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
Self-discharge
Rapid charge/discharge
Seconds
Hours
Low-Temperature Performance
Good
Bad
High-Temperature Performance
Good- up to 70̊ C
Good- up to 60̊ C
Bad – up to 40 ̊ C
Internal Resistance
Maintenance
Lifetime
Long
Short
Safety and Flammability
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.
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