Comparison of the Different Anode Technologies Used in Thermal ...

voltage (V)
30
25
20
15
10
5
0
LiAl @ 490°C 2.2
LiAl @ 575°C 2.2A
LiSi @ 490°C 2.2A
LiSi @ 575°C 2.2A
LAN @ 490°C 2.2A
LAN @ 575°C 2.2A
0 200 400 600 800 1000 1200
time (s)
Fig. 1 discharge @ 2.2A, 490 and 575°C
Note that the hot LiSi discharge ended at 1000s, thus
explaining the sudden tail end
voltage (V)
voltage (V)
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25
20
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5
0
30
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5
0
LiAl @ 575°C 4.4A
LiSi @ 575°C 4.4A
LAN @ 575°C 4.4A
0 200 400 600 800 1000 1200
time (s)
Fig. 2 discharge @ 4.4A, 575°C
LiAl @ 575°C 13.2A
LiSi @ 575°C 13.2A
LAN @ 590°C 13.2A
0 100 200 300 400 500 600
time (s)
Fig. 3 discharge @ 13.2A, 575°C
Remark 1: the hot LiSi batteries showed some overheating
after post-mortem (Fig. 2 and 3). That explains why the
FeS2 transition from the 1 st to the 2 nd plateau appears earlier
for LiSi batteries than for the other ones, due to increased
self-discharge of the cells.
Remark 2: Figures 2 and 3 show that the capacity of the
LiSi anode is more of the order of 4000A-s than the
estimated 3600A-s, if both the 1 st and 2 nd plateaus are
considered.
Remark 3: in Fig.1, the cold batteries are cooling down.
The performance is thermally limited.
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Analysis
The LAN anode technology gives by far the best
performance in terms of voltage in a given battery volume.
This is due to the higher cell electromotive force, the higher
weight density and the lower polarization, which is
estimated by linear regression of the 2.2A discharge curves
in the time frame 80 to 500s and in cold conditions as:
LiAl -0.14 mV/A-s
LiSi -0.11 mV/A-s
LAN -0.08 mV/A-s
In the 2.2A discharge, the energy and average power (till
voltage drop to 75% of the initial maximum voltage) are:
70
60
50
40
30
20
10
0
Energy (kJ)
Power (W)
LAN LiAl LiSi
Assuming we could take the same double layer (electrolyte +
cathode) for all kinds of anodes, one could integrate then 12
alloy cells (either LiAl or LiSi). In this case LAN still remains
the best anode followed by LiSi and then LiAl. In terms of
internal resistance, LAN gives also the best results: at 600s,
R=9.0mΩ for LAN, 9.3mΩ for LiSi and 11.6mΩ for LiAl.
Furthermore, LAN is an anode technology, which is tolerant of
a high cell temperature. It is thus a much safer technology than
the alloys. The following figure presents two discharges in the
same test conditions with a cell temperature of 640°C.
voltage (V)
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25
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5
0
LAN @ 640°C 4.4A
LAN @ 640°C 4.4A
0 100 200 300 400 500 600
time (s)
Fig. 4 LAN cell @ 4.4A, 640°C
Such a hot cell temperature is not possible for alloy based
cells, which would fail in thermal runaway. On the
example, we can nevertheless see that the LAN cell life is
shortened by the thermal decomposition of the cathode.
This can be mitigated by improving the cathode.