Page 368 - Lindens Handbook of Batteries

LiTHiUM PriMAry BATTerieS 14.33

100 20°C
Capacity retention, % 80 70°C

60
1 2 3
Storage time, y at 20°C and months at 70°C
FIGURE 14.22 Capacity retention of Li/SOCl cylindrical bobbin
2
battery. 24

After storage, the Li/SOCl battery may exhibit a delay in reaching its operating voltage because
2
of the formation of the LiCl film on the lithium surface. The voltage delay becomes more pro-
nounced with a heavier discharge load and lower discharge temperature. The voltage delay of the
Li/SOCl cells can be improved by an in situ coating of the lithium anode with an ionic conductor-
2
solid-electrolyte interface. The improvement is shown in Fig. 14.23, which compares the minimum
voltage and the load after 2 years of storage for both the standard construction and the coated one.
it shows the dependence of the closed-circuit voltage on the discharge current of AA cells after
2 years of storage at 25°C. Once the discharge is started, the passivation film is dissipated gradually,
the internal resistance returns to its normal value, and the plateau voltage is reached. The passivation
film may be removed more rapidly by the application of high-current pulses for a short period or,
alternatively, by short-circuiting the batteries momentarily several times until the cell is activated.
The use of a pulse provides more reproducible results.
Special Characteristics. The bobbin batteries are designed to limit the possibility of hazardous
operation and to eliminate the need (in some designs) for a safety vent. This is achieved by mini-
mizing the reactive surface area and increasing the heat dissipation, thus limiting the short-circuit
current and a hazardous temperature rise, respectively. These cells also are cathode-limited, a feature
26
that was found safer than anode-limited cells for this design. The batteries have withstood short

FIGURE 14.23 Li/SOCl cylindrical AA-size bobbin batteries—
2
minimum voltage vs. load after 2-year storage at 25°C; (a) standard
construction; (b) with loading on lithium anode.