lead-acid batteries, invented by French physicist Gaston Planté in 1859, are the oldest type ofrechargeable battery🇧🇷 Despite a very low energy-to-weight ratio and low energy-to-volume ratio, their ability to deliver high peak currents means the cells maintain a relatively high power-to-weight ratio. These properties, together with their low cost, make them attractive for automotive use to supply the high current required by automotive starter motors.
Lead acid car battery
|Energy/Consumer Price||7 (sld)-18 (fld) Wh/US$|
|cycle stability||500-800 cycles|
|Nominal cell voltage||2.105 V|
When charged, each cell contains electrodes made of elemental lead (Pb) and lead(IV) oxide (PbO2) in an electrolyte of approx. 33.5%v/v(4.2 molar) sulfuric acid (H2ALSO4).
When discharged, both electrodes convert to lead(II) sulfate (PbSO4) and the electrolyte loses its dissolved sulfuric acid and becomes mostly water. Due to the freezing point depression of water as the battery discharges and the concentration of sulfuric acid decreases, the electrolyte is more likely to freeze in winter.
The chemical reactions are (from discharge to charge):
Due to the open cells with liquid electrolyte in most lead-acid batteries, overcharging at high charging voltages produces oxygen and hydrogen gases by electrolysis of water, forming an explosive mixture. The acidic electrolyte is also corrosive.
Practical cells are not generally made from pure lead, but have small amounts of antimony, tin, calcium, or selenium bound into the plate material to strengthen it and simplify manufacture.
Voltages for general applications
These are general voltage ranges e.gsix cellslead batteries:
- Idle (rest) at full load: 12.6V to 12.8V (2.10-2.13V per cell)
- No load when fully discharged: 11.8V to 12.0V
- Charged when fully discharged: 10.5V
- Trickle Charge (Float): 13.4 V for gelled electrolyte; 13.5V for AGM (absorbent glass mat) and 13.8V for flooded cells
- All voltages are 20°C (68°F) and must be adjusted to -0.022V/°C for temperature changes.
- Float voltage recommendations vary based on manufacturer recommendation.
- Accurate float voltage (±0.05V) is critical to longevity; Too little (sulfation) is almost as bad as too much (corrosion and electrolyte loss)
- Typical (daily) charging: 14.2V to 14.5V (depending on manufacturer recommendation)
- Equalizing charge (for flooded lead acid): 15 V for a maximum of 2 hours. The battery temperature must be monitored.
- Carburation Limit: 14.4V
- When fully charged, the terminal voltage drops quickly to 13.2V and then slowly to 12.6V.
Portable batteries such as miner's cap lamps (headlights) typically have two cells and use one-third of those voltages.
Measuring the state of charge
A hydrometer can be used to test each cell's specific gravity as a measure of its state of charge.
Since the electrolyte takes part in the charging and discharging reaction, this battery has a great advantage over other chemistries. It is relatively easy to determine the state of charge by simply measuring the specific gravity (S.G.) of the electrolyte, the S.G. decreases when the battery runs out. Some battery designs contain a simple hydrometer with colored floating balls of different densities. When used on diesel-electric submarines, the SG was periodically measured and written on a board in the control room to indicate how much longer the boat could remain submerged.
The lead-acid cell can be demonstrated using lead plates for the two electrodes. However, such a setup only produces about an ampere for postcard-sized boards, and only for a few minutes.
Gaston Planté found a way to provide a much larger effective surface area. Planté's production process remains largely unchanged and will continue to be used in stationary applications.
Faure's bonded plate construction is typical of car batteries. Each plate consists of a rectangular grid of lead bonded with antimony or calcium to improve mechanical properties. The grid holes are filled with a paste of red lead and 33% diluted sulfuric acid. (Different manufacturers vary the mix). The paste is pushed into the grid holes, which are slightly tapered on either side to better hold the paste. This porous slurry allows the acid to react with the lead inside the plate, increasing the surface area many times over. At this stage the positive and negative plates are similar, however the expanders and additives vary their internal chemistry to aid in operation. After drying, the plates are stacked with suitable separators and inserted into the battery container. Usually an odd number of plates are used, with one positive plate than one negative plate. Each alternate card is connected.
The positive and negative plates are manufactured already molded, so simply add sulfuric acid and the battery is ready to use. The positive plates are the chocolate brown color of lead(IV) oxide and the negative plates are the slate gray color of 'spongy' lead and are referred to as 'formed' in this charged state.
One of the problems with plates is that the plates increase in size as the active material absorbs sulfate from the acid during discharging and shrink as they release sulfate during charging. This will gradually loosen the plaques from the paste. It is important that there is space under the boards to contain this spillage. If it hits the plates, the cell short-circuits.
The paste contains soot,solid white(barium sulfate) and lignosulfonate. Blanc fixe acts as a seed crystal for the reaction of lead to lead sulphate. The Blanc Fixe must be fully dispersed in the paste to be effective. The lignosulfonate prevents the negative plate from forming a solid mass during the discharge cycle, allowing long needle-shaped crystals to form. Long crystals have a larger surface area and are easily converted back to their original state when loaded. Soot neutralizes the formation-inhibiting effect caused by lignin sulfonates. Sulfonated naphthalene condensate dispersant is a more effective expanding agent than lignosulfonate and accelerates formation. This dispersing agent improves the dispersion of barium sulphate in the paste, shortens the hydro-setting time, produces a more shatterproof panel, reduces fine lead particles and thus improves handling and bonding properties. It extends battery life by increasing end-of-charge voltage. Sulfonated naphthalene requires about one-third to one-half the amount of lignosulfonate and is stable at elevated temperatures.
Approximately 60% by weight of a lead-acid automotive battery rated at approximately 60 Ah (8.7 kg of a 14.5 kg battery) is lead or lead internal parts; The rest consists of electrolyte, separators and the housing.
Separators between the positive and negative plates prevent short circuits from physical contact, mainly from dendrites (“treeing”), but also from active material spillage. The separators impede the flow of ions between the plates and increase the internal resistance of the cell. Wood, rubber, fiberglass mat, cellulose, and PVC or polyethylene plastic have all been used to make separators. Wood was the original choice, but it has deteriorated in the acidic electrolyte. Rubber separators were stable in battery acid.
An effective separator must possess several mechanical properties; such as permeability, porosity, pore size distribution, specific surface area, mechanical design and strength, electrical resistivity, ionic conductivity and chemical compatibility with the electrolyte. In operation, the separator must have good acid and oxidation resistance. The area of the separator should be slightly larger than the area of the plates to avoid material short circuits between the plates. Separators must remain stable within the battery's operating temperature range.
Wet cell standby (stationary) batteries, designed to be deep discharged, are commonly used in large emergency power supplies for telephone and computer exchanges, mains energy storage, and off-grid electrical power systems. Lead-acid batteries are used in emergency lighting during power outages.
Traction batteries (driving batteries) are used in golf carts and othersbattery electric vehicles🇧🇷 Large lead-acid batteries are also used to power the electric motors in diesel-electric (conventional) submarines and also in nuclear submarines. Motor vehicle starting, lighting and ignition (automotive) batteries provide power to start internal combustion engines.
Valve regulated lead-acid batteries cannot leak their electrolyte. They are used in backup power supplies for alarm systems and small computers (particularly in uninterruptible power supplies), as well as for electric scooters, electrified bicycles, marine applications, battery electric vehicles or micro-hybrid vehicles and motorcycles.
Lead-acid batteries were used to provide heater voltage (usually between 2 and 12 volts, with 2V being most common) in early vacuum tube (valve) radio receivers.
starting the batteries
Lead-acid batteries used to start car engines are not designed for deep discharge. They have a large number of thin plates that are designed for maximum surface area and therefore maximum current output, but are easily damaged by deep discharge. Repeated deep discharges lead to loss of capacity and ultimately to premature failure as the electrodes disintegrate from the cycle due to mechanical stress. Starter batteries that are continuously trickle charged will corrode the electrodes and lead to premature failure. Starter batteries should be kept open but charged regularly (at least every two weeks) to prevent sulphation.
deep cycle batteries
Specially designed deep cycle cells are much less prone to cycling and are required for applications where batteries are regularly discharged such as B. Photovoltaic systems, electric vehicles (forklifts, golf carts, electric cars and others) and uninterruptible power supplies. These batteries have thicker plates that can deliver lesspeak current, but can support frequent discharges.
Marine/RV batteries, sometimes referred to as "leisure batteries," are something of a middle ground between the two, as they can be discharged more than car batteries but less than deep cycle batteries.
Fast and slow loading and unloading
The capacity of a lead-acid battery is not fixed but varies depending on how quickly it is discharged. There is an empirical relationship between discharge rate and capacity known as Peukert's law.
When a battery is charged or discharged, initially it only affects the reacting chemicals that are at the interface between the electrodes and the electrolyte. Over time, at the interface, which we call the "interfacial stress", these chemicals spread by diffusion throughout the volume of the active material.
If a battery is completely discharged (e.g. car light left on overnight) and then charged quickly for only a few minutes, it only builds up a charge near the interface during the short charging time. After a few hours, this interfacial charge spreads over the entire volume of the electrodes and electrolyte, resulting in an interfacial charge so low that it may not be enough to start the car.
On the other hand, if the battery is charged slowly, which takes longer, it will charge more because the interfacial charge has time to redistribute to the volume of the electrodes and electrolyte and still replenish the charger. .
If a battery is subjected to a rapid discharge for a few minutes (like starting a car that draws around 200 amps), it will also appear discharged. Most likely it just lost the interface load; After waiting a few minutes, it should appear ready to use. On the other hand, if a battery is slowly being discharged (e.g., with a car light on that only draws 6 amps), then if the battery appears to be discharged, it is probably completely discharged.
In a valve-regulated lead-acid battery (VRLA), most of the hydrogen and oxygen produced in the cells recombine in the water. Leakage is minimal, although some electrolyte still escapes when recombination cannot keep up with gas evolution. Because VRLA batteries do not require (and make impossible) regular checking of electrolyte levels, they are namedmaintenance-free batteries🇧🇷 However, this is a bit inappropriate. VRLA cells require maintenance. When electrolyte is lost, VRLA cells "dry out" and lose capacity. This can be determined by regular measurements of internal resistance, conductance or impedance. Regular testing will show if more extensive testing and maintenance is required. Recently, maintenance procedures have been developed that allow for "rehydration", often restoring significant amounts of lost capacity.
VRLA types became popular on motorcycles around 1983 because the acidic electrolyte is absorbed by the separator and cannot leak out. The separator also helps them withstand vibrations better. Due to their small size and installation flexibility, they are also popular in stationary applications such as telecom sites.
The electrical characteristics of VRLA batteries differ slightly from wet lead-acid batteries, which requires caution when charging and discharging.
Lead-acid batteries lose their ability to hold a charge if they are discharged for a long period of timesulfation, the crystallization of lead sulfate. They generate electricity through a double sulfate chemical reaction. Lead and lead(IV) oxide, the active materials in battery plates, react with sulfuric acid in the electrolyte to form lead sulfate. Lead sulphate initially forms in a finely divided amorphous state and readily converts to lead, lead oxide and sulfuric acid when the battery is recharged. As batteries undergo countless discharges and charges, lead sulfate slowly transforms into a stable crystalline form that will not dissolve on recharge. Thus, not all lead is returned to the battery plates and the amount of usable active material needed to generate electricity decreases over time.
Sulfation occurs in all lead-acid batteries during normal operation. It clogs the grids, prevents charging and eventually expands, cracking the plates and destroying the battery. Also, the sulfate portion (of lead sulfate) does not return to the electrolyte as sulfuric acid. The large crystals physically prevent the electrolyte from entering the pores of the plates. Sulphation can be avoided if the battery is fully recharged immediately after a discharge cycle.
Sulfation also affects the charge cycle, resulting in longer charge times, less efficient and incomplete charging, and higher battery temperatures.
Often the process can be at least partially prevented and/or reversed by a desulfation technique called pulse conditioning, in which short but strong current spikes are repeatedly sent through the damaged battery. Over time, this process tends to break down and dissolve the sulfate crystals, restoring some capacity.
Higher temperatures accelerate both desulfation and sulfation, although too much heat damages the battery by accelerating corrosion.
risk of explosion
Overcharging will electrolyze some of the water, releasing hydrogen and oxygen. This process is
Car battery after explosion
known as "gassing". Wet cells have vents to vent generated gas and VRLA batteries have valves installed in each cell. Wet cells come with catalytic caps to recombine emitted hydrogen. A VRLA cell will normally recombine any hydrogen and oxygen produced in the cell, but malfunction or overheating can cause gas to build up. When this happens (e.g. due to an overload), the valve releases the gas and normalizes the pressure, creating a characteristic smell of acid. However, valves can sometimes fail when dirt and debris builds up, which allows pressure to build up.
When the hydrogen and oxygen accumulated in a VRLA or wet cell is ignited, an explosion occurs. The force can rupture the plastic case or blow off the top of the battery, causing acid and debris to spurt out of the case. An explosion in one cell can ignite the fuel gas mixture in the remaining cells.
The cell walls of VRLA batteries typically swell as internal pressure increases. Deformation varies from cell to cell and is greatest at the ends where the walls are not supported by other cells. These pressurized batteries must be carefully isolated and disposed of, protected by goggles, overalls, gloves, etc.
According to a 2003 report titled "Getting the Lead Out" from the Environmental Defense and Ecology Center in Ann Arbor, Michigan, road vehicle batteries contained an estimated 2,600,000 tons (2,560,000 LT; 2,870,000 ST) of lead. Lead is extremely toxic. Prolonged exposure to small amounts of lead can cause brain and kidney damage, hearing loss and learning disabilities in children. The auto industry consumes over 1,000,000 tons (980,000 LT; 1,100,000 ST) each year, 90% of which goes into conventional lead-acid automotive batteries. While lead recycling is an established industry, over 40,000 tonnes (39,000 LT; 44,000 ST) end up in landfills each year. According to the Federal Toxic Release Inventory, an additional 70,000 tonnes (69,000 LT; 77,000 ST) are released during the mining and manufacturing process of lead.
Partly because of concerns about the environmental impact of improper disposal and lead smelting, attempts are being made to develop alternatives (mainly for use in the automotive industry). Alternatives are unlikely to replace them in applications such as engine starting or backup power systems as there is no cheaper alternative if weight is not an issue.
Lead-acid battery recycling is one of the most successful recycling programs in the world. In the United States, between 1997 and 2001, 97% of all battery lead was recycled. An effective pollution control system is a necessity to prevent lead emissions. Continuous improvements in battery recycling facilities and furnace designs are required to keep up with lead smelter emissions standards.
Chemical additives have been used since the 1950s to reduce lead sulfate deposits on plates and improve battery condition when added to the electrolyte of a vented lead-acid battery. These treatments are rarely, if ever, effective.
Two compounds used for such purposes are Epsom salts and EDTA. Epsom salt reduces internal resistance in a weak or damaged battery and can provide a small increase in lifespan. EDTA can be used to dissolve sulfate deposits from heavily discharged plaque. However, the dissolved material is no longer available to participate in the normal charge/discharge cycle, so a battery temporarily reactivated with EDTA should not have a normal life expectancy. Residual EDTA in the lead-acid cell forms organic acids that accelerate corrosion of lead plates and internal connections.
The active material changes its physical form during discharge, resulting in plaque growth, active material deformation, and active material detachment. Once the active material has fallen off the plates, no chemical treatment can put it back in place. Likewise, internal physical problems such as cracked circuit boards, corroded connectors, or damaged separators cannot be repaired chemically.
Corrosion of the external metal parts of the lead-acid battery results from a chemical reaction of the battery terminals, terminals and connectors. It can be caused by:
Corrosion on the positive terminal is caused by electrolysis due to an incompatibility of the metal alloys used in the manufacture of the battery terminal and the cable connector. White corrosion usually comes from lead crystals or zinc sulfate. Aluminum connectors corrode to aluminum sulphate. Copper connectors produce blue and white corrosion crystals. Minimize corrosion by coating them with a suitable rubber or plastic spray or using a commercially available product.
If the battery is heavily filled with water and electrolyte, thermal expansion can push some of the liquid out of the battery openings and onto the top of the battery. This solution can then react with the lead and other metals in the battery connector, causing corrosion.
Electrolyte can leak from the plastic seal where the battery posts penetrate the plastic case.
Acid fumes evaporating through vent covers, usually caused by overcharging, and poor battery case ventilation can allow sulfuric acid fumes to build up and react with exposed metals.