Why do we need a Battery and its Types

Key Concepts

1. The chemical reactions inside a cell

2. The structure of a battery

3. Differentiation between a primary cell and a secondary cell

4. Differentiation between a wet cell and a dry cell

5. Give examples of primary cell, secondary cell, wet cell, and dry cell from daily life.

Introduction

“My phone is discharged, let me put it up on charging,” you must have heard this statement so many times. The thing that gets discharged is “battery” and the way to charge it back is by plugging it into an energy source. In this section you are going to study about many such batteries and cells. You will also be learning about the composition of a battery and the chemical reactions that happen inside it.

Explanation:

Cell: 

It is a single electrochemical unit which has one cathode, one anode and an electrolyte. It converts chemical energy stored in it into electrical energy and vice-versa.  

The most common application of an electrochemical cell is in remotes and clocks.  

Let us have a look at an electrochemical cell and the reaction happening inside it.  

Zinc electrode is taken as anode and copper electrode is taken as cathode. The reactions which take place here are:  

Oxidation at the Zinc electrode (anode) : 

Zn (s)−−−−→ Zn+2(aq.)+2 e−Zn s−−−−→ Zn+2aq.+2 e−

Reduction at the Copper electrode (cathode): 

Cu+2(aq.)+2 e− −−−→Cu (s)Cu+2aq.+2 e− −−−→Cu (s)

2H+(aq.)+2 e− −−−→H2 (g)2H+aq.+2 e− −−−→H2 (g)

An electrochemical cell has two electrodes made of two different metals. Electrodes are in electrolyte, which is a substance that conducts electricity.  In an electrochemical cell, electrodes are usually made up of copper and zinc. Acidic electrolyte attacks zinc electrode, causing it to lose an atom but leaving electrons behind, resulting in oxidation of zinc. This makes zinc electrode negative. Electrons are pulled off from copper electrode resulting in reduction of copper making copper electrode positive. This difference in charges results in voltage across the battery. 

The symbol of a cell in circuit diagram is: 

Types of cell: 

On the basis of the times, they can be used, cells are classified into two categories: 

1. Primary cell 

2. Secondary cell 

Primary cell : These are the cells that can be used only once. Example: Zinc carbon cell. 

Secondary Cell : These are the cells that can be recharged and can be used again and again. Example: Nickel metal Hydride cells. 

Let us list the difference between the two: 

Battery: 

A collection of cells connected in series or in parallel makes a battery. 

A battery has two terminals. Terminal of the battery which gains electron becomes negatively charged and is known as negative terminal. Terminal of the battery which loses electron becomes positively charged and is known as positive terminal. When a battery is connected to any device, electrons start flowing through the wire from the positive terminal to negative terminal of the battery, thus switching “on” the device in the process. 

The symbol of a battery in circuit diagram is: 

Types of battery: 

 Based on the type of electrolyte a battery is classified into two types:  

1. Dry Cell  

2. Wet cell 

Dry cell: 

Dry cell is also known as leclanche cell. In a dry cell, the electrolyte is a moist paste. Few of the real-life applications of a dry cell are the batteries in devices like flash-light, portable CD players, and watches. They are small in size. There is no leaking of chemicals. It is easy to handle. It is expensive as compared to wet cell. It is difficult to manufacture. It cannot withstand overcharging. 

Wet cell:  

In a wet cell, the electrolyte is a fluid. Few of the real-life applications of a wet cell are the batteries in cars, motorcycles and electric wheelchairs. They are large in size. Corrosive chemicals tend to leak. It is difficult to handle. It is less expensive as compared to dry cell.  It is easy to manufacture and can withstand overcharging. 

Questions and answers 

Question 1: What makes a battery stop working? What gets used up? 

Answer: 

When a battery is connected to a circuit, the charge moves through the circuit and a chemical reaction occurs inside to separate the charges. 

The strength of this reaction diminishes over time as the chemicals get used up and the battery dies. 

Question 2: Could the battery experiment work with other vegetables or fruits such as lemon?  

Answer: 

Any citrus fruit such as lemons, oranges, gooseberry and grapefruit will work because they all have citric acid for the electrolyte.  

Since the electrolyte needs to be acidic so the electrochemical reaction will occur. 

Sweet ripe citrus fruits are less effective, but work a little. 

Question 3: Describe the energy transformation when a battery is attached to a loudspeaker. 

Answer: 

The chemical energy inside the battery gets converted into electrical energy.  

This battery when connected to a loudspeaker convert into electrical energy that is further converted into sound energy. 

Summary

• Cell is an electrochemical unit with two electrodes made of different material and an electrolyte.

• Group of cells connected in series make a battery.

• Cells are of two types:

1. Primary cell: This can not be charged.
2. Secondary cell: This can be charged.

• Batteries are of two type:

1. Wet cell: It has fluid as an electrolyte.
2. Dry Cell: It has moist paste as an electrolyte.