Power Electronics

New Hybrid Capacitor Increases Energy Density by 115 Percent

A hybrid capacitor combines EDLC (electric double-layer capacitor) and lithium-ion technology, resulting in an energy density up to 115 % higher.

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HYBRID CAPACITORS, developed by Ioxus, are similar to lithium-ion batteries, but they retain a far superior cycle life with more than 20,000 charge/discharge cycles possible rather than the hundreds or few thousand delivered by batteries. These capacitors store charge at the surface of the electrodes instead of within the electrodes as batteries do. Hybrid capacitors store 85 to 115% more energy than a conventional ultracapacitor, while retaining a higher cycle life than a battery. Hybrid capacitors have more power than lithium ion batteries, but less energy storage.

These hybrid components offer other advantages over standard ultracapacitors, which have an energy density of 12.8 Wh/L. The hybrid capacitor offers an enhanced capability of energy storage, providing power to applications more quickly and efficiently. Ioxus hybrid capacitors (Fig. 1.) can be charged from 1.0 VDC up to 2.3 VDC. These hybrid cells offer a maximum power of up to 5kW/kg, compared with up to 3kW/kg for “power batteries.”

Ioxus' hybrid capacitor offers benefits because of its operating temperature range of -25°C to +60°C. At the low end of the temperature range, the hybrid capacitor loses only 5% of its energy while comparable battery energy loss would by 50% or more. These hybrid ultracapacitors are 90 to 95% efficient compared with batteries that are approximately 70% efficient.

A federal appropriation earlier this year enabled the company to work with Binghamton University to increase EDLC energy density. The company began developing hybrid cells capable of storing significantly more energy than traditional EDLCs. As a result, its hybrid ultracapacitor supports the high cycle, wide temperature range and high power demands of applications like automotive subsystems, memory back-up, LED lighting and other consumer-focused markets.

For automotive applications, these hybrid capacitors can be used for short-term back-up power for memory and power windows. When disconnecting the battery, the computer loses power. If a hybrid capacitor is used, the computer will retain its power. This can be performed many times due to the high cycle life of the hybrid capacitor. For power windows or door locks, in the event of an emergency, the hybrid capacitor can provide power to unlock the doors or lower the windows when the rest of the electrical system has been compromised.

Ioxus hybrid-capacitors can be recharged as quickly as they can be discharged, allowing a rapid charge to support a high power demand. In hybrid capacitors, you can charge with up to 8A, depending on cell size.

Hybrid capacitors can be used for several applications, including:

  • Flashlights
  • LED applications
  • Memory Back-up
  • Portable Hand Tools
  • Solar Charge applications
  • Off-grid lighting
  • Automotive subsystems such as power windows and door locks

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  • High energy density
  • High power density
  • Low internal resistance (ESR)
  • 10 year life
  • High cycle life (+20K cycles)
  • RoHS compliant


Among the many applications for this EDLC technology is powering LED devices, which are much more energy efficient than their incandescent predecessors. For example, the hybrid capacitor can benefit new LED-based flashlights, which are brighter, lasts much longer and consumes less than one-third the power and energy of comparable halogen products.

Device manufacturers can now design hybrid capacitors permanently into these flashlights because capacitor cycle life generally matches or exceeds device life. Besides no longer needing to replace batteries, users can quickly recharge devices before use, unlike battery-operated products that usually take hours to recharge. Compared with a nickel cadmium or lithium-ion battery, hybrid capacitors provide more than 20 times the cycle life and 60 times faster recharge rates. Fig. 2 shows an LED flashlight driven by a hybrid EDLC. An initial charge on the hybrid EDLC allows it to power the LED for many minutes. The table shows specifications for the hybrid capacitors.

Operating Temperature Range -25 °C to +60 °C
Storage Temperature Range -30 °C to +70 °C
Rated Voltage 2.3 V DC
Surge Voltage 2.5 VDC
Capacitance Tolerance ±10%
Cycle Life (25°, VR) After 20,000 cycles between rated voltage and half rated voltage under constant current at 25 °C
ΔC < 30% decrease, ESR < 200% increase
Life Time* After 10 years at rated voltage and 25 °C
ΔC < 30% decrease, ESR < 200% increase
Endurance After 1000 hours application of rated voltage at 60°C
Capacitance Change Within 30% of initial specified value
Internal Resistance (ESR) Within 200% of initial specified value
Shelf Life After 1000 hours storage at 70°C without load (0 volts DC)
Capacitance Change Within 20% of initial value
Internal Resistance (ESR) Within 200% of initial value
**Life time is a provisional value
Part Number Unit RHE2R3227SR RHE2R3307SR RHE2R3807SR RHE2R3108SR
Diameter mm 22 22 35 35
Height mm 45 45 68 88
Volume ml 17 17 65 85
Weight g 25 25 91 120
Capacitance F 220 300 800 1000
Impedance(AC 1kHz) mΩ ≤20 ≤15 ≤8 ≤7
ESR (DC) mΩ ≤45 ≤35 ≤15 ≤14
Max Stored Energy Wh 0.162 0.220 0.588 0.735
Specific Energy Wh/kg 6.47 8.16 6.46 6.12
Wh/L 9.45 12.89 8.99 8.68
Maximum Power kW/kg 2.65 3.27 1.82 1.57
Max Leakage Current mA 0.27(72h) 0.55 (72h) 0.5 (72h) 0.7 (72h)
**All specifications subject to change without notification; please contact Ioxus for the latest information

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