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2.2.2 COMPONENTS OF THE BATTERY-POWERED ELECTRIC
DRIVETRAIN
2.2.21 BATTERY SYSTEM
For use in motor vehicles the secondary cells must be brought to-
gether in battery systems. For this, modules are formed from the
individual cells. The cells can be coupled in a series circuit to in-
crease voltage. The usual values for battery systems in vehicles
can be as high as 400 V. These modules are then bundled together
in an overall system to increase the capacity [Blazejak (2009)]. In
addition to the cell modules, an overall battery system also inclu-
des components for electronic, electric, thermal, and mechanical
integration (see Fig. 8).
Different requirements, such as cooling and packaging, imposed
on the overall system are derived from the different cell types. This
has a direct influence on the complexity and the overall cost of the
system. Consequently, it is necessary to understand the battery
as a total system and accordingly not only to improve individual
components in order to achieve a system improvement, but also
to pursue systemic optimization. This holistic consideration for the
design and optimization of the system is necessary because it has
a direct influence on the characteristics of the overall system.
BATTERY MANAGEMENT
Battery management monitors the charge status of the individu-
al cells, regulates communication between the modules and the
overall battery, analyses relevant sensor data and controls mea-
sures for eliminating undesired deviations, for example through
activation of battery cooling, charge equalization between cells
(cell balancing) and extends to safety switch-off at critical status.
The electrolyte system of the lithium-ion cell is not capable of
being overloaded, and thus it is sensitive to overcharge or deep
discharge. Production differences result in different cell charac-
teristics, that drift farther apart over time. Battery management
organizes these differences and consequently is viewed as the
key component for sustainable use of Li-ion batteries in vehicles.
BATTERY THERMAL MANAGEMENT
In addition to battery management, lithium-ion high-performance
batteries also require active thermal management to control the
cooling and warming of the battery.
Aging of a lithium-Ion battery depends, in particular, on use (char-
ge currents, discharge currents, deep discharges) and implemen-
tation conditions, and determines the useful service life. Automo-
tive manufacturing requires an end-of-life (80 percent residual
capacity/DoD) equal to the useful life of a vehicle (10 to 15 years)
at operating temperatures of approx. 40°C [Brotz (2007); Fehren-
bacher (2009)].
9 Authors‘ own illustration; image material: Saftbatteries (2011) I Battery module (2011) I Johnson Controls (2011) I SB LiMotive (2011) I ELAB 2011
Fig. 8: The value creation stages of battery production
9
Chapter 2