How a Battery is made?
How a Battery is made?
The battery is made of 6 equal cells that are connected to each other, each cell has plates with a negative charge and plates with a positive charge alternately.
The cells are separated so that either the positive or the negative charged plates (depends on the way of production) is inside an “envelope” with small holes that allows the acid to touch the plates but still separates the positive and the negative plates so that a shortage won’t occur, each cell has between 9 -33 plates, depends on the application and the size of the battery.
Production Stages
Plates
The primary material of which the plates are made of is Lead (Pb), the plate is made of a lead grid and lead acid which is spread over the grid.
Pure lead on its own is too soft to be a raw material for the grid it’s needed to add different substances including antimon and calcium in order to strengthen it.
The grids are being made with a special casting machine that gives the gird its unic shape.
There are several main kinds of grids including Lead-Antimon, Lead-Calcium and Lead-Calcium Silver, Each kind has its own unic benefits.
For example Lead-Calcium and Lead-Calcium Silver grids are more resistant to corrosion and there for “dry” more slowly than Lead-antimon grids.
Antimon causes the liquid to fade and that’s why you need to add purified water every now and then.
The advantage of using an antimon grid is the grid’s strength that helps increasing the battery’s time of service.
On top of the grid there is an active material that’s made mainly out of Lead-Acid and in technical terms is called “Pasta”.
Lead-Acid
The lead which makes the acid PbO is very clean and is contained with more than 99.98% pure lead.
The process of making the acid is made by streaming liquefied lead inside a machine that looks like a big pot that’s called Barton.
The oxygen in the air has a chemical reaction with the acid drops and creates a lead casing around each drop, after this chemical process the percentage of pure lead decreases to below 27%.
Active Material (Pasta)
After the acid is ready and has been cooled down the pasta is being made (positive and negative) which in turn is being smeared over the grids.
Then the acid is added to a large mixer and some special solid substances are being added in order to improve the qualities of the battery like fibers which gives the pasta enhanced mechanical characteristics.
The negative pasta is being added with materials that enhance the surface of the pasta and improves other chemical elements within the pasta that ultimately improves the batteries performance.
Those materials are being mixed by the mixer and then water and sulfuric acid are being added until there is a homogenous compound that has all of the desired qualities and characteristics.
When the pasta is ready it will be smeared over the plate using a special machine designed for it until ultimately all of the plate will be covered with pasta that’s made out of lead acid.
After that the plates are being dried, using a special oven for a few seconds for the surface to dry out and so that the plates won’t stick to each other while collecting them.
After the plates are collected they are immediately stored in the “healing” room.
The “Healing” Process
The curing/healing process is in order to decrease the percentage of free lead and to make the pasta chemically bond with the grid, and for the pasta to become pore with complete granules.
The kind of curing is according to the plate and the kind of battery that is being manufactured, mostly this process is two staged: the wetting phase and the drying phase.
In the wetting phase the plates are being entered a low temperature room in which they are getting slightly moisted for a few hours. After that in the drying phase the temperature is being increased in order to remove all of the moist, this takes several hours until the plates are fully dry.
In the end of this process the pasta is made out of sulfate lead PbSO4, lead acid PbO and some free lead.
Assembling
The plates and the envelopes are being stacked together in groups by a machine, all of the plates in the group will get soldered to one another by “dipping” the grids in melted lead. After that the group of plates will then be entered to the cells inside the battery’s plastic box until all six cells will be filled with plates and after that the plates will be soldered.
In the end of this stage a test will be conducted in order to guarantee there isn’t a shortage inside the battery. The box will be sealed with a fitting lid and the battery terminals will be soldered to the box and then polished. In the end of the assembling stage the cells will be filled with electrolyte, which is lead acid with a fitting concentration, and the batteries will be charged.
The Charging and Formation Phase
The batteries will now be put inside a “tub” that’s full with water not too deep to avoid covering the lid, and organized in a way that all of the positive terminals will point to one direction and the negative to another direction. Each battery has its own charging plan and time that varies according to the demands it’s required to.
In the formation phase the lead acid PbO will become PbO2.
In the end of the charging phase the specific gravity of the acid will be between 1.25-1.28 depends on the temperature for the application of the battery.
For example in Israel where it’s hot you need a specific gravity of 1.25 while in European countries where it’s colder you can make do with 1.28, the concertation has to be high enough in order to allow good ionic flow and to fulfill the electro-chemical requirements, but not too high to not hurt the envelopes and cause the corrosion of other parts within the battery cell, which will shorten the batteries time of service and will increase the self-discharge rate substantially.
Refinement
Eventually when the battery is ready it goes through a series of electrical tests in order to make sure it’s proper and safe for use. After that the battery will be washed, dried and will be branded with stickers accordingly.
And after that the battery will be ready for shipment.
Batteries after the refinement phase
After the refinement phase the batteries are ready to be shipped
General Chemical Reactions inside a Battery
The discharge process includes:
Pb+PbO2+2H2SO4 → 2PbSO4+2H2O
The charge process includes:
2PbSO4+2H2O→ Pb+PbO2+2H2SO4
During the discharge process the lead and lead dioxide will have a chemical reaction with the acid and there for lead sulfate and water will be created.
When you go to a fully charged mode, most of the lead sulfate PbSO4 will revert to lead Pb and lead dioxide PbO2. If you will continue charging the battery, the cell’s voltage will rise and a process of overcharge will be set in motion where Hydrogen and Oxygen will form and water will begin to fade as a result.
The nominal voltage for each cell in a Lead-Acid battery is 2V. The open circuit voltage is a direct function of the specific gravity of the lead acid and has range of between 2.125V for a cell with a specific gravity of 1.28 to 2.05 for a cell with a specific gravity of 1.21
During the discharge process the specific gravity of the acid decreases proportionally to the Ah/Hr discharge rate, and that’s why you can now the battery’s charge using only the acid’s specific weight.
