Capacitor technology is expanding beyond the printed circuit board, as demand grows for a new generation of supercapacitors that are capable of performing energy storage applications – supplementing or even replacing batteries in applications including data storage, wearable devices, electric cars and smart grids.
The market for supercapacitors – also known as supercaps – is projected to more than double, rising to $836 million in 2018, up from $466 million in 2013, according to Lux Research.
Capacitor vs. Batteries
Conventional capacitors are ubiquitous in today’s electronic systems, with billions of units shipped every year for virtually every product and application market, from computers, to wireless handsets, to televisions, to cars. Widely used for regulating power, capacitors hold electric charges by using pairs of conductors that are separated by an insulator.
While sometimes compared to batteries, capacitors and batteries have basic differences in their composition and performance that makes each type of device suitable for different uses. Capacitors are passive components, which gather electrical charges from circuits, store them for a short period of time, and then release them all at once. In contrast, batteries serve as the source of energy for electronic systems. Batteries store electrical energy in electrochemical cells. They can carry large amounts of electrical charge for long periods of time and can slowly release their charges.
Advantages of Supercapacitors over Batteries
However, the arrival of new types of supercapacitors is blurring the distinction between capacitor and battery technologies.
Supercapacitors can store as much as 100 times more energy per unit volume than electrolytic capacitors. They also can charge and discharge much more quickly than batteries. Furthermore, supercapacitors can endure many more cycles of charging and discharging than conventional rechargeable batteries.
Other advantages for supercapacitors include greater power density, a higher peak power delivery capability, smaller size and lower equivalent series resistance (ESR). Finally, supercapacitors have the capability to release their charge slowly, like conventional batteries.
Current supercapacitors are made from active carbon. However, researchers are evaluating materials that deliver higher performance, such as graphene and nanostructured carbon. Scientists are also developing devices that combine features and technology of supercapacitors and batteries.
Supercapacitors Backup Power
Supercapacitors are replacing batteries in applications where high levels of power are needed for short periods of time. One such area is backup power for data storage. This application plays to the strengths of supercapacitors, requiring medium or high levels of current for brief durations.
Specific products include solid-state drives (SSDs) and redundant arrays of independent disks (RAID) systems. RAID systems are designed to protect data in the face of adversity, such as power failures. An interruption in electricity flow can cause the loss of information stored in volatile memory.
Advances in memory have made it possible to replace batteries with supercapacitors in RAID power-backup applications. To help engineers develop RAID-backup systems, Linear Technology Corp. is offering a set of microchips that can be used with a supercapacitor to implement a RAID-backup system. Linear Technology's solution consists of its LTC®3625 supercapacitor charger, its LTC4412 PowerPath™ controller and its LTM®4616 dual output μModule® DC/DC converter.
Supercapacitors forElectric Vehicles
Graphene is enabling the creation of new types of supercapacitors that are suitable for use in electric vehicles (EVs).
The Gwangju Institute of Science and Technology in Korea announced it has constructed graphene-based supercapacitors that store almost as much electricity as lithium-ion batteries, but can charge up in a mere 16 seconds. This kind of performance is useful for recovering energy used when braking, which requires fast charging.
Smart Electric Grid Technology
Emerging supercapacitor technology also could be applied to storage for new smart electrical grids.
Electricity generation from solar and wind is rising rapidly. However, the unpredictable nature of this type of electricity generation is hindering greater adoption of these renewable energy sources. Solar only generates power when the sun is shining and wind works exclusively when it’s breezy.
Grid-based storage can alleviate this issue by banking renewable energy for use at a later time. However, conventional supercapacitors and batteries have limitations in terms of capacity and speed of charging.
Researchers from Drexel University’s College of Engineering have addressed this issue with the development of a technology that combines elements of batteries and supercapacitors.
Drexel’s electrochemical flow capacitor (EFC) consists of an electrochemical cell connected to two external electrolyte reservoirs, a design similar to the kind of flow batteries that are used in EVs.
The design of EFC allows it to be constructed on a big enough scale to store large amounts of energy – like a battery. At the same time it allows for rapid withdrawal of the energy when demand dictates – like a supercapacitor.
Hybrid Supercapacitor Technology
UCLA’s California NanoSystems Institute announced it has developed a hybrid supercapacitor that exhibits features of both batteries and supercapacitors. The new hybrid supercapacitor stores large amounts of energy, recharges quickly and can last for more than 10,000 recharge cycles, according to UCLA. UCLA also announced a microsupercapacitor version of the technology.
The UCLA components combine laser-scribed graphene (LSG) with manganese dioxide. LSG is capable of storing an electrical charge, is highly conductive and can charge and recharge rapidly. Meanwhile, manganese dioxide is the same material now used in alkaline batteries due to its capability of holding large quantities of charge. Manganese dioxide is also cheap and plentiful.
The microsupercapacitor announced by UCLA has a compact form factor suitable for use in wearable or even implantable devices. Despite being just one-fifth of the thickness of a sheet of paper, the microsupercapacitor can hold more than double the charge of an average thin-film lithium battery.
Capacity for Change
While many of these technologies are in the early stages of development, supercapacitors could be destined to play an increasing role in energy storage, supplementing, augmenting or even replacing batteries in a range of new applications.