Environmental Engineering Reference
In-Depth Information
Li ion
dV
0
20
40
60
80
100
SOC (%)
Figure 10.15 Li ion charge characteristic
Several interesting characteristics are revealed in Figure 10.16. First, none of
the battery technologies have reciprocal charge/discharge characteristics with SOC.
The discharge power is greatest at high levels of SOC for all the technologies and
decreases monotonically with DOD. Charge acceptance, on the other hand, is high
for low SOC and diminishes monotonically as SOC approaches 100%. Charge
acceptance for lead-acid is relatively constant as SOC increases, but NiMH and Li
ion (or Li-polymer) have very strong shifts, particularly when SOC approaches
80%. An NiMH pack must have its charge rate decreased when SOC
>
80%, and
especially when SOC
>
90%. Li ion/polymer, on the other hand, requires con-
tinuous reduction of charge rate from low SOC all the way to 80% SOC. Above
80% its charge rate must be closely monitored, particularly cell potential, so that
overcharging is not encountered.
Peak power (10 s)
NiMH (1×)
Li ion
(3×)
Pb-acid (6×)
0
10
20
30
40
50
60
70
80
90
100
SOC (%)
Figure 10.16 Comparison of specific power of NiMH, Li ion and Pb-acid
batteries (42 V nominal)
