Batteries are the most common power source for basic handheld devices to large scale industrial applications. A battery can be defined as; it is a combination of one or more electrochemical cells that are capable of converting stored chemical energy into electrical energy.
Working of Battery:
A battery is a device, which consists of a various voltaic cells. Each voltaic cell consists of two half cells connected in series by a conductive electrolyte holding anions and cat ions. One half-cell includes electrolyte and the electrode to which anions move, i.e. the anode or negative electrode; the other half-cell includes electrolyte and the electrode to which cat ions move, i.e. the cathode or positive electrode.
In the redox reaction that powers the battery, reduction occurs to cations at the cathode, while oxidation occurs to anions at the anode. The electrodes do not touch one another but are electrically connected by the electrolyte. Mostly the half cells have different electrolytes. All things considered every half-cell is enclosed in a container and a separator that is porous to ions but not the bulk of the electrolytes prevent mixing.
Each half cell has an electromotive force (Emf), determined by its capacity to drive electric current from the interior to the exterior of the cell. The net emf of the cell is the difference between the emf of its half-cells. In this way, if the electrodes have emf and in other words, the net emf is the difference between the reduction potentials of the half-reactions.
How to maintain the Battery?
To maintain the battery in good condition, battery equalization is necessary. Due to aging, all the cells do not charge similarly and some cells accept charge extremely fast while others charge gradually. Equalization can be done by marginally over charging the battery to allow the weaker cells also to charge completely. The terminal voltage of a completely charged battery is12V, automobile battery shows 13.8V in its terminals while a 12 volt tubular battery will show 14.8V. Automobile battery should be firmly fixed in the vehicle to avoid shake. Inverter battery should be placed on a wooden plank if possible.
2 Types of Batteries
1) Primary Batteries:
As the name indicates these batteries are meant for single usage. Once these batteries are used they cannot be recharged as the devices are not easily reversible and active materials may not return to their original forms. Battery manufacturers recommend against recharge of primary cells.
Some of the examples for the disposable batteries are the normal AA, AAA batteries which we use in wall clocks, television remote etc. Other name for these batteries is disposable batteries.
2) Secondary Batteries:
Secondary batteries are also called as rechargeable batteries. These batteries can be used and recharges simultaneously. They are usually assembled with active materials with active in the discharged state. Rechargeable batteries are recharged by applying electric current, which reverses the chemical reactions that occur during discharge. Chargers are devices which supply the required current.
Some examples for these rechargeable batteries are the batteries used in mobile phones, MP3 players etc. Devices such as hearing aids and wristwatches use miniature cells and in places such as telephone exchanges or computer data centre’s, larger batteries are used.
Types of Secondary (rechargeable) Batteries:
SMF, Lead Acid, Li and Nicd
SMF Battery:
SMF is a sealed maintenance free battery, designed to offer reliable, consistent and low maintenance power for UPS applications. These batteries can be subject to deep cycle applications and minimum maintenance in rural and power deficit areas. These batteries are available from 12V.
In today’s informative world, one can’t overlook the requirement for battery systems are designed to recover crucial qualified data and information and run basic instrumentations for desired durations. Batteries are required to deliver instant power. Unreliable and inferior batteries can result in the loss of data and equipment shutdowns that can cost companies considerable financial losses. Subsequently, the UPS segments calls for the utilization of a reliable and proven battery system.
Lithium (Li) Battery:
We all use it in portable devices such as cell phone, a laptop computer or a power tool. The lithium battery has been one of the greatest achievements in portable power in the last decade; with use of lithium batteries we have been able to shift from black and white mobile to color mobiles with additional features like GPS, email alerts etc. These are the high energy density potential devices for higher capacities. And relatively low self-discharge batteries. Also Special cells can provide very high current to applications such as power tools.
Nickel Cadmium (Nicd) Battery:
The Nickel Cadmium batteries have the advantage of being recharged many times and possess a relatively constant potential during discharge and have more electrical and physical withstanding capacity. This battery uses nickel oxide for cathode, a cadmium compound for anode and potassium hydroxide solution as its electrolyte.
When the battery is charged, the chemical composition of the cathode is transformed and the nickel hydroxide changes to NIOOH. In the anode, formation of Cadmium ions take place from Cadmium Hydroxide. When battery is discharged, the cadmium reacts with NiOOH to form back nickel hydroxide and Cadmium Hydroxide.
Cd + 2H2O + 2NiOOH —> 2Ni(OH)2 + Cd(OH)2
Lead Acid Battery:
Lead Acid batteries are widely used in automobiles, inverters, backup power systems etc. Unlike tubular and maintenance free batteries, Lead Acid batteries require proper care and maintenance to prolong its life. The Lead Acid battery consists of a series of plates kept immersed in sulphuric acid solution. The plates have grids on which the active material is attached. The plates are divided into positive and negative plates. The positive plates hold pure lead as the active material while lead oxide is attached on the negative plates.
A completely charged battery can discharge its current when connected to a load. During the process of discharge, the sulphuric acid combines with the active materials on the positive and negative plates resulting in the formation of Lead sulphate. Water is the single most important step in maintaining a Lead Acid battery. The frequency of water depends on usage, charge method and operating temperature. During process, the hydrogen atoms from the sulphuric acid react with oxygen to form water.
This results in the release of electrons from the positive plates which will be accepted by the negative plates. This leads to the formation of an electric potential across the battery. The electrolyte in the Lead Acid battery is a mixture of Sulphuric acid and water which has a specific gravity. Specific gravity is the weight of the acid-water mixture compared to equal volume of water. The specific gravity of pure ions free water is 1.
The lead-acid batteries provide the best value for power and energy per kilowatt-hour; have the longest life cycle and a large environmental advantage in that they are recycled at an extraordinarily high rate. No other chemistry can touch the infrastructure that exists for collecting, transporting and recycling lead-acid batteries.
Along with this article, Lithium ion battery is discussed with its advantages and disadvantages.
Working of Lithium – Ion Battery
Lithium –Ion batteries are now popular in majority of electronic portable devices like Mobile phone, Laptop, Digital Camera, etc due to their long lasting power efficiency. These are the most popular rechargeable batteries with advantages like best energy density, negligible charge loss and no memory effect. Li-Ion battery uses Lithium ions as the charge carriers which move from the negative electrode to the positive electrode during discharge and back when charging. During charging, the external current from the charger applies an over voltage than that in the battery. This forces the current to pass in the reverse direction from the positive to the negative electrode where the lithium ions get embedded in the porous electrode material through a process called Intercalation. The Li- Ions pass through the non aqueous electrolyte and a separator diaphragm. The electrode material is intercalated lithium compound.
The negative electrode of the Li-Ion battery is made up of carbon and the positive electrode is a metal oxide. The most commonly used material in the negative electrode is Graphite while that in the positive electrode may be Lithium cobalt oxide, Lithium ion phosphate or Lithium manganese oxide. Lithium salt in an organic solvent is used as the electrolyte. The electrolyte is typically a mixture of organic carbonates like Ethylene carbonate or Diethyl carbonate containing lithium ions. The electrolyte uses anion salts like Lithium hexa fluoro phosphate, Lithium hexa fluoro arsenate monohydrate, Lithium per chlorate, Lithium hexa fluoro borate etc. Depending upon the salt used, the voltage, capacity and life of the battery varies. Pure lithium reacts with water vigorously to form lithium hydroxide and hydrogen ions. So the electrolyte used is non aqueous organic solvent. The electrochemical role of the electrodes charge between anode and cathode depends on the direction of current flow.
In the Li-Ion battery, both the electrodes can accept and release lithium ions. During the Intercalation process, the lithium ions move into the electrode. During the reverse process called de intercalation, the lithium ions move back. During discharging, the positive lithium ions will be extracted from the negative electrodes and inserted into the positive electrode. During the charging process, the reverse movement of lithium ions takes place.
Advantages of Lithium – Ion Battery:
Lithium Ion batteries outperform NiCd batteries and other secondary batteries. Some of the advantages are
- Light weight compared to other batteries of similar size
- Available in different shape including Flat shape
- High open circuit voltage that increases the power transfer at low current
- Lack of memory effect.
- Very low self discharge rate of 5-10% per month. Self discharge is around 30% in NiCd and NiMh batteries.
- Eco-friendly battery without any free lithium metal
But along with the advantages, like other batteries, Li-Ion battery also suffers from some disadvantages.
Disadvantages of Li-Ion Battery:
- The deposits inside the electrolyte over time will inhibit the flow of charge. This increases the internal resistance of the battery and the cell’s capacity to deliver current gradually decreases.
- High charging and high temperature may leads to capacity loss
- When overheated, Li-Ion battery may suffer thermal run away and cell rupture.
- Deep discharge may short circuit the Li-Ion battery. So to prevent this, some makes have internal shut down circuitry that shut down the battery when its voltage is above the safe level of 3 to 4.2 volts. In this case, when the battery is not using for long time, the internal circuitry will consume power and drain the battery below its shut down voltage. So to charge such batteries normal chargers are not useful.
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