Environmental Engineering Reference
In-Depth Information
batteries offered an even greater energy density then nickel-metal hydride
batteries, improved self-discharge, shorter charge times, and an increased
discharge voltage of about 3.7 V compared to 1.4 V for nickel-metal hydride
batteries.
Li-ion batteries look similar to most batteries. Inside a cylindrical metal
casing are three sheets tightly spiraled together and surrounded by a liquid
electrolyte. The three sheets serve as a positive electrode, a negative elec-
trode, and a separator. The positive electrode is generally lithium cobalt oxide
(LiCoO
2
) and the negative electrode is generally graphite (C
6
). During charg-
ing, Li ions flow from the positive electrode (LiCoO
2
) through the porous
separator and intercalate into the negative electrode (C
6
). During discharg-
ing, the ions flow in the opposite direction and reintercalate into the LiCoO
2
.
When the Li ions detach and move to the opposite sheet, an electron will be
detached as well because Li ions are positively charged. This electron will
flow out of the battery and to the component it is running and then back in to
the opposite side to again meet up with the Li ion. This process can be seen
in Figure 6.9.
Although Li-ion batteries appear effective for improving the limits of bat-
teries, they are not perfect.
11-13
For example, all Li-ion batteries require com-
plex circuitry to prevent overcharging. Overcharging can compromise the
stability of the cathode, resulting in the breakdown of a battery. Complex
circuitry includes a shutdown separator for over-temperature, tear-away
tab for internal pressure, vent for pressure relief, and thermal interrupt
for over-current and overcharging. Another major restriction is the cost
of production. On average, a Li-ion battery costs 40% more to manufac-
ture than a nickel-cadmium battery. The high price may be attributed to
e
-
e
-
V
Discharge
Charge
Li
+
Charge
Li
+
Li
+
Li
+
Li
+
Li
+
Discharge
Li
+
Li
+
Anode
Li
x
C
Cathode
Li
1-X
M
Y
O
Z
FIGURE 6.9
Charge and discharge cycles of typical lithium ion battery.
