Page 170 - Battery Reference Book

9/10 Lithium batteries
to that of the lithium-sulphur dioxide cell, except W
that hermetically sealed cells are mandatory at present. - L 4.0- Cathode
The lithium-thionyl chloride system is a very low- 2 3.0
pressure system and, because of that, it is potentially 2 'E 2.0
.-
superior to lithium-sulphur dioxide systems in high- f .3 1.0
E5
I
temperature and/or unusual form factor applications. 2 2 0 1.5 3.0 4.5 6.0 7.5 9.0 10.5 12.0
The cells are manufactured without any initial internal 8
gas pressure and, because the discharge reaction gen- 0
W
E
erates only a limited amount of gas, the need for
venting is eliminated. The system appears to be safe
in low-rate cell designs, and may be safe, if prop-
erly vented, in high-rate cell designs; however, there
is an insufficient database on the system (particularly I I I I I I I I J
in the high-rate configuration) to make that claim with 0 1.5 3.0 4.5 6.0 7.5 9.0 10.5 12.0
a high degree of confidence. One manufacturer claims Time (h)
to supply cells that have an energy density in excess of
1100 W h/dm3 and 660 W Wkg. Another manufacturer Figure 9.6 Honeywell lithium-thionyl chloride cell: polarization
and voltage delay of a lithium-thionyl chloride cell at 24°C after 3
claims an energy density of 800 Wh/dm3, compared weeks' storage at 24°C; loads 120 mA (30 min) to 45 mA (30 min);
to 400 W h/dm3 for zinc-mercury, 200 W h/dm3 for electrolyte 1.5 M LiAICI4 (commercial grade) SOCln (Courtesy of
zinc-carbon and 300 W h/dm3 for alkaline manganese Honeywell)
dioxide (the corresponding W hkg data for the four
types of cell are 420, 100, 80 and 100). A,
Yet another manufacturer claims the following - -0cv
energy densities at low rates of discharge: 1 >3 n
Small cells 500Whflcgp1
100owwdm-~ - -
Large cells 700 W h/kg-' J 1- / ,tlO%SO,
1000 w ww3 -e---
Theory 1489 W fig-' 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
2000 W h/dm-3
Cells operate at temperatures between -55 to 150°C.
They have a shelf life of up to 10 years due to their
negligibly low self-discharge rate, e.g. 97% of original
capacity is retained after five years' storage. Earlier
versions of this battery exhibited severe passivation of
the lithium anode, which severely limited shelf life.
For example, at discharge current density as low as greater than 5 weight % level. At these higher sul-
0.6 mA/cm2, significant initial voltage drop and volt- phur dioxide levels after 2 weeks at 74"C, cells were
age delay were observed at 25°C after storage periods found to be anode limited and showed severe polariza-
as short as 1 week at 72°C. The primary cause of the tion under a 120mA load when they were discharged
voltage drop is the formation of a film. which results in at -29°C.
excessive anode passivation. This becomes evident on Short circuiting of lithium-thionyl chloride cells
closed circuit as a sharp initial voltage drop and a long with the risk of subsequent cell explosions have led
recovery before the voltage stabilizes (that is, voltage to a limited use of these cells in particular areas, e.g.
delay). This is clearly illustrated in Figure 9.6, which military and medical applications.
shows the strong anode polarization and initial cell These cells are available in small prismatic and
voltage drop followed by a slow recovery to a useful cylindrical cell designs with capacities up to 1 Ah and
cell voltage. Investigations by workers at Honeywell in flat, cylindrical and prismatic designs with capacities
have shown that the passivation film on the anode pro- up to 20000Ah. Twenty year reserve cells are also
duced in the lithium-aluminium chloride electrolyte available.
consists of lithium chloride. They have also shown
that the formation of this film can be prevented by the 9.4 Lithium-vanadium pentoxide
inclusion of 5% sulphur dioxide in the electrolyte. It is
significant that effective control of lithium passivation primary batteries
appears to be critically dependent on the sulphur diox- This system utilizes the lithium anode, a car-
ide concentration. As shown in Figure 9.7, discharge bon-vanadium pentoxide cathode and a double-salt
performance after storage can be adversely affected at metal fluoride electrolyte (lithium hexafluoroarsenate