A supercapacitor, also known as an ultracapacitor, is a type of capacitor that has a very high capacitance in comparison to other capacitors, but lower voltage limits. This allows it to store a significant amount of electrical energy in a small volume.

Here are the key features of supercapacitors:

1. High Capacitance: They can store 10 to 100 times more energy per unit volume or mass than electrolytic capacitors, can accept and deliver charge much faster than batteries, and tolerate many more charge and discharge cycles than rechargeable batteries.
2. Energy Storage and Release: Supercapacitors store energy through a mechanism that is different from traditional batteries, which store energy chemically. In supercapacitors, energy is stored electrostatically on the surface of the material, leading to faster charge and discharge cycles.
3. Materials: They typically use two porous plates that are separated by an electrolyte. These plates can be made of several materials, including various forms of activated carbon, graphene, or certain metal oxides, which are chosen for their ability to increase the surface area (and hence the capacitance).
4. Applications: Because of their ability to quickly release energy, they are used in applications requiring rapid bursts of power. Examples include regenerative braking systems in vehicles, where they quickly store energy when the brakes are applied and then release it to help accelerate later. They are also used in power stabilization, wind turbine pitch control, and as peak power sources in consumer electronics.
5. Lifecycle: Supercapacitors have a much longer life cycle compared to batteries. They can typically endure hundreds of thousands to millions of charge-discharge cycles, whereas conventional batteries might only handle a few thousand cycles before degrading.

Supercapacitors are considered a complementary technology to batteries, with each having its strengths and weaknesses depending on the specific application requirements.

A supercapacitor shares some similarities with batteries in that both store electrical energy, but they function in significantly different ways and have different characteristics:

1. Storage Mechanism: Supercapacitors store energy electrostatically on the surface of the material, meaning the energy is stored in the electric field between electrodes that are separated by an electrolyte. Batteries store energy chemically within the materials of their electrodes through electrochemical reactions.
2. Charge and Discharge Rates: Supercapacitors can charge and discharge much faster than batteries. This is because their energy storage is based on physical processes (electrostatic, not chemical), which are quicker to start and reverse.
3. Cycle Life: Supercapacitors can typically endure many more charge and discharge cycles (hundreds of thousands to millions) compared to batteries. Batteries generally have a lower cycle life due to the wear and tear caused by chemical reactions during charging and discharging.
4. Energy Density vs. Power Density: Batteries generally have higher energy density, meaning they can store more energy for a given volume or mass than supercapacitors. However, supercapacitors have higher power density, which means they can deliver energy much faster than batteries.
5. Durability and Maintenance: Supercapacitors are more robust under conditions of frequent charging and discharging and are less sensitive to temperature changes compared to batteries. This makes them more durable and maintenance-free.
6. Application Usage: While supercapacitors are excellent for applications needing quick bursts of energy (like regenerative braking in vehicles or power stabilization in electrical grids), batteries are better suited for applications requiring long-term energy storage (like powering electronic devices or electric vehicles over extended periods).

Thus, while they might be considered similar because they both store electricity, supercapacitors and batteries serve different roles in the field of energy storage, often complementing each other based on the application’s specific needs.