Batteries: Composed of 5 materials
Batteries are devices that store electrical energy in chemical form and then release it as direct current in a controlled manner. All types of batteries contain a positive and a negative electrode immersed in an electrolyte, and the complete set is housed in a container.
Most of batteries are lead-acid, which means that they have positive and negative electrodes made up of lead compounds in a dilute sulfuric acid electrolyte. Lead-acid batteries are secondary batteries, which means they can be recharged after they have been discharged. Primary batteries can be discharged only once and then must be disposed of, such as some types of radio and flashlight batteries.
Batteries how it works?
The positive electrode is composed of lead dioxide and the negative one of porous lead. When an electrical load (for example, headlights or a starter) is connected across the battery, a current flows through the battery electrolyte and through the external load. This causes the battery to discharge, which causes the chemical composition of both electrodes to transform into lead sulfate.
To recharge the battery, a current must be passed through it from an external source of electricity such as an alternator, a dynamo or a charging unit.In this way, the lead sulfate is transformed back into the original materials: lead dioxide and porous lead.
As the battery charges, electricity begins to break down (hydrolyze) the water in the electrolyte into its constituent elements, hydrogen and oxygen, which are released as gas. For this reason, batteries release gases when they are charged.
Batteries are made of?
Since the positive and negative electrodes are made of brittle materials, they need the mechanical support provided by a grid made of a lead alloy; lead alone would be too soft. In addition to supporting the electrodes (the active material), the grid also conducts electricity from the electrodes to the external load.
In principle, the electrodes are made up of a mixture of lead oxide and lead sulfate, which transforms into lead dioxide on the positive plate and into porous lead on the negative plate when the battery is charged for the first time. In addition, the negative electrode contains small amounts of additives to provide the battery with good discharge performance at low temperatures and thus improve starting. The combination of grid and electrode is what is commonly called the plate.
The electrolyte is dilute sulfuric acid. It acts as a conductor to transport electrical ions between the positive and negative plates when the battery is charged or discharged. The acid also participates in the discharge because the sulfate ions react chemically at the electrodes to produce lead sulfate.
The separator is an insulator that is placed between the positive and negative plate for short circuits. It must be microporous with very small holes to allow ions to flow through the separator from one plate to the other. In addition, it must be able to withstand the high temperatures and extremely acidic oxidation conditions encountered in a battery.
Most modern separators are made of microporous polyethylene, which has the right properties to meet the demanding conditions inside the battery.
Container and lid
They are usually made of polypropylene, which is a lightweight but strong plastic. Unlike some plastics, it does not become brittle in the cold and therefore can withstand shocks during handling. It is resistant to acid and fluids commonly found in a vehicle (gasoline, diesel, brake fluid, antifreeze).
What makes a battery maintenance-free?
30 years ago, batteries were leaking water at high speed and drivers were advised to check the acid level at their weekly checks. Modern maintenance-free batteries do not require water to be added throughout their useful life, under normal operating conditions. Coincidentally, over the same period of time, the battery life has doubled from 2 years to 4 or 5 years.
Previously, battery grids were made of an alloy of lead with 10 percent antimony; which was intended to provide rigidity since pure lead was too soft by itself. Unfortunately, some of the antimony dissolved in the acid, causing the battery to leak water.
With improvements in battery technology, we have been able to reduce antimony content from 10 percent to 1.5 percent, and this reduction has made the batteries low-maintenance. Now you only have to pay attention to them once a year.
The latest improvement has been the use of 0.1 percent calcium as a hardener in the gratings instead of antimony. This reduces acid contamination and reduces water loss, so the battery is maintenance-free and no need to add water during its life.
Modern vehicle charging systems allow only a small current to flow through the battery when it is fully charged. However, if there is a fault in the alternator, a much higher current will pass through the battery during the time the car is running. This current will cause the battery to lose water quickly, thus ending the maintenance-free characteristics of the battery, as well as reducing its life by damaging the positive grids.
An unmistakable sign of overload is the dark brown / black color on the underside of the vented plugs.
If an alternator (vehicle without start-stop) has a voltage higher than about 14.8 volts at normal temperatures, it is a sign that the charging system is faulty. The usual rectifier diode breakdown will see charging voltages of 16.0 V across the battery. The alternator should be repaired immediately to prevent further damage to the battery.
Note that in modern start-stop vehicles with energy recovery during braking, higher voltages (15.2 V) are used to minimize charging efficiencies and reduce alternator charging times.
Modern charging systems keep the battery in a high state of charge while the car operates under most operating conditions. However, the battery will discharge under abnormal conditions or if the vehicle is left stationary with a load on, for example the headlights. The battery of modern cars, when parked, is constantly discharged by components such as the computer, alarm systems, the clock, etc. and this will cause the battery to discharge. Depending on the vehicle, this process can take weeks or months.
Vehicle batteries are designed to accept some discharge and recharge cycles, but not for applications where there are constant charge and discharge cycles (deep cycles). Service batteries are designed for these types of applications and have a special structure that allows them to continuously deep cycle.
Continued deep cycling in vehicle batteries causes breakdowns because the active material on the positive plate will gradually fall to the bottom of the battery, reducing the ability of the plates to store electricity.
A large amount of small black / brown particles in the electrolyte clearly indicates that the battery has gone through a deep cycle.
Sulfation is a normal part of battery operation and occurs when the battery is discharged. When the battery is recharged, the sulphation (lead sulfate) is transformed back into active material.
If the battery is left discharged for a period of time, this sulfation slowly transforms until it can no longer be transformed into active material, and thus, after charging, the battery will not be able to return to its original performance. If the sulfation is severe enough, the car will not start. This is the problem that is usually called sulfation.
Insufficient charging occurs if the battery does not receive enough charge to return it to a fully charged state; which will slowly cause sulfation. This breakdown can occur if the car is only used occasionally for short trips or on urban start-stop engines. There may also be insufficient charge if the alternator voltage is between 13.6 – 13.8 volts.