Environmental Engineering Reference
In-Depth Information
the driving range obtainable with BEVs is about half with respect to that of
vehicles fueled with compressed hydrogen (both 250 and 600 bar) with severe
penalties in terms of vehicle weight, while very lower range values could be
reached with Pb/acid and NiMH systems. Then the problem of developing new
batteries characterized by specific energy comparable to that of conventional fuels
or compressed hydrogen appears to be the key factor towards the successful
introduction of electric vehicles in the consumer market and for their affirmation
as future transportation means at high efficiency.
The analysis of the different types of energy storage systems for electric
vehicles will be effected later (see
Sect. 5.1
), meanwhile in this paragraph, the
main functional parameters which characterize the performance of these systems,
i.e. storage capability and output voltage, are examined for different electro-
chemistry pairs, in order to highlight the current status of developing of BEVs and
give further indications useful to compare electricity and hydrogen as future
energy carriers in the transportation sector. In Table
1.8
, the open circuit voltage
and specific energy are summarized for some today available batteries (Pb/acid,
Ni/Cd, NiMH) and other systems still under study (lithium and metal/air) [
57
-
60
].
The theoretical values of open circuit voltage (OCV) represent the electro-
chemical potentials of the single cell reaction, while the theoretical specific
energies are calculated applying the Faraday law.
When a practical battery is assembled, the weights of inactive components
(current collectors, electrolyte, binders, packaging) add to the total weight of the
battery without contributing to energy, then the actual values for both parameters
are also reported in Table
1.8
to take into account the characteristics and/or
limitations of the real systems and the possible variations among different battery
manufacturers [
61
]. In different countries, various organizations have been funded
with the aim of promoting research activities in this field, with the final goal of
developing new types of batteries characterized by improved cycle life, safety,
reliability and cost, but overall by a major breakthrough as regard the energy
Table 1.8 Open circuit voltage (OCV) and specific energy values for different types of battery.
Specific energy values for USABC and gasoline
Battery
Theoretical
OCV, V
Actual
OCV, V
Theoretical specific
energy, Wh/kg
Actual specific energy,
Wh/kg
Pb/acid
2.1
2.0
252
30-45
Ni/Cd
1.35
1.2
244
40-51
NiMH
1.35
1.2
206
50
Li/ion
4.1
4.1
410
150
Li/polymer
(MnO
2
)
3.5
3.0
1000
120
Zn/air
1.65
1.5
1350
200-300
Al/air
2.7
1.6
8140
300-500
USABC
-
-
-
200
Gasoline
-
-
-
13000
Adapted from Ref. [
57
-
60
]
