Getting Supercapacitor Selection Right

Batteries and supercapacitors store energy through fundamentally different mechanisms, and that difference determines where each technology belongs in a design.

In a battery, charges are transferred between electrodes and electrolyte through chemical reactions, producing an electrical current through an externally connected circuit. This chemistry is what gives batteries their high energy density—and why they’re well-suited to applications requiring sustained current draw over long periods, such as electric vehicles and grid-scale storage.

Supercapacitors work differently. Like a conventional capacitor, they store charge electrostatically, but the double layer of stored charge (between each electrode and a wall of oppositely charged ions in the electrolyte) gives them far higher capacitance than a standard capacitor. The result is a device that can deliver power almost immediately, without the chemical overhead of a battery. Because charge storage in a supercapacitor doesn’t involve chemical reactions, supercapacitors generally offer better thermal management, a longer cycle life, better performance across high and low temperatures, and higher efficiency than batteries.

The trade-off is energy density. Where batteries excel at storing energy for long-duration discharge, supercapacitors are optimized for rapid charge and discharge—making them the right choice for pulse power delivery or short-term hold-up power, but not a direct replacement for batteries in energy-intensive loads.

Selecting the right device means matching a capacitor’s characteristics to specific application demands. Eaton addresses this through a broad portfolio spanning several distinct capacitor technologies, including a supercapacitor lineup that covers a wide range of requirements.

Eaton’s capacitor portfolio

Eaton’s electronic components division carries capacitors across four major families.

Aluminum polymer capacitors use a conductive polymer electrolyte in place of the liquid or gel found in standard aluminum electrolytics. The polymer construction yields lower equivalent series resistance (ESR) and improved high-frequency performance, making these capacitors a natural fit for power supply decoupling and filtering.

Aluminum electrolytic capacitors use a liquid electrolyte and an aluminum oxide dielectric formed on etched aluminum foil. The etching dramatically increases effective surface area, enabling high capacitance values in a compact package. These capacitors are widely used for bulk energy storage and filtering across industrial and consumer applications.

Metalized polypropylene film capacitors use a polypropylene dielectric with a thin layer of deposited metal, wound around a core. The dry, non-polarized construction gives these capacitors stable capacitance over temperature, with the ability to handle high ripple currents, high pulse and surge voltages, and high-frequency operation.

A key characteristic of the metalized construction is self-healing. If a dielectric fault occurs from overvoltage, overheating, or a transient event, the resulting discharge vaporizes the surrounding metal layer, isolating the fault and preventing a permanent short circuit. Eaton’s film capacitor range includes DC link types for EV powertrains and solar inverters, as well as safety-rated Class X and Class Y types for AC line filtering. AEC-Q200 and THB Grade IIIB qualified versions are available for automotive and industrial use.

Electric double-layer capacitors (EDLCs)—also referred to as supercapacitors or ultracapacitors—store charge electrostatically between two carbon-based electrodes and a liquid electrolyte. Ions in the electrolyte are attracted to the electrode surface during charging and released during discharge, with no chemical transformation at the electrodes. This purely physical mechanism is what allows EDLCs to sustain millions of charge-discharge cycles with minimal degradation. Eaton’s supercapacitor lineup includes individual cylindrical cells, hybrid variants, and complete modules.

How to size a supercapacitor

The starting point for sizing a supercapacitor is identifying which of two common use cases the application falls into.

Hold-up power applications require the supercapacitor to sustain load power for seconds or minutes. Common examples include parking a disk drive’s read/write head when power is cut, or keeping a system running long enough for a safe shutdown. In these situations, capacitance is the specification to size for. The device needs enough stored energy to supply the load from its working voltage down to the minimum the system can tolerate.

Pulse power applications are characterized by a low continuous current with short, intense bursts. A GSM/GPRS modem, for instance, can draw up to 2 A during a transmit period measured in fractions of a millisecond. During a pulse, the voltage drop comes partly from ESR and partly from the depletion of stored charge. For very short pulses, the resistive contribution is larger, making ESR the more important specification to optimize.

When a circuit’s working voltage exceeds the maximum rating of a single cell, supercapacitors can be placed in series. Series arrangements should be balanced to ensure equal voltage sharing across devices.

Eaton’s supercapacitor calculator steps through the capacitance and ESR calculations for both application types.

Eaton’s supercapacitor families

Eaton’s supercapacitor products fall into six categories.

Coin cells

Coin-cell supercapacitors are compact devices for use cases like real-time clock and memory backup. An extended-temperature option covers -40°C to +85°C for industrial environments where standard coin cells fall short. Applications include utility meters, medical devices, network equipment, computers, and industrial controls.

Small cylindrical cells

Eaton’s small cylindrical cells offer capacitance from under 1 F up to 110 F, with variants spanning operating temperatures from -40°C to +85°C. An automotive-qualified version is available for safety applications such as emergency door locks and eCall. Across the range, typical use cases include smart utility meters, GPS and asset tracking, RF radios, and storage servers.

Cylindrical packs

Cylindrical packs combine two cells in a single assembly with integrated cell balancing, providing higher operating voltages than individual cells without external balancing circuitry. The use cases are similar to the small cylindrical range—smart meters, GPS tracking, storage servers, and automotive safety devices—where a higher system voltage is needed.

Large cells

Large cylindrical cells cover capacitance from 300 F to 3,400 F for applications requiring high energy storage or peak power in a single device. Applications range from engine starting and peak power shaving to energy regeneration, industrial backup power, and UPS.

Hybrid supercapacitors

Standard EDLCs have lower energy density than lithium-ion batteries and tend to self-discharge more quickly. Eaton’s hybrid supercapacitor series addresses both constraints by combining EDLC and lithium-ion construction within a single device.

In a standard EDLC, both electrodes are carbon-based, and charge is stored electrostatically as ions are attracted to the electrode surface during charging and released during discharge. In a hybrid supercapacitor, one electrode is replaced with a lithium-doped carbon electrode, similar to the anode in a lithium-ion battery. Charge is stored electrochemically as a thin film that builds up on the surface during charging.

The lithium doping also lowers the electrode potential, which raises the maximum working voltage to 3.8 V, compared to approximately 2.7 V for a standard EDLC. A higher cell voltage means more energy per device and fewer cells needed to reach a target system voltage. Hybrid supercapacitors have up to 10 times the energy density of a standard EDLC.

Lithium-ion batteries use metal oxide cathode materials, which make them susceptible to thermal runaway when shorted or punctured. Hybrid supercapacitors avoid metal oxide cathodes entirely, making them a safer option.

Eaton offers three series within the hybrid supercapacitor family:

• HS series: Capacitance from 5 F to 220 F at 3.8 V, with a cycle life up to 500,000 charge-discharge cycles. The high operating temperature capability makes the HS suitable for industrial backup power, IoT devices, and automotive subsystems that require frequent cycling.
• HSL series: Same capacitance and voltage range as the HS, optimized for low-temperature operation and lower ESR, with a cycle life up to 250,000 cycles. The HSL suits designs in cold environments where both energy delivery and pulse performance need to be maintained.
• HSH series: Capacitance from 3 F to 1400 F, with approximately 65% higher capacitance density than the HS and HSL, and a cycle life up to 250,000 cycles. The HSH is the highest energy-density option in Eaton’s hybrid lineup, for applications that require substantial energy storage within a compact footprint.

Modules

Supercapacitor modules integrate multiple cells with built-in balancing and management into a ready-to-install unit. The integrated balancing prevents individual cells from being overstressed, and the absence of electrochemical degradation means the modules can be rated for as long as 20 years of maintenance-free service. Low ESR across the assembly supports high peak power delivery while minimizing internal heating.

Eaton’s module range runs from 16 V to over 300 V as standalone units, scalable to 1,500 V through series and parallel combinations. Lower-voltage modules suit engine starting, material handling equipment, light rail, and traction systems, with IP65-sealed options for harsh environments. Higher-voltage modules are deployed in datacenter UPS, grid storage, renewable energy firming, and heavy industrial and transportation applications.

Taken together, Eaton’s supercapacitor families provide designers with flexible options for addressing a broad range of application needs, making it easier to select the right solution for a given design.

To learn more, visit Eaton’s Capacitor Portfolio.