What Is Dry Cell?

A dry cell is one type of electric battery which is generally used for home and portable electronic devices. A battery is a device that consists of one or more electrochemical cells, which convert chemical energy into electrical energy. A dry cell is one of the electrochemical cells developed by “German scientists Carl Gassner” in 1886, after the development of wet zinc-carbon batteries by Georges Leclanche in 1866. Modern dry cells were developed by Yai Sakizo, who is from Japan, in the year 1887. Nowadays, the most commonly used batteries are dry cell batteries, which vary from large flashlight batteries to minimised flashlight batteries, and are mostly used in wristwatches or calculators.

A dry cell is an electrochemical cell consisting of low moisture immobilised electrolytes in the form of a paste, which restricts it from flowing. Due to this, it is easily transportable.

Working Principle and Types of Dry Cells

Depending on the nature of the dry cell, it can be classified as a primary cell or the secondary cell. A primary cell is one which is neither reusable nor rechargeable. Once the electrochemical reactions consume all the chemical reagents, they fail to produce electricity. On the other hand, a secondary cell can be rechargeable by using battery charges to regenerate the chemical reactions.

Primary Cell

1. Zinc-Carbon Cell

A dry cell consists of a metal container in which a low-moisture electrolyte paste covers the graphite rod or a metal electrode. Generally, the metal container will be zinc, whose base acts as a negative electrode (anode), and a carbon road acts as a positive electrode (cathode). It is surrounded by manganese dioxide and low moisture electrolytes like ammonium chloride paste, which will produce a maximum of 1.5 V of voltage, and they are not reversible.

The half-cell reaction process has the following steps:

Step 1:

During the process, a reduction reaction occurs within the moisturised electrolyte, which comprises manganese dioxide (MnO₂) and ammonium chloride (NH₄Cl), and graphite serves as solid support for the reduction reaction

2NH₄⁺ + 2MnO₂ →Mn₂O₃ + 2NH₃ + H₂O

Step 2:

The zinc container serves as an anode and undergoes an oxidation reaction

Zn → Zn²⁺ + 2^e-

Zinc-carbon cell is the most common dry cell and is also called the Leclanche cell. The alkaline battery has almost the same half-cell reaction, where KOH or NaOH replaces the ammonium chloride, and half-cell reactions are

ZNCl₂ + 2NH₃ → Zn(NH₃)₂Cl₂

2MnO₂ + H₂ → Mn₂O₃ + H₂O

The overall reaction is,

Zn + 2MnO₂ + 2NH₄Cl → Mn₂O₃ + Zn(NH₃)₂Cl₂ + H₂O

2. Alkaline Battery

The alkaline battery will have almost the same half-cell reactions as the zinc-carbon cell, where KOH or NaOH replaces the ammonium chloride, and half-cell reactions are

Zn + 2OH^– → ZnO + H₂O + 2e^–

2MnO₂ + 2e^– + H₂O → Mn₂O₃ + 2OH^–

3. Mercury Cell

In the mercury cell, HgO serves as a cathode and zinc metal serves as an anode, and the reaction involves the following steps:

Step 1: At the anode

Zn + 2OH^– → ZnO + H₂O + 2e^–

Step 2: At the cathode

HgO + H₂O + 2e^– → Hg + 2OH^–

The overall reaction of the cell

Zn + HgO → ZnO + Hg

4. Silver Oxide Cell

In the basic medium, silver metal acts as inert support in the reduction of silver oxide (Ag₂O) and in the oxidation of zinc.

Step 1: Reaction at the cathode

Ag₂O + 2H⁺ + 2e^– → 2Ag + H₂O

Step 2: Reaction in the electrolyte

2H₂O → 2H⁺ + 2OH^–

Step 3: Reaction at the anode

Zn + 2OH^– → Zn(OH₂) + 2e^–

Step 4: Overall reaction

Zn + H₂O + Ag₂O → Zn(OH₂) + 2Ag

The overall reaction in an anhydrous medium

Secondary Cell

1. Nickel-cadmium Cell (NiCd Cell)

The Nickel-cadmium cell comprises cadmium as an anode and a Nickel plate as a cathode, and a separator acts as an insulator between the anode plate and cathode plate. Sodium hydroxide or potassium hydroxide acts as an electrolyte.

Note: On disposal, cadmium causes harmful effects on the environment. Therefore, these days NiCd cells are not in use.

2. Lithium-ion Cell

These are popular batteries used nowadays on laptops, iPods and cellphones. The electrodes of the cell are made up of lightweight carbon and lithium. They are low-maintenance batteries, and no memory is required to enhance battery life. They are less harmful even after disposing, and self-discharge is less than half of the NiCd cell.

3. Nickel-metal Hydride Cell

In the Nickel-metal hydride cell, NIMH acts as an anode and hydrogen-absorbing alloy acts as a cathode. The electrochemistry of the rechargeable Ni-MH battery is as follows:

Step 1: Reaction at the cathode

H₂O + M + e^– ⇋ OH^– + MH

Step 2: Reaction at the anode

Ni(OH)₂ + OH^– ⇋ NIO(OH) + H₂O + e^–

And at the end of the reaction, nickel oxyhydroxide NiO(OH) is formed.

Advantages of a Dry Cell

• They are easy to use in a simple electronic device.
• There is no worry about linkage in the dry cell.
• Dry cells are safe during transportation.
• They are small and lightweight.

Summary

• There are a variety of dry cells, some can be rechargeable, and some have limited shelf life.
• The battery should be stored in a cool place because the self-discharge of the battery accelerates at high temperatures.
• Depending on whether a dry cell is rechargeable or not, it is further classified as a primary cell and a secondary cell.