Key Differences Between Primary and Secondary Batteries
Though Batteries and cells serve the common purposes of providing the source of power for many electronic devices, yet, they are still different. A cell is the electronic device that stores chemical energy and transforms it into electrical energy to supply power to electronic devices. Now, moving on to what is a battery? A battery is an electronic device that acts just like a cell, the only difference is that it has one or more cells grouped together.
Functioning of a Battery
A battery and a cell both can only supply DC voltage and current. They have some chemical reaction stored inside them that gives rise to the electrons on one electrode. Further, the free electrons move from one electrode to another through the electrolytic solution present inside the cell. With this, an electric circuit is established inside the battery cell, giving rise to the electric current that can be used for the functioning of many electronic devices.
Now, you must have developed an idea of what is a battery cell, and how it functions.
Dry Cell
A dry cell is a type of electric battery that is mainly used for home appliances and other portable devices. It is the type of electrochemical cell that was developed in 1886 by Carl Gassner, a German scientist. A dry cell is a variety that is currently used in all types of batteries. The dry cell consists of immobilized electrolytes with lower moisture and is mainly in the form of a paste.
Different Types of Batteries
Moving on to the battery types, there are two main types of battery based on the nature of the cell. Batteries can be classified into primary and secondary batteries. A primary one is non-rechargeable, and the secondary one is rechargeable.
Given here is a brief on primary cell and secondary cell.
What is the Primary Battery?
A primary cell or battery is non-rechargeable, and cannot be reused once its electrolyte is all consumed. Once these batteries get discharged, they serve no more purposes and must be disposed. Some common examples of primary cells are the ones used in remotes, wall clocks, watches, and mini electronic gadgets.
There are Two Main Types of Primary Cells/Batteries.
1. Alkaline Batteries
Chemical composition of Zinc with Manganese dioxide forms these batteries. The electrolyte that is used in these types of batteries is potassium hydroxide, and since all the contents are purely alkaline, it is termed as an alkaline battery.
2. Coin Cell Batteries
The coin cell batteries also have alkaline electrolytes, and additionally, they also have the chemicals of lithium and silver oxides. These types of primary batteries are highly efficient in ensuring stable and steady voltage.
What is a Secondary Cell?
A secondary cell or battery is the one that is rechargeable and serves multiple purposes for a longer span. Passing current opposite to the direction of discharge, one can effectively recharge the cell again to its original state. Common examples of secondary cells are the ones used in Cars, UPS, robotics, cordless phones, solar lights, drones, etc.
After learning the secondary cell definition, let us move on to the types of secondary cells.
1. Lead-acid Batteries
These batteries contain lead-acid that is cheaper and used mostly in vehicles. They generally come with a voltage range of 2V to 24V and have a power density of 7 Wh/Kg.
2. Ni-Cd Battery
This type of battery is made of Nickel and Cadmium. It has a lower price, and has a lower discharge rate. These batteries come in multiple sizes and have a minimal voltage of 1.2V. The power density of this battery is 60 Wh/Kg.
3. Ni-MH Battery
These batteries are more preferred than Ni-Cd ones. They have a nominal voltage of 1.25V, are easily available, and have a lower impact on the environment. Their power density is 100Wh/Kg.
4. Li-ion Battery
These batteries are made up of Lithium metal. They are compact and can easily be used in portable devices. These are the best batteries in the secondary categorization, have a normal voltage of 3.7V and a power density of 126 Wh/Kg.
5. Li-Po battery
These batteries are also known as Lithium-ion Polymer batteries as they use polymer gel or electrolyte instead of liquid ones. These batteries are a bit costlier but are highly protected as compared to the Li-ion batteries. They have a power density of 185 Wh/Kg.
FAQs on Types of Batteries: Primary and Secondary Cells
1. What are primary and secondary cells in chemistry?
In chemistry, batteries or electrochemical cells are classified into two main types based on their ability to be recharged. Primary cells are non-rechargeable batteries where the electrochemical reaction is irreversible. Once the chemical reactants are consumed, the cell stops producing electricity and must be discarded. Secondary cells, on the other hand, are rechargeable batteries where the cell reaction is reversible. They can be restored to their original state by passing an external electric current, allowing them to be used multiple times.
2. What is the main difference between a primary and a secondary battery?
The fundamental difference lies in the reversibility of the chemical reactions that occur within them.
- Primary Battery: The electrode reactions are irreversible. It can only be used once and is often called a “use and throw” battery. The reactants are consumed permanently during discharge.
- Secondary Battery: The electrode reactions are reversible. It can be discharged and recharged hundreds of times by applying an external power source, which reverses the chemical process.
3. What are some common examples of primary and secondary batteries used in daily life?
Examples are common in everyday devices:
- Examples of Primary Batteries: These include the dry cell (Leclanché cell) used in torches and wall clocks, the mercury cell found in watches and hearing aids, and alkaline batteries used in TV remotes and toys.
- Examples of Secondary Batteries: Common examples are the lead-acid battery used in cars and inverters, the nickel-cadmium (Ni-Cd) cell, and the lithium-ion (Li-ion) battery which powers most modern electronics like smartphones, laptops, and electric vehicles.
4. How do primary batteries work, and why can't they be recharged?
Primary batteries work by converting stored chemical energy into electrical energy through an irreversible electrochemical reaction. The anode and cathode materials are permanently consumed and changed into new products during the discharge process. They cannot be recharged because applying an external current cannot reverse these chemical changes to restore the original reactants. For instance, in a common dry cell, the zinc casing (anode) is oxidised and consumed, a process that cannot be efficiently reversed.
5. Explain the working principle of a common secondary battery, such as the lead-acid battery.
The lead-acid battery, a common secondary battery, works on a reversible chemical reaction. It consists of a lead (Pb) anode and a lead dioxide (PbO₂) cathode, both submerged in a sulfuric acid (H₂SO₄) electrolyte. During discharging, both electrodes react with the electrolyte to form lead sulfate (PbSO₄). During charging, an external voltage is applied, which forces the reaction to reverse. The lead sulfate on the electrodes is converted back into lead and lead dioxide, and the sulfuric acid is regenerated, thus recharging the battery.
6. What are the key components of an electrochemical cell or battery?
Every electrochemical cell, whether primary or secondary, has three essential components:
- Anode: The negative electrode where oxidation (loss of electrons) occurs.
- Cathode: The positive electrode where reduction (gain of electrons) occurs.
- Electrolyte: A substance containing ions that conducts electricity by moving ions between the anode and cathode, completing the electrical circuit internally.
7. In what real-world applications are secondary batteries more advantageous than primary batteries?
Secondary batteries are more advantageous in high-power drain applications or devices that are used frequently, where replacing primary batteries would be expensive and impractical. Key applications include:
- Automobiles: For starting the engine, which requires a very high current for a short time.
- Consumer Electronics: For powering laptops, smartphones, and digital cameras that have high energy consumption.
- Energy Storage: For storing energy from solar panels or for grid-level power backup systems.
8. Are 'Type 2' batteries the same as secondary batteries?
No, the term 'Type 2' is not a standard scientific classification for batteries and is often a point of confusion. The correct terms based on rechargeability are primary (non-rechargeable) and secondary (rechargeable). Battery classifications like AA, AAA, C, or D refer to the physical size and shape of the cell, not its chemistry or rechargeability. Both primary (like a standard AA alkaline) and secondary (like a rechargeable AA Ni-MH) batteries can exist in these common sizes.
9. What determines the voltage of a battery?
The voltage of a battery, also known as its electromotive force (EMF), is determined by the chemical nature of the materials used for its electrodes. Specifically, it is the difference in the standard electrode potentials (E°) between the cathode and the anode. A larger difference in the tendency of the two materials to gain or lose electrons results in a higher cell voltage. It is an intrinsic property of the specific electrochemical reaction and is independent of the battery's size.
10. Besides being non-rechargeable, what are the main limitations of primary cells?
Besides their single-use nature, primary cells have other limitations compared to secondary cells. They often have a lower power density, meaning they cannot deliver a very high current quickly, making them unsuitable for high-drain applications. Additionally, their voltage is not constant; it tends to drop steadily as the reactants are consumed. This can affect the performance of electronic devices that require a stable voltage supply to function correctly.
