Page 166 - Battery Reference Book

9/6 Lithium batteries

4.0 r "205 SOCI, satisfactorily at temperatures as low as -55°C with
efficiencies approaching 50%.

9.1.3 Long active shelf life
Another significant benefit offered by lithium-based
0 25 50 75 100 systems is their potential for long active shelf life. Her-
Percentage of active life metically sealed cells, made possible by using systems
that do not generate gas during discharge, protect the
Figure 9.5 Voltage discharge profile of lithium-vanadium pen- cell from impurities from external environments and
toxide (V~OS), lithium-thionyl chloride (SOCIz), lithium-sulphur prevent leakage of electrolyte from the cell. This, in
dioxide (SO2) lithium-molybdenum trioxide (MoOQ) cells (Courtesy
of Honeywell) addition to the absence of self-discharge reactions, or
the low rate at which they occur, gives lithium sys-
tems in active primary batteries the potential for 5-10
electrochemical couples. Lithium, having the highest years' shelf life without providing special storage envi-
potential of metals in the electromotive series, provides ronments. Also, the discharge products of most lithium
an operating voltage of about twice that of traditional systems are such that they do not contribute to, or
systems. The voltage discharge profiles of the systems increase the rate of, self-discharge. Therefore, lithium
mentioned above are shown in Figure 9.5. cells can also be reliably used intermittently over sev-
eral years in applications where it is advantageous or
required. A comparison of the projected shelf life for
9.1.2 Superior cold temperature performance various cell systems is shown in Table 9.5. In this com-
parison, acceptable shelf life is defined as the time
Because of the non-aqueous nature of the electrolytes after which a cell will still deliver 75% of its ori-
used in lithium systems, the conductivity of these ginal capacity. Hermetically sealed lithium-sulphur
systems at cold temperatures is far superior to that dioxide double-C cells after storage for 180 days at
of previously available systems. Table 9.4 compares 71°C deliver 88% of their fresh cell capacity when dis-
the relative performance of two lithium systems with charged at room temperature into an 8 !J load. By some
the cold temperature performance of other systems. standards 180 days' storage at 71°C is approximately
The lithium-vanadium pentoxide and lithium-sulphur equivalent to over 12 years at room temperature. This
dioxide data shown are from tests conducted on prac- would imply that these cells would exhibit about
tical hardware configurations and at moderate dis- 1% annual degradation at room temperature. This
charge rates. The numbers given reflect the percentage has been confirmed by discharge of non-hermetically
of room temperature performance that is achievable sealed Honeywell lithium-sulphur dioxide double-C
at the colder temperatures. Lithium-vanadium pentox- cells which were stored for approximately 1 year at
ide and lithium-sulphur dioxide systems will operate 27°C. After storage these cells exhibited no losses in

Table 9.4 Cold temperature performance of lithium-organic electrolyte systems

Temperature Percentage of room temperature performance
("C)
Lithium- Lithium- Merculy Magnesium Alkaline Carbon-zinc
vanadium sulphur
pentoxide dioxide
-7 88 96 0 58 15 5
- 29 78 85 0 23 3 0
-40 13 60 0 0 0 0

Table 9.5 Comparison of projected shelf life for various lithium-organic electrolyte cell systems
Storage Lithium Mercury Magnesium Alkaline Carbon-
tempe rature manganese zinc
("C) dioxide

21 10 years + 3-4 years 5-7 years 2-3 years 1-2 years
54 12 months + 4 months 7 months 2 months 1.5 months