Environmental Engineering Reference
In-Depth Information
More recently there has been experimental work on comparing the pulse dis-
charge characteristics of a lithium ion battery with a high power ultra-capacitor [8].
The graphic in Figure 10.17 compares a commercial 12 Ah lithium ion cell versus a
production 3,000 F, 2.7 V ultra-capacitor cell in the ability to capture regeneration
energy in an HEV and then discharge it back into the vehicle system. Notice that at
100 s the lithium cell will capture five times more energy than the ultra-capacitor
and return this with relatively high efficiency (the dotted trace). However, at 10 s
both capture the same energy, but the ultra-capacitor discharges this back at
>
95%
efficiency whereas the lithium ion can only discharge 50%. Therefore, for 10 s
power the ultra-capacitor is twice as effective as the lithium ion in cyclable energy
transfer. It is also evident that the ultra-capacitor applicability extends up to 20 s
versus lithium ion.
1,000
b
a
tt
ery
100
captured
capacitor
10
stored
1
1
10
100
1,000
10,000
Charging time (s)
Figure 10.17 Energy shuttling comparison of lithium ion versus ultra-capacitor
( from Reference 8 with permission)
Today there are considerable varieties of lithium cell chemistries, most deal
with replacing expensive cobalt in the cathode active material with less expensive
elements such as nickel, aluminium, manganese, iron vanadium and to a lesser extent
with the types of conductive and binding agents used [9]. To improve safety, by
enhancing thermal stability, iron, magnesium and copper are used. Non-graphite
anodes continue to receive significant attention with Li
4
Ti
5
O
12
for improved safety
and Li
1.1
V
0.9
O
2
for improved capacity. For any of these cell types, cost is driven to a
first order by the separator material with polymers, ceramics, non-wovens and metal
oxide composites. Alternate materials for the separator section include natural as
well as synthetic materials. For natural separators, the products are mostly cellulose
products or their chemically modified derivatives. For the synthetic counterparts,
polymers of many types including nylons, polyolefins, PTFE and polyamides (to
name a few) are used, as well as synthetic inorganic forms such as ceramics and
