Lithium ion capacitor
Encyclopedia
A lithium-ion capacitor (LIC) is a hybrid type of capacitor
. Activated carbon
is used as cathode
. The anode
of the LIC consists of carbon material which is pre-doped with lithium
ion. This pre-doping process lowers the potential of the anode and allows a high output voltage
.
) employs activated carbon material at which charges are stored in an electric double layer which is developed at the interface between the carbon and the electrolyte similar to electric double-layer capacitors (EDLC).
The negative electrode (anode) is made of a properly designed carbon material, which is pre-doped with lithium ions. This pre-doping process lowers the anode potential and results in a high cell output voltage. Typically, output voltages for LICs are in the range of 3.8–4.0V. As a consequence, LICs have a high energy density. Furthermore, the capacity of the anode is several orders of magnitude larger than the capacity of the cathode. As a result, the change of the anode potential during charge and discharge is much smaller than the change in the cathode potential.
The electrolyte used in an LIC is a lithium-ion salt solution.
In order to avoid direct electrical contact between anode and cathode, a separator material is used.
Batteries
, EDLC and LICs all have their own properties, which make them suitable for specific applications.
The lithium-ion capacitors have a higher power density as compared to batteries, and LIC’s are safer in use than LIB
s, in which thermal runaway
reactions may occur.
Compared to the electric double-layer capacitor (EDLC), the LIC has a higher output voltage. They have similar power densities, but energy density
of an LIC is much higher.
The Ragone plot (figure 1), shows that the lithium-ion capacitor combines the high energy of LIBs with the high power density of EDLC’s.
Cycle life performance of LICs is much better than batteries and is similar to EDLCs.
Potential applications for lithium-ion capacitors are, for example, in the fields of wind power
generation systems, uninterruptible power source systems (UPS), voltage sag compensation, photovoltaic power generation, energy recovery systems in industrial machinery, and transportation systems.
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
. Activated carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
is used as cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
. The anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
of the LIC consists of carbon material which is pre-doped with lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
ion. This pre-doping process lowers the potential of the anode and allows a high output voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
.
Concept of LIC
The positive electrode (cathodeCathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
) employs activated carbon material at which charges are stored in an electric double layer which is developed at the interface between the carbon and the electrolyte similar to electric double-layer capacitors (EDLC).
The negative electrode (anode) is made of a properly designed carbon material, which is pre-doped with lithium ions. This pre-doping process lowers the anode potential and results in a high cell output voltage. Typically, output voltages for LICs are in the range of 3.8–4.0V. As a consequence, LICs have a high energy density. Furthermore, the capacity of the anode is several orders of magnitude larger than the capacity of the cathode. As a result, the change of the anode potential during charge and discharge is much smaller than the change in the cathode potential.
The electrolyte used in an LIC is a lithium-ion salt solution.
In order to avoid direct electrical contact between anode and cathode, a separator material is used.
Properties of LIC
Typical properties of an LIC are:- High cell capacity, because of the large anode capacity
- High energy density (14 Wh/kg reported in )
- High powerElectric powerElectric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...
density - High reliability
- A wide span of typical operating temperatureOperating temperatureAn operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
s ranging from −20 ⁰C to 70 ⁰C. - Low self-discharge (<5% Voltage drop at 25⁰C over three months reported in [Ref 1]).
Comparison to other technologies
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
, EDLC and LICs all have their own properties, which make them suitable for specific applications.
The lithium-ion capacitors have a higher power density as compared to batteries, and LIC’s are safer in use than LIB
Lithium ion battery
A lithium-ion battery is a family of rechargeable battery types in which lithium ions move from the negative electrode to the positive electrode during discharge, and back when charging. Chemistry, performance, cost, and safety characteristics vary across LIB types...
s, in which thermal runaway
Thermal runaway
Thermal runaway refers to a situation where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result...
reactions may occur.
Compared to the electric double-layer capacitor (EDLC), the LIC has a higher output voltage. They have similar power densities, but energy density
Energy density
Energy density is a term used for the amount of energy stored in a given system or region of space per unit volume. Often only the useful or extractable energy is quantified, which is to say that chemically inaccessible energy such as rest mass energy is ignored...
of an LIC is much higher.
The Ragone plot (figure 1), shows that the lithium-ion capacitor combines the high energy of LIBs with the high power density of EDLC’s.
Cycle life performance of LICs is much better than batteries and is similar to EDLCs.
Applications
Lithium-ion capacitors are quite suitable for applications which require a high energy density, high power densities and excellent durability. Since they combine high energy density with high power density, there is no need for additional electrical storage devices in various kinds of applications, resulting in reduced cost of ownership.Potential applications for lithium-ion capacitors are, for example, in the fields of wind power
Wind power
Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, windmills for mechanical power, windpumps for water pumping or drainage, or sails to propel ships....
generation systems, uninterruptible power source systems (UPS), voltage sag compensation, photovoltaic power generation, energy recovery systems in industrial machinery, and transportation systems.
External links
- Introducing JM Energy Lithium Ion Capacitor, JM Energy
- Lithium Ion Capacitor, JSR Micro