Supercapacitor technologies vs. batteries

To understand why supercapacitors have not replaced batteries, it’s important to understand the differences between these two types of devices, which stem from their architectures.

• Batteries have a high energy density but low power density (slower energy discharge), making them suitable for long-term applications where a consistent, slow release of energy is needed.
• Supercapacitors have a lower energy density but a higher power density (faster energy discharge). As a result, they cannot store as much energy as batteries but can be charged and discharged much faster. This property makes them more suitable for applications in which quick bursts of energy are needed and where they can be readily recharged.

The differences in energy and power density are due to the way each of these technologies stores charges, which affects their capacitance and energy density.

• Batteries store and release energy electrochemically, limiting their rate of charging-discharging by the kinetics of the corresponding electrochemical reactions. Ions are intercalated within the electrode, not on the surface, forcing ions to diffuse through the electrodes and further slowing their charging-discharging rate.
• Supercapacitors store energy electrostatically on their electrode surfaces. Energy is released by a simple movement of ions instead of a slower electrochemical reaction. Because charges (ions) are stored only on the electrode surface and no ions are intercalated within the active material, only the surface participates in the charge-discharge process, providing a much lower energy density than batteries.