supercapacitor

supercapacitor
Name	Supercapacitor
Caption	A typical cylindrical supercapacitor
Type	Passive
Principle	Electrostatic / Electrochemical
First production	1957, Standard Oil of Ohio
Inventor	General Electric, NEC

supercapacitor. A supercapacitor is a high-capacity capacitor with a capacitance value much higher than other capacitors but with lower voltage limits. It bridges the gap between electrolytic capacitors and rechargeable batteries, typically storing 10 to 100 times more energy per unit volume than traditional capacitors. These devices, also known as ultracapacitors or electric double-layer capacitors, are prized for their rapid charge and discharge cycles, high power density, and long operational life, making them critical components in modern energy storage and power management systems.

Overview

The development of supercapacitors can be traced to the General Electric engineer H. Becker in 1957, with later commercialization efforts by companies like Standard Oil of Ohio and NEC. Unlike batteries, which rely on slow faradaic reactions, supercapacitors primarily store energy through the physical separation of charge in an electric double layer at the interface between an electrode and an electrolyte. This fundamental difference underpins their exceptional performance in applications requiring bursts of power, such as in the regenerative braking systems of vehicles from Toyota and Volkswagen. Major manufacturers today include Maxwell Technologies, Panasonic, and Skeleton Technologies.

Principles of operation

The core operating principle involves the formation of an electric double layer, a concept first described by Hermann von Helmholtz in the 19th century. When a voltage is applied across the electrodes immersed in an electrolyte, ions in the electrolyte migrate to form two charged layers at each electrode surface, separated by a single layer of solvent molecules, effectively creating two capacitors in series. This process is complemented in some designs by pseudocapacitance, where fast, reversible redox reactions occur at the surface of materials like ruthenium oxide or conducting polymers. The absence of bulk electrochemical reactions, as seen in lithium-ion batteries, is key to their longevity and power capability.

Types and materials

Supercapacitors are broadly categorized by their charge storage mechanism and materials. Electric double-layer capacitors (EDLCs) use high-surface-area carbon materials like activated carbon, carbon nanotubes, and graphene for their electrodes, with electrolytes ranging from acetonitrile-based organics to aqueous solutions like potassium hydroxide. Pseudocapacitors utilize metal oxides such as ruthenium(IV) oxide or manganese dioxide, and conducting polymers like polyaniline. Hybrid types combine these approaches; for instance, lithium-ion capacitors pair an activated carbon electrode with a lithium titanate electrode. Research at institutions like the Massachusetts Institute of Technology and University of California, Los Angeles continues to explore novel materials like metal-organic frameworks.

Performance and characteristics

Key metrics include exceptionally high power density, often exceeding 10 kW/kg, which is significantly greater than that of lead-acid or lithium-ion batteries. Their energy density, while lower than batteries, is continually improving with new materials. They exhibit a long cycle life, often over 1 million charge-discharge cycles, with minimal degradation. Performance is influenced by factors like equivalent series resistance (ESR), which affects power delivery, and operating temperature range. Standards from organizations like the International Electrotechnical Commission (IEC) govern their testing and classification.

Applications

Supercapacitors are deployed where high power delivery or rapid energy capture is essential. In transportation, they are used in regenerative braking systems for trams, buses, and Formula One cars, and for engine starting in severe climates. They provide backup power and load leveling in industrial settings and for smart grid applications. In consumer electronics, they are found in devices from Samsung and Sony for memory backup and peak power support. They also play a role in renewable energy systems, such as smoothing the output from wind turbines and solar panels.

Comparison with batteries and capacitors

Compared to electrolytic capacitors, supercapacitors offer vastly higher capacitance and energy storage but with higher equivalent series resistance and lower voltage ratings per cell. Against rechargeable batteries like those based on nickel–metal hydride or lithium polymer chemistry, supercapacitors provide superior power density, faster charge/discharge rates, and much longer cycle life, but at the cost of lower energy density and higher self-discharge rates. This makes them complementary technologies; hybrid systems, such as those developed by Tesla and Audi, often combine supercapacitors with batteries to optimize both power and energy.

Category:Capacitors Category:Energy storage Category:Electronic components