Page 445 - Handbook of Battery Materials

14.8 Examples of Lithium Alloy Systems 417

X (at. %)
Li
46 50 55
-3
600 °C
560 °C
505 °C
460 °C
-4 415 °C
log D (cm 2 /sec)

-5

-6
-0.15 0 0.15 0.25
δ in Li 1+δ Al

Figure 14.3 Variation of the chemical diffusion coefficient
with composition in the ‘LiAl’ phase at different tempera-
tures [28].

composition containing 44 wt% Li, where Li/Si = 3.18, has been used in commercial
thermal batteries developed for military purposes.
Experiments have been performed to study both the thermodynamic and kinetic
properties of compositions in this system [22], and the composition dependence
◦
of the equilibrium potential at 415 C is shown in Figure 14.4. It is seen that the
commercial electrode composition sits upon a two-phase plateau at a potential
158 mV positive of pure lithium. As lithium is removed the overall composition
will first follow that plateau. The potential will then become more positive as it
traverses the other plateaus at 288 and 332 mV versus lithium, in that order.
As a result, the cell voltage will decrease during the discharge, regardless of the
behavior of the positive electrode.

14.8.3
Lithium–Tin System

The lithium–tin binary system is somewhat more complicated, as there are six
intermediate phases, as shown in the phase diagram in Figure 14.5. A thorough
study of the thermodynamic properties of this system was undertaken [27]. The
◦
composition dependence of the potential at 415 C is shown in Figure 14.6.