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Electrochemistry – Cells and Batteries

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A collection of electrochemical cells used as a power source is referred to as a battery. An oxidation-reduction reaction forms the basis of an electrochemical cell. In general, every battery is a galvanic cell that generates chemical energy through redox reactions between two electrodes. Batteries are globally used in several electronic devices as a source of power.

Working of a Battery 

The battery is an essential component that ensures the smooth operation of many electrical devices. It holds chemical energy and gives various devices electrical energy. The image given below shows us what a conventional cell(battery) looks like.

Cell or Battery

 

The battery’s capacity to work is supported by an electrochemical cell. Electrochemical cells can range in number from one to many in a battery. Two electrodes are present in every electrochemical cell, and an electrolyte separates them. One electrode produces electrons as a result of the chemical process occurring inside the cell. When the electrons start travelling, electricity is created. A chemical process takes place inside a battery, and the electrons move from one electrode to the next to create an electric circuit.

Let’s study battery features and types in the article.

Features of a Battery

A battery should have various features for it to be widely useable. Some of the most important features that a battery should have are,

  • For ease of transportation, it should be small and light.
  • It should last for a respectably longer time both when it is in use and when it is not.
  • A battery or cell must be able to supply a steady voltage. Additionally, the battery or cell’s voltage must not change while being used.

Different Types of Battery

There are primarily two types of batteries or functional cells used commercially.

  • Primary Batteries or Cells
  • Secondary Batteries or Cells

Primary Batteries or Cells

They are known by the name of non-rechargeable batteries. These are the batteries that are only useful when used once. These batteries are not rechargeable or reusable. Alkaline batteries and coin cell batteries are typical examples of primary batteries. Typically, watches, clocks, torches, and other inexpensive electronic gadgets use these types of batteries. These batteries only allow one direction for redox reactions.

Dry Cell

The dry cell, a type of household battery commonly used to power clocks, TV remotes, and other gadgets, is an example of a primary battery. In these cells, a carbon rod serves as the cathode and a zinc container serves as the anode. The cathode is surrounded by a powdered manganese dioxide and carbon combination. A moist paste made of ammonium chloride and zinc chloride is used to fill the area between the container and the rod.

These cells undergo the following redox reaction:

At anode:

Zn(s) → Zn2+ (aq) + 2e

At cathode:

2e + 2 NH4+ (aq) → 2 NH3 (g) + H2 (g)

2 NH3 (g) +Zn2+ (aq) → [Zn (NH3)2]2+ (aq)

H2 (g) + 2 MnO2 (S) → Mn2O3 (S) + H2O (l)

Overall cell equation is as follows:

Zn(s) + 2 NH4+ (aq) + 2 MnO2 (S) → [Zn(NH3)2]2+ (aq) + Mn2O3 (S) + H2O (l)

In the area between the cathode and the anode, there is a mixture of MnO2 and a viscous paste of charcoal, zinc chloride, and ammonium chloride (NH4Cl). The porous paper’s lining keeps the paste and zinc container from contacting each other directly. It serves as a bridge for salt. Pitch or wax is used to seal the cell from the top.

Mercury Cell

The mercury cell is a new type of cell that is used in small electrical circuits such as those hearing aids, watches, and cameras. A zinc anode and a mercury (II) oxide cathode make up this component. The electrolyte is a KOH and ZnO paste.

The cell undergoes the following reaction: 

At anode:

Zn(Hg) + 2OH¯→ ZnO(s) + H2O+ 2e¯

At cathode:

HgO(s) + H2O+ 2e¯ → Hg(l) + 2OH¯
 

Overall cell equation is as follows:

Zn + HgO(s) → ZnO(s) + Hg(l)

It has the benefit that its potential stays basically constant during the course of its existence. The mercury cell has a voltage of about 1.35 V.

Secondary Batteries or Cells

These batteries are also called Rechargeable batteries. These batteries are long-lasting, reusable, and excellent for a variety of uses. They are a little more expensive than primary batteries, but when used carefully, safely, and with caution, they last the users longer. Lead-acid batteries and lithium-ion batteries are a few common examples of secondary batteries. The primary applications for these batteries are robots, solar lighting, luxury toys, etc.

Lead Storage Battery

A lead storage battery used in cars and inverters can only be recharged a select number of times. A lead anode and a lead grid filled with lead dioxide make up the cathode of a lead storage battery. As an electrolyte, a 38% concentration of sulfuric acid is utilized.

At anode:

Pb → Pb2++ 2e

Pb+ SO42– → PbSO4 + 2e

At cathode:

2e+ PbO2 + 4H+ → Pb2++ 2H2O

2 e+ PbO2 + 4H++ SO42- → PbSO4 + 2H2O

These batteries can be recharged by transferring the charge in the other direction and reversing the process, which turns PbSO4 back into Pb and PbO2.

Overall reaction can be written as: 

2PbSO4 (s) + 2H2O → Pb(s) + PbO2 (s) + 2H2SO4

It functions as a voltaic cell and generates electricity when used to start the car’s engine. It functions as an electrolytic cell while being recharged.

Nickel Cadmium Storage Cell

Another rechargeable cell is the nickel-cadmium storage cell. Although it costs more than lead storage batteries, it lasts longer than lead storage cells. However, because it is lighter and smaller, there are certain benefits. Appliances that are portable and cordless can use it.

  • It has a cadmium anode and a metal grid acting as a cathode that contains NiO2.
  • The electrolyte used in this cell is KOH.

The reaction can be written as: 

At anode:

Cd(s) + 2OH¯ → CdO(s) +H₂O(l) + 2e¯

At cathode:

2Ni(OH3)(s) + 2e¯ → 2Ni(OH)2(s) +2OH¯(aq)

Overall cell equation is as follows:

Cd(s) + 2Ni(OH3)(s) → CdO(s) + 2Ni(OH)2(s) + H2O(l)

The reaction byproducts typically attach to the electrodes and can be changed back into something else by charging the cell. Similar to how a lead storage battery is charged.

Lithium Ion Battery

A lithium-ion battery is a specific kind of rechargeable battery that stores energy through the reversible reduction of lithium ions. It is the most common type of battery used in electric vehicles and portable consumer gadgets. Li-ion batteries don’t suffer from the memory effect, have low self-discharge, and have high energy densities.

During a discharge cycle, lithium atoms in the anode are ionized and separated from their electrons. The lithium ions move from the anode through the electrolyte to the cathode, where they combine with their electrons and turn into electrically neutral molecules. Because of their small size, the lithium ions can pass through a micro-permeable separator that separates the anode from the cathode.

Different materials can be used as electrodes in Li-ion batteries. The most common cathode and anode materials are lithium cobalt oxide (cathode) and graphite (anode), and these materials are most commonly found in portable electronic devices like laptops and cell phones. Lithium iron phosphate and lithium manganese oxide, which are used in hybrid and electric vehicles, respectively, are additional cathode components. Ether, a group of organic compounds, is frequently utilized in Li-ion batteries as an electrolyte.

Oxidation-reduction (Redox) reactions take place inside a lithium-ion battery.

Cathode is where reduction takes place. Lithium-cobalt oxide is produced, when cobalt oxide and lithium ions react (LiCoO2). The partial reaction is:

CoO2 + Li+ + e → LiCoO2

Anode is where oxidation takes place. There, lithium ions and graphite (C6) are formed by the graphite intercalation complex (LiC6). The partial response is:

LiC6 → C6 + Li+ + e

Complete reaction will be, (right to left = charging; left to right = discharging).

LiC6 + CoO2 ⇄ C6 + LiCoO2

Uses of Battery

Batteries are used for a variety of purposes. The most common uses of batteries are:

  • Batteries are used in Medical Equipment and Home Appliances.
  • Implantable medical devices like pacemakers and insulin pumps utilize bio-batteries.
  • Batteries are used in Construction.
  • Batteries can be used in toys as well as in different gifting products. 
  • Batteries are used in Emergency Response and Firefighting.
  • Batteries are used in Military Operations, surveillance, and spying devices.
  • Batteries are used in Electric and normal automobile batteries. 

Read, More

FAQs on Cells and Batteries

Question 1: What is a Battery?

Answer:

 A device that transforms chemical energy into electrical energy, one or more electrical cells make up a battery.

Question 2: What is the functioning of the dry cell?

Answer:

A wet paste of NH4Cl and ZnCl2 is present in the cell. A dry cell can only function if the paste inside it is moist. Even when the zinc container is not in use, the acidic NH4Cl paste continues to corrode it.

Question 3: What is Electrochemistry?

Answer: 

Electrochemistry is the study of how energy is stored in batteries and changed from one form to another. It is necessary for functioning of the batteries. 

Question 4: What is the life cycle of a battery? 

Answer: 

A battery is considered to have completed a cycle when it is fully charged and then drains to 80% of its initial capacity. The cycle life of a battery is determined by how many cycles it can go through.

Question 5: What are charging current and charging voltage?

Answer: 

Charging Current: It is the highest possible current that can be used to charge the battery.

Charging Voltage: It is the highest possible voltage that should be used to effectively charge the battery.


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Last Updated : 14 Feb, 2023
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