The most crucial element that makes devices mobile and wireless in today's technology is energy storage systems. From smartphones to electric cars, we see the dominance of lithium-ion batteries in every field. However, in recent years, special components we call "supercapacitors" (or ultracapacitors) have begun to revolutionize the areas where batteries fall short.
So, can supercapacitors with hundreds, or even thousands, of Farads capacity replace traditional chemical batteries? In this article, we will compare supercapacitors and batteries through the concepts of energy density and power density.
Two Different Storage Mechanisms
The fundamental difference between a battery and a supercapacitor is how they store energy. Batteries store energy through chemical reactions. During charging and discharging, ions within the battery move between the anode and cathode, and chemical bonds are formed or broken. This chemical process allows for storing a very large amount of energy, but it is inherently slow.
Supercapacitors, on the other hand, store energy in an electrostatic field (and via a double-layer capacitance mechanism), just like standard capacitors. Here, no chemical reaction is needed to store or release energy; ions simply accumulate physically on the electrode surface. The fact that a physical process is much faster than a chemical process defines the character of supercapacitors.
To understand the net amount of energy stored by a supercapacitor and compare it with batteries, you can use our Capacitor Energy Calculator tool and convert the calculated Joule values to compare with the Watt-Hour (Wh) values of batteries.
Power Density
If your application requires a massive amount of energy to be delivered (or recovered) within a very short time, the winner is undoubtedly supercapacitors. Supercapacitors can accept and discharge their charge in seconds or fractions thereof. Batteries, however, are forced to deliver energy slowly due to their chemical bottlenecks; rapid discharge causes overheating in the battery and permanent damage to the cell.
For example, supercapacitors easily provide the high peak power required when heavy machinery starts moving instantly or when an electric bus accelerates while pulling away from a stop. "Power density" indicates how fast a component can transfer energy, and the power density of supercapacitors is tens of times higher than that of batteries.
Energy Density
If your application requires energy to be provided steadily and slowly over long hours (such as keeping your smartphone screen on all day), the winner is definitely batteries. "Energy density" expresses the total amount of energy (Joules or Wh) that can be stored in a specific volume or weight.
Even today's best supercapacitors can only store about 5% to 10% of the volumetric energy density of a standard lithium-ion battery. For instance, if we designed a supercapacitor the size of the lithium battery in your phone, your device could perhaps run for only 10-15 minutes, not the whole day.
As you may recall from the $U = \frac{1}{2} C V^2$ formula, energy in capacitors increases with the square of the voltage. However, the operating voltages of supercapacitors are quite low due to their structure (usually around 2.7 V per cell). This low voltage limit creates a bottleneck in designs when trying to increase energy.
Lifespan and Efficiency
Another important area where supercapacitors outshine batteries is lifespan. A lithium-ion battery typically loses a significant portion of its capacity due to the degradation of its chemical structure after 500 to 2000 charge/discharge cycles.
In supercapacitors, since there is no chemical reaction, mechanical wear is close to zero. A supercapacitor can easily withstand 1 million charge/discharge cycles and operate at high efficiency in harsh temperatures (between -40°C and +70°C) for years without experiencing capacity loss.
Hybrid Systems: Bringing the Best Together
The industry has found ways to utilize the high energy density of batteries and the high power density of supercapacitors in the same system. In modern electric vehicles, lithium-ion batteries are used for long-range cruising, while integrated supercapacitor banks are used to instantly recover the massive energy generated during braking (regenerative braking) and feed the motor during rapid accelerations. This way, both long range is achieved and the lifespan of the main battery is extended by protecting it from harmful instantaneous peak currents.
Understanding energy formulas correctly and performing practical calculations in capacitors has a direct and critical impact on the overall efficiency of systems. By the nature of electronic engineering, predicting how theoretical relations will yield practical results on circuit schematics is a fundamental process that must be examined in detail at every stage to enhance the reliability of designs.
Understanding energy formulas correctly and performing practical calculations in capacitors has a direct and critical impact on the overall efficiency of systems. By the nature of electronic engineering, predicting how theoretical relations will yield practical results on circuit schematics is a fundamental process that must be examined in detail at every stage to enhance the reliability of designs.
Understanding energy formulas correctly and performing practical calculations in capacitors has a direct and critical impact on the overall efficiency of systems. By the nature of electronic engineering, predicting how theoretical relations will yield practical results on circuit schematics is a fundamental process that must be examined in detail at every stage to enhance the reliability of designs.
