286
5 – Applications
7. Figure 116 shows a schematic of a simple Na / S cell in a tubular configuration.
Figure 116 – Schematic
of a simple Na / S battery.
8. The theoretical capacity of a battery is the maximum charge that it can supply
to the exterior. This depends on the amount of active substance present at
the electrodes and corresponds to the disappearance of one of the reactants.
For a given electrode, the expression for the charge Q is
Q
F n
i
e
i
ν
ν
=
where ν e is the stoichiometric coefficient of the electron, ν i is the stoichiometric coefficient of the active species i (Ox or Red), and n i is the number
of moles of the active species.
The electrode with the lowest capacity dictates the capacity of the battery.
For the sodium electrode, we have the reaction
Na ℓ m Na
+ + e
or
Q
1
1 96 480 23
230
964 800 C
Na =
=
#
#
For the sulfur electrode, the following reaction must be considered:
S
x
e
5
2 1 5
+
−
`
j m
x
S
S
5
x
5
2
5
2
+
−
−
−
Given that x = 1, we obtain
5S + 2.4e m 0.2S 5
2− + S 4
2−
The capacity of the sulfur electrode is
.
Q
C
5
2 4 964 800 32
800
1157 760
S =
=
#
#
VWHHOFRQWDLQHU
SRVLWLYHWHUPLQDO
LQVXODWRU
QHJDWLYHWHUPLQDO
FDUERQ
VXOIXU
FDUERQIHOW
ȕDOXPLQDWXEH
FDUERQIHOW
VRGLXPUHVHUYRLU
DOXPLQXP