Lead-acid batteries can be classified as secondary batteries. The chemical reactions that occur in secondary cells are reversible. The reactants that generate an electric current in these batteries ( chemical reactions ) can be regenerated by passing a current through the battery (recharging).
Lead acid battery comes under the classification of rechargeable and secondary batteries. In spite of the battery’s minimal proportions in energy to volume and energy to weight, it holds the capability to deliver increased surge currents. This corresponds that lead acid cells possess a high amount of power to weight proportions.
These are the batteries that utilize lead peroxide and sponge lead to convert chemical energy into electrical energy. These are mostly employed in substations and power systems due to the reason they have increased cell voltage levels and minimal cost.
The chemical process of extracting current from a secondary battery (forward reaction) is called discharging. The method of regenerating active material is called charging.
In the lead acid battery construction, the plates and containers are the crucial components. The below section provides a detailed description of each component used in the construction.
This container part is constructed with ebonite, lead-coated wood, glass, hard rubber made of the bituminous element, ceramic materials, or forged plastic which are placed on the top to eliminate any kind of electrolyte discharge. Whereas in the container bottom section, there exist four ribs where two are placed on the positive plate and the others on the negative plate.
Here, the prism acts as a base for both the plates and additionally it safeguards the plates from short-circuit. The components that are utilized for the construction of the container should be free from sulphuric acid, they should not bend or permeable and do not hold any kinds of impurities which leads to electrolyte damage.
The plates in lead acid battery are constructed in a different way and all are made up of similar types of the grid which is constructed of active components and lead. The grid is crucial to establish conductivity of current and for spreading equal amounts of currents to the active components. If there is uneven distribution, then there will be loosening of the active component. The plates in this battery are of two kinds. Those are of plante/formed plates and Faure/pasted plates.
The formed plates are mainly employed for static batteries and they have heavyweight and expensive too. But they have long durability and these are not easily prone to lose their active components even in continuous charging and discharging processes. These have minimal capacity to weight proportion.
While the pasted process is mostly used for the construction of negative plates than that of positive plates. The negative active component is somewhat complicated and they experience a slight modification in charging and discharging processes.
The component which actively involves in the chemical reaction processes that happen in the battery mainly at the time of charging and discharging is termed as an active component. The active components are:
These are of thin sheets that are constructed of porous rubber, coated leadwood, and glass fiber. The separators are positioned in between the plates to provide active insulation. They have a grooved shape on one side and a smooth finish on other edges.
It has positive and negative edges having diameters of 17.5 mm and 16 mm.
As sulphuric acid is used as an electrolyte in the battery, when it gets dissolved, the molecules in it are dispersed as SO4– (negative ions) and 2H+ (positive ions) and these will have free movement. When these electrodes are dipped in the solutions and provide a DC supply, then the positive ions will have a movement and move towards the direction of the negative edge of the battery. In the same way, the negative ions will have a movement and move towards the direction of the positive edge of the battery.
Every hydrogen and sulfate ions collect one and two-electron and negative ions from the cathode and anode and they have a reaction with water. This forms hydrogen and sulphuric acid. Whereas the developed from the above reactions react with lead oxide and forms lead peroxide. This means at the time of the charging process; the lead cathode element stays as lead itself whereas the lead anode is formed as lead peroxide which is dark brown in color.
When there is no DC supply and then at the time when a voltmeter is connected in between the electrodes, it displays the potential difference between electrodes. When there is a connection of wire between the electrodes, there will be the passage of current from the negative to the positive plate via an external circuit which signifies that the cell holds the ability to provide an electric form of energy.
The lead–acid battery consists of two electrodes submerged in an electrolyte of sulfuric acid. The positive electrode is made of grains of metallic lead oxide, while the negative electrode is attached to a grid of metallic lead. Lead–acid batteries are classified into two types: flooded and valve-regulated.
So, this shows the lead acid battery working scenario.
The lead acid battery types are mainly categorized into five types and they are explained in detail in the below section.
Flooded Type – This is the conventional engine ignition type and has a traction kind of battery. The electrolyte has free movement in the cell section. People who are using this type can have accessibility for each cell and they can add water to the cells when the battery gets dried up.
Sealed Type – this kind of lead-acid battery is just a minor change to the flooded type of battery. Even though people hold no access to each cell in the battery, the internal design is almost similar to that flooded type one. The main variation in this type is that there exist enough amount of acid which withstands for the happening of smooth flow of chemical reactions throughout the battery life.
VRLA Type – These are called Valve Regulated Lead Acid batteries which are also termed as a sealed type of battery. The value controlling procedure permits for the safe evolution of O2 and H2 gases at the time of charging.
AGM Type – This is the Absorbed Glass Matte type of battery that permits the electrolyte to get stopped near to the plate’s material. This kind of battery augments the performance of the discharge and charging processes. These are especially utilized in the power sports and engine initiation applications.
Gel Type – This is the wet kind of lead-acid battery where the electrolyte in this cell is with silica-related which makes stiffening of the material. The recharge voltage values of the cell ate minimal when compared with other types and it has more sensitivity too.
The chemical reaction in the battery happens mainly during discharging and recharging methods and in the discharge process it is explained as follows:
When the battery is completely discharged, then the anode and cathodes are PbO2 and Pb. When these are connected using resistance, the battery gets discharged and the electrons have the opposite path at the time of charging. The H2 ions have a movement towards the anode and they become an atom. It comes in reach with PbO2, thus forming PbSO4 which is white in color.
In the same way, the sulfate ion has a movement towards the cathode and after reaching, the ion is formed into SO4. It reacts with lead cathode thus forming lead sulfate.
PbSO4 + 2H = PbO + H2O
PbO + H2SO4 = PbSO4 + 2H2O
PbO2 + H2SO4 + 2H = PbSO4 + 2H2O
During the recharging process, the cathode and anodes are in connection with the negative and positive edges of the DC supply. The positive H2 ions move in the direction of the cathode and they gain two electrons and forms as H2 atom. It undergoes a chemical reaction with lead sulfate and forms lead and sulphuric acid.
PbSO4 + 2H2O + 2H = PbSO4 + 2 H2SO4
The combined equation for both the processes is represented as
Discharge and Recharge Process
Here, the downward arrow indicates discharge and an upward arrow indicates the recharge process.
The optimum functional temperature for lead acid battery is 250C which means 770F. The increase in the range of temperature shortens longevity. A per the rule, for every 80C increase in temperature, it reduces the half-life of the battery. While a value regulated battery that functions at 250C has a lead acid battery life of 10 years. And when this is operated at 330C, it has a life period of 5 years only.
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