Difference between Capacitor and Battery

The battery and capacitor both are energy-storing devices but both of them have their own way of storing the energy. The battery uses the chemical reactions for storing the energy while the capacitor uses the electric field for the same. A battery is an active device that provides energy/power to the circuit while a capacitor is a passive component. In this article, we will see the exact difference between capacitor and battery.

The voltage across the battery remains constant during its operation, it goes down only when it is almost or completely discharged, while the voltage across the capacitor goes on decreasing.

Capacitor vs Battery

Now let’s throw some light on the difference between capacitor and battery with the help of a table.

Basis of comparison Capacitor Battery
Mode of storing energy The potential energy is stored in the electric field in the case of capacitors. It stores its potential energy in the form of chemicals before converting it into electrical energy.
Type of electrical component A capacitor is a passive component of the electrical circuit. It is an active component of the electric circuit.
Voltage The voltage is variable in the case of capacitors and it is directly proportional to the amount of electrical energy or charge stored on the plates. The voltage across the terminals of a battery remains constant.
Energy density The energy density of capacitors is comparatively lower than the batteries. The energy density of batteries is quite high which means a high amount of energy can be stored in a small volume.
Rate of charging/discharging Charging and discharging rates are faster because energy is stored directly on the plates. Charging and discharging rates are quite slow because chemical energy is converted into electrical energy.
Price of availability It is comparatively more expensive than a battery. It is available at a cheaper price.
Usage It is used for AC applications. It blocks the DC component of the circuit. It is generally used as a DC component.
Polarity The polarity of the circuit remains the same in the case of charging and discharging for the capacitor. While charging a battery the polarity of the circuit must be reverse of what it is during the discharging.

What is a battery?

A battery is an electrochemical device that converts the chemical energy stored to electrical energy in order to provide static electrical charge for power. A battery supplies electricity in the form of direct current (DC) and is a constant source of power.

It uses electric energy while charging to carry out the chemical reactions (convert one chemical into the other) while in case of discharging the chemical reactions proceeds in the reverse direction. Since electrical energy is being used both in the case of charging as well as discharging to carry out the chemical reactions, the usable energy available is much below the energy spent in charging. Therefore the conversion efficiency is less than 90%. The conversion efficiency of a Li-ion battery is 80% while that of a lead-acid battery is typically 65%.

Batteries are slow to charge up but will store electricity for a longer duration of time. Batteries have a higher energy density which means they store more energy per unit of the volume. It maintains a constant voltage across its terminals and the voltage goes down when the battery is almost or completely discharged. It always has a polarity.

What is a capacitor?

The capacitor is a device that stores electrostatic energy in the electric field between the plates. It is a passive component of the circuit. It consists of two or more plates and the spaces between the plates are filled by a dielectric medium. They are capable of releasing energy very quickly.

The efficiency of a capacitor can go beyond 98%, this is because no conversion of energy in another form is involved. Energy is absorbed as electrical energy and when required is obtained in the form of electrical energy.

The voltage across a capacitor is variable and it depends on the amount of electric charge stored on its plates. A capacitor has two or more conducting plates which are separated by a dielectric. When an electric current is supplied to the capacitor, the current enters the plates, the dielectric stops the flow of current and a charge builds up and this charge is stored in the electric field between the plates.

The charge stored by a capacitor depends on the surface area of the conductors. The larger the surface area of the conductors, the more charge the capacitor can store and vice versa. The energy density of capacitors is lower than that of batteries.

Conclusion

Here we have concluded that both capacitor and battery are energy storing devices. A battery stores its potential energy in the chemical form while a capacitor stores its potential energy in an electrostatic field. Batteries are slow to charge up while capacitors are really quick.

The voltage across the terminals of a battery remains constant during its operation. Since the voltage across a capacitor depends on the energy stored, its voltage will keep on decreasing as its energy is being used up.

Author
Deepak Yadav
Aligarh Muslim University, Aligarh

References

1. https://www.machinedesign.com/automation-iiot/batteries-power-supplies/article/21831866/whats-the-difference-between-batteries-and-capacitors
2. http://www.differencebetween.net/technology/difference-between-capacitor-and-battery
3. https://www.quora.com/What-is-the-difference-between-a-capacitor-and-a-battery
4. https://www.sciencenewsforstudents.org/article/explainer-batteries-capacitors

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