Environmental Engineering Reference
In-Depth Information
Even with the current technology the lithium polymer batteries represent the
state of the art in the field of electric energy storage systems, since they are
characterized by very interesting values of the basic electrochemical parameters,
as already reported in Table 1.8 in comparison with other batteries today available.
The main advantage of lithium-ion batteries consists in the fact that they can be
charged and discharged faster than other batteries, such as Pb-acid and NiMh
batteries, because of the quick reversibility of the lithium ions. Moreover, the
specific energy of lithium-ion batteries is about 150 Wh/kg, this means for electric
vehicles a large increase of driving range with respect to the previous types of
batteries (Fig. 5.14 ; Table 1.8 ).
As with Pb-acid and NiMH batteries, lithium-ion batteries must be controlled
during their operation to prevent that overcharging conditions might occur dam-
aging the battery. For this reason the development of battery management systems
to guarantee the correct behavior in each working condition is a key issue for this
type of batteries.
The Li batteries have recently received much attention from automobile
industries thanks to their characteristics of light weight and good specific power;
however, the lower costs of Ni-MH batteries, together with their demonstrated
durability and reliability performance, could retard the application of Li ion sys-
tems [ 33 ].
5.3.2.7 Zinc-Air Batteries
These are non-rechargeable batteries (so-called primary batteries, while
rechargeable ones are known as secondary batteries) which utilize a metallic
zinc anode, an aqueous solution of KOH as electrolyte and a porous carbon-
based air diffusion cathode. The discharge semi-reactions are the following:at
the anode:
Zn þ 4OH ! Zn O ð 2 4 þ 2e
ð 5 : 23 Þ
where oxidation of zinc produces electrons that flow through the external circuit,
while at the cathode water and oxygen from air react to form hydroxyls, which
migrating through the electrolyte reach the zinc anode:
O 2 þ 2H 2 O þ 4e ! 4OH
ð 5 : 24 Þ
The overall cell reaction is:
2Zn þ O 2 þ H 2 O þ 4OH 2Zn O ð 2 4
ð 5 : 25 Þ
to which a cell voltage of 1.65 V at room temperature is associated.
The main problem of this type of battery is the scarce recharge ability of the
negative electrode due to the formation on zinc of deposits which degrade the
anode behavior [ 34 ]. As a consequence, these batteries are usually recharged by
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