Page 285 - Battery Reference Book

2418 Lithium batteries
equipped with a gas release vent and are housed in a
stainless steel can.

24.2 Lithium-thionyl chloride primary
batteries
The cell reactions in the lithium-thionyl chloride cell
are postulated as follows:
4Li + SOC12 -+ 4LiCI + SO2 + S (24.5)
Figure 24.7 Honeywell lithium-sulphur dioxide battery 20A h
reserve battery components (Courtesy of Honeywell)
On a partially discharged cell stored at 60°C and above,
a possible consistent reaction could be:
Figure 24.8 presents data recorded during a test 2soc12 + 3s -+ 2s2c12 + so2 (24.6)
at 10°C with a 20Ah activator. A constant Freon
pressure of 3.72 kg/cm2 absolute was noted throughout The electrolyte used in lithium-thionyl chloride bat-
the electrolyte delivery cycle. This is as expected since, teries consists of a solution of 1 SM lithium aluminium
at this temperature, sufficient Freon is packaged to chloride (LiAlC4) dissolved in thionyl chloride. This
remain in a saturated condition within the activator. electrolyte is usually doped with 5% sulphur dioxide
On activation, the electrolyte was allowed to flow into to prevent passivation of the anode by a lithium chlor-
an evacuated volume, which simulated the internal ide film. The anode is pure lithium foil mounted on
volume environment of a cell stack. The tubes used a stainless steel collector plate, and the cathode is
for transfer of the liquid were identical to those used a cold-pressed sheet of 80% Shawinigan carbon and
in a finished battery. 20% Teflon mounted on stainless steel. The active
In this test, 305cm3 of electrolyte were pack- lithium-thionyl chloride battery is available in capac-
aged, 270cm3 of which were delivered to the simu- ities of 1.3, 160, 380 and 517Ah. The battery is con-
lated battery volume within 75s after activation. This structed in a jelly-roll configuration with the electrodes
represented a delivery efficiency of approximately separated by a glass mat separator.
88%, which provides a sufficient quantity of elec- Lithium-thionyl chloride is often cited as having
trolyte/oxidant to the cell stack to achieve the 20 Ah the highest performance potential of any of the lithium
output required. cells. It is particularly promising for high-current
The latest designs of lithium-sulphur dioxide cells applications, though it has been used for low currents
feature a cathode comprising Teflon bonded acetylene as well.
block laminated to an aluminium grid, an electrolyte According to some experts in the field, this type of
comprising sulphur dioxide dissolved in acetonitrile cell might replace carbon and alkaline C and D cells for
and a microporous polypropylene separator. The cells general consumer and industrial applications. It is cur-
are hermetically sealed, of spiral wound construction, rently limited to military applications. Lithium-thionyl
chloride cells being produced now have five to eight
times the capacity of an ordinary carbon cell, so the
300 r Delivery higher cost (84-9) is within reason. The growing in-
mmdetion clination of retailers to stock products with batteries on
the shelf is another good argument for using long-life
lithium cells as an alkaline replacement.
Like the sulphur dioxide combination, thionyl chlor-
53.0 psia constant / ide has been haunted by safety questions. One safety-
related problem exists when a gas forms during the
cell's operation, placing the cell under pressure. If
> heating occurs, there could be an explosion, or at least
an output of toxic gases through the safety vents.
w _/Electrolyte Y At the same time, one applications disadvantage of
thionyl chloride is that it has the same reaction delays
/ "O'IJme
and position sensitivity of sulphur dioxide. In fact, the
10 20 30 40 50 60 70 response delays can be several seconds long, which
Time (5) could be a problem in memoryhack-up use.
Eagle Picher also manufacture lithium-thionyl
Figure 24.8 Activation delivery characteristics against time at chloride reserve batteries. Three types of electrolyte
-1 0°C. 20 Ah activator hardware, 305 ml electrolyte packaged,
270ml (88.5%) delivered, four-capillary tube with 10°C delivery reservoir configurations are available, as shown in
(Courtesy of Honeywell) Figure 24.9, with the following characteristics: