Why Are Supercapacitors’ Capacities Lower Than Batteries?

In the field of energy storage, supercapacitors and batteries play indispensable roles in electronic devices. They each have unique characteristics and application scenarios.

Although both supercapacitors and batteries are energy storage devices, the capacity of a supercapacitor is significantly lower than that of a battery. So, why is this the case?

1. Energy Storage Mechanism and Principles

Battery Energy Storage Mechanism
Batteries store and release energy through chemical reactions. The chemical reaction between the positive and negative electrodes causes the transfer of electrons, generating a potential difference inside the battery, thereby storing electrical energy.

Battery Energy Density
Since chemical reactions can store large amounts of energy, batteries have a high energy density, allowing them to store a significant amount of electrical energy in a relatively small volume.

Supercapacitor Energy Storage Mechanism
Supercapacitors store energy mainly through double-layer or pseudocapacitive mechanisms. Double-layer supercapacitors store energy by separating charges between the surface of the electrodes and the electrolyte, while pseudocapacitors involve rapid redox reactions on or within the surface of electrode materials.

Supercapacitor Energy Density
Because the energy storage process in supercapacitors is primarily physical, without the complexity and energy loss of chemical reactions, their energy density is relatively low. This means that, for the same volume or mass, supercapacitors store much less energy than batteries.

2. Material Characteristics

Batteries:
The positive and negative electrode materials in batteries are typically chosen for their high energy density, such as lithium cobalt oxide (positive electrode) and graphite (negative electrode) in lithium-ion batteries. These materials can provide a large number of electrons and ions during chemical reactions, enabling high energy density storage.

Supercapacitors:
The electrode materials for supercapacitors are usually chosen for their high surface area, such as activated carbon, metal oxides, or conductive polymers. These materials can provide many charge adsorption sites, but due to the limitations of the energy storage mechanism, their energy density is much lower than that of battery materials.

This explains why the capacity of supercapacitors is so much lower than that of batteries. However, despite having lower capacity, supercapacitors have the advantage of faster charging and discharging speeds, which is something batteries lack.

As long as you select the appropriate energy storage device based on the specific application scenario and the advantages of supercapacitors and batteries, you will be able to use them effectively.