Page 347 - Battery Reference Book

30/18 Primary batteries
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Time (months)
Figure 30.49 Available capacity of a Mallory lithium-sulphur
dioxide cell after storage for up to 4 years at 20 and 55°C
(Courtesy of Mallory)
30.5.4 Lithium primary batteries
Lithium-sulphur dioxide batteries that no capacity was lost at these temperatures over
the 42-day discharge period. The lithium system is
Lithium- sulphur dioxide batteries have an excellent capable of maintaining more stable voltage plateaux at
shelf life even at 71°C. Energy loss (Whkg) is less higher currents than any other cell of comparable size.
than 10% during 2 years' storage at 71°C. In 1975 Mallory introduced their new glass-to-metal
After extended storage, a reactivation time of the hermetic seal to reduce sulphur dioxide losses from
order of a few seconds is required for the system to the cell and consequent capacity loss and corrosion
achieve operating voltage. This is not a feature exclu- effects during storage. Such cells with hermetic seals
sive to lithium-sulphur dioxide cells, but one which have been stored for 1.75 years at 21°C and 4 months
is also exhibited by lithium-vanadium pentoxide and at 72°C without leakage.
lithium-thionyl chloride cells.
On standing unloaded, lithium-sulphur dioxide cells
develop a passive inhibiting film of thionite on the Lithium-manganese dioxide primary cells
anode, formed by the initial reaction of lithium and The capacity or service life of lithium-manganese
sulphur dioxide, which prevents any further reactions dioxide cells, normalized for a 1 g and a 1 cm3 cell,
or loss of capacity during storage. By virtue of this at various temperatures and loads, is summarized in
trait, shelf life is excellent over a wide range of tem-
perature. Short-term accelerated tests indicate retention Figure 30.50. These data can be used to calculate the
performance of a given cell or to select a cell of
of 50% of capacity after 10 years. The passive film is suitable size or weight for a particular application. It
quickly removed when a load is applied to the cell. is to be noted that, since the actual cell performance is
Lithium-sulphur dioxide cells now being supplied dependent on cell size and construction and other such
by leading manufacturers are claimed to retain 75% factors, these data are only approximate. These cells
of initial capacity after 5 years' storage at 21°C. Cor- are a relatively new type and consequently only limited
rected for sulphur dioxide leakage, true capacity loss storage life data are available. Projections suggest that
is estimated at 6% in 5 years, or 1% per year. Capa- cells will provide 85% of initial capacity after 6 years
city loss curves for lithium-sulphur dioxide batteries storage at 20°C.
produced by Mdlory are shown in Figure 30.49. For
the Mallory cell approximately 80% of the nominal
capacity of the battery is available after storage for 30.5.5 Manganese dioxide-magnesium
4 years at 55"C, compared with 95% when stored at perchlorate primary batteries
20°C (Figure 30.49). Hermetic cells retain 65% of ini-
tial capacity after 6 months at 72°C and about 50% Field experience has shown that shelf life is an out-
after 12 months at 72°C or 6 months at 87°C. standing characteristic of manganese dioxide-magnes-
Although permissible for shorter periods, prolonged ium perchlorate batteries. After 18 months' storage at
storage at such high temperatures is detrimental to the room temperature, magnesium batteries have yielded
capacity as well as to the high-rate properties of the 90% of their initial capacity. Storage for 90 days at
system and should be avoided in applications in which 55°C has shown that the battery still retains 85% of
such properties are important. Discharge tests at the its initial capacity, and after storage at 71°C for 30
42 day rate (1OmA) at 49 and 60°C have indicated days the capacity retention is 85%. The shelf life of