2.6. Batteries

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 basically a galvanic cell where the chemical energy of the redox reaction is converted into electrical energy.

Batteries serve as a vital source of electrical energy in numerous devices. They are essentially collections of one or more galvanic cells, which convert chemical energy derived from redox (reduction-oxidation) reactions directly into electrical energy. This makes them crucial for powering everything from small gadgets to larger machines.

Think of a battery as a reservoir of energy, much like a water tank. Just as water flows from the tank to power your home's plumbing, a battery allows electrical energy to flow to power devices such as radios or electric cars.

However, for a battery to be of practical use it should be reasonably light, compact and its voltage should not vary appreciably during its use. There are mainly two types of batteries.

To be effective, batteries must be lightweight and compact, ensuring they can be easily transported and utilized without causing significant fluctuations in voltage as they deplete. The two main types of batteries are primary batteries, which are non-rechargeable and are used until they are depleted, and secondary batteries, which are rechargeable after use.

Consider primary batteries like a bag of chips; once it’s opened and consumed, it can't be reused. In contrast, secondary batteries are like a reusable water bottle; you can fill it up again and again, making it a more sustainable option for energy storage.

In the primary batteries, the reaction occurs only once and after use over a period of time battery becomes dead and cannot be reused again.

Primary batteries operate on the principle that their electrochemical reactions take place once. Once the reactants are exhausted, the battery is rendered useless and cannot be recharged, which is different from secondary batteries where the reactions can be reversed.

Think of primary batteries like one-use cameras. Once you take all your pictures and develop the film, you can't reuse that camera. Similarly, once a primary battery runs out of energy, it's effectively discarded.

The most familiar example of this type is the dry cell (known as Leclanche cell after its discoverer) which is used commonly in our transistors and clocks.

Dry cells are a common type of primary battery widely used in everyday electronics. The Leclanche cell, a specific variety of dry cell, incorporates a zinc container as the anode and a carbon rod as the cathode, with a paste that acts as the electrolyte.

Many devices we use daily, like remote controls for TVs and clock batteries, rely on dry cells. Imagine a dry cell as the energy source of a small radio, powering it until it's no longer able to produce sound.

Mercury cell, suitable for low current devices like hearing aids, watches, etc. consists of zinc – mercury amalgam as anode and a paste of HgO and carbon as the cathode.

Mercury cells are designed for devices that need a steady and low current output over long periods of time. The cell functions well without significant changes in voltage during its life, making it ideal for precision instruments.

These batteries are like the quiet, reliable friends who help you with tasks without drawing attention to themselves. Just as we depend on reliable friends to support us quietly, we depend on mercury cells for gradual energy supply in devices like hearing aids.

A secondary cell after use can be recharged by passing current through it in the opposite direction so that it can be used again.

Secondary batteries, unlike primary batteries, can be recharged after they've been depleted. When electricity is passed through the battery in the opposite direction, the chemical reactions occurring within are reversed, restoring the battery’s capacity to hold energy.

Imagine a sponge that absorbs water. Once it’s full, you can squeeze it out to reuse it. Secondary batteries work similarly; they can recharge and be used again, unlike a sponge that you have to toss once it's 'full.'

The most important secondary cell is the lead storage battery... A 38% solution of sulphuric acid is used as an electrolyte.

The lead storage battery is notable for its widespread use in automobiles due to its longevity and ability to withstand many charging cycles. The reactions involving lead and lead dioxide release energy when in use, and upon recharging, these reactions reverse.

Think of the lead storage battery as a hardworking employee who puts in long hours and can take breaks (recharge) to ensure they can keep performing effectively over time.

Another important secondary cell is the nickel-cadmium cell... The overall reaction during discharge is: Cd (s) + 2Ni(OH)3 (s) ® CdO (s) + 2Ni(OH)2 (s) + H2O (l )

Nickel-cadmium batteries are known for their longer lifespan and reliability, making them excellent for repeated use. Despite being more expensive than lead-acid batteries, their performance in various conditions makes them favored in specific applications.

These batteries are like premium sneakers; while they may cost more upfront, their durability and performance can save money in the long run as you won't need to replace them as often.

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