A battle as old as the technologies themselves: ultracapacitors and batteries rule the energy storage industry, fighting for a place at the top. Batteries, as the older and more established technology, wear the crown, but ultracapacitors have taken huge technological leaps forward in the past decade, and are now overtaking batteries in lifetime and usability in the high power density for short-term energy storage.
Ultracapacitors and batteries differ in one significant way: ultracapacitors store energy in an electrostatic field and batteries store energy as part of a chemical reaction. Now, if you just need to power your flashlight, you can buy a set of Alkaline batteries and go on your merry, well-lit, way.
But if your application is more complex and has more demanding requirements, it's vital to understand the characteristics of each technology.
Ultracapacitors are what's known as fast energy storage and:
- have the high power density, meaning they can provide very high currents (Thousands of Ampères) during a short time (Ideally, less than 10 seconds)
- charge and discharge very quickly (less than a minute)
- have a lifetime of over 1 million charge-discharge cycles
- have very low internal resistance (a few tenths of a milliohm) and work close to 100% efficiency
- are significantly lighter than batteries
- have high tolerance for extreme temperatures
- don’t contain harmful chemicals or toxic metals
- will never overrun of start a fire, they will always fail in a nice way
- have a significant leakage current, meaning they discharge if no used, but not totally
Batteries are known as slow energy storage and:
- have much higher energy density, meaning they can operate for a long time (a few hours)
- charge and discharge slowly (a few hours)
- usually have a lifetime of about 2000-3000 charge-discharge cycles, sometimes longer depending on how they have been treated
- have an efficiency of about 70 to 80% which result in heat that requires dissipation
- do no like to pushed hard during charging or discharging, fast charging shortens lifetime
- sensitive to overcharging and 0% charged stated
- have a very low leakage current
- operate poorly in very cold or warm temperatures
- contain toxic and environmentally harmful chemicals.
- can overrun and cause a fire, although this is now very rare
Batteries and ultracaps both have their uses and can be complementary after some considerable amount of integration.
The infographic below gives a basic understanding on the technologies behind ultracapacitors and the most widely available battery types, and provide you with the knowledge to make the decision on what's best for your needs.
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