What Is Dry Cell?

A dry cell is one type of electric battery, which is generally used for the home and portable electronic devices. A battery is a device that consists of one or more electrochemical cells, which converts chemical energy into electrical energy. A dry cell is one of the electrochemical cells, developed by the “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 of 1887. Nowadays, most commonly used batteries are dry cell batteries, which vary from large flashlight batteries to minimized flashlight batteries and are mostly used in wristwatches or calculators.

A dry cell is an electrochemical cell consisting of low moisture immobilized 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 and the secondary cell. A primary cell is the 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

Dry cell - 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 electrolyte like ammonium chloride paste, which will produce a maximum of 1.5V of voltage and they are not reversible.

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The half cell reaction process has the following steps

Step 1:

During the process, a reduction reaction occurs within the moisturized 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:

Zinc container serves as an anode and undergoes an oxidation reaction

Zn → Zn2+ + 2e-

Zinc-carbon cell is the most common dry cell and is also called Leclanche cell. The alkaline battery has almost 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 same half-cell reactions as 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 is 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

Overall reaction of silver oxide cell in anhydrous medium

Secondary cell

1. Nickel-cadmium cell (NiCd cell)

The Nickel-cadmium cell comprises cadmium as an anode and Nickle 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 disposing, 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, 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 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 in size and lightweight.

Summary

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