138
Electrochemical Supercapacitors for Energy Storage and Delivery
0.6
0.2
0.4
0.0
–0.2
–0.4
Voltage (V)
–0.6
–0.8
–1.0
0.6
0.2
0.4
0.0
–0.2
–0.4
Voltage (V)
–0.6
–0.8
–1.0
Cathode: Nickel hydroxide plate
NiOOH + H 2 O + e
–
Ni(OH) 2 + OH
–
Anode: Cadmium plate
Cd + 2OH
–
Cd(OH) 2 + 2e
–
Open Circuit Cell Voltage ~1.3 V
Electronic double layer
Electronic double layer
FIGURE 4.1
Voltage separation and characteristic ion diffusion layer from bulk caused by half-cell reactions in NiCd battery system.
the device [3,5]. The anode is more active than the cathode and spontaneously oxidizes, losing electrons and cations to the electrolyte solution. The
electrons move through the circuitry as current to the cathode material; this
reduces and creates an excess of anions in solution. The reaction proceeds at
a constant rate until only a small amount of energy remains present in the
cell, at which time the voltage produced by the cell will quickly drop off.
Depending on material properties and the nature of the reactions, the performance, safety, packaging, design, and application characteristics of batteries will vary. Table 4.1 showcases a number of commercial battery materials
that dominate the energy storage market [5].
Figure 4.2 illustrates the lead acid battery that, until the invention of lithium
storage technology, dominated the rechargeable battery industry ($18.4 billion of the $28 billion market in 2003) [5]. Lead acid batteries contain alloyed
lead anodes and opposing lead oxide cathodes that share a sulfuric acid electrolyte. They are the oldest rechargeable devices and have lower volumetric
(80 Wh.L –1 ) and gravimetric energy density (40 Wh.kg –1 ) than some of the
more modern battery chemistries.
The main advantage of lead acid batteries is their ability to handle large
surge currents and their low cost [3]. In the discharged state, the electrode
plates become lead sulfates and most of the sulfuric acid in the system is
absorbed, leaving the electrolyte as water. The water-heavy electrolyte lacks
the abundance of ions that block gas evolution, making the cells susceptible
to water loss during operation. The moisture loss dries out the battery and
reduces its capacity over time, thus requiring maintenance. An important
Electrochemical Supercapacitors for Energy Storage and Delivery
0.6
0.2
0.4
0.0
–0.2
–0.4
Voltage (V)
–0.6
–0.8
–1.0
0.6
0.2
0.4
0.0
–0.2
–0.4
Voltage (V)
–0.6
–0.8
–1.0
Cathode: Nickel hydroxide plate
NiOOH + H 2 O + e
–
Ni(OH) 2 + OH
–
Anode: Cadmium plate
Cd + 2OH
–
Cd(OH) 2 + 2e
–
Open Circuit Cell Voltage ~1.3 V
Electronic double layer
Electronic double layer
FIGURE 4.1
Voltage separation and characteristic ion diffusion layer from bulk caused by half-cell reactions in NiCd battery system.
the device [3,5]. The anode is more active than the cathode and spontaneously oxidizes, losing electrons and cations to the electrolyte solution. The
electrons move through the circuitry as current to the cathode material; this
reduces and creates an excess of anions in solution. The reaction proceeds at
a constant rate until only a small amount of energy remains present in the
cell, at which time the voltage produced by the cell will quickly drop off.
Depending on material properties and the nature of the reactions, the performance, safety, packaging, design, and application characteristics of batteries will vary. Table 4.1 showcases a number of commercial battery materials
that dominate the energy storage market [5].
Figure 4.2 illustrates the lead acid battery that, until the invention of lithium
storage technology, dominated the rechargeable battery industry ($18.4 billion of the $28 billion market in 2003) [5]. Lead acid batteries contain alloyed
lead anodes and opposing lead oxide cathodes that share a sulfuric acid electrolyte. They are the oldest rechargeable devices and have lower volumetric
(80 Wh.L –1 ) and gravimetric energy density (40 Wh.kg –1 ) than some of the
more modern battery chemistries.
The main advantage of lead acid batteries is their ability to handle large
surge currents and their low cost [3]. In the discharged state, the electrode
plates become lead sulfates and most of the sulfuric acid in the system is
absorbed, leaving the electrolyte as water. The water-heavy electrolyte lacks
the abundance of ions that block gas evolution, making the cells susceptible
to water loss during operation. The moisture loss dries out the battery and
reduces its capacity over time, thus requiring maintenance. An important