56%, for example 1.28 g / cm³ → 100%, 1.19 g / cm³ → 50%, 1.104 g / cm³ → 2% residual capacity.

Mode of action

Schematic representation of the discharge reactions

The operation of the lead-acid battery can be based at the charging and discharging or the current draw represent ongoing chemical processes.

The following chemical processes take place during discharge:

Negative pole:

${\displaystyle \mathrm {Pb+SO_{4}^{2-}\longrightarrow PbSO_{4}+2\,e^{-}} }$

Positive pole:

${\displaystyle \mathrm {PbO_{2}+SO_{4}^{2-}+4\,H^{+}+2\,e^{-}\longrightarrow PbSO_{4}+2\,H_{2}O} }$

The discharge consists in a spontaneous comproportioning .

When loading, the processes run in the opposite direction, it is a forced disproportionation .

The overall reaction when discharging and charging:

${\displaystyle \mathrm {Pb+PbO_{2}+2\,H_{2}SO_{4}\rightleftharpoons 2\,PbSO_{4}+2\,H_{2}O} }$

To the right, the lead-acid battery is discharged under energy output, and to the left under energy supply, it is charged.

From the electrochemical equivalents , a charge of 2 * 96485 A * s ( Faraday constant ) is calculated for the “electrical energy” . This corresponds to a lead battery with 53.6 Ah.

From the electrochemical voltage series one can now calculate the potential difference, i.e. ultimately the electrical voltage that arises.

${\displaystyle \mathrm {Pb+SO_{4}^{2-}\longrightarrow PbSO_{4}+2\,e^{-}} \quad |-0{,}36~\mathrm {V} }$

${\displaystyle \mathrm {PbO_{2}+SO_{4}^{2-}+4\,H^{+}+2\,e^{-}\longrightarrow PbSO_{4}+2\,H_{2}O} \quad |+1{,}68~\mathrm {V} }$

${\displaystyle E_{\mathrm {Ges} }^{0}=1{,}68~\mathrm {V} -(-0{,}36~\mathrm {V} )=2{,}04~\mathrm {V} }$

Self discharge:

${\displaystyle \mathrm {2\,PbO_{2}+2\,H_{2}SO_{4}\longrightarrow 2\,PbSO_{4}+2\,H_{2}O+O_{2}} }$

Lead (IV) oxide is not stable in sulfuric acid solution.

The overvoltage of the hydrogen, which makes charging a lead accumulator possible in the first place, slows this process down.

Usage properties

The nominal voltage of a cell is 2 V, but the voltage fluctuates between about 1.75 and 2.4 V depending on the state of charge and the charging or discharging current. The energy density is 0.11 MJ / kg (30 Wh / kg), while modern NiMH cells almost three times this value.

Lead accumulators can deliver high currents for a short time, so they have a high power density. This property is necessary, for example, for vehicle and starter batteries and is one of the strengths of lead-acid batteries. On the other hand, because of this property , short circuits lead to extremely high currents, which can lead to burns (heating of tools) or fires (wiring). In the event of a short circuit, the electrodes can become deformed.

To avoid accidental short-circuits, starter batteries should always be disconnected at the ground pole (negative pole in vehicles) and connected to this last. This avoids the possibility of a short circuit that can result from handling the positive pole and simultaneously touching the vehicle chassis when the ground pole is not disconnected (e.g. when a conductive tool slips off).

A lead accumulator can outgas if it is contaminated with precious metals . Parts of the noble metal are deposited on the lead electrode and thus reduce the overvoltage of the hydrogen . Oxyhydrogen gas can be produced, especially during charging . This can ignite through sparks and lead to dangerous deflagrations. There is a risk of sparks in particular when connecting or disconnecting the battery connections or in the event of electrostatic charging (for example the plastic housing due to rubbing) or after activating the starter due to induction voltages . Therefore, closed rooms in which lead-acid batteries are charged must be ventilated.

Care and lifespan

Sulphated lead plates of a 12 V 5 Ah accumulator.

Lead batteries can have a very long service life of several years. While insufficiently regulated accumulators can often only be used as starter batteries for 2 to 4 years, high-quality designs can fulfill their function for up to 10 years. Drive batteries (traction batteries) or storage batteries can have a service life of between 5 and 15 years, depending on quality and load. In lead-acid batteries of the same capacity and size, but with different weights, the heavier battery is usually more durable because the lead frames are stronger. The resilience when new is not directly influenced by this, since a weaker lead structure with a large active surface can be implemented (structuring). In general, accumulators age and count as wearing parts. This is for lead accumulators in the first place on the inner corrosion (with only external corrosion, see also: terminal grease ) of the lead frames, electrodes, in the formation of fine short circuits and to the sulfation of the lead which causes the PbSO that ₄ crystals to join forces in ever larger alliances. This reduces the electrochemically active surface of the PbSO ₄ . Due to this smaller surface, the PbSO _{4 dissolves} more and more poorly. It takes a very long time until a sufficiently high concentration of Pb ²⁺ is present. In addition, the electrical conductivity of sulfate is lower than that of lead. The resulting increased internal resistance of the cell leads to a greater voltage drop under load.

A suitable charge regulator must be used for charging , in order to avoid the harmful overcharging , especially with closed bonded lead batteries (lead gel, lead fleece) and to limit gassing . Overcharging is less critical in open lead-acid batteries with liquid electrolyte, since the losses caused by outgassing can be compensated with distilled water and the gassing leads to a thorough mixing of the acid and prevents disadvantageous acid stratification. Charge regulators suitable for lead-acid batteries provide a maximum charging current until the cell voltage has reached a typical value of 2.3 to 2.35 V, after which they keep the voltage constant.

Lead accumulators should not be deeply discharged (cell voltages below 1.8 V), as this can render the accumulator unusable. For economic reasons, the batteries should therefore not be discharged below 20% of the capacity, this corresponds to an electrolyte density of approximately 1.16 g / cm³. Below this value, an accumulator is considered to be deeply discharged and should be recharged as quickly as possible. A deep discharge protection can prevent deep discharge, while the charge controller protects against overcharging.

Impurities in the electrolyte such as iron or precious metal salts reduce the overvoltage of the hydrogen and therefore initiate a spontaneous self-discharge .

Charging method

Use a charger for charging . The electronic circuit contained in the device, the charge regulator , controls the charging process and implements the charging process.

Essentially, the charge goes through the phases

• Main charge
• Boost charge
• Equalization charge (wet batteries only)
• Charge hold (float)

Charge regulators suitable for continuous operation provide a charging current which in amperes (A) usually corresponds to 1/10 of the capacity in ampere hours (Ah) of the battery. This is maintained until the cell voltage has reached a typical value of 2.3 to 2.35 V. The operating mode is then automatically switched to constant voltage, which compensates for the self-discharge.

In the case of closed bonded lead batteries (lead gel, lead fleece), the charge controller is used in particular to avoid harmful overcharging and to limit gassing . In the case of cell voltage-controlled chargers, the cell voltage is monitored in the main charging phase until it has reached 2.35 V per cell. The charging voltage is then increased to 2.4 V for a few hours, and then reduced to the charge maintenance voltage.

With open lead-acid batteries with liquid electrolyte, overcharging is less critical, as the losses caused by outgassing can be compensated for with distilled water. Gassing is even desirable with wet lead batteries, since the rising gas bubbles cause the acid to circulate according to the principle of the mammoth pump and thus reduce the possible formation of acid layers of different densities over time.

use

Comparison of power and energy density of some electrical energy storage devices ( Ragone diagram ).

Reliability, availability and economic efficiency due to low costs are particularly important for use. In Germany, the lead-acid battery took an outstanding position in research and production due to the great experience gained from its use in submarines from the First World War . However, the economic viability of lead-acid batteries is increasingly in question due to the falling costs for other battery systems, especially in the case of robust lithium iron phosphate batteries . In addition, there is the disadvantage of high weight, which is an obstacle in electromobility , because it reduces the range of the vehicle. Compared to lithium accumulators, lead accumulators in stationary use (for example as solar batteries ) have the advantage that they do not require a battery management system to monitor the accumulator cells. Stationary storage systems with lead accumulators can therefore be offered more cheaply and usually work more economically than systems with lithium accumulators.

EFB / AFB car battery

An EFB (enhanced flooded battery) or AFB (advanced flooded battery) is an improved starter battery for vehicles with internal combustion engines.

Start-stop systems with EFB battery technology are used to reduce emissions through automatic engine shutdown . It is a further development of the conventional wet battery (accumulator). These batteries are deep-cycle and vibration-proof and have better aging stability, better charge acceptance and thermal stability than conventional starter batteries. They are cheaper than AGM batteries and are used where the deep discharge properties (deep cycle) of an AGM battery are not required. Another advantage is the longer shelf life of this battery. This not only benefits the dealers, but also the drivers who only use their vehicle seasonally. Its basic structure is similar to that of a conventional wet cell battery. The difference is in the details.

The addition of special carbon additives to the lead plates reduces sulfate formation and reduces internal resistance. The battery can be discharged more deeply and has a better charge absorption. It can be charged faster and has better thermal stability. This enables use in both cold and hot regions.

Another difference lies in the plate structure. The positive lead plates are packed in a special polyester fabric and placed in an ion-permeable pocket separator. The plate sets of an EFB battery have medium compression. After the EFB battery has been filled with liquid electrolyte, the polyester fabric soaks up and expands. This creates pressure on the positive plates, which gives the active material additional support.

Another possible use is in vehicles with strong vibrations such as tractors, off-road vehicles, excavators and boats.

Sealed lead-acid batteries

Lead-acid batteries can also be manufactured in a closed design, which can be operated in any position. These include the VRLA accumulators . The acid is bound in glass fiber mats (AGM, absorbing glass mat) or as a gel in silica . Your advantage is that when the cells are charged correctly, only a little oxyhydrogen is produced and there is no need to refill with distilled water. If too much gas is developed too quickly by charging with too high a voltage, pressure relief valves open before the housing bursts.

Even when charging according to regulations, some oxyhydrogen gas is produced, which recombines to form water on the negative electrode. However, some of the gas is inadvertently lost through diffusion and leaks. This is why VRLA accumulators slowly dry out. They are usually unusable after 4 to 5 years because of the increased internal resistance and reduced capacity.

Stationary application

Example of a small UPS with a lead-acid battery

Lead accumulators are primarily used as backup batteries . Backup batteries support or replace the power supply in the event of a failure. The high weight and volume only play a subordinate role. Application examples:

• Uninterruptible power supply (UPS) ( emergency power supply , alarm systems )
• central power supply systems for emergency lighting
• Solar batteries in photovoltaic systems ( island systems )

In many cases, lead-acid batteries are already being replaced by lithium-ion batteries . The currently (2019) higher purchase price, usually 4 times, is often offset by the higher performance and service life, usually 15 years.

Mobile application

Shelf with lead-acid batteries for a larger UPS

Lead accumulators are primarily used as starter batteries , but also as traction batteries in vehicles. Starter batteries provide electricity for starting an internal combustion engine with a starter and constantly buffer the on-board voltage. They supply electricity if the alternator fails and the engine is not running. Traction batteries provide the drive energy for vehicles. In forklifts , lead-acid batteries also serve as a balance mass (counterweight) for the load picked up in front of the front axle.

The lead-acid battery will gradually be replaced by other types of battery because of its high mass, low energy capacity and service life. Decentralized or mobile applications are rather rare today (2017) due to their high mass and are limited to a few applications (e.g. some household vacuum cleaners and electric fencers ). This contrasts with the robustness and good cold resistance of lead-acid batteries.

Compartment of an electric scooter with a lead-acid battery

Application examples:

• Starter batteries for vehicles with internal combustion engines
• electric wheelchairs
• older or inexpensive electric bicycles
• older or inexpensive electric scooters
• older electric cars
• electric forklifts
• Submarines and electric torpedoes

literature

• Chapter 16: Alvin Sakind, George Zuris: Lead-Acid Batteries. In: Thomas B. Reddy (Ed.): Linden's Handbook of Batteries. 4th edition. McGraw-Hill, New York 2011, ISBN 978-0-07-162421-3
• Karl-Joachim Euler: Sinsteden - Planté - Tudor. On the history of the lead accumulator. Comprehensive University of Kassel, Kassel 1980, OCLC 918271350 .
• Heinz Wenzl: Battery technology / optimization of the application - operational management - system integration. Expert-Verlag, Renningen-Malmsheim 2002, ISBN 3-8169-1691-0 .
• DAJ Rand, PT Moseley, J. Garche, CD Parker: Valve-regulated Lead-Acid Batteries. Elsevier, 2004, ISBN 0-444-50746-9 .
• Chapter 2.1. The lead accumulator. In: P. Birke, M. Schiemann: Accumulators: Past, Present and Future Electrochemical Energy Storage , H. Utz Verlag, Munich 2013, ISBN 978-3-8316-0958-1 , pp. 68–119
• Chapter 8 Lead-Acid Batteries. In: Dell, Rand: Understanding Batteries , Royal Society of Chemistry, 2001, ISBN 0-85404-605-4 , pp. 100-125

Web links

Commons : lead acid battery  - collection of pictures, videos and audio files

• Lead-acid battery internals, technical details
• Exide, December 2008: Manual for stationary lead accumulators (PDF; 3.1 MB), 101 pages, 3rd edition
• basytec, Andreas Jossen, The lead battery - basics, sealed design, aging
• Varta battery encyclopedia ( Memento from April 8, 2006 in the Internet Archive )
• Article about lead-acid batteries on elektronikinfo.de

Individual evidence

1. Jump up ↑ The Lead Acid Battery - Chapter 2: History. Retrieved October 21, 2009 . 
2. ↑ Jos. A. Massard: 1886–1996, one hundred and ten years of electric light in Echternach. (PDF; 13.6 MB) pp. 9–10 (108–109 according to page numbering) , accessed on October 21, 2009 . 
3. ↑ Batteries, charging concepts and chargers. (No longer available online.) EGSTON Holding GmbH , archived from the original on December 13, 2009 ; accessed on October 31, 2009 : "NiMH battery energy density up to 90 Wh / kg"  .
4. ↑ EN 50272-3
5. ↑ Rotek Bilder-Dienst: Diagrams of cycle stability , open circuit voltages during discharge , accessed March 23, 2012.
6. ↑ Battery Basics, Section Economic Consideration. RN-Wissen.de, accessed on September 14, 2014 . 
7. ↑ Winston Battery: Intelligent Uninterruptible Energy Storage Cabinet . Retrieved March 8, 2012.
8. ↑ Winston Battery: WB-LP12V90AH, data sheet block battery 12V 90Ah LiFePO4 as a starter battery . Retrieved March 8, 2012.