What is a Lithium-Ion Supercapacitor?

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Editorial Team - everything PE

Feb 13, 2023

A lithium-ion supercapacitor (LIC) is a type of supercapacitor that combines the energy storage mechanisms of both a lithium-ion battery (LIB) and an electrical double-layer capacitor (EDLC). This hybrid energy storage device uses an electrostatic positive electrode and an electrochemical negative electrode. EDLCs uses electrostatic charge, and Li-ion batteries use an electrochemical method to store energy. 

Working

Lithium-ion supercapacitor has a carbon-based material that is capable of absorbing lithium ions as the negative electrode material, and it improves energy density by adding lithium ions to it. This creates the so-called pseudo-capacitance electrode while using the principles of a general ELDC on the other electrode. This hybrid model overcomes some of the drawbacks of ELDC and Li-ion batteries resulting in better energy density than an ELDC with lower self-discharge characteristics.

Hybrid LIC

While the positive electrode operates by the principle of an Electrical Double Layer, the negative electrode charges, and discharges by the redox reaction of lithium. The high energy density compared to conventional capacitors is large because the pseudo electrostatic capacitance of the negative electrode is increased by pre-doping/pre-lithiation. Pre-doping also helps increase the potential difference across the electrodes without having to apply too much positive voltage at the anode. Apart from the electrodes, a LIC also contains electrolytes and a separator membrane. LIC separators are used in Li-ion batteries as they are chemically inert and provide electrical insulation between the anode and cathode but allow ions through to support LIC operation. A lithium-based salt solution is used as the electrolyte, which is very similar to that used in Li-ion batteries.

An electric double layer is used to store energy in the cathode of a LIC. The cathode materials include carbon materials, Li+-intercalation compounds, and composite materials. The porous carbon material is widely used in LIC's cathode which is characterized by a high specific surface area (more than 1000 m2/g), good electron conductivity, and proper electrolyte accessibility to the intrapore space of the carbon materials. 

For the Anode preparation, an active material and a conductive material are mixed to ameliorate the electron conductivity of the structure.

Energy is expressed below


Power is expressed below


Comparison between LIC, ELDC, and Li-ion Batteries

As compared to a Li-ion battery, ions are not extracted or added into the carbon lattice rather, they are simply absorbed and desorbed on the electrodes’ surface. Hence, no crystalline change takes place which gives the LICs more number to charge/discharge cycles which in turn increases the longevity of the LICs exponentially compared to Li-ion batteries. LICs do not contain oxygen or oxides, so they are immune to thermal runaway conditions, making them a safer alternative to Li-ion batteries. A table representing the comparison between LIC, ELDC, and Li-ion batteries is shown below:

Parameters

LIC

ELDC

Li-ion Battery

Energy density

Medium
 (Higher at high current)

Low

Very High

Power density

High

High

Low

Self-discharge

Low

High

Low

Rapid charge/discharge

Seconds

Seconds

Hours

Low-Temperature Performance

Good

Good

Bad

High-Temperature Performance

Good- up to 70̊ C

Good- up to 60̊ C

Bad – up to 40 ̊ C

Internal Resistance

Low

Low

High

Maintenance

Low

Low

Very High

Lifetime

Long

Long

Short

Safety and Flammability

High, flammable

High, flammable

Low, flammable
 (Self-heat up / igniting)

Application

Very high power/ Medium energy

Very high power/ Low energy

Low Power/ High Energy

Applications

LICs are used for power electronics, renewable energies, spacecraft, satellites, railways, pulsed power, grid connection, and hybrid/electric vehicle applications. As compared to conventional supercapacitors, lithium-ion capacitors are more suitable for power electronic device applications as they can tolerate a higher frequency than the other established technologies. They also have higher efficiency in partial load conditions. During a high current gradient or high current amplitude, the LIC can handle the power and smoothen the output power. Another application of LICs is as a replacement for flywheels for pulsed power applications. LICs are also being used as a replacement for batteries and SCs in transport systems like trams etc. One of the most promising technologies counted as the end-user of LIC technology is the regenerative braking system (RBS), which collects energy from the braking of EVs or HEVs, trains, trams, and other types of automotive vehicles.

While there are many merits of using a LIC such as low life-cycle cost, high power density, high energy density, high safety, and wide operating temperature range, there are certain limitations associated with Lithium-ion capacitors. It is a relatively new technology, and much research is yet to be done in high-power, high-temperature, and high-frequency applications. The manufacture and fabrication of LIC are very expensive still thus, limiting its market reach. 

Click here to learn more about Lithium-Ion Supercapacitors.

Click here to learn more about EDLC.