Handbook of Energy Storage for Transmission or ... - W2agz.com

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There are many ways to compare capacitor products. One way is to examine their powerenergy
behavior. Figure 2 shows Ragone plots of several large electrochemical
capacitors available as commercial products or as fully packaged prototype products.
Most of the devices were tested as single cells. However, the ELIT was tested as a multicell
module rated at 290Vdc. The operating voltage window was from rated voltage Vr
to one-half rated voltage, which represents 75% of the stored energy in an ideal capacitor.
100.00
Specific Energy (kJ/kg)
10.00
1.00
Maxwell 2500F
NESS 5000F
0.10
Panasonic 2000F
SAFT 3200F
Elit 290V (sym)
ESMA 130000F
Montena 2600F
0.01
0.01 0.10 1.00 10.00
Specific Power (kW/kg)
Notes:
1. Calculated using equivalent circuit models and voltage window of V r to 0.5 V r
2. Module and cell voltages vary, Elit 290 V, ESMA 1.6V, others are rated at 2.3 - 2.7 V
3. Montena has since been acquired by Maxwell
Figure 2 Energy and power relationships for several large electrochemical capacitors (i.e., Ragone
plots)
As shown in Figure 2, at low power levels different capacitors types tend to group,
depending on their design. For instance, energy performance at low power of the type II
capacitors are all approximately 10 kJ/kg (3 – 4 Wh/kg). The type I (Elit) capacitor is at
a lower energy value of ~1 kJ/kg (~0.3 Wh/kg). The type III (ESMA) capacitor is at a
higher level ~35 kJ/kg (~10 Wh/kg). This type III is a “traction” type capacitor, which
has been optimized for, high-energy density applications. Note that the type I capacitor is
rated at 290V and is comprised of hundreds of cells connected in series. This product
uses bipolar construction as opposed to individual cell construction. The voltages of
individual cells in the series stack have been de-rated to allow for the unique high voltage
module.
On the other hand, capacitor power performance is not well grouped, but widely spread.
For the type II capacitors, this suggests that these commercial devices have different
types of carbons with different electrode thickness. The electrolyte for all of these type II
capacitors is believed to be acetonitrile based. Even with the larger mass and volume
required to achieve the higher voltage rating, the type I capacitor shows good specific
power and power density, albeit at lower energy density and specific energy.
The asymmetric capacitor design can offer energy density advantages over symmetric
designs, as explained under Operating Principles below. Another advantage of an
Electrochemical Capacitors 15