Batteries: Class 12 Chemistry Notes, Definition, Types, Properties, Reactions, Uses & Examples

As per the NCERT, the definition of batteries is " Any battery (actually it may have one or more than one cell connected in series) or cell that we use as a source of electrical energy is a galvanic cell where the chemical energy of the redox reaction is converted into electrical energy".

Explanation: A Battery is a source of energy where chemical energy is converted into electrical energy. An AA-type battery is an example of the galvanic cell.

Batteries are broadly classified into two categories:

1. Primary Batteries: These are non-rechargeable batteries designed to be used until their chemical reactants are exhausted. After that, they are discarded.
2. Secondary Batteries: These are rechargeable batteries that can be used multiple times. The chemical reactions is reversed by applying an external electrical source, regenerating the reactants.

Primary Batteries

1. Dry Cell (Leclanché Cell)

• • The most common example of primary battery.
  • Anode: Zinc container.
  • Cathode: Carbon (graphite) rod surrounded by powdered manganese dioxide and carbon.
  • Electrolyte: A moist paste of ammonium chloride and zinc chloride.

Cell Reaction:

The ammonia produced reacts with

 

• Voltage: Approximately 1.5 V.
• Uses: TV remotes, clocks, transistors, and toys.

Limitations:

• Voltage decreases with use.
• Cannot be recharged.
• The acidic ammonium chloride can corrode the zinc container over time, leading to leakage.

• A carbon graphite rod (cathode) is placed in the Zinc container, which acts as an anode  

• The carbon graphite rod is surrounded by powered manganese dioxide and carbon.  

• The space between electrodes is filled with a moist paste of ammonium chloride (NH4Cl) and Zinc Chloride (ZnCl2).

Mercury Cell

• Provides a more stable voltage and has a longer life than the dry cell.
• Anode: Zinc-mercury amalgam (Zn-Hg).
• Cathode: Mercury (II) oxide (HgO) and carbon.
• Electrolyte: Potassium hydroxide ( KOH ) and zinc oxide (ZnO) paste.

Cell Reaction:

• Voltage: Approximately 1.35 V.
• Uses: Hearing aids, watches, and other small electronic devices.

Advantage:

• Constant voltage output.
• Longer shelf life than dry cells.

Disadvantages:

Contains mercury, which is toxic, so proper disposal is crucial.

Secondary Batteries

1. Lead Storage Battery

• Commonly used in automobiles and inverters.
• Anode: Lead (Pb).
• Cathode: A grid of lead packed with lead oxide (Pbo2).
• Electrolyte: Sulfuric acid (H₂SO₄) solution (38% by mass).

Cell Reaction:

• Discharging:

• Charging: The reverse of the discharging reaction.

• Voltage: Approximately 2 V per cell; a 12 V battery consists of six cells connected in series.

Advantages:

• High current output.

Disadvantages:

• Heavy and bulky.
• Contains corrosive sulfuric acid.
• Lead sulphate formed during discharge can harden and reduce the battery's capacity (sulfation).

Nickel-Cadmium (Ni-Cd) Battery

• An older type of rechargeable battery, now largely replaced by lithium-ion batteries.
• Anode: Cadmium (Cd).
• Cathode: Nickel (IV) oxide (NiO₂₎.
• Electrolyte: Potassium hydroxide  solution

Cell Reaction:

• Discharging

• Charging: The reverse of the discharging reaction.
• Voltage: Approximately 1.2 V per cell.
• Ni-Cd batteries are lighter and more compact than lead storage batteries. They have a longer cycle life but suffer from the "memory effect," where repeated partial discharges can reduce their capacity.

Advantages:

• Longer lifespan than lead-acid batteries.

Disadvantages:

• Cadmium is toxic, raising environmental concerns.
• "Memory effect": If not fully discharged before recharging, the battery may lose some capacity.

Lithium-ion (Li-ion) Batteries

• The most prevalent rechargeable battery in modern devices.
• Anode: Typically, graphite.
• Cathode: Various lithium compounds
• Electrolyte: A lithium salt LiPF6 in an organic solvent

Cell Reaction:

• Lithium ions (Li+) move from the anode to the cathode during discharge. The reverse happens during charging.

• Voltage: Typically, 3.7 V per cell.

Advantages:

• High energy (store more energy per unit mass).
• Low self-discharge rate.
• No memory effect.

Disadvantages:

• More expensive than other battery types.
• Turns to be flammable if damaged or improperly charged.

The capacity of a battery is the amount of electrical charge it can store. It is expressed in ampere-hour (Ah). For example, a battery with a capacity of 1 Ah, means it can provide a current of 1 ampere for 1 hour. 

The knowledge of redox reactions, electrode potentials, and cell potentials (EMF) is important to understand batteries. The EMF of a battery is calculated using the standard electrode potentials of the half-cells involved.

Where E°cathode and E°anode are the standard reduction potentials of the cathode and anode half-cells, respectively. The spontaneity of the battery reaction is related to the cell potential by the Gibbs free energy change ( ΔG ): 

Where n is the number of moles of electrons transferred in the balanced redox reaction, and F is the Faraday constant (approximately 96,485C/Mole). A positive E° cell and a negative ΔG°indicate a spontaneous reaction, which is important for the operation of a battery.

• Temperature: Battery performance can be affected by the temperature. It may decrease at very high or very low temperatures.
• Discharge Rate: The higher discharge rates can reduce the battery's effective capacity.
• Age: The capacity of the battery gradually decreases with age.
• Charging and Discharging Cycles: A battery has a limited charging and discharging cycles.
• Batteries are used in various equipment based on their properties and performance. 

Batteries are used in various equipment based on their properties and performance. The properties of batteries are mentioned below.

• Power Capability
• Life cycle
• Capacity 
• Electrode materials
• Voltage
• Energy density
• Shelf life
• Charging current
• Safety

Battery Use in Vehicle 

Now the world is moving to today's Electric Vehicles (EVs). These vehicles are powered by lithium-ion batteries. These batteries are rechargeable and have a good lifespan.

Uses of Batteries in Homes 

Many devices in our home are equipped with disposable and reusable batteries. TV remotes, clocks, and torches use disposable batteries. While mobile phones, digital cameras, video games, etc. use reusable batteries. Moreover, inverters are used for power backup.

Uses of Batteries in Health Instruments 

Engineers have developed various health instruments that are powered by batteries. Devices such as hearing aids, insulin pumps, pacemakers, artificial limbs and many other instruments use batteries for functions.

Batteries are mainly of two types: primary and secondary. Below are examples of batteries and their usages.