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Components and Materials for Electrochemical Supercapacitors
Alternative cathode materials are utilized, depending on application,
to mitigate the disadvantages of the lithium chemistry. These alternatives
include lithium manganese oxide (lower cost, better safety, poor temperature stability), lithium iron phosphate (costly production, very good
safety, low energy), and improved electrode designs that allow higher
power density and solid polymer electrolytes to help reduce dendrite
growth [3].
The appropriate electrode chemistry for a given application can be determined by considering an assortment of important parameters. The ideal
battery electrode chemistry includes high storage ability (energy and
power), long term stability, flat discharge shape, large operating temperature range, low cost, reduced safety issues, recharge capability, long cycle
life, and short charge time [5]. Flat discharge shape allows for easy integration into electronic circuitry as a power supply and increased utilization
of the energy stored in the battery. Storage ability is also dependent upon
reaction efficiency; side reactions that emit stored energy as heat reduce
usable energy.
After manufacture, batteries are held at a high chemical potential and their
chemistry must remain stable during storage to extend shelf life before and
during use. Stability issues include chemical side reactions, electrode phase
changes, and corrosion reactions. All of these stability issues can reduce
chemical storage capacity over the lifetime of a device. Ideally, rechargeable
electrodes exhibit a return to the same material composition as before discharge. In real operation, electrode phase changes occur over time and can
reduce cycle life and storage ability of a battery.
An example is the lithium device in which recharging can lead to long
dendrite formation [3]. Eventually a shift in phase could lead to penetration
of the separator, causing a short circuit. Side reactions lead to gas build-up
or corrosion of casing materials. These can be concerns because electrode
materials must operate safely in the designed application without causing
thermal runaway, explosion, release of toxic gas, or corrosion of dangerous
chemicals.
Issues arise when batteries are required to operate at high power, charge
quickly, or act outside their designed temperature ranges. High loads tax a
battery and the efficiency begins to drop due to side reactions. Limitations
stem from an insufficient ability for ions to diffuse from bulk and for reaction
rates to meet the power requirements put on the electrode materials. Thermal
side reactions waste energy as heat, increasing the changes of by-product
phase shift reactions. Stress caused from operating a battery beyond its rated
power level can significantly decrease cycle lifetime through reduced storage ability and material corrosion.
Components and Materials for Electrochemical Supercapacitors
Alternative cathode materials are utilized, depending on application,
to mitigate the disadvantages of the lithium chemistry. These alternatives
include lithium manganese oxide (lower cost, better safety, poor temperature stability), lithium iron phosphate (costly production, very good
safety, low energy), and improved electrode designs that allow higher
power density and solid polymer electrolytes to help reduce dendrite
growth [3].
The appropriate electrode chemistry for a given application can be determined by considering an assortment of important parameters. The ideal
battery electrode chemistry includes high storage ability (energy and
power), long term stability, flat discharge shape, large operating temperature range, low cost, reduced safety issues, recharge capability, long cycle
life, and short charge time [5]. Flat discharge shape allows for easy integration into electronic circuitry as a power supply and increased utilization
of the energy stored in the battery. Storage ability is also dependent upon
reaction efficiency; side reactions that emit stored energy as heat reduce
usable energy.
After manufacture, batteries are held at a high chemical potential and their
chemistry must remain stable during storage to extend shelf life before and
during use. Stability issues include chemical side reactions, electrode phase
changes, and corrosion reactions. All of these stability issues can reduce
chemical storage capacity over the lifetime of a device. Ideally, rechargeable
electrodes exhibit a return to the same material composition as before discharge. In real operation, electrode phase changes occur over time and can
reduce cycle life and storage ability of a battery.
An example is the lithium device in which recharging can lead to long
dendrite formation [3]. Eventually a shift in phase could lead to penetration
of the separator, causing a short circuit. Side reactions lead to gas build-up
or corrosion of casing materials. These can be concerns because electrode
materials must operate safely in the designed application without causing
thermal runaway, explosion, release of toxic gas, or corrosion of dangerous
chemicals.
Issues arise when batteries are required to operate at high power, charge
quickly, or act outside their designed temperature ranges. High loads tax a
battery and the efficiency begins to drop due to side reactions. Limitations
stem from an insufficient ability for ions to diffuse from bulk and for reaction
rates to meet the power requirements put on the electrode materials. Thermal
side reactions waste energy as heat, increasing the changes of by-product
phase shift reactions. Stress caused from operating a battery beyond its rated
power level can significantly decrease cycle lifetime through reduced storage ability and material corrosion.