What are Batteries?

A battery is simply an electrochemical cell or group of cells that generate electric current. Batteries are the devices that generate current using redox reactions. These reactions proceed by the transfer of electrons. An ideal battery or cell should produce a constant voltage. A battery should actually be light in weight.

What are the Different Types of Batteries?

Basically, batteries are characterized into two main categories:

Primary Cells or Batteries

Primary cells or batteries are one-time-use batteries and cannot be charged again. They generate current through unidirectional and irreversible chemical reactions. These cells become dead after some time. Its examples include the Daniel cell, mercury cell and dry cell.

Secondary Cells or Batteries

The secondary cells or batteries are also termed repeated action cells or lead storage batteries. They are rechargeable and are frequently used in automobiles, cars, etc., to generate power. It is inexpensive and produces the high voltage required by automobiles.

Types of Primary Cells

Primary cells are capable of generating power with the use of a single chemical reaction. Various types of primary cells used in our day-to-day life are discussed below.

Daniel Cells

The Daniel cell involves the redox reaction that occurs between cupric ions and zinc to generate electricity or power. It consists of a copper vessel filled with copper sulfate solution acting as a depolarizer and diluted sulfuric acid acting as an electrolyte. A zinc rod is immersed in a zinc sulfate solution.

The Daniel cell uses a zinc rod bathed in zinc sulfate solution. At the left, the Zn electrode acts as an anode, and at the right, the Cu electrode acts as the cathode.

The construction of a Daniel cell is as follows:

An image shows Daniel's cell with a zinc electrode immersed in zinc sulfate, acting as an anode at the left. A copper electrode immersed in a copper sulfate solution acts as a cathode at the right. Both electrodes are connected via a salt bridge, and the flow of electrons is from anode to cathode.
CC BY 3.0 | Image Credits: https://commons.wikimedia.org | Rehua

The zinc metal oxidizes at the anode with the liberation of two electrons, and they travel from anode to cathode via a metal wire connecting both the electrodes. The electrons’ flow generates power opposite to its flow, i.e., from cathode to anode. Salt bridge helps in completing the inner circuit. It produces an e.m.f of 1.1 V.

At the anode, ZnS→Zn2+aq+2e-

At the cathode, Cu2+aq+2e-→CuS

The overall redox reaction in the cell is: ZnS+Cu2+aq→CuS+Zn2+aq

Mercury Cells

Mercury cells function by electron transfer between zinc and mercury oxide electrodes. The cathode comprises pure mercury (II) oxide (HgO), and the anode comprises zinc compounds. NaOH or KOH acts as an electrolyte that ionizes to conduct electricity.

The construction of a mercury cell is as follows:

An image shows a mercury cell with an anode cap, zinc anode and mercury (II) oxide acting as a cathode.
Representation of mercury cell

At the anode, ZnHg+2OH-aq→ZnO+2e-+H2OI

At the cathode, HgO+H2O+2e-→Hgl+2OH-aq

The overall redox reaction is: ZnHg+HgO→ZnO+Hgl

Mercury cells have the following features:

  • Produce a constant voltage of 1.35 V.
  • Inexpensive.
  • Long life and high capacity.

Dry Cells

Dry cell or LeClanche cell is composed of a zinc container that serves as an anode. The outer zinc content is crinkled from inside through a spongy paper, and the carbon rod serves as a cathode.

The space between anode and cathode is occupied by a mixture of manganese oxide, ammonium chloride, zinc chloride, and charcoal.

An image shows a dry cell with graphite rod as cathode, zinc container as the anode, and a paste of ammonium chloride and manganese oxide filled in between them.
Representation of dry cell

The reactions involved at both electrodes are as follows:

At the anode, ZnS→Zn2+aq+2e-

At the cathode, MnO2+NH4-+e-→HOH+NH3+Mn2O3

Unlike its name, the dry cell carries a wet mixture of ammonium chloride and manganese oxide. It produces a power of 1.5 V.

Secondary Cell or Lead Storage Battery

Secondary cells are used in automobiles. The lead storage battery is basically rechargeable and is capable of generating high power.

An image shows a lead storage battery with plates supports and positive and negative terminals.
Representation of lead storage battery

Every cell present in this battery produces a voltage of 2 V. When six such cells are  connected in series, they can generate 12 V car battery. Due to their high-power generation capacity and cost-effectiveness, they serve as an excellent source of power for automobiles starter motors.

At the anode, Pb(s)+HSO4-(aq)PbSO4(s)+H+(aq)+2e-

At the cathode, PbO2(s)+HSO4-(aq)+3H++2e-PbSO4(s)+2H2O(l)

The overall redox reaction is: Pb(s)+PbO2(s)+2H2SO4(aq)PbSO4(aq)+2H2O(l)  

Here, the forward reaction gives solid lead (II) sulfate, which helps build plates and decreases the sulfuric acid concentration. When a car runs, its generator helps to recharge the battery. During this process, the given overall reaction proceeds in the backward  direction. Thus, lead is regenerated.

Some Other Types of Battery

Lithium-Ion Batteries

Many portable devices involve the use of popular rechargeable batteries. They produce a constant voltage of 3.7 V. They provide a large voltage. These are designed to last 15 or more years. In a lithium battery, metal lithium acts as an anode and the charge tends to move from anode to cathode.

Button Cell

As the name suggests, it is a button-like cell with a diameter of 5–25 nm. Its anode is  lithium or zinc and its cathode is manganese dioxide.

Common Mistakes

Students may get confused with primary and secondary batteries. Both are used to generate power, but the primary battery cannot be used again.

  • The reaction involved during the charging of a secondary battery is just the reverse of the reaction involved during the discharging of the battery.
  • Primary batteries offer high resistance, while secondary batteries offer less resistance.
  • Primary batteries are used in small devices such as watches, torches, etc., whereas secondary batteries are used in large devices such as automobiles.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, such as

Bachelors in Chemical Engineering

Bachelors in Chemistry

Masters in Pure and Applied Chemistry

Electrochemical cells

Galvanic cells

Redox reactions


Practice Problem

Q1: Which kind of batteries are used to generate a power of 1.5 V?

(a) Dry cells

(b) Leclanche cells

(c) Mercury cells

(d) Heavy cells

Correct option: (a)

Q2: Which batteries are employed in electric vehicles?

(a) Lithium-ion batteries

(b) Fuel cells

(c) Mercury cells

(d) Non-rechargeable batteries

Correct option: (a)

Q3: What is the purpose of connecting batteries in series?

(a) To reduce the voltage

(b) To increase the voltage

(c) To recharge the battery

(d) To increase the life of the battery

Correct option: (b)

Q4: What is the effect of connecting batteries in parallel?

(a) Provides a constant voltage in the circuit

(b) Increases the voltage in the circuit

(c) Completes the circuit

(d) Starts the circuit

Correct option: (a)

Q5: Daniel cell is a:

(a) Primary cell

(b) Secondary cell

(c) Tertiary cell

(d) Quaternary cell

Correct option: (a)

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